Rubber isolation feet worsened speaker performance?

[theglobalelite]

As an experiment to try to reduce bass sounds overheard by neighbors*, I attached these SVS SoundPath Subwoofer Isolation Feet to my floorstanding Paradigm Monitor 9 speakers. They are "designed" and primarily advertised for subwoofers use, but it's really just a simple rubber donut so I figured it might be a worth a shot to try with speakers. I did some research prior to buying and found a few other users who tried the feet with their floorstanders and noticed no audible difference, also contacted SVS who said they should work fine on the floorstanders.

The results were not good! Bass became noticeably more boomy and bloated with less impact. And I got MORE noise complaints!*. I've only gotten 1 noise complaint in 3 years, but after installing these, I got 2 in 2 weeks! It must be transmitting more bass through the floor?!

My question is, does this make any sense? I didn't expect to get the exact opposite of the intended isolation effect. Rubber is a very common isolation material and should have some isolating effect, no?
I'm quite certain it's only transmitting lower and mid bass (~50-90hz) frequencies to neighbors because it's a modern upscale complex with concrete slabs between units. I don't hear any loud noises (above 100hz) from any neighbors, but I do hear EDM bass bumping from the unit directly above me. So I can only assume the unit below me hears bass frequencies from me, hence this experiment with isolation feet.



*I truly try to not be the dickhead neighbor who blasts music all hours of the day, I seriously try to keep a reasonable volume at reasonable times.

 

[theglobalelite]

After I typed the original post I remembered I had some 35 cent cork pads lying around somewhere, so once found I also dug out the speaker's carpet spikes and ordered some little spike feet for them to compare and to my surprise they performed much better than $50 SVS feet! Sound was not negatively affected by the cork pads and vibrations transferred past the spike was basically eliminated. With the SVS rubber feet I could feet vibrations in the rubber, but I felt nothing from the cork.

SVS feet:

Spikes + cork pads:

 

[GD Fan]

Could it be a durometer / speaker weight mismatch problem with the SVS donuts?

 

[theglobalelite]

I don't think so, per SVS support, the SVS feet are rated at 35-40 lbs. per foot, and the speaker only weighs 42 lbs.

 

[sweetchaos]

I was thinking of getting the SVS feet to be used with my towers at some point, so the results of your test surprised me.

Here’s an idea to try:
Place a phone with an accelerometer app on the floor, then play some sound clips, record the result of the acceleration and repeat with different feet. It might show the same thing, but with some data to compare. Just a thought...

 

[theglobalelite]

I actually was just doing that! I'm testing with my SVS SB-2000 subwoofer that also has the SVS feet though, since it's a hassle to swap the speaker feet again.

Here's just the SVS feet attached to the SB-2000 subwoofer playing the opening of Edge of Tomorrow. I placed my phone on the floor a few inches from the back of the subwoofer.

Now here's the same setup, but I stuck the cork pads underneath the SVS donuts:

 

[NTK]

I don't think so, per SVS support, the SVS feet are rated at 35-40 lbs. per foot, and the speaker only weighs 42 lbs.

That is the problem. The speakers are too light (which is the same as saying that the SVS feet are too stiff). You are only loading the feet to ~1/4 of their rated (design?) load.

What happens is the natural frequency of the "spring-mass system" becomes too high. A spring-mass system is effectively a low-pass filter. When the vibration frequency is below the natural frequency (cut-off frequency), the springs do nothing (the vibration is in the pass-band). Or worse, if the vibration frequency is close to the natural frequency and there is insufficient damping, the system will resonate and the "cure" is worse than the disease.

The optimal is to get viscoelastic vibration isolators as squishy as possible but still have a good amount of travel after loaded with the speaker (e.g. about 20% compression set).

 

[restorer-john]

The most interesting thing is the output of the accelerometer. Very cool.

 

[theglobalelite]

Thank you for the sciencetific explanation @NTK ! Interestingly, the promotional photos of the SVS donuts appear to feature the SB-2000 sub in them, the same sub I have, which weighs even less at 35 lbs!

 

[FitmanNJ]

I actually was just doing that! I'm testing with my SVS SB-2000 subwoofer that also has the SVS feet though, since it's a hassle to swap the speaker feet again.

Here's just the SVS feet attached to the SB-2000 subwoofer playing the opening of Edge of Tomorrow. I placed my phone on the floor a few inches from the back of the subwoofer.

Now here's the same setup, but I stuck the cork pads underneath the SVS donuts:

Curious — which app are you using to record your phone’s accelerometer response?

 

[theglobalelite]

Curious — which app are you using to record your phone’s accelerometer response?

