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How exactly does a subwoofer work?


26 replies to this topic

#1
Bumpindemlowzz

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I dont know if this has been discused before but i personally never got into the technical workings of a subwoofer... I know that power is sent through the tensil leads then into the voice coil then with the different low frequency signals it moves differently. I never also understood why subwoofers can only handle so much power depending on magnet (motor size). Sounds like a stupid question but im just trying to get a indepth understanding of how a subwoofer works. On the forum its been talked about how amplifiers work, how subs are put together and i thought this would be a nice addition to the know how.

Edited by btlcavalier, 23 October 2009 - 08:35 PM.

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#2
tripleb45

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not a bad topic I am in the process of figuring that out. Many will probably talk down on you so just ignore them and sooner or later someone with actual good input will come along. I wish I knew though.

#3
S15_Silvia

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OK, as I understand it:

-Current goes through the voice coil, causing it to create its own small electromagnetic field. This opposes the already-present field made by the motor, which makes the coil move.


I guess some of the major factors in the construction of a woofer that would cause it to blow would be a very thin gauge wire used for the coil, a spider that allows the coil to hit the back plate really easily, or some abnormality in the suspension that allows coil rock. I guess you could also include bad adhesive used to pair up the basket and the suspension, but I haven't really seen a sub 'come apart at the seams' so to speak.

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#4
Bumpindemlowzz

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i know the basics but i would like to know everything. Im sure there more people out there with less experience that would benifit from a great writeup.

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#5
Kranny

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the bigger the magnet, generally the more efficient the woofer will be. when the current is going through the voice coil, its electromagnetism is affected by the magnetic field of the strong motor, which causes the voice coil (which is attached to the cone) to move more air.

kind of like comparing an Xplod to a BTL. stronger motor (along with other characteristics) is a means for a louder woofer with higher sensitivity.

http://www.bcae1.com/speaker.htm
http://www.bcae1.com/speakrat.htm

Edited by Krannyman92, 23 October 2009 - 08:47 PM.

Lol overpriced amp huh. Shows how much you know. I know folks. Dont be mad you run a piece of shit amp. You and all the other dont know bbetters can say man itd awesome its awesome and I got it for 125 bucks. Ive spent more on glue.

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#6
Nirvalica

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This isn't really to help you, but I thought it was funny. I was talkin to this guy at work who had two RF P1's in a small sealed box. The cones were broken and they looked and sounded like shit, but he told me the cones were just "covers" and it didn't affect the sound. I didn't feel like tellin him, so I just let him believe it. Later he was tryin to tell me that a lot of people believe that the bigger the magnet on a sub, the more powerful it is, but he said that's not true. He was trying to tell me all the magnet is used for is for cooling of the voice coil. TBH, I was kind of impressed he knew there was such a thing as a voice coil in the sub. But again, I just kept my mouth shut. Didn't want to argue because he seemed to think he knew his shit and there probably would be no convincing him otherwise.

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#7
MickyMcD

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A dynamic coil loudspeaker consists of a diaphragm, often circular, held in a suspended position. The diaphragm has a Coil Former attached to one side in the dead center position. On this coil former is a long length of conductive ceramic insulated wire, rolled and wrapped into a coil. The ceramic insulation prevents the formed coil from short circuiting between lengths.

The coil former with coil attached is positioned in a tight clearence circular gap in the walls of the magnet. Often, the magnet has a circular cutout made, and the pole piece is inserted through the center of the hole, forming the tight clearance gap.

The magnet is a permenant magnet, in that it is permenantly exerting a magnetic field on other ferrous materials.

When electrons are sent through a length of wire, a magnetic field is created at 90 degrees to the incident. In high-school physics, this is referred to as the SLAP rule. Hold out your hand as if you were to slap someone with an open hand. Your thumb represents the electron path, and your fingers represent the path of the emmitted mangetic field.

So, by forming a coil, all lengths of wire on the former (apart from those connecting the coil to the terminals) exert a field in the same direction, which interfaces with the magnetic field exerted from the magnet. If the magnet is a permenant North magnet, when the coil shows a North field, the diaphragm will move away from the magnet and out of the gap. If the coil shows a South field, the diaphragm will move towards the rear of the magnet.

