Couple vs De-couple speaker to stand?

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kenreau

Couple vs De-couple speaker to stand?
« on: 7 Jun 2010, 11:50 pm »
Steve,

This has no doubt been addressed in one form or another, but I am attempting to understand the logic of wanting to couple vs. de-coupling of a speaker box to stand interface.  And, maybe, I'm using the terms incorrectly?

I have been under the impression the desired goal is to get the speaker box vibrations/ringing drained away.  I recall reading speaker reviews where they bolted (hard couple?) the bottom of the speaker to the top of the stand.  It is my impression the vibrations work their way out, down the stand to the spikes at the floor.

Intuitively, to me, it seems like a de-coupling / compliant interface would be a barrier & trap the harmful vibrations at the speaker box and prevent them from dissipating away.

I have Harbeth 40.1 speakers sitting on Skylan mdf speaker stands.  They come with small thin sorbothane(?) discs at all four corners as the interface.  I read an article in PF where an Acoustic Revive speaker stand $$$ (see below link) used a certain quartz disc as the interface providing a rigid(coupled or decoupled or semi-coupled?) transfer. 
article excerpt
At each corner of the top plate a receptacle is machined into the surface to accept an Acoustic Revive RIQ-5010 smoky quartz isolator, which the loudspeaker rests on. To further improve vibrational control, a thin vibration control sheet is placed inside the receptacle that the quartz insulator disk sits on. The vibrational control sheet consists of a polymeric material...developed to transfer and eliminate vibrational energy by turning it into electrical energy that is dissipated as heat.

I read another article where someone used round flat refrigerator magnets (rigid metal-oxide discs) to good effect as well.  They placed clear wrapping tape on either side for a minor compliant surface.  These approaches seem to be at odds with the compliant de-coupling approach, if I'm using the terms correctly?

Does the ideal approach depend on the speaker design?  The Harbeths speaker boxes are large, relatively thin and supposedly tuned to resonate favorably.  Although they are large and weigh ~70 pounds, they are not typical dead / mega mdf boxes.

http://www.positive-feedback.com/Issue47/acoustic_revive.htm


Thanks,
Kenreau

« Last Edit: 7 Jan 2011, 06:34 am by ServerAdmin »

Herbie

Re: Couple vs De-couple speaker to stand?
« Reply #1 on: 8 Jun 2010, 02:44 am »
Hi, Kenreau. The goal is to get the speakers performing to their best potential. Holding the baffle as vibration-free as possible usually accomplishes this. At the same time, you want the speakers' design parameters, i.e., the resonant qualities of the cabinet woods, internal bracing, and other factors to remain unfettered. If the speaker is designed to "breathe" a little, you want to allow that.
 
The problem with "draining" vibrations is that vibrations don't drain as well in real-life as they do in theory. A cabinet suffering from some of the higher frequency vibrations that cause glare and other distortions will sometimes just jitter around on rigid material. Vibrations that are drained to the floor become floor-borne vibrations that can mess up the rest of your audio system. Vibrations simply don't follow the rules; they go every which way, traveling readily between and through hard materials. They'll reverberate right back up the way they came, too.

Decoupling with compliant materials like Sorbothane is usually worse. Your intuition about compliant interface, with speakers, is correct. With compliant materials, the idea isn't to let vibrations dissipate, but is to absorb vibrations (transfer the energy to heat). Rubber and Sorbothane, and most squishy materials will absorb some vibrations but yet by their compliant nature will also allow the cabinet to vibrate unconstrained to some degree. Speaker drivers will then drive even more cabinet vibration. Then, the rubbery materials will introduce resonances of their own into the cabinet that affect the speakers' drivers. Any benefit you get is usually at the cost of some detrimental trade-off.
 
With loudspeakers, rigid coupling tends to deliver a harsh, rigid musical result. Compliant decoupling often gives ill-defined bass and some loss of high frequency articulation.

The solution is something in-between, something that's neither squishy nor hard. Herbie's dBNeutralizer material used with Big Fat Dots is formulated specifically to address this loudspeaker/stand interface. The material is relatively hard and rigid, yet just compliant enough to block the transfer of vibrations and to intimately absorb unwanted cabinet vibrations. Natural qualities of the speaker woods are tamed but not conquered, allowing speakers to perform as they are designed to do.
 
With the occasional exception of very small monitor and desktop speakers, dBNeutralizer provides the best interface we know of with just about any speaker and stand. Speakers that rely on lots of rigid bracing will work optimally, as well as cabinets designed to "breathe." Harbeth speakers, with a "favorable resonance" design approach, do exceptionally well on Big Fat Dots (or Square Fat Dots).
 
Depending on speaker design, results can often be further improved by placing a granite slab on top of each speaker cabinet, filling hollow stands with sand or sand/lead shot, internal cabinet damping with rope caulk around speaker baskets, wire connectors, binding post mounts, crossover mounts.

With lots of speakers/stands, you might get a satisfactory improvement with cones, carbon discs, refrigerator magnets, and other devices. Even Sorbothane. But in most cases you can do better.
 
With 40.1 speakers at 75 pounds on MDF stands, the best solution is virtually a no-brainer: replace the Sorbothane discs with Big Fat Dots. Your speakers will thank you and breathe easy.

Steve Herbelin
Herbie's Audio Lab
« Last Edit: 24 Jan 2011, 07:50 am by Herbie »

poseidonsvoice

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Re: Couple vs De-couple speaker to stand?
« Reply #2 on: 8 Jun 2010, 03:52 am »
FWIW Herb is right. I have my Abbey's that weigh about 70 lbs a piece on 40 lb maple stands filled with sand. They are decoupled with Big Fat Dots. Big major subjective difference between that and regular old blue tack. Much sharper imaging, cleaner bass lines, etc...

Best,
Anand.

kenreau

Re: Couple vs De-couple speaker to stand?
« Reply #3 on: 8 Jun 2010, 04:50 am »
OK, thanks guys.  I will give them a try.  I just placed a Big Fat order for a variety of goodies to try out.

Kenreau