Everything you need to know about car audio

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Sound is simply vibrating air. How fast, how much, and when the air is vibrated, determines what we will ultimately hear as sound. The science of this process is called acoustics. When a speaker cone (or anything else that has the ability to vibrate in the auditory range) moves forward, the air molecules in front of the cone are compressed, causing the molecules to form an accelerating wave forward. This continues to happen until the speaker cone moves in the opposite direction, which causes a rarefaction (or thinning) of the air mass between the speaker and the listener. This is the basic concept of how sound waves are produced.


A word prefacing certain circuits in which the processing is performed by use of transistor or tube juctions, rather than passive componenets such as resistors, capacitors, and coils. Such items as crossovers and equalizers may be constructed either way. Active processing usually affords more more options, and greater precision, albeit at greater cost.

Air Gap

In a speaker's motor section, the space between the top plate and the pole piece. This is where the magnetic flux field is concentrated and where the voice coil interacts with it.

Alternating Current

Electricity which flows in opposite directions, alternating at a certain rate (Hz). As supplied by power companies, AC in the United States alternates 60 times per second and is deemed as 60 Hz power. However; some countries have a 50 Hz system, and ships and aircraft may use 400 Hz.

Alternator Whine

A siren-like whining that appears as the rotational speed of an engine increases. The noise is usually the result of a voltage differential created by more than one ground path or a poor ground path to the affected equipment.

Amperes (A)

Ampere is a unit measurement of current of electrical energy equal to one coulomb of charge per second. Most DC applications refer to positive current - current which flows from a positive potential to a more negative potential, with respect to a reference point which is designated as zero or neutral potential (usually ground).

The electrons in a circuit flow in the opposite direction as the current itself. Ampere is commonly abbreviated as "amp", not to be confused with amplifiers, of course, which are also commonly abbreviated "amp". In computation, the abbreviation for amperes is commonly, "I".

Amplification Classes

All sound is a sinosoidial waveform. It has alternating peaks and valleys. The center point of each wave is the zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave. When a tube or transistor amplifier operates in Class A, the output tubes or transistors amplify the entire waveform without splitting it into positive and negative halves. In Class AB, used in the overwhelming majority of amplifier designs, the signal is split into two halves, positive and negative, and each half is sent to a tube or transistor circuit for amplification. Both sides work in tandem, and the two halves are recombined at the output section to reconstruct the whole signal. This technique increases the amount of power that can be applied, but increases distortion. Class A amps usually provide lower, often imperceptable distortion, but at the expense of reduced power output.Class D or High Current operation is essentially rapid switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Theoretically, since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero; and when the device is off, the voltage is large, but the current is zero. Consequently, class D operation (often, but not necessarrily digital) is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product yet to be made; meanwhile designs do exist with efficiencies approaching 90%. This is a design that is increasimgly popular for use in bass systems, where maximum power is necessary, and slightly elevated levels of distortion are easily tolerated.


The strength or intensity of an AC signal applied by the amplifiers output to a speaker's input. Also, a measure of the relative power of any variable recurring phenomenon. Typically, measurements are made in Decibels.


The act of reducing the Amplitude or intensity of a signal. In speaker systems, high frequency drivers are commonly more efficient than low frequency drivers. This creates a need to adjust the driver levels to create a uniform overall frequency response. L-pads are commonly used for many passive systems


A species of dedicated audio nut who actually reads definitions like this.


Acronym for American Wire Gauge, a standard for measuring the diameter of wire commonly used in electrical circuits. The higher the AWG number, the smaller the thickness of the conductor. For power carrying, choose lower numbers; for signal only wires, choose a higher number.

Back Plate

The part of the woofers metal Basket or frame on which the Magnet structure is mounted.


A flat panel that divides the front and rear sound waves produced by a woofer. Sometimes baffle is used to mean an enclosure or the front panel on which the speaker is mounted .


An enclosure that is specifically tuned to give maximum energy to a very limited range of frequencies, usually the lowest. In this arrangement, the woofers are fully enclosed in the box with the sound pressure being vented through one or more ports.

Bandpass filter

A filter that has a finite passband, neither of the cutoff frequencies being zero or infinite. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, the Midrange driver may be fed by a bandpass filter.

Bandpass Gain

The increase (or decrease) in efficiency of loudspeakers, due to the enclosure size and tuning. This is measured by the midband sensitivity of the speaker as a whole.


Abbr. BW The numerical difference between the upper and lower -3 dB points of a band of audio frequencies. Used to figure the Q, or quality factor, for a filter.


The metal frame structure of a standard dynamic loudspeaker. In larger, heavier speakers, this may be made of cast metal for extra strength and rigidity. All the other elements of the speaker are mounted on this structure.

Bass Boost/Enhancer Circuit

An active low pass amplifier section added to some receivers, equalizers, and amplifiers that allows as much as an 18 decibel boost to be applied to an audio signal in the low frequency 35 to 90 Hertz range.

Bridged Power

Bridging an amplifier, combines the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Because of this high power output, bridging is the best way to drive a single subwoofer. If the amp is bridgeable, the owner's manual will have directions that tell you how. Usually, an amp is bridged by connecting the speaker leads to the positive (+) terminal from one channel and the negative (-) terminal from the other channel. However, be sure to consult your owner's manual before attempting to bridge your amp!

Also, keep in mind that most amplifiers need to see a 4-ohm load when bridged to mono operation. When bridging an amplifier, use one 4-ohm speaker or, if you prefer multiple woofers, connect two 8-ohm speakers in parallel. Again, consult your manual before operating your amp in bridged mode.

Bullet Horn (tweeter)

A type of tweeter in which the radiator has a large passive, bullet-shaped device above its center that extends the nominal dispersion angle of the sound, thus allowing it to cover a greater area with high frequency radiation

Buss or Bus

A signal-carrying conductor or electrical pathway designed to carry multiple signals. A mixing console auxiliary bus may carry signals derived from several channels on that console. The term is sometimes used to refer to a power distribution circuit, or "mains".

Cabin Gain

A low frequency boost normally obtained inside a vehicle interior when woofers are optimally in phase, and with the proper enclosures.


The property of an electric device that permits the storage of energy as a result of electric displacement when opposite surfaces of conductive plates are maintained at a difference of potential. In a capacitor, capacitance is the measure of the property (the amount of charge that can be stored) equal to the ratio of the charge on either surface to the potential difference between the surfaces. Capacitance is measured in Farads, and micro, or pico-farads for smaller units..


Power stabilizing capacitors store the necessary power amplifiers need to punch larger bass notes while limitingclipping. They store energy during intervals when it is not required, which is most of the time, and release it when demand exceeds what is available from the car's power system. The amount of capacitance to be used is half (.5) farad per 500 watts of available RMS power. Capacitors are not used with amplifiers that supply less than 300 watts RMS in total.


