Damping material adds non-linearity & friction??

Hi everybody,

I have come across 2 different sc. "High End" loudspeaker manufacturer who claims some odd ideas about damping materials inside the loudspeaker enclosure.

First YG Acoustics (https://www.ygacoustics.com/YG_Acoustics_Ad_for_Stereophile_Sep_2008.pdf)
(Backup link: https://web.archive.org/web/2010033.../YG_Acoustics_Ad_for_Stereophile_Sep_2008.pdf)
the say the following things directly copy-pasted:

elimination of resonances
at the source, rather than their
absorption through stuffing,
dramatically lowers enclosure losses.


and

The downside of the competitor’s use
of stuffing is its side-effect – friction


YG concludes the higher loss, eg. more stuffing creates the following "problem":

A loudspeaker with a high-loss
enclosure suffers from boxy, slow
sound.


Second Neeper Acoustic (((o Neeper Acoustics o)) - technology)
(Backup link: https://web.archive.org/web/20100327005618/https://www.neeper-acoustics.com/tech.html)
they are saying the following:

The second solution - acoustic damping - is often used to suppress resonances. And it actually does work! But it also kills the resonances and the energy in the music! The problem with acoustic damping materials such as Rockwool, acoustilux, etc., is that the resultant damping is non-linear. It simply kills the dynamics, life and energy of the music!

Any damping material/stuffing expert here around who could comment this?
I am at loss on these new fashionable ideas of loudspeaker designing.

Cheers Michael

Edit: Added web archive links as well as attached the documents below as the original links are dead.
 

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The problem with acoustic damping materials such as Rockwool, acoustilux, etc. [snip] It simply kills the dynamics, life and energy of the music!

I am at loss on these new fashionable ideas of loudspeaker designing.

New?

Here's a couple of snips from the book "Loudspeakers" by G.A.Briggs (founder of Wharfedale):

"Having stated that a listening test is more important than a response curve as the final arbiter of speaker performance, there must be instances where the two are in conflict, ..."

"An almost perfect illustration of this point now follows. It is some seven or eight years since we built our first corner brick enclosure ..."

"We naturally tried damping and padding the inside and fitting felt partitions to remove standing waves etc., but we soon decided that the benefits were outweighed by a loss of brilliance and "life" in the reproduction, so out came the trimmings."

(response curves are given, showing the theoretical benefits of damping)

"I would wager the proverbial little apple that nine technicians out of ten would plump unhesitatingly for the treated cabinet of Fig. 9/14, but I still prefer the livelier performance of the untreated cabinet of Fig. 9/12, and so do the majority of listeners."

That's from the 1958 edition!

Wonderful book, btw - highly recommended if it's still available anywhere.

Edit: OK, he did also say that for small rectangular boxes, some damping is essential.
 
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Product differentiation
From Wikipedia
In marketing, product differentiation (also known simply as "differentiation") is the process of distinguishing a product or offering from others, to make it more attractive to a particular target market. This involves differentiating it from competitors' products as well as a firm's own product offerings.

Differentiation can be source of competitive advantage. Although research in a niche market may result in changing a product in order to improve differentiation, the changes themselves are not differentiation. Marketing or product differentiation is the process of describing the differences between products or services, or the resulting list of differences. This is done in order to demonstrate the unique aspects of a firm's product and create a sense of value.

regards
James
 
Hi everybody,

I have come across 2 different sc. "High End" loudspeaker manufacturer who claims some odd ideas about damping materials inside the loudspeaker enclosure.

First YG Acoustics (http://www.ygacoustics.com/YG_Acoustics_Ad_for_Stereophile_Sep_2008.pdf) the say the folowing things directly copy-pasted:
elimination of resonances
at the source, rather than their
absorption through stuffing,
dramatically lowers enclosure losses.

and
The downside of the competitor’s use
of stuffing is its side-effect – friction

YG concludes the higher loss, eg. more stuffing creates the following "problem"
A loudspeaker with a high-loss
enclosure suffers from boxy, slow
sound.


Second Neeper Acoustic (((o Neeper Acoustics o)) - technology) they are saying the following:
The second solution - acoustic damping - is often used to suppress resonances. And it actually does work! But it also kills the resonances and the energy in the music! The problem with acoustic damping materials such as Rockwool, acoustilux, etc., is that the resultant damping is non-linear. It simply kills the dynamics, life and energy of the music!



Any damping material/stuffing expert here around who could comment this?
I am at loss on these new fashionable ideas of loudspeaker designing.

Cheers Michael

I think there is a lot more to this than meets the eye. First of all, what frequencies are we addressing? At long wave lengths a box acts like a pressure vessel with uniform but time dependent pressure inside. The compression/expansion process is nonlinear to start with. Adding damping still results in a nonlinear process, but it tends to be more linear because it drives the process to an isothermal one. The nonlinearity of the air in the box makes a nonlinear spring which can introduce distortion. However, unless the box is small and the change in volume due to driver excursion is large (Big woofer in small box) this nonlinearity is pretty insignificant. The biigest problem with damping at low frequencies is the possibility of the dmaping material moving around in the box. This can add nonlinearity, but to what degree is of question.

