Again I have a bit of trouble understanding you. My apologies.
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Broad discussion on speaker cabinet materials.
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Again I have a bit of trouble understanding you. My apologies.
Imagine you had two accelerometers. And you were actually interterested in the very nature of those infamous panel resonances. I mean, for real. After reading the basic literature, plus papers on derivative investigations targeting speaker boxes in particular. ‚Critical reading’—like ‚critical listening’. And it were two, instead of just one sensor. And the other equipment would allow to deploy the two simultaneously.
There‘s a lot one can do. Not big science, but anyway, good questions come up immediately. I‘m under the impression, that people are way to humble as to apply their natural creativity to audio.
Alas, without the riddle solved, it doesn‘t make sense to explain how Danny‘s NoRez works (or could, if done right) for virtually no money and effort. To give just an example of an wondrous X-material.
Ok, a step by step instruction. Disclaimer: it doesn‘t replace reading and critical understanding.
- get two accelerometers, operational simultaneously
- place one at the geometric center of a panel
- be prepared to place the second at differing positions on the same panel
- run a sweep to energize the panel via the speaker driver for several positions of second sensor
- identify resonances
- let your meas/ gear calculate the phase of second relative to first sensor at frequencies of interest for each position of second sensor
- schould be the bullet at position (0): develop an expectation of what should happen according to a model,of causation
What I found, though, goes like this:
No phase flip, harmonic relation. Bummer!
Hypothesis to explain the observations from a causation model:
The resonances seen are all(!) not actual panel resonances. Those originate in the air inside the enclosure driving homogeneous movement of the panel. Peaks of panel movement reflect resonances of the air, they are not the panel resonating in itself. More plausibility is derived from countermeasures targeting the air‘s behavior. Damp internal cavity resonances, the peaks of panel movement decrease accordingly. Apply more sophisticated methods addressing the air’s dynamic, resonances are virtually gone.
That‘s no less than a paradigm shift. Extraordinary claim needs extraordinary evidence? Well, stop repeating Mr. Fink‘s and other‘s „the more the better, just to be safe“ mantra. Do your own research. You won‘t believe me anyway, because I do not present an authority, I‘m just as you. Fair enough.
add.: the resonance frequencies were checked against those (read: other) when ‚knocking‘ against the panel. They differ in behavior. Save your knuckles …
Season‘s greetings!
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Doenerkunde
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But isn't that just what Fink Team has been doing?
And could the japanese company you mentioned in post 48 be Pioneer with their US Patent 6324292? Because the way Fink Team handles standing waves with Helmholtz absorbers seems to be based on this patent. The whole Fink Team approach seems like the total opposite of „the more the better, just to be safe“ to me.
PDF of said Pioneer patent: https://www.diyaudio.com/community/attachments/pioneer-standing_wave_reduction_us6324292-pdf.369084/
If the frequency sweep exhibits any sort of peak, it still likely a panel resonance. Lack of additional modes in the panel, given that the driving force is almost certainly primarily the air pressure inside the cabinet doesn't mean this isn't a panel resonance. It is good evidence that mechanical coupling from say the drivers, isn't important.
What would be useful would be to measure different panels. If the top, sides and back all have the same peak frequency, then it would be hard to claim panel resonances, but I would be very surprised if they were the same. I would be betting on 0th mode resonances for each panel size.
I agree peaks aligned with internal acoustic resonances (say half wavelengths of the dimension of the cabinet between sides) may well be present as well. So not just panels causing problems. But the actual numbers should tell a story. It should be possible to ground truth the frequencies of peaks to an expected phenomenon.
Maybe the range of excitation frequency matters, as once the wavelength is getting smaller than the cabinet there become more possibilities to excite higher panel modes. Perhaps small two way designs may find themselves running into this, but only just. I generally doubt this is going to be much of an issue. I would really never expect to see anything other than base resonant modes, and would not use the absence of higher modes as evidence against panel resonances.
Wow, the Fink team banishes laminated iron-core inductors from their crossovers, only to then use an autotransformer (of course with a core) in the tweeter. This raises the impedance to such an extent that the series capacitor in front of the tweeter can be made smaller, which—due to its reduced size—supposedly sounds better. The cap/ is a very special unit, custom-developed and wound-up to their own specifications. That is hardly a reference, and accordingly we find no indication of this topic there either. You’ve probably read more into it than is actually written. But then again, that’s exactly what it’s designed to do.
