Loudspeaker builders/repairers - help!

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Eric The Viking

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Bristle, CUBA (the County that Used to Be Avon)
My beloved Monitor Audio MA7s (circa 1980) have finally blown a bass unit. I think the voice coil must have overheated as it's open circuit and rubbing all round. I think it's beyond hope.

Can anyone recommend an alternative supplier to Wilmslow for low/med power 6" Hi-Fi drive units? I've emailed MA asking for enough of the specs to be able to source replacements, but I'm not hopeful -- their present designs are "active enclosures"* and the drivers high-excursion, inefficient jobbies. I've no doubt they are wonderful, but these cabs are rigid and old fashioned.

I'm stupidly fond of them - rebuilt the crossovers and relpaced the tweeters with Audax soft dome ones to good effect years ago. They've been abused, even used for PA, but survived until the era of the X-factor, which seems to have done for them.

So any source of relatively old-fashioned bass/mid drivers would be much appreciated.

Cheers,

E.

PS: The budget is around £140 (tops) for a pair. They're nominally 8 Ohm units, DC resistance probably about 6 Ohms (remaining one is 6R3), but unless I get something back from Monitor Audio I can't be more specific.
 
Hi, Eric

What about that company in London that repairs speakers, Wembley?
Found them.
http://www.wembleyloudspeaker.com/

Apart from them get a search going on Ebay for a pair.

I just sold a pair of Spendor BC3's they sounded nice after I replaced the thinest wire I have ever seen in a speaker fror some 2.5mm csa stuff.

Pete
 
I haven't bought from them for a while (not a reflection on them, I just haven't needed to), but Richer Sounds used to be pretty good for seperates.
 
Thanks all.

Maplins I ought to look at again. I've bought good units from them in the past, in fact the current Audax tweeters came from them (but they are AUDAX!)

I may give Wembley a call, but I think they're outside my budget (just love the design of those Volt units though! I think ATC use them in their larger systems, too).

Wilmslow have some similar units to the damaged one but they're nominally a bit lower Z than the ones I have to replace. Size+shape is fine, it may be a bit insensitive, and it's a bit honky (37Hz), although I haven't got numbers to compare it to.

I might get away with adjusting the crossover (it's just LC, no R at the moment), but last time I tried measurements, I realised I didn't really have a suitable space to do it in. I can probably borrow the necessary mic. (my old C451s aren't flat enough at LF, probably) and I have a good storage scope and suitable mic amps. I guess I could measure the one remaining driver in free air and see what I get - it's half term and smallest might be interested in the experiment...

If you can think of another supplier of decent drive units, please shout.

Cheers,

E.
 
Sorry to hear about your speakers Eric, it sounds as if the voice coil has become detached, at least in part from its former. Trying to rewind a voice coil could be fun.
As for free air measurement, that would be a bit dodgy this time of year. However a close-ish approximation could be achieved with a blanket/duvet walled 'tent' in a big room, have the mic towards the back of the tent. Now tents and small ones go well together.
xy
 
Eric, I have just come across this site. I was trying to find out if the MA7's are vented. There is a frequency response curve shown. Any similar curve taken with your setup, preferably open-air, or see above, could be compared and an environment/set up correction worked out to apply to future response curves.
http://www.avforums.com/forums/speakers ... akers.html
Of course if one of your speakers still works then, irrespective of your set up, comparisons will work well.
xy
 
AndyT":196hj43f said:
Eric - I only know this place by walking past and window shopping but it looks from their website as if they might be worth a look - long established audio equipment technicians and repairers: http://www.electrofix.com/service.HTM

They are in Clifton, in Alma Vale Road - streetview link: http://goo.gl/maps/nY9aJ
Click to expand...

Ah yes! I didn't know they were still going...

... They used to be part of a recording studio business ("Studio 34", Greg Someone-or-other?) in the 1970s-80s . An old friend of mine had his EMI 1" 8-track based there, in the days when all multitracks were rare.

In the 1980s I used to look after the PA systems for a number of Bristol churches, and had weird problems with radio mics at All Saints Pembroke Rd. Unexpected voices kept coming up loudly on the same channels, "1... 2... 3... testing..." happily never during a service, but making the churchwardens jump!

People in Studio 34 were testing PA systems, but well below ground (IIRC their basement studio was two levels down). By rights nothing should have been escaping and they weren't using overly-high-powered kit.

It turned out there was a large, disused, cast iron water main that ran along Alma Vale Rd. near Studio 34's basement, smashed in places but largely intact over the distance. Part of All Saints is below ground level too. We concluded it had been acting as a waveguide! The compromise was to give Studio 34 a schedule of services, and remind the churchwardens to turn off the PA at other times!

Happy days...

E.
 