At higher frequencies were really are not so interested in whether the processes is linear or nonlinear. What is of interest is if internal reflections and standing waves are damped. If not damped the internal reflections and standing waves impact on the rear of the cones and will be retransmitted through the cone, coloring the sound just as room modes color the low frequency reproduction in a room. If when damping material is added to the box the sound becomes dull it is more likely because higher frequency hash bouncing around inside the box that is ultimately retransmitted through the cone is no longer present. In effect, what is radiated is cleaner sound.

These is a possibility that the damping of these internal shorter wave lengths is not 100% and in such cases there may still be some sound form inside the box retransmitted through the cone. And there may be some distortion associated with the retransmitted sound. The damping process is generally by friction, as noted, and by flexing of the fibers of the damping material. All this generates heat and the heat generated is going to be, in general, proportional the the velocity squared of the air motion in the box, which is nonlinear. But again, this is not that significant as the velocitied are small at higher frequencies.

If the sound of the stuffed box is is "slow", what ever that means, it is because the lack of re-radiated high frequency as altered the frequency response which should be evident in a simple measurement.

YG states that the way to avoid this it to eliminate the resonances at there source. However, the box itself is the source. So if you want to eliminate box resonance without some form of damping or dissipation of the energy radiated inside the box, then eliminate the box, which is what OB speaker do, with another whole set of design issues. Certainly boxes can be and have been designed which minimize the strength of discrete standing waves, but the energy inside the box will be re-radiate through the cone (or even box walls) or ultimately dissipated by friction, if by nothing else, between the molecules of air inside the box. To counter YG's statement I woudl say that a speaker with high loss enclosure radiates only the sound from the front side of the cone and is therefore more actuate. And Neeper Acoustic's statement that damping also damps the resonances in music are true, if they are referring to those radiated from the back side of the cone into the box, but not those radiated form the front side. A correctly designed and damped box should act like an infinite baffle, except at low frequencies where it alters the alignment. There will be some nonlinearity introduce but it will typically be insignificant compared to the nonlinearity of the driver itself, except perhaps, at low frequency as noted above (large woofers in small boxes). The bogger issue with boxes is panel resonnaces which can color the sound significantly, which I am sure you are all ware of.
 
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YG states that the way to avoid this it to eliminate the resonances at there source....

Ok I am going to get a lashing for this... Without the driver the box is just a piece of furniture. The driver is the source. Sure the panel will resonate when driven via the driver and color sound but I think the reference was the driver/magnet resonance.

I agree with everything else you said however.
 
Ok I am going to get a lashing for this... Without the driver the box is just a piece of furniture. The driver is the source. Sure the panel will resonate when driven via the driver and color sound but I think the reference was the driver/magnet resonance.

I agree with everything else you said however.

Stuffing a box would not have any significant effect on driver/magnet/basket resonances. Such resonances would either be transmitted by the cone or baffle or not. Stuffing the box would not change that.
 
Thanks John K for your detailed reply!

I can't more than agree with you, it's all known to me and I have built own designed speakers since long time back, from a subjective point of view I always preferred to damp the enclosure quite hard which yielded into a clean but as some might call it a "boring" sound, after some time of listening the ears become acquainted with the new sound profile of the speakers and the lesser listening fatigue and one realize it's a more relaxed sound with better micro-details to use a subjective expression.

That our ears need time to get acquainted to new equipment reminds me how often sellers and some scruple less manufacturers speak of "burn in" when it's an excuse for the fact they could never tell a customer hers/his ears must adjust to the new sound profile, a "burn in" process is much easier reason for a customer to buy then that the customer have to get "used" to, however loudspeakers are a clear exception of cause.

Going back to what YG said in the PDF slide provided by the link in my first post if we alter the viewpoint of losses and resonance as YG is addressing it they are claiming on the result is a higher resonance peak for their mid-woofer as if it would be a quality mark. That's fine for me if they want to persuade their customer it's something to striver after, while in fact a resonance is stored energy released over a comparatively long time from the point the resonant tank was loaded/excited blurring the sound stage, eg. acoustic noise and higher IM.

Cheers Michael
 
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John - that was my point. The YG comment said "elimination of resonances
at the source, RATHER than their absorption through stuffing, dramatically lowers enclosure losses" The source being the driver. I was pointing to the mechanical coupling of the driver/baffle system to the rest of the enclosure which is not discussed but certainly a source of vibration that can lead to resonance in an enclosure panel.

I could load the .pdf but now I was able to open it and see they are talking about box geometry.
It is a hyperbole ad to say the least.
 
