Vibration & Character
This is a central and extensive issue, and and I do not really know how to best start this chapter. I think it's best to start with a common understanding:
Does mechanical vibration has any influence on your hifi-system ?
Well, as we all remember, mechanical vibration can have an effect on a turntable. If you jump on the floor, the needle may also jump out of the groove.
Any more ?
Imagine you have a low quality hifi-amplifier, with power transformer hum, that means, if you put your hand on the amplifier case, you feel the 50 or 60Hz vibration.
You may also hear the hum, if the room is silent or you put your ear on the amplifier.
If a turntable sits on top of the amplifier or in the same rack, will the hum influence the turntable's performance ?
What about a CD-player? Will it's performance - although its digital - be affected by the mechanical vibration of the amplifier hum ? Or will the CD-player's performance also be influenced by its own mechanical vibration, as it has its own transformer and motors / actuators at work, in order to read the disc?
Perhaps, you would say, if you have a cheap CD-player in a cheap plastic housing. But what happens if you have hi-quality components ? You have an amplifier where you neither feel nor hear any hum, and the reading operation of your massive CD-player is dead quiet. If you then put the CD-player or the amplifier (or both) on three spikes (instead of their 4 built -in feet), will they sound the same ?
I think, many of You know, that they will not sound the same, and that placement of the individual components of a hifi-system is an issue.
In fact, if you ever bought a hifi-rack, a platform, any kind of spikes or squishy feet, you have already accepted the influence of mechanical vibration to your hifi-system. Although, you may feel no vibration at all, when touching the components, you may know - by listening - that they sound different, when putting them on spikes. They will also sound different when putting them on squishy feet.
This is a central point: You see no difference (except other feet), you feel no difference when touching the component (no vibration), but you hear quite a difference.
As there is no obvious reason for this change in sound, which you perceive with certainty, and you long for an explanation of it, you pull a drawer in your mind and put in something like: "maybe this has to do with more subtle vibration".
And You're right.
But where does this subtle vibration come from and why does it change the sound ?
If you take into account the presence of sound-waves coming out of your speaker and reaching your hifi-components, what will happen? Every enclosure has a volume and thus a resonance frequency. It will react to soundwaves and will vibrate in its own resonance frequencies and its own sound.
If the enclosure comes into resonance, the internal electrical components also vibrate. Many of today's electronic components are very small and normally nothing big can happen, but as they are all mounted on a circuit board, which has a considerable size, there may be an effect. The circuit board picks up the vibration from the enclosure a) due to mechanical connection (screwed to case) and probably less significant b) due to sound waves inside the enclosure.
But hey, what's the matter ? It's only electronic components.
Well, there are explanations available: If the printed circuit board vibrates, all components are flexed to a certain degree. If you flex a capacitor, you do not change its actual charge, but the distance between the isolated plates. If this distance varies, the capacity of the capacitor changes (smaller distance -> higher capacity). If you change the capacity while keeping the actual charge constant, the voltage across the capacitor changes.
You have just generated a Signal.
Nothing special, almost all of you had that lesson in the physics class.
By remembering that lesson, we must now admit, that there is a connection between mechancal and electrical effects, two things, that we liked to seperate from each other.
But it's not only capacitors. Similar effects may be at work with semiconductors, i.e. transistors, dac-chips, operational amplifiers, Voltage regulators, etc...
We started with a harmless mechanical vibration and now we have generated an electrical signal, that's not on the recording, shit !
How big is this microphony effect ?
In terms of numbers, I would say, it is very small. It may partially show up in the total harmonic distortion spec. of your hifi-component. I say partially, since the engineers do not bang on the devices, while doing the measurment. The device is measured in silence.
In Terms of Character ,
I would say, the effect is bad.
If you want to encounter the character of this kind of distortion, go to your hifi-system and knock on the case of any device. How does that sound ? In almost all cases, you will hear the trashy sound of thin sheet-metal, dumb plastic, and only with the most expensive hifi-components: ringing and rattling (unproperly supported) aluminium top- and bottom-plates.
Every musician knocks on the instrument that he is interested to buy, in order to check the tonal character and quality. When we go to buy hifi-stuff, we look on a sheet of glossy paper with insignificant numbers, that we don't even understand.
Is it possible that we trade quantity for quality ?
If you are courageous you can perform the following experiment:
Listen to any hifi-component.
Then remove the top of the case and listen again (okay, only if you know how to do that,don't grab in there while connected to mains, preserve necessary precautions, and don't let your pets jump in).
Big time ?
By removing the top of the case, you have eliminated large parts of the case resonances that stimulate the circuit board.
Now shut the component off and remove the mains plug.
With open case, you see the printed circuit board, and see that it is attached to the case by a number of screws. Now, with your fingernail, pull up one edge of the circuit board (just a little) and let it pop back.
How does that sound ? "Parrrarrrrrr ..." Don't worry, You're not alone.
Now, if we have accepted that vibration has an influence on the perceived sound, and have explained in theory that the vibration indeed affects the electrical performance of a hifi-device, and have found out, that the inherent vibration of the device's case and circuit board sounds really crappy, what to do?
Energy - Retaining or Damping ?
We can try to dampen the whole case, in order to avoid part of the rattling. We can put the device on damping feet. If heat dissipation is not a problem we could fill the interior with sound-absorbing foam. We can put rubber blocks between the heatsinks of the amplifier, in order to prevent that 'ping' sound.
This is one approach -> Eliminate any vibration by damping.
Another, interesting approach would be -> Improve the Character of the Vibration.
At the very basis of this idea lies the simple realization, that you cannot completely avoid vibration by damping, since vibration is the very nature of the game.
First: Since what we want to have IS a vibration *music*. With any damping effort we will also remove energy (transforming the vibration into heat) from the musical performance. This is what you hear, when you listen to a CD-player that rests on soft squishy feet: The performance sounds somewhat tired.
Second: If we follow the idea even further to the very core, nothing exists, but vibration. Heat is the vibration of tiny parts, and everything else is the vibration of even tinier parts, and beyond that, even the parts are gone... Sounds strange ? They call it modern physics ;-)
So in order to keep this universe from collapsing, why not retain the energy and just improve the Character of the Vibration ?
In practice: If anything sounds so bad, that you would like to damp it, don't use it for music.
Altmann Micro Machines Dipl.-Ing. Charles Altmann Erlenstrasse 15 42697 Solingen Germany
phone +49-212-233-7039 email