2235 mystery

[Anthony L100]

I guess this is DIY. I have refoamed the 2235s in my 4430s and hit an unusual problem. I've tried to suss it out before posting but it's a mystery to me. The original foam was intact but powdery, the spiders looked very good, no sag, so ideal candidates for a refoam. The job went very well and I let it all cure for a couple of days. I hooked up the 30Hz test tone and they were perfect. Back into the cabs and a quick listen, everything was fine. I use the 4430s in my workshop and left the 30Hz tone running for a couple of hours to break in the foam. Next day I had a chance for a good listening session , sounded great! After a few hours I noticed a strange noise from one of the 2235s, sounded a bit like a thin wood panel rattling or buzzing on a certain drumbeat. Not a bass drum, probably a kick drum?? (a little higher). I removed the unit and tested it in isolation and yes, definitely a problem. I inspected the spider and the new surround, everything looked OK. I then tried a 20Hz and a 30Hz signal to Xmax with no noise at all. Today I re-installed the driver, played the same track and it was fine... wierd. Then the same problem occurred again this evening . I use a S/S Rotel power amp 300+300 well within limits. Any ideas please guys?

[norealtalent]

This probably, and hopefully, isn't the case for you but worth checking. I had a similar symptom with a pair of 4333 one time. I did a recone and it all checked great until I installed it. On certain songs and with pretty good volume, I got a noise that I could not identify. I took the woofer back out, did all the checks, stuck it back in and it was fine...until I hit some similar notes at similar volumes. It ended up being a loose front baffle.

[Robh3606]

I had the same thing happen to me on a new recone. I sent it back, it was fine for months and then every once in a while it will come back??? A gentle tap on the cone and it goes away. The only thing I can figure is there is something loose in there. Mine was not a loose baffle as it would occur outside the box.

Good Luck Rob

[edgewound]

Sounds like maybe the input wires from the crossover are smacking the back of the cone when installed in the cabinet, or the voice coil tinsel leads or terminal solder lugs are making contact with the cone. Could be the mass ring has become de-bonded from the voice coil collar.

Could also be a metal chip has migrated into the gap vicinity. Sometimes they will move into and away from the gap. Can't do much about it short of removing the dust cap and find ing the chip.

Then...there's always a recone....

[Mr. Widget]

Doubt it will help, but try mounting the woofer upside down. You may have a very slight VC rub.

...or you may have a loose mass ring and hadn't noticed it before. Checking and fixing that will require a dust cap removal and replacement... unless you are very sure handed the glue line will never look quite the same.


Widget

[Mr. Widget]

Sounds like maybe the input wires from the crossover are smacking the back of the cone when installed in the cabinet, or the voice coil tinsel leads or terminal solder lugs are making contact with the cone.

I've had that... certainly worth checking... if that's the problem it's an easy fix.


Widget

[Anthony L100]

Thanks for all the replies

Definitely not the baffle as it happens outside the box.
I wondered if there was some tiny contaminant within the V/C area that moved as this is intermittent. I may try to push the foam/gauze dust filter away from the polepiece and see if anything drops out.
I have checked the input leads which are well clear, but I will next check the tinsel leads and lugs for proximity.
I did not consider mounting it 180 deg round, but I certainly will now, although the cone moves freely to both extremes.

As it's nearly midnight here, I won't get the chance to test 'till the morning, but I will report back.

I'm glad I asked now as it seems a few have had similar problems. I guess if I can't resolve this externally it's gonna be two new cones which cost an arm an' a leg over here but it will be done because they're worth it. Any more ideas are very welcome. Thank you. Tony.

[Anthony L100]

Could be the mass ring has become de-bonded from the voice coil collar.

Could also be a metal chip has migrated into the gap vicinity. Sometimes they will move into and away from the gap. Can't do much about it short of removing the dust cap and find ing the chip.

Then...there's always a recone....

Yes Edgewound, this sounds favourite, which maybe is the best I can hope for as it will only require removal of the dustcap to verify. As I would only recone them as a pair, i'm hoping it's a bit of crap in there.

[jbl_man_uk]

I had a pair of reconed K140s, one of them did that very same thing Tony,was really iritating....it turned out to be a tiny peice of debris from the old coil assembly/former had found its way into the cast magnet "pot" at the back,and was rattling at certain frequencies.Grrrrrrr.

[pelly3s]

i had a driver do that one time and the problem was a loose foilcal. it was a faint sound but it was there. there could be so many problems and i think everyone covered what it could be

[edgewound]

i had a driver do that one time and the problem was a loose foilcal. it was a faint sound but it was there. there could be so many problems and i think everyone covered what it could be

Ya know pelly3s...that reminds me of another possibility. If it has a foilcal, there is a small round screen that covers the rear vent hole... sandwiched between the foilcal and the backplate. Sometimes it can come loose and rattle too. Long shot... but worth a look while poking around.

[Anthony L100]

Not the foilcal Pelly3s (unfortunately) i've checked all the peripheral stuff. I'm leaning toward the debris theory Ian, but didn't want to remove the dustcap until all avenues had been explored as other than this annoying problem these drivers are mint. I have been playing them today and the buzz remains. I will remove the cap tomorrow as I have now checked all of your suggestions without surgery. If I can remove the cap cleanly enough, fix the problem and replace the cap with a perfect glue line, then OK, I may be able to live with it. Otherwise, it's gonna be two new cones£££. I will let you know. Just spotted your post Edgewound, these 2235s have a piece of foam at the upper (V/C) end of the vent hole which is attached properly. Tony.

[edgewound]

Are you sure they're torqued down evenly and not too tight,and the baffle is true?

[Anthony L100]

Are you sure they're torqued down evenly and not too tight,and the baffle is true?

I've tried the errant driver in the other cab with the same result. I've also tried the good 2235 in the other cab and it's fine, so I don't think it's a torque/baffle problem. I guess I suspected all along that I would have to go "inside" to find the problem...

[edgewound]

I've tried the errant driver in the other cab with the same result. I've also tried the good 2235 in the other cab and it's fine, so I don't think it's a torque/baffle problem. I guess I suspected all along that I would have to go "inside" to find the problem...

Well....I hope you're able to kill that gremlin.