How Should Speakers be Stabilised?

[RBFC]

Great post, Gary. With all your time constraints, we truly appreciate the effort you make here.

Lee

 

[Steve williams]

Gary

Unlike some pesty gnats we have swarming over this thread and another not only was it a wonderful post but you brought with a breath of fresh air. I can honestly say that having spent the past 3 days with Gary he is not only extremely knowledgeable about any and all things stereo but he is an absolute gentleman who is always looking for the best solution with the least amount of money spent. Kudos to Gary who maintains equanimity under stress

 

[Ron Party]

What Lee & Steve wrote. A fantastic post, Gary.

 

[fas42]

I've been avoiding this thread because I'm just way too busy right now, but there is just way too much misinformation here for me not to weigh in, lest readers get led astray. We have to examine everything in the context of the loudspeaker and cannot just take vibration on its own.

Thanks for this valuable input, Gary, it's exactly what I was hoping would be brought into the conversation when I started this thread. As an enthusiastic amateur, the information I have introduced stems from my own experiences with a variety of small to mid-sized box speakers which have all benefited from the ways of dealing with them that I have mentioned here. Those with completely different styles of loudspeakers may need other approaches for getting best sound from them.

Viscoelastics are materials that exhibit both viscous and elastic properties when undergoing deformation. The viscous property gives the material a strain rate that is time dependent. Different viscoelastic materials have a different strain rates. Blu-tack has a very LOW strain rate, which means that the viscosity is very high - it takes a long time before it departs its viscous properties and absorbs extremely low frequencies (with a "blob" far, far less than 1Hz). Sorbothane (the usual "audiophile" example, though) has a high strain rate, and hence loses viscosity very quickly - which is why is it good at absorbing higher frequencies.

However, you have to understand that the mechanical-to-heat conversion happens INSIDE the material. Sitting a loudspeaker on a viscoelastic material transfers some of the vibrations from the loudspeaker to the material depending on how well the loudspeaker is coupled to the viscoelastic material and those vibrations that are transmitted to the material are absorbed (or dissipated as heat). This protects the surface on which the viscoelastic material sits - which is why you use these materials as a vibration shield.

Good technical rundown, but I'm not sure what you mean by that last line

With ANY viscoelastic material, there is a pass-band beyond which it will couple. For example, a 20lb loudspeaker on three 2-inch sorbothane pucks may decouple at say 60Hz and above. On four pucks may decouple at say 30Hz and above. But de-coupling the speaker also makes it free to vibrate at those frequencies. Until you couple the vibration to the sorbothane, the sorbothane does not dissipate the energy of the vibration as heat. (Then, to solve all these vibrations, you have various vibration-controlling devices that you stick on or place on top of loudspeakers.)

This I find confusing: are we trying to couple or de-couple? My point is that the frame of the speaker will start vibrating or resonating in reaction to the movement of the cones and air movement in the room as well, at frequencies quite independent of the sound spectrum of the audio, and that energy needs to be dissipated. My experience, is that the coupling with Blu-Tack to a very massy object changes that energy spectrum to one such that the particular viscoelastic properties of Blu-Tack are beneficial in dispersing that energy.

Studying the technology (and there is a lot of good engineering in vibration control) of mounting diesel engines, jet engines, etc. will help, but cannot be relied on for audio. We are concerned with chaotic vibrations (there is no fixed period and magnitude) and not a constant vibration.

But aren't we dealing with resonant frequencies of the speaker box or frame to some degree?

If you blu-tac a tiny monitor loudspeaker to a safe as Frank has suggested, you have mass-loaded the loudspeaker, and then it would depend on the design of the loudspeaker. I guarantee you that it will sound different. Whether it will sound better will depend on the loudspeaker. There is no universal solution.

I would go further: the speaker will now very precisely reveal every deficiency of itself and the rest of the system, all the electronics. That may be a little too revealing on some systems, so a little fogging of the sound may be beneficial.

If you blu-tac Tim's speaker to his desk (no matter how much blu-tac you use) you will add the sound of his desk to the loudspeaker. If you put a concrete slab between the blu-tack and the desk, then you are mass-loading the loudspeaker. Tim's way is much better if the speakers are well-designed and he likes the sound of his loudspeaker and not his desk.

So you feel the sound of the desk would still have come through the slab?

I won't go into loudspeaker design because the thread topic asked about how loudspeakers should be stabilized (I still don't get how Frank can put spikes under a lot of weight and blu-tack between the speaker enclosure and what's under it - where does the blu-tack go, between the speaker and the spike?)

The original design that proved the case for me was to create a very heavy mass, in concrete, which was coupled to a concrete floor with 3, not 4, spikes which were embedded in the concrete. The concrete mass had a flat top, to which the bookshelf speakers were very firmly Blu-Tacked at the corners. This created a high level of mass damping, which was further helped by adding very significant weight on top of the speakers yet again.

