Tannoy MG15 distortion problem

Diggy Fresh

Member
2013-02-19 10:13 pm
Hi, i just aquired a pair of vintage Tannoy monitor gold 15" from an uncle and i need some advices on a problem.

They were sounding good for a month until one driver started to devellop some kind of low mid distortion with bass notes and it also lost some bass it seems. The high frequencies sound very nice and don't seem to have any problem.

I narrowed it down to the driver, i also redid the crossover and contacts to verify it wasn't the problem but it hasn't cured it. ( i even changed the connectors and bypassed the crossover switches).


When i apply a small pressure with my finger at some spots on the dust cap or some spots on the cone, the distortion goes away and the bass come back sounding clear and very good.

Which makes me think it's a mechanical problem at this point and i'm pretty bummed..

The speakers have low usage and probably never were abused and I cannot see any visual signs of damage. (these are not the version with the foam surrounds).


Anybody has seen these kind of problems with Tannoys dual concentrics before? What are the possible causes? any fix?


I'm kinda out of ideas but my next step might be to try to rotate the speaker 180 degree in case it is related to the "spider sagging" as i have read here.


I realy hope i can revive these .. :(

Thanks.
John
 
Your point about pressing the cone and dust cap and applying pressure seems very strange behaviour.

Maybe the tinsel wire between the connector and the voice coil is fraying badly or has a dry joint at the junction between it and the voice coil winding?

You may have to remove the driver from the cab to view both sides of the cone to make 100% sure. Maybe a very strong led light could let you see through the dustcap if that hides the connection on the front face of the cone.
 

Diggy Fresh

Member
2013-02-19 10:13 pm
thanks guys, update:


I finaly rotated them (heavy!!), i did not wait too long before testing them and the cone distortion was unfortumately still there.... :(

i experimented a bit, I found that if i apply a light pressure with my finger on the outer rim of the cone the problem disapear, (not on the dust cap as previously said).

Without pressure the sound is just bass lacking and sound boxy with heavy distortion on the low mids. The highs seem unafected.

When i apply the pressure on the outer rim of the paper cone the bass comes back very clean and distortion disapear totally until i let go.


I'm hoping it's sag, and i will wait a bit until it hopefully settles more to test again. But for sure the problem seems mechanical..


It is as if something in the woofer came loose and it can't reproduce bass, it just farts... I realy hope i can find a solution and i pray it doesnt need recone... The pressure thing has me baffled, for sure if there was a tear somewhere the pressure wouldnt change anything.


Any help is appreciated, if anybody had ecperience with a similar problem with another brand of speaker let me know .

And if anybody knows a forum or group where Tannoy gold experts are hanging, i realy hope i can find the cause. ( the yahoo group is defunct..)


Thanks,
John
 

Diggy Fresh

Member
2013-02-19 10:13 pm
Thanks Brinkman, i will look into DATS, i don't often deal with speakers but it looks usefull to test other stuff (i'm more of a studio guy).

If the problem is indeed the voice coil rubbing, what can be done about it?

I already rotated it 180 degree, i will wait more to see if it changes anything.

But if it doesn't fix it what can be done? recone? rebuild? This is not a normal speaker with the dual concentric stuff and fabric surrounds, That's making me extra nervous..
 

Brinkman

Member
Paid Member
2007-08-17 5:48 pm
Oakland, CA
It depends on the severity of damage to the voice coil. If the voice coil magnet wire enamel has been rubbed off you run the risk of shorted turns or, worst case scenario, broken/loose coil wires. Best case scenario, the enamel is still intact and finding someone to redo the surrounds will re-center the coil and fix the problem.

But don’t go down this path until you know for sure it’s voice coil rub.
 
If it has taken all these years to sag and cause a problem maybe you should wait a few more days at least.

If there is no improvement after a few days can you lay the cabinet or speaker on its back and listen to some music to see if you still have a problem. You may have to be careful with connections between the speaker and the amp so as not to damage anything, or shorting the amp output, but it should be doable with some spacers, cushions etc to stop damaging the speaker terminals and plugs.

As you say they are not foam surrounds, is the edge of the surround screwed to the chassis with several small screws, and probably glue. Maybe an expert in re coning could re centre the cone for you if old age and a large sag is the problem.
 
When i apply a small pressure with my finger at some spots on the dust cap or some spots on the cone, the distortion goes away and the bass come back sounding clear and very good.

Which makes me think it's a mechanical problem at this point and i'm pretty bummed..

Most likely the voice coil is off-centre and rubbing on the magnet or centre pole of the motor.

The general fix for this is to have the speakers re-coned. Do both of them so you can be sure of identical behaviour.
 

Diggy Fresh

Member
2013-02-19 10:13 pm
Great advices! thanks guys! i'm glad i asked.

Yes these are the "hard edge" surrounds i think, and not foam. There is alot of small screws on the whole circumference. So i'm kinda scared about reconing.
Is there even experts who still work on these and recone them with the fabric surrounds? parts availlable.

I will wait a bit before attempting something more drastic.. and try a few things to compare it with my other good driver.

I will try to research as much as i can, i realy appreciate the time you guys take to help.

John
 
Yes Cathy is probably your best bet as I assume it would be cheaper to send it to Tampa Fla than to London UK.

Although I know Lockwood can do just a recoil rather than a full recone and I do not know if that is an option with Speaker Exchange (The Speaker Exchange - Speaker repair, replacement, recone, refoam, parts and diy kits.).
There is another reliable (to the best of my knowledge) Tannoy specialist in Australia whose name escapes me right now but I suppose postage would be silly.

Once reconed/recoiled it will take a LOT more power as the limiting factor is not the voice coil but the cardboard former and the glue which keeps the coil on the former.
Roger Lockwood (may he rest in peace) referred to those as 'dub coils'. Tannoy were and are popular with reggae artists and their heavy, heavy bass and he did a lot of recoiling for those guys.

Either way I suggest you have both done if you go with that option.
 
Last edited:
Before reconing or recoiling - check that the spider hasn't shifted.
The older Tannoys' spiders are not glued in place but held by 4 nuts on studs.
Backing off the 4 nuts allows adjustment of the spider and centering of the coil in the gap.
You just feel the movement of the cone while moving the spider around until it moves nice and free...
Won't cost you anything to try and is a common problem I find with old Tannoys…
 

Diggy Fresh

Member
2013-02-19 10:13 pm
realy great advice guys,

Great to hear it's a common problem (with the spider),
i was looking all over the net for info like this.

I will definetely check how i can adjust the spider if the rotating don't help.

The problem apeared maybe one month after moving the whole heavy cabinet with (speakers inside), very low usage since and low volume, so i am hoping it!s a small problem.

Thanks alot guys!

John