A signal that results from an amplifier that is either overloaded or underpowered relative to the signal Amplitude it being asked to generate. A clipped waveform is one in which the gently rounded peaks and valleys of the AC audio wave are instead sliced off or clipped, to yield what looks a lot like a square or alternating DC wave. When DC is applied to a speaker, the voice coil has no means of propelling itself relative to a constant magnetic field. Instead, it can only convert the incoming current to heat, and ultimately burns up. The effect of alternating DC on speakers is remarkable, irritating, painful, and short. If you are able to hear evident Distortion at high volume levels, or smell smoke, reduce the volume. It may already be too late for your speakers, but at least you may be able to save the amplifier.


1. An increase in density and pressure in a medium, such as air, caused intermittently by the passage of a sound wave. 2. The region in either air or material in which this occurs.


The cone-shaped diaphragm of a speaker. This is directly attached to the voice coil motor which actions produces the pulsation's of air that the ear detects as sound. Also useful for holding ice cream.

Cone Area

The effective area of the diaphragm. The higher the cone area, the more air that will be displaced.


A device or passive circuit used in systems with separate tweeter and/or midrange Drivers. It Rolls Off frequencies above and below certain points in the range, to allow the sound to be tailored for the specific driver to which it is sent. Most speakers have crossovers that consist of passive elements such as capacitors, coils, and resistors to separate the various frequencies. In a bi-amped or multi-amped system, the crossover is an active device that feeds the various frequency bands to the inputs of the amplifiers that operate the individual drivers.


The volume or quantum of the flow of electrons through a conductor, as opposed to voltage, which is the measure of the intensity or velocity of the electrical flow.


Acronym for Deutsche Industrie Norm (Deutsches Institut fuer Normung), the German standardization body. A world reference standard for the mounting parameters of many common receivers ( Head ends) as well as other types of cables and equipment. Single DIN is the standard face size for receivers, and measures 7-3/8"wide by 2-1/4" high. DIN+1/2 measures 7-3/8"wide by 3-3/8"high. Double DIN measures 7-3/8"wide by 4-1/2" high.


The measurement of cubic volume that an item (such as a speaker or port) takes away from the internal volume of an enclosure. When designing an enclosure, this figure must be added to the enclosure volume .


An alternate term for: speaker, transducer, or radiator. Properly speaking, the term speaker should refer to an entire sound producing system with whatever combination of woofer, midrange and tweeter; in whatever enclosure type it is housed.


The ability of an audio system to convert electrical energy (watts) into mechanical energy (Decibels of acoustical energy). This ratio is usually given as the amount of energy measured in Decibels at a distance of one meter from the input of one watt of electrical energy. In most speakers, the greater the efficiency rating, the louder the unit will play in response to the same setting of the volume control, in comparison to less efficient types. The overall efficiency for most speakers systems is under 20 percent. Typical speakers can be rated at anywhere from 85 to 110 dB. Keep in mind, of course, that efficiency is only one parameter of a speaker's overall quality.

Extended Pole Piece

Extended pole pieces on the magnet assembly allow for more voice coil travel, and thus lower Frequency Response, and less chance of "bottoming out"

Farad (F)

The basic unit of capacitance. A capacitor has a capacitance of 1F when a charge of 1 Volt across the capacitor produces a current of 1 Ampere through it. Named after Michael Faraday.

Flat Response

An output signal in which fundamental frequencies and harmonics are in the same proportion as those of the input signal being amplified. A flat frequency response would exhibit relatively equal response to all fixed-point frequencies within a given spectrum.

Fletcher-Munson Curves (equal-loudness contours)

Fletcher and Munson were pioneering researchers who provided the basis of High Fidelity in the '30s. They accurately measured and published a set of plots showing the human's ear's sensitivity to loudness verses frequency. They conclusively demonstrated that human hearing acuity is essentially dependent upon loudness. The curves show the ear most sensitive to sounds in the 3 kHz to 4 kHz area. This means sounds above and below 3-4 kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as "equal loudness contours." They represent a range of sensitivity from "barely heard," (0 dB SPL) all the way to "painfully loud" (120 dB SPL), usually plotted in 10 dB increments.


The cylindrical portion of a speaker's voice coil section. A wire is wound around this cylinder to form a coil such that when current interacts with the magnetic field it produces a pumping motion that alternatively compresses and rarifies air, and creates the velocity for such air masses to reach our ears as sound.

Harmonic Distortion

A type of Distortion in which resonance or sympathetic ringing vibrations are added to the original sound to produce second and third harmonics of a fundamental tone in a way that was not present in the original signal. Choosing good Drivers and a well-made enclosure design is essential in overcoming this tendency in speakers.

Heat Sink

Parts of an amplifier, typically heavy metal "fins," and a section of the frame of the speaker used to conduct and radiate heat away from the ponit of electrical consumption, or motor assembly.

High Pass Filter (HPF)

An electronic filter of a type commonly incorporated in Crossover circuits that permits the passage of high frequencies while suppressing lower ones. The place in the frequency spectrum where this occurs is called the crossover point and is different for each set of Drivers being considered. The most basic form of such filter is a non-polarized capacitor. Typical values for such a unit would be in the range of 1 to 100 microfarads


Imaging describes the extent to which an audio system reproduces the directional cues that enable the listener to locate the instruments and vocalists as they were positioned during recording and mixing (See also Soundstagebelow). Good imaging creates a listening experience that seems natural and lifelike. Since directional cues in sound come mainly in the higher frequencies, the key to attaining the best possible imaging is to have equal and unobstructed path lengths between the tweeters and the listener's ears. That's one of the reasons why matched component speakers, with their versatile tweeter placement, sound as good as they do.


The totality measured in Ohms of all electrical opposition to current flow: resistance, reactance, capacitance, as well as all mechanical factors inhibiting the completion of energy transfer in a contained system. In practical terms, this means that most Drivers are assigned a certain nominal impedance based on their DC voice coil resistance and mechanical stiffness. For car audio this is usually 4 ohms; for home stereo, 8 ohms is the standard.

Infinite Baffle

An infinite baffle speaker design is defined as an enclosure that contains a greater volume of air than the Vas requirement of the driver. An infinite baffle system can easily be applied to an automobile. This is accomplished by mounting the speakers on a board and using the trunk of the vehicle as the other walls of the enclosure. It is important that the enclosure be tightly sealed such that no air moves from the front to the back of the cone. Look for speakers where the Qts is greater than .6, and a Vas figure lower than the volume available, when selecting a woofer for an infinite baffle system.


Sometimes spelled Isobaric, this is an enclosure design in which two or more Drivers are coupled together by a sealed air mass to operate as a single driver. With proper sealing and design, very impressive results can be obtained from an unusually small box. A popular version of this simply consists of two woofers placed over each other in a 'clamshell' design. The downside consists of the fact that it does require at least twice the amplifier power as would be needed for a conventional speaker, in order to be operated successfully.


