The importance of thin-wall cabinets for small speakers, any solutions?

[ojg]

One of the most important reasons DIY'ers and commercial manufacturers alike choose to make small speakers is that we want them to take up less space in our room. We would all prefer large speakers if this wasn't important to us.

The smaller the speaker get the more critical the wall thickness of the cabinet becomes. The table below illustrates this, I have calculated the internal and external volume of cabinets from 1 to 10 liters with internal dimensions related for this example by a so called golden ratio of 1.6 and wall thickness of 10mm (already considered by many to be very thin).

Internal volume, External volume, Increase in %
1.0000 1.7820 78.2000
2.0000 3.1944 59.7202
3.0000 4.5357 51.1901
4.0000 5.8381 45.9518
5.0000 7.1146 42.2916

The same internal volumes but this time with wall thickness of 5mm
Internal volume, External volume, Increase in %
1.0000 1.3558 35.5750
2.0000 2.5536 27.6785
3.0000 3.7183 23.9447
4.0000 4.8648 21.6211
5.0000 5.9991 19.9828

As you can see the difference for small volumes is quite dramatic. Commercial manufacturers solve this by using thin walled cabinets of molded plastic or cast aluminum. These methods are not available to DIY'ers so how could we best make thin walled small cabinets?

[mdocod]

Those hollow plastic fence post builds around the net offer some insight into a method if getting thin-wall boxes made by the DIYer with minimal fuss. Just glue in a cutout to the top and bottom ~1/2" thick or whatever floats your canoe.

[ojg]

Interesting, had not heard about those fence post builds.

Plastic tubes may be a valid solution, if they are stiff enough. It limits the choice of dimensions though, the width and depth has to be equal which isn't ideal.

For those interested here are the internal dimensions of the speaker volumes in the first post in cm:
6.2500 10.0000 16.0000
7.8745 12.5992 20.1587
9.0141 14.4225 23.0760
9.9213 15.8740 25.3984
10.6873 17.0998 27.3596

and external dimensions for 10mm wall thickness
8.2500 12.0000 18.0000
9.8745 14.5992 22.1587
11.0141 16.4225 25.0760
11.9213 17.8740 27.3984
12.6873 19.0998 29.3596

[mdocod]

Here's one: Fence Post Speaker 2.0 - AudioKarma.org Home Audio Stereo Discussion Forums

There are some on the youtooob, some on other forums. I personally think it's a great idea. I think a guy could make some pretty respectable little micro speakers for dirt cheap utilizing them. or the tall skinny floor standing units as pictured above are certainly interesting (I think they are actually attractive personally).

Eric

[sreten]

Hi,

Probably by using thin ply and lining the cabinet internally with
perforated zinced steel sheeting, attached by a thick contact
adhesive layer that would act as a constrained damping layer.

Something similar has been done in the past.

A wackier idea is thin ply, a layer of porous but stiff foam and then
a further layer of holed pegboard / hardboard internally, the walls
would form absorbers at certain frequencies but below those the
foam layer would contribute to the effective internal volume.

I've had some wacky ideas regarding the issue over the years,
including thin ply walls with an internal matrix of varnished
holed corrugated cardboard as effective bracing.

Mission allegedly made a small sealed speaker with thin walls
and completely filled with fairly stiff porous foam as "bracing".

Using something like 1/4" steel plate for the front baffle helps.

rgds, sreten.

[AllenB]

It's worth noting that smaller boxes will hold smaller woofers which are probably used to a higher frequency. There is therefore a call to make the walls more stiff. Further to that, the front baffle, which holds other drivers/ranges, should probably be even more solid.

[benb]

Originally Posted by ojg

...
As you can see the difference for small volumes is quite dramatic. Commercial manufacturers solve this by using thin walled cabinets of molded plastic or cast aluminum. These methods are not available to DIY'ers so how could we best make thin walled small cabinets?

The plastic thing is getting closer to reality with reprap machines. Here's the latest:
MakerBot Replicator? - MakerBot Industries
The build area (volume) is still too small for a (full-range) cabinet, and substantial wall thickness would take a lot of plastic, but perhaps a cabinet could be build up from several "prints." Also this (melted and extruded plastic built up in layers to make the cabinet) may not be the same as molded plastic, but I have the bottle opener right in front of me, and even though it's a not-quite-competed print, it seems pretty strong to me.

Also, with "printing" the walls, they don't have to be flat, they can have built-in beams for strength and raising resonant frequencies of the panels, and/or have weird patterns on the inside and/or outside as sreten was mentioning. I'm trying hard not to mention the infamous "E" word here...

[planet10]

PVC tubing makes good thin wallenclosures.

You might find suitable metal tubing.

dave

[mdocod]

there are heavy duty PVC and Fiberglass "square" tube with rounded corner profiles available. Up to 6x6" at mcmaster. Not exactly cheap stuff but... you could probably get quite a few little "micro towers" out of a 5' section ($100+ depending on size).

Eric

[ojg]

Originally Posted by sreten

Hi,
A wackier idea is thin ply, a layer of porous but stiff foam and then
a further layer of holed pegboard / hardboard internally, the walls
would form absorbers at certain frequencies but below those the
foam layer would contribute to the effective internal volume.

I like this kind of whacky idea!

You could build up a board from many thin layers (~1mm each?) where only the outer layer was solid, the others were holed out, sort of like swiss cheese. Bonded together it would be just as stiff as a solid board of same total thickness I would think.

I was also thinking about prestressing thin plywood by forcing it to bend. For example the sidewall could be thin ply that was bent outwards by tightening bolts that went from front to back panel. Prestressing it like that should make it resist the internal airpressure better.