Speaker Foam

[gregz]

"gregz"

** Richard Small ( of Theile and Small ) made that same observation back in
the 1970s.

Seems he and I were at the University of Sydney in 1972 - though he is a
few years older than me.



** Have you done any testing to verify results ?

I have tried 4 cycle sine wave tone bursts and close micing with some
success - you may need to be outdoors or far from walls to eliminate
extraneous reflections in the scope trace.



... Phil

It's hard to be sure of results, but something is better than nothing. I
originally was trying to find differences in materials. As far as delay, I
don't think it's relative to today's thinking.

http://www.pitt.edu/~szekeres/relay.htm

Greg

 

[gregz]

"gregz"


** Those 41/2 inch drivers were not Bose by any chance ?


.... Phil

Some of them, yep. As far as I know, they are still working. I had bought
some of the original 901 drivers, made by CTS, with square magnets and
cloth surrounds for projects, in the 80's. Others various brands, including
Pyle Driver.

Greg

 

[gregz]

"gregz"

** Shimming sounds like the proper way to do it.

Same as when re-coning.


... Phil

Another thing, I like to try and clean the gap. Sometimes corrosion
develops, narrowing the gap.

Greg

 

[Phil Allison]

"gregz"

It's hard to be sure of results, but something is better than nothing. I
originally was trying to find differences in materials. As far as delay, I
don't think it's relative to today's thinking.

** Who mentioned delay ?

The idea of a tone burst is that it goes silent regularly, allowing acoustic
energy bouncing around inside the box to be picked up by a microphone and
seen on a scope when it emerges through the stationery cone.

I used 4 cycles on followed by 16 cycles off, varied over the frequency
range of the woofer, mid or tweeter.

Bare boxes show lots of after signal, padded ones much less.

An ideal box would show nothing during the silent periods.




.... Phil

 

[gregz]

Another thing, I like to try and clean the gap. Sometimes corrosion
develops, narrowing the gap.

Greg

One other detail. I try to straighten the spider. It often sags in, or out.
I moisten it and hold in place while drying.

Greg

 

[Phil Allison]

"gregz"

One other detail. I try to straighten the spider. It often sags in, or
out.
I moisten it and hold in place while drying.

** That really works ?

I used to regularly see off center speakers, both PA and guitar amp types.

Some of them were new and famous brand.

My test was to use pink noise with a SPL meter at about 0.5 metre and move
the cone in and out with my finger tips.

If the SPL increased in one direction and dropped in the other, the cone was
not centred.



.... Phil

 

[stratus46]

I have four infinity speakers.
they all need new foam (maybe).
infinity say they have no replacement speakers (what?) and offered no
repair kits.
i do have a few local places that refoam but have not called for prices
yet.
the speakers still sound fine to me except when there is some low
frequency music that cause the speakers to rattle.

1) what is the purpose of the foam?  dirt? rattle?
2) how do I measure the speaker to buy a foam kit?
   speaker diameter?  cone diameter? what?
3) if I can live with it, does it further damage the speakers without
the foam?
4) what destroys the foam?

If i just want to replace the speakers, what is recommended.  Mine are
9 inches outside diameter so should be easy to find replacements.
Want good enough sound not expensive.

I've re-foamed 6 Advent woofers. The first kit came with shims for the
voice coil requiring removal / replacement of the dust caps. I did it
as instructed and they work fine. Later kits did not include dust caps
so I didn't shim the voice coils. Those drivers also work fine but
took less time. Old Advent drivers have a masonite reducer ring that I
removed on the first set ( kit with shims ). I used silicone bathtub
caulk to re-bond the masonite to the baskets with an army of
clothespins to hold it together while it cured. I don't recall exactly
what glue I used on the cones but it was not rigid white glue nor was
it contact cement but it is flexible. Later (but sill old) Advent
drivers eliminated the reducer ring by altering the basket stamping
and are easier than the masonite units. Figure an hour on each driver
plus any drying / cure time of the glues. It's well worth the effort.

This is way more than I paid but will give you an idea.

http://www.parts-express.com/cat/speaker-surround-refoam-kits/328

G²

 

[gregz]

"gregz"

** That really works ?

I used to regularly see off center speakers, both PA and guitar amp types.

Some of them were new and famous brand.

My test was to use pink noise with a SPL meter at about 0.5 metre and move
the cone in and out with my finger tips.

If the SPL increased in one direction and dropped in the other, the cone was
not centred.



... Phil

It does work in the short term. Never followed up.

Greg

 

[Mac Decman]

"gregz"

** That really works ?

I used to regularly see off center speakers, both PA and guitar amp types.

Some of them were new and famous brand.

My test was to use pink noise with a SPL meter at about 0.5 metre and move
the cone in and out with my finger tips.

If the SPL increased in one direction and dropped in the other, the cone was
not centred.



... Phil

Many manufactures like to center the coil on the gap instead of based
on the BL vs. Displacement curve. This leads to oil-canning of the
suspension over time. The only way to fix them is to re-center the
coil in the proper position.

Mark