And add a HUGE surface area out of time with the actual cabinet/drivers it sits on. One arrives at your bottom and the other at your ears. This has been known for years. You will receive the vibration to your bottom FIRST on a stim wall suspension or a non-friction peer-ATTACHED slab. This has been known about in all engineered concrete construction slab work. Especially in places with Bay Mud, tidal sub-soils like the west coast, and even in "Las Vegas Caliche" where you can feel the freeway on the Palace floor if not for sinking 140-180 feet of 6" reinforced torqued strand to thousands of pounds of torque. Those strands are on 4-foot centers and tie back the sides and basement flooring, holding up a 50-story building.
The building's upright structure is then set on huge decoupling isolators so the building can move within that secured vault (50-100 ft deep) as much a 2-5 feet side to side. They are moving very slowly all the time. Depending on the height, they can and do use strands and accumulators hooked from the bottom to the top for high winds.
Decoupling has been around and was practiced even on the Twin Towers. It was also used in sandy loamy soils in like Berlin, Germany, and perfected there at the turn of the 19th century.
Need to catch up a bit there.
Regards
As already posted above, the joist wood floor my smallish living room calculates out to 1800 lbs. Claiming the feet of an under one foot square, 32 lb floor standing speaker (random example, Polk ES50) materially alters the native resonant behaviour of this mass meets the extraordinary smell test.
What do you make of the Citroen hydro-pneumatic suspension? It was licensed to Rolls-Royce and Mercedes and others way back when, and outlawed in racing for its obvious unfair advantage...
I play the cello so I can address this part of the discussion. Some cellos have a rubber tip, though most have a spike that sticks into a wood floor. A rubber tip is hard rubber, so there would be no isolation. A cello puts out a surprising amount of acoustic energy, both into the air and via body vibration. Years ago I had a house with a finished basement, with carpet over cement. One day I was playing my cello which has a spike, and a friend was standing 2-3 feet away. He felt in his feet the cello vibrations that coupled into and through the cement!
Ice-skating and car suspension are really applicable analogies here wrt to decoupling and general physics. Next up is cannons and cannon balls!
And yet you seem to doubt structure born excitations.
By the way you said; "if anything, a large speaker would tend to damp the floor vibration by adding its own mass to the floor"
Added mass doesn't add damping it just adds mass, which changes the resonant modes of the floor, but it does nothing to "damp" them.
Not at all. I doubt that a competant loudspeaker cabinet flexes enough to create sufficient energy to benefit from isolation. That's totally different from a cello that obviously needs to vibrate and resonate in order to work at all. I'm sure you understand this difference, so I'm confused why you even brought that up.
This reminds me of a guy who sells speaker isolation products, and uses a video of a music box mechanism as proof that decoupling is needed for loudspeakers. The vibration of a music box mechanism is mean to be coupled to a larger surface, much like a tuning fork. But this guy is dishonest because he knows the difference between a music box and a loudspeaker, yet he uses that as an example anyway
As for a large speaker on the floor, you are correct that it will add mass. But it might also tend to push the floor down closer to its lower excursion limit, which would reduce its travel from coupled vibration. That's more what I was thinking, to possibly reduce or even stop any resonance.
It's not about cabinet flexure, it's about coupling a vibrating mass - as a lumped mass because the cabinet is solid - will couple to any structure on which it is mounted. One can isolate this vibration through feet isolators/dampers. That's my only point, but you seem to be disagreeing. I read your test and it backs up what you and I both believe is that this generally isn't worth doing. But physics says that it does something (and we need to get that right to begin with) and in certain circumstances, it could matter. (My other "only point")
Let's assume that the structure has "settled" and there are no more significant nonlinearities. (This is a virtual certainty.) Then the most that a massive sub would do on even a weak floor structure (it's mass being insignificant to the floors weight) is shift the resonance frequencies a little (very little) and with no change is the "Q". The resonances can't be "stopped" and "reduced" is a stretch. And that doesn't really change the physics of signal transmission through the floor.
IF large structural sound paths do exist, and you yourself have alluded to this, then the reason that this is such an issue is that these waves travel many times faster than sound in air. Thus it is possible to detect a vibration before your ear hears it. This can be very disconcerting and a problem that should always be resolved. For me its not an issue, so I don't study it much. My listening room is a corner poured concrete - typical midwestern construction - with damped walls apposing There are no structure borne issues.
Very interesting thread. Was just reading article linked in the above quote, and came across the following statement, "If these products really do affect the sound from a loudspeaker as claimed, it will be easy to prove using standard measurements of frequency response and ringing decay time."
