Speaker De-coupling

[Siwel]

I don't have a machine shop, but I do have a drill press. Anyway, I think we agreed that retirement was worth whatever it cost!

 

[Siwel]

You don't need time domain to check if you have issues with room modes - MMM RTA with pink noise will do. If you choose to do it here is a nice video that explains how it should be done. It's very easy and quick procedure.

I know that not being versed in using REW (I am reasonably versed in the principles however) has been a missing piece of my education. I have everything I need (but a sound card) so at some point I will just have to break down and get with the 21st Century. I guess.

 

[Frank Dernie]

The Townsends are very expensive but in addition, I can't find anyplace that they are for sale on this continent. Even if I was of a mind, I'd have to buy them on a dare. I thought the Gaia design wasn't based on polymers, that it was a tuned spring based system. To be honest, I know little about any of these dedicated devices except what I have read.

It is difficult to find exactly what the Gaia is. Maybe it is a ball in cup type, in which case it may well be good at decoupling horizontally but not vertically.

 

[Kvalsvoll]

I decided to finally get rid of all the various mechanical buzzes and noises in my room. I ran tone at various frequencies between 20Hz and 100 Hz and just followed my ears to the various sources of mechanical noise in the room. This included framed pictures, a loose access panel in the ceiling, and a particularly obnoxious CD rack whose panels vibrated like a drum. One by one I eliminated these resonating objects,by damping them with various dime store rubber bumpers or tying them down. I finally got to the end of the noise but one buzz/vibration remained.

To my surprise I discovered that the speakers themselves (both of them) were emitting sympathetic noise, between 20Hz and 100Hz, the worst of which seemed centered between say 40Hz and 90Hz. Salon 2s weight the better part of 175 pounds and I also have a pair of heavy JL Audio Subs contributing to the energy but it's the speakers themselves that are emitting the noises. The subs are crossed over to the Salons at 40Hz but don't seem to actually be producing spurious noises of their own. They may be contributing energy to the general situation that is causing the Salons to resonate but they are not the audible problem per se. The speakers are on their spikes which then want to penetrate a thick carpet and pad. Unfortunately, the underlying floor is soft and you can sense that it is likely part of the moving system that is creating this problem.

I thought rather than to try to couple the speakers to the floor with their spikes, I might look into isolating (decoupling) them instead. If I tilt either speaker onto two (of the four) spikes, the buzzes are significantly reduced. If I balance it on just one spike, the combination of whatever damping I am physically applying with my hands and the suspension of the whole speaker onto just one spike reduces the vibrations almost to inaudibility.

Sorry for this long winded explanation but perhaps it explains my interest in decoupling the speakers from the floor to the extent possible. So I'm looking into what materials and approach I can use to accomplish this at reasonable cost. Companies like Isoacoustics offer rather expensive solutions that may work but I am hoping that this can be done in a clever (cheaper) fashion if indeed such treatment is the most practical solution.

In sum, your experience with taming mechanically transferred vibrations of this type is welcomed and encouraged. I wasn't the guy who thought that isolating all the components in a system (at great expense) was a practical or necessarily proven thing to do but between the way the floor and my speakers and subs interact, I think I've got I've got a problem I can solve but I'm not sure exactly what to use to do that.

The vibrations of objects in various locations in the room are caused by the acoustic sound in the room, not so much from direct mechanical coupling from the speakers.

The sound induces motion on surfaces such as floor, walls, due to coupling from acoustic pressure into mechanical vibration. This means it will not have any effect on vibration level to decouple speakers mechanically, you need to remove the sound. Since that is not a viable solution, you can try to fix the problem by silencing the objects that vibrates.

In this article I measured vibration levels with and without decoupling:
https://www.kvalsvoll.com/blog/2018/03/29/myth-or-fact-vibration-damping-platforms-for-loudspeakers/

 

[Siwel]

The vibrations of objects in various locations in the room are caused by the acoustic sound in the room, not so much from direct mechanical coupling from the speakers.
........./

I already dealt with the sympathetic resonances of the offending objects in the room. The remaining resonance is coming from the speaker. Quoting myself from my first paragraph, which you also quoted :

I ran tone at various frequencies between 20Hz and 100 Hz and just followed my ears to the various sources of mechanical noise in the room. This included framed pictures, a loose access panel in the ceiling, and a particularly obnoxious CD rack whose panels vibrated like a drum. One by one I eliminated these resonating objects by damping them........

 

[RayDunzl]

Being cheap... and practical... for $16 I'd try:

Put a couple of these (or similar) on the carpet under the speakers.

Weight is 56 lbs each.

