Vintage Products

Re: Beovox S80.2 Refoam

Rich — Tue, 24 Aug 2010 11:06:09 GMT

Claus:

Thanks for the reply re: scraping.

I, too, like both beer and wine, but I do not like both kinds of music: Country and Western.

Re: Beovox S80.2 Refoam

Evan — Mon, 23 Aug 2010 13:03:20 GMT

That's good news Claus!

Re: Beovox S80.2 Refoam

Claus — Mon, 23 Aug 2010 02:19:03 GMT

Jon:

Wow! You're brave! So, just to get this straight, you were playing the 30Hz test tone while you were aligning the spider and gluing it in place?

Jon - Correcto señor: The spider was glued to the cone already and was glued to the frame using the 30 Hz tone.
The point is, that playing the 30 Hz tone actually alligns the coil in the center of the magnet gap. This happens even at low/moderate level where it's possible to work with/glue the outer part of the spider (and the surrounds), so it's not so weird as it might sound.

That beeing said, I must admit that fixing the spider and the surround was more of a job than just glueing surrounds.

Rich:

If you hear scraping, haven't you just damaged the voice coil?

Rich - if it's only for a short period of time "a little" scraping doesn't damage the coil.
The problem and damage occurs if the scraping is ”serious” (but again: the coil tends to align itself) or goes on for a longer period (so the isolation on the coil wire is rubbed of against the magnet – and makes the coil short cut).

evman140:

Another JBL enthusiast!
Oh no, caught out in the open!

evman140 - Mmmm... and I also like both wine and beer

Re: Beovox S80.2 Refoam

Evan — Sun, 22 Aug 2010 23:29:30 GMT

Another JBL enthusiast!

Oh no, caught out in the open!

Re: Beovox S80.2 Refoam

Jon — Sun, 22 Aug 2010 22:46:28 GMT

Claus:

Actually, on one of the M75 woofers I had to dismantle the cone completely from the frame and repair the coil (a bit of the voice coil wire had come loose and had to be glued).
This meant removing and remounting the spider (as well as mounting the new surrounds).

The 30 Hz-method worked well for aligning the coil/cone in this case too, so I’ll stick to it for a while. On the picture you’ll see the cloth pins on both the spider (below) and surround (above) – the gluing was done in two steps: Spider first – surround last.

Wow! You're brave! So, just to get this straight, you were playing the 30Hz test tone while you were aligning the spider and gluing it in place?

Jon

Re: Beovox S80.2 Refoam

Rich — Sun, 22 Aug 2010 20:34:38 GMT

Claus:

Very interesting approach, but....

"...Listen for scraping sounds....if you hear scraping...."

If you hear scraping, haven't you just damaged the voice coil?

Re: Beovox S80.2 Refoam

Claus — Sun, 22 Aug 2010 13:47:42 GMT

Dillen:

Besides, it's not uncommon to see the spider sagged a bit too (due
to gravity) and that will definitely have to be corrected another way.

Actually, on one of the M75 woofers I had to dismantle the cone completely from the frame and repair the coil (a bit of the voice coil wire had come loose and had to be glued).
This meant removing and remounting the spider (as well as mounting the new surrounds).

The 30 Hz-method worked well for aligning the coil/cone in this case too, so I’ll stick to it for a while. On the picture you’ll see the cloth pins on both the spider (below) and surround (above) – the gluing was done in two steps: Spider first – surround last.

Martin – let us know your experiences, if you get “tempted” to try

Re: Beovox S80.2 Refoam

Dillen — Sun, 22 Aug 2010 13:03:10 GMT

Thanks, Claus. Greatly appeciated.

Having refoam'ed woofers for about 10 years, I'm quite surprised that I
haven't seen this method before (and I've seen many).
Call me stubborn and old fashion but I'm not convinced that simply
playing a low frequency signal will center the voice coil particularly good.
Besides, it's not uncommon to see the spider sagged a bit too (due
to gravity) and that will definitely have to be corrected another way.

Whilst the above shown method may work for you and others, and I accept that
fact, I think I will stick to what I've done so far, which also is more
comparable to what was done by the producer.
That doesn't mean that I won't try it some time, I'm always curious.

Another thing is that many of the woofers that arrive here are failed
DIY attempts, it can often be a challenge and the "conventional" method
is the only way.

Martin

Re: Beovox S80.2 Refoam

Claus — Sun, 22 Aug 2010 11:03:08 GMT

I'll be glad to explain.
Actually – I’m surprised that this method is unknown here. On the Lansing Heritage forum (JBL-stuff and where I started my speaker repair "career") it seems to be the preferred DIY-method, but I’m glad to share the experience from the one world to the other.