Having tried one of the referenced products myself, namely, Primacoustic Recoil Stabilizers, with a pair of NS-10m near field monitors, I agree with the common subjective assessment that they tend to tighten up bass and improve imaging. Well, it turns out in more recent years the science of imaging audibility is something I have spent some time reading about and trying to better understand.
With the above in mind my question for @Ethan Winer would be, what science supports your claim which seems to be to the effect that if sound is affected by an isolator in such a way as can be perceived by humans (e.g. bass 'tightness' and or imaging), it it must only be from changes easily seen in frequency response and or ringing decay time?
Last edited:
Why would harmonic distortion components be ignored? Physical surfaces are unlikely to be ideal resonators.
Actually physical surfaces, structures are most likely ( almost certainly) to be linear vibrators.
When I tap the desk it doesn't return a sine wave. This discussion is becoming a fascinating view into a social world where technocratic abstractions counter prosaic daily experience.
If you tap a desk it emits sound, right? That sound is always composed of sine waves - plural. So it does emit "a" sine wave along with likely many more. It's a complex signal, not purely sinusoidal. But if I drive a structure with a pure sine wave then only pure sine waves will exist. This is simply the way physics works.
One thing that I forgot to mention is that structure borne sound is dispersive - meaning that different frequencies travel at different speeds. That is quite unlike air, but for the most part it is still linear in that no new signals are created when the signal propagates.
One thing that I forgot to mention is that structure borne sound is dispersive - meaning that different frequencies travel at different speeds. That is quite unlike air, but for the most part it is still linear in that no new signals are created when the signal propagates.
Yes, exactly. And then all the rest is irrelevant. Whether flanking paths exist doesn't matter if there's no vibration to pass. Whether adding the weight of a speaker affects the resonance of a floor doesn't matter because there's no vibration to excite the resonance. And so forth.
What else could it possibly be? What aspect of sound do you believe is not represented by the Room EQ Wizard software?
First, I would like to say you haven't really answered my question. As is you effectively questioned the integrity of some people who make a living from listening. That seems pretty bold based on a couple of simple measurements.
Nonetheless, I will try to respond to your question as a way to try to delve deeper into the science of what might account for the change in sound.
When I put the NS-10m speakers on the Recoil Pads, I noticed the sound was coming much more out of the speakers and much less from the table tops they were sitting on. Easy to localize that with very normal human abilities. In regard to that, there is a whole wiki article on sound localization (imaging perception) at: https://en.wikipedia.org/wiki/Sound_localization
Seems to me that for the most part it has very little to do with FR and room mode decay times (except maybe the reverberant decay properties of the recording space as applies to depth localization).
Perhaps most interesting is ITD localization which relies on timing differences of as little as a few microseconds between stereo channels. If speakers are vibrating on a desktop surface a little differently for each channel, I could imagine how ITD might be affected. For one thing, I don't see how room FR and or decay time would be a suitable way of checking for an effect of that type.
There is also the issue of 'tightened' bass. Maybe another effect involved there, but let's skip that for now.
Last edited by a moderator:
Except that it is not irrelevant because there is "vibration to pass". The enclosure could be made of steel and it would still excite any surface that it is placed on. And it is the flanking path that determines if this is an issue or not. Just because I may except your conclusions does not mean that I accept your rational for them, because I do not and that is why I am making an issue of this.
Markw4 makes a very strong case and the reason why I have said that flanking structural sound could be an issue. Placing speakers on a table top is a very bad idea for just the reason that the speakers will shake the table which will reradiate the sound. A perfect example of where isolators might work - but simply as a bandaid to very poor placement in the first place.
I would caution that in the psychoacoustics literature "sound localization" is not the same thing as "imaging" in a playback system. Some concepts are common, but they are still separate things. Imaging has more to do with the very early room reflections and source diffractions which degrade imaging even though one can localize the main source of the sound.
@gedlee, I haven't started to talk about raised wood floor construction and the effects on floorstanding speakers yet. Of course its not ideal, but its the reality in many situations.
Regarding imaging and localization, for what I would consider to be a "good" stereo system the system has to be able to produce a pretty convincing and very precise virtual image (sound stage) between and behind the speakers. And that effect has to be plainly audible at the listening position without significant degradation by room sound problems. Its hard to do well. No wonder it has been claimed by some that most people have never heard such a system.
Regarding imaging and localization, for what I would consider to be a "good" stereo system the system has to be able to produce a pretty convincing and very precise virtual image (sound stage) between and behind the speakers. And that effect has to be plainly audible at the listening position without significant degradation by room sound problems. Its hard to do well. No wonder it has been claimed by some that most people have never heard such a system.
Last edited: