2445 Diaphragm Buzz Help

[maxwedge]

I bought some new Truextents for a pair of my 2445's (I have 4 and 2 not in use) and have a problem with one of the 2445's. The 1st went fine: I cleaned the gaps using masking tape & canned air and then ran a 1k tone while slowly snugging down the screws in a cross pattern. After that I tested from 700hz up to about 15k.

The 1st one no problems, but the 2nd one I would come across one screw that will make it buzz with the 1k tone. This is on the 1st tightening pass. I tried moving the diaphragm around but it didn't help. It's just random as to which screw will make it buzz. Usually near the end of tightening pass.

The driver is very clean so I think wtf!? I got a bad diaphragm?
So I put the JBL diaphragm back in with the same results!
So I've been listening to this thing like this for all this time?!
But then I didn't test it before I took it apart either!

Anyway so I pulled one of my spares out from under the bed and put the Truextent in it and it went smooth as butter, with no buzzing.

So the question is, what do I do next. Visually the gap looks good and I suppose that I can measure it to confirm, but after that I think that is all that will be within my ability to do.
Edit: Actually I haven't found any specs on the gap so the best I could do is make sure it is concentric.

Any ideas?

Scott

[more10]

Check the surface of the driver. If there is something uneven there the diaphragm will be slightly bent.

[maxwedge]

Thanks for the reply.

That makes sense and I could see the diaphragm tweek as the last few screws were lightly snugged down as the buzz started. The surface look real good but I'll have to take a 2nd look.

[edgewound]

I bought some new Truextents for a pair of my 2445's (I have 4 and 2 not in use) and have a problem with one of the 2445's. The 1st went fine: I cleaned the gaps using masking tape & canned air and then ran a 1k tone while slowly snugging down the screws in a cross pattern. After that I tested from 700hz up to about 15k.

The 1st one no problems, but the 2nd one I would come across one screw that will make it buzz with the 1k tone. This is on the 1st tightening pass. I tried moving the diaphragm around but it didn't help. It's just random as to which screw will make it buzz. Usually near the end of tightening pass.

The driver is very clean so I think wtf!? I got a bad diaphragm?
So I put the JBL diaphragm back in with the same results!
So I've been listening to this thing like this for all this time?!
But then I didn't test it before I took it apart either!

Anyway so I pulled one of my spares out from under the bed and put the Truextent in it and it went smooth as butter, with no buzzing.

So the question is, what do I do next. Visually the gap looks good and I suppose that I can measure it to confirm, but after that I think that is all that will be within my ability to do.
Edit: Actually I haven't found any specs on the gap so the best I could do is make sure it is concentric.

Any ideas?

Scott

It's possible that the coil is slightly out of round or has a high voice coil winding. Did you make sure that the terminations to the terminals are aligned with the reliefs in the gap?

[maxwedge]

It's possible that the coil is slightly out of round or has a high voice coil winding. Did you make sure that the terminations to the terminals are aligned with the reliefs in the gap?

This buzz is with 2 voice coils, the original and the Truextent. Unfortunately I didn't test the driver before I took the JBL diaphragm out.

Before I took the JBL diaphragm out I marked the driver as to where the positive terminal lines up with a red pen and I saw those two reliefs but didn't understand their purpose. This driver is one of two in an Ebay buy so I don't know if the phragms were ever replaced before. I'll pull it out and look again and might as well test the other one under my bed, LOL!

Thanks edgewound, to bad you're all the way down in the LA area because some of my old JBLs need some tlc.

[subwoof]

Make sure the phaseplug is level / seated all the way down. Some of the first gen 2445's we got for a big club install used the same phase plugs and throats as the 2441 and a few were not aligned...

That one drove us nuts on the bench...

[maxwedge]

I have it on the bench and am going to recheck it after I take a shower. All 4 of my 2445s are mid 80's with low 30k ser#'s. Are the phase plugs just pressed in?

Thanks

[maxwedge]

The phase plug seems all the way down and the diaphragm is aligned with the reliefs. I rechecked the surface with a magnifying glass and I don't see any protrusions, unevenness or damage to the machined surface.

I'm going to try again to tighten the diaphragm without it buzzing...

Here's a couple pics..

[subwoof]

chances are the machined area that the diaphram sits into isn't perfectly centered. here's how to fix that:

Get a good 90 degree tool edge ( like the side of a wood chisel ) and shave off a little material all around the diaphram's bottom edge. This way you have more room to "adjust" the centering before tightening. Nearly all of the 2445's have required this - in the old alnico days we would enlarge the guidepin holes 1/64 to achieve the same result.

This should do the trick. It's actually rare that all the tolerances align esp when mixing and matching parts from different decades.

This is the biggest reason that JBL insists that these be installed by a service center - if one doesn't fit the center can try another OR do some of these tricks to make sure it performs correctly.

Some of the old LE85's and LE175's were an absolute bitch to work on....

sub

[maxwedge]

Ok I get that.
I've been trying to get it centered right now and find that the diaphragm deffinitly likes to be more over to the negative side and only takes a very small nudge to get the buzz to go away but tightening or loosening a screw just a tiny bit will change it.

I've just got the bare driver with the throat flat on the table with no horn on it and listening to the back side of the diaphragm. Is this how you guys normally set them up?
When I 1st swapped in the Be diaphragms I had my horns on them.

Thanks a lot subwoof

[subwoof]

use a horn installed if possible otherwise a resonance might sound like a "buzz". I used a small horn with a carpet glued to the face to keep the volume down.

[maxwedge]

Ok Thanks. I'll have to go out to the shed and grab a 2380. That's all I have available.
Yeah, I gotta put my ear plugs in when doing this lol.
I'm going to mod that diaphragm now.

[maxwedge]

She's all better now and thanks to all who replied.


Comparing the Be and Ti diaphragms now

[Mr. Widget]

I think you could fit ay least one more horn and driver in there.


Widget

[subwoof]

nah...those are little book shelve speakers....