Audiolics Anonymous Chapter 2
Unwanted Acoustic Vibrations
by Bill Gaw
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  Hello, fellow Audiolics! Welcome to another meeting of Audiolics Anonymous, our support group for the insatiable tweaked. Hopefully, you've been able to curtail those urges to experiment and have actually enjoyed listening to something since the last meeting.

If you remember at the end of our last session, I stated that I would be discussing problems associated with electricity. But, as usual, I became sidetracked with experimentation again and have decided to discuss another nemesis keeping us from nirvana; i.e., room vibration.

If your equipment is super high end with vanishing low distortion levels, and your speakers are of super high quality, there are still three other distortion components that will damage the sound reaching your ears. First, noise riding on your electric lines. Second, EM and FR in the air. Third, reverberation from the room. Fourth, vibration energy from inside and outside of the room. The first three will be discussed at future meetings, the last is the topic for today.

Even if your sound system is off and you make your room as quiet as possible, there will still probably be 40 to 60 dB of background noise. Both air and structure born. This background noise is being transmitted both through the structure and air, and being produced in the room. I can still remember the one time that I was in an audiologist chamber that presented a true silence What the difference is between what we think is silence and that which really is! Even with all of the windows and doors shut, and with soundproofing on the walls, there will still be leakage from outside. This is why the Radio Shack Sound Level Meter starts at 60 dB, as most rooms are at least that noisy. And this noise extends through the entire 20Hz to 20,000kHz sound band... and way beyond on both sides. And the most easily passed are the very low frequencies approaching 0 Hz such as traffic rumbling, house movements due to wind motion, and even seismic waves traveling through the earth. These vibrations, can actually be below 1 Hz., i.e., 1 cycle/2,3,4 sec., etc.

In addition there are the noises emanating within the room. Each piece of equipment has a transformer that hums at 50 to 120 Hz, depending on configuration and AC frequency. Each cap and resistor in the power supply, especially switching types, also hums along. Then there are the fans that are cooling some of the equipment not to mention all that digital circuitry humming along at high frequencies. Every person in the room is breathing, hearts are pounding, and some are singing along. But of course the worst offenders are our loudspeakers pumping out +100 dB of energy. All of this sound energy is feeding back to each piece of electronic equipment which in turn vibrates along until the energy is damped out, and causing distortion in the sound. This has the same effect as feedback in the electronics (i.e. blurring of images, loss of low level detail, and soundstage distortions). While electronic feedback is probably in the range of 10 dB, room vibration will be as high as the output of your speakers and will be in the milli, rather than microsecond range of electronic feedback. Which do you think is more significant, electronic or vibration feedback?

There are three ways of trying to improve on the situation. First, to try to prevent it from reaching the equipment. Second, try to change the frequency at which it occurs to one less harmful to the sound. Third, to damp it out as rapidly as possible. Very few pieces of electronic equipment are able to do the first using some form of springs or soft energy absorbing feet and most do very little with the second, usually with special wood pucks, lead dots, etc., and some help the third, with damping materials like lead shot, or sand, or paints. Obviously, eliminating the vibration from reaching the equipment first will work much better at preserving the original sound, rather than trying to change it afterwards. This is a little more difficult than one would suppose, especially at low frequencies.

One can think of isolation devices as being low pass crossovers. There are two parameters that are important to both. First is the frequency where the crossover or isolation occurs, and second is how much of a slope or falloff there is per octave. The lower the crossover point and the steeper the slope, the better the isolation. They work by using a combination of mass (metal chassis or lead or sand weights) with some form of suspension (springs) or compression (air bladders, various wood, neoprene or metal feet) to adjust the slope and crossover point. Unhappily, one needs a high large mass or very compliant springs or feet to accomplish much isolation.

Over the years I have tried various fixes for the vibrations. First came various types of feet, from the original aluminum points, which I still use under my RPG Diffusers, to wood points, various compliant feet, ceramics, etc. All work by either isolation from the surroundings (compliant feet) or by tuning the frequency of vibration to a different frequency (various hard feet). Then came the cabinets and shelving, from Arcici, Sound Designs, Stable Table, etc. All of these give a couple of dB of isolation, but, more importantly, only eliminated the vibrations above a few hundred Hz. This did something for the air vibrations, but very little for the structural born, which are strongest in the very low frequencies. Next step up were various damping materials for the chassis such as rubber and bituminous sheets and borosilicate paints, hundreds of pounds of lead shot and sand on top of and inside cabinets and speakers. Add to that some Shun Mook products and Marigo dots on the cabinets, speaker cones, and even walls, and 3-M damping rings for the tubes. All of these treatments did something, probably changing the frequency of the vibrations, and dampening out their ringing, but only over a fairly high frequency band and with a very shallow slope.