The coil, former, diaphragm and magnet are all held in place by a basket to make the device one unit.

Also, the diaphragm has two main methods of suspension. The Surround is a sealing device that joins the edge of the diaphragm to the edge of the basket. It also aids in keeping the diaphragm centered, and aids in controlling excursion. Then there is your Suspension, or spyder (spider). This is a tightly rolled circle of cotton (or other materials, hard to keep up now) that joins the coil former to the basket. This is usually quite firm, and aids in stopping cone motion after signal and to keep the coil within the mangetic gap.

I have left a LOT of information out. This is the very, very basic. There are many different designs, many ways to achive loudspeaker design. There are ribbons, planar transducers, electrostatic loudspeakers and rotary fans. Metric Dicktonnes of designs.

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#8
xX MocK

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A dynamic coil loudspeaker consists of a diaphragm, often circular, held in a suspended position. The diaphragm has a Coil Former attached to one side in the dead center position. On this coil former is a long length of conductive ceramic insulated wire, rolled and wrapped into a coil. The ceramic insulation prevents the formed coil from short circuiting between lengths.

The coil former with coil attached is positioned in a tight clearence circular gap in the walls of the magnet. Often, the magnet has a circular cutout made, and the pole piece is inserted through the center of the hole, forming the tight clearance gap.

The magnet is a permenant magnet, in that it is permenantly exerting a magnetic field on other ferrous materials.

When electrons are sent through a length of wire, a magnetic field is created at 90 degrees to the incident. In high-school physics, this is referred to as the SLAP rule. Hold out your hand as if you were to slap someone with an open hand. Your thumb represents the electron path, and your fingers represent the path of the emmitted mangetic field.

So, by forming a coil, all lengths of wire on the former (apart from those connecting the coil to the terminals) exert a field in the same direction, which interfaces with the magnetic field exerted from the magnet. If the magnet is a permenant North magnet, when the coil shows a North field, the diaphragm will move away from the magnet and out of the gap. If the coil shows a South field, the diaphragm will move towards the rear of the magnet.

The coil, former, diaphragm and magnet are all held in place by a basket to make the device one unit.

Also, the diaphragm has two main methods of suspension. The Surround is a sealing device that joins the edge of the diaphragm to the edge of the basket. It also aids in keeping the diaphragm centered, and aids in controlling excursion. Then there is your Suspension, or spyder (spider). This is a tightly rolled circle of cotton (or other materials, hard to keep up now) that joins the coil former to the basket. This is usually quite firm, and aids in stopping cone motion after signal and to keep the coil within the mangetic gap.

I have left a LOT of information out. This is the very, very basic. There are many different designs, many ways to achive loudspeaker design. There are ribbons, planar transducers, electrostatic loudspeakers and rotary fans. Metric Dicktonnes of designs.

Cheers,
Mick

You sir, is smart.

#9
HHR Ed

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I dont know if this has been discused before but i personally never got into the technical workings of a subwoofer... I know that power is sent through the tensil leads then into the voice coil then with the different low frequency signals it moves differently. I never also understood why subwoofers can only handle so much power depending on magnet (motor size). Sounds like a stupid question but im just trying to get a indepth understanding of how a subwoofer works. On the forum its been talked about how amplifiers work, how subs are put together and i thought this would be a nice addition to the know how.


I didnt read other people's responses but.

Motor (magnet) size has little to do with power handling and efficiency.

The coil is electrified with an AC current.

This AC current magnetizes the coil sitting in a magnetic field.

The AC current is a changing current which changes the poles back and forth.

This causes the coil to oppose the Magnet and move, creating an electric motor.

The Coil and coil former is attached to a piston (cone) which when moved back and forth, causes air molecules to vibrate at the rate of the AC current being fed to the coil.

This vibration of air molecules is sound.


