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#1
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
I realise that this post and question is a little outside of the remit of
this group but I'm at a loss as to where else to find this information. I recently bought a pair of Wharfedale Dovedale III speakers from ~1970 or so. I'd read reports on-line (including the original 'Gramophone' review that is no longer available) which praised these for their faithful reproduction of most of the frequency spectrum but in particular their 'deep, clean bass'. I have a pair of Goodmans Magnum SL speakers that are similar design (3-way acoustic suspension) and vintage and, after replacing the x-over capacitors they sound pretty good. I was hoping for a similar result with the Dovedales which were their (British) competition at the time. They had been in storage for a decade before I took possession of them (from a deceased estate) so, before parting with my money I asked for them to be connected to an amp and played so I could test that all drivers were working (as I'd heard of people who'd had their tweeters fail). The only source available was a lo-fi CD / radio player so I only turned up the volume enough to hear (through my trusty cardboard tube) that all six drivers worked. I parted with my money and bought them home. Alas, on getting them home I discovered that the 'rubber' surrounds of the 12.5" woofers had gone hard - they felt almost like bakelite! Of course they produced no bass and I didn't dare 'drive' them for fear of damaging the cones. After some frantic Googling I found that at least one other person had also had this happen (but no follow-up on how, or if it was fixed). I then spent quite a bit of time contacting various suppliers of replacement driver surrounds but am unable to find anything for these. Being 12.5" I can't just try a generic surround either as nothing fits. I got a couple of quotes to have them repaired but they're way out of my rather limited budget. It seems that these really well-built drivers were previously used in other Wharfedale cabinets, also acoustic suspension, but fitted with doped cloth surrounds - and that quite a few of these speakers are still going strong. It's only the rubber-surround ones that have failed.... So I'm trying to find out how to make my own doped cloth surrounds to replace the (now cracked and broken) 0.5mm thick hardened 'rubber'. I'm an invalid on welfare so I have time, just not much money. The only instructions I've found on the web that come close are for making 'siliconed' cloth surrounds. However apparently no glue will stick them to paper cones other than silicone - which is a once-only job as the only way to remove it from paper cones (if the desired result isn't achieved first try) destroys the cones. As I'd like to preserve these lovely old speakers I'd like to have a shot at making something similar to the stuff that used to be used for 'doped cloth' speaker surrounds - the problem is I don't know what cloth or indeed 'dope' to use! I can just try to use something I consider might be suitable (maybe cotton and 'rubber cement' or similar - but how to shape and dry it?) but it sure would be great if anyone can give me guidance or information as to what used to be used. I'd love to have pointers on how to do it as well but I'll settle for *any* information I can get rather than trying to re-invent the wheel. Help please? Thanks in advance for any useful input. I've had them nearly six months now while I tried to find answers and I'd really like to try to bring them back to life. (The highs and mids sound great for speakers of this vintage!) -- Regards, Shaun. |
#2
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
In article ,
"~misfit~" wrote: Help please? Thanks in advance for any useful input. I've had them nearly six months now while I tried to find answers and I'd really like to try to bring them back to life. (The highs and mids sound great for speakers of this vintage!) -- Regards, Shaun. Speaker re-coning services DO exist, although I've never used one. http://www.parts-express.com/speakerrepaircenter/ http://www.speakerreconing.com You can also buy the supplies and re-cone them yourself: http://www.simplyspeakers.com/speaker-recone-kits.html I suspect that if you decide to have it done, that you will have to remove the drivers from their cabinets and send them off. I think that I would recommend having a pro do it, because they are most likely to get it right, with materials that are compatible with the original design. Speaker cones aren't just paper, after all. They have specific characteristics of speaker cone material, suspension compliance, cone free-air resonance, as well as specific materials. Just installing any replacement cone will be unlikely to to return the speaker to anywhere near it's original performance, but a shop that specializes in speaker re-coning can probably come a lot closer than either you or I could to getting it right. You might also contact Wharfedale directly: http://www.wharfedale.co.uk/Contact/...0/Default.aspx They should be able yo put you in touch with authorized service centers where you are located. --- news://freenews.netfront.net/ - complaints: --- |
#3
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
On 7/17/2013 12:46 PM, Audio_Empire wrote:
In article , "~misfit~" wrote: Help please? Thanks in advance for any useful input. I've had them nearly six months now while I tried to find answers and I'd really like to try to bring them back to life. (The highs and mids sound great for speakers of this vintage!) -- Regards, Shaun. Speaker re-coning services DO exist, although I've never used one. http://www.parts-express.com/speakerrepaircenter/ http://www.speakerreconing.com You can also buy the supplies and re-cone them yourself: http://www.simplyspeakers.com/speaker-recone-kits.html I've used these guys and am happy with the results: http://www.speakerdoctor.com/ Don't know if they'll do Wharfdale. As for doing it yourself, it's certainly possible, but if you are like me it'll take 5 recone jobs to get to an acceptable level of competency. I learned at a PA company back in the 80's when we had lots of speakers to recone. But as it's been 20 years since the last time I did it, I just send it out to someone who's skills are current. YMMV. -- //Walt |