Then I came up with the bright idea of trying to eliminate them by isolating the equipment from the environment so I placed all of my source equipment in a separate room and ran long (35 foot) interconnects to the amps and speakers in the listening room. This eliminated most of the vibrations from the speakers but did little for the environmental component. Plus it added new coloration from the long cables. I re-placed the equipment in the listening room and bought some small bicycle inner tubes blown up about half way to stop transmission (compliance), and lead shot bags on top to dampen any that got through (mass) and found that the vibrations improved significantly. By adjusting the amount of air in the tire, and the weight of the mass on the cabinet, I could change the frequency downward to maybe 12 Hz., but only get a 3 to 6 dB slope. But the sound stage coalesced, became clearer, and each instrument or voice took on a tighter space and image. Obviously, I was on the right track.

The above worked so well that I went looking for high end replacements. First up were the Townsend Audio Seismic Sinks. These are two solid metal platforms separated by two to four pump up air rubber bladders, which do a good job at filtering out vertical vibrations, but did little for the horizontal ones. Arcici also makes a similar product as a turntable base and isolation equipment cabinets, which I haven't tried, but have heard good things about.

This brings me finally to the reason for this column today, i.e., the best isolation device I have found so far. The VIBRAPLANE! Distributed by Steve Klein of Sounds of Silence in Nashua, New Hampshire. They are constructed as a very heavy metal platform with large air bladder feet. The platform is damped with either a borosilicate compound or sheets of 3-M damping compound and are isolated from mechanical vibration in both the horizontal and vertical planes (which is very important as most isolation devices only isolate well in the vertical plane). They isolate down to about 2.5 Hz. with a 12 dB per octave roll off above that. I won't go further into the construction of them. They are fairly expensive at $1695 for the passive which use a bicycle pump to blow up the bladders, and $4950 for the active which run off of a supplied air compressor to give instantaneous pressure changes. Regardless, they are well worth every penny. What they do is almost completely remove the acoustic feedback from the room to the equipment, opening up the stage, removing smearing from the image, tightening up individual images, reducing the noise floor so that more of the micro information shines through. They work especially well on turntables and CD players and line equipment, but also on the amplifiers. Steve even includes one with the Simon Yorke turntables that he sells. Each will hold 275 pounds before crying uncle and have a large enough surface area to take on the largest pieces of equipment. They also have a larger one which will support up to 450 pounds for really heavy equipment (or for one of my tweaks below). They were originally developed for electron microscopes, which are very sensitive to minute vibrations.

Of course, I did do a little experimentation to tweak the tweak, and to follow my scotch heritage of penuriousness. Please forgive me, Steve Klein, for the following money saving tips.

First is to use a rack on top of the Vibraplane, thus floating multiple pieces of equipment with one unit. I built a long shelf of butcher block (hard maple), placed my Walker Proscenium turntable in the center and an Arcici rack on both sides with my video equipment on one, and audio on the other. Then I placed the monoblock amps near the speakers on two others. Be sure to place the most sensitive pieces (turntable, CD player, etc.,) closest to the center of the unit and lowest on the racks.

Second, buy the passive units or the active units without the supplied pump. This will save between $1000 and $2200 per unit. I originally had the passive units, which can be blown up with a supplied bicycle pump, and they worked as well for isolation as the active units. The active units will self level, which is great for turntables and CD decks and look very cool as they lift and self level the equipment. They are also great for demo purposes. Play a piece with the air off, then fill the bladders and watch both the sound stage and your guest's faces expand with joy and wonderment. It really is amazing to hear the difference that true acoustic isolation brings.

With the extra money buy one or two more units to isolate the rest of your equipment. If you buy the active units without pump, purchase a 20 gallon air compressor from your local hardware store, HQ, Home Depot, etc. Place the air compressor in your garage or basement and run an air hose to the listening room and feed off of this to your several Vibraplanes. Steve can supply an air splitter which will allow you to run several Vibraplanes, or air bearing arms or turntables from one pump (which is what I did for my Walker turntable.. another tweak to be discussed in a future column). Because the Vibraplanes lose almost no air, the pump will probably not run at all during your listening session and therefore even less noise will be produced. In addition, with the same pump you can blow up tires, use air tools, blow dry your hair or your driveway, or blow women's skirts into the air if that is your sexual perversion. I learned this last one going to a fun house at Old Orchard Beach in Maine as a five year old and I've been twisted since (so that explains it --ED :-{)  ). Total cost for pump and hoses: about $350.

Third, add more borosilicate or other damping materials to the unit. Three coats did the trick for me. This cuts down on the reverberation of the Vibraplane, and opens things up one smidgen more.

Fourth, load them up. I think they improve the isolation, the closer one gets to their maximum bearing weight.

Fifth, if you still have Seismic Sinks or other isolation devices, place them on top of the Vibraplane under the racks or under the individual pieces of equipment on the racks as that will further improve the isolation slope... like going to higher order crossovers.

If the improvement in sound quality doesn't make you stop tweaking and just listen to your system for at least a week, I'll promise to be tied down in my listening chair and suffer through an entire side of the Sheffield Track Record again (oh no, not that! -- ED).

Well, enough of the jabbering for now as I must get back to experimentation. I won't go into what I plan on writing about next month as it will probably change as something new for experimentation pops into my head. Remember, listening is the road to recovery.