Mechanical Isolation Devices: Myth?

[DonH56]

Well, actually it would be quite possible for us to test devices in such way. We once had an industrial client, who was considering to use our isolator for their products. But they wanted to be sure that the final result is in agreement with required specifications. Therefore he gave us the vibration spectrum that was measured at the clients floor, and we should show how our isolator would perform in such condition.
In order to make these measurements, we had to develop our own shaker, and control the vibrations in such a way, that it generates the same spectrum (given in one-third terz band amplitudes) as at the clients place. Then we placed our isolator on top of that shaker, and we could measure how the isolated spectrum would look like.

Reproducing a vibration spectrum with coloured noise is much more challenging than for example just outputting white noise, or some harmonic vibration, which could also be done by it.

Do I understand your intention correctly, and would this help you with your tests when placing the different equipment on top?

You could do a swept tone (single vibration frequency, though suppose you'd also have to define the axis of the force applied). Applying high-level white noise to a speaker would fry tweeters, but for your test system I don't think anyone really cares. The main point I and others are making is that, to be relevant to audio, you should look at the audio output of the device under test. You could then build a set of plots for different devices showing their relative sensitivity (or resistance) to vibration, and demonstrate how your product reduces that sensitivity. That is an engineering, not audiophile, approach, but would provide a simple comparison for lay folk.

Note I would not be doing this testing; my current day job is a different world than audio (or aerospace).

one additional remark that might be interesting, and maybe relevant in this context:
if we used a wav-file of some music recording, and send this as the control signal to our shaker, we could actually hear that music, since the plate of the shaker acted like a microphone. That proves our shaker also works in the audible frequency range, and the amplitudes could be adjusted from extremely small to rather large ones.

It would be cool to show that the audio band is covered, though then you'd have to show the frequency response of your shaker. I've been trying to think back and frankly have no idea how high our shaker went; it was higher than I expected, but I just can't recall how high. I remember discussing it with several engineers and how large vibration modes could be generated along with ultrasonic waves through the airframe and such. I no longer work on flight HW; sometimes miss it, but after the design phase was over, testing and handling all the real-world brutality was a PITA.


For the record, I really appreciate your insights into this, and seeing the results of this sort of testing would be of great interest to me (and probably many others).

 

[kemmler3D]

Not sure if it's come up ITT yet, but mechanical isolation of speakers can be really important if you have downstairs neighbors. Audibility in-room remains questionable but outside of the room is worth considering. Has anyone actually measured the noise reduction in adjacent rooms from use of such products with speakers, and subwoofers in particular?

 

[Sal1950]

Not sure if it's come up ITT yet, but mechanical isolation of speakers can be really important if you have downstairs neighbors. Audibility in-room remains questionable but outside of the room is worth considering. Has anyone actually measured the noise reduction in adjacent rooms from use of such products with speakers, and subwoofers in particular?

That would be an interesting paper.
Subtracting the speakers input of the music directly into the floor via isolation feet, while the air-borne pressures still have an open path everywhere else in the room would be very enlightening. For that downstairs neighbor my gut feeling is there might not be a huge difference.

 

[kemmler3D]

my gut feeling is there might not be a huge difference.

Depends on the structure. You get one transmission loss between speaker foot and wood. The losses aren't going to be that high because the speed of sound in metal and wood is close-ish. Then, presumably, everything is in physical contact between the wood floor and the neighbor's ceiling. So you get no more loss until the sound escapes from the ceiling back into the air.

The air -> wood losses will tend to be higher than the metal -> wood losses, I think, because the speed of sound is much lower in air.

If that's correct then adding layers between the foot of the speaker and the floor might be appreciated by the neighbors.

Would be a pretty easy test to do at home for anyone with access to a sub, two stories, a mic and a variety of materials or devices to put under the sub...

e: If this works, then I think in certain rooms, it would also impact the in-room sound. Reasoning: if an audible amount of sound is mechanically pumped into the floor by the speaker, some will radiate out into your neighbor's room and annoy them. However, some of that sound must also (because the waves bouncing around in variegated media are pretty chaotic) radiate back into your room, too.