1. Referring to mechanical movement, the ability of the voice coil to move in and out in the air gap without moving side-to-side. Non-linear movement can damage the voice coil.

2. Referring to woofer response, the ability to maintain power or movement without loss of drive force.

3. Referring to enclosure port operation, the relationship bewteen the amount of air moving through the port vs. the amount of air moved by the cone. Non-linear response in a port can cause audible distortion


The resistance or impedance to which energy is being supplied. In amplifiers, the speaker or speakers connected to the output of the amplifier.

Low Pass Filter (LPF)

A network of components which attenuate all frequencies above a predetermined frequency selected by the designer. Frequencies below cut-off are passed without any effect.

Magnet/Magnet Structure

A combination of magnetic material and connected field concentrators that creates the magnetic field within which the voice coil interacts to produce sound. Magnetic materials have changed greatly over the years to produce much higher concentrations of magnetic fields (rated in gauss) with lighter and smaller volumes of material.

In marketing speakers, a great deal of hype is often applied to the question of magnet weight. But many of these claims should be treated with skepticism. With greater and greater concentrations of gauss fields being developed from ever lighter and smaller mass metallurgical materials, the only good measure of adequate power handling is the manufacturer's RMS Wattage rating. Hefty magnets may look impressive, but while capable,they are no longer an essential index to a speaker's power capacity.


Those frequencies roughly between 100 and 300 Hertz. (CPS)

MOSFET (Metal Oxide Semiconductor Field Effect Transistor)

A type of large output transistor used in the final stages of many power amplifiers, and commonly found in most car and home amplifiers today. These field-effect transistors are controlled by voltage rather than current, like a bipolar transistor. MOSFETs have a significantly higher switching speed than bipolar transistors. They generate almost no loss (little heat generation), which lends the power supply fast response, excellent linearity, and high efficiency.

Mosfet transistors are most often discrete devices, used with smaller driver transistors and other devices, to convert a small signal to a large one. They are highly stable and efficient, compared to the bipolar types that preceded them.

Motor Structure

In speakers, the complete sound generator or transducer that converts incoming electrical signals to mechanical/acoustic energy or sound. In a dynamic Driver, this includes the magnet, its directive field concentrators or Pole Pieces, and the voice coil that interacts with them.

Mounting Depth

The amount of physical space required to mount a Driver without having any of its parts touch objects below. This is particularly relevant to car speakers where such mounting spaces may be sharply limited as to their ability to accommodate deep speakers with large magnets. Door panels with movable windows are a typical example of where care must be taken in selecting speakers to be mounted. (see Mounting Ring, below)

Neodymium Magnet

A magnet material providing 7.5 times the magnetic strength of standard magnetic materials.

Net Volume

The amount of airspace that is enclosed within a speaker's enclosure. This does not include the airspace taken up by bracing, vents, or the speaker itself.

Notch filter

A special type of cut-only equalizer used to attenuate ( no boosting ) a narrow band of frequencies. Three controls: frequency, bandwidth and depth, determine the notch. Simplified units provide only a frequency control, with bandwidth and depth fixed internally.


In audio, the interval between any two frequencies having a ratio of 2 to 1. One octave up from 100 Hz is 200 Hz, where one octave down from 100 Hz is 50 Hz. A harmonic is a doubling (2nd harmonic), tripling (3rd harmonic), quadrupling (4th Harmonic... etc) of a fundamental frequency. Musical instruments (with the exception of electronic synthesizers) do not create pure tones. The fundamental (main frequency) is combined with its harmonics at various levels to create the sonic signature, or timbre of that instrument.


The measurement of electrical resistance and system impedance. It is a measure of the degree to which electrons are limited in both velocity and quantity in passing through a circuit. In Impedance measurements, this takes into account, the mechanical resistance inherent in the motion of transducers. The standard is usually 4 ohms for car audio and 8 ohms for home and commercial audio. Some specialty woofers may be rated at 16 ohms.

Passive Radiator

Sometimes known as a "drone cone," these passive devices respond to internal pressure within the speaker and react to it to produce reinforcing emissions to extend the output of the lower frequencies below the resonance point of the active woofer. They may look like Drivers but they lack an active motor assembly.

Peak Power Handling (MAX)

Peak power handling refers to the amount of power a speaker is estimated to handle during a brief high-intensity musical burst. Since this can vary with both frequency and amplitude, it is a much less accurate way to judge speaker durability and performance than RMS (see RMS).

Pole Piece

The ends or "Poles" of a magnet from which the magnetic lines of force, measured in Gauss, are at the greatest strength. In a typical speaker, this will be at the gap within which the voice coil is located. (see Bumped & Vented

Power Handling

A rating of a Driver's ability in optimum conditions to handle a specified amount of audio power (electrical current power) on a constant basis, without damage. This is generally considered to be a conservative and reliable figure to use in judging what types of amplifier power will be most successful with a particular speaker design


In sound waves, the opposite of compression. An area of decreased air pressure caused by a sound wave. In a graphical depiction of a cyclical waveform rarefaction occurs when the wave is in the bottom segment. Sound is simply the alternating compression and rarefaction of air at varying and often overlapping frequencies, within a range to which humans are sensitive.


Most all conductors of electrons exhibit a property called resistance. Resistance impedes the flow of current. It is measured in units called Ohms. With a water hose, resistance could be regarded as friction between the water and the hose. A larger hose would create less friction and have a lower resistance than a smaller hose. In electrical circuits, small round cylinders with wires on either end are called resistors. These typically reduce the flow of electrons to serve the specific requirements of the circuit elements, such as amplification or switching functions

Roll Off

A graduated reduction in the strength of audio output above and below certain specified frequencies. (SeeCrossover)

Sound Pressure Level (SPL)

An acoustic measurement of sound energy. 1 dB SPL is the smallest increment in sound level to which the average human is sensitive. Theoretically, 0 dB SPL is the threshold of human hearing while approximately 120 dB is the threshold of pain.

Standing Wave

A phenomenon where a sound is reflected between two parallel surfaces, such that certain sounds are made more intense and others diminished in given parts of a listening environment. Technically they are created by room modes, which are modes of vibration of air in the room. The sound waves interfere with one another to produce a series of places where the sound pressure level (SPL) at some frequencies is high, and another series of places where they are low. The places are sometimes called peaks and nodes. A standing wave exists in a room where a frequency is such that the distance between any two surfaces is equal to one half of its wavelength. For a given distance there will be many frequencies that will generate standing waves, each a multiple of the fundamental frequency whose wavelength is related to the dimension in question. Standing waves are always detrimental to the acoustics of a room, but can be avoided by careful room design, or minimized by absorbing certain frequencies where they build up, which is usually along walls or in corners.


