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Speakers with no internal damping

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#1
Hello everyone, this is my first post here.
I"m an audio enthusiast for 15~ years or so, and have been avoiding writing in forums for about a decade due to the well known phenomenons of anti-science, anti-reason, unreasonable subjectivity, snake oil etc. So I'm glad to have found this place. :)

Anyway, I wanted to ask if anyone can elaborate on the subject of speakers with no internal damping, which I've had a very positive experience with, although they seem to be a small niche design wise. I've had about 25 pairs of speakers come and go over the years, in the range of up to about 8,000$~ (I've also worked in HIFI sales for 2-3 years, so there was a lot of traffic of 2nd hand equipment). There is one pair that I always keep on the side as reference, and they never disappoint- the Morel Octave Signature (Bookshelf).

A few words about these babies- these are not exactly Morel speakers. Morel is a (very good) driver manufacturer, but they don't really know how to make complete speakers. In 2005 they partnered with the veteran speaker designer with roots in B&W, Russell Kauffman, who designed these for them, and it was a one-hit-wonder. I'll save the superlatives, and just say that it seems that the rigid, internally braced, un- dampened cabinets makes the speakers sound much bigger than they really are, but does so in a very clean way. Absolutely no audible sign of cabinet resonance or "coloration".
I've actually compared them to a pair of Merlin TSM-mme I used to have, which uses very similar Morel drivers (with a larger 6.5 inch woofer, compared to the Octave's 5.25), in a sealed, heavily dampened (and heavy) cabinets. The Merlin simply sounded small in comparison depite having more woofer surface (although generally being a very nice speaker).

It seems that Russell keeps going forward with this design principle in his own speaker brand:
http://www.russellk.co.uk/the_concept.php#
(I don't know who makes the drivers, but not Morel).

So, does mr. Kauffman hold some arcane knowledge others don't? Why don't we see more of these? or maybe this design principle has disadvantages or practical difficulties making other speaker designers give it up? Any thoughts?
 

HammerSandwich

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#2
I don't have any direct experience here, but I'll offer a few observations. FWIW:
  1. We need to distinguish between damping the enclosure walls & absorbing acoustic energy inside the box. Either way, damping is the key to dissipating energy.
  2. (Some argue that extremely rigid boxes don't require damped walls. They believe that higher-frequency, high-Q resonances are unlikely to be excited in the first place. I'm not totally convinced by this and don't see how damping can hurt.)
  3. Various studies indicate that mechanical coupling from the driver, not internal air pressure, is the dominant factor in wall vibration. KEF LS50 whitepaper is a good read for this.
  4. See the 2 Morel speakers in Stereophile's "stand mount" reviews. The Octwin's cabinet-wall modes are fairly low level; the Octave 6's are not. Both show port resonances.
  5. Russell K's "cabinet agility" description seems to contradict itself. If damped walls help the midrange, why brace a cabinet, raising its resonances into the mids? They admit the cabinet vibrates, but I'm not clear if they still use damping or if the bracing replaces it.
  6. RK's "drive unit loading" technique may reduce port resonances. It sounds like a bandpass design, which isn't exactly new witchcraft. But it's still good design, assuming it's implemented well.
 
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#3
Thanks for your thoughts.

A few years ago I was really expecting the Octave 6 to come out, and boy was I disappointed. I don't know what were they trying to do, but it didn't work (and stereophile's measurements back it up). It sounded lean and bodyless. I don't have any experience with the Octwin, but if I recall correctly, the cabinets were made of corian, while in the newer signature they went back to standard MDF. I suppose it changes performance this way or the other, despite the principle being the same.

BTW, regarding whether or not the cabinets are actually damped, I've opened my Octaves and had a look; they're devoid of any material whatsoever. However, there seems to be considerable bracing and internal division of the cabinet.
 
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Blumlein 88

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#4
I've heard your Morel speakers. I didn't think they had more bass than the size would suggest, but what it had was very clear and clean. My impression was you heard low frequencies a bit attenuated, but clearly low frequencies. I do think the cabinet was sized and braced braced in a way that resonances were not excited by low frequencies. Which I think gave it a 'meaty' midrange which had the effect of it not sounding small.

Reading the Russel K link it does sound like he is using a modified bandpass arrangement. I don't know I agree with his assertions there altogether, and haven't heard his current speakers. My guess is he was simply talented at balancing out everything to get a sound he wanted. And for talented what I mean is he went to the trouble to think it all thru and balance things out well.

What little speaker DIY building I've done, I think the best sound is when the cabinet is thick, stiff and massive. In essence when you can hear only the driver working. Next best is a cabinet with lots of internal bracing to make it very stiff without so much mass. Again you don't get much contribution from the cabinet. Such speakers however if using small woofers tend to sound thin. Small speakers sometimes seem to benefit from a bit of cabinet sound in the low end to make them sound bigger. Doing that is a trade off some manage better than others.
 
