So, I love the idea of innerchoic speakers, like the PNB line. And it seems to be a really great concept. But here's the question... If one were to design a cabinet with this arrangement, does it negate the need for sound damping? Does it eliminate the need for polyfill or Acoustic foam? And if I combine thick walls (i.e. mass) with the shape, do I get a double benefit?
Designing the shape for a router template is so easy. And so tempting.
Designing the shape for a router template is so easy. And so tempting.
The kinetic energy in a sound wave is converted to heat by the action of viscosity in regions of high velocity gradients in the air. Squeezing air through small passages in foam achieves this in an anechoic chamber. Little bumps of wood on the wall of a speaker create no significant velocity gradients and so convert no energy in the sound waves into heat.
I am no acoustician but looking at the pnb site it looks like they are trying to reduce internal standing waves by providing a textured inner to the speaker. I guess the novelty is doing it by layering up the cut MDT slices, thus may provide a slightly stiffer cabinet depending on the profiles and how well they are glued together. However, there is no reason why the same effect can’t be had by using flexy ply or rib cut MD’s over three or four formers and putting the egg box type foam on the inside which may be easier for the diyer unless you have a cnc router or deep pockets as it will generate a lot of waste.
Just my pennies worth.
Just my pennies worth.
To be effective, hard objects (obstacles) should have dimension comparable to a sound wavelength (a good fraction of it). Small bumps inside the Innerchoic enclosure are effective only for frequencies above 3-4 kHz. Even the cheap B&W DM302 had bigger wedges on the back panel! One-inch foam will absorb 100% of sound wave at this frequency. So, Innerchoic is a pure snake-oil.
Adding to some of the above...
Not to this jaded designer it doesn't. I can't think of any particular harm (other than the ridiculous waste of material caused by translaminate construction) but nor can I think of any spectacular advantages either. Yes, it will reduce lateral standing waves (but it's a curved box anyway), but those wavelengths are easily killed by damping given that the frequency is high. Which is a lot cheaper and easier to build.
Not if you want high performance it doesn't.
Those are sound damping, so see above.
Chances are you'll simply lower panel Fs into the main box operating region where the maximum amount of energy is available to excite it. High mass is not ideal for bass enclosures (fine for midrange & HF) since it's almost impossible to lower panel Fs < Fb without resorting to ridiculous thicknesses or extreme materials.
Which is the primary reason people want to build them.
Not to this jaded designer it doesn't. I can't think of any particular harm (other than the ridiculous waste of material caused by translaminate construction) but nor can I think of any spectacular advantages either. Yes, it will reduce lateral standing waves (but it's a curved box anyway), but those wavelengths are easily killed by damping given that the frequency is high. Which is a lot cheaper and easier to build.
Not if you want high performance it doesn't.
Those are sound damping, so see above.
Chances are you'll simply lower panel Fs into the main box operating region where the maximum amount of energy is available to excite it. High mass is not ideal for bass enclosures (fine for midrange & HF) since it's almost impossible to lower panel Fs < Fb without resorting to ridiculous thicknesses or extreme materials.
Which is the primary reason people want to build them.
That's more like what I was thinking. I'm no acoustician, either, but as I understand it, the eggcrate cancels the standing wave, and the fill is for tweaking the tuning. But this seems to be a really contentious topic.
I've not seen any other fill material in the PNB speakers, but admittedly, I've not seen them up close. But I do find it hard to believe that anyone can sell snake oil for $30,000 a pair, for any amount of time.
Not for me. To me, they're just plain beautiful. I like the aesthetic of end grain. And I don't waste the leftover material. Every last scrap gets re-purposed in my shop.
I've built a few translaminate enclosures. Always with curved sides and back. So, it would be your assertion that the curves are worth more than an overlapping eggcrate structure?
Sorry, I didn't see your reply earlier.
If I have a curved cabinet, there have been differing opinions that I've seen on how and what to apply. Some have said only foam behind the driver, others have said polyfill the entire enclosure, others yet say no poly near drivers, others say no foam at all, etc, etc, etc...
I spent a lot of time building enclosures only to have such a wild swing of information on this one topic. Maybe the best way to understand this, would be to ask how one ideally tests this. Traditional logic for square boxes seems to be to line the back wall first, and then add gradually, while testing in-between.
Eggcrate should have dimension of several feet high to be effective. There is no argument against the laws of acoustics.
There are many snake oil products costing more than $30,000 and they are selling well, for years.
Statement of fact rather than assertion. There is zero practical acoustic benefit to internal solid profiling like an eggcrate (in those dimensions), although it's unlikely to cause any harm either. Basic laws of physics / acoustics, no mystery here.
For curved panels, yes. Marginally. In the same way that some parts of the Titanic are marginally less underwater than others. That's as far as the internals are concerned. Externally -of more use.
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Not saying that you're wrong. Just wanted to see it substantiated.
I'm no expert on acoustics, so this is all learning.
The amount and where to place foam for maximum effect in a speaker depends on what you want it to do. It varies with subwoofer, woofer, midrange and tweeter enclosures. It varies with sealed, vented, transmission line, horn,... type enclosures. If you know what you want the foam to do then what to measure should follow.
My curvy cabinets are sealed, 2-way, and approximately 20L. They are a Zaph ZRT design. I have internal bracing ONLY behind the midrange/woofer. I don't like polyfill, but if it's the tool for the job, so be it.
Also, I have 2 subwoofer enclosures, just built. They are 1.5" thick baltic birch construction, with internal bracing that spans each panel like a cross, perfectly centered, and is 1.5" wide by 3/4" deep. This box is stiff as concrete. It was originally my idea to cut a square of acoustic foam, and put it in each quadrant of the panels, between the bracing. But I wonder what my strategy should be in a case like that. (sealed sub)
Also, I have 2 subwoofer enclosures, just built. They are 1.5" thick baltic birch construction, with internal bracing that spans each panel like a cross, perfectly centered, and is 1.5" wide by 3/4" deep. This box is stiff as concrete. It was originally my idea to cut a square of acoustic foam, and put it in each quadrant of the panels, between the bracing. But I wonder what my strategy should be in a case like that. (sealed sub)
I'm with Dave on this one. Offsetting interrupts the equal exciting of the panel on either side of the brace.
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