Thank you. Yes, I considered those effects would be a possibility, but I don't think they would be an issue regards a subwoofer, however, I am interpretting ballooning to be a no-resonant issue, I might be wrong?
Breathing mode. The box will return to its normal shape using this mode. Can be responsible for one note bass.
Alas the equations for plate deflection are fiendish, and depend strongly on how stiff the support for the edge of each wall is, but I suspect even with quite thick walls any bracing will dominate the flexing stiffness and is worth it.
That's interesting, I've not come across breathing mode before, nor can I find any information on it. It sounds feasible, so a partially resonant effect then but only in one direction?
The panels move in both directions along with the driver. This mode is where all the panels move in the same direction at the same time (inward or outward), and based on this, the highest effective radiation through the cabinet compared to other panel modes.
These panels and their resonances, together represent a box resonance that will restore the panels to their resting position whenever they are/have been moved, transferring energy to that frequency.
These panels and their resonances, together represent a box resonance that will restore the panels to their resting position whenever they are/have been moved, transferring energy to that frequency.
Yep. Think of the box as a wood balloon. The woofer pumping in and out will expand and contract the box walls.
There doesn't seem to be much information here on "how think does it have to be" and that might be because measuring the panel resonances is no mean feat. There is a thread from earlier this year about attempts to measure box panel resonances (it was mentioned earlier in this thread). Measuring only the panels isn't easy. I actually built a laser/mirror/photo-diode contraption to attempt panel measurement. It was promising, but was very hard to get right, as you might imagine.
There doesn't seem to be much information here on "how think does it have to be" and that might be because measuring the panel resonances is no mean feat. There is a thread from earlier this year about attempts to measure box panel resonances (it was mentioned earlier in this thread). Measuring only the panels isn't easy. I actually built a laser/mirror/photo-diode contraption to attempt panel measurement. It was promising, but was very hard to get right, as you might imagine.
I forget who did it, but one DIYer built a sealed box with a driver rigidly mounted inside to 'drive' it and experimented with bracing, etc., mounted on the outside to determine what worked best overall.
Same thot came to me, but the experiment on the outside is a new trick.
That the brace is not also against an opposing wall results would apply to only those kinds of braces. I imagined a box built into the wall, driver on one side, box to measure in the anechoic chamber on the other side.
dave
That the brace is not also against an opposing wall results would apply to only those kinds of braces. I imagined a box built into the wall, driver on one side, box to measure in the anechoic chamber on the other side.
dave
You mean completely enclosed inside? How could that affect the cab in the way reciprocating pressure does when the driver is on a baffle exposed to the outside?
Also, I'm wondering why fired clay is not used for this purpose. Sandwiched between two layers of something would render it virtually inert. It just does not resonate at the frequencies of interest, apparently.
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This?
Measuring the sound radiation of speaker cabinet walls
Some more links & stuff in this thread.
Measuring sound output from speaker cabinet walls
My own experiment (done with a mini speaker inside a larger speaker) indicated that the sound inside the cabinet (airborne acoustic energy) mainly exits the box by radiating straight back through the woofer cone, far more than through the walls.
A woofer cone is a thin layer of paper (or fibreglass or whatever), so will always be a jillion times more transparent to sound than a slab of plywood.
I don't see why. It may be more free to move like it's not in a box. Weren't you talking about cone deformation?
It just seems the ability of the cone to maintain it's shape under pressure would be overcome by the stiffness of the cab by orders of magnitude. OTOH, I should mention I'm the first to admit I actually don't know what I'm talking about. 
In engineering every structure, no matter how stout or how high the modulus of the material it's made of is a spring and a mass and it has a resonance. Make it stiffer while holding everything else constant (good luck) and the resonance rises in frequency. Make it more massive while holding everything else constant (good luck) and the resonance falls in frequency. Everything you do in a real structure will change both stiffness and mass and the net effect will be the result of an interplay between these two fundamental properties. No matter how thick you make a panel adding a brace behind it will stiffen it to some degree. When an engineer thinks of a structure the focus is the loads that the structure transmits, ultimately to ground and the efficiency with which those loads are transmitted. Maximum stiffness with minimum mass is the ticket to driving resonances higher and making panels arbitrarily thick is not an efficient way to accomplish that goal.
Correct, used to excite the box to hear how it 'sings' [or not].
The typical speaker box is presumed to have a uniform particle density, so can only expand/contract the box ['breathe'], though normally not an issue per se if properly designed for its intended BW.
Correct.
No, but thanks for the links! Finally remembered and IMNSHO should be required reading for neophyte DIYers: Art Ludwig's Sound Page
Right and what we're trying to eliminate!