On Thu, 10 Sep 2009 18:15:09 +0100, "Keith G"
wrote:


"Keith G" wrote in message
...

"Dave Plowman (News)" wrote in message
...
In article ,
Keith G wrote:
All sounds typically very scary, but my suspicion is that no normal
person would be able to tell the difference between a record played
directly on the mat/platter/whatever and the same record lifted up on,
say, only three bearing points.

You certainly will if you wind up the wick. It will feed back. Unless in
a
well sealed enclosure. It acts beautifully as a diaphragm.


Well aware (after nearly half a century as a user) that a record deck can
act as a transducer but the question is still the is any FB discernable
in normal use or even wicked up?

I might give it a go later but I notice the mint imperials haven't been
opened and I don't like them anyway, so it'll have to be with Tic Tacs...



OK, I have recorded identical samples with and without Tic Tacs and there's
not an iota of difference that I can hear.

Pic of the *unopened* Mint Imperials and the Tic Tacs in situ on my Show N
Tell page, along with the samples which, unfortunately, all have a ton of
hum that I didn't know I was getting! (Hasty wiring to this computer - I was
cutting grass at the time!!)

But hum or no, the samples are of an identical recording setup and are good
enough for a quick comparison!



I've done the same thing here, but I've measured what happens.

Two recordings, both of the same piece of silence between tracks 1 and
2 of a typical record. Then invert one channel and sum to mono. That
gives the vertical movement of the stylus - which is what this is all
about.

Now downsample to 200Hz to see low frequencies nicely, and take an FFT
of both recordings. Here is the result:

http://81.174.169.10/odds/six.gif

First, at the expected 3.3Hz, we have a level about 22dB higher on the
point-suspended disc (that is nearly ten times the voltage for the
preamp to contend with), but a similar difference continues all the
way down in the general subsonic rumble area. I have to say I wasn't
actually expecting it to be quite that much worse. I now think I
wouldn't take one of these turntables as a gift.

d