Damping material adds non-linearity & friction??

[Ultima Thule]

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_Acoust...e_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

[godfrey]

Originally Posted by Ultima Thule

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.

[planet10]

No damping will, on the other hand, maximize the back EMF caused by microphone effects inside the boc.

dave

[infinia]

MARKETING 101 less is more
Sombody has to have a new angle to sell , its all the same stuff and it depends on other things... least of all problems IMO

[tvi]

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

[john k...]

Originally Posted by Ultima Thule

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_Acoust...e_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.

[planet10]

Thanx John, that was good.

dave

[stephenmarklay]

Originally Posted by john k...

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.

[john k...]

Originally Posted by stephenmarklay

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.

[Ultima Thule]

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