Subwoofer components and their effects on Thiele-Small Parameters

[Joseph7195 10+ year member]

I am about to build up some old Fosgate motors, and it had me wondering. How can I make the most informed decisions on the components to build my subwoofers?

How does cone weight affect the sub?

Does magnetic gap and voice coil length change characteristics of the sub substantially?

What affects do the materials and stiffness have on the spiders?

What I would really like is someone to explain to everyone, how changes to a subwoofers many components, can change its characteristics, and how someone could use this knowledge to build a subwoofer to fulfill all of one's needs.

I know all the Thiele-Small parameters, and their meanings, but how can they be changed to benefit us in the real world.

Maybe someone could tag some builders like Jacob at sundown, Dave flstrongman, or Spl Cory.

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[Papermaker85 5,000+ posts]

without a program to help you build a speaker. you can only use the formulas and get parts and measure them to be-able to use the formulas. for example measuring the stiffness and elasticity of the spiders to get the CMS/FS desired once you know your MMS.

chance are there is a good woofer on the

market that will do what you want it to.

 

[ciaonzo 5,000+ posts]

This is great topic but a long conversation. It's certainly a balancing act. A good start would be to separate the electrical parameters from the mechanical ones, to know how they really interact with each other and how they are influenced by any changes in any one part. I'm at work so I can't go long right now but I'll touch on the ones you listed.

How does cone weight affect the sub? - (Mms) Too heavy and it will not only eat into sensitivity (very important if you want loud), but it will also negatively impact the impedance magnitude at Fs (huge peak), especially if the motor is weak.

What affects do the materials and stiffness have on the spiders? - (Cms) Too soft with a strong motor and you can shred them if not used in a small sealed enclosure. Too stiff with a weak motor and you will run into thermal issues because motor force will be low and you will try to compensate with more power.

Does magnetic gap and voice coil length change characteristics of the sub substantially? - (BL, Qes) Long coil/ short gap is good for linearity in the stroke. Too long a coil (potentially Mms and bottoming issues). Shorter coil/ short gap is good for vented as long as there are enough windings in the gap and motor force (BL) is adequate. Shorter coil also gets you back to lower Mms. Just stay away from even-hung topology. Good for sensitivity but not for frequency response linearity if you want low frequencies.

People that want to get loud should find tight gap motors, run coils that don't have many layers and are not too long, and stay away from parts that are too stiff. Let the enclosure do the work to control the cone and shape the frequency response.

People that want linearity over output should find larger gaps (not too large), run long coils with decent layers, and stay away from parts that are too stiff. Let the driver do most of the work and the enclosure to have a minimal but necessary impact on frequency response.

Those are pretty vague statements, so please don't kick me in the nuts. There's a lot missing in between all that. I realize lots of guys these days are running what I call forced alignments with good results. I do the same. I'm just saying some of this to get the conversation rolling.

 

[Joseph7195 10+ year member]

I am about to build up some old Fosgate motors, and it had me wondering. How can I make the most informed decisions on the components to build my subwoofers?
How does cone weight affect the sub?

Does magnetic gap and voice coil length change characteristics of the sub substantially?

What affects do the materials and stiffness have on the spiders?

What I would really like is someone to explain to everyone, how changes to a subwoofers many components, can change its characteristics, and how someone could use this knowledge to build a subwoofer to fulfill all of one's needs.

I know all the Thiele-Small parameters, and their meanings, but how can they be changed to benefit us in the real world.

Maybe someone could tag some builders like Jacob at sundown, Dave flstrongman, or Spl Cory.

This is great topic but a long conversation. It's certainly a balancing act. A good start would be to separate the electrical parameters from the mechanical ones, to know how they really interact with each other and how they are influenced by any changes in any one part. I'm at work so I can't go long right now but I'll touch on the ones you listed.
How does cone weight affect the sub? - (Mms) Too heavy and it will not only eat into sensitivity (very important if you want loud), but it will also negatively impact the impedance magnitude at Fs (huge peak), especially if the motor is weak.

What affects do the materials and stiffness have on the spiders? - (Cms) Too soft with a strong motor and you can shred them if not used in a small sealed enclosure. Too stiff with a weak motor and you will run into thermal issues because motor force will be low and you will try to compensate with more power.

Does magnetic gap and voice coil length change characteristics of the sub substantially? - (BL, Qes) Long coil/ short gap is good for linearity in the stroke. Too long a coil (potentially Mms and bottoming issues). Shorter coil/ short gap is good for vented as long as there are enough windings in the gap and motor force (BL) is adequate. Shorter coil also gets you back to lower Mms. Just stay away from even-hung topology. Good for sensitivity but not for frequency response linearity if you want low frequencies.

People that want to get loud should find tight gap motors, run coils that don't have many layers and are not too long, and stay away from parts that are too stiff. Let the enclosure do the work to control the cone and shape the frequency response.

People that want linearity over output should find larger gaps (not too large), run long coils with decent layers, and stay away from parts that are too stiff. Let the driver do most of the work and the enclosure to have a minimal but necessary impact on frequency response.

Those are pretty vague statements, so please don't kick me in the nuts. There's a lot missing in between all that. I realize lots of guys these days are running what I call forced alignments with good results. I do the same. I'm just saying some of this to get the conversation rolling.

This This and This!!!!!!!!!!!! I hope we can get some information about how to make better decisions when building subs. I know there is a lot to learn, but I hope we can get it all in one spot.

Richard(KHA) Sent me some eBooks i read, and it helped tremendously.

 

[Papermaker85 5,000+ posts]

it took me years. i had a few drivers built. its not easy but when you have a general understanding on how they work its much easier.