If we assume that there is a neighbor-audible difference between isolating a speaker and not isolating it, we should also assume the in-room re-radiated sound is plausibly audible, and therefore the effect of a speaker-floor isolation product is plausibly audible.

Whether it's actually audible remains to be measured, I guess!

 

[Sal1950]

Whether it's actually audible remains to be measured, I guess!

I don't know either,
Just kicking around what might be the results-gains for the neighbors I guess.

 

[DonH56]

The problem of isolation in-room is usually bass, which "gets through" walls and ducts no matter how well the speaker is isolated from the floor. Been there, done that... Isolation does help if you are on a wood or thin floor not well supported, and blocking ducts can reduce HF transmission, but bass is still an issue.

 

[Seismion]

You could do a swept tone (single vibration frequency, though suppose you'd also have to define the axis of the force applied). Applying high-level white noise to a speaker would fry tweeters, but for your test system I don't think anyone really cares. The main point I and others are making is that, to be relevant to audio, you should look at the audio output of the device under test. You could then build a set of plots for different devices showing their relative sensitivity (or resistance) to vibration, and demonstrate how your product reduces that sensitivity. That is an engineering, not audiophile, approach, but would provide a simple comparison for lay folk.

Note I would not be doing this testing; my current day job is a different world than audio (or aerospace).


It would be cool to show that the audio band is covered, though then you'd have to show the frequency response of your shaker. I've been trying to think back and frankly have no idea how high our shaker went; it was higher than I expected, but I just can't recall how high. I remember discussing it with several engineers and how large vibration modes could be generated along with ultrasonic waves through the airframe and such. I no longer work on flight HW; sometimes miss it, but after the design phase was over, testing and handling all the real-world brutality was a PITA.


For the record, I really appreciate your insights into this, and seeing the results of this sort of testing would be of great interest to me (and probably many others).

As I wrote, in our previous tests we (digitally) filtered the white noise with a number of third-octave band passes, to realize the vibration spectrum at the client base. So, naturally there is no excessive high level white noise which could damage anything.
Concerning the frequency response of our shaker: on top of it we placed a commercial, high-quality acceleration sensor (Wilcoxon 731A, which was used to control the amplitudes. As this sensor is calibrated, I guess we can say the same for our shaker.
As our shaker is based on piezoelectric actuators, it covers the whole audio band and of course also ultrasound frequencies.

Anyway, I believe the easiest and most convincing solution is the real-world test under various equipment. Anybody who is seriously interested might reply here or in a pesonal message. We absolutely consider to send out demo samples, if the tester is agreeing to post the results.
May I ask, how many here already use active vibration isolators? Of course, if anybody dares to purchase our isolator, he/she is more than welcome We still offer our product under direct sale, without any distributor taking his portion.

Marcus

 

[Speedskater]

MB Dynamics shaker tables. I worked there (along with Rod Holt) some 40 years ago.

PM-Series Shakers - MB Dynamics

Our general-purpose shakers are heavy duty, industrial-quality equipment with a proven track record of lasting 20 or more in demanding applications.

www.mbdynamics.com

 

[DonH56]

As I wrote, in our previous tests we (digitally) filtered the white noise with a number of third-octave band passes, to realize the vibration spectrum at the client base. So, naturally there is no excessive high level white noise which could damage anything.
Concerning the frequency response of our shaker: on top of it we placed a commercial, high-quality acceleration sensor (Wilcoxon 731A, which was used to control the amplitudes. As this sensor is calibrated, I guess we can say the same for our shaker.
As our shaker is based on piezoelectric actuators, it covers the whole audio band and of course also ultrasound frequencies.

Got it. Second time this morning I've been tripped up by popping in and out without reading the whole thread, blah.

The last time I had to do vibration testing was going on 10+ years ago now. We had mechanical and piezo tables, but the piezo versions were too small to accommodate much more than a small hybrid, so I didn't think about that. Brain fart. We built an elaborate driver array to generate vibrations using acoustic waves up to about 60 kHz.

Anyway, I believe the easiest and most convincing solution is the real-world test under various equipment. Anybody who is seriously interested might reply here or in a pesonal message. We absolutely consider to send out demo samples, if the tester is agreeing to post the results.

