Mordaunt Short - Carnival Series 2 (1976) Crossover and Tweeter Help Needed!

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I'm going to research some cheap replacement drivers
I presume you mean replacement tweeters.

The mid/bass drivers are Mordaunt Short DSB 208. These are very good drivers and, unless faulty, are in no need of replacement.

See this link for description and specification of the DSB 208:

stereonomono - Hi Fi Compendium: Mordaunt-Short DSB 208

The paper cone tweeters I suggested earlier are not expensive, and it's well worth taking the gamble that such or similar replacements will blend in satisfactorily in conjunction with the existing crossover.

If that proves not to be the case, then return to the forum for further assistance.
 
I presume you mean replacement tweeters.

The mid/bass drivers are Mordaunt Short DSB 208. These are very good drivers and, unless faulty, are in no need of replacement.

See this link for description and specification of the DSB 208:

stereonomono - Hi Fi Compendium: Mordaunt-Short DSB 208

The paper cone tweeters I suggested earlier are not expensive, and it's well worth taking the gamble that such or similar replacements will blend in satisfactorily in conjunction with the existing crossover.

If that proves not to be the case, then return to the forum for further assistance.


Thanks Galu - Yes I meant tweeters, and should I decide to change them, I will start with the ones you recommended which can be procured locally for not very much money.



The re-cap I did last week has really improved things, but I am noticing some tweeter-cone noise from time to time that I'd like to be able to reproduce - "for research" :)


Today I'm putting together some tweeter test patterns in ableton - audio loops, percussion stuff, wave sweeps etc. For purely subjective measurement / reproduction of physical failure modes - rather than to measure response etc - if that makes sense. Basically a selection of neverending loops I can pan and EQ to see how the tweeters handle them.
 
Ihalha, take a look at Wagner Electronics who supply to the repairs industry.
They will likely have suitable tweeters plus everything else you could want.
You asked about replacing the polycarbonate capacitor (the multicoloured) one.....this is a solid cap so should be electrically fine but all capacitors types have a characteristic sound, by juggling capacitor types you can voice your speakers somewhat.



Dan.


Tweeters
Polypropylene capacitor
 
Hi all,


So I was enjoying these and getting ready to buy the new tweeters, when I noticed that the bass driver has stopped working on one of them.


The crossover I updated "looks" ok and was working for a week or so - but maybe I have introduced a short that has knackered the bass driver?


Testing with a DMM gives a decent reading (see attached). Disconnected from the crossover, and connected directly to a small amp, the driver reproduces the music I put into it, perfectly audibly but only very quietly and only high frequencies. There is no visible or physical cone movement.


There is plenty of advice on the web, but it all seems to say "if your DC impedance is good, the driver is good".


One thing I have not tried is this same test on the other working speaker, simply because the drivers are hard solders to the crossover wires and it's a real pain to work on. I have updated the broken one to new internal wire and removable lugs deliberartely as part of this investigation. But I have done the obvious (to me) things like try different amps and both L&R outputs of each amp etc.

Thanks,
2Q==


lhalha
 

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The crossover won't have damaged the bass driver.

Did the bass driver stop working completely while it was still in the speaker cabinet?

Check that you have soldered your replacement capacitors in securely - use your ohmmeter to confirm continuity between the capacitor leads and the copper tracks on the board.

Push the bass cone down gently with your thumbs placed on opposite edges of the cone. Can you hear or feel any rubbing of the voice coil in the magnet gap?
 
Thanks for jumping back in!


Did the bass driver stop working completely while it was still in the speaker cabinet?


Yes. There is no noise or scratchy feel when I depress the cone. Just as an aside, the rubberised paint on these things is super tacky and *does* make scratchy noises as your fingers unstick themselves from it...


Pretty sure my testing of the driver connected directly to an amplifier has ruled out there being an issue with the crossover / sodering etc.... The wiring looks intact too...


I've uploaded another pic that hopefully also shows that the wiring to the coil appears to be fine (and we know that *some* sound is being generated)




Edit - unfortunately I don't know what could have happened in the interim but the speakers were unplugged and moved around several times...
 

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Hmm - With the magnet on the tabletop, I can get my fingers into the basket and push up gently from underneath. There is some (what I believe the mtb suspension people call) "sticktion" and then the cone suddenly loosens and pop up a little. Doing this with music playing increases the volume somewhat - but the speaker drops back into its normal and quieter position. Gently applying pressure to the cone whilst music is playing very quickly causes distortion and I can feel obvious vibration.


This is probably the feeling you get when you breal your own speakers even further whilst attempting to fix them - so I will await further instructions before attempting again.


I could post an audio / video clip if that would help?
 
Does your amp work properly with a known good speaker?

Yep I have double checked the amp - I'm using a 5W Muse chip amp, and at 50% volume the other speaker is sounding sweet. This bad driver (either mounted or out of its cab) currently just sounds like a bad tweeter.


I did just run a tone generator through both. There is decent audible bass (at that pretty low SPL) down to 38Hz in the good one, and it sweeps through to 1000Hz perfectly. I really hope I can get this thing back up and running !


Did you play the woofer very loud recently?
It was connected to the lounge room AV Receiver for a couple of weeks and there is a good chance someone pushed it hard briefly by mistake. The old "turn down the foxtel via the remote" trick, and then the mrs. puts the volume back up to +25dB on the receiver..... Fine until you come to switch to a different source.... Or something like that.
 
Maybe the voice coil former has been damaged, possibly caused by it hitting the bottom plate due to excessive excursion.

When you move the cone outward and it becomes free, it is probably because the voice coil former is no longer within the gap and has stopped rubbing on the pole piece.

Perhaps you could remove the dustcap and try and look to see if the end of the voice coil former has "peened over", if so you might be able to fit suitably sized shims down within the gap between the pole piece and the voice coil former, to help try to push the "peened over" edge on the bottom of the voice coil former out of the way, so that it no longer rubs on the pole piece.

cheers and good luck, Arthur

PS. if that isnt the problem, you might have to remove the cone assembly to see what the problem is.
If so, unsolder the tinsels, use solvent on the spider (acetone), and the rubber surround should just prise/peel away from the metal basket edge (bit of solvent might help)
 
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