Does mechanical vibration has any influence on a 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.
Is that all ?
Imagine you have a low quality hifi amplifier, with a significant power transformer hum. If you put your hand on the amplifier case, you could 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 this amplifier or in the same rack, will the hum influence the turntable's
performance ?
What about a CD-player ? Will its performance, although its digital nature, 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 at work, in order to read the disc ?
Perhaps, if you have a cheap CD-player in a cheap plastic housing, you would promptly say yes.
But what happens if you have high 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 ?
As many of you know, they will not sound the same and the placement of the individual components of a hifi-system is not a trivial issue.
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. Why this ? Has this something to do with a more subtle vibration ? 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 sound waves 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 due to mechanical connection (screwed to case) and 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 and so does the voltage across the capacitor. You have just generated a signal.
We must now admit that there is a connection between mechanical and electrical effects, two things, that we liked to separate from each other.
But it's not only capacitors. Similar effects may be at work with semiconductors, i.e. transistors, operational amplifiers, voltage regulators, etc...
We started with a harmless mechanical vibration and now we have generated an electrical signal...but how big is this microphony effect ?
In terms of numbers, it would probably be very small. It may partially show up in the total harmonic distortion specifications of your hifi component. I say partially, since the engineers do not bang on the devices, while doing the measurement. The device is measured in silence.
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 of 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 often restrict ourselves to just have a look at a sheet of glossy paper full of numbers.
In the past there were constructors like Grundig that have done big researches along this way. Note that I am not speaking about the actual Grundig. The old Grundig went bankrupt in the late '80s and just from 1976-77 to 1986-87 the Grundig hifi products benefited from such researches.
If you are courageous you can perform yourself the following experiment: listen to any hifi component. Then remove the top of the case and listen again.
Big time ?
By removing the top of the case, you have eliminated large parts of the case resonances that stimulate the circuit board.
Now, if we have accepted that vibration has an influence on the perceived sound, what to do?
We can try to dampen the whole case, in order to avoid part of the rattling. We can put the device on dampening feet. If heat dissipation is not a problem we could fill the interior with sound-absorbing foam. We can put rubber blocks between the heat sinks of the amplifier, in order to prevent that 'ping' sound and so on...
Keeping in mind all these aspects we designed the ROSSO amplifier family.
We have chosen a simply strategy:
- All the PCBs and electronic components of the ROSSO amplifiers are encapsulated in a potting compound so to highly dampen mechanical vibrations.
- The core amplifier assembly is enclosed into a high quality wooden case with a special hand carved opening (a sort of violin f-hole) such to improve the character of the residual vibrations.
If you knock on a ROSSO amplifier you can feel the difference!
