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Advice on refoaming vintage speakers

Last response: in Home Audio
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July 31, 2011 3:11:33 AM

I am about to break into refoaming speakers . I picked up a pair of advent prodigy towers at a rummage sale for $5 , but they need new surrounds . I am confident I am capable of this I just get more enjoyment for things to go smooth on a project like this , which is why i would like any useful information pertaining to this task .

The old foam is very crumbly and will remove easy , I am aware of an alignment that needs to be maintained to keep the voice coil from rubbing or scraping .And that is about all I know. Thank you in advance for any helpful tips or pointers .
July 31, 2011 4:25:46 AM

is there any surround left and does the voice coil scape at low levels?
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July 31, 2011 2:38:33 PM

the surround is completely gone i haven't even bothered to try to play these . you are able to move the cone some without scrapping or rubbing , but only if you move it straight all sides evenly . my impression is that these are refoamable but the tolerance for alining it all is going to be tight .
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July 31, 2011 8:05:17 PM

too bad the surrounds are completely gone?

four pieces of junk tape might help you determine if rotating the cone just a little bit makes the speaker sound better.

but remember.. if the speaker sounds better and there isnt enough room on the tinsel lead for the speaker to move in and out.. you will have to suffer? with less cone movement.
because if you replace the tinsel with something else.. it could change the character of the sound you are listening to.

of course..
you could always break the tabs off and let them hang in such a way to keep the spider safe and allow the cone to move without making contact with the broken tab.


since your foam is evaporating..
you need to get a hard foam surround (try it)
and a soft foam surround (try it)
one of them is going to sound better?
one of them is going to make the speaker last longer?


if your alignment doesnt work with the shims inside the voice coil former.. you will have to shim the outside of the former.
but
that means removing the spider and glueing the cone first.. then remove the shims, and glue the spider.
but you have to be careful to keep the cone aligned while removing the shims.

you could use some very light glue and some wooden or plastic rods to glue the cone to the basket so it stays there nice and solid while you remove the shims under the spider.
glue the spider down and wait for it to dry.
then remove the rods from the cone and things should be good to go.. unless you decide to sand away some of the glue on the cone with a dremel tool.
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July 31, 2011 8:25:13 PM

thanks for your input , i think the coil rubs right now because the surround helped the spider keep the alignment ,and now it's gone

i think these have a softer spider than most speakers , they are low power .
i have seen some car subwoofers that were very stiff after playing long enough to call broke in , but these were 1500-2000 watt rms .

as far as i can tell these should be fine after being refoamed if i can get it right or at least i am going to try and see , just looking for any input from anyone who has done this , you know the sort of things that the instructions wouldn't tell a guy
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Best solution

July 31, 2011 8:43:13 PM

no matter how much you try to glue the thing without using shims.. if you are off, the speaker has a higher chance of self-destructing.


now..
for some instructions that wouldnt normally be told.
make the cone move outwards and watch carefully to see which way the cone buldges out.
if it leans to the left or right, you could offset that lunge by gluing the new surround offset.
that way.. when the speaker tries to lean sideways, it will be held in place to remain linear.

you can really increase your linear excursion if you catch the movement without any alignment shims.
if you cant catch it with your eyeballs.. try using a video camera.


there are TWO points:
1. keep the coil from rubbing the side
2. keep the coil from wiggling as the cone moves in and out.

the voice coil could be calibrated to be inflicted by the magnet at each moment the cone moves inwards or outwards.
to say..
'every move is magic' because all of it is calibrated.

so if the copper coil is supposed to STAY 1mm away from the magnet as the cone moves in and out.. you would need to correct the cone as it tries to lean left or right.
that keeps the gap 1mm and the audio output might give thanks.
if it doesnt..
then simply keep the coil from rubbing on the side.

the instructions should tell you to take the dust cap off and put shims down in there.
but
'advanced instructions'
would tell you to re-consider the shims and look for a chance to correct a problem.


sometimes the gap between copper coil and magnet is SUPPOSED to go from 1mm to 3mm
and the coil was wrapped that way because they knew it was going to happen.
(or.. they picked those tinsel leads because they knew it was going to happen)
or..
they chose this specific amplifier because they knew it was going to happen.

not much else can be said i suppose.
maybe try some soft rubber for an even softer surround?
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August 7, 2011 4:58:29 AM

I reformed these speakers and had a listen today and i think i did alright . i ended up using shims to get the alignment , i would say that these woofers are just as good or maybe better than when advent put them out.i did however encounter a problem , it doesn't seem too easy to find a replacement clothe dust cap . i guess that is minor. i guess i am not sure what these would have sounded like in there day , they do sound descent today , the 8 inch woofers in these make a surprising amount of bass .
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August 7, 2011 4:59:47 AM