That doesn’t specifically address the problem mentioned either. Furthermore, the patented solution comes with a bigger issue: the anti-resonators are much smaller than the primary resonating volume. In order to provide damping, their Q factor would therefore have to be much higher—the matching simply isn’t correct. See also the ‘metamaterial’ discussion at KEF; they’re doing it properly.
But then the characteristic features of an intrinsic panel resonance are missing.
I see higher modes, as already stated many times. Only that they correlate to a series of cavity resonances, not to intrinsic panel resonances.
Essentially, you want me to pursue this line of reasoning further. I could do that. But I won’t. The side effects you’ve inferred from it—and that’s all they are—carry very little plausibility.
I’m no longer interested anyway, because I’ve given up on tinkering in the direction of ‘best of the world’ designs and now focus solely on verifying elementary relationships occasionally, currently having no plans whatsoever. See also my practical reply to KEF’s LS3/5. Mine doesn’t have an issue in this respect either, since it’s a three-way design. My intentions are essentially just to demonstrate how absurd this topic is when it’s abused for marketing purposes—and, unfortunately, as can be seen here, quite successfully so on a board full of scientifically mindes people.
If interested, do your own research ;-)
olieb
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There are two pathways for vibrations to reach the panels.
diaphragm movements -> baffle bending movement (Newton 3rd) -> panel vibrations
diaphragm movements -> air pressure (cavity resonances) -> panel vibrations
You claim that the first path is of little importance. IDK, maybe so, but at least for the baffle it will be significant.
Let's look at the second path.
The air pressure in the cabinet will only build up to high values at cavity resonance frequencies ("standing waves"), and only at those parts of the panel where pressure maxima are present.
The panels will react to the force exerted by the pressure as an elastic plate (more or less fixed at the edges). With high pressure there will be some movement (especially in the center, the "softest" part) and at certain frequencies (plate resonances) this will be stronger than at others, but the dampening of the (thick) wooden plate will reduce that effect.
So I would expect to see a convolution of cavity FR and plate FR.
Here is a webpage (German) that looks into that with some effort.
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
www.waveguide-audio.de
Translation:
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
www-waveguide--audio-de.translate.goog
ADDED:
Two strategies seem to be successful.
Make the panels stiffer with strong material, stiffeners or struts.
Reduce cavity resonances with porous materials or with (Helmholtz) absorbers (as Fink does).
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Dave Fabrikant, owner of Ascend Acoustics, discusses why he choose V-LAM solid laminated bamboo for many of his speaker designs: https://forum.ascendacoustics.com/h...es-electronics/2355-sierra-the-cabinet?t=2597
A well performing cabinet does not require crazy thick panels or esoteric materials, it will just require reasonably thick and dense MDF with proper bracing.
As @Francis Vaughan suggested, at some frequency the intrinsic resonance of the panel accidentially might match a cavity resonance--at the right position, so that the cavity couples and excites higher panel modes. But that's expectedly quite rare. Alas, I once had this and the enclosure was dumped.Here is a webpage (German) that looks into that with some effort.
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
In the investigation you quoted we see resonances in the lower treble, 2.5k, that appear to be a bit stubborn. Neither stiffening, nor wool address them well, while the bitumen falls short likewise. It's the strongest close to the driver, measurement position (1). There's a lot to be discussed. I did my investigations independently, not knowing of waveguide audio.
Well, we have a hypothesis that carries an uncertain degree of plausibility. We cannot prove it—just as in science, that is always impossible. However, the standard hypothesis—independent plate oscillations—has been falsified. As a rule, the enclosure walls do not oscillate in that way. Moreover, the energetic excitation has been identified. From this, engineering measures can already be derived. If successful, these measures would support the hypothesis, but as mentioned, they would not ‘prove’ it.
The idea is to isolate the outer walls from the internal sound pressure, especially at the cavity's resonances of higher frequency. The lower frequencies are addressed by stiffening using some quite uncritical cross-bracing (no elaborated scheme needed).
see => https://www.westmarine.com/west-marine-acoustical-foam-P006_180_006_004.html
see => https://www.acousticalsurfaces.com/noise_barrier/bardec.htm
Or in general: "Mass‑Loaded Barrier with Acoustic Lining"
My version, tested o/k. The foam is of heavier type; watch the open edges which provide a flow path for lower frequencies, preserving the internal volume for bass tuning. The enclosure gets damped by additional wadding as usual, preferrably in the middle. With bass reflex the recommendation to leave out the middle is outdated. Maybe that settles the case
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I would add resonances. The forces are of course there and are ampified at resonance.There are two pathways for vibrations to reach the panels.
diaphragm movements -> baffle bending movement (Newton 3rd) -> panel vibrations
diaphragm movements -> air pressure (cavity resonances) -> panel vibrations
You claim that the first path is of little importance. IDK, maybe so, but at least for the baffle it will be significant.
