If you double the vibrating mass of the box, I would expect the amplitude to decrease by 6 dB, assuming ideal piston motion, and even then you're likely increasing the surface area and radiating efficiency at the same time.
With a rapidly diminishing rate of return like that, I'm inclined to rethink the whole idea. Sealing off the back-wave arguably has some major benefits for bass efficiency, but -- call me a heretic -- I'm questioning the whole ideal about getting the sound to enamate from a "point source". Expensive hard-coned drivers will tend to maintain very small phase shifts across the cone, and if you combine that with a box resembling a block of lead with a hole drilled into it, it should be very tight indeed. But that still doesn't mean it will sound good.
No doubt there is a certain quality that is retained when minimising the 'noise' of vibrating panels, with all their phase shifts and resonances. But that can also shift the focus to a peep-hole effect, where echo-location brings everything back to the speaker cone.
Look at how cellos are built: with thin layers of curved veneer and light braces. And if you pluck one of its strings, the decay is remarkably quick. I think it's not so much the wood flexing that causes the quick decay, but the large surface area allowing the air to quickly absorb the energy of the vibrations.
If I could rebuild some of my older speakers, I would put less focus on thick heavy panels, and more focus on diffraction effects and eliminating 90° cuts. Taken to its logical conclusion, unless the speakers are force-cancelling, the vibrations are practically impossible eliminate completely, so in my mind treating them a bit like DML actuators is a good alternative.
With a rapidly diminishing rate of return like that, I'm inclined to rethink the whole idea. Sealing off the back-wave arguably has some major benefits for bass efficiency, but -- call me a heretic -- I'm questioning the whole ideal about getting the sound to enamate from a "point source". Expensive hard-coned drivers will tend to maintain very small phase shifts across the cone, and if you combine that with a box resembling a block of lead with a hole drilled into it, it should be very tight indeed. But that still doesn't mean it will sound good.
No doubt there is a certain quality that is retained when minimising the 'noise' of vibrating panels, with all their phase shifts and resonances. But that can also shift the focus to a peep-hole effect, where echo-location brings everything back to the speaker cone.
Look at how cellos are built: with thin layers of curved veneer and light braces. And if you pluck one of its strings, the decay is remarkably quick. I think it's not so much the wood flexing that causes the quick decay, but the large surface area allowing the air to quickly absorb the energy of the vibrations.
If I could rebuild some of my older speakers, I would put less focus on thick heavy panels, and more focus on diffraction effects and eliminating 90° cuts. Taken to its logical conclusion, unless the speakers are force-cancelling, the vibrations are practically impossible eliminate completely, so in my mind treating them a bit like DML actuators is a good alternative.
You mix stuff here ...
When doubling the mass and doubling the width of a material you increase stiffness and lower coincidence frequency. You don't increase the "radiating area" that much - it will dampen better 6dB at lower frequencies.
When you double the mass with adding dense material like metal sheets ... more complicated but this can be a great mix when you can accept heavy housings.
A proper built cabinet doesn't add significant to the emmited sound! And propper absorption in the cab will keep internal sound from doing mess back on the membrane. Therefore i don't like reflex cabinets for Lowmid drivers - when you do proper dampening ther is no energy for the reflex port left ... keep your mids closed.
Cellos emit MOST of their sound through their housing! It's a mechanical amplifier for the string vibration in giving them radiation area.
No - you DON'T want that in a speaker! And they also don't have quick decay - magnitudes higher as a speaker housing.
But I'm with you with diffraction effects and hard edges - don't build unnecessary mistakes in speakers ...
When doubling the mass and doubling the width of a material you increase stiffness and lower coincidence frequency. You don't increase the "radiating area" that much - it will dampen better 6dB at lower frequencies.
When you double the mass with adding dense material like metal sheets ... more complicated but this can be a great mix when you can accept heavy housings.
A proper built cabinet doesn't add significant to the emmited sound! And propper absorption in the cab will keep internal sound from doing mess back on the membrane. Therefore i don't like reflex cabinets for Lowmid drivers - when you do proper dampening ther is no energy for the reflex port left ... keep your mids closed.
