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Recommendations on MG 15 Rebuild

Tony L said:
A fantastic speaker design, one if the best ever, but built by British Leyland.
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Haha very funny description. tbf I think some of these matching issues are down to Tannoy not tightening their tolerances when they/listening moved to providing stereo pairs and the problem is compounded somewhat by the age(ing) of the drivers. The oft quoted example of the off kilter drilling of the comp phase plug is in fact only a cosmetic issue as the path lengths are within spec.
 
Tony L said:
I went down this route with my very first pair. It was before I had measurement ability but one was maybe 4db down on the other around 4-8kHz so the image wouldn't centre properly. I tried everything including replacing both compression drivers, but ended up putting the originals back as they were impossible to centre properly. I've gone through three near-mint looking pairs of Golds now and come to the conclusion the pair matching is just shite. A fantastic speaker design, one if the best ever, but built by British Leyland. My current pair are the best I've had, but even so I'm currently running one with a click back on the roll-off and just a nudge of amp balance control back up to compensate for the loss, this gets them within 2db right through the mid and treble and I can live with this. The Decca ribbons help a bit too.

PS It needs to be pointed out I am just unbelievably picky here, I'm a total hot-seat image freak and OCD about system setup to the extent it is almost an illness - the things that bug the living crap out of me most so called audiophiles wouldn't even hear! This is exasperated to some degree by the fact that my ears are not longer perfect and I do have a slight notch on the right side, so in some respects I can actually benefit from very slightly mismatched speakers!
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Tony, how 'stepped' is the effect of the rolloff controls on your LSU crossovers? I experimented with mine last night to try to match up the 10kHz-20kHz response of my two MG12 drivers but I find that even one click on the rolloff has too much effect (approximately 5dB per click):

36347187354_7ec1c136c3_b.jpg


The Energy control on mine has a much finer effect, approximately 1dB per click, which is far more useful IMO. Just wondering if your crossovers exhibit similar behaviour?

I wish iTunes etc offered a dual-channel EQ, then it would be a breeze to tweak left/right matching without the need for additional hardware and/or software!
 
I suspect mine are just the same, the roll-off settings are too crude to achieve the subtle change I need perfectly hence needing to suppliment with the balance control on the amp. The energy control just alters the level, it doesn't change the contour, which is no use in what I was trying to do (lose a 3-4db or so rise on one side at 8-10kHz). Mine now measure within 2db at the listening seat and aren't driving me nuts, though I would still pay a large amount of money for a mint pair that were well genuinely within 2db right across the range and also sounded exactly the same. If I didn't love my cabs so much I'd be looking very carefully at buying the new Ardens as they should be a similar sounding speaker but with modern quality control and it wouldn't be an expensive swap at all as mine certainly have some significant value. I really wish Tannoy would remake the vintage units as a stand alone unit only, I'd happily pay say £5k or so for a brand new perfectly matched pair of 15" Reds and crossovers!
 
PS Here's where I was last time I measured it:

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That's measured from the listening seat, right Roll-Off -1, Decca Ribbons in and I think balance on the Quad adjusted, though I can't remember, it may have been centred (the room does sound a bit different left to right). As I've stated on other threads I find measuring a bloody nightmare as just moving the mic 2cm in any direction impacts the measurement by more db than I'm trying to compensate for. It is borderline useless to be honest, I adjust to my ears at the end of the day.

It is so hard to get at the Roll-Off controls (involves taking the backs off the cabs) I don't have a -1 vs. 0 from this measurement set, and I don't think I kept the last set as they were so frustrating due to mic positioning errors - it is just impossible to keep the mic at the listening seat over a few days tweaking and also listen to the changes! Move the mic at all and the whole thing just turns to crap!

After I did this I did try swapping the speakers left to right and the difference between the one with the roll-off at -1 became much more pronounced, i.e. part of my issue is Tannoys, part is room - they are not actually as miss-matched as the measurements imply. I'd bet they were actually within about 3db of each other flat in an anechoic chamber.
 
