[TenTec] improved audio from 961 speaker & pwr supply

[Carl R. Gansen]

I purchased a used 962 power supply and even though forewarned, I was 
disappointed in the audio quality from the internal speaker.  I started 
looking into transplanting a better speaker into the supply when I came 
to the realization that the speaker was not the culprit as much of the 
cabinet.  Ken, K7ZUM's recent post suggests that he came to the same 
conclusion albeit from a slightly different perspective.  I noticed that 
the audio was better(poorer) at different frequencies and by sweeping 
through a carrier I could actually get the speaker to couple significant 
acoustic energy into the cabinet.  The cabinet was vibrating at various 
mechanical resonance modes drawing energy from the speaker and because 
of the mechanical Q of the cabinet was adding kazoo like sounds to the 
audio when hitting resonant peaks.
  
   The solution I pursued was to purchase some acoustically dead steel 
(I'll refer to it as ADS) from Small Parts Inc. ADS is a laminate of 
soft steel and polymers.  As you flex the material the energy required 
to flex it gets translated into a shearing motion in the polymer layer
absorbing the energy.  This makes the material low Q and unlikely to 
vibrate.  You can demonstrate the principal to yourself in the 
following manner.  Lay the front of one of your hands flat on the back
of your other hand. Now bend your hands into a cupped position and
take notice of the sliding that one hand does with respect to the
other.  This is the shearing action that transfers the energy.  I also
purchased JB-Weld epoxy glue at my local automotive store.  I recently
noticed Wal Mart handles it ($1.30 cheaper) in their automotive
section.
   I had the material cut by a local heating contractor on his
sheet metal shear to avoid distorting the material with a tin snips.
It is important that the material be kept as flat as possible. I cut
one 10.25" X 6.5" panel and two 2.75" X 9.75" panels.  The next step
was to put a thin film of epoxy over one entire side one of the ADS
pieces.  I glued this to the inside side of the 962 cover.  TAKE CARE
TO AVOID BLOCKING COOLING HOLES. BE CERTAIN TO LEAVE ENOUGH EDGE ROOM TO 
CLEAR THE CHASSIS MOUNTING TABS OR THE COVER WILL NOT GO BACK ON.
DO NOT COVER THE VOLTAGE SELECTION SWITCH PORT.  Measure, check,
measure, check...  It is advisable to clamp the ADS in place until 
the epoxy cures so that it stays put and also because the ADS is 
most effective if FULLY bonded.  I did this for both inside sides 
and the inside top surface so that all 3 inside surfaces had a bonded
ADS panel.  

  The end result is a no holes & invisible modification that makes 
the 962 cover much less acoustically active.  In the case of my 962,
it made a substantial improvement in audio quality.  This modification 
is reversable only in the sense that you can order a new cover from
Ten Tec.  Assuming that my 962 is typical, you should enjoy better 
audio.

  If you are a tinkerer, you will really enjoy a Small Parts catalog.
They can be reached at 13980 NW 58th Court, PO Box 4650, Miami Lakes,
Florida 33014-0650.  OR 800-220-4242 OR www.smallparts.com.  I am not
affiliated with Small Parts Inc. in any way.  This may be difficult
to believe, but in my experience, they can give even TenTec a run
for the money in service and delivery.  Their part number for the 
ADS is O-NS-0482-C Laminated Metal Composite.  That will get you a
12" X 12" piece for about $14.00 plus shipping.   The epoxy from
Wal Mart will cost less than $5.00 bring the total cost of the mod to 
about $25.00.  

  I know it could have been cheaper to get a good external speaker
but I was determined to have the 962/Omni 6+ combo working as intended
and shown in the pretty pictures in the advertisements. :)

  Ken, K7ZUM's earlier solution is interesting and obviously cheaper
and maybe a combination of the two will deliver good results.  Boxing
in the speaker may allow for shaping of the tonal response.  

Good Luck & 73

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