Best answer selected by jacobboe89.
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August 7, 2011 10:25:14 AM

i remember throwing away an mb quart rwe302 12 inch subwoofer after i blew it feeding it 100 watts RMS more than it is rated for.
(it lasted about 7 days.. or was it 3?)

anyways..
certainly not the first time i have thrown something away and later on regretted it.
i knew speakers could be repaired when i threw it away.
but
i already knew the truth about buying new voice coils.. different coils sound different.
the sub sounded so very good in the bandpass box i had it in.. i felt the velvet need to simply throw it away.

cloth dustcaps might not prove to be overly difficult.
i think finding the right cloth is much more difficult.
how much air the cloth cap allows through could play a small roll on the final sound quality.

if you are in the market for new cloth caps.. maybe you could try a few different ones to re-shape the sound a bit.
i dont know if you will hear it much when the volume is down.. but it should matter quite a bit with the volume up loud.


using shims to do a quick repair on a speaker is super easy as long as the glue lets you in there, and your hands dont ache.
i wish i would have kept that subwoofer though.. because i could have always tried to use a much smaller wattage voice coil with the speaker basket and magnet.
ever turn a 500 watt subwoofer into a 100 watt speaker that is much easier to run in the house?

of course it isnt going to have the same amount of cone pressure.
it takes a stronger magnet to do that.
but
the point is to get a non-working speaker that would normally require an amplifier costing at least a thousand dollars..
wrap it all up into something that puts out some helpful output on an amplifier that costs a garage sale bargain.

hell..
i have seen some youtube videos of people building their own subwoofers out of a foam plate and some tape!
they really werent audiophile.
but
i swear they sounded better than some of the muddy subwoofers on the market today.
some of the spider braces were a bit disappointing.
not very many rubber bands.. but less rubberbands might have allowed the speaker to move more.

anyways..
maybe you have to make your own dustcaps from a piece of cloth and some hairspray to make the cloth stiff.

or
maybe you get a regular sealed dust cap and poke some holes in the cone to let the air circulate.
but
watch what you are doing with the holes.
if one hole has the basket in front of it.. and the other hole doesnt have the basket in the way..
your cone might jerk to the side.

i wish i knew if hairspray was acidic or safe for speaker cones.
because i would say use some hair spray or some spray adhesive (like the spray glue for photo albums)
spray that on the new hole to keep it kinda sealed up and safe from rotting away.

quite a bunch of the new speakers are seeing holes under the dustcap to keep the thing cooler.
i think you usually have to use at least three holes to keep the air level as it moves in and out.
but
sometimes that air creates a roadblock for cone travel in the voice coil area.
and
maybe it is better for you to use four holes as a minimum.


tearing this down and rebuilding them.. doing it wrong can cost you a new cone.
trying to play it safe can also allow too much and force you to try going back a step.

what i am certain of...
the things i would do if i had the money to support a hobby.
i dont have the money to go playing around with wasted cones.
but
if you do make a wrong cone.. you could always keep it and try those holes on a different speaker later.


i really suppose i should keep my mouth shut about tweaking speakers to make them sound better.
it is easier to go out there and demand (or know where to get) the better sounding speakers.

but as usual..
with a little bit of practice, you might be able to listen to a speaker and know exactly what you need to do for it to sound better.
could be a softer spider or surround.. could be adding some holes under the dustcap.
then working your way to the perfect box size.


the industry sure does get ugly.

talking about the speaker size..
any speaker that has a cone moving in and out more than a few millimeters, you can build a box to zoom in and focus on that movement to really explode the movement you are seeing.

some people get their breath taken away when you connect some 50 or 60 watt speakers to a 100 watt amplifier.
and that is because the 50 or 60 watt speaker starts to sound really good before the amplifier volume ever gets to 50%
and then there is some disappointment from the person on the volume dial when they try to make the speaker more loud by pushing the volume up over 50%

they dont realize the speaker was already working at 100%
and they dont know if the speaker is distorting or if the amplifier is distorting.
that is when the person controlling the sound system is about as clueless as a person who spent $150 on a generic bookshelf system.



of all my years being alive and interested..
i have always come to this conclusion:
any time i get excited about a speaker that rises to the occasion early on , with only a little bit of adjustment to the volume knob - the speaker always distorts before the volume reaches 75%


soo.....
how does the rain sound on those speakers from the beginning of this song:
http://www.youtube.com/watch?v=sOS9aOIXPEk

??
the rain sounds real over here. :hello: 
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