Jump to content

Welcome to the SMD forum!

JohnP

Members
  • Content Count

    14
  • Joined

  • Last visited

Community Reputation

6 Neutral

About JohnP

  • Rank
    120db

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. One Point Two... In multi speaker and amplifier setups in car, home, commercial and professional audio if multiple speakers are covering the same frequency range for the objective of increased sound pressure level there's the risk of one speaker cancelling out another. This can be quite easily noticed by turning up the volume for one speaker and noticing a drop in overall volume level when the volume for another speaker is increased. In this case the speakers are acoustically out of phase. I've seen this very thing happen in both my own system and when people came to me with the same exact problem with faded hopes of more volume for more speakers and amps. Sometimes it's a simple as reversing the wires to the speaker, other times it involves changing the location of the speakers relative to each other and other times it means using a fairly elaborate and expensive Digital Signal Processor (DSP) to see if delaying the material to one of the speakers causes them to get back into phase and stop cancelling each other out. One problem in some quite elaborate home systems I've dealt with: The use of a DSP in things like echo, reverb, delay, and various and sundry sound effects programmed into the DSP can make the system sound much worse and in some cases it can make it sound better. Of course worse and better are subjective to the listener. Would you please discuss the issues of the thread and not me ? Realize it or not in shifting the discussion to me you're saying more about yourself. No disrespect intended. If I'm wrong post your opinion as to what you think wrong, we can respectfully discuss it, and hopefully we all as the forum can benefit. Thank You.
  2. "Old Electronics Geek" trying to survive being kept in my cage, smoke, hot temperatures, and a presidential election year.  Audio and my faith and trust in God will be the glue that gets me through all this.