Hamm Seismograph on iOS: https://apps.apple.com/us/app/hamm-seismograph/id704450894

 

[Adhoc]

To reach a natural resonance frequency of 20 Hz, a foot of solid rubber and hardness of, say 60 Shore A, needs to be compressed about 6-7 mm ( = a lot !!!). It will then start to isolate / not transmit speaker vibrations from 20 x root (2) Hz and upwards (>28,2 Hz). At its resonance frequency it will reinforce the vibration several times over. Somewhere below its resonace frequency, it may "only" transmit the vibration.

You can notice this on a washing machine with its drum and motor supported by rubber bushings. When the machine just starts to centrifugate at low rpm = low frequency, there is little vibration. As it picks up in rpm = higher frequency, the machine starts to rustle back and forth more and more before reaching a maximum. Then later on with still higher rpm, say 1200 rpm / 20 Hz, the machine stands almost still again, -rpm / vibrations are now above the rubber bushing's natural frequency. It is not very different with isolation feet under a speaker. Weight / foot needs to be correct if you are aiming to isolate it from the floor. Isolating down to 20 Hz would be 20 / root (2) = 14 Hz or lower. Very tricky with light weight speakers, you would need some steel springs for that low a frequency.

 

[Feanor]

A few decades ago British speaker makers came up with the idea of putting speaker cabinets on spikes. Let's be clear that the purpose of spikes is to couple the speakers to the floor, not to isolated them from it.

 

[NTK]

Thank you for the sciencetific explanation @NTK ! Interestingly, the promotional photos of the SVS donuts appear to feature the SB-2000 sub in them, the same sub I have, which weighs even less at 35 lbs!

In the quick specs section of the product page, for "4 foot compatibility" SVS included models from SB-1000 to SB-16-Ultra. The unboxed weight of the SB-1000 is 27 lbs. The unboxed weight of the SB-16-Ultra is 122 lbs — a 4.5X difference. It makes as much (engineering) sense as saying you can use the same suspension springs and shocks for a Suburban as for a Miata

 

[GD Fan]

In the quick specs section of the product page, for "4 foot compatibility" SVS included models from SB-1000 to SB-16-Ultra. The unboxed weight of the SB-1000 is 27 lbs. The unboxed weight of the SB-16-Ultra is 122 lbs — a 4.5X difference. It makes as much (engineering) sense as saying you can use the same suspension springs and shocks for a Suburban as for a Miata

This is my scenario exactly - an SB-1000 which I've mounted on the SVS rubber donuts. Now at least I know where to deflect the blame when my downstairs neighbors come knocking!

 

[NTK]

This is my scenario exactly - an SB-1000 which I've mounted on the SVS rubber donuts. Now at least I know where to deflect the blame when my downstairs neighbors come knocking!

Use spikes. You can then blame the Brits

 

[win]

I have these feet on my 2 subs. Anecdotally, they rattle the walls less but move the subs more.

I wasn't surprised to see that the accelerometer showed the subs vibrating so much. Conversely, this should show that less sound energy is passed into surroundings.

regarding the neighbors new complaints, probably just the result of your new testing?

 

[theglobalelite]

It might be possible to get the durometer specs of the cork pads from DiversiTech, I was able to find this detail durometer info of their higher performance rated EVA foam pads (3:1 vs cork), at the prohibitively expensive cost of twice the price of the cork pads:

Hardness specs for Diversitech’s EVA MP2E 2”x2” anti-vibration pads are as follows:
The black rubber component has a Shore A scale rating of 55 +/-7.
The blue foam layer has an ASKER C rating of 70 +/- 7 [as defined by SRIS 0101 (Standard by the Society of Rubber Industry, Japan)].
- https://forum.audiogon.com/discussions/vibration-isolation-2

Would it be possible to compile a sort of weight class list for these budget isolation materials based on their durometer ratings?
for example, 1-100 lbs - cork, 100-200 lbs - rubber, 200-300 lbs - EVA foam?

 

[Chrispy]

Isolation stuff like this sure creates some interesting thoughts. Spikes, too.

 

[Benedium]

I had the same suspicions about the svs soundpath feet on my pb1000.

First thing I did not like were that they were not height-adjustable for slightly uneven flooring.

Then even when i managed to find a flat placement area, I could see the pb1000 rocking back and forth as I finger-nudged it.

I believe this cannot be good as i always thought speakers or subwoofers alike ought to be anchored and completely un-movable for the drivers to work optimally.

During movie playback, although more things rattled around the house for some reason, I strongly believe the bass had become slower and less accurate.

I have since gone back to the original/stock feet and managed to further improve sound quality by finding better placement options. And to be honest I don't think much vibration is transferred to the floor from the 4 tiny feet anyway.