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#5
I totally agree and my experience suggests the same- cabinets should be as "dead" as possible. There are exceptions here and there, but I agree that's the general rule. That is why, BTW, I'm more inclined towards high-performance bookshelf speakers + a subwoofer. To my experience, in the realm of reasonable costs, it's difficult to find a large volume speaker with it's cabinets sufficiantly "dead". Most of them, at least the commercial ones, have relativly thin & light cabinets. Usually they're also combined with inexpensive drivers, and the result, to my ears, is usually quite disappointing.
 
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#6
I think the Wilson approach of massive cabinet construction to stomp drivers into submission is usually overkill and an excuse to ramp up the cost (one reason I am an open baffle fan) but cabinets that sing along with the music are not something I would be advertising.
 
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#7
Correct me if I'm wrong, but aren't manufacturers like Harbeth (and other BBC style speaker makers) endorse their vibrating cabinet's thin walls as a design choice?
 

Soniclife

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HammerSandwich

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#10
You can find the original BBC research by Harwood & Mathew, 1977, as PDF. Mathers, 1988, also includes a small bit about this, though that paper covers much more ground.
 
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#11
Also, Harbeth's founder (Alan Shaw), is known to have challenged people to double blind amps of similar specs on his speakers, claiming that similarly measured amps will sound the same, so he's got points from me on that. Maybe his design principles also hold water.
 

Soniclife

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#12
Also, Harbeth's founder (Alan Shaw), is known to have challenged people to double blind amps of similar specs on his speakers, claiming that similarly measured amps will sound the same, so he's got points from me on that. Maybe his design principles also hold water.
Almost everything Alan says makes sense, and I like his speakers, but he goes a bit cult leader in his forum from time to time sadly.
 
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#13
And uses rather cheap tweeters & super tweeters (the woofer is home-made), so his speakers are probably not the best version of themselves.
 

Frank Dernie

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#14
Harbeth's founder (Alan Shaw)
Dudley Harwood was the founder of Harbeth. Alan Shaw bought it when Dudley retired. He has expanded the model range but not moved too far from the originals though the original tweeters are no longer available and he has incrementally updated the main driver several times.
 

maty

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#15
The speaker furniture must be able to absorb the vibrations. The best idea is thick baltic plywood. If MDF, better, thick HDF. A very good idea is to add viscoelastic material to the walls (inside) to absorb vibrations with f < hundreds of Hertz, 500 Hz I think. 4 kHz.

From last summer my modded KEF Q100 5.25" coaxial speakers had more weight than KEF LS50. It was a substantial improvement.

These improvements I have verified in several loudspeakers, starting first with cheap ones (fullrange).

Old picture:

panel-fibra-vidrio-tecsound-sy-70-x2-quilosa-sandwich.jpg


Tecsound SY 70 + acrylic adhesive + tecsound SY 70 + acrylic adhesive + fiberglass

http://www.texsa.com/en/pl39/productos/id63/tecsound-sy.htm?fcat_39=146#pestanyesProducte2

[PDF] http://www.texsa.com/pdfproducto/en/pl39/productos/id63/tecsound-sy.pdf?fcat_39=146

There are designed speakers that work as an acoustic instrument. In those few cases it is better to leave them as they are.
 
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Soniclife

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#16
And uses rather cheap tweeters & super tweeters (the woofer is home-made), so his speakers are probably not the best version of themselves.
I'm annoyed by the tweeter in a lot of speakers, but not in harbeths, so the implementation works, probably the high crossover point helps.
 

maty

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#17
Viscoelastic material like Spanish Tecsound SY works like spring-mass system. That is, not only do they add mass they also dampen the waves.

https://en.wikipedia.org/wiki/Viscoelasticity

https://en.wikipedia.org/wiki/Effective_mass_(spring–mass_system)

In addition, sandwich construction is always convenient, since the change in the density of the materials dampens the waves more than just a dense material.

Tecsound-SY-pdf.png

Combined with sound-absorbent materials, it offers products with high acoustic performance.
Fiberglass (ugly to work, gloves), rockwool or more diyers / audiophile materials.

Mass: Tecsound SY 70 (3.5 mm) only 7 Kg / m2
 
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Frank Dernie

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#18
works like spring-mass system
No it doesn't.
Spring-mass systems like crankshaft "dampers" don't work like these bond ons, I have used a similar material called coustilam fs, the inner layer damps the panel it is on (a tiny bit) the lead barrier is a good sound barrier because of its density and the inner foam reduces internal reflections. In order to use a mass/spring system you need to know the precise frequency and mode shape of the resonance you wish to change the mode shape of (mass-spring systems change the mode shape of a resonance such that a different part of the structure resonates at the frequency causing damage and the part previously vibrating os moved near a node at that frequency).
As well as crankshaft dampers (the mass of the "damper" oscillates instead of the crank) they are effectively used in machine tools to reduce chatter.
 

maty

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Julf

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#20
And uses rather cheap tweeters & super tweeters (the woofer is home-made), so his speakers are probably not the best version of themselves.
Is price a reliable indicator of sound quality?
 
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