On Thursday, August 07, 2008 10:41 AM, Aaron Levinson wrote:

> Interestingly enough I have seen a few adverts recently 
> for a record flattening device. It seems to cost about 
> $1600 USD.  Does anyone know about this thing and is it 
> "dishwasher safe" so to speak. I wonder about it's efficacy 
> but with an unplayable record I guess you don't have that 
> much to lose...except the $1600 of course!

The Audio Archive has been using such a flattener for nearly
three years now with excellent results.  We only use the 
flattener when faced with extreme warpage or bend problems.
It works on shellacs, LPs, and dictation discs like Edison
Voicewriter and Gray Audograph.

Our criteria for using the disc flattener is:

   - disc is absolutely unplayable at any speed, such as:
       - cartridge hitting the disc (not a cartridge 
         suspension problem)
       - severe kinks such as paper clip bends in a dictation

We'll always ask the client first to see if they want to 
have their disc flattened.

The flattening process is highly controlled, very low 
temperature, and slow.  It can take as many as three 
multi-hour passes to get a severely warped shellac flat.
Vinyl discs for which the unit was designed usually respond
with a single multi-hour pass.

What is unknown about the process, is if there is any 
effect on the frequency response due to groove wall 
relaxation (akin to annealing).  There might be a 
slight change in EQ as a result.  Since the discs we 
flatten are unplayable to begin with, we have no way to 
do a before-and-after test of the disc frequency response.

Ideally, we would do a number of controlled experiments,

    - take a flat disc, measure the frequency response,
      run it in the flattener, then re-measure the
      frequency response to see if there is any change
      in frequency response due to potential groove 
      wall relaxation.

    - take a flat disc, measure the frequency response,
      warp the disc, flatten the disc, then re-measure
      the frequency response.

          - do this for varying warp severity
          - do this with LP and shellac discs
          - do this with dictation discs (difficult
            to create or obtain for testing)

The shellac discs will have a smooth polished area where
the warp contacts the flat plates of the flattening device
(at points of disc convexity).  These smooth areas do not
interfere with playback in any way.

With LP and dictation discs, it is impossible to tell 
visually that the disc was ever warped after the flattening
process.  This creates the potential for a new kind of 
collector fraud - someone can buy a warped collectible LP
at a vastly reduced price, and then flatten it and resell
it as "mint".

In any case, we have found the flattener valuable in our 
work for dealing with severely warped or bent discs.  You'll
need a fair number of warped discs to justify such a flattener.

Eric Jacobs

The Audio Archive, Inc.
Tel: 408.221.2128
Fax: 408.549.9867
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