The benefits? The speakers could go very loud with complete clarity, superb dynamics, the bass was exceptionally tight, zero boom.

The downside? It was obvious that the electronics had problems, every little bit of distortion there was ruthlessly exposed, and so my sad journey began ...

It will ALWAYS depend on the design of the loudspeaker. If Tim isolates his monitors with bricks and a rubber wedge (sort of a partial decoupling) and it sound best to him, that's probably best for his speaker. If your speaker sounds best spiked or blu-tacked to the floor, then that's probably the best for your floor and your speaker.

Fair enough, it is a hobby, after all ...

For floor-standing speakers, I generally find some de-coupling necessary in the US because of resonant floorboards. Most of the time, carpets are insufficient to dampen all vibrations in the floorboard unless the carpet has a foam or sorbothane backing. Blu-tac-ing your carpet to the floorboards will not help here. Coupling helps most of the time if the floor is non-resonant and solid.

Floorboards obviously can be a problem. My solution is to add as much weight under the speaker as possible. Again, this is why the Wilson and all the mega-heavy speakers automatically win: put their drivers and crossovers in a typical low cost box and it would be a disaster ...

For monitor loudspeakers, if you blu-tac the speaker to the stand, you will couple to the stand, which then mass-loads the speaker, and adds the sound of the stand to the loudspeaker. Which is why there are so many different designs of loudspeaker stands. If you spike the speaker to the stand, you also couple the speaker to the stand, but if you don't couple the speaker to the spike with blu-tac, then you have an interface between the bottom of the loudspeaker to the top of the stand that is coupled at some frequencies and decoupled at other frequencies depending on the material of the spike, and the material of the bottom of the speaker..... unless you blu-tac the spike to the loudspeaker.

Yes, the sound of the stand becomes relevant, my low cost way would be to use the bulkiest lump of concrete possible, not shiny but nice tone!

There are lots of coupling and de-coupling tweaks, and they all sound different. There is no universal solution like there is no universal loudspeaker or environment.

Amen!

Frank

 

[Phelonious Ponk]

Gary, thanks for the detailed response. I was going mostly on logic and common sense, and while it seems that I missed some details with that imprecise approach, I got the main point right: Yes. I like the sound of my speakers better than the sound of my desk. I have seriously considering using studio mounts, from the wall behind the desk, which would be lag-bolted directly into 2x4 studs. Can you tell me if that would be better?

Tim

 

[fas42]

Just to add a bit more "weight" to Blu-Tack's defence, from www.needledoctor.com:

BLU-TACK is a product of England that has been favorably reviewed in both the British and American press. In their Sept. '92 issue Stereophile tested various speaker/stand interfaces such as Tone Cones, German Acoustics Damping Feet, ISO Bearings, Monster Footers, Mod Squad Feet, Navcom and BLU-TACK. It was concluded that "the winner in this comparison is the cheapest: BLU-TACK."

and

BLU-TACK is a non-reactive, resistive damping polymer which behaves like a tacky, flexible, semi-liquid when being handled but like a solid at audio frequencies. It comes in thin flexible sheets that can be cut up or pulled apart as needed. It provides excellent mechanical energy transmission properties at audio frequencies even though it is a semi solid.

It is used primarily between the top plate of loudspeaker stands and the bottom of loudspeakers. This mechanically couples the loudspeaker to the stands much like spikes would but without damaging the loudspeakers. The BLU-TACK will take a "set" after a few hours and adhere to both surfaces preventing the speakers from shifting on the stands if knocked. BLU-TACK can be removed by rotating the loudspeaker on the stands to break the seal. BLU-TACK is reuseable and has many other uses such as holding up posters, cards or photos on a wall. It also holds screws to the tip of screwdrivers or holds parts while soldering. One package is enough for a multitude of uses.

Now this echoes what Gary said, and in that sense my emphasis on Blu-Tack being viscoelastic IS incorrect: I'm not a mechanical engineer! What is key in the above quote is the phrase "excellent mechanical energy transmission properties", so the benefit of this material is the extremely tight coupling that the speaker then achieves with whatever it's interfacing.

So, from my point of view, the dilemma with Tim's desktop is that the speaker either needs to coupled extremely tightly with it, or not at all. It's the halfway house that that introduces the problems, because that can easily induce resonances in the desk surface, and then the fact that the interface between the desktop and speaker is not tightly controlled makes things worse. Taking goo materials out of the equation, if I bolt a large mass to the table top with a liquid filler that sets between the top and the mass, and do the same thing with the mass and the bottom of the speaker, that would be an overkill version of using the Blu-Tack. The speaker has now become as one with the desk, equivalent to the mini-monitor locked on top of the safe.

