Good point, but will sand be effective for sound waves as well?
Has anyone here tried to talk throu a wall of sound bags?
The sources of box sound are from; 1. reaction energy from the driver exciting the box, this particularly so at the boxes natural resonances, and, 2. the internal rear wave energy from the cone bouncing around in the box and re-exiting through the cone.
The former is addressed by choice of box material being low Q, and chipboard is better than MDF in this respect, but bracing and corner reinforcing with Scotia or isosceles triangle wood is very effective because this transfers energy from one panel to the others dissipating much. It also pushes up the resonant frequencies to a less objectionable range.
Damping the box with layers of absorbent also absorbs the secondary emission of energy from the box panels turning it into heat. It is usually of quite high mass, lead sheeting has been used, bitumen sheet is often commercially used, and I have used carpet underlay of the type which has reconstituted car tyre attached to a wool layer, and with considerable success.
The rear cone energy can best be absorbed by layers of suitable absorbent, long haired wool, BAF, and sponge, but loft insulation is unpleasant and unhealthy. If the whole internal volume is filled this will attenuate any bass reflex resonance, which may not be desirable, and should not be necessary in a correctly designed system. It is used however by manufacturers who attempt to match drivers and boxes which are not designed for each other.
I use BAF enclosed in Dacron envelopes so that I can change the amount at will, they fastened to the walls with Velcro.
I also damp the driver frames, paying particular attention to the area behind the cone which will potentially reflect directly through the cone.
The former is addressed by choice of box material being low Q, and chipboard is better than MDF in this respect, but bracing and corner reinforcing with Scotia or isosceles triangle wood is very effective because this transfers energy from one panel to the others dissipating much. It also pushes up the resonant frequencies to a less objectionable range.
Damping the box with layers of absorbent also absorbs the secondary emission of energy from the box panels turning it into heat. It is usually of quite high mass, lead sheeting has been used, bitumen sheet is often commercially used, and I have used carpet underlay of the type which has reconstituted car tyre attached to a wool layer, and with considerable success.
The rear cone energy can best be absorbed by layers of suitable absorbent, long haired wool, BAF, and sponge, but loft insulation is unpleasant and unhealthy. If the whole internal volume is filled this will attenuate any bass reflex resonance, which may not be desirable, and should not be necessary in a correctly designed system. It is used however by manufacturers who attempt to match drivers and boxes which are not designed for each other.
I use BAF enclosed in Dacron envelopes so that I can change the amount at will, they fastened to the walls with Velcro.
I also damp the driver frames, paying particular attention to the area behind the cone which will potentially reflect directly through the cone.
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I'd say your ideas are excellent, since I incorporated them in my infinite baffle bass build. This is somewhat of an inverted concept verses the last picture I posted in this thread. In effect, the listener hears the back of the cone.
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If you want a lossy box you could try this, based on the BBC Ls3/5a. The bead of PVA and gap provide a slightly soft joint and the difference between the real wood and MDF seem to give a very dead box. Having the front and back screwed on ( or held on by tension springs as I sometimes do ) also reduces sound transition. The ladder rungs attached to the MDF are baffles to help " defend " the sides from sound from the driver and to try and detract it as it bounces back. On my traffic light speakers I also added square steel bars to the front baffle to add weight and to stiffen it, quite a complicated speaker that one.
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True, however the cabinet has around 16 times the area to leak sound through ( and radiate from mechanical vibration transmitted from the driver ) than the driver cone, and the sound leaking through the cone has to bounce of something first. All three areas have to be addressed to reduce box sound.
Indeed, it would be great to have a way of testing this, isolating the sound that leaks throu the box, maybe by mounting some anechoic cups over the drive units?
I do believe more sounds then one might think is leaking throu cab the walls, and much likely to the point that it smears driver output.
I can imagine that this is most problematic in the lower range, maybe in the range where the woofer starts to roll of, with low sound levels on the outside while the levels is high inside the box?
I was fiddling with the crossover of my box in a box speakers last night ( it'll be several weeks before I can get the right chokes ), when you listen to a speaker with greatly reduced box noise it's a bit like the change going from ported enclosures to closed or aperiodic, you think where has the bass gone? - until it starts - and you smile. I was listening to Nirvana live in New York and the sound of the applause was totally different to what I'm used to, much, much sharper. Once I've got used to the sound ( or lack of it ) it'll be interesting to go back to six bits of wood and drivers to see if I could go back.
Making a box non resonant can be done, Arthur Khoubessarian of the Funk Firm said of my rebuild, (earlier pictures), that there was no box sound. Each had 53 braces in, but this is labour intensive, and perhaps proclusive in commercial situations.
My ADAMs have a sand filled cavity in the middle/top box.
My ADAMs have a sand filled cavity in the middle/top box.
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