Try the speaker spiked or soft footered.

https://www.homedepot.com/p/Oldcast...-White-Concrete-Step-Stone-12052330/100427064

 

[bugbob]

The Townsends are very expensive but in addition, I can't find anyplace that they are for sale on this continent. Even if I was of a mind, I'd have to buy them on a dare. I thought the Gaia design wasn't based on polymers, that it was a tuned spring based system. To be honest, I know little about any of these dedicated devices except what I have read.

If mechanical vibration -

If wanting to do this on the cheap is the goal, and if looks aren't critical, and you're willing to DIY- check out the spring store. The following is I hope a DIY extension of what Frank Dernie already said. There are many different springs that you can get, you may find something suitable there. To be effective it needs to be tuned to your specific weight situation - this is important. This will be a simple isolator, working mainly in the vertical component - which given your stated problem ( mechanical transfer through the floor ), I'm hoping would suffice.

https://www.thespringstore.com/compression-spring-force-examples.html

Given your carpeted floor, perhaps get 2 small flat patio stones ( you can paint black ) that are bigger than your speaker base and quite weighty. Use one as your flat base on the carpet, and one will be on top of the the springs. Your speakers with or without spikes will sit on the second platform. Another suitable material would be some of that 2" thick bamboo composite board cut to desired size ( note that it's difficult to cut ) .

You will then have to calculate for the desired springs. There are calculators for calculating spring rate on the site. Use 4 springs per isolator for stability. Measure the weight of your speakers, or speakers with stand if using it ( it looks quite short ), and the weight of one of the stones. Choose a spring that has a good width ffor extra stability. You will want at least a 1" deflection ( as per Frank Dernie ) for the isolator as a whole with your combined speaker and one stone weight. As you have 4 springs, you will need to enter the number of springs for the combined desired defection ( I'm assuming the calculator includes this function ) .

The above is isolating only, but for a very tiny bit of frictional damping through movement at connections, material internal losses, etc. This is desirable if wanting to cover a broader range of audio frequencies generally.The downfall would be be too much movement, or perhaps movement for too long. This may or may not be an issue with the subs being close. If you want to add some damping you could add a rubber sleeve, rubber tape, etc. to the outside of the springs ( which is commonly seen ). This may cut out some of it's higher frequency isolation, but that's not the issue you're trying to resolve so shouldn't be an issue if wanting to try - ( should it turn out it's wobbling for too long, etc..) . At this point you've created a crude DIY Townshend Isolator ( but for not having tuned the damping ). Try it naked first though, and only add damping if required. Start with light damping, as I believe the frequencies the isolator covers will reduce as you increase the damping, and you don't want to have your highest trouble frequency not isolated well.

It's been a while since I looked at this stuff, I'm hoping the above is generally in order, but before commencing if desired, you should wait to hear from Frank Dernie ( as he's a bonafide expert on this subject ) or hopefully another mechanical engineer on the forum will pipe in with corrections.

 

[Siwel]

Being cheap... and practical... for $16 I'd try:

Put a couple of these (or similar) on the carpet under the speakers.

Weight is 56 lbs each.

Try the speaker spiked or soft footered.

https://www.homedepot.com/p/Oldcast...-White-Concrete-Step-Stone-12052330/100427064

Worth a peek. See below.

If mechanical vibration......................I'm hoping the above is generally in order, but before commencing if desired, you should wait to hear from Frank Dernie ( as he's a bonafide expert on this subject ) or hopefully another mechanical engineer on the forum will pipe in with corrections.

Thank you for that suggestion. I have a marble slab that can act as the base (concrete would be fine but I have the marble) and has been kept in my life for just such apurpose. It is not large enough to make a sandwich for two speakers but could act as a base for both. One problem I think somebody else mentioned is that at some point the Revel's tweeters, which are already pretty elevated, get uncomfortably high. Actually, the whole shooting match could get uncomfortably high given that it requires an inch of deflection from the springs which need to be sandwiched between something (presumably) dense.

My wife suggested that I just tear the floor up and start all over, sister some joists, stuff in some rock wool and go to town. I think she was kidding. At least I hope so because that seems terribly messy. However, I'm not kidding. She actually said that!

 

[RayDunzl]

She actually said that!

Let her do it.

 

[NTK]

I think you may want to try Sorbothane pads first. They are cheap and they are engineered for this purpose.

Attached is my calculations for the Salon 2 using their web calculator. Assuming 40 lbs load per pad, 4 sets of 1.5 inch diameter stack of 0.5 inch and 0.25 inch thick 70 Durometer discs, the natural frequency (i.e. low pass corner frequency) is 13.8 Hz. As long as you aren't playing LFE of <20 Hz with your Salon 2's, they should work very well.

https://www.sorbothane.com/Data/Sites/31/edg/vibration-calculator.html

 

[bugbob]

Worth a peek. See below.




