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Vibrations on HiFi components

our villain

[Italian version]
Author: Dejan Veselinovic

[are we a little loose?]
Are we a little loose?

We may not realize it, but vibration has more ways of getting to us than is immediately obvious. When somebody mentions vibration, most audiophiles think of turntables and speakers, and that's all right as far as it goes. The trouble is, it doesn't go far enough.

Let's leave the turntables out of it for a moment - most of those who still own them know about their associated problems well enough anyway. Let's look at some often forgotten aspects of other items.

We all know speakers should be decoupled from the floor or their stands, and that is quite true. But what we tend to forget is that speakers are composite items, consisting of the cabinet, drivers, crossover and back sided connections. Now, if we know that decoupling is good because the cabinet as a whole vibrates, why do we forget the drivers? They are the prime source of vibration, and therefore will tend to come undone. Not literally, of course, but after a time, say 6-12 months, I'm willing to bet you will discover that the screws holding the drivers to the cabinet can be turned clockwise, some more and some less. But the very fact that they can be turned is proof enough that vibration has been working hard, that your drivers vibrate more and differently than intended, and as a consequence, you are hearing sound below what you could and should be hearing.

About an hour ago, I tightened two times 16 screws on my JBL Ti600 speakers, plus two times four more on the back. Quite frankly, I was unpleasantly surprised just how much turning they took to become tight again. I was also both pleasantly and unpleasantly surprised at the difference in sound - which is what made me sit down and write this text.

The explanation is easy enough. Loose drivers tend to vibrate much more than tightly bolted ones simply because they are allowed to do so. If they are loose enough, air will start leaking around their perimeter, which will ruin the concept of any speaker, bass reflex or acoustic suspension, simply because both principles assume no air leakage except through precisely calculated and manufactured vents with reflex and no air leakage at all for acoustic suspension. Loose drivers produce muddled sound, bass tends to loose definition and start spilling uncontrollably all over the place, but also loses its true depth capability. Conversely, when screwed really tight, bass drivers will once again start acting as they were meant to, which means a general cleaning up of their overall performance.

Midrange drivers are much the same. When loose, they will lose their definition and sound will be out of focus. Tighten them and all will be well again, or as well as the drivers permit. You may be surprised to hear that more or less the same will happen with tweeters - my JBL seemed to have lost some top extension, but after tightening up, it all came back. As I said, it's surprising just what a difference simple tightening of the driver screws can do.

CD players are not too dissimilar. I have never yet opened any one of them, no matter what it costs, which could not have its drive mechanism tightened. And that is the only mechanical part of the CD player, and therefore the prime source of internal vibrations. If it vibrates, you are likely to have a muddy sound stage, possibly with some shifting, though this depends on the construction of the mechanism as well.

This can be very bothersome; I've had CD players on test which simply failed to make the grade. Since I have to open them up anyway to make the photographs, I never miss the opportunity to use a screwdriver to check up on tightness. And it hasn't happened yet that there was no tightening to be done, ever. Sometimes more, sometimes less, but always with beneficial results for the sound, sometimes more, sometimes less. Rotel's 951 CD player was particularly affected by this tightening, and it was taken brand new out of the box. Not to mention older players, which have seen several years of service - they must be in a bad way there.

By the same token, most modern recording machines, such as cassette recorders, MD recorders and CD recorder/players, would surely benefit from a tightening up of their associated screws. It often makes me wonder why this is not battled the same way manufacturers used to take care of that problem on old open reel tape machines. There, head blocks were tightened like you never could unless you had some serious power tools, then sealed so they have less chance of coming undone, as that would be disastrous for the recording. All of them knew how to do it - Revox, Telefunken, Philips, Uher, Tandberg, Ferrograph, Sony, TEAC, not to even mention the professional sector, such as Studer, Ampex, MCI, etc. The only answer I can come up with is price - all that is very nice, but it costs money, apparently more than manufacturers are willing to spend. A pity.

© Copyright 2001 Dejan Veselinovic - http://www.tnt-audio.com

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