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In Reply to: RE: Vibration Control. posted by kirillzolotov on April 18, 2010 at 17:41:06
As suggested, "Bad Vibes" is an extremely good article.
For my part I think that 2 important issues your suggestion ignores are the following:
1) vibration in equipment can get transferred to the signal chain as noise, either because the electronics are microphonic to some degree or simply because, in the case of a transducer like a phono cartridge, any vibration picked up by the stylus is converted to sound because the cartridge doesn't distinguish between vibration due to the groove and vibration due to the movement of the LP because of vibration transferred to the platter.
2) digital players use a motorised assembly for laser tracking and vibration introduced to the disc will result in minute adjustments by the laser assembly as it tracks. Those adjustments require an additional power draw and variations in the power being drawn by the transport mechanism may impact on power supply to the decoding/DAC/analog stages of the player which may in turn impact on their performance.
When it comes to competing strategies for vibration control, then I really suggest that you read "Bad Vibes" because not all means of controlling vibration rely on isolation. Coupling can also be beneficial in some cases and approaches using minimal point contact work via coupling rather than isolation. It's worth noting that coupling can't transfer more vibration from one thing to another than is present in the first layer. When spring systems are used for isolation, vibration at frequencies below 1.4 times the resonant frequency of the spring will actually be magnified in the transfer so effective isolation will only occur above a frequency determined by the properties of the spring and below that frequency things can actually be made worse.
David Aiken
Follow Ups:
After reading the article you recommended "Bad Vibes", it seems that a combination of the two methods (damping and coupling) is the best approach. I have a stand with spikes so that takes care of coupling. I now will look into damping products to finish off my system rack.
But I do want to say that in my opinion the 1.4 ratio for damping is not very significant because I think vibrations of low frequency are not as damaging to equipment as vibrations of high frequency.
You obviously either don't have a turntable and below 20 Hz vibration in the system or you're using a "rumble filter" or your speakers roll off significantly by 20 Hz.
Low frequency vibration can be a very big problem under some circumstances and magnifying it makes it a bigger problem.
Actually I believe that if you could do an A/B type comparison between a system set up with good low frequency isolation and the same system without, you'd probably notice a difference and prefer to have the isolation. The problem with some things like vibration control is that you only start to notice the damage that gets done to the sound by vibration when you hear the sound with less vibration. The reason you don't notice it before then is that it's always there as part of the sound, you're used to it and you don't have any reason to expect things to be able to sound different. It's only once you hear the sound without the contribution that vibration makes that you realise how much effect it was having.
David Aiken
David you are right, I do not have a turntable and my speakers roll off at about 40hz. I will say that even if I had a turntable and bigger speakers that could produce a 20Hz in my room (which is a feat in itself), I wouldn’t worry as much about these frequencies because little recorded material has them.
My main point is that what breaks materials is:
1) DECELLERATION
2) CHANGE OF DIRECTION
3) ACCELERATION
The three components above make up one vibartion.
So more emphasis should be placed on slowing down the rise time (quickness) of acceleration and deceleration of a component (change of direction is unavoidable), rather than reducing the magnitude of the vibration or filtering out a particular frequency. And it seems to me that damping materials do just that and hard coupling devices do not.
You say "My main point is that what breaks materials is…" but no one has suggested before you in this comment that the purpose of vibration control in audio was to stop materials breaking. I've never thought that the idea was to prevent something breaking, I've always understood it to be the prevention of audible colourations introduced into the reproduced sound by the vibrations.You also say " I will say that even if I had a turntable and bigger speakers that could produce a 20Hz in my room (which is a feat in itself), I wouldn’t worry as much about these frequencies because little recorded material has them." I think several things need to be said in response:
- first, though the lowest note on a bass is an E at approximately 41 Hz, the lowest note on a piano is an A at approx 29 Hz. Some orchestral wind instruments go lower. That means that pitched tones down to below 30 Hz may be found on recordings including a piano and on orchestral recordings. Modern music using synthesisers can easily go as low or lower and organ music often goes lower. In fact I can recall years ago seeing a list of recordings with content below 20 Hz and noticing that the lowest frequency mentioned was an 8 Hz tone on an organ recording. I suspect there's a lot more low music content around on disc than you believe.
- second, live recordings made in large halls and containing enough "hall sound" to convey the sense of the hall's acoustic signature can often include resonances that are sub-harmonics of the bass tones contained in the music so live recordings of music which does not extend below, say 40 Hz, could in some circumstances contain content down to an octave or so below that in the hall's reverberation.