The surround is the flexible ring around the edge of the speaker cone. In conjunction with the inner suspension element called a Spider, it determines the overall impedance of the speaker. Pleated, treated cloth surrounds are usually stiffer and less compliant than their foam and rubber rolled edge cousins. A flexible suspension system in the speaker usually indicates greater efficiency. For some units, it is desirable to have suspensions that are pliable enough to let the woofer cone travel freely in and out. A technical specification for this characteristic in more expensive speakers, is XMS. The further the cone can travel and the more compliant it is, the stronger the bass can be in enclosures that take advantage of it. However, certain types of very good enclosures require a more limited, stiffer cone movement to develop their more controlled and High Fidelity response. Surrounds are usually made of cloth, foam or rubber. Rubber tends to last longest.


Total harmonic distortion is a measure of the how much a given audio device may distort a signal through the introduction of added harmonics or overtones. These figures are usually given as percentages. THD figures below approximately 1% are inaudible to most people. However, distortion is a cumulative phenomenon, so that if a receiver, equalizer, signal processor, crossover, and amplifier are all rated at "no greater than 1%THD", together, they could produce 5%THD, which may well be noticeable in the perceived sound.


An electrical inductive device that can be used to provide circuitry isolation, signal coupling, impedance matching, or voltage step-up


The tendency of an enclosure to produce no spring or pressure on the woofer. Unloading produces an uncontrollable over-excursion of the woofer cone (it vibrates out of control); the speaker will exhibit inadequate power handling at lower frequencies.

Voice Coil

The voice coil is the coil of wire fixed to a cylinder at the apex of the loudspeaker cone that interacts with a magnetic field. With the help of other speaker components, the voice coil is the active transducer that converts electrical signals from the amplifier or receiver into mechanical energy, which we hear as sound. The voice coil cylinder is the part of the speaker around which the voice coil is wound. More advanced speakers offer a heat-resistant voice coil to prolong speaker life.


Voltage is an electrical charge, or potential difference, between two points, one being of higher relative voltage than the other is. A 1.5-volt 'C' battery has 1.5 volts of difference between the positive and negative terminals, for example. The unit of voltage is called the "volt," named after Allesandro Volta. Voltage can be thought of metaphorically as a pressure, such as water pressure in plumbing, that is available to initiate action or work. It, however, cannot do any work until a circuit is complete so that current (measured in amperes) can flow.


A measurement of power. In speakers, wattage is a term that indicates power-handling characteristics in dealing with electrical voltage inputs from the amplifier. RMS or continuous power handling is the only accurate basis for comparing the capabilities of Drivers. In determining the proper power input for a speaker, use this measure only. So-called Peak Power handling is often only the manufacturers best guess at the power dissipation point, beyond which the unit will fail.


The waveform of a signal is a depiction of its instantaneous voltages versus time. In audio, for example, we are always dealing with periodic waveforms that make up what we hear. These periodic waveforms can be plotted on a graph and will show up as some type of squiggly line. The graph chart rom left to right represents time and from top to bottom is the amplitude of the sound or voltage at those points in time. The familiar sine wave is an example of this.

Edited by Neo_frog
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T/S Parameters:

A.N. Thiele and Richard H. Small defined most of the relationships and terms we now use to describe what happens in a speaker and between a speaker and a particular enclosure's type and size. Their work has become the standard for speaker measurement criteria and is known as the Thiele-Small parameters. All speaker manufactures use the Thiele-Small parameters in describing their products which allow you to do a direct characteristics comparison of different speakers as well as give your the necessary information for designing the crossover network and enclosure.

The most commonly used Thiele-Small parameters are listed below:

B - Magnetic flux density in gap, in Tesla-meters

BL - The magnetic strength of the motor structure. "Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!"

C - Propagation velocity of sound at STP, approx. 342 m/s

Cas - Acoustical equivalent of Cms

Cmes - The electrical capacitive equivalent of Mms, in farads

Cms - The driver's mechanical compliance (reciprocal of stiffness), in m/N

D - Effective diameter of driver, in meters

EBP - Is used loosely to decide what type of enclosure will be best for any given speaker. It is calculated by dividing the Fs by the Qes. A result closer to 100 is usually best suited for an vented enclosure while an EBP closer to 50 will usually require a closed box design. This is just the "rule of thumb", some well designed high quality system violate this rule so use the EBP as a guide if the speaker manufacturer doesn't make a recommendation.

Fs - This is the free-air resonant of a speaker; it's the frequency that the speaker wants to vibrate at. This is a result of the weight of the moving parts (cone, etc) in balance with the stiffness of the speaker's suspension. At a speaker's Fs the speaker will over emphasize (make louder) that frequency and cause crossover points to change due to impedance variances. For accurate sound reproduction these frequency peaks must be controlled (kept flat).

Fb - The enclosure resonance (bass reflex).

Fc -The enclosure resonance (sealed enclosure systems).

Fp -Is the free-air resonant (Fs) frequency of a passive radiator.

F3 - Is the frequency where the response (loudness) is down from the reference level by 3 dB. Anything below this frequency is often too quiet to be useful; so F3 help defines a speaker's useful range. Look at the graph down below at the Qtc 0.707. The reference frequency is 90 dB, look along the line and look where it crosses the 87 db. The F3 for this speaker in a box with a Qtc of 0.707 is aprox 45 Hz

L - Length of wire immersed in magnetic field, in meters

Lces - The electrical inductive equivalent of Cms, in henries

Le - "This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.

Lv - Is the length of the speaker enclosure's port.

Ms - The total moving mass of the loudspeaker cone.

Mmd - Diaphram mass, in grams

Mms - The driver's effective mechanical mass (including air load), in kg. "This parameter is the combination of the weight of the cone assembly plus the ‘driver radiation mass load’. The weight of the cone assembly is easy: it’s just the sum of the weight of the cone assembly components. The driver radiation mass load is the confusing part. In simple terminology, it is the weight of the air (the amount calculated in Vd) that the cone will have to push."

n0 - The reference efficiency of the system (eta sub 0) dimensionless, usually expressed as %

p - (rho) Density of air at STP 1.18 kg/m^3

Pa - Acoustical power

Pe - Is defined as the maximum continuous (RMS) power-handling capability of a speaker.

Power Handling - Is rated on how much power a speaker can handle without causing damage. The most important consideration is the speakers ability to get rid of excessive heat. Factors that effect this include magnet and voice coil size and their ability to handle heat, venting, and the adhesives used in voice coil construction.

