Isolation Theory Question

Hi Mre2007,

Anytime you have a rigid device under a component any vibration trying to enter from underneath has a direct path into the component's chassis. That includes points, blocks or slabs of rigid material. The material from which the device is constructed (as well as its size and shape) will determine the resonance modes of the device - the material will store and then release vibration energy over time. Wood has significant resonances. That is why it is selected as a material from which to construct many musical instruments since each invidual instrument SHOULD have its own particular signature or voice. An audio system (or a component) that reproduces the sound of many different instruments that have been captured in many different recordings SHOULD NOT have a particular signature or coloration or it will impart that distortion on to EVERY recording that it reproduces.

Sometimes the introduction of a device or material into a system that colors (alters) the signal that has been captured in the recording will sound "better" to an individual than how the system sounded before the device was introduced. This may be because the device is adding some kind of complementary coloration to the system. In actuality, the system had a problem (or multiple problems) and afterwards the problem was less apparent or it has hyped up other areas that are exciting to the listener. The individual should be aware that the problem has not been eliminated and that now there is a new set of problems that have been introduced by the device and that system is not necessarily closer to accurately reproducing the sound of the original instrument as it has been captured in the recording.

Some may say "I like it so that's what's important". I believe that it is important to like the sound of one's system but without using the truthful sound of live, unamplified instruments as the reference people assembling audio systems are in the "wild west" and pretty much anything is legitimate as long as they like it. We might as well add lots of equalizers to our systems or have Bose Waveradios if faithfulness to the source is not of particular importance.

Mre2007, please note that my comments are of a general nature and are not necessarily a criticism of your particular system.

Best Regards,

Barry

Barry Kohan
President
Bright Star Audio

Disclaimer: I am a manufacturer of vibration control devices (I have been asked by Audiogon to make this disclaimer when I comment on vibration control).

I'm certainly no expert. But from what I've read - and experimented with conciderably - it seems that rubbery devices (like vibrapods) seek to absorb vibrations and solid devices (like cones, wood blocks, etc.) attempt to dissapate vibrations. I don't know if there is a theoretical basis for determining which components do best with which type of treatment. My own experience has demonstrated to me the the differences they make can best be determined by trial and error. Based, of course, on your own personal listening preferences.

You might want to go to a local hardwood retailer and pick up 1-2' of various hardwood boards, cut some small blocks and experiment. Different woods definitely yield different sounds. I've tried oak, maple, walnut, bocote, myrtlewood, mahagony, teak and zebrawood. My RadioShack SPL meter shows definite differences in Db levels at different frequencies which with type of wood used. I've found the zebrawood by far to be my favorite. There is a very good discussion on wood isolation blocks in Stereo Times online under "Archives -> Art and Science of Audio Tuning; Part 4."

Of the softer 'absorber" devices, Mapleshade offers 'Isoblocks' which work quite well. They are a sandwhich of ribbed rubber-cork-ribbed rubber at 4/$24. However, you can find the vary same device at any Heating & Air Conditioning retailer for $2 apiece - they are called 'V-pads' - and they are 4 times as big as the Mapleshade version.

Sometimes these devices work best in combination. I have a less than ideal wooden cabinet holding my audio electronics - CDP, tubed preamp and amp. On top of the cabinet are V-pads supporting a 1 1/2" maple board, on top of that are zebrawood blocks directly supporting the chassis of each component. Sounds pretty good. In fact, it sounds amazing!
However, the same combination under my SS integrated for my modest HT setup yields too bright a sound image so I eliminated the v-pads and use Vibrapods instead which reduced the harshness.

Again, I think the key here is expeimenting with varius devices and in various combinations until you get the sound you find most satisfying.

Everything you put under your equipment will have an effect on the sound whether you use wood blocks, vibrapods/sorbothane or cole slaw.

Everything has a resonant frequency, or a frequency at which that item will vibrate. There are many theories about which items to use to control any given frequency, but what manufacturers try to do is eliminate vibrations arriving at your gear, or possibly in the case of your dac, transport, and turntable, eliminate/reduce vibrations caused by your equipment.

A product that vibrates at a given frequency will accentuate that frequency when it is played because the music is exciting item or material. For example if a wood block vibrates at 5000Hz, when you play music in that frequency range, the music will cause the wood block to vibrate, and prevent the wood block from doing what you intend it to do. Materials generally do not vibrate in the small frequency I just mentioned, but over a much bigger range.

Ideally a person wants to use items whose resonant frequency is outside the audible lisening range, but these items are very expensive.

What some companies do is employ layers of materials which have different resonant frequencies so that vibrations are reduced/eliminated by the time the have to pass through these layers. Sota turntables use this idea in their Cosmos armboard. There are layers of Plex, and aluminum, and rumor has it they will be adding more layer in the newer models. Maybe a layer of carbon fiber would work well.

So, in conclusion, what was the question again???

When you say "... I seem to prefer", you said everything. As for looking to vibration theory for guidance, I have yet to see any vibration mfr, reviewer or dealer put forth a reason for why one strategy is better than others and back it up by applying the complex mathematical and physical models for even just one audio system with room structural and acoustical interaction.

In my system, I found that brass cones under the DAC makes a positive improvement. The tubed amp and prea-amps, the stock feet work best, cones do not make a difference and rubber makes it worse. Under the transport, the stock feet again work best. Speakers worked better with the included spikes on carpet, worse with the spikes on hardwood. Don't know why it is so, don't care. All are very slight differences with the exception of my one-time Digital Lens which saw a vast improvement with a brick on top - it stopped the xfmr induced humming. (Something to be said for mass loading theory, I guess). Trying to predict all that ahead of time with theory would have been futile, in my opinion.

Trial and error with an open ear - that's the surest bet for your particular setup and environment.

I have an off-the-wall question: Has anyone actually fastened a component to your rack? What I mean is removing the feet and actually bolting a pre or cdp or whatever to a support structure [rack or shelves] in place of using cones. Perhaps using a brass or steel bushing between the component and the rack would help clean up this kind of installation. Wouldn't this be like "direct coupling" the component to the rack?

This thought just crossed my mind, sort of taking the audio point kind of theory to its extreme...so I guess it is really directed towards Barry at Bright Star Audio.