The other option, to totally separate the speaker from the desktop acoustically is impossible, as I mentioned earlier, and has the extra big drawback of giving no path for the vibrational energy to be dissipated: the louder the speaker goes the more congested the sound is likely to become.

So, my apologies for misrepresenting the value and contribution of viscoelasticity in this precise area, can you forgive me, Tim? ...

Frank

 

[fas42]

An implication in what Gary said, and what I have just read elsewhere, is that sorbothane in itself won't do the best job, because it won't tightly couple acoustically with the objects it's interfacing. So a possibility is to use Blu-Tack, in a relatively thin layer, to "glue" the sorbothane to the surfaces it's touching. Is this reasonable, anyone tried this? Note, I've never tried sorbothane myself ...

Frank

 

[fas42]

An interesting thread at www.gearslutz.com/board/so-much-gear-so-little-time/557144-monitor-stands.html, for people interested in pursuing a pure viscoelastic solution, I took the liberty of extracting some of a key post :

I've done a bit of research about decoupling, I think it really pays off in bass "tightness" and sound isolation (most of the isolation problems are at low frequency). Spikes on the ultimate MS-36/45 stands I think are great for decoupling the stand from the floor, but for decoupling the monitor from the stand I think the best for me is vicoelastic gel, I've tried auralex mopads, they are pretty low perfomance, I've tried some foams and some of them were good, but not long-lasting, after a couple of weeks they start to lose their properties, then I've tried sorbothane heel cushions, they were good, not as good as some foams but at leas it was long-lasting.. eventually I've found viscoelastic gel heel cushions, I was shocked at the performance, better than anything I've tried!.. I was shocked when at high level music playing I wasn't able to feel anything in my hand whe grabbing my stands!..

In order to measure the different decoupling material I attached a piezo pick-up with blu-tack to my stand and measure the vibration with different ones, mopads, sorbothane and gel.. Mopads were the worst performers and the most expensive ones, viscoelastic gel heel cushions were best and most affordable. I haven't tried many of them but these are the ones I'm using, I guess there could be even a better ones, I guess that the best one it depends on the footprint of your monitors and its weight. I also realize that to cut small pieces of the cushion and to put one on each corner of the monitor base is the best aproach

http://www.spenco.com/products/footc...-heel-cushions

Nice thing about the piezo pick-up test is hat you can actually measure the best decoupling material for your monitors, and it really is quick and not expensive, you could even have one of those around for your acoustic guitar..

Frank

 

[fas42]

And for those who really want to understand Viscoelastic Materials at a technical level, there's this: http://uu.diva-portal.org/smash/get/diva2:281490/FULLTEXT01

Warning: just a touch mathematical ...

Frank

 

[fas42]

Took a bit of hunting, but looks very interesting, I haven't read it yet, but noted the comments about Blu-Tack on page 6: http://www.stereophile.com/features/806/index.html -- The Sound of Surprise (the loudspeaker/stand interface)

Frank

 

[NorthStar]

Thanks Frank for all that research and links.

It is from discussions, ideas, experiments, readings, that we grow stronger.
We don't have to agree with everything that's been said, but we can for sure respect all.

And here I'm still learning...

So thanks to all who participate in these discussions.

 

[fas42]

Thanks, Bob ...

Frank

 

[NorthStar]

Frank, I tried to send you a PM, but it says your box is full, so I cannot send anything to you!
Gotta speak to you man.

 

[fas42]

Sorry, Bob, got rid of some bits and pieces; go for it!

Frank

 

[garylkoh]

Gary, thanks for the detailed response. I was going mostly on logic and common sense, and while it seems that I missed some details with that imprecise approach, I got the main point right: Yes. I like the sound of my speakers better than the sound of my desk. I have seriously considering using studio mounts, from the wall behind the desk, which would be lag-bolted directly into 2x4 studs. Can you tell me if that would be better?

Tim

Tim, I will have to say it depends. It depends on three things - the loudspeaker, the mount, and the wall.

The loudspeaker you use, I assume, is very well designed. Cabinet resonances are well controlled (to the extent that the designer has controlled it) which means that the cabinet vibrates minimally - however, it WILL vibrate. You can mass load the cabinet - but all that will do is that it will delay the release of vibrations unless there is some way to dissipate the vibrations.

If the mounts are what I think they are, they are an arm with a platform that holds the speaker, and rigidly (or as rigidly as they are designed to be) mounts to the wall. Depending on the mount, they might have a pass band where the speakers are decoupled (usually you will recognize these by the fact that there is a long arm). If some cabinet resonances are in the pass band, then you will emphasize those frequencies and may get a "honky" sound. Then, you also have to consider how you will mount (couple or de-couple) the speaker to the mount.