Mechanical factors are also considered, such as the power required to cause;

1. The coil to hit the back plate or come out of the gap

2. The cone buckling from too much outward movement.

3. The spider bottoming on the top plate.

But still the most common cause of speaker failure is simple abuse; cranking it up beyond its power rating while asking the speaker to produce frequencies lower than it's frequency rating. So be sure to take into account the suggested usable frequency range and the Xmech parameter in conjunction with the power rating of the speaker to avoid such failures.

The Thiele-Small Q's - The control of those peaks at resonant frequency (Fs) is done with the speaker's suspension (spider, surround) balanced off against the opposing force of the voice coil and magnet. The measurements used in describing the control (dampening) the movement of the speaker's suspension are the Qms, Qes and Qts. If the manufacturer does this right they can often put the resonate frequency of the speaker outside; either above or below its intended frequency range use which helps results in a more "flat" frequency response speaker.

Q - The relative damping or system losses of a loudspeaker in an enclosure. The ratio of stored to dissipated energy

Q Parameters - "Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.

As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance."

Qa - The system's Q at Fb, due to absorption losses; dimensionless

Qms - Is the measurement of control from the mechanical suspension system at resonance (Fs) which include the spider and the surround. They allow and control the movement of the speaker cone.

Qes - Is the measurement of control from the electrical suspension system at resonance (Fs) which include the voice coil and the magnet; the "engine" of the speaker.

Qts - The opposing forces from the mechanical and electrical suspensions acting against each other is the total Q of a speaker in free air at resonance (Fs).

Qmc - The Q of a speaker in a sealed box considering only the mechanical resistance.

Qec - The Q of a speaker in a sealed box considering only electrical resistance.

Qtc - Put a speaker into an enclosure and you then change how that speaker will act due to the resistance of the air pressure inside of the enclosure. When the speaker cone moves in or out the air pressure within the enclosure will put a resistance on its movements. The size and type of enclosure you build will depends upon the Qtc value you desire.

To decide upon your loudspeakers enclosure size you will need some loudspeaker software or good math skills and the math formulas; I prefer the software approach. In the software programs you will be asked to enter the required Thiele-Small parameters about the drivers such as the Q's, Fs, Vas, etc, some also ask enclosure type, number of drivers, etc. Then for the program to calculate the enclosure size it will want to know the Qtc value you want. The Qtc value you choose is a personal preference. A value of 0.707 is what most designers aim for, it will give you the flattest frequency response (accurate sound reproduction) and the lowest possible F3 (widestusable frequency range). Some people may not like this sound and want to enhanced base response so they may aim for 0.8 or higher.

In general high quality accurate loudspeakers Qtc are around 0.707, while loudspeakers that are designed to enhance the base may range from 0.8 to a max of 1.1. The more you move away from 0.707 anything over that will slowly start to sound boomy and unnatural and the base response will become more restricted.

If you want loud clean base go with larger drivers in larger enclosures, don't overwork a smaller speaker and try to increase the base by stuffing it in a small enclosure. Don't make the enclosures to big either; the more you oversize the enclosure (Qtc below 0.707) the more "tinny" it may sound, because you loose loudness (dB's) on the lower frequencies.


On this graph the vertical dB's represent how loud it is, the horizontal represents the frequencies. So looking at the chart you can compare the loudness of the various frequencies. Look at Qtc 1.500 and notice that all the frequencies below 60 Hz have been lost and then you have a huge (loud) peak at around 110 Hz and then it drops back rapidly, this is obviously not the desirable flat response that we want, unless all you want is single note boom box.

Now compare it to the Qtc 0.500 and note that there are no loud peaks, but now a lot of the frequencies below 50 Hz (F3 Value) will be too quiet. The best compromise is the Qtc of 0.707, no loud peaks and the loudness of the lower frequencies build quickly.

R - Ripple, in dB

Re - "This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load."

Ras - Acoustical equivalent of Rms

Res - The electrical resistive equivalent of Rms, in ohms

Rms - "This parameter represents the mechanical resistance of a driver’s suspension losses. It is a measurement of the absorption qualities of the speaker suspension and is stated in N*sec/m."

Revc - DC voice coil resistance, in ohms

Rg - Amplifier source resistance (includes leads, crossover, etc.), in ohms

Rms - The driver's mechanical losses, in kg/s

Sd - Effective piston radiating area of driver, in square centimeters. "This is the actual surface area of the cone, normally given in square cm."

SPL (Sensitivity) - It is a representation of the efficiency and loudness that you can expect from a speaker relative to the input power. Keep in mind that it requires twice the power to increase the volume of a speaker by just 3dB. Don't look at efficiency alone; also consider that often there is a trade off between the low frequency reproduction capability and its sensitivity. Remember that lower frequencies require a lot of air to be moved and that requires a lot of power. So a speaker which is capable of doing very low frequencies will usually have lower SPL ratings.

Vap - Is defined as the volume of air that has the same compliance as the suspension of a passive radiator.

Vas/Cms - Represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. The compliance or stiffness of the driver suspension is determined by the surround and the spider. It is simply a measurement of its stiffness.

Vb - The internal volume of a enclosure with a vent or passive radiator.

Vc - The total internal volume of a sealed enclosure.

Vd - No, it not that kind of VD. This Thiele-Small parameter is the Peak Diaphragm Displacement Volume which the total volume of air the cone will move. It is calculated by doubling Xmax then multiplying the result by Sd (Surface area of the cone). The higher the Vd figure is the better it is for use as a sub-bass driver.

Xmax/Xmech - (Maximum Linear Excursion) By definition it is the peak linear travel of a driver. Speaker output becomes non-linear when the voice coil begins to leave the magnetic gap. Non-linearity the point at which the number of turns in the magnetic gap which is exposed to the voice coil decrease. This excessive movement will increases speaker distortion.

Xmax is measured at the voice coil height minus top plate thickness, divided by 2. Xmech is expressed as the lowest of four potential failure condition measurement multiplied by 2.

The four possible failures are;

1. The spider crashing onto the top plate.

2. The voice coil bottoming on back plate.

3. The voice coil coming out of gap above core.

4. The physical limitation of cone.

Take the lowest of these measurements then multiply it by two. This gives a distance that describes the maximum mechanical movement of the cone.

Zmax - This term represents the speaker's impedance at resonance.

Z - The total impedance, this includes the reactive and resistive resistance's

Edited by Neo_frog

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NOTE: This section is for definitions that aren't commonly used every day, but we see a bunch on the forums.

Start posting some, and I'll get em defined.

Frequency Multiplier

A frequency multiplier is commonly used in a radio receiver or radio transmitter to multiply the base frequency of the oscillator by a predetermined number. This multiplied frequency is then amplified and sent to the final drive stage and into the antenna tuning/coupling circuit for delivery to the transmitting antenna. The advantage is that a highly stable reference such as a crystal oscillator can be used, which may not be practical to manufacture for a higher frequency of interest.

