The Workbench

Re: Beovox 3702 low frequency distortion

Søren Mexico — Sun, 22 Jan 2012 22:33:00 GMT

If you go on check here too, read the whole thread. What about your midrange ??

Re: Beovox 3702 low frequency distortion

Søren Mexico — Sun, 22 Jan 2012 22:10:45 GMT

I'm worried about your warped spiders, before ordering surrounds, cut the dust cap and do the shimming, if you get more pressure at one of the 3 points, I woulden't go farther, its a tight fit and if the spider do not track parrallel its a lost cause.

Re: Beovox 3702 low frequency distortion

Søren Mexico — Sun, 22 Jan 2012 21:55:18 GMT

Be very carefull with the shimming, check everything 2/3 times, its the most important step in the whole operation, and be sure the plastic strip are all the way to the bottom.

Re: Beovox 3702 low frequency distortion

pepps — Sun, 22 Jan 2012 21:45:34 GMT

Thanks v much for this 'walk-thru'. I appreciate the detail and can visualise what needs to be done.

I'll let you (all) know how I get on.

Re: Beovox 3702 low frequency distortion

Søren Mexico — Sat, 21 Jan 2012 12:19:18 GMT

to refoam, I use plastic film, 0.1 and 0.3 Mm. thick, I cut strips 10x70 mm and put in the strips at 0, 120 and 240 degrees, allways the same at all 3 points, I fill up with the strips until I get a tight fit where the cone still can move in and out, like if you put in a 0.1 at one of the 3 points, the cone wont move freely, but taking the strip out again it will. Be sure to place the strips all the way to the buttom of the voice coil

I use Arleens sticky glue, before shimming I glue the surround to the cone, leave to dry for at least 4 hours, normaly over night. Then shim.

Then I apply glue to the basket and with my fingers carefully press the surround to the glued area, without pulling or pushing sideways, having contact all the way around, I leave it for 15 min. the glue is still fluent and the surround will settle slowly.

After 15 min. I put a saucer or an item that fits exactly to the outer surround glued area, I settle that very carefully on the surround and then put a cup of water or another driver on it to apply pressure, leave over night.

I've done S45s easy, a lot more gap in the voice coil, RL 140s less gap, like 3702, and never had any problems

Re: Beovox 3702 low frequency distortion

pepps — Sat, 21 Jan 2012 11:35:17 GMT

See also HarryPierce and his 3702 thread

The 3702s (type 6244) remain unfixed. I need to crack on and sort them out.

I've taken off the dust cap from one of the woofers. The tollerance between the magnet and the inner sleeve are insanely small! I can't see how I can stop the grinding/rubbing with cardboard and manage to glue the foam surrounds in place

Also after seeing Soren's 3702's I noticed I'm running completely different tweeters and mid-range drivers. My tweeters are the same as those found in 1702s - as for the mid-range set they look to have been swapped in from something else. They look a bit shabby really and not part of the original lineup. Does anyone recognise these mid-range units?

Re: Beovox 3702 low frequency distortion

Søren Mexico — Mon, 12 Dec 2011 23:52:36 GMT

Here a pic from my 3702/6463 driver

Re: Beovox 3702 low frequency distortion

pepps — Sat, 03 Dec 2011 19:21:29 GMT

Ah. I forgot to answer: they're 6244s

This evening I unstuck the new foam from the metal chassis and this has cured almost all the scraping. I may still fluke this!

Re: Beovox 3702 low frequency distortion

Step1 — Sat, 03 Dec 2011 19:12:10 GMT

Not sure what happened to the recone folks in Huddersfield??? This is not a job for the casual refoamer that's for sure!

Re: Beovox 3702 low frequency distortion

dmacri — Fri, 02 Dec 2011 17:14:00 GMT

Yes, those spiders are not supposed to have that wave to it. I've had success in replacing the foam surrounds, but I've never had to fix a spider. Maybe someone on the forum has this experience or can suggest someone who can help you. Good luck.

Re: Beovox 3702 low frequency distortion

pepps — Wed, 30 Nov 2011 18:32:41 GMT

Martin, always grateful for your thoughts. Yes indeedy I made a half-arsed attempt to refurb the woofers. Darn. Should've done more research. Got too excited about it

Those CX50s are in such a mess! I guess that's one of your projects - good luck with them

Well, as you say there's still plenty of other routes to try.

**Shout out to UK-based Beoworlders who may be able to help**

I'm not sure the spider is sitting very comfortably at all. If you would kindly cast your eye over the spider pic and let me know what you think I'd appreciate it hugely.

Re: Beovox 3702 low frequency distortion

Dillen — Wed, 30 Nov 2011 11:03:00 GMT

Well, you are not the first to believe it when the foam surround sellers state that it's
sooo easy to do a refoam job yourself.