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The driver can be clamped to the cabinet. The cabinet can be made like a wedge. An acoustic "swamp" can be made staring with no damping around the driver, then soft, then harder and then even harder material. I usually watch the impedance curve, A dynamic speaker is a reciprocal device so in a way a microphone. Actually Baxandal had an AES paper where he has shown how to transfer a speaker into a microphone. Watch the small wricles in the impedance curve. The phase of the impedance is usually more sensitive visually then the magnitude. The cabinet shows it´s presence usually in the fundamental tone range between 150 and 300Hz provide the cabinet is of "medium" size. Wrinkles higher up can be the sesult of bad cone termination and can not be influenced by damping material. When the wrikles in the impedance curve are JUST gone the damping is optimal in my experience. More damping will lower the sensitivity of a reflex box for example and more damping may bring no benefit to lower the sound that comes back trough the cone. One exeption is a closed box where more damping can extend the frequency response in the lower reaches because it has a strong effect on the Q and resonance frequency. A totally overstuffed small box can have a surprisingly low resonance. Rockwool is best for that kind of experiment because it is quite heavy and dense.
I usually like "soft" boxes better then metal boxes two. A double wall construction can have both benefits.
 
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Well with YG I would think they are kind of implying there metal boxes are less resonant than wood. Or something along those lines. They are keeping it open ended and letting your imagination and the pictures fill in the blanks haha.

Does YG decouple their drivers from the baffle? I've seen speakers with decoupled tweeters or something but has anyone really made speakers that are decoupled with mechanical bushings or something? Or does that just kill the whole baffle loading effect and force you to use more power or drivers?
 
I've mentioned poor results due to "stuffing" several times before. Here is one thread:

http://www.diyaudio.com/forums/full-range/75940-my-fostex-fe-108ez-project-part-2-a-2.html

Notably:

Me:

"..Stuffing should increase resistance and subjectively "suck the life" out of the drivers. (the closer the stuffing to the driver, the worse the effect.).."


Taperwood:

"Scott,

Just this afternoon I tried stuffing in the CC. I tried it directly behind the driver and also just in the V-shape part, both a lot and a little bit. You are right, the life is completely sucked out. It was like sticking your ear up to a midrange driver (well, not that bad but close). My wife stuck her head in the room and said "there's something wrong with that recording."

However, it seemed that vocal resolution was better, but I don't know if that was because it was so forward or something else going on."


Me:

"If your wife says that then you KNOW something is wrong. Funny thing is that it will actually measure better on a CSD plot. This is another classic case of measurements leading to a WRONG conclusion. This could have to do with the altered behaviour being wrong in the microsecond range and not the millisecond range. In otherwords every CSD plot I've seen is millisecond, not microsecond - and so it won't really be visible.

I bet another thing occured:

..centered imaging remained about the same (maybe better, maybe worse - likely moved forward near the plane of the speakers), but off center imaging probably sounds a lot closer to the speakers (perhaps even as if its comming from the speakers).

The cleaner vocals was likely a product of removing ambiant information from the track and leaving just the vocals/instruments. (..kinda like scrubbing out the sound stage.) My guess is that there would be very little change for tracks with close mic vocals and little or no hall-sound/reverb (..possibly a little better).

The funny thing is that topic seems to be restricted to the fullrange forum. The other so-called "progressive" forums dealing with "real" speakers never seem to talk about this (..except for the question "what happened to imaging depth?")."


Taperwood:

"Scott, that is exactly what happened. I couldn't have described it any better by writing an entire book. Thank you."




Of course now I "stand" corrected - it now *is* being "talked about.
 
Well with YG I would think they are kind of implying there metal boxes are less resonant than wood. Or something along those lines. They are keeping it open ended and letting your imagination and the pictures fill in the blanks haha.

Does YG decouple their drivers from the baffle? I've seen speakers with decoupled tweeters or something but has anyone really made speakers that are decoupled with mechanical bushings or something? Or does that just kill the whole baffle loading effect and force you to use more power or drivers?


Actually they are referring to linear decay.

You can generally improve a driver's linear decay along traditional time measurements with added stuffing - particularly if the driver doesn't have well suppressed diaphragm modes and is NOT made with a material that has high internal loss.

In this case what they are saying is that drivers they have selected already have good linear decay, and don't need to be "cleaned up" via stuffing.


The same is particularly true for tweeters.

Note that the more expensive the tweeter in a "line", the *less* stuffing it has in it's rear chamber (generally).

In fact manufacturers like scan speak go to great lengths to create chambers to "sink" the rear output of the driver. i.e. multiple labyrinths.
 
The nonlinearity of the air in the box makes a nonlinear spring which can introduce distortion. However, unless the box is small and the change in volume due to driver excursion is large (Big woofer in small box) this nonlinearity is pretty insignificant.

are there any user-friendly formulas for calculating this effect? I mean for rough determination if the box is too small for a given displacement?
What kind of distortion can arise? Does non-linear in this context
mean harmonic? If so, what is tha scale of the problem? In other words how much distortion in what frequency bands can arise when the box is too small for a given displacement?

I ask becasue I wonder what volume of a closed box is best compromise.
From the perspective of internal reflections and standing waves the smaller the better, isn't it?

Which one of the two sources of distortion/colouration is measurably and/or audibly worse: "a nonlinear spring" or "retransmission of sound through the cone" becasue of "internal reflections and standing waves"?

best,
graaf