Tony L said:
PS Here's where I was last time I measured it:

37014046912_6627b690c7_b.jpg


That's measured from the listening seat, right Roll-Off -1, Decca Ribbons in and I think balance on the Quad adjusted, though I can't remember, it may have been centred (the room does sound a bit different left to right). As I've stated on other threads I find measuring a bloody nightmare as just moving the mic 2cm in any direction impacts the measurement by more db than I'm trying to compensate for. It is borderline useless to be honest, I adjust to my ears at the end of the day.
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When I measured my MG12s in free air they were an excellent sonic match, both measured and to the ear. The biggest divergence across the spectrum was a 3dB difference above 10kHz. Rather strangely, since installing both drivers into my Edinburgh enclosures the divergence is now more audible and measurements show it has increased to 5dB. It's still only barely noticeable to the ear when both speakers are playing, but you know what my OCD tendencies are like!

Changing the crossover settings on the 'hot' driver to one click down on the roll-off and one click up on the energy gets the drivers closer in terms of measured response but the affected driver doesn't sound as clean/transparent to my ears at this setting so I'm just going to leave the controls at level.

I've just found and downloaded a free AU plugin which provides a 3-band parametric EQ for left and right channels independently so I'm going to have a play about with that and see if I can get the >8kHz response matched up by more sonically transparent means.
 
After 20 minutes of messing with a parametric EQ I can safely conclude that it is far easier to sonically match the drivers this way than to use the rolloff and energy controls. This is the measured response from my listening seat before and after EQ'ing (ignore the significant divergence in the bass, as this is due to room placement).

Before EQ:
36350724664_5c035fd2d9_b.jpg


After EQ:
36997561356_f881faea30_b.jpg


Using the following EQ settings:
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The before and after at 2.5kHz-4kHz and 8kHz-16kHz looks drastic on the graphs but it's actually very subtle to the ear, much subtler than the rolloff and energy control combination. In a blind A/B test I'd probably struggle to identify whether the EQ is on or off, but at least it eases my OCD a bit!
 
Thank you again to everyone who chimed in. The speakers are on their way to Speaker Repair Pro's along with the crossovers and switches. Hopefully the only issue will be the diaphragm. Will post again once they have had a chance to look things over. For a short (very short) period of time I had toyed with the idea of selling them off as a local guy has been looking for a pair. I auditioned some new floor standing speakers which sounded pretty good, a pair of Altec 19's and Klipschorn Belles, IMF 80's and my pals JBL 250Ti's. All could have found a place in my home but none sounded quite like the GRF's. I must remind myself not to get tempted again like that. ;-)
 
Bao from Speaker Repair Pro's called today. Crossovers check out perfectly, switches and wiring all good. Compression drivers, no issue at all. Woofers the same. So what did he find? The magnet in the speaker that exhibited the lower volume is over 1000 gauss below the other one. He is going to try and recharge the magnet and see what that does. While I've heard of speaker magnets losing some potency over time, this is the first I've experience it directly and was surprised when he said how much lower one was than the other. I have to say it was the last thing I expected and no one I've talked to about the issue I'm having made any mention of it. I guess it's not typical?
 
I’ve mentioned the potential de-maging of AlNiCo Tannoys many times but it’s unlikely given the low power handling( a power input sufficient to cause it usually burns out the voicecoil before any damage is done.)the other main cause of demagnetisation is physical shock so unless they’ve been dropped or hit with a hammer they should be ok. Time is not a factor- thier charge doesn’t/ can’t drain away.
 
Sorry to bring back a 2 year old post, but its relevant to my question.

I know this is a mg-15 post, but they use the same tweeter. I have a pair of Devon's with HPD-315 drivers and one tweeter that is not very good. Of course the 7900 0205 diaphragm is no longer available, and Ebay prices are crazy high.

I've found a 7900 0105 diaphragm for less that may be usable , but according to this post it says there will be a performance change. It looks like one of the only differences is the paper gasket. I'm assuming I can just use my old gasket if needed.

loisjames mentions a larger aluminum ring, but wouldn't they have to be the same size to be interchangeable?

