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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 29th Aug 2016, 7:43 am   #1
rswanborough
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Default Improved sound from old loudspeakers

The sound from older loudspeakers with corrugated cardboard surrounds can be improved by buying plain glycerine in your ladies' beauty section (very cheap) and, using a toothpick or match, spreading a little glycerine over the corrugated surround (not the cone). It soaks into the cardboard and makes the surround much more flexible - improves bass and mid responses - and effectively lasts forever.

I have never had a problem with this technique and it also makes the speaker surrounds last much longer.

NB, it is particularly effective on little radio loudspeakers.
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Old 29th Aug 2016, 9:22 am   #2
Hartley118
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Default Re: Improved sound from old loudspeakers

I seem to remember reading about the glycerine treatment decades ago, and I did try it.

What I found was that a lower resonant frequency isn't necessarily an improvement. For a speaker in a simple baffle or open cabinet, it can reduce the power handling capability due to the cone 'flapping' rather too freely.

Also, beware that glycerine is hygroscopic - that why it's used in royal icing to keep it soft. So your cone surround will be forever slightly damp - and the treatment tends to spread into the rest of the cone.

By all means try it as an interesting experiment on an old speaker, but I'd be cautious.

Martin
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Old 29th Aug 2016, 11:21 am   #3
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Default Re: Improved sound from old loudspeakers

I don't like messing about with old speakers if they still perform well.
But occasionally I'll treat a cone to a coating of PVA sealant to stiffen it up if it's become fragile or soft.
I did this to a Bush Dac 90a speaker and it really improved the sound.
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Old 29th Aug 2016, 1:01 pm   #4
rswanborough
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Default Re: Improved sound from old loudspeakers

Thanks, great tip.
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Old 7th Sep 2016, 3:51 pm   #5
Pete_kaye
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Default Re: Improved sound from old loudspeakers

I have some powdered glycerine , which is used in cooking( jellies etc). I think I will try this as I have 5 small speakers. How does it improve my beauty?
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Old 7th Sep 2016, 4:01 pm   #6
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Default Re: Improved sound from old loudspeakers

I think you'll find what you have is actually gelatine powder - that's a very different material.

Alan
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Old 7th Sep 2016, 4:12 pm   #7
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Default Re: Improved sound from old loudspeakers

Yes it dissolves in hot water and cools to a gel.
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Old 7th Sep 2016, 9:19 pm   #8
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Default Re: Improved sound from old loudspeakers

When I worked for a loudspeaker company, there were various substances used on cones and suspensions. Often referred to as "dope" and usually some kind of plastic dissolved in a volatile solvent.

"Plastiflex" and "opanol" were two trade names that I can remember.

There was also a specialist PVA adhesive that came from the book-making trade and had the advantage that it remained flexible after setting.

I've never heard of Glycerine being used (and very definitely not Gelatine! )
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Old 8th Sep 2016, 10:43 am   #9
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Default Re: Improved sound from old loudspeakers

It depends if the corrugation is an extension of the cone material or if it is a separate
fabric or foam. All plastic adhesives end up hardening, One could use a silicon
bathroom sealant, but my preferred choice is a rubber solution glue, e.g. Copydex.
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Old 8th Sep 2016, 4:38 pm   #10
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Default Re: Improved sound from old loudspeakers

I've always used Copydex for cone edge repairs and it always works a treat.

Regards,
Paul
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Old 8th Sep 2016, 4:42 pm   #11
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Default Re: Improved sound from old loudspeakers

Agreed,

I've used Copydex for over 50 years on speakers that were past their prime. Seems to do the job.
Of course this assumes that the formula hasn't been recently changed.


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Old 8th Sep 2016, 8:05 pm   #12
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Default Re: Improved sound from old loudspeakers

In pursuit of 'improved sound' from a 1949 Buick Eight's car radio speaker, found to be badly warped (and thus jammed) I detached the cone, lightly soaked it with water and then left it to dry out, clamped between two upturned cereal bowls.

I have now re-attached the 're-formed' cone and all appears to be well. It moves freely. I am hopeful that when the rest of the work on the radio is complete, it will sound fine.

Steve
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Old 14th Sep 2016, 9:04 am   #13
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Default Re: Improved sound from old loudspeakers

Too much PVA on the corrugated rim of a speaker (outer suspension) will cause it to stiffen and severely effect the base response of the speaker. I do use PVA sparingly but I dilute it 50:50 with water so that it forms a thinner coating and helps to bind the paper fibres together. I use paper kitchen towel, it is very strong, as in the adverts. I separate the layers and use just one layer on both sides to reinforce a tear in the diaphragm.
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Old 14th Sep 2016, 9:46 am   #14
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Default Re: Improved sound from old loudspeakers

The bookbinding adhesive was probably something like EVA (non-plasticised ethylene-vinylacetate). Neutral pH, archival quality, fast drying, and suitable for gluing spines and linen hinges. £7 for a 500ml tub from Shepherds (London). Evostick also remains flexible, and paperbacks whose spines I re-glued with Evostick in the 1960's are still in excellent condition. I just hope they haven't changed the formula for something more environmentally-friendly but less effective: they did change the solvent a few years ago.
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Old 23rd Sep 2016, 3:33 pm   #15
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Default Re: Improved sound from old loudspeakers

A little humour - my good lady reminded me that this is probably the only other use for KY jelly that she could think of.
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Old 8th Dec 2016, 10:25 am   #16
RodolfoRobbins9
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Default Re: Improved sound from old loudspeakers

This is one great tip thanks a ton!
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Old 25th Jan 2017, 5:34 pm   #17
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Default Re: Improved sound from old loudspeakers

I use Nu-Skin - pains on to cuts that don't heal. Works well and is very flexible.
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