Isolation Theory Question

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.

Hi Dbld,

Thank you for your question.

Rigidly affixing the component to the rack will allow any vibration within the rack (sourced from the floor or from the rack's structure vibrating in sympathy with air-borne vibration) to have a more efficient path INTO the component. That would increase the amount of vibration that is contaminating the signal flowing through the component.

A properly designed vibration control set up would also address internally-generated vibration (from spinning motors, humming transformers and cooling fans) besides just addressing floor-borne and air-borne vibration.

Best,

Barry