Broad discussion on speaker cabinet materials.

[Thomas_A]

Consider a lead-made enclosure; resonances? Why this sharp focus on resonances?

Because they exist? If you look at the following link

Measuring the sound radiation of speaker cabinet walls

Measuring the sound insulation of different types of woods used in speaker cabinets: MDF, plywood, OSB.

www.tonestack.net

You can see that the sound radiating from MDF ≈650 Hz is unaffected by stuffing. Also not coinciding with any standing wave, but coinciding the Fs of the tweeter (!) used for this.

 

[Heinrich]

Because they exist? If you look at the following link

@Thomas_A , I did and found for one an affirmation of my reasoning, but second, the little experiment wasn't model driven. It was meant to be anecdotal, not conclusive. Fair enough, but not science. Science has a model of causation. That's missing so badly with all the old stuff. It is written with all the good intentions, but addresses the tinkerer's will to optimize easily w/o the appropriate background of scrutiny and honest cross checks. Sorry to say: common imagination of what is happening is distorted and imcomplete and alltogether inappropriate.

I reinvented for you the 'black hole 5' technology that might go back to quite standard tech/ in acoustics. I could link again to a commercial offer that addresses the same problem in yachting, but see some posts above.

BH5 was a flop, because its use was quite a challenge, cost was demanding also. My tip on the howto, once the problem's origin is understood, is found again some posts above.

 

[Thomas_A]

@Thomas_A , I did and found for one an affirmation of my reasoning, but second, the little experiment wasn't model driven. It was meant to be anecdotal, not conclusive. Fair enough, but not science. Science has a model of causation. That's missing so badly with all the old stuff. It is written with all the good intentions, but addresses the tinkerer's will to optimize easily w/o the appropriate background of scrutiny and honest cross checks. Sorry to say: common imagination of what is happening is distorted and imcomplete and alltogether inappropriate.

I reinvented for you the 'black hole 5' technology that might go back to quite standard tech/ in acoustics. I could link again to a commercial offer that addresses the same problem in yachting, but see some posts above.

BH5 was a flop, because its use was quite a challenge, cost was demanding also. My tip on the howto, once the problem's origin is understood, is found again some posts above.

Of course stuffing reduces the internal standing waves but once there you also have the driver moving. Where is that 650 Hz peak coming from? I did not expect a tweeter would give that but it did, particularly for the MDF case. A stiff wall raises Q and what you can do is brace to move it up in f or reduce Q by using a softer wall. I do not expect much audibility of linear distortion but as you know by now, I do measure non-linear distortion as well. A model is of course needed to explain that, and I can only refer to several attempts with MDF cabinets giving the same result. Until I made it ”softer” with CLD.


R

 

[Heinrich]

Of course stuffing reduces the internal standing waves but once there you also have the driver moving. Where is that 650 Hz peak coming from? I did not expect a tweeter would give that but it did, particularly for the MDF case. A stiff wall raises Q and what you can do is brace to move it up in f or reduce Q by using a softer wall. I do not expect much audibility of linear distortion but as you know by now, I do measure non-linear distortion as well. A model is of course needed to explain that, and I can only refer to several attempts with MDF cabinets giving the same result. Until I made it ”softer” with CLD.


R

@Thomas_A , the only way for the driver to excite resonances other then via sound pressure, is reactive forces du to inertia. How much of an intertia do you expect from a dome tweeter? To expect a 0.1g dome to excite a 10kg speaker box to significant resonance is exactly what I was talking about: insufficiant cross check, lack of a proper model.

 

[AsciLab]

@AsciLab has considered the issue of cabinet resonances. They should be visible in a directivity chart that's high enough resolution. And also, it would seem that most of the issues can be mitigated by proper bracing.

Differences in Klippel NFS Measurements Based on Enclosure Thickness and bracing

I plan to compare measurement differences using the Klippel NFS based on wood thickness and the presence or absence of bracing. Three different boxes will be used for the test. The drivers to be tested are the SB Acoustics SB17nbac and the test boxes are currently complete, and measurements will...

www.audiosciencereview.com

I’m not super expert about cabinet resonance, but the important thing that I know is that the cabinet resonance has to be divided to each different problems.

1. Newton force
2. Plane resonance
3. Internal standing wave

#1 is usually treated by dual opposite mounting. But it is only efficient for sub range. To reduce midrange problem, there should be a lot of technics like damping the basket, holding the magnet, etc.

#2 is usually damped by internal bracing. Wide flat plane of enclosure can be resonated by internal SPL. High density with high internal damping material can help to this.
Or typical MDF needs internal bracing to make the stiffness higher to push the resonance frequency up and weaken.

#3 is widely known issue. Best solution is to have short longest cabinet length to push the resonance above the driver reproducing range. Internal absorber make the resonance reduced but also higher the mechanical damping (low Qms). To avoid this issue Helmholtz or quarter wavelength pipe can reduce some specific resonances.


These three problems are often overlooked as a same problem. But it is complex and has to be treated one by one.

 

[Thomas_A]

@Thomas_A , the only way for the driver to excite resonances other then via sound pressure, is reactive forces du to inertia. How much of an intertia do you expect from a dome tweeter? To expect a 0.1g dome to excite a 10kg speaker box to significant resonance is exactly what I was talking about: insufficiant cross check, lack of a proper model.

Still, you have vibrations not affected by stuffing and not being those matching with stqnding waves AND varies with kind of wood that is used.

 

[Heinrich]

Still, you have vibrations not affected by stuffing and not being those matching with stqnding waves AND varies with kind of wood that is used.

Yep, what you say. That means, it is the internal sound, not structure born resonance? There are itchy questions raised, but private investigation I know of isn't ever conclusive. If it was me, I would never publish such preliminary results.
Engineering: implicate a model of causation (how to design a bridge) and attach data to it by established measurement, confirmative
Science: explicate a model of causation (space versus time and energy) and scrutinize it by creative measurement, innovative
Tinkering: skip modelling and causation, run into confirmation bias after extensively doing what you just can, anecdotal

Internal absorber make the resonance reduced but also higher the mechanical damping (low Qms).

Such absorbers never can fit, because of their smaller volume they need to be of way higher Q than the original resonance to do anything at all. This caveat I raised earlier wasn't picked up. It contradicts confirmation bias, that's why.

@AsciLab , anyway, thanks for your investigation that shows a) the need, and b) how little is enough.