Thank you for that suggestion. I have a marble slab that can act as the base (concrete would be fine but I have the marble) and has been kept in my life for just such apurpose. It is not large enough to make a sandwich for two speakers but could act as a base for both. One problem I think somebody else mentioned is that at some point the Revel's tweeters, which are already pretty elevated, get uncomfortably high. Actually, the whole shooting match could get uncomfortably high given that it requires an inch of deflection from the springs which need to be sandwiched between something (presumably) dense.

My wife suggested that I just tear the floor up and start all over, sister some joists, stuff in some rock wool and go to town. I think she was kidding. At least I hope so because that seems terribly messy. However, I'm not kidding. She actually said that!

Sorry - wasn't paying attention to the height issue. Given that - it looks like you may be able to maintain approx. the same height IF your built in looking mini stands are removable. If so, two 1/4" steel, 1/2" marble or other material, and springs look like they would still work from the photo. You would have to do measuring and figuring. Whatever interface between speaker and slab could be played around with - mini spikes, pad, etc.. .

 

[JustAnandaDourEyedDude]

^I'm as confident as I can be that it's the floor, not the speakers. I tilted them onto a single spike (always a physical act of courage)while running tone to test the theory. I would have physically lifted them entirely off the floor if I could have but that ain't happening! Trying to reduce the effect of transfer/contact to the floor by putting all the weight on one spike while taking as much weight a I could off of that contact point reduced the vibes to virtual inaudibility. Drop the speaker back onto all four spikes and the harmonic buzz returns. It's to do with the way they interface to the floor and how the floor responds and the energy gets transferred back and forth. Or so I think.

Those are very good tests that you did. It is unclear to me whether the "harmonic buzz" you hear is a distortion of the sound put out by the drivers due to spurious vibration of the drivers, or whether it is due to some other part of the speaker vibrating. When you hold the speaker, can you feel vibrations through your palms that correlate with what you hear? Is it both speakers? For example, if you unplug each speaker in turn, does the harmonic buzz manifest itself for each? I assume the buzz is something you actually hear and not just a distortion of a pure tone on a measuring graph.

The problem may not necessarily be due to your floor being too elastic and resonating with the speaker. Your floor may be rigid enough, and the problem may manifest itself even with spikes coupling to a more rigid floor.

In spite of the results of your tests that I quoted, is it possible that the speaker is normally rocking back and forth and dancing or hopping on the four spikes due to some internal imbalance and not just due to the normal acoustic pressures of the music on the cabinet walls? Attempting to lift the speaker on a single spike or tilting it back on two spikes may have sufficiently altered the internal imbalance to damp it. Damping using absorbent matter would likely diminish the problem then, but the drivers may still be experiencing spurious vibration. It is highly unlikely that such top-notch (I assume) speakers would have a design flaw or that units would be shipped by the manufacturer with any resonance problems. However, it remains a logical if unlikely possibility that a joint in the cabinet or a driver fastener is sufficiently loose to allow relative motion. Though it is practically impossible that it would happen to both speakers.

 

[Wombat]

Spikes couple the gear to surfaces in a manner analogous to a sound box.

If the surface has high enough mass and damping, transferred vibrations will be deadened. Suspended wooden floors are probably the worst case for vibration transmission.

Check out sand box isolation on the WWW.

 

[JustAnandaDourEyedDude]

Spikes couple the gear to surfaces in a manner analogous to a sound box.

If the surface has high enough mass and damping, transferred vibrations will be deadened. Suspended wooden floors are probably the worst case for transmission.

Check out sand box isolation on the WWW.

You are saying that the coupling resonance between speaker and floor is causing spurious vibrations of the drivers which is heard as the harmonic buzz? And it is not just a resonant vibration (due to the coupling with floor) of the cabinet walls themselves that is audible?

I agree with all the posters that it is likely due to resonant coupling with the floor, as the OP himself said. I just wanted to point out the bare possibility of something loose in the speaker itself.

 

[Kvalsvoll]

I already dealt with the sympathetic resonances of the offending objects in the room. The remaining resonance is coming from the speaker. Quoting myself from my first paragraph, which you also quoted :

I ran tone at various frequencies between 20Hz and 100 Hz and just followed my ears to the various sources of mechanical noise in the room. This included framed pictures, a loose access panel in the ceiling, and a particularly obnoxious CD rack whose panels vibrated like a drum. One by one I eliminated these resonating objects by damping them........

I did read it, but missed much the content. This is tricky - low frequency, heavy and tall speaker - difficult to decouple. Easy and cheap solutions will easily create an unstable foundation for the speaker.