The wall with 2x4 studs may get excited by the resonances passed through from the loudspeaker through the mount if the speaker is tightly coupled. In that case, you will have to find some way to absorb those resonances. This is where constrained layer damping may came in. One I found to work very well and designed for audio frequencies is http://www.greengluecompany.com/

Then, you have to consider the proximity effects of the wall on your speakers but I'm sure that you can equalize these away if you believe in room equalization.

With well designed loudspeakers, very rigidly mounted, you will get an improvement in image specificity and PRaT. Very highly decoupled, you will get an improvement in detail, resolution and clarity. Unfortunately, all solutions we have are somewhere between coupled and de-coupled to one extent or another.

Sorry I haven't answered your question if it will be better, but those are the things that you have to consider.

 

[garylkoh]

Frank, Thanks for doing the research to support some of my points. For that, you have my respect. That doctoral thesis by Agnes Rensfelt is very important. I've only had time to skim through it, but there's a lot to learn in it.

The big problem I have is that some audiophile designer will develop a product based on some incomplete understanding of a principle, sell it at some X-times cost (ridiculous audiophile pricing), and then because it changes the sound of things have some reviewer rave over it.

I'm sure that someday, someone will encase a blob of blu-tac in some skin or compliant case because he understood the viscoelastic properties of blu-tac like you understood it (before diving into more research) and sell it for $200 each. Then, someone who knows better will roll his or her eyes and think that some audiophiles are mad to buy such a thing.

The problem is that he will probably genuinely think that it is an honest product because it worked for him, and he thought that he understood the properties of blu-tac (having read the great reviews). Until it is pointed out that the blu-tac is elastic at audio frequencies (acting like a solid) and viscous at much, much lower frequencies, it seems like a great idea. And it "worked" well (changing sound and garnering rave reviews).

 

[Phelonious Ponk]

Tim, I will have to say it depends. It depends on three things - the loudspeaker, the mount, and the wall.

The loudspeaker you use, I assume, is very well designed. Cabinet resonances are well controlled (to the extent that the designer has controlled it) which means that the cabinet vibrates minimally - however, it WILL vibrate. You can mass load the cabinet - but all that will do is that it will delay the release of vibrations unless there is some way to dissipate the vibrations.

If the mounts are what I think they are, they are an arm with a platform that holds the speaker, and rigidly (or as rigidly as they are designed to be) mounts to the wall. Depending on the mount, they might have a pass band where the speakers are decoupled (usually you will recognize these by the fact that there is a long arm). If some cabinet resonances are in the pass band, then you will emphasize those frequencies and may get a "honky" sound. Then, you also have to consider how you will mount (couple or de-couple) the speaker to the mount.

The wall with 2x4 studs may get excited by the resonances passed through from the loudspeaker through the mount if the speaker is tightly coupled. In that case, you will have to find some way to absorb those resonances. This is where constrained layer damping may came in. One I found to work very well and designed for audio frequencies is http://www.greengluecompany.com/

Then, you have to consider the proximity effects of the wall on your speakers but I'm sure that you can equalize these away if you believe in room equalization.

With well designed loudspeakers, very rigidly mounted, you will get an improvement in image specificity and PRaT. Very highly decoupled, you will get an improvement in detail, resolution and clarity. Unfortunately, all solutions we have are somewhere between coupled and de-coupled to one extent or another.

Sorry I haven't answered your question if it will be better, but those are the things that you have to consider.

It may be best to leave well enough alone as they're sounding pretty good right now. Thanks again.

Tim

 

[fas42]

With well designed loudspeakers, very rigidly mounted, you will get an improvement in image specificity and PRaT. Very highly decoupled, you will get an improvement in detail, resolution and clarity. Unfortunately, all solutions we have are somewhere between coupled and de-coupled to one extent or another.

Now that's very interesting, Gary: I appreciate the improvements via rigid mounting, but the positives of highly decoupled don't make sense to me. Could you point me to some material which explains this in greater detail, perhaps?

Frank

 

[fas42]

It may be best to leave well enough alone as they're sounding pretty good right now. Thanks again.

Tim

Tim, you might be interested in the article in Stereophile I referenced: it's a major effort by JA, with plenty of explanation and measurements ...

Frank

 

[garylkoh]

Now that's very interesting, Gary: I appreciate the improvements via rigid mounting, but the positives of highly decoupled don't make sense to me. Could you point me to some material which explains this in greater detail, perhaps?

Frank

There have been very few speakers that work very well highly decoupled. I once hung my Maggies from hooks set into the ceiling.

I'm going to work on a white paper on coupling/decoupling loudspeakers. Stay tuned.