The spider is the inner coil support where the foam surround is the outer.
They support the cone and coil etc. for a perfectly parallel axial movement.
Put very short; The coil needs to sit perfectly centered inside the magnet, around the centerpiece and
therefore it needs to be shim'ed and held in place while the surround is fitted.
To do this, the dustcap (center dome) needs to be removed (and renewed) and some
type of tool(s) put into work. I use some rings and holders specifically CNC'ed to each type of driver
to make sure every repair ends a success.
Some foam sellers include some strips of cardboard or what do I know but they obviously won't
fit all types and makes of woofers since the tolerances and clearances are quite different.

You lost whatever you paid for the surrounds, postage and the time you spent but I don't think
you actually ruined the drivers (some people do!). I obviously haven't seen them but at least it doesn't
sound like it and it may still be possible to rescue them. (Don't rub them anymore, you may risk damage
to the coil former).
There are UK members on this forum who may be able to refoam the drivers properly and the 3702's
are worth it ! They are not too plentyful, particularly with good cabinets.
BTW are yours type 6244 or 6263 ?
(It's found on the serial number label)

The woofers are custom made for B&O by Philips and they are (of course) long out of production.
Finding suitable modern replacements is practically impossible. There are lots of 8 inch drivers out there
but none with T/S parameters close enough.
I may be able to find a pair of original drivers already refoam'ed but I'm not sure of the postage
cost from Denmark. It may be a cheaper solution to find someone in the UK to help you.

I hate those "see how easy it is" - selling videos.
People are free to do with their things whatever they like but it makes me so sad everytime someone
brings failed DIY projects to me of rare drivers that were perfectly repairable before the owners
attempted to do it themselves.
Some woofers are fairly easy to refoam, others are definitely not.
Some owners stop while there is still a chance (like you, thanks), others don't.

For your entertainment and comfort, here is a photo of the result from someone with less luck than you.
This pair of (otherwise mint condition) white CX50 speakers arrived just a couple of days ago.
One woofer has its cone torn in half, the other cone sits at a most disturbing angle.
This owner definitely got off at the wrong foot (or WITH the wrong foot).

Martin

Re: Beovox 3702 low frequency distortion

pepps — Wed, 30 Nov 2011 10:32:08 GMT

I didn't align anything. Um. Oh dear. I followed the advice given on a video from the website I bought the re-foam rings from. (www.speakerrepairshop dot com)
I carefully removed the 'dead' foam from the cone and the metal speaker 'case'. Glued the edge of the cone, glued the foam inner, fixed it to the speaker cone. Waited. Glued the metal speaker 'case' and stuck the foam down.

Is there a slight possibility I screwed up here?

The terms 'coil' and 'spider' are not ringing any bells.

Crumbs. Please advise.

I feel a telling off looming...

Re: Beovox 3702 low frequency distortion

Dillen — Wed, 30 Nov 2011 10:20:05 GMT

Sorry but this sounds like a typical failed DIY refoam job. I've seen so many, you wouldn't believe it.
There's no other way than to start over with a new surround and dustcap etc.

A grinding noise like this suggests the aligning of the coil/center piece and/or the spider is far off.
How did you align it ?

Martin

Beovox 3702 low frequency distortion

pepps — Wed, 30 Nov 2011 09:42:30 GMT

Hi once more - thanks to everyone's fast, friendly and accurate responses I'm happy to ask again for your opinions on the following:

I just scored a stunning pair of Beovox 3702s from fleabay - paid £11.99 for the pair!

Sadly there was a good reason for this - upon connecting the speakers to my Beomaster 5500 and playing some music through them I found the low frequencies to be seriously distorted. High frequencies sounded fine.
After removing the grilles and taking a peek inside sure enough the foam surrounds on the woofers had perished. I ordered spares and carefully replaced them. However - upon connecting them to my Beomaster after the repair and playing music through them once more I was gutted to hear the distortion remains. In fact it may have worsened as a result of my repair job.

When I gently press the driver in on itself there's a bit of resistance; sort of like a grinding sound/feel. My lovely little 1702s don't make this sound at all when I gently press the woofers in on them to compare. In fact I've not noticed this on any woofer.

Is there some inner suspension of some sort which may have failed?
If so can I fix this? Or should I look out for some 'new' woofers for these cabinets?

Does anyone think it's crossover-related? I've not taken the wadding out to have a look at the crossovers - I wouldn't know how to tell if they're damaged.

I'd love to fix these drivers - the cabinets on this particular pair are the best I've ever seen. They're literally in showroom condition - beautiful grilles and aluminium surrounds. The woodwork is truly stunning! I can't let them go.

Any advice gladly received - or any tips on sourcing replacement drivers if these can't be fixed.

Thanks for reading,

Pepps