 

[JustAnandaDourEyedDude]

Four USB-powered drones per speaker to keep it off the ground.

 

[Siwel]

Well then, a lot of ideas to chase down.

Those are very good tests that you did. It is unclear to me whether the "harmonic buzz" you hear is a distortion of the sound put out by the drivers due to spurious vibration of the drivers, or whether it is due to some other part of the speaker vibrating. When you hold the speaker, can you feel vibrations through your palms that correlate with what you hear? Is it both speakers? For example, if you unplug each speaker in turn, does the harmonic buzz manifest itself for each? I assume the buzz is something you actually hear and not just a distortion of a pure tone on a measuring graph.

The problem may not necessarily be due to your floor being too elastic and resonating with the speaker. Your floor may be rigid enough, and the problem may manifest itself even with spikes coupling to a more rigid floor.

In spite of the results of your tests that I quoted, is it possible that the speaker is normally rocking back and forth and dancing or hopping on the four spikes due to some internal imbalance and not just due to the normal acoustic pressures of the music on the cabinet walls? Attempting to lift the speaker on a single spike or tilting it back on two spikes may have sufficiently altered the internal imbalance to damp it. Damping using absorbent matter would likely diminish the problem then, but the drivers may still be experiencing spurious vibration. It is highly unlikely that such top-notch (I assume) speakers would have a design flaw or that units would be shipped by the manufacturer with any resonance problems. However, it remains a logical if unlikely possibility that a joint in the cabinet or a driver fastener is sufficiently loose to allow relative motion. Though it is practically impossible that it would happen to both speakers.

It is perplexing. That they both exhibit this behavior suggests to me that the problem isn't a broken speaker per se.

 

[Kvalsvoll]

^I'm as confident as I can be that it's the floor, not the speakers. I tilted them onto a single spike (always a physical act of courage)while running tone to test the theory. I would have physically lifted them entirely off the floor if I could have but that ain't happening! Trying to reduce the effect of transfer/contact to the floor by putting all the weight on one spike while taking as much weight a I could off of that contact point reduced the vibes to virtual inaudibility. Drop the speaker back onto all four spikes and the harmonic buzz returns. It's to do with the way they interface to the floor and how the floor responds and the energy gets transferred back and forth. Or so I think.

Nonetheless, I want to thank everyone who is participating in this discussion and assure that I am hearing everybody's ideas. I will be reporting back on the efficacy of the cheap isolation devices I bought resulting from Kal's link and will entertain everybody else's notions.....including eq!.....with my simple biases intact but my mind open to your ideas.

If it is easy to unscrew the spikes, you could remove the spikes, and place the speaker directly on the carpet. Then the mechanical coupling will be very different - one larger flat surface vs 4 points, and this may pehaps be enough to eliminate the problem.

 

[JustAnandaDourEyedDude]

Kvalsvoll's suggestion of removing the spikes is also a good one, to change the speaker-floor coupling. Additionally, the spikes (or their holders) may have developed slight play in their seats in the speakers, due to the speakers being bumped into or moved around the room or stood on individual spikes. I realize that the spikes must be very sturdy (hardened steel, etc.) and their (metal?) seating into which they are screwed be very securely embedded into the speakers, but every material has its mechanical limits, be it wood or metal. The play may not be noticeable to the touch, but it may take only a little give to resonate with the woofer's excursions. Kvalsvoll's suggestion would also remove such a play issue.

 

[Siwel]

If it is easy to unscrew the spikes, you could remove the spikes, and place the speaker directly on the carpet. Then the mechanical coupling will be very different - one larger flat surface vs 4 points, and this may pehaps be enough to eliminate the problem.

I think that's a good idea and in my case easy to try. I visited your paper but didn't have time to do more than scan it. I look forward to reading it later this evening.

I realize that the spikes must be very sturdy (hardened steel, etc.) and their (metal?) seating into which they are screwed be very securely embedded into the speakers, but every material has its mechanical limits, be it wood or metal. The play may not be noticeable to the touch, but it may take only a little give to resonate with the woofer's excursions. Kvalsvoll's suggestion would also remove such a play issue.

I don't make a habit of tilting the speakers on their spikes but I think your suggestion is a possibility. It will be interesting to look at the whole thing when I lay them over to change out the spikes which can be done without waiting for materials. As you might guess, I didn't install the spikes until the final placement was settled on and that took a number of weeks with a bit of a learning curve. New (to me) room with a new to me system. I was happy to put the spikes on because the speakers felt a little unstable without them. But I haven't had any reason to turn attention to them until I discovered this phenomenon.