- third, it sounds as if you're suggesting that the size of your room prevents the reproduction of low notes. If that were the case, one couldn't get bass in a car and there would be no sales of automotive sub-woofers. The lowest fundamental room mode, the frequency associated with the longest dimension of a space, does not represent the lowest frequency reproducible in the space, merely the lowest frequency at which the space will exhibit resonance. In actual fact lower tones can not only be reproduced in a room but under some circumstances the room can actually support and boost such tones. That's why bass from a small speaker can often surprise listeners in a small room. The speaker may definitely be rolling off but the room is not only supporting but in some cases even boosting low frequency tones and a speaker's actual measured in room response can well be better than it's specifications which are normally based on anechoic measurements suggest.
Your reasons for why you don't think low frequency vibration would be a problem in your room really aren't valid. I'm not saying you have a problem because you may not, but the reasons you've given for not having a problem don't hold up.
Do what you like but I will repeat my comment that until you've heard the same system both with and without good vibration control extending down to below the lowest octave, you really have no idea of how much vibration at those frequencies can affect things. Further, until you've heard your system in your room both with and without good vibration control extending well down into the bass frequencies, you don't really know whether or not such control will offer anything beneficial to you.
Finally, you say that "more emphasis should be placed on slowing down the rise time (quickness) of acceleration and deceleration of a component". Well, frankly the idea is to have any vibration introduced decay as quickly as possible. If you slow the deceleration, you extend the decay time. If the vibration is producing an audible effect and you slow decay time, it becomes much more likely that the vibration will continue to be audible for longer than the silences between legato notes in the music, ie notes which are played distinctly and which decay to silence or near silence before the next note starts. If that occurs and audible vibration masks the silences between legato notes, then you lose the sense of legato playing and actually change the character of the music. ASC, the people who make Tube Traps, actually created a test signal which allows you to hear the effect of the room's modal resonances on distinct legato test tones and that test gives a very audible demonstration on how the character of a distinct series of quick tones with silence between each tone can be totally changed by room resonances intruding into those silences simply because they don't decay quickly enough. I've noticed similar effects in my system but only after vibration control reduced the problem and I could hear the notes played clearly for the first time. Until then I'd thought that having no silence between certain notes was the way things were supposed to be. Hearing the music clearly with the clarity of each individual note restored was somewhat of a revelation in some cases.
As I said, do what you like, but I do think your understanding of some of the things you're suggesting is a little flawed.
David Aiken
Edits: 04/27/10
David,
Let me clarify what I meant by “break equipment” in my previous response.
I believe that physical forces can cause changes to electrical properties of electrical components (resistors, diodes, capacitors, transformers, inductors) inside audio equipment which in turn can have an impact on the sound of audio equipment.
I also believe that one of the physical forces that I described above is vibrations.
If we agree on the point above, then let me define a vibration.
To me a vibration is movement which consists of two directions: forward and back, or up and down, or both (but for the arguments sake, let’s keep it one dimensional). Looking into one vibration further we notice that it is made up of acceleration and deceleration with a change in direction between them.
Which brings me to my point:
It is the change in direction, or rather the fast acceleration and deceleration, that exert physical forces on components inside audio equipment that change the equipment’s sound. So we need to concentrate on reducing their speed. I want to note that the vibration’s frequency is less important because that criteria alone doesn’t say anything about the acceleration and deceleration of the change in direction of that vibration.
Your point of vibrations being able to decay as fast as possible is valid but is in my view primarily for components that generate vibrations themselves. If my speakers create floor vibrations, than I am interested in preventing them from reaching my equipment. Now yes, some equipment makes its own vibrations and some equipment will vibrate because of air pressure caused by the speakers. In those cases your point stands, but I am personally not concerned with that scenario because I do not have speakers that can pressurize the room to such levels and I do not listed at those levels.
I also think we shouldn’t spend much more time discussing the impact of sub sonic or very low frequencies on audio components. My speakers cannot produce anything below 32HZ and they produce 32HZ at -10db in my room. I do not have any organ recordings and am not a big fan of classical or piano recordings.
My original question was on the theoretical differences between two types of vibration reducing/controlling devices that are currently sold. Namely, damping and coupling/tuning. After this discussion I am still unconvinced that the latter is the best way to go for my system.
The reason low frequency vibration is such a big issue is that it excites the natural frequency of critical elements of source components. Consider that natural frequencies of a stereo cartridge, turntable platter, tonearm and the suspension of a CD laser are in the range 8-12 Hz. These are very low frequencies. Therefore, *de-coupling* of the component from the room structure is required!
Edits: 04/23/10
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