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Tannoy mg15 distortion problem
Tannoy mg15 distortion problem
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Old 18th January 2020, 08:06 PM   #1
Diggy Fresh is offline Diggy Fresh  Canada
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Join Date: Feb 2013
Default Tannoy mg15 distortion problem

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
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Old 18th January 2020, 08:17 PM   #2
phase_accurate is offline phase_accurate
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Maybe suspension sag. Could you try to rotate the driver by 180 degrees ?

Regards

Charles
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Old 18th January 2020, 08:31 PM   #3
raymondj is online now raymondj  United Kingdom
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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.
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Old 18th January 2020, 09:29 PM   #4
Charles Darwin is offline Charles Darwin  United Kingdom
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I had a very similar sounding problem with some 12s.

Did what Charles suggested above and rotated them.
Problem disappeared and hasn't returned in 15 years since.
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Old Today, 04:19 PM   #5
Diggy Fresh is offline Diggy Fresh  Canada
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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
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Old Today, 05:34 PM   #6
Brinkman is offline Brinkman  United States
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Tannoy mg15 distortion problem
This sounds like maybe the voice coil is rubbing. If you have DATS you can test a driver for rub & buzz
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Old Today, 05:52 PM   #7
Diggy Fresh is offline Diggy Fresh  Canada
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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..
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Old Today, 05:59 PM   #8
Brinkman is offline Brinkman  United States
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Tannoy mg15 distortion problem
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 donít go down this path until you know for sure itís voice coil rub.
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Old Today, 06:05 PM   #9
Lojzek is offline Lojzek  Croatia
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You can save yourself the expense and drive a unit with REW sound generator (5Hz sine) hooked up to an amplifier and then to a driver with a volume setting just high enough to start seeing a small cone movement.
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Old Today, 06:29 PM   #10
raymondj is online now raymondj  United Kingdom
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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.
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