Let's look at the second path.
The air pressure in the cabinet will only build up to high values at cavity resonance frequencies ("standing waves"), and only at those parts of the panel where pressure maxima are present.
The panels will react to the force exerted by the pressure as an elastic plate (more or less fixed at the edges). With high pressure there will be some movement (especially in the center, the "softest" part) and at certain frequencies (plate resonances) this will be stronger than at others, but the dampening of the (thick) wooden plate will reduce that effect.
So I would expect to see a convolution of cavity FR and plate FR.
Here is a webpage (German) that looks into that with some effort.
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
Translation:
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
ADDED:
Two strategies seem to be successful.
Make the panels stiffer with strong material, stiffeners or struts.
Reduce cavity resonances with porous materials or with (Helmholtz) absorbers (as Fink does).
There will always be resonance peaks in the cabinet wall that are excited by the driver movement. If Q is high you will see them in accelerometer measurements.As @Francis Vaughan suggested, at some frequency the intrinsic resonance of the panel accidentially might match a cavity resonance--at the right position, so that the cavity couples and excites higher panel modes. But that's expectedly quite rare. Alas, I once had this and the enclosure was dumped.
In the investigation you quoted we see resonances in the lower treble, 2.5k, that appear to be a bit stubborn. Neither stiffening, nor wool address them well, while the bitumen falls short likewise. It's the strongest close to the driver, measurement position (1). There's a lot to be discussed. I did my investigations independently, not knowing of waveguide audio.
Well, we have a hypothesis that carries an uncertain degree of plausibility. We cannot prove it—just as in science, that is always impossible. However, the standard hypothesis—independent plate oscillations—has been falsified. As a rule, the enclosure walls do not oscillate in that way. Moreover, the energetic excitation has been identified. From this, engineering measures can already be derived. If successful, these measures would support the hypothesis, but as mentioned, they would not ‘prove’ it.
The idea is to isolate the outer walls from the internal sound pressure, especially at the cavity's resonances of higher frequency. The lower frequencies are addressed by stiffening using some quite uncritical cross-bracing (no elaborated scheme needed).
see => https://www.westmarine.com/west-marine-acoustical-foam-P006_180_006_004.html
see => https://www.acousticalsurfaces.com/noise_barrier/bardec.htm
Or in general: "Mass‑Loaded Barrier with Acoustic Lining"
My version, tested o/k. The foam is of heavier type; watch the open edges which provide a flow path for lower frequencies, preserving the internal volume for bass tuning. The enclosure gets damped by additional wadding as usual, preferrably in the middle. With bass reflex the recommendation to leave out the middle is outdated. Maybe that settles the case
View attachment 499273
One can say that the above experiment maximises the effects of cavity pressure when the enclosure is elongated and the driver sits at the end with a very small front baffle. Placing an accelerometer at the driver position would mean placing it close to the adjacent walls which act as braces.There are two pathways for vibrations to reach the panels.
diaphragm movements -> baffle bending movement (Newton 3rd) -> panel vibrations
diaphragm movements -> air pressure (cavity resonances) -> panel vibrations
You claim that the first path is of little importance. IDK, maybe so, but at least for the baffle it will be significant.
Let's look at the second path.
The air pressure in the cabinet will only build up to high values at cavity resonance frequencies ("standing waves"), and only at those parts of the panel where pressure maxima are present.
The panels will react to the force exerted by the pressure as an elastic plate (more or less fixed at the edges). With high pressure there will be some movement (especially in the center, the "softest" part) and at certain frequencies (plate resonances) this will be stronger than at others, but the dampening of the (thick) wooden plate will reduce that effect.
So I would expect to see a convolution of cavity FR and plate FR.
Here is a webpage (German) that looks into that with some effort.
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
Translation:
Vibrationsmessungen und Nachbetrachtungen - http://www.waveguide-audio.de
ADDED:
Two strategies seem to be successful.
Make the panels stiffer with strong material, stiffeners or struts.
Reduce cavity resonances with porous materials or with (Helmholtz) absorbers (as Fink does).
olieb
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I agree to the first part, but whether these resonances will be excited by the driver is another thing.
