Hence me saying i was mistaken earlier and i'm now just going to use some good quality 18mm plywood
I am no longer in that field (using khorns) but a solution I have always found attractive is some sandwich construction which could be:
12mm plywood -
some lists, say 15mm thickness -
masonit in danish, that kind of cardboard used as wind barrier in houses made of wood -
the whole thing glued together in strategic places and filled up with DRY sand; avoid as always symmetry.
It could give some very fine results, cheap, rigid with the right braces if you place the lists right.
The front plate should be very rigid and heavy. Poul Ladegaard thought that if possible the mass of the magneto (motor) should be at least 1000 times heavier than the moving mass, which could easily for a normal direct bass radiator be 60grams which gives 60kilograms of lead to glue on the loudspeaker...
12mm plywood -
some lists, say 15mm thickness -
masonit in danish, that kind of cardboard used as wind barrier in houses made of wood -
the whole thing glued together in strategic places and filled up with DRY sand; avoid as always symmetry.
It could give some very fine results, cheap, rigid with the right braces if you place the lists right.
The front plate should be very rigid and heavy. Poul Ladegaard thought that if possible the mass of the magneto (motor) should be at least 1000 times heavier than the moving mass, which could easily for a normal direct bass radiator be 60grams which gives 60kilograms of lead to glue on the loudspeaker...
MDF is okay to work with but everytime I swear it will be my last time... the dust is hell. Deciding to use ply is a good start. Bracing is more important in my experience and have found some will overlook good bracing yet go the extra mile in other areas. Always a head scratcher.
Revisiting this question now we know the OP wants to build a single cabinet for all 3 drivers.
Bolting the midrange directly to a large cabinet is not particularly wise because it will drive the lowest energy containing resonance of the main cabinet. The woofer may or may not drive the lowest resonance depending on how light and stiff the main cabinet can be made to raise the frequency above the passband of the woofer. 3/4" birch plywood and effective bracing may well achieve this. Assuming this is done for the main enclosure then it won't need any effective damping if it is isolated from the midrange enclosure with a soft damping gasket and/or grommets around the bolts to prevent the resonances from being driven.
The midrange enclosure need not be stiff but would benefit from damping because enclosure resonances will inevitably be in the midrange passband. CLD or a BBC approach may be appropriate. However this is unlikely to be too critical because the midrange cabinet will radiate sound into the air of the main enclosure and not into the listening room. The large volume and stuffing for the sealed loading in the main enclosure will absorb most of this plus the large impedance mismatch between air and wood will mean little sound reaching the walls will be transferred to the main cabinet with most of it being reflected to get absorbed by the stuffing again.
I hope this image hosting works so i can get across the rough design i've got so far.
As said before, 18mm ply main carcass with a 25mm front baffle. 25mm front baffle so i can have a decent sized 45 degree bevel on the edges to help reduce diffraction. I was going to do the bevels like Troels Gravesen but i don't think it will look to great, but if you guys think my bevels will perform worse than the TG bevels i might revise my design.
Mid enclosure is an inverted polygon that will attach to the front and rear baffles.
I was thinking of doing a separate mid/tweeter enclosure but i wanted to maximise the amount of air space i can give the woofer v's keeping the speaker as small as practicable.
As said before, 18mm ply main carcass with a 25mm front baffle. 25mm front baffle so i can have a decent sized 45 degree bevel on the edges to help reduce diffraction. I was going to do the bevels like Troels Gravesen but i don't think it will look to great, but if you guys think my bevels will perform worse than the TG bevels i might revise my design.
Mid enclosure is an inverted polygon that will attach to the front and rear baffles.
I was thinking of doing a separate mid/tweeter enclosure but i wanted to maximise the amount of air space i can give the woofer v's keeping the speaker as small as practicable.
An externally hosted image should be here but it was not working when we last tested it.
MDF/Ply
Andy:
I've built some enclosures with 3/4 MDF laminated to 3/4 ply; 3/4 particle board laminated to 3/4 hardwood, 3/4 Appleply laminated to HDF, etc. They were all pretty non resonant.
Assuming local suppliers carry it, I'd use HDF rather than MDF
But, in general, I vote for Planet 10 approach. High quality ply, extremely well braced. I'd recess all braces whenever possible, or use biscuits.
Good luck!
Andy:
I've built some enclosures with 3/4 MDF laminated to 3/4 ply; 3/4 particle board laminated to 3/4 hardwood, 3/4 Appleply laminated to HDF, etc. They were all pretty non resonant.
Assuming local suppliers carry it, I'd use HDF rather than MDF
But, in general, I vote for Planet 10 approach. High quality ply, extremely well braced. I'd recess all braces whenever possible, or use biscuits.
Good luck!
In that vintage picture there are many errors:
1) the drivers are not aligned vertically
1a) the drivers are too BIG
2) The drivers are not isolated each one respect to the others and
2a) the box is not conceived to be placed in free standing
3) It uses wood
😱🙄
1) the drivers are not aligned vertically
1a) the drivers are too BIG
2) The drivers are not isolated each one respect to the others and
2a) the box is not conceived to be placed in free standing
3) It uses wood
😱🙄
Previous related threads on enclosure wall construction and vibrations on this forum:
constrained layer damping with MDF and Ply
how to brace a speaker cabinet?
Woofer choice : maple or mdf ?
Cabinet structure MDF vs HDF
Measuring sound output from speaker cabinet walls
Material............................Stiffness (Modulus of E)...............Damping Factor
Laminated Bamboo Lumber....1,500,000 psi..............................0.2 (good damping)
Baltic Birch Plywood..............1,100,000 psi..............................0.04 (little damping)
MDF.......................................450,000 psi..............................0.02 (little damping)
constrained layer damping with MDF and Ply
how to brace a speaker cabinet?
Woofer choice : maple or mdf ?
Cabinet structure MDF vs HDF
Measuring sound output from speaker cabinet walls
Material............................Stiffness (Modulus of E)...............Damping Factor
Laminated Bamboo Lumber....1,500,000 psi..............................0.2 (good damping)
Baltic Birch Plywood..............1,100,000 psi..............................0.04 (little damping)
MDF.......................................450,000 psi..............................0.02 (little damping)
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Not really. If you stick the speaker in an anechoic chamber and measure it you will be measuring the sound from the driver not the cabinet. The sound from the driver needs to be separated from the sound from cabinet.
One might consider a microphone array to focus on a location away from the driver but the signal to noise will be insufficient to overcome how close and loud the driver is to where you wish to measure.
The approach used in industry is to use a vibrometer to measure the deflection at many points over the complete surface of the cabinet, use the values to solve a boundary integral and then calculate the SPL at any point outside the cabinet from the boundary integral. This can be done just as well in a room as an anechoic chamber.
some just don't think things through or seem capable of interpreting information at times....
good thing i have scotch...
good thing i have scotch...
off the wall, down the garden path and across the dale....but as both me and my judgement are pickled in scotch who am to say such things...
Andy, you picture is behind your dropbox login.
Attach the picture to this forum (advanced or post reply and then look for manage attachments.
Or out it in a publicly accessable place.
dave
diyAudio moderation team
The best organic sheet material we hav eused for loudspeaker cabinets is sanded/fossilized bamboo plywood.
These use the Neopolitan from Plyboo. The finish is clear coat.
dave