I've also found a 7900 1351 that claims to be a replacement for the 7900 0105 so would this also be viable for my HPD-315's ?

If I can use any of these diaphragms, I also have a better shot at finding a used one.

Of course another issue will be two different tweeters, but it sounds ok now even with the slightly bad tweeter, so I'm hoping two good ones will be an improvement even if they are slightly different. . I'd also be more willing to buy 2 tweeters if they were affordable too.

Thanks for any help you can provide me.


louisjames said:
Note from The Speaker Exchange for reference:

Both diaphragms can be used for the Monitor Gold 15” speaker. The 7900 0205 is the diaphragm used for speakers produced pre 1979 and costs $225.00. We have them in stock. http://reconingspeakers.com/product/tannoy-diaphragm-7900-0205-hpd295-hpd315-hpd385/
7900 0105 has an integral card shim (which alters the spacing and interface) and is harder to center because it has a larger aluminum ring than the 0205. It is used for those speakers produced from 79-90. We also have that in stock, $255.00 http://reconingspeakers.com/product/tannoy-diaphragm-7900-0105/
You can use either one but there will be some performance changes if you substitute one for the other.
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Shawnnnn said:
Sorry to bring back a 2 year old post, but its relevant to my question.

I know this is a mg-15 post, but they use the same tweeter. I have a pair of Devon's with HPD-315 drivers and one tweeter that is not very good. Of course the 7900 0205 diaphragm is no longer available, and Ebay prices are crazy high.

.
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What steps have you taken to establish the issue is that particular tweeter, have you swapped crossovers, swapped tweeter diaphragms over?
 
I haven't swapped tweeters, I will try that.

I have swapped crossovers though, and the problem does follow the one bad speaker.
 
Sorry, the wording does get a little confusing. I think the crossovers are fine.

When I moved the bad speaker to the other cabinet it still sounded bad. The good speaker sounds about the same with either crossover.
 
Well, its apparently not the tweeter. I'm so glad you recommended I switch them, thanks cooky.

The one bad speaker is bad with either tweeter. It's also bad with either crossover, I checked again just to make sure. I also switched the speaker wires on my amp just to be sure that wasn't the problem. It's not.

I assumed it was the tweeter because the highs are so dull. The good speaker is very clear and bright. The bass on the bad one is fine but it has nowhere near as much detail as the good one. It's almost muted compared to the other one.

These are my first Tannoys, and I've never had speakers like these before. I refoamed them myself, but I've done many other speakers before and I'm confident I did these correctly. I did re-use the old cones.

Could the woofer voice coil be bad? Some cone kits have recently sold on Ebay. I wonder if they are still available, if that's the actual problem.

Thanks again for the help.
 
That sounds like an alignment issue or incorrect number of spacers. First off make sure the magnet gap is spotlessly clean, any gunk or debris in there can prevent the compression driver moving. Also the orientation you bolt it in can have an impact as they are imperfect things, so try all four possibilities. Finally don’t over-tighten it, I don’t even use a screwdriver with my MG 15s as they sound better just snugged up with my fingers. Vintage Tannoys are fiddly things!

When you are commenting on the bass do you mean with both compression drivers removed? If so and the one speaker is a lot worse than the other on both bass and treble I guess there is a chance it has lost some magnetism (possible with alnico), which would be a harder fix. Frank (Cooky) will likely have some ideas here.
 
Thanks Tony, I was commenting on the sound with both drivers being in the cabinets.

So I pulled them both out, and the bad one is acting much different than the good one. The cone on the bad one is vibrating significantly more than the other one. Even on lower volume its shaking a lot.
 
Frank will be able to advise far more than me as he understands the foam-edge HPDs far better than me, but that's starting to sound like a suspension thing (surround or spider). Have these speakers been 're-foamed' at all?
 
Yes. Refoamed by me using the original cones. I bought these from the original owner who hadn't used them for at least 25 years.

The foam looks fine though. I used shims so they are definitely not rubbing. They move up and down freely.
 
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