Broad discussion on speaker cabinet materials.

[PristineSound]

So I've heard a hand full of Acora speakers at two shows lately, including CAF that is going on right now. Compared to all the speakers that I have heard so far at shows, where most of them sound terrible, because of room acoustics, the Acora sounds relatively pretty good. Tonal balance is off, with accentuate highs, like typical show room speakers, but I have not heard any resonance, nor distortion from these Acora speakers, spatial performance is pretty good as well, fairly clear and intelligible vocals. In some rooms, there were what appears to be some room resonance, of course any speakers can suffer from that.

It's a bit of a surprise to me, I must say. I didn't think the designer have advanced speaker know how based on the time I spoke with him at the first show these speakers last year. I guess inert cabinet makes a huge difference?

 

[bmc0]

I guess inert cabinet makes a huge difference?

I would've thought that someone with "Science" as their avatar might be more cautious in assuming causation.

 

[PristineSound]

I would've thought that someone with "Science" as their avatar might be more cautious in assuming causation.

Do you not see the question mark at the end of the sentence?

 

[bmc0]

To me, it reads like you're not completely certain, but happy to accept that the cabinet material explains what you heard (in uncontrolled, sighted conditions).

 

[PristineSound]

To me, it reads like you're not completely certain, but happy to accept that the cabinet material explains what you heard (in uncontrolled, sighted conditions).

Yes, uncertain indeed. There is the word "guess" and the sentence ended with a question mark. I am very versed in the art of verbiage CYA

 

[Jack B]

I remember fondly a DIY speaker project I built right after I got out of College. Two 4 cubic ft approximately drainpipes with 1" plywood caps on each end. The 12" dual cone speaker and the 4" port mounted on one end and I had a relatively decent sounding speaker for not much money. Best I recall this was based on a project published in Popular Electronics back in the early 70s.

I vaguely remember reading about that, but never followed through (never built one). Envy your experience!

 

[John Galt]

Ascend Acoustics has some very nice VLAM laminated solid bamboo cabinets.

 

[Heinrich]

Panel resonances became an issue when British BBC started to investigate the topic. It was funded by the government. Read the paper. That gave us the LS3/5, and its peculiar paradigms eventually.

Then Japanese company followed up, with a reasonable three-way, taking the 3d construction into account. That reduced the problem, compared to 2d focus at the BBC, by a factor of 100.

##
From a system perspective there is no use in panels. E/g—from effing measurements done in my kitchen, that easy it is—a speaker panel‘s vibration is always homogeneous. Same phase over all its surface area. Think it over, always at every resonance peak at different frequencies. What does it tell? Again, no higher modes of typical panel resonanes seen at any of the multiple frequencies. I leave it to you, because I revealed the mechanisms several times now to no avail.
##

The ‚material‘ discussion is a hoax. It addresses layman in the field. It is fair to be a layman. But one can likewise do measurements and reasonably investigate, before ventilating fairytales.

 

[Audionaut]

Is it not the case that if weight is not an issue, very dense, stiff materials are best?
However weight (and cost) are often the limiting factors.

I have various tests on the materials here somewhere, but I couldn't find them quickly.
Heavy materials are generally very good, but they usually have their own resonance frequency, which can be excited and cause them to sound like a bell.
This can be solved by using a multi-layer construction, but the advantages of a very heavy material over, for example, a 22 mm wood panel in a multi-layer construction are minimal, and not everyone likes to have extremely heavy speakers at home.
In practice, 20 mm wood, an aluminum butyl layer, and a 1 cm thick pressed mineral fiber layer are usually sufficient.
This is the material structure that has consistently performed excellently in several tests. Add to this the necessary stiffeners at the resonance points of the enclosure, and you are on the safe side.

 

[Audionaut]

The ‚material‘ discussion is a hoax. It addresses layman in the field. It is fair to be a layman. But one can likewise do measurements and reasonably investigate, before ventilating fairytales.