Completely agree.

May I ask, how many here already use active vibration isolators? Of course, if anybody dares to purchase our isolator, he/she is more than welcome We still offer our product under direct sale, without any distributor taking his portion.

Marcus

Not on my stereo system. I actually had an active table years ago but sold it. It did not have enough dynamic range (amplitude) to stop my TT from skipping when grandma walked across the floor, but helped otherwise. It did drop the noise a bit on a big reel-to-reel machine, but the machine's own motors were the biggest noise source in that application.

I am, and perhaps others are, more interested in proving or debunking some of the claims made for large audible improvements when things like preamps and power amps are isolated. Without proof many of those claims get lumped into "snake oil". This has nothing to do with how well your product performs, more to do with the sensitivity of the components. Using your active isolation scheme, it would be interesting to check out those claims. I have plenty of experience with active isolation and its benefits -- for many years my day job included IC die and wafer probing where isolation was critical. Active isolation was very expensive, but provided broadband mechanical isolation without a specially-built room (which fabs do, natch) or a lot of specially-tuned springs and dampers that tended to drift over time and temperature.

Thanks again - Don

 

[Seismion]

Got it. Second time this morning I've been tripped up by popping in and out without reading the whole thread, blah.

The last time I had to do vibration testing was going on 10+ years ago now. We had mechanical and piezo tables, but the piezo versions were too small to accommodate much more than a small hybrid, so I didn't think about that. Brain fart. We built an elaborate driver array to generate vibrations using acoustic waves up to about 60 kHz.


Completely agree.


Not on my stereo system. I actually had an active table years ago but sold it. It did not have enough dynamic range (amplitude) to stop my TT from skipping when grandma walked across the floor, but helped otherwise. It did drop the noise a bit on a big reel-to-reel machine, but the machine's own motors were the biggest noise source in that application.

I am, and perhaps others are, more interested in proving or debunking some of the claims made for large audible improvements when things like preamps and power amps are isolated. Without proof many of those claims get lumped into "snake oil". This has nothing to do with how well your product performs, more to do with the sensitivity of the components. Using your active isolation scheme, it would be interesting to check out those claims. I have plenty of experience with active isolation and its benefits -- for many years my day job included IC die and wafer probing where isolation was critical. Active isolation was very expensive, but provided broadband mechanical isolation without a specially-built room (which fabs do, natch) or a lot of specially-tuned springs and dampers that tended to drift over time and temperature.

Thanks again - Don

May I ask you which active isolator that was, which you sold again?
We have quite a good overview about the other products that are sold in this field. Some of them only work for very small vibration amplitudes (in which they do their job good), but for larger excitations like TT certainly are, they are not very useful, since they turn off, of at least do not generate the required control forces.
Don't get me wrong - I don't say these are bad products, but just maybe they were designed for a different application. So you cannot blame the isolator, just maybe that they are also sold in the audio field, in which they don't suit so well.

I really can say our isolators have no problem with the excitation like TTs, in the WBF thread you see several positive replies for exactly that application, but also for other equipment.

And don't worry - I fully understand and agree with you. The question is how sensitive the devices are concerning vibrations. If vibrations don't influence the output result, then there is no room for improvement using vibration isolation.

 

[DonH56]

May I ask you which active isolator that was, which you sold again?
We have quite a good overview about the other products that are sold in this field. Some of them only work for very small vibration amplitudes (in which they do their job good), but for larger excitations like TT certainly are, they are not very useful, since they turn off, of at least do not generate the required control forces.
Don't get me wrong - I don't say these are bad products, but just maybe they were designed for a different application. So you cannot blame the isolator, just maybe that they are also sold in the audio field, in which they don't suit so well.

I have no idea, too long ago, and it was a work surplus unit I took home for a song. I do not and never did blame the isolator; it was not meant to handle what it got hit with in on the second floor of our old, old house. It allowed me to measure the displacement; I do not remember the amplitude, but it was larger than I expected, and well beyond its capability. I briefly considered another unit being replaced at work that almost certainly would have handled the problem, but it was much larger and heavier (not sure I could have manhandled it up the stairs). I ultimately used a set of old mattress springs with some foam rubber stuffed in them to tweak the frequency response to damp the footfalls. It was decidedly unaesthetic (ugly) but worked well.

