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Old 5th December 2007, 12:36 AM   #11
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Join Date: May 2006
Location: Netherlands
Hi Frank,

thanks for sharing your mod. I'm going to try it and see what it does. One question, I suppose you don't have the original damping mat that is attached to the rear grill in place with these mods, do you? Did you compare the placement of a single mat with your mod?

thanks,
Arend-Jan
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Old 5th December 2007, 04:40 AM   #12
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Join Date: Dec 2007
Hi.
Yes - the Hessian mat is still in place - it does have its advantages re: overall rear attenuation...as mentioned I got a new pair of mats from QUAD in '95 along with the other 'bits' - including new rectifier diodes/caps for the transformer..

[I did do a slight mod re: the Hessian though -I used some black nylon curtain 'backing' - very thin (use it for my B&W grilles..) against the rear-grille (held in place using double-sided tape round the edges (looks nicer too) - then I 'anchored' the Hessian by sewing it onto the grille @ various points...it's less 'flappy' that way.
As it was new I also cut it so that it *completely* covered the rear-grille...with the QUAD-type cut various parts of the bottom are left 'exposed'.]

Re: the treble mods - as mentioned firstly, the foam strips are removed - re-seated with clear glue - just near the dust cover/wood-frame junction..this allows the 'flare'.. with the acrylic felt (held in place with double-sided tape on bass panel edges & foam-strip tops + top/bottom plates (I also put some foam in the 'U' of the plates before covering with the felt).

Also, in the rear, I put a felt/foam pad @ the bottom as the treble felt doesn't properly reach that point (& the Cavity Resonance there is pretty bad with the treble felt just loosely fitted, as per original)
[The one-piece thick acrylic felt is also far superior to the previous cotton flock/3 layer affair!]

The only reason folks think of 'tinkering' with this design is a feeling it's 'not quite right'. That 'sensation' disappeared, for me, @ the point all my 'tinkering' stopped..I'm glad to say!

There is also one additional point; The felt behind the treble does provide some 'acoustic ehancement' - so placing the tensioned felt behind the bass panels too tends to make the 3 units more 'integrated'.

Frank
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Old 5th December 2007, 07:46 AM   #13
oshifis is offline oshifis  Hungary
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Join Date: Mar 2004
Location: Budapest, Hungary
Frank, thanks for the details and the sketch, it is clear now. I follow a different approach, though. I completely removed all rear damping, this gives a more transparent, open sound IMHO.
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Old 5th December 2007, 10:26 AM   #14
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Join Date: Dec 2007
Hi.
Yes - the panels, on their own, are 'transparent'.
Unfortunately, by removing the various damping, the 'chassis' they are placed in then makes its presence felt even more...

So you get (in no particular order of 'annoyance')..masses of treble diffraction from the front bass sides/top/bottom 'cavity'...rear diffraction/reflections both from the metal grille & wooden treble structure..frame resonances (even worse if you omit the rear grille)...reflections from the huge Transformer...

Have tried all this - but became aware of the 'problems'..but yes..you get 'more air' without damping.

However, 'The Secret' of my method is that the *highly tensioned internal wool 'panel' removes the structural problems - and provides a more 'neutral' setting for the bass panels.

Just one final note:-
The bass felt does need a couple of 'slits' to accomodate the bass terminal...& the felt is best aligned from the top edge (pinned under the top frame..) and the large drawing pins do need slight adjustment to get the felt absolutely 'taut' - like a drum-skin.
If the felt isn't taut then it won't 'dampen' the frame - also you can hear/feel it behind the bass panel - but, tensioned, you can't..

Frank
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