Power handling is dependant on the wire gauge used on the coil as well as the height and diameter of the coil and the cooling characteristics of the motor geometry.
Mechanical Power handling is also determined by the strength and design of the suspension (surround and spider)

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#10
Boon

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Larger motor means 2 things generally - more BL or motor force so the woofer is more efficient and it generally indicates that there's a larger voice coil hidden inside there. Larger coil = more heat dissipating capacity so it can take more power and also generates a larger electromagnetic field, making the woofer louder, generally... of course there are exceptions to all of this :)
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#11
HHR Ed

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the bigger the magnet, generally the more efficient the woofer will be. when the current is going through the voice coil, its electromagnetism is affected by the magnetic field of the strong motor, which causes the voice coil (which is attached to the cone) to move more air.

kind of like comparing an Xplod to a BTL. stronger motor (along with other characteristics) is a means for a louder woofer with higher sensitivity.

http://www.bcae1.com/speaker.htm
http://www.bcae1.com/speakrat.htm


Thats not really true,

Larger motor has very little to nothing to do with efficiency and sensitivity.

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http://www.stevemead...08/#entry511451

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New Ride, 2008 HHR SS. Build under way.
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#12
Bumpindemlowzz

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great responses guys thanks.

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#13
Kranny

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Thats not really true,

Larger motor has very little to nothing to do with efficiency and sensitivity.


i know its not really that true, hence i put "generally"

edit: but then why does lets say, the example i gave, the xplod and BTL. both being 12" speakers, giving lets say 100w to each. the btl would be louder since its much more efficient since the motor has a MUCH stronger force (and other things)

Edited by Krannyman92, 23 October 2009 - 09:57 PM.

Lol overpriced amp huh. Shows how much you know. I know folks. Dont be mad you run a piece of shit amp. You and all the other dont know bbetters can say man itd awesome its awesome and I got it for 125 bucks. Ive spent more on glue.

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#14
HHR Ed

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BL, and motor force is kinda like Torque for a car motor vs. Horsepower.

A strong motor doesnt mean a woofer will be sensitive, it just means that it will have the strength to push a more massive cone and be able to push through power compression.

In the higher SPL range over 155 dB, tremendous air pressure is placed on the cone as it moves. So alot of force is need to push against this air resistance, thats when powerful motors are needed.

But sensitivity and efficiency is more based on the coil charachteristics and mass and weight of the moving parts as well as how the suspension allows the cone to travel.

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http://www.stevemead...08/#entry511451

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#15
MickyMcD

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But sensitivity and efficiency is more based on the coil charachteristics and mass and weight of the moving parts as well as how the suspension allows the cone to travel.


This.

Cheers,
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#16
tripleb45

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this is teaching me something

#17
fritosaregood

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no one has mentioned the top plate. isnt that what the coil is repelling from (when it is turned into an electromagnet)

#18
Boon

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no one has mentioned the top plate. isnt that what the coil is repelling from (when it is turned into an electromagnet)


The top plate, AFAIK, is more for focusing the energy of the motor into the gap.
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#19
Forevrbumpn

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top plate is kind of light a lens, it focuses on the magnetic field, different top plates will achieve different results- narrow, or widen the magnetic field, with a loser, or tighter VC gap, or taller top plate, or shorter top plate, or you can use a top plate with a split design, to created a dual magnetic field, for more coil travel, more linear excursion, without causing distortion, or losing motor strength
There is also Under hung design, and over hung design
1 the coil is taller than the top plate
the other the top plate is really tall, maybe 1.5" tall, and the coil is really short 1.5" tp vs a 0.75 vc example

Power handling is mostly dependent on coil surface area, to dissipate heat, and wire gauge has a little to do with that as well

Different wire gauge gets you lesser or higher ohms common wire gauge is about 24/25g on a 2.5" coil, 22-18gauge on a 3" coil, and about 18-17gauge on a 4" coil

How many layers a coil has, 2, 4, 6, 8 layers determine other factors, like mH - Le of the coil, which will deal a lot with the efficiency of the coil/cone assembly in the magnetic gap

A lot of people are using lesser layers, and much longer winding widths now to produce higher efficiency woofers, to create higher Bl, and lower handling woofers
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#20
Bumpindemlowzz

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Nice to know thanks guys. Im always up to learn something new.

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