  3. Hi Backwoods, Given what you write about using shorter screws to secure down the amplifier leads me to believe there may be some kind of mechanical issue within the amp possibly causing the heatsink to ground out something on the internals of the amplifier that should not ground out. Alternatively it may be causing the circuit board to flex and a solder joint somewhere on the amp to open when it should not. Soldering issues in mass produced consumer audio and video has been an issue especially when there was a movement to lead free solder in the whole RoHS (reduction of hazardous substances) movement within the electronics industry. You would be surprised to know how many failed electronics I've ressurrected using not much more than a magnifying lamp and not even a pennies worth of solder. Cheers !
  4. Hi, From my desk.... Going "bigger" in increasing the volume of a given enclosure with the hopes of enhancing the low frequency response or increasing the port volume size probably won't give the desired results and may result in a damaged speaker. One function of a sealed box is to provide sufficient air mass within the box such that the voice coil and former does not travel too far back within the magnet and pole pieces slamming against the rear pole piece. A ported box gets a bit more complex as the port acts as a chamber vent at certain frequencies and not at others. A function of this action is port volume, box volume, and speaker cone volume. One way to see just what would work or not: If you have access to box construction software ("boxware") on your device of choice you could use it to get an idea of what kind of response curves the manufacturer's boxes give versus what you might propose in "going bigger". One thing to look out for in a bode plot of SPL (db) versus frequency (Hz) is any large peaks or dips as such would suggest quite rapid cone acceleration that may suggest in some cases risk of mechanical failure . The "engineering" is pretty much done in a manufacturer's box suggestions and they may have a motive in hedging against warranty claims being conservative with the box designs however it's not a bad point of reference if you want to experiment.
  5. For what it's worth and where I've been.... The last time I saw a potentiometer (pot) with more than two gangs was tearing down a quadraphonic (4 channel) home receiver made somewhere around 1970. It had a four gang pot serving as a main volume control for all four channels and two stereo linear pots (sliders) for balance controls on the front and rear channels. I'm sure multi gang pots are probably in some almost jurrassic test equipment through flea markets, yard sales, or even a search on e-bay however it's hit or miss and I can't say what pots are in what make and model of equipment. Two gang (Stereo) pots are still in proliferation as new or as NOS (New Old Stock). One could make a N gang pot using gears, or pulleys springs, and fairly hefty string to drive the shafts in unison from a single shaft. Alternatively small stepper motors and couplers even as crude as rubber tubing fitting on the shaft of pot and motor would also work. There's all kinds of electronic solutions in things such as voltage controlled amplifiers (think LM 13700) and N gang volume controls one can program using SPI and an Arduino. Analog Devices, New Japan Radio, and Texas Instruments have a proliferation of choices and design examples.
  6. One Point Two.. To answer your question directly: No. The whole point I am hoping to make is knowledge is power. For the sake of expediency I presented the JL audio article and YouTube video as but two examples of what are the issues resident to bandpass, vented, and sealed enclosures echoed by electrical engineers, mechanical engineers, academics, and experienced hobbyists within the realm of audio. Am I saying the JL audio article and You Tube Video are absolute irrefutable gospel and the last word ? Absolutely not. Am I evangelizing against bandpass boxes ? Absolutely not. All I'm saying is here's what one faces when building or buying such an enclosure and know what you're getting involved with. One can do with the information what they wish and assign credibility value to it as they see fit. I can see an Nth Order bandpass box having some real value as a mid range especially if the -3dB skirts can be tuned to work without overlaps or peaks in a three way system using a low, mid , and high frequency driver. I've been in things computers, electronics, and audio for over forty years and in terms of speaker box construction: We live in an incredible time where one can run through any number of box designs on or offline and evaluate such designs without picking up a power saw. It's much easier to change designs and parameters with a few screen movements than go through all constructing a box. Yes I was building boxes way before "boxware" and yes I have a few great ideas that didn't work so great. In that same time space I also know there's absolutely no experience for hands on building and testing and to treat simulation and modeling software as absolutely irrefutable covering all engineering is just absurd. Such software is supposed to work as but one tool of many in any kind of engineering endeavor. Alas I must admit in my first post I was confusing Nth order active bandpass filters with Nth order bandpass boxes. Stuff happens. I think the original poster has had their question answered and now they can at least be somewhat motivated to gather more both on and offline and at least make an informed and intelligent decision as to what they wish to do.
  7. Just my opinion and some experience... In terms of grounding what I've found works best is a "star" ground also known as "single point ground" . Typically this can be implemented as a comparatively short thick wire running from the battery negative to a rather large stud where the stud serves as a point to where all other ground wires are connected. In this case and ideally: One ground wire to the engine block, another to the starter motor, another to the alternator case, and others to amplifiers, head units, etc. What this does is two things: One is the elimination of "ground loops" and two provides a superior electrical connection over relying on the integrity of the welds, screws, nuts and bolts used to hold the car together. Yes it can be almost impractical to implement and drive the wiring cost through the roof however it's worth it. If I had a nickel for every ground related problem...
  8. Just my humble opinion and observation... Looking at the entire shared video paying attention to the graphs and discussions for sealed, ported, 4th and 6th order bandpass boxes raises some concerns especially around the time marks in the video mentioned earlier. Reading the entire JL audio article also raises some construction and tuning issues I think one should be aware of especially if building their own enclosure or buying one in some way, shape, or form. In any kind of formal or even impromptu engineering there's decisions and trade offs. Do I want the benefits of increased SPL offered by a bandpass box at the risks involved ? What happens if something fails and what would be the loss or propensity to repair ? If someone is building their own box how can mistakes be corrected ? Murphy's Law does reign supreme . How do the various graphs of frequency versus SPL read and what are the graphs of port velocity versus wattage, frequency, cone excursion, and if so available dispersion patterns in two and three dimensions read ? Bottom line: Want more sound pressure ? Move more air. How to move more air ? Add more drivers, swap in more efficient drivers, or leverage the air in however many chambers in the box to move. All have their risks, rewards, and trade offs.
