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Seismic Isolation for Loudspeakers (Bound and Gagged No More!)

Posted by bdiament (A) on December 30, 2002 at 07:33:40

In a recent post to the Tweaker's Asylum, I mentioned experimenting with seismic isolation for my loudspeakers. Having enjoyed the tremendous sonic benefits of seismic isolation on the rest of my gear (Hip Joints for the horizontal planes and air bearings on the Enjoyyourshelf rack for the vertical planes), I began listening to my loudspeakers while they sat on Hip Joints instead of directly on the floor.

I wrote of preliminary findings that seemed encouraging, the speakers appearing to show the same degree of benefit as the CD player with an increased sense of dynamics, bandwidth extension, soundstage expansion, much better focus and an overall "opening up". While this seemed at odds with the conventional wisdom of mounting the speakers as rigidly as possible, I wanted to test the conventional wisdom and see if it held up.

Yesterday, after having gotten a good sonic fix on how the system sounded with the speakers "floating", I removed the Hip Joints and put the speakers back in direct contact with the floor. It took only a few moments to recognize the not at all subtle differences. With the speakers back on the floor, the system sounded quite degraded. Dynamics sounded compressed, the soundstage shrunk, cymbals lost a sense of the metal from which they're made and started to sound more like the release of compressed air, bass lost definition, a good amount of the air was gone and vocals developed a rough edge.

I replaced the Hip Joints and smiled at the immediate return of focus, dynamics, air, bass definition and smoothness. I am starting to feel Hip Joints make an even larger difference with speakers than they do with CD players. Put another way, rigidly mounted loudspeakers are effectively bound and gagged.

If there was going to be a negative effect from floating the speakers, I suspected it would be in the low bass. My suspicions were unfounded as floating the speakers freed the bass, upper, mid and low. As I thought about it, I realized my trepidations were based on the conventional wisdom about rigidly mounting the speakers. It would seem to make sense that a floating speaker would re-act in Newtonian fashion, by rolling backward when the speaker element pushed forward. What the experience taught me was the expected Newtonian action-re-action does not occur here. Why? I believe the very low resonant frequency of the Hip Joints comes into play. With a resonance well below what the speaker (or even a good sub) will produce, the Hip Joints don't respond. They only roll for seismic frequencies, hence leave only their benefits, i.e. preventing entry of seismic vibrations into the speaker elements and crossover.

If you've enjoyed the benefits of seismic isolation on any of your components, I encourage you to try it on your speakers if you can.

Happy Listening!
Barry

P.S. #1: It is important that the balls in the roller bearings make contact with a hard surface. Placing speakers directly atop them will cause slight indentations on the bottom of the speaker and inhibit the function of the roller bearings. For my Magnepans, I started with a platform of 1" maple ply sized to accommodate the full "H" pattern made by the speakers' feet. Since the ply didn't provide a hard enough surface for the balls to roll against, I used a 12" x 12" x 1/2" marble tile, finished side facing down, between the Hip Joints and the speaker platforms.

P.S. #2: Because some misunderstood what I meant by "seismic isolaion", I'll re-state that I mean devices with a very low frequency of resonance. This excludes heavy platforms and cones and spikes (which do not isolate at all). Sorbothane and the "isolating rings" found on most racks have way too high a resonant frequency to give meaningful isolation. Devices that require damping (e.g. to silence the "boing" of springs) have diminished effectiveness. Seismic isolation can be effectively achieved with roller bearings, like Hip Joints and with air bearings, such as those used in the Enjoyyourshelf rack. Devices that use multiple air bearings as a means of balancing gear with asymmetrical weight distribution are compromised because when you stiffen a spring (for example, to lift the heavier part of an amplifier) you raise its resonant frequency.

b

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