I wish I had my notes from those experiments some 40 years ago! Lost to time and all the moves since then.

I really can say our isolators have no problem with the excitation like TTs, in the WBF thread you see several positive replies for exactly that application, but also for other equipment.

My bad, I need to quit trying to post today, crazy at work. I did not mean to imply anything about your products; I have no experience with them and was just reminiscing about my previous trials. I have not looked at the WBF thread. I have worked with active isolation systems that would have no problem with a turntable, again many years in the past. The last was shipped as part of a microwave wafer probe system and I remember the probe station manufacturer (Cascade) but not the maker of the isolation table.

And don't worry - I fully understand and agree with you. The question is how sensitive the devices are concerning vibrations. If vibrations don't influence the output result, then there is no room for improvement using vibration isolation.

No worries, this is something you know way more about than I. I was just reading your posts as one who has dealt with such things before and was excited to see an expert on board looking into an "out of the box" application for them.

 

[kemmler3D]

large audible improvements when things like preamps and power amps are isolated. Without proof many of those claims get lumped into "snake oil".

Shouldn't it be pretty easy to measure (or at least validate) these effects if you have an accelerometer and some kind of audio analyzer? You just pound on the desk a bit and you can at least get a rough but credible estimate of how much vibration might show up in amps' output voltages based on the amount of vibration.

 

[DonH56]

Shouldn't it be pretty easy to measure (or at least validate) these effects if you have an accelerometer and some kind of audio analyzer? You just pound on the desk a bit and you can at least get a rough but credible estimate of how much vibration might show up in amps' output voltages based on the amount of vibration.

One would think, but how many of us have a calibrated accelerometer? For the analyzer a sound card or audio interface is probably good enough for fun, but you'll get hit with the old "it ain't good enough to measure that" argument. And for test and comparison purposes you really need (or maybe just I want) a known, consistent vibration source. Pounding on the desk, or cranking the music, and watching the output is probably good enough for a quick self-test but for ASR (or maybe just me) I want something better defined. For the word at large, without a calibrated, or at least consistent, system you're going to have to deal with an endless string of "How do you know how hard you hit the table?", "That's unrealistic, nobody does that to a preamp!", "It depends upon the music, that song's no good anyway.", "That's because your system has lousy isolation, mine's much better." and the like.

 

[kemmler3D]

One would think, but how many of us have a calibrated accelerometer? For the analyzer a sound card or audio interface is probably good enough for fun, but you'll get hit with the old "it ain't good enough to measure that" argument. And for test and comparison purposes you really need (or maybe just I want) a known, consistent vibration source. Pounding on the desk, or cranking the music, and watching the output is probably good enough for a quick self-test but for ASR (or maybe just me) I want something better defined. For the word at large, without a calibrated, or at least consistent, system you're going to have to deal with an endless string of "How do you know how hard you hit the table?", "That's unrealistic, nobody does that to a preamp!", "It depends upon the music, that song's no good anyway.", "That's because your system has lousy isolation, mine's much better." and the like.

Good points all around. However, the worse the measuring equipment, the more convincing a positive result would be.

"I jumped on the floor next to my preamp, you can see here on the trace that it causes XYZ in the output which is within theoretical audible thresholds" - that's all we need to establish the existence of this effect.

You would want better gear to judge the relative effectiveness of different isolators, but just to establish the fact that "vibration in your gear is sometimes audible" all we need is one example demonstrating it's possible. In fact, you'd think such examples would already exist if this were demonstrable, since it's not a really complex test to run. Show me an effect higher than -60dB from the main signal caused by vibrations and I'm sold, no?

Otherwise it's just another audiophool "well, I can clearly hear it so measurements are worthless / not as sensitive as my ears / not measuring the right thing" wild goose chase where we're trying to measure someone's placebo effect with FFTs.