I rather suspected you might know them already! Maybe a better bet than the obvious other choices like Paul Roberts on Gloucester Road or Audio T on Park Street.
 
xy mosian":2dmdragq said:
Eric, I have just come across this site. I was trying to find out if the MA7's are vented. There is a frequency response curve shown. Any similar curve taken with your setup, preferably open-air, or see above, could be compared and an environment/set up correction worked out to apply to future response curves.
http://www.avforums.com/forums/speakers ... akers.html
Of course if one of your speakers still works then, irrespective of your set up, comparisons will work well.
xy
Click to expand...

Sorry - I rudely didn't reply - XY, that's really useful.

There's enough info to see what I'm aiming at there. As I mentioned, I replaced the originals with better Audax tweeters after one of the originals died about 20 years ago. I've still got both of them somewhere, but IIRC it wasn't repairable easily, unlike the early Audax ones, which can be disassembled. With the replacement tweeters the HF is a lot smoother and better all round (the imaging is better too, but I think that's down to tighter crossover tolerances, also improved in the past - swapped back-to-back electrolytics for polyester). The original boxes weren't all that special (yes, they're front ported - usual toilet roll arrangement), but the mods transformed them.

I think it's a very good idea to measure the one remaining LS. I've got an oscillator, a pretty flat amp, and a decent mic or two to use, and a probably big enough front room with lots of soft furnishings. Worth a go, definitely.

Later,

E.
 
Hi Eric, Your comments about crossovers is interesting. During the seventies, and I assume into the eighties, it was not unusual to find that tolerances in drive units were significantly tighter than those on the electronic components used in the crossovers. Many is the time I could be found sorting capacitors into matched pairs for 'specials'. The inductors did not have the same variations, probably because they were wound 'in house' and of course had easier construction. The company I worked for set up BBC 'B' based testing of very crossover panels for some of the high-end models to ensure good matching of pairs.
During the same period a lot of loudspeaker design was guided by the work of Theile. He wrote two significant papers, one on Loudspeakers in vented boxes and the other on Loudspeakers in sealed enclosures. If you fancy trawling through the theory I'll try to find available downloads.
xy
 
Yes, it's interesting.

IIRC, those back-to-back electrolytics were popular because, when new, they delivered big values of C cheaply, but they deteriorated quickly because of the lack of a polarising voltage (well, current really).

It's a long time ago now (1980s at a guess), but I think the reason for changing mine was that one crossover failed. My Dad was an audio designer of some repute in his day (electronic musical instruments, mainly, but he also did amps, etc.), and he suggested replacing the electrolytics with polyester. I was amazed at the improvement (I'm not easily hoodwinked by audio snake-oil, either). The crossovers look a bit of a mess now, as there's a 'mushroom farm' of little orange things on them, but they work very well and have withstood a lot of abuse down the years. As they're both now disassembled, I'll post up a snap if I remember.

I'm hoping Monitor Audio might have the necessary Thiele-Small values for the bass/mid units, but they haven't replied yet, so I don't know if I'll have success. I've done a bit more Googling this morning, and there are any number of suppliers out there, but very few of them provide enough info to let you decide which units are suitable for what.

When you add-in the idea that most of these new-style 6" drivers are listed as good for 100-150W "power handling" (whatever that means), it's evident that snake oil is still in great demand. If anything, it's proof that general science education in secondary schools leaves a lot to be desired. :-(

E.
 
Eric, Your mention of your Dad, tickled my memory. I think that my first boss, Ken Russell mention someone with the same surname as yourself, Viking :) . Unfortunately my copies of Gilbert Brigg's books are buried in the loft, I'm sure there is a reference in there.
xy
 
Racers":1mgpqd3s said:
Hi, Eric

What about that company in London that repairs speakers, Wembley?
Found them.
http://www.wembleyloudspeaker.com/

Apart from them get a search going on Ebay for a pair.

I just sold a pair of Spendor BC3's they sounded nice after I replaced the thinest wire I have ever seen in a speaker fror some 2.5mm csa stuff.

Pete
Click to expand...

I didn't know you were 'into' Spendor's, Pete? Still have a couple of early BC1's.
 
Hi, Roger

I was given them :shock:

They did some nice things after a rewire, 12" bass units do have some advantages, but they where BIG

DSC_0006.jpg


As I understand they are BC1 with a 12" bass unit.

They went for quite a bit on Ebay so I am happy and so it the wife!

I have put the Shahinian Arcs back in now, and I think it sounds better, less bass but clearer.

Pete
 
Ah, BC1s, they take me back.

The BBC built-in amp supposedly didn't do them any favours, however I monitored on them for years. Very smooth and good for nearfield use too, albeit slightly underpowered (may just have been those amp boards).

I got a reply from Monitor Audio, incidentally. They didn't have the driver details but sent me the tech sales literature, probably from around 1977! It's comprehensive, and actually useful in context.

The crossover is 18dB/octave, centred on 3.5kHz, bandwidth 70Hz-20kHz (-4dB points) and 40Hz bottom end (yeah, right!). Sensitivity 96dB(A?) at 1m for 20Wrms (pink). The curve is pretty tight for something that size, too.

It's more to go on than I started with, although more info on the bass unit would've been really helpful. My guess is that they no longer have it.

E.
 

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