Cellos emit MOST of their sound through their housing! It's a mechanical amplifier for the string vibration in giving them radiation area.
No - you DON'T want that in a speaker! And they also don't have quick decay - magnitudes higher as a speaker housing.
But I'm with you with diffraction effects and hard edges - don't build unnecessary mistakes in speakers ...
I've ordered my 7mm aluminium U channel which will make up the sides and half of the top and bottom of my intended new 15 litre cabinet. That accounts for the rigidity. I have heavy butyl sheets for the internal damping. The new cabinet is for a 165mm mid-bass. Thanks for the attachment - a good read.
The single cabinet I have up and working is another 11 litre design for a 150mm mid-bass, and the 8mm aluminium U channel makes up the front and most of the sides. It is so much cleaner than my existing Wharfedale and Mission MDF cabinets that I now have a hard time putting up with cabinet coloration from mediocre commercial cabinets. The difference is really day and night. Once you've heard a solid aluminium cabinet it's a shock to go back to basic commercial cabinets. Cabinet construction is something to take seriously, as this thread usefully shows!
Sealed or ported is another but related issue. If I can get away with the bass from a sealed cabinet that will be my choice. The Magico A1 sealed cabinet is my reference.
'Sounds' like you would have enjoyed a way back when buddies' blown/dual 4bbl Chrysler 392 hemi- Morris Mini; no wheelie bars, so potentially a real wheel stander at every intersection!
If my neighbor still has pics, I'll PM his late/great Triumph Spitfire roadster bodied monster truck (ne' stretched Jeep bodied nowadays). His daily driver is nothing to 'sneeze' at either! 23 yrs later and it still turns heads, especially when he 'kicks' it down out of overdrive to spool up the turbocharger for a 'roaring' quick pass......
If you double-check, you'll see that I mentioned the box mass moving as a piston. Of course in real life there will be partial oscillations, similar to how a speaker cone breaks up at higher frequencies.
To an extent, the magnet vibration should basically be a mirror image of the cone vibration, so I don't see anything inherently wrong with the box panels vibrating, as long as the sound is clear and undistorted. It's all in how well the system is executed, rather than some overriding principle that the box shouldn't vibrate at all.
You compare 8mm aluminium with 8-9mm MDF? That's a "little" different ... to be compareable you would need >30mm MDF!
8mm Aluminium is already in a range where it will have a strong ringing and coincidence frequency in the middle of the range (about 1500Hz). But weight and mass damping is compareable with 35mm MDF ... so that's pretty good.
@abstract - did you do measurements of pannels in your life? Or tried to get a linear frequency response with exciters? You would think different about using the housing for emitting sound ...
The problem here is that there is no meaningful definition of 'clear', while audible panel resonance in a loudspeaker is by definition distortion. The panels have their own amplitudes and radiation patterns, and the delay involved (none of this is not a matter of speculation or opinion, just cold, hard engineering reality) will result in the output from this passive sub-emitter lobing with the direct output of the drive unit, causing destructive interference.
I'd love to see that!
A 'proper' use for the Spitfire... not that I mind a Spitfire when it was working, even if it wasn't exactly 'quick'. Not exactly a problem when using the body for a monster truck though...Ye gods -I like that F-350. 7.3 litre TDi? That's not going to be slow on the old in-gear times. I had chance to drive one of the V10 Touaregs before they discontinued it.
Only 5 litres but it sounded like Thor gargling his hammer when you put your foot down.But what causes resonance in the first place? Reflections. And what causes that? Any kind of discontinuity like a corner where 2 panels at different angles are connected together, or one panel connects to another with different mass, or the vibrations split off in 2 directions because of bracing. So a curved surface would help in multiple ways.
For a spherical style of box made of 2x Ikea bowls, a bending wave could reach the back of the box and then return to the front, forming a resonance that way. The vibrations shouldn't go full-circle without losing a significant portion of their energy, and the surrounding air could be put to good use here. Elastic damping in solids seems to introduce a bit of non-linearity.
The magnet mass and basket material could also be important parameters to look at, and possibly modding the basket or contouring the thickness of the box material to suit.