#4
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
Somewhere on teh intarwebs Walt wrote:
On 7/17/2013 12:46 PM, Audio_Empire wrote: In article , "~misfit~" wrote: Help please? Thanks in advance for any useful input. I've had them nearly six months now while I tried to find answers and I'd really like to try to bring them back to life. (The highs and mids sound great for speakers of this vintage!) -- Regards, Shaun. Speaker re-coning services DO exist, although I've never used one. http://www.parts-express.com/speakerrepaircenter/ http://www.speakerreconing.com You can also buy the supplies and re-cone them yourself: http://www.simplyspeakers.com/speaker-recone-kits.html I've used these guys and am happy with the results: http://www.speakerdoctor.com/ Don't know if they'll do Wharfdale. As for doing it yourself, it's certainly possible, but if you are like me it'll take 5 recone jobs to get to an acceptable level of competency. I learned at a PA company back in the 80's when we had lots of speakers to recone. But as it's been 20 years since the last time I did it, I just send it out to someone who's skills are current. YMMV. Thank you both very much for your input - I stopped writing the post when I did as it was getting long but there are some things I should probably have included; Firstly I'm in New Zealand and the most respected speaker repair outfit here didn't reply to *three* seperate emails. (I could have phoned them, I'm told it's the best way to get in touch, but they have an email address and I find email the better media - especially for explaining 'curly ones' - jobs that are a bit more complex than re-foaming ~10 year old Infinitys.) I've used this outfit before but they're expensive and that was before my injury and subsequent loss of income. Oh, the *cones* are fine, (as are the spiders - they've been looked after) it's only the outer suspension that is shot. One outfit local did quote me for the job but, when I quizzed them about where they were going to get the 12.5" replacement surround they said with odd sized surrounds they normally get the next size up (15" in this case) and cut-and-overlap it! At $200 a driver quoted I expected more than that! The other thing I should have mentioned is I've been 'messing about with speakers' for over 30 years. As a teenager in the 70s I loved 'music', built my own stereo speakers and, for three brief and carefree years until I was 22 I toured with a band doing their live soundmixing. (I built some great stereo speakers when I had access to commercial drivers - but that is the least of my happy memories of that time. ;-) ) Long story short - I've actually done a few driver surround replacement jobs myself and am confident that - if I can get the right material - I can fix these Wharfedales. (The only drivers I've had repaired or restored 'commercially' were dome tweeters, getting new diaphragm / voicecoils fitted. There was a NZ company who built beautiful speakers using Vifa drivers but they crossed the tweeter too low and they were prone to voice-coil burnouts.) I already know that these particular drivers were hand-assembled to very tight tolerances (that's how they got such punchy clean bass out of ~30 watt amps using acoustic suspension boxes) and am prepared for that. Oh, I've contacted several international companies who supply driver surrounds, a couple in Europe, as well as a guy in the UK who I got to know a while back (as he handles all of the repair work for JPW speakers and I have some vintage JPW boxes - cabinets made in Dartmoor prison). Nobody can help with surrounds for these - that's why I think my only recourse is to make my own surrounds. I *did* try emailing Wharfedale but didn't get far - I was told that they don't support speakers made in the 1960s (my drivers have '67 penciled onto the back of the cones). I'm familiar with T/S parameters (having designed and built quite a few speaker systems myself) and the importance of getting the compliance as close as possible to the original specs. I'm a member of several on-line forums devoted to audio and have asked on the relevant ones with no luck (other than the silicone-impregnated colth idea) and am out of ideas. Other than to try to make positive and negative moulds, lay cloth in/on each and coat each side in turn with 'Ados' or similar rubbery glue, trying to get it to impregnate the cloth to try to approximate the earlier surrounds that these drivers sported. However before I do that and after reading some posts here by very knowledgeable people - I thought I'd make one last attempt at possibly finding out if anyone knows what the old 60s and 70s (and earlier) doped cloth surrounds were made from and maybe even how they were made. With my budget being so tight these days I likely couldn't afford to pay to get them done by someone else anyway as they are such rarities - and most outfits who've quoted me seem less aware of the importance of getting them close to original than I am - saying they'd use the ubiqutous 'foam' and cut it to fit (and charge me as much as I spend on food for a month)! So please, if anyone can help me with advice on the construction of doped cloth surrounds before I go at it with no knowledge of the material other than what I'm able to deduce and assume I'd be deeply indebted. Regards, -- /Shaun. "Humans will have advanced a long, long, way when religious belief has a cozy little classification in the DSM." David Melville (in r.a.s.f1) |
#5
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
I don't know anything about doped cloth surrounds on speakers, but I had
a friend who built large model airplanes and in the '60s they doped their own cloth for them. Maybe try a model airplane shop for materials and shaping advice. Greg |
#6
Posted to rec.audio.high-end
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Vintage driver repair advice wanted.