Blow-through (Blow-thru/cut-through)

A blow through is most commonly cutting through the bed, window, or entire rear of the passenger compartment of a pick up truck in order to utilize the space for an enclosure without restricting functionality of the cab.

Edited by Neo_frog

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NOTE: This is not a section for box designs or equipment specific troubleshooting. This is commonly asked questions. I do not have ALL the answers so help me out gents. :drinks:

Some examples:

What's the best way to do a blow through?

How do I match up the quarter wave?

In a wall if the port opening is located ¼ of the tuned frequency’s wave length away from the windshield/microphone you gain constructive interference. This occurs because the originating wave (from the port) and the reflected wave (from the windshield) will "mix" with each other at the peaks & troughs of their wave form. This effectively boosts the amplitude (hence volume) of the wave. Thats the theory.


Aside from helping to boost the SPL measured at the microphone, you'll also get a condition in which woofers will handle far more power that they are rated to handle, provided the burp is very short. Ever seen a shattered cone in an SPL car and the owner blames it on "unloading", this is what they mean. That the load on the cone (caused by the pressure waves) wasnt great enough to hold them together, a good SPL system exploits the waves load to increase the power handling of the system.

If the system is run at a frequency other than tuned frequency, the proximity of woofers and ports to the microphone is more critical because destructive interference between woofers and the port is possible. With destructive interference, the waves mix and the peaks are lowered as they dont co-incide.


OK so all this sounds great ! How can I give it a try ? Determine the distance (in feet) from the baffle to the windshield. Multiply that measurement by 4. Divide 1132 (which is the speed of sound at feet per second at sea level) by the result. Thats the 1/4th wavelength frequency that corresponds to the distance between the baffle and the windshield.

In other words, that’s the frequency which you should be tuning your system to.

What's a good program to tune/design a box?

-There are quite a few out there, but one of the best right now is Torres' box calculator. It will give you everything you need.

What is impedance rise (box rise)?

-The impedance is the resistance of the coil when AC is applied. Since the coil acts like an inductor, the impednace changes with frequency.

What people call impedance rise is due to the woofer being put in a box. If you look at the impedance plot of a woofer in free air, the impedance rises at the resonant frequency of the driver. Once in the box, the cone has a different reaction with pressure behind it, which can change the impedance plot. You also have new impedance spikes due to the box size, port tuning, etc.

Impedance rise may in fact not even be a higher impedance at all frequencies (more than likely will be an increase in the overall average, but the spike at the driver's resonant frequency may still be the highest impedance). Many times it is just additional humps/spikes in the impedance plot, or even changing of the impedance spike seen with the woofer in free air. For someone playing music, the additional humps/spikes will increase the average impedance seen while playing music. For someone burping at a single frequency, they need to know the impedance at their frequency to match the amp to the sub. There is a good chance the impedance will be higher near the frequency they burp at, since it not far above port tuning.

For the average person, ignore "impedance rise". The hardcore competitor uses the actual true impedance to his advantage to get all the power he can from the amps

Here is an impedance plot that shows peaks and valleys.


What's the function of running multiple 1/0 wires?

-Every wire has an ampacity, which is how much amperage can sufficiently travel through it without excess heat burning it up. If you are running amplifiers that will draw a higher load than your ampacity, you will blow fuses or start a fire. Running multiple wires increases the amount of current potential and distributes the load evenly.


What's the function of running negative wires to the front?

-Running a negative wire guarantees a consistent path for electrons to flow, but it's not required for a good connection. Due to newer body designs and structural integrity of older vehicles, the chassis grounds may have less potential in some cases.

Where can I buy a TermLAB?

You can go here to purchase one, or check out For Sale sections for used meters.

How does a TermLAB work and why does everybody refute other meters?

-The TL sensor actually reads on harmonics. It reads 3 frequencies: the peak you are playing, 1hz higher, and 1hz lower. Then it displays the average as your score. Thats why the TL is about 7dB lower than most other SPL meters, and it does show your peak SPL in the bar graph. So a TL doesnt really display actual SPL, but a score. This has been adopted by IASCA and others as the official meter. And based on scoring methods, the other meters mean nothing.

How do you seal off from the trunk?

-There are plenty of build logs of those who have done it. You can either use expanding foam around the edges of the box, then shave away for a flush look or you could fiberglass directly to the trunk entrance in the cab. It will look prettier that way, but take more time.

What's the difference firing forward vs backward in a trunk?

-Firing forward will yield a higher resonance and most likely a higher score on the meter. You will lose some low end response, so you will have to tune a box lower to compensate. Facing backwards gives the port something to load off of and virtually increases the effective port length, dropping your tuning.

This brand vs. that brand?

-Every answer you will get is entirely subjective. Your best bet is to try them both, or make up your own mind. Chances are, if you're comparing very similar equipment, you will be happy (or disappointed) with both.

What is the best way to tune my amp?

There's a 'best' way and there's a 'quick' way. The best way requires an o-scope and DMM, while the quick way only requires a DMM. Both will need -3 to 0 dB reference tones on a CD. These procedures are generalized for the average build as numbers will change based on the setup.

GAIN (Best)

GAIN (Quick)

How do I set my filters on the amplifier?

-The printed dials on the sides of amplifiers aren't necessarily accurate. They are just used as a reference (like most things) for the average enthusiast.

NOTE: This is all application dependent! Given numbers are for the average system!

As a general reference, set your "highs" amp to HPF and set it to 12db @ 100-125hz. Depending on what speakers you are using or passive crossovers in the circuit, it may be best to run Full or modify the frequencies. See the manual for your speakers for more information.

Set your "sub" amp to LPF at 12 or 24db @ 70-80hz. The dB setting is the rolloff rate or how hard the slope drops in the response above your chosen frequency.

Set the head unit and amp to the same crossover points to match them or try only setting the head unit and set the amps to pass or vise versa.

Set the subsonic filter 5-7 hertz below tuning frequency. This filters out "subsonic" (meaning sound that cannot safely be reproduced) frequencies.

The best way to verify your values is by playing a tone reference and turning the dial until it starts to fade. Even if the printed numbers don't match up, you will know you are electrically accurate.

Where can I get tones or noise tracks?

You can download majority of common tones from ROE. Download what you need, burn to a track and play them for your tuning desires.

If they do not have what you need, you can create and export any tone with Audacity.

What should I tune my box to?

Here's my advice to you. Unless you are building for competition, your best bet is to build for daily listening. 99.9% of the time, you will be driving around listening to your music whether it be low low bass or double kick metal. Do what you will enjoy the most. Don't get all hellbent on numbers that really don't mean anything unless you're a big competitor. Having a high SPL on SMD won't make you popular.

