Blown speaker???

[spook123_uk]

Hi all,

I've just (today) changed all my Celestion G12C's in my Marshall 4x12 over to g12h's. I've got 2 2nd hand heritage ones and 2 rola blackback ones from the 70's.
It might be my ears but one of the heritage ones seems to be slightly quieter than the others and gives a slight buzz on the bass notes as they tail off.

I've only had chance to try this at relatively low volume and can't do a vol test with my Marshall 2203 until I get to a gig on Friday.

I've re-seated the speaker and re-flowed the solder on the wires.. Is there anything else I should be checking?
Also, given that this is more of an annoyance at the moment, are there any real dangers with gigging it at high vol on Friday?
If it is bust, could I get away with running 3 x 30w 16ohm g12h's temporarily with 1 x 16ohm 25w 12c?

I did do a quick test last week with the heritage's before I acquired the blackbacks by mixing with 2 of the g12c's and didn't notice this then

Thanks,
Rich

[ICBM]

Try either varying the tightness of the mounting screws, or rotating the speaker into a different orientation (swap it with the other one if the wires won't reach), and see if that cures it. Did you have the same speakers in the same positions in the cab when you tried it earlier?

I had one recently with the same problem, when rear-loaded with the terminals at the top it buzzed exactly like that, and I thought it was knackered - which was puzzling because it had worked fine up til then in another amp - but when put back in the other amp, front-loaded and with the terminals at the side, it worked perfectly again.

I can only assume it's a manufacturing defect so the voice coil is not centred correctly in the coil gap, so the combination of the weight of the magnet hanging in a particular direction and a slight frame distortion caused by the mounting will make it rub. Don't use it with it rubbing, it will kill it fairly quickly.

I also came across one with a cold solder joint between the voice coil and the cone braid, leaving the speaker dead and unrepairable without a re-cone. Not impressed, given what they cost. I've never had a problem with a Chinese one...

Yes, you can certainly use a mixture of speakers to get you through if you have to.

[spook123_uk]

Thanks for that... I'll try moving it and see if it cures... In the short term, aside from any sonic differences, would there be any reason why I couldn't drop a 25 watt g12c back in it's place whilst I sort?

[spook123_uk]

Sorry.... Only just read the bottom line of your post!!! ignore question..

[ICBM]

That's because it wasn't there until I edited it .

[spook123_uk]

I've just had a quick check... They were in the same positions as earlier. I've removed the pair and turned them upside down to I can get at the front of the cone.
I read somewhere that you can check for rubbing by pushing the centre of the cone. If I do this, I can hear nothing from the good one and the suspect on is a slight rubbing noise in and out.

[ICBM]

I read somewhere that you can check for rubbing by pushing the centre of the cone. If I do this, I can hear nothing from the good one and the suspect on is a slight rubbing noise in and out.

Be careful, because these cones are so pliable that you can twist them slightly when you're pushing and make it seem like it has a rub when there isn't really one, but that doesn't sound good.

I'd try it in all four orientations in the cab, on it's own - just at fairly low volume of course! - and if it does it all ways round, it's knackered unfortunately.

[spook123_uk]

Tried all 4 ways round now and it does it on all. Some ways round are more noticeable then others but basically, it is a bbmmmph (almost like an artificial distort) sound that is there on the lower notes as they attack in and on the ring out a little (e and a string).
I've temporarily swapped it out for a G12C and all is clear again so it looks like I'm on the lookout for another speaker again!

Cheers

Interestingly (at low volume) the 70's rolas I have in there appear a lot more responsive than the heritage that is left in there.. Could be that they are properly worn in and in the top of the 4x12 though. Guess I'll find out when it's at volume!

[TheEvilForcesOfSkeletor]

if its rubbing by hand its not a good sign generally speaking. but could just be dirt or an off center cone, rather than being blown.

the first thing I always check on a buzzing/rattling speaker is the spider support. its a less common problem on modern speakers because they use decent glue nowadays, but the blackbacks are definitely contenders.

go all around the edge and brush the tip of your finger upwards and see if it lifts off anywhere. if it does, thats your problem. it needs to be glued down all around.

also check for gaps in the glue around the dust cap, or small metal objects stuck to it anywhere.



very common problem on the early greenbacks, blackbacks etc. that old glue just hasnt stood the test of time on a lot of speakers.