If you read any info regarding sound insulation of sound studios, there is allways double layer walls mechanically decoupled from each other. Why not build a box within a box with minimum of mechanical coupling? A really stiff well braced box on the inside and then a thinner limper (is that a real comparative?) taking care of what ever is transmitted thorough the inner box?
Right, what you want are relatively huge impedance mismatches. A good one that's better overall than box-air-box is a MDF or Medite exterior cab with thin metal or alum. panels suspended with something lossy such as a flexible sub-floor & deck adhesive: http://www.duspec.com/DuSpec2/produ...=70&productCode=LN-902&documentType=datasheet
GM
GM
Early on, I did a MLTL for the FE168Σ. 18mm MDF with 6"sq ceramic tiles attached with acrylic mastic. Worked well, very dead to the knuckle rap. The problem with ceramic tile is that cutting them to fit anything but 6" or 12" is a real pain. Using multiple 4" tiles would significantly reduce the benefits. So I moved on to using "HardiBacker", a fiber reinforced cement board. This is not plaster board (drywall). This is hard stuff that requires a diamond saw to cut. Worked out very well until the stigma of MDF forced me to plywood.
I have not tried plywood/HardiBacker. This seems like an oxymoron: Light wood, heavy backing. I am thinking that two layers of 6mm separated by something. Possibly just air. The 6mm pieces could be dado'd into the corner posts with a predetermined air gap
Bob
I once built a plywood box within a plywood box (1/2 inch) separated by closed cell neoprene (camping mattress blue) foam to contain the sound from a portable generator (with ducting for air cooling and intake and exhaust). It worked really well. I forgot all about that as it was many years ago and I wasn't even thinking of speakers back then.
Hi Bob - I'd look at GM's recommendations. I'm not sure air will be of any use - you're going to have to link the panels somewhere and the air won't do anything to damp the panel resonances. That's the advantage of the sand between the layers; it transfers to sound energy from inside the cabinet into movement/ heat in the sand and provides a very well-damped panel.
TNT-audio's DIY writer did some experiments with different types of panel damping, which may be of interest
Cabinet walls and Loudspeaker Energy Preservation - [English]
I'm not convinced about his finding re the BBC thin-wall technique as it counters the BBC research.
TNT-audio's DIY writer did some experiments with different types of panel damping, which may be of interest
Cabinet walls and Loudspeaker Energy Preservation - [English]
I'm not convinced about his finding re the BBC thin-wall technique as it counters the BBC research.
I noticed that the author in 'Get Stuffed' more than once has mentioned that MDF 'suppresses the life' of recordings which is something I've also noticed compared to baltic birch plywood or solid hardwood. I've tended to assume that this is from the fact that most of the strength of MDF comes from its plastic resin which should then reasonably dominate the overall sonic profile much more than its actual quantity as a filler material would indicate. Generally speaking, a conventional (non viscoelastic) 'plasticky' sound has never seemed optimal to me from prior encounters.
That's not to say that MDF would be expected to sound worse than standard plywood or certain other types of wood products.
Speaking of unexpected sounds, I was surprised myself when I first built the Iron Lawbreakers - I had enough 19mm baltic birch plywood to compete everything but the back panels, and the back panel (~ 26 x 18") had two substantial lateral braces, IAC, so I went to Home Depot and bought this approximately 9 ply stuff that 'appeared' something like baltic birch plywood for the back panels and finished the two boxes. I noticed while cutting them, that the wood they were made of was considerably less flexible than birch but also not as strong as birch, and there seemed to have been a few minor interlaminate gaps.
IAC, I was initially disappointed and later astounded after I discovered how much the back panels alone degraded the sound after doing this. The deficiency was one or perhaps two panel resonances in the lower midrange (where the 2220 operated up to about 570 hz). After a couple days, I ripped them out, bought real baltic birch for the back panels which seemed to effectively remove these particular colorations and completed the cabinet constructions otherwise identically, including the braces.
That's not to say that MDF would be expected to sound worse than standard plywood or certain other types of wood products.
Speaking of unexpected sounds, I was surprised myself when I first built the Iron Lawbreakers - I had enough 19mm baltic birch plywood to compete everything but the back panels, and the back panel (~ 26 x 18") had two substantial lateral braces, IAC, so I went to Home Depot and bought this approximately 9 ply stuff that 'appeared' something like baltic birch plywood for the back panels and finished the two boxes. I noticed while cutting them, that the wood they were made of was considerably less flexible than birch but also not as strong as birch, and there seemed to have been a few minor interlaminate gaps.
IAC, I was initially disappointed and later astounded after I discovered how much the back panels alone degraded the sound after doing this. The deficiency was one or perhaps two panel resonances in the lower midrange (where the 2220 operated up to about 570 hz). After a couple days, I ripped them out, bought real baltic birch for the back panels which seemed to effectively remove these particular colorations and completed the cabinet constructions otherwise identically, including the braces.
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IMO.
The "life" that supposedly gets sucked out by MDF, BSC filters, etc. is really exaggerated mid- and high frequencies. MDF, for all of it's faults, is better damped and less transparent at higher frequencies. Less higher frequencies means less bright, less "lively". BSC filters work the same way. The reduce the higher frequecies -- make the speaker less bright, less "lively".
Now, I am not saying that a bit of brightness is a bad thing. EQ a speaker to dead flat. It will sound dull and, well, "lifeless". What you want for balance is the inverse of the F-M curve at whatever listening level you choose.
The "life" that supposedly gets sucked out by MDF, BSC filters, etc. is really exaggerated mid- and high frequencies. MDF, for all of it's faults, is better damped and less transparent at higher frequencies. Less higher frequencies means less bright, less "lively". BSC filters work the same way. The reduce the higher frequecies -- make the speaker less bright, less "lively".
Now, I am not saying that a bit of brightness is a bad thing. EQ a speaker to dead flat. It will sound dull and, well, "lifeless". What you want for balance is the inverse of the F-M curve at whatever listening level you choose.
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