I wouldn't necessarily describe all the engineers in the companies that deal with this as laymen.
Many English companies try to utilize the resonance in the enclosures and therefore build resonant side walls, for example.
Germans, such as Karl Heinz Fink, try to completely eliminate the resonance of an enclosure.
These are two fundamentally different approaches and schools of thought.
The Borg enclosure, for example, is extremely low in resonance and is the result of many series of measurements and experiments.

 

[Heinrich]

… performed excellently in several tests. ….and you are on the safe side.

… low in resonance and is the result of many series of measurements and experiments.

This always leads to arguments, because the lack of data. If given, as rarely as it gets, it is utterly irrelevant. Rule is, the more effort the more praise.
If you don‘t mind please mind my riddle stated in post #48 in between
##
…
##
It should be very easy. For starters into a worthwhile discussion, a problem statement, if you will

Thanks a lot!

 

[thewas]

Then Japanese company followed up, with a reasonable three-way, taking the 3d construction into account. That reduced the problem, compared to 2d focus at the BBC, by a factor of 100.

Can you please post some information where this can be found?

 

[Heinrich]

Can you please post some information where this can be found?

Forgot, maybe Technics or some other major company. But, again, my quest stated in post #48? If such cannot be resolved, what would further debate contribute?

 

[sigbergaudio]

Forgot, maybe Technics or some other major company. But, again, my quest stated in post #48? If such cannot be resolved, what would further debate contribute?

I'm not sure I understood your question in #48, a slight language barrier perhaps. Can you try to elaborate / rephrase?

 

[thewas]

Forgot, maybe Technics or some other major company.

Maybe this one which I have posted few times in the past in this forum?

Index of /Audio/Papers/Loudspeaker with honeycomb disk diaphragm

 

[Heinrich]

I'm not sure I understood your question in #48, a slight language barrier perhaps. Can you try to elaborate / rephrase?

I got a bit pathetic, my bad. I measured the acceleration of several panels of a ready-to-use speaker box using two accelerometers at different locations, energizing the enclosure of reflex type with a sweep fed into the driver.

I found the acceleration to be in-phase for the two accelerometers regardless of position and frequency, while resonant peaks of 10dB, and corresponding dips were present. The the level, though, varies getting continuously lower towards the edges.

What is happening?

Add.: the resonant peaks didn‘t replicate the pattern measured when knocking (using a small hammer) against the panel at different points.

 

[Roland68]

I got a bit pathetic, my bad. I measured the acceleration of several panels of a ready-to-use speaker box using two accelerometers at different locations, energizing the enclosure of reflex type with a sweep fed into the driver.

I found the acceleration to be in-phase for the two accelerometers regardless of position and frequency, while resonant peaks of 10dB, and corresponding dips were present. The the level, though, varies getting continuously lower towards the edges.

What is happening?

Add.: the resonant peaks didn‘t replicate the pattern measured when knocking (using a small hammer) against the panel at different points.

May I ask what kind of accelerometer you used and what bandwidth was used for the measurement?

 

[Heinrich]

May I ask what kind of accelerometer you used and what bandwidth was used for the measurement?

Any work, in case you want to scrutinize the results yourself. Bandwidth was sufficient with mine, don‘t you think?

 

[sigbergaudio]

I got a bit pathetic, my bad. I measured the acceleration of several panels of a ready-to-use speaker box using two accelerometers at different locations, energizing the enclosure of reflex type with a sweep fed into the driver.

I found the acceleration to be in-phase for the two accelerometers regardless of position and frequency, while resonant peaks of 10dB, and corresponding dips were present. The the level, though, varies getting continuously lower towards the edges.

What is happening?

Add.: the resonant peaks didn‘t replicate the pattern measured when knocking (using a small hammer) against the panel at different points.

I may still be misunderstanding you, but naturally the panel is stiffer closer to the edges where it is supported by adjacent panel(s), so not strange that the level goes down when you measure closer to the edge.

 

[Heinrich]

I may still be misunderstanding you, but naturally the panel is stiffer closer to the edges where it is supported by adjacent panel(s), so not strange that the level goes down when you measure closer to the edge.

I suggest, in all humility, to repeat the experiment, and if it was just theoretically. Isn‘t this about scientifically sound engineering?