On Thu, 10 Sep 2009 22:13:12 +0100, "Keith G"
wrote:


"Don Pearce" wrote in message
news:4aa94700.29085171@localhost...
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.


It is? I thought it was all about what you might or might not be able to
*hear*, not measure...??


I've been through that - and the mechanism. I'm doing the
measurements. This is all about how much of the systems performance is
used up in just dealing with the inaudible nonsense provided by this
ridiculous turntable.



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.


I'm not sure ****ing about with the 'silence' is really where it counts -
that's for geeks; I rely on the music to soak up all sorts of **** when I'm
listening to it on LP...!! :-)


Of course.

d
--
Pearce Consulting
http://www.pearce.uk.com