Since the tolerance of the magnet gap at the classic JBL units are smaller than the ones of Seas etc. (thus making them more critical to centring the voice coil), I think you can safely rely on the method for B&O speakers as well.
I’ve refoamed both the woofer and the phase-unit of my Beovox M75 (and a lot of JBL units) this way without any problems whatsoever.

Here’s what I’ve done:

After removing the old foam surround, glue the new one to the cone by centring it optically as good as possible.
Leave to dry completely (over night).
Before adding glue to the side of the surrounds that meets the metal frame, connect an amplifier directly to the terminals of the speaker unit and feed it with a low frequency signal at low level. (I use 30 Hz from a cd that comes with the JBL-kit)
While the cone is moving (slightly), add glue to the surround and the frame.
Use glue that allows to be “worked on” for at least 15 minutes before it sets.
Increase the level to moderate cone movement (a little at a time and never more than 1/3 of full movement) while you listen for scraping sounds (meaning that the coil is touching the magnet).
If you hear this – adjust the surround by moving it in the frame while the glue is still wet and can be worked with till the scraping sound disappears.
When the cone moves free of scraping, put on cloth pins (or the like) to ensure that the surround and frame are pressed together while drying. The low frequency tone will assure that the coil is aligned while the glue sets.

Martin, to your remarks of alignment and vibration:
Alignment: When you feed a (low frequency) signal to a voice coil in a magnet gab, it’ll try to center itself – not move towards one of the sides of the magnet gab. (Here we’re of course talking about the up/down/left/right-directions – not the forward/backward-movement that produces the sound).
Vibrations: With only moderate cone movement, the glue I’ve used is able to keep contact between the frame and surround – meaning that the outer part of the surround doesn’t move while the glue sets.

I hope this clarify the method and that it’ll be useful to others.

I attach two scans of the instruction from the JBL surround supplier.

Part 2:

Re: Beovox S80.2 Refoam

Dillen — Sun, 22 Aug 2010 04:12:58 GMT

Yes, could we have some details please ?
I can't see how this method aligns anything, let alone how you can glue
something that vibrates.
My experience (several hundreds of woofers) is that everything needs to be fixed
exactly in position and held tight and steady while the glue sets.
Glueing is always done in two, sometimes three or four steps with the glue fully
curing in between. I've also found the need for having special holding tools
for specific woofers CNC fabricated to get it right everytime.
Claus, you will have to explain.

Martin

Re: Beovox S80.2 Refoam

Jon — Sun, 22 Aug 2010 02:40:07 GMT

Claus:

I use a low frequence tone (30 Hz) at low level (1-5 Watts) to center the voice-coil during the proces of glueing the surround to the frame.
This works fine, saves a lot of work - and keeps the original look of the speaker.

I'm curious - with the cone moving back and forth like that at 30 cycles, how do you keep the surround steady enough for it to be centered well?

Jon

Re: Beovox S80.2 Refoam

Claus — Sat, 21 Aug 2010 14:09:11 GMT

BoxOPwn:

Would you happan to know the diameter of the dustcaps on these woofers? The speakers will not arrive until next week, so I cannot measure this as of yet, but would like to order the parts soon.

You really don't have to change the dust caps - or take of the old ones - to center the cone when mounting new surrounds.

I use a low frequence tone (30 Hz) at low level (1-5 Watts) to center the voice-coil during the proces of glueing the surround to the frame.
This works fine, saves a lot of work - and keeps the original look of the speaker.

Re: Beovox S80.2 Refoam

Dillen — Fri, 20 Aug 2010 14:47:12 GMT

I must admit to not remembering all dustcap sizes but they should be fairly large.
Something like 95-100mm or so.

Martin

Re: Beovox S80.2 Refoam

BoxOPwn — Fri, 20 Aug 2010 11:24:03 GMT

Would you happan to know the diameter of the dustcaps on these woofers? The speakers will not arrive until next week, so I cannot measure this as of yet, but would like to order the parts soon.

Re: Beovox S80.2 Refoam

Dillen — Fri, 20 Aug 2010 00:24:12 GMT

I would recommend using the original material.
And use nothing but real speaker cement. It will hold on to almost anything, it is incredibly strong, it doesn't
harden and crack but will remain just that little bit flexible so any strains in the cone and surround materials at the
glue edges are "softened" out.
Also make sure to get new dustcaps to mount when you are done aligning the coils and spiders.
I like to mount slightly larger dustcaps to cover any glue remains of the originals.

Martin