If you can make the panels stiff (and the cavity small) enough the lowest resonance might be above the range the driver is used, in particular for a sub or a woofer (certainly in a 3-way).
On the other hand one can (try to) suspend the driver soft enough (thick gasket + rubber washers) that no force couples to the baffle. So only the basket (and magnet) will be vibrating.
Yep, at the same time the vibrations from the driver bending the front baffle are minimised, because the driver mounting is very close to the "fixed" edges and so the small baffle is very stiff. In a bigger cabinet there might be more bending waves travelling around the edge into the panel where the acceleration is measured.
As I mentioned before, the impact of the bending wave path is not so clear to me and will depend on the size and make of the cabinet. Probably it will be the more important the higher the frequency (tweeter).
This I do not understand. Lost in translation.
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It is no technical challenge to build the best speaker cabinet for a task. Facts are known and materials not even that expensive.
What it in fact is, is a marketing problem and opportunity. You need to have something others don't use. So the more secretive, mystical and expensive the composition is, the better. Real results are bad for business.
Stability and damping of different kind are all that is needed and can simply be achieved by using simple construction materials.
A small two way needs a different construction than a subwoofer, but that is no secret for anyone in the business.
So the best cabinet material is a wide field for voodoo and sales talk. A nice argument to sell someone new speakers, by the way. That is why suitable materials, like particle board, MDF and the like are bashed by many that pretend "to know".
What it in fact is, is a marketing problem and opportunity. You need to have something others don't use. So the more secretive, mystical and expensive the composition is, the better. Real results are bad for business.
Stability and damping of different kind are all that is needed and can simply be achieved by using simple construction materials.
A small two way needs a different construction than a subwoofer, but that is no secret for anyone in the business.
So the best cabinet material is a wide field for voodoo and sales talk. A nice argument to sell someone new speakers, by the way. That is why suitable materials, like particle board, MDF and the like are bashed by many that pretend "to know".
If the baffle is small as in the experiment, the accelerometer needs to be placed e.g. at a corner beside the driver. Where it is rather stiff due to the side panels attaching.
Consider a lead-made enclosure; resonances? Why this sharp focus on resonances? For starters, where's the force coming from, then you need an exchange of different forms of energy, e/g tension versus kinetic. So, question is, if your model as implicated is sound, once it's explicated. I argue that you still won't see the infamous panel resonances, because an enclosure is not an isolated panel. Damping mechanisms appropriate for panels might fail with a 3d structure entirely.
Another is the investigation you thankfully dropboxed above. I had a look. It proves my point, actually.
It says: "... modes at 187.50Hz, 243.16Hz,287.11Hz, and 383.79Hz ..."
The author didn't cross check if the spacing (not absolute number) of frequencies is halfway consistent with the panel model. They didn't check if the expected phase flip at higher modes is there. They also didn't wonder why the frequencies never changed when they tried different panel types ranging from a tripled 3/4 board of MDF to a heavily lead loaded panel of single 3/4 MDF. I would, from theory of panel resonance, expect vastly differing frequencies. But in reality only the amplitudes changed.
And again the conclusion must be, that the implicated model of isolated panels in structural driven resonance energized by the intertia of the driver doesn't fit.
The effort to (computer) model an enclosure is rarely taken, and even if, the test of expectation against reality is skipped mostly. This lack of information leaves room for confirmation bias. Especially as many are not so much interested in real understanding, but improving speakers in a short step. As Fink Team was mentioned as a high end house using laser and all, did they show--no, nothing. We use laser they say and neither a picture nor a discussion of anything further. I'm not impressed.
Look how easy life gets, once you get to the foundations od 'science'. Cheap materials combined easily solve the problem, and then you find, it all has been there for ages!
Reiterated: https://www.westmarine.com/west-marine-acoustical-foam-P006_180_006_004.html
As long as passive multi-way speakers are bought, developers like FINK will be needed.
You have to build a very, very bad cabinet to make the material change the sound the auditor will receive. Also you can not steer the sound in some direction by using different materials, as far as they are used right.
Did anyone notice that expensive, considered "good" speakers are always heavy? Why...
You have to build a very, very bad cabinet to make the material change the sound the auditor will receive. Also you can not steer the sound in some direction by using different materials, as far as they are used right.
Did anyone notice that expensive, considered "good" speakers are always heavy? Why...
@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.
www.audiosciencereview.com
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
