My insane Peerless subwoofer

[BassAwdyO]

interesting... I'd like to do a few of my own tests on that

All I know is a thicker baffle is better for subs as the stiffness will increase and thats what we're really after

[nunayafb]

When two layers of material such as wallboard are glued firmly together, they behave like a single thick layer with an associated lowering of the coincidence frequency.

simon5, I think you are confusing coincidence frequency with resonant frequency,

"Transmission loss graphs for stiff materials show dips in particular frequency ranges where the sound transmission losses are reduced below those expected from mass law. This is called the coincidence effect and often leads to a reduced STC rating." (from the above link)

My interpretation of the article was that the coincidence frequency is the point in which there is an increasing loss of transmission below that frequency.

Whenever you increase the rigidity(thickness) of a panel you increase the resonant frequency, for speakers the r.f. should be above the highest freq. reproduced.

[simon5]

The coincidence frequency is the frequency where you see a dip in damping. You have less transmission losses, so if that frequency is produced inside the enclosure, it will be transmitted on the outside with less damping.

If it's a dip in damping, it's a peak in resonance.

Reverse the first graph to understand what I mean.

I'm not an expert, so correct me if you believe I'm still wrong.

[nunayafb]

yeah simon5 I'm not an expert either but I do know that sound reproduction is a function of motion. In terms of purely sinusoidal forcing a panel will move more if the amplitude of the input is increased or if the frequency is reduced. I believe that panels follow the same frequency/dispacement law(or close enough) as dynamic speakers, one octave reduction requires 4x the displacement.

If panel thickness is increased, the potential for flexure is reduced, and so is the ability to transmit low frequencies.

Think about it this way, if your interpretation of the article was right, you would want the thinnest walls possible to raise the resonant frequency above audible. To go to the extreme, picture a box made from veneer!
(Not trying to be a smart@$$)

BTW were not hijacking this thread, we're impatiently waiting for pictures and stories of structural damage, tic-toc buddy

[simon5]

Well like I said in my first post... World of compromises.

Thicker means you lower the transmission of sound alot but also shift the resonance peak lower. For a midrange enclosure you could build it very very thick so you shift it very low so it doesn't matter.

But with subwoofers you can do that the other way, by bracing very very extensively so you shift the resonance frequency so high it doesn't matter.

According to the chart you can also use other materials like lead with a A constant of 55000 Hz so a 2" thick subwoofer made of lead would resonate at 1 kHz which would be a non issue also. That would also need a crane to carry but that's a story for the next episode.

[RHosch]

A thicker baffle will not result in a lowering of that panel's resonant frequency so long as the bond line between panels is rigid (enough so that the panels effectively behave like a single thicker panel).

Regardless of what convoluted explanations might be found elsewhere, the math is rather straightforward as is the physical explanation.

Bracing is a more efficient way to achieve a desired stiffness/mass (i.e. frequency) result (i.e., takes less wood, and less weight), but the increased thickness has the additional benefit of increased damping.

The downsides are "only" weight, cost, and manufacturability.

[simon5]

I like the word manufacturability.

Well an enclosure with a lot of bracing is hard to manufacture too...