Somewhere on teh intarwebs Greg Wormald wrote:
I don't know anything about doped cloth surrounds on speakers, but I had a friend who built large model airplanes and in the '60s they doped their own cloth for them. Maybe try a model airplane shop for materials and shaping advice. Thanks Greg, I also used to build model airplanes (with my older brother, in the late 60s / early 70s), mainly large gliders that were covered in doped cloth. They flew for ages! We lost more than one - even using a fuse to burn through a rubber band so that it released the 'flaps' and theoretically made it stall and descend. That was a different process - with the 'planes the light cloth was fitted over the wings as tightly and neatly as possible and glued in place. The 'dope' was then applied and it tightened and stiffened the cloth making a very light but rigid covering for the wings that also pulled all of the (balsa) wood framing tightly together strengthening the whole assembly. That's the first thing that I thought of myself when I first heard the term 'doped cloth' applied to speaker surrounds. However the desired result with speakers is different to the result for 'planes. For the speakers the 'dope' is more like a rubber in a sovent that (as far as I can tell), as the solvent evaporates it leaves the rubber compounds behind which then hold the cloth on shape, 'build it up' a bit and also make it air-tight - essentially making a light rubber surround using the cloth as a scaffold. I have successfully repaired rips in this type of surround using diluted 'contact adhesive' and fabric patches. However the shape was already there for me, I merely patched it. The bit I'm struggling with mentally is how to get the cloth to hold it's shape while the first application (and later applications) of 'dope' dries - without sticking to whatever I use as a former. I figure that I need some type of releasing agent - but then that means the solvent won't be able to evaporate from one side of the new surround.... I guess I'm going to have to make it in stages, one side at a time - alternately. Googling and searching forums a few months back I found where a guy had done this using silicone as the 'dope' (as I mentioned earlier). He used a large lathe to make a wooden mould of the 'dipped' side of the surround, sanded it back and coated it with a release agent. He then used it to cast a plaster mould (which he also coated with release agent) so he had both a positive and negative former. However he then put silicone / cloth / silicone on the one and bolted the two together until it cured. With a rubber dope I won't be able to do that, I'll need to paint layers of it on/in to the cloth and leave it open to the air to let it dry - and I'm struggling over how to hold the cloth in shape while I do that. I guess I'll just have to 'suck it and see' - maybe just make the wooden part of the mould, coat it with release agent, paint it with diluted rubber cement and stick the cloth to it. Then paint the other side and hope that when I peel it off (if it even works) that it retains it's shape. So now, other than getting the use of a lathe, I just need to work out what cloth to use, what rubberised solution and solvent and what 'release agent'. This is the info I hoped that someone might know already and be able to help me with. I'd rather not have to make a whole bunch of 'failures' first - I have limited mobility. I'm guessing that 50 years ago doped cloth would have been the best way to make prototype drivers surrounds. These days all of that sort of thing is done inside a CPU then ordered from China. :-/ You know, it the drivers didn't have inverted surrounds that are impossible to get to I would try to use the one that isn't broken up as a mould. However the outer side of the curve that I'd need to use is under the lip of the cast alloy basket - inaccessable. I don't think using the inside of the curved surround would work as the result would have a smaller curve... But I've started thinking....... What can I coat old 'rubber' with that will act as a release agent for 'rubber cement' and won't destroy the cone if it gets on it? Thanks again. -- /Shaun. "Humans will have advanced a long, long, way when religious belief has a cozy little classification in the DSM." David Melville (in r.a.s.f1) [Sent from my OrbitalT ocular implant interface.] |
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