I would be mindful of a couple of situations:
-A heavy magnet connected to dense & hard box material via basket spokes that are not well matched to that, so the energy that reaches the box is already coloured by the spokes' resonant modes.
-The entire basket is very heavily built, but the baffle thickness is not contoured and starts off too thin. That also seems like a mismatch.
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None of which appears to alter or contradict what I said above. 
Audible panel resonance is by definition distortion, so assuming that isn't wanted (some do, and power to them if that's what they like), then the object is to avoid audible structural resonances by whatever method is preferred.
Audible panel resonance is by definition distortion, so assuming that isn't wanted (some do, and power to them if that's what they like), then the object is to avoid audible structural resonances by whatever method is preferred.
That answer is incorrect. Most box resonances are caused by direct reaction to the cone moving in and out and transmotted thru the box material.
dave
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Absolutely. That's why we've got the longitudinal & driver braces that Dave rightly promotes, & the pioneers went to such lengths rear-mounting drivers by clamping the magnet with a metal pillar to a semi-floating front baffle.
so the usual 3/4 " material rather MDF or Plywood works fine.
and just needs bracing. and bracing not evenly spaced or equal distance.
are we talking large panels or small panels.
18" or little 4" fullrange.
some mystical magically box wont do much for 4" speaker.
likely in typical small 2 ways the usual garbage impedance curves
that can be seen likely is larger contributor to SQ
if a large panel with some elastic layer the outer layer just vibrates more
and inner layer where measurements are taking will measure lower
and just needs bracing. and bracing not evenly spaced or equal distance.
are we talking large panels or small panels.
18" or little 4" fullrange.
some mystical magically box wont do much for 4" speaker.
likely in typical small 2 ways the usual garbage impedance curves
that can be seen likely is larger contributor to SQ
if a large panel with some elastic layer the outer layer just vibrates more
and inner layer where measurements are taking will measure lower
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Ask those with Frugel-Horn Mk3s about how much bass can come from one of those small 4”.
A larger driver, producing LFs will have more potential to provide energy to the box that you do not want. But at any specific loudness level within the capability of the 2 differen loudspeakers, the vibrational energy will be the same (but the larger driver usually capable of paying louder and lower giving it a vibrational potential exceeding that of the smaller driver (due to that drivers LF limitations).
But killing the reactive movement of a driver is more important in a driver producing higher frequencies as, given the shrinking of the wavelengths, is much more sensitive to movement, burying small pieces of information in the movement. A differen tissue than preventing the box from moving.
There has been at least one anecgotale comment ref a rebuild of a set of Thors (in. proper line), with holey driver braces, it was not the much improved bass that most impressed but the greater level of information thru the midrange.
dave
Well no, it doesn't. If box vibrations can be cleaned up so as to be non-resonant with a nice even spectrum (not necessarily flat but without big spikes or bad phase either), then by then I think the interference pattern should be pretty benign.None of which appears to alter or contradict what I said above.
the actual driver cone distortion would have way bigger impact.
and normal high frequency reflections that even extremely minimal
absorption gets rid off
I have definitely heard actual cabinet rattle, ringing.
but that is only time its actually audible.
when the cabinet construction has to be very poor
to actually hear anything.
once you have basic well braced cabinet.
any real world audible impact is gone.
and the cross ram intakes comments is hard to ignore
because majority of Chrysler intake designs are works of art
. Hard to get, but with easier to get common aftermarket tunnel rams.
Holding them wide open through a drag race. The runners
would actually ice up for a short time. even on warm days.
extremely strange phenomena
and normal high frequency reflections that even extremely minimal
absorption gets rid off
I have definitely heard actual cabinet rattle, ringing.
but that is only time its actually audible.
when the cabinet construction has to be very poor
to actually hear anything.
once you have basic well braced cabinet.
any real world audible impact is gone.
and the cross ram intakes comments is hard to ignore
because majority of Chrysler intake designs are works of art
. Hard to get, but with easier to get common aftermarket tunnel rams.
Holding them wide open through a drag race. The runners
would actually ice up for a short time. even on warm days.
extremely strange phenomena