For trunk cars that play everything, tuning mid to high 30s will cover a wide range. You'll hit hard on metal and the trunk will take care of the low end extension (facing backwards). If it's facing forward and sealed off from the trunk, you will probably want to stick to low to mid 30s since you'll have nothing to load off of but still want to play everything.

If you are listening to strictly rap and slowed music, you will be fine from 28-32hZ tuning depending on your taste. This is a WIDE range so pay attention to song peaks to get an idea where you stand. While people can tell you their favorite tuning, it means NOTHING in your car.

For walls, if you are asking this question, you probably shouldn't have one. Facing any ports into a large volume of air like the cab will change the acoustics of everything and will sound nothing like a trunk tuning. My personal taste in a CAR is having a 36hZ peak, which (for me) requires a 32hZ tuning and sounds great on ALL music. Every car is different.

If you are skilled, you can build tunable ports to change your tuning from daily to meter killer whenever you please.

How much louder will I be in this incredibly awesome new scenario? (i.e. bigger subs, new box tuning, same setup different car, etc..)

Well well. If it isn't the famous "what will be louder?!?" question in different words. Nobody will ever be able to definitively tell you if you are going to get louder with a new setup. While everybody looks for the "magic" system, changing only one component of the install doesn't necessarily make your sound go up.

Example: Bigger sub, same everything else including box.

Buying a bigger sub and cutting a bigger hole is more common than you think; however, it's perfectly acceptable. Just consider it an experiment rather than an upgrade. A few points to be made are that the cone area of a larger sub is...well, larger, so the displacement of air each time the cone travels will be higher, generally yielding perceivably louder music. While it seems you're golden, you have to remember that the sub displacement has gone up, compliance (Vas) has gone up significantly, and transitively your box efficiency has dropped while tuning has gone WAY up, so your response may completely change and overall SPL go down.

Will buying a bigger sub change my sound and make me louder?

Well the reproduction is highly dependent on the box, but you can't say the response won't change. While the "loudness" does increase with cone area, the response of the entire driver does too. Different size subs have different electrical and mechanical compliance, different resonant frequencies, and different sensitivities, so putting them in a similar enclosure to the smaller sub WILL in fact yield a different sound.

I have already explained how higher SD will yield more air movement, but technically a general trend is that the FS of a certain model will go down as the size gets bigger. That means the "bigger" sub will play lower in the correct environment, but there is no reason to ever think that 10s or 12s won't stop your heart with subsonic frequencies.

Which of these subs will be better for daily music?

The answers will be entirely subjective. Each person has their own "ear tuning" that they go by. Things you can look for in SQ subs are a high Qts and low Fs as a start, but those specs may not be what YOU are looking for. By it and try it.

What qualities of a subwoofer provide maximum cooling?

Which sub will move more air?

Assuming the box is built per the operating parameters of the subwoofer, there are a few things that may create more displacement of air.

-More power = more transfer of kinetic energy into audible air vibrations

-More cone area = Higher Sd will have a higher surface area and therefore displace more as the cone travels

-Higher XMAX = More allowance for linear travel

-Lower tuning = Longer wavelengths will seem to "move" more air, but it's just that the displacement is more noticable.

Moving more air doesn't necessarily mean higher SPL. (See below)

Does a higher XMAX mean more SPL?

This is always an interesting and controversial topic. Every couple of weeks, a debate rages regarding the relevance of high Xmax and whether it is truly valuable to achieving SPL scores. Perhaps the greatest argument is that Digital Designs Audio drivers, who have a very impressive track record in SPL competition, have been routinely tested to show below average Xmax numbers. How is it possible that a driver with limited linear excursion can still be amongst the loudest? The answer is simple and complex all at once: Xmax is relevant to SPL and it's not. Now that I've confused you, let's proceed.

I'll touch on how a speaker makes sound and how it's interpreted at a later time, but let's skip to some ground works. Acceleration is a critical component of creating SPL. The higher the rate of acceleration, the more pressure that can be created. Let's figure out how to get there.

If you've been through any high school physics classes, you're probably very familiar with this equation.


Hey, that looks like Newton's Second Law of Motion. In short, it states that the net force of an object is equal to the product of it's mass and it's rate of acceleration. Of course, we can re-write the simple formula to better suit our needs.

F/m = a

After our spinning, the formula reads that the rate of acceleration is equal to the net force of an object divided by it's mass. Let's apply this to speakers for a moment, shall we? The force of an speaker is determined by the two factors:

1. BL - the combination of the magnetic field strength (B ) and the length of the voice coil in the gap (L)

2. i - the level of input current

Taking that information and our above equation, we can easily translate this to a speaker relevant equation.

(BL* i)/m = a

Let's make some logical conclusions from this formula.

1. Increasing the magnetic field strength (B ) or the length of the voice coil in the gap (L) will increase the rate of acceleration

2. Increasing the level of input current (i) will increase the rate of acceleration

3. Increasing the mass of the driver will decrease the rate of acceleration

Naturally, the inverse of these conclusions holds true as well. For example, if you decrease the moving mass of the driver, the rate of acceleration will increase. Simple stuff, me thinks. Now we have our foundation for understanding why Xmax is and is not relevant to SPL.

We know what we want to have a really loud driver, don't we? Huge BL, ability to take a lot of power, with extremely low moving mass. When looking at thiele/small parameters, we are looking for something with a high BL^2/Re, high power handling, and low Mms. It's odd that Xmax isn't factored into that equation, don't you think? Ahh, but it is, in a sense.

Once we apply current to the voice coil, it moves. We know that as the voice coil moves out of the gap, BL decreases. It stands to reason that as the voice coil moves out of the gap, BL decreases, and based on our previous conclusions, so does the rate of acceleration! In this sense, high Xmax is a good thing because it means the driver is capable of moving further without an alarming decrease in BL. In this sense, high Xmax is a great thing. A driver that can move great distances while keeping BL very linear can make for a very good, very loud driver. This is handy for competitions like Bass Race, where everyday music is played for longer durations.

With that said, there is another aspect of SPL competitions where high Xmax may not matter so much. In DBDrag style competition, high Xmax is not always critical. Typically, a competitor plays a short burst sine wave near the resonant frequency of the port(s) used in their enclosure. This excites the air mass in the port, causing it to become the primary source of our pressure. Meanwhile, the driver that is exciting the air mass is relatively stationary; it is not excurting itself very much at all. If your driver is only moving +/- 2mm, what is the difference in BL between a driver with 16mm of Xmax and a driver with 100mm of Xmax? Not much at all.

There is one more important consideration in the "high Xmax vs. SPL" equation. Again, looking back at that original equation, we know that high moving mass decreases our rate of acceleration. Let's pretend I'm engineering a driver for a client who wants high Xmax using conventional designs (more on this another day). How do I do so? Quite simple: I add length to the voice coil. There is, however, a caveat to adding length to your voice coil: more wire (be it copper, aluminum, etc) adds mass to the driver as well. This is not a good thing from an SPL standpoint.

