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help! JBL 4312C distortion noise on left channel woofer.

Rai Chen

Rai Chen

New Member
Recently I bought a pair of used JBL 4312c in a decent shape. In that seller’s listen room it sounds amazing with tube amp.

and yet after I got back to my place, I did found distortion noise on left channel woofer, it feels like the sound being hold back and can’t not perform it it’s best, meanwhile the right channel sound totally okay.
especially during some songs like Miles Davis “So What”.

I try to troubleshooting by switch right speaker to the left.
I try using a different amp (phono mode in Marantz Pm 6007),
or using cable to connect streaming (Tidal).

it still had the same problem.

and before this one I had AE Acoustic Energy AE100, never seems to had a problem like this.

my equipment are
Pre amp: Schiit Mani
Amplifier: Marantz PM 6007
Turntable: Rega P3
Speaker: JBL 4312c

This problem be bothering me for days, please help!
 
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Did you try swapping woofers to see if it followed the woofer or stayed with the same cabinet? That would prove whether it’s the woofer or a crossover issue.

Does the woofer that sounds different move freely when you push on the cone?
 
elitopus said:
Did you try swapping woofers to see if it followed the woofer or stayed with the same cabinet? That would prove whether it’s the woofer or a crossover issue.

Does the woofer that sounds different move freely when you push on the cone?
Click to expand...

it that case it's probably the crossover issue cause it's happened on the left channel only, I trying to push on the cone last night, there's a lit bit of whooshing sound(probably a little bit coil jammed?), I think gonna take out the woofer and go for repair tomorrow..

thanks!
 
Rai Chen said:
it that case it's probably the crossover issue cause it's happened on the left channel only, I trying to push on the cone last night, there's a lit bit of whooshing sound(probably a little bit coil jammed?), I think gonna take out the woofer and go for repair tomorrow..

thanks!
Click to expand...

Try rotating the woofer 180 degrees in the cabinet. Then check again for distortion before you bring it in for repair
 
I was just trying to think of something that would have happened to them between the sellers house and the OPs. If they truly didn’t have any issues when he bought them.

Things I can think of

Shifted magnet
Crossover component coming loose
Something else coming loose

If I understand what the OP is saying, he swapped woofers and the problem stayed with the same cabinet.
 
elitopus said:
I was just trying to think of something that would have happened to them between the sellers house and the OPs. If they truly didn’t have any issues when he bought them.

Things I can think of

Shifted magnet
Crossover component coming loose
Something else coming loose

If I understand what the OP is saying, he swapped woofers and the problem stayed with the same cabinet.
Click to expand...

Did you place the speakers in a different alignment? Sideways instead of upright?
 
Does the 4312C even have any crossover components going to the woofer? Many of those little 3 ways just let the natural roll off of the woofer do the job.

Could be gunk in the voice coil gap or bubbled varnish on the voice coil wire itself. I would expect suspension sag to cause noise, but reduced output seems to point to something binding in the gap.

Getting the surround and spider loose to inspect will be tricky, you'll have to reuse them both as JBL almost certainly doesn't support that speaker any longer.
 
These internal foam filters can ( & should ) be removed via careful vacuuming//suction ( using an attachment meant for computer cleaning > which limits the overall suction ) through the back magnet vent ( if the foil-cal is present & in the way it needs to be removed first via some heat and a putty knife )..

:)
 
elitopus said:
I was just trying to think of something that would have happened to them between the sellers house and the OPs. If they truly didn’t have any issues when he bought them.

Things I can think of

Shifted magnet
Crossover component coming loose
Something else coming loose

If I understand what the OP is saying, he swapped woofers and the problem stayed with the same cabinet.
Click to expand...

the only thing that happened, between the sellers house and my place is I put it in my car with the woofer side up and put it in flat surface.
I did rotating the woofer 180-degrees, and it do the trick (like 70% better?) I'd wonder the longer it gets would the gravity make it better?

but I can totally see that blog has a valid point, it could probably causing the problem too, which in that case the seller offer me to go for a repair and he'll pay for it (what a nice guy), I think I gonna have to wait and see for a few more days.

again, thanks everyone's help! it's really helpful advice!
 
Rai Chen said:
which in that case the seller offer me to go for a repair and he'll pay for it (what a nice guy),
Click to expand...

Unless you bring it to a repair tech who is intimately familiar with classic JBL's, I would be worried about a hack job.

Your posts aren't very clear about what you have done so far to isolate the problem.

Did you swap woofers between the two cabinets to see if the problem followed the woofer?
 
Last edited:
Mr Boochie said:
So, you are talking about a recone job, to fix the gooey mess?

Thanks!
Click to expand...

I don't think there are any recone kits for that woofer, he'd be tasked with removing the surround and spider carefully enough to reuse, and then hope the voice coil is undamaged.
 
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