  9. Here's what I see. Increasing the driver count increases the sound pressure level by virtue of the fact you are moving more air. Adding a second amplifier of same exact kind doubles the current draw on your car's electrical system. To realize an increase in sound pressure using two of a kind speakers: They have to be acoustically in phase. Meaning: They both have to be moving air such that one's not pushing it out of the box while another draws it in or speakers are not otherwise cancelling each other out to whatever degree. Putting two subs in one box can be a challenge because the idea is to get two drivers to operate as one. This may not happen for variances in speaker manufacturing as well as box dimensions and port dimensions used . In my opinion and having tried two drivers in one box: The best is to partition the box into two separate chambers and do all the engineering for one box at a time. "Not Enough Bass" can have two meanings: The sound pressure level is not to your tastes or the low frequency response is too low. In other words you are not hearing frequencies below 100 Hz or lower at the intensity you otherwise would. Perhaps a box redesign or modification would serve better than adding speakers, amps, and electrical load. Are you using online, freeware, or some kind of box software to plot the frequency response curve of the box and design being used ? Are you using a manufacturer's recommended sealed or ported design ? The great thing about "boxware" is it's much easier to change the type of box and critical dimensions with a few keystrokes than it is to cut lumber and building materials.
  10. My .02 worth... This has all the tell tale signs of a failing voltage regulator or a bad ground. One very impromptu and rather inaccurate way to test for a failing regulator would be to drive the car for a while and turn on your headlights. With the high beams on the voltage at the battery should not dip below 14 volts. This assumes the battery is capable of holding a charge. Charge the battery overnight, start the car in the morning, and see what the voltage looks like right after starting versus after driving. Keep the electrical load minimal as possible. Grounds: Even with an old school cast iron engine I've found the best is a thick cable to the battery negative going to a 3/8" stud through the fender wall close to the battery. From the stud there's one ground cable to the engine block, another to the alternator case and a third directly to the case of the starter. There is a noticeable difference cranking the starter and battery charging voltage. Doing some rather rough engineering: An 1800 Watt amp running full power assuming about 80 percent electrical efficiency would require 2,250 Watts. At 12 volts this uses 187 Amperes of current. Is a 250 A alternator "enough" ? It all depends at what speed is the alternator producing 250 Amperes of current, how the car is being driven, and the total electrical load.
  11. As I know and understand it: Car audio does not generally appreciate with age and what something's worth depends on the market quirks and who is willing to pay what . Tube audio gear was once almost relegated to junk however it's had a resurgence of sorts and a growing market similar to the re appearance of Vinyl LP records. With the current pandemic who knows what to expect. I know of what you speak. Memories of youth: Priceless. I have some jurrassic Sanyo PA 6100's bought at a flea market about ten years ago for just about nothing. The things looked like pulls from a flooded out car. Had to have 'em because of the memories back in their day where I was and what I was doing. Any other reason is sheer nonsense. The Sanken Hybrid thick film Power IC's used for the amplifiers are probably obsolete and how the things still manage to work I don't know beyond belief in miracles. About the only real tangible value is the aluminum in the heat sinks and chassis. If you have the knowledge to it: Car audio can make great home audio so not all is lost.
  12. Hi, What you describe is internal oscillation within the amplifier. As described I would posit something else connected to your car battery is emitting noise being conducted in the power feeds to the amplifier. The battery +12V input and "key on" (amp on) are both capable of allowing noise to enter and ultimately cause the problem you speak of. It could be coming from something else connected to your car's battery and one quick way to test would be to remove fuses from the fuse box one by one until it stops. Suspect anything connected to the battery. Even your car's engine and vehicle management computer however use caution when working with that particular box. What you could try is various means of suppression in filter capacitors rated 25 volts , 100 micro farads (uF) placed close to the amplifier on the key on and battery terminals. Alternatively a "parasitic suppressor" , also called a "zobel network" consisting of a .1 uF capacitor in series with a ten ohm resistor may also work. Connect the 10 ohm resistor to the positive connection and the capacitor to ground. What you've made is an RC circuit that filters out high frequency oscillations. A very large "beer can" sized capacitor may solve the problem however I would advise not connecting it to the key on terminal as the current draw to charge such a capacitor would probably blow whatever fuse the key on wire ultimately is connected to. I'm inclined to believe it's not within the amplifier itself as if it was the amplifier would make the same noise even if connected to it's own battery and nothing else.
  13. Pretty good article on band pass boxes here: Bandpass Enclosure Characteristics – JL Audio Help Center - Search Articles And this individual does a pretty good job with the box software in terms of frequency response, applied wattage, and cone excursion for sealed, ported, 4th and 6th bandpass boxes Sealed vs Ported vs Bandpass speaker box/enclosure - YouTube The graph action really starts at around 2:27 . Watch at 5:56 and pay attention to cone excursion.
  14. Here's how I see it: A "bandpass" box or n'th order bandpass box, has a very narrow range of frequencies in comparison to a ported or sealed enclosure optimized to the drivers in question. The greater the n'th order the narrower frequency range and the greater the peak around the frequency the box is tuned to. Generally they are rather difficult to construct and tuning can sometimes mean getting it wrong and the drivers going up in smoke. Whistling is but one example of making your mouth into a "bandpass" box and why you whistle loudest at one particular frequency and not at all at lower frequencies. I've found a simple ported and well constructed box gives adequate for my particular tastes. What's going to determine "how hard it will hit": 1) The rated SPL (Sound Pressure Level) of the drivers in question. Every 3 DB (3 Decibel) increase requires twice the amp power used to the prior sound level. So in essence the higher rated SPL of a given driver the more efficiently it converts electrical energy to mechanical energy in sound pressure. Speakers make either sound or heat. 2) The response curve or "bode plot"of the driver in question and any associated passive crossover components used in the design. 3) The box and how the dimensions of it, any vents if so present, against the cone resonance (Fs) and Thiele Small parameters for the speaker being used. Hypothetically the more drivers one has the greater sound pressure level as increasing the driver count increases the mass of air moved. Assuming they are all operated in phase and in suitable enclosures. To get things louder simply move more air. By far the "hardest hitting'" enclosures are probably very massive (Think 12 feet wide by four feet tall and six feet deep ) horn loaded monsters built by JBL used in outdoor commercial sound applications. These things are very scaled up versions of a horn tweeter but built for bass and lots of it. In this case there's a LOT of air in the horn cavity of these beasts that hits like a freight train once it gets moving. Understand: "How Hard it Will hit" depends on your own personal preferences: It could very easily be you may enjoy a third or forth order bandpass box tuned to about 40 Hz over a ported tuned down to 20. I would definitely ask around and listen around to what others have done and try to get some idea from there forward.
  15. Hi All !  Glad to be here.   "Old Electronics Geek" in more ways than one.  

     

×
×
  • Create New...