As we can clearly see, high Xmax and SPL are not necessarily mutually exclusive; in fact, sometimes they go hand in hand. At the same time, some situations call for very little Xmax. This is why companies like Fi Car Audio deserve more credit than they receive: there is no one answer for every question, but we'll allow you to customize our answer to suit your question.

The point comes back to a daily engineering focal point: where can I afford to make sacrifices for the application? And that ultimately brings us to Newton's Third Law:

For every action, there is an equal and opposite reaction.

How do I determine whether or not a coil/subwoofer is blown?

Generally you can measure the impedance of the coil to determine its integrity. If the coil measures an extremely high or overloaded impedance (i.e. continuity) then it has been ruined. You can also do a limited visual inspection through holes in the basket to see scratches or burns, but the above test works best.

If the coil measures higher than its nominal rating, it may have loaded unevenly in the enclosure, but will still function properly.

What is a "blown" woofer?

A blown woofer is one that fails to reproduce mechanical motion when an AC voltage is applied to some or all of the coils. Just because a dust cap is missing or the cone/surround is damaged does not mean it's blown.

Can I blow a subwoofer by underpowering it?

Yes and no. ;)

When you turn the volume down on your head unit, you are decreasing the AC voltage applied to the subwoofer causing it to move less. Having a properly tuned amp giving less than rated power (at full volume) is performing the same operation.

Electrical energy applied to the coil is transferred to mechanical motion and heat. The subwoofers cooling properties will take care of the heat in high power applications. At low power, the heat build up isn't enough to cause the lack of air flow to blow the woofer. Unless...

Clipping is the worst thing you can send to your subwoofers. Running a pure square wave (which is damn near MAX clipping) can potentially destroy a subwoofer on 1/4 RMS. When a clipped signal is applied, the coil loses linear travel and much more heat is released. Due to the lack of cone travel and excess heat build up, the woofer can easily blow on low power.

When do I need to start doing electrical upgrades?

The first thing you need is the draw. You need to know how much amperage that your current (or future) system is going to pull before making any decisions. This will determine the following:

-How many wires you need

Every wire has an ampacity, or how much amperage can safely travel through it without burning up. If you are pulling in excess of 300A on music, you should consider running two 1/0 wires to have some overhead and scalability.

-How many/what size alternators

Ideally, the amperage output of your alternator should match or exceed the load demand of the system. Once you create a build that's impossible to supply enough amperage, you would rely on multiple batteries with good charging properties to make up for the loss.

-How many/what size batteries

The batteries are going to be the reserve. Once the alternator output is exceeded, the system will pull from the most potential being the batteries and your alternator will recharge the batteries in the mean time. The number of batteries can be calculated based on your wattage. Generally, websites will have battery calculators for you to use. These numbers may not apply in every situation, but they are a very good reference.


The amount of amperage parallel fuses provide should exceed the current draw of the system. Fuses are great fail-safes, but they aren't necessary for normal operation.

How do I determine the proper range on my DMM?

Edited by Neo_frog

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Why would speakers need breaking in? Are there any measurements or tests that have been done before and after performance that has shown a measurable difference?

Well, there are indeed several mechanism that are at work that cause the operating parameters of drivers to change through use. However, the notion that once one gets a speaker home it requires "breaking in" suffers from several problems.

First, as a driver comes off the line, its actual performance is fairly far from it's intended performance target. Reasons for this include the fact that the centering spider, typically manufactured from a varnish- impregnated linen, is far stiffer than needed. Working the driver back and forth loosens the spider considerably.

Now, one might say: there's objective proof of the need to "break in" a loudspeaker! Not so fast. The break-in period for the spider is on the order of several seconds, and if it takes you several seconds or minutes or whatever once you get the speakers home to loosen the centering spider, it's not proof of the need to break them in; it's proof that the speaker you just bought HAS NEVER BEEN TESTED!

But, on to other points.

When a driver is measured, there is a significant change in a variety of operating parameters as the speaker is driven. Usually, in a woofer, the resonant frequency drops as the speaker is used, often by as much as 10-20% (sometimes much more). This is due, as the question suggests, to a relaxing of the elastomers used in the suspension.

However, if one turns the stimulus off, within a few minutes, most, if not all, of the change has completely recovered, and we're back to go again. The elastomer has recovered from it's stresses (this is especially true of certain polybutadene-styrene surround formulations).

There are plenty of other real physical changes. For example, one can see a reduction of the electrical Q with time under heavy use, simply because of the positive temperature coefficient of the resistance of the voice coil. Allow the speaker to cool down, and it's completely recoverable.

Get it hot enough, and you might permanently lose some flux density in the magnet. But you have to get REAL hot to do that. Hotter than most of the compounds used in making a speaker can endure without catastrophic failure (damned few glues, varnishes, cones and insulating materials can withstand the temperatures needed to reach the Curie points of the typical magnetic materials found in loudspeakers).

What about the adaptive signal processing abilities of the brain? Could it be not the speakers which get broken in, rather one's ears?

When this has been suggested, despite the fact there's about a century of research backing it, it is more often than not greeted with jeers and sneers. See, you can't sell special "break-in" CD's if the speakers aren't broken in.

Why do people have so many opinions on this then?

Well, there will be loads of opinions. However, actual data on several thousand drivers don't seem to give two shits about opinions, the usual claims of "mysterious unmeasurable quantities" notwithstanding.

So what's the final verdict on subwoofer break-in?

It's a myth created by those who don't fully understand how a driver works. The only time you'd really have to worry is when the ambient environmental temperature is so cold that the drivers performance is affected. And even then, the dispersion of heat through the suspension is rapid. The ectothermia the driver goes through is enough to overcome the extreme cold temperatures rather quickly. But on a side note, drivers (and amplifiers) have been known to perform better down to 0°C (32°F) under the right circumstances.

Edited by Neo_frog
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Edited by Neo_frog

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God damn, dude, good shit here. Did you type all this or cut and paste?

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God damn, dude, good shit here. Did you type all this or cut and paste?

Definitely did NOT type all of the definitions lol. I did chop it up and modify some things though. I read through everything and tried to correct anything that wasn't 100%, then modified it to look pretty.

I did however write the majority of the FAQ. ;)

Edited by Neo_frog

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-Addz to Favorites-

:good: :good: Nice!! bro, lots of good info here.

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Vote for a sticky on this for sure. Neo im gonna have to meet you sometime you seem like a smart dude.

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Vote for a sticky on this for sure. Neo im gonna have to meet you sometime you seem like a smart dude.

x2 some serious dedication there, thx for all of the info man, will come in handy :)

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vote for sticky. will help noobs asking noob questions about noob stuff lol

even myself lol

Edited by cmamtower

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