box in a box

[Slothrop]

I've been contemplating a loudspeaker enclosure and I'm hoping to get some feedback. I'm sure this is an old idea, but I haven't had any luck finding similar designs. Maybe that just means it's a bad idea.

Suppose you want a sealed box, acoustic suspension. Now suppose you want to kill as much of the sound from the box itself as possible. Instead of making the walls of the box super-stiff or ultra-dead or damped or whatever, what if you put the box in another box, and fill the bigger box with soud-deadending material? Something roughly like the attached illustration.

Thanks in advance for any thoughts. - Paul in Michigan

[picowallspeaker]

Not very clever !!!!
But it might be some point to start to think from .
in the past a very useful suggestion was to make sandwich construction ,and to fill with sand the space in between . Nowadays we can find more kind of high-tech materials ( which ? I really don't know ! ) to do some composite...multi layer constrained damping.
If you see it from the speaker side...well ,the membrane of the cone moving , needs a certain ratio of volume and ,as we don't want to hear also the backwave ,this has to be
stopped . Also parallel walls should be avoided . Looking at your particular design , if you put one duct between the chambers and one to the outside ,you would obtain a double reflex chamber enclosure ....reaching much lower frequency limit .

[speaker dave]

I'm not sure it is either space or cost effective but it could be made to give good performance.

Look up "wall STC" and you will find a lot of references to building construction and how different wall constructions lead to a varying amount of sound issolation between you and your meighbors. In general, high wall masses and then a good air coupling space will give highest noise issolation. This becomes a third order filter with a mass-compliance-mass general property. The same applies whether we are talking about loudspeaker cabinet radiation or room to room noise transmission.

In the end much of the issolation will be short circuited by the common front baffle, so you won't pick up as much as you think.

As a practical high performance approach, look up the recent threads on the Harwood study of cabinet wal damping. He found that increasing the ratio of damping to wall stiffness gave best performance, and that thinner walls could work better than thick walls since they made it easier to achieve a high damping to stiffness ratio.

David S.

[Slothrop]

Thanks very much for pointing me toward the Harwood papers, Dave. Very interesting and just the sort of thing I'm looking for. I'm sketching ways of separating the driver baffle from the front of the cabinet and decoupling them. - Paul

[strawberry]

What I do, and this can be done to any cabinet that rattles, is reach in through the hole of the woofer with the largest square thick tile of plywood that fits. Glue the tile to the center of the long/large side wall with wood glue. This kills vibrations greatly. On top of that, glue a standing edge of 2x4 which will rip apart standing waves. Enjoy.

[tvrgeek]

Several companies used sand filled boxes back in the 60's. Tanoy or Warfdale? The space and weight is better used with other materials.

I built some subs with ceramic plates laminated between plywood and MDF. They worked extremely well. The secret ceramic plates were 12 inch floor tiles. They were laminated with compliant glue and the box design was such that the forces were transferred to the corners. Using my standard phono cartridge measurement, there was only ambient vibration on the box externals. This worked better than a typical well braced box.

I am not a convert to decoupled drivers. I need to look/build/test some more.

[901Fixer]

Maybe if you put some woofers in that air space it wouldn't be such a waste. Are your enclosures making that much noise?

[sreten]

Hi,

It has been done. Foam sleeved open front box to slip over popular
small speakers. Apparently it worked. Died a retail death though.

rgds, sreten.