 

[Seismion]

Good points all around. However, the worse the measuring equipment, the more convincing a positive result would be.

"I jumped on the floor next to my preamp, you can see here on the trace that it causes XYZ in the output which is within theoretical audible thresholds" - that's all we need to establish the existence of this effect.

You would want better gear to judge the relative effectiveness of different isolators, but just to establish the fact that "vibration in your gear is sometimes audible" all we need is one example demonstrating it's possible. In fact, you'd think such examples would already exist if this were demonstrable, since it's not a really complex test to run. Show me an effect higher than -60dB from the main signal caused by vibrations and I'm sold, no?

Otherwise it's just another audiophool "well, I can clearly hear it so measurements are worthless / not as sensitive as my ears / not measuring the right thing" wild goose chase where we're trying to measure someone's placebo effect with FFTs.

Kemmler: your points are totally valid!
But let's go back to the video with isolator and TT that I posted somewhere above in this thread. Wouldn't this exactly be the test case that you suggest?
We had some ambient excitation, as well as some additional foot-fall excitation. Then we took the output signal of the TT. Here we just show the timesignal for easier understanding. But we could aswell also calculate the spectrum of it.
Then we could repeat the test and play some music with the TT. Again taking the spectrum of the output. Lastly, we compare the spectrum of the noise without the music (NOT on the isolator, but just sitting on the ground), with the spectrum of the music, and we would see how much dB the noise is responsible for. That is a clear indication how sensitive that equipment is. The worse the signal-to-noise ratio, the more sensitive the equipment is for vibrations.
We could repeat with other equipments and check what are the results then.

Finally, you can also take the output when isolation is turned on, and you would see a better signal-to-noise ratio.

Of course, for a more consistent result, we can artificially generate the disturbance by the shaker, to have it exactly the same for all equipments. But even without a controlled disturbance, you would already get a good indication of it.

 

[NTK]

Just hit it with a hammer

 

[gene_stl]

I have a three foot by two foot active vibration table new in the box if anybody wants to buy one.

2212 Series Active-Air BenchMate - Kinetic Systems

Kinetic Systems' BenchMate Vibration-Free Platforms enhance the performance of precision tabletop equipment.

www.kineticsystems.com

And a matching size steel table to put it on. It will also come with a two stage regulator and small gas cylinder (empty for schipping)

It has been sold for audio use before. Complete with bullshit audiophile testimonials. However if you think one of these things might be worthwhile , this is a good one that publishes horizontal and vertical frequency response curves.

Vibraplane Platform | Sounds of Silence

www.soundsofsilence.com

 

[kemmler3D]

video with isolator and TT

Well, for TT yes, but the question was whether this is doable with amplifiers or other solid state electronics. I think the microphonic nature of TTs and tubes is well established, but some contend that vibrations can impair the output of (say) a Class-D amp... which is doubtful.

The test is pretty straightforward for someone with the right measurement equipment, time, and inclination, which unfortunately rules me out (no sufficient equipment or time).

 

[DonH56]

Kinetic Systems, I think that's what we had at work, among others.

And yes, I don't think anybody doubts the TT application, it is for the other components that the need for isolation is questioned.

 

[SamR]

Kinetic Systems, I think that's what we had at work, among others.

And yes, I don't think anybody doubts the TT application, it is for the other components that the need for isolation is questioned.

Happy to provide my experience on this topic. I am using a Seismion under a field coil power supply. The difference is massive! Keep in mind this is a power supply for the electromagnetic drivers, which are not directly; but indirectly in the signal path.

For the first time, I could hear the nuance of a trumpet player’s breath between passages. Notes are “crisper” and more “alive”. Dynamic, loud, swings, are now distortion free — I never noticed distortion before, mind you.

No offence to anyone here but I don’t think this forum is the right place to discuss something like this. Many of you will scoff at the price ~$5k. And I get it, if your system costs about the same, then I’m not sure it’s worth it. For those with a world-class system (unfortunately it means it has to cost a considerable sum), the Seismion is a must-have. From what I’ve read, it outperforms its competitors and costs 1/2-3/4 less. It’s a no-brainer if you can, and want to, afford it.