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From: Patent Tactics, George Brock-Nannestad

Hello, Milan Milovanovic asked:
> 
> Speaking of micro versus wider grooves, would wider grooved cut record be 
> more resistant to micro scratches and easier to get clean from dust etc. 
> than "microgrooved" LP record?
> 
> Also, would 78 rpm speed be more suitable for recording/reproducing 
> especially at the last 1/5 of disc with no groove distortion added in this
> area (often connected to ordinary 33 rpm records)?
> 

----- I have in front of me an article printed in Audio magazine in April 
1963. It is "A 78-rpm Stereo Record" by Allan R. Keskinen. The record itself 
is a test record that permits instantaneous evaluation of a stereo cartridge, 
and he says:

"    In the preparation of this record, the 78.26-rpm standard record speed 
was chosen in order ot reduce stylus-tracing-geometry and wavelength effects. 
The resulting long wavelengths and the large groove size used, reduce tracing 
distortion to a minimum and extend record life. The bottom of the groove has 
a radius of approximately 0.0002 in. permitting use of styli as small as 
0.0005 in. without danger of bottoming.   .....".

This is obviously not a stereo record in the commercial sense of the word, 
but the article shows the thoughts that decided the selection of the highest 
speed. The article as such is otherwise very good and instructive. Keskinen 
was the chief engineer at Astatic.

The speed, groove spacing and modulation, and duration are all interlinked, 
and the purpose decides the compromise that is used in practice. In my view, 
the best present sound is obtained from a disco single, which has a wider 
groove, a higher speed and also a lower cross-over frequency than an LP 
because it permits higher amplitudes at lower frequencies. This means that 
the DJ does not have to use so much bass amplification for a given bass 
output, and that reduces the risk of acoustic feedback to the pickup via the 
turntable. And I think that this freedom from feedback was what decided the 
issue for digital recordings (=CDs), not anything to do with quality as such.

I do not think that there is an industry standard covering disco singles, but 
I would like to be corrected and to have somebody give a reference.

Kind regards,


George

> 
> ----- Original Message ----- 
> From: "George Brock-Nannestad" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, October 08, 2009 6:52 PM
> Subject: Re: [ARSCLIST] late date 78
> 
> 
> > From: Patent Tactics, George Brock-Nannestad
> >
> > Hello,
> >
> > Mike Biel wrote:
> >
> >> Theoretically the best sound at 78 would be with a microgroove size
> >> groove since it would be capable of higher frequency response than a
> >> wide groove, or a microgroove at slower speeds.
> >
> >
> > ----- now, I am speculating why this should be so. I do not understand why
> > a
> > microgroove should give a higher frequency response than a NORMAL groove.
> > It
> > has to do with the maximum acceleration of the tip and the ability of the
> > tip
> > to trace precisely the groove shape. If the smaller radius of an 
> > elliptical
> > stylus (or the radius of the edge in a line contact stylus) is able to 
> > trace
> > without error a curve in one flank of the groove, it does not matter
> where
> > the other flank of the groove is.
> >
> > If microgroove is associated with a higher groove pitch (which would
> mean
> > well above 200 grooves per inch), then the maximum amplitude would be 
> > reduced
> > compared to the ca. 100 grooves per inch in a traditional 78 rpm record.
> > If
> > we maintain the 100 grooves per inch but reduce the groove width and 
> > depth,
> > we would have more land to use, and the modulation could be higher,
> which
> > would give a low frequency advantage. That is the rationale behind disco
> > singles (albeit at 45 rpm). And all of this without variable groove pitch.
> > If
> > that is used, then we are even better of, bass-wise.
> >
> > Kind regards,
> >
> >
> > George