JBL 2241H buzz/rattle

[whoaru99]

Fired up the garage system tonight and noticed a buzz/rattle noise coming from one of the 2241H drivers in one of the SR4719X subs. Seems like it's actually more noticeable at (relatively) low level than if turned up a bit more. Pretty confident it's not "blown" so to speak from cranking as it didn't do it previously and the system has not been used even remotely near capacity in the mean time.

Is there anything known to come loose in these drivers from just old age/shit happens sorta thing? They stay in my non climate controlled Minnesota garage year around.

 

[dshoaf]

There's always the risk of delamination of one or more windings on the voice coil bobbin. Here's a good way to figure out if there's really a problem or not:

- Download a frequency generator for your smartphone or PC. I'd suggest Room EQ Wizard, that has this function built into it - and its free!

- Then, hook up the driver to a low power amp and connect the PC soundcard to the power amp input.

- Use the manual control function of the signal generator so that you can choose what frequency to drive the speaker with. See the Help Facility for how to get to it.

- Then, get the cone moving up and down with enough travel to see it move. Use the volume control to get it that way.

- Lastly, vary the frequency up and down. At some point you'll hear the noise or buzzing that you've heard prior but only fleetingly. Zero in on the frequency that makes it buzz with the frequency control.

- Then, using a rubber tube placed to one ear, use the other end as a probe to figure out where the buzzing is coming from around the woofer.

- You may find more than one frequency where the buzzing appears. It will likely be a harmonic of the lowest frequency you detect.

If you find that it is coming from inside the spider or from under the dust cap, you've likely got a loose wire on the voice coil bobbin. The permanent fix is to recone the speaker, if so. That's your worse-case scenario.

Look closely and see if there's some sort of washer or other hardware that was drawn to the magnet/motor system that's lodged in a place where it can cause the buzzing.

Cheers,

David

 

[whoaru99]

Haven't gone that far, yet, but I did pull off the grill and you can hear the noise from that one driver when tapping on the cone.

Pressing on the cone I don't detect scraping/rubbing, but the noise sure seems like it's coming from the VC area/under the dust cap.

I made a recording with cell phone, hopefully it comes through OK. You can hear the distinct thump of the tap followed by the sorta resonant buzzing, for lack of better term.

Recording of noise

 

[SaturationPt]

I had a similar symptom from my NOS 4312As (2213H) playing Deadmau5 STROBE (which makes a pretty good speaker test track). Buzz from one woofer around 600hz (guess), how can this be in a new speaker? Can't replace, ... I was bummed.

Removed the woofer and found that the tinsel was actually touching the woofer frame! I adjusted the terminal where it attached so that there is a little clearance, and all is well.

I hope that your fix is as easy as mine.

There are some woofers that have a damping foam in a hole in the magnet, which can get sucked in as it degrades into bits. I don't know if yours has this, but it certainly can cause many symptoms and problems as it makes its way into the magnet/could air gap.

<<edit>>

Just looked at the back of a 2242H in our sub, no vent. Probably no vent in your 2241H then, so scratch that last paragraph.

 

[whoaru99]

There are three vents on the back of 2241H. They are covered by very fine mesh screen.

 

[Lo-Fidelity]

The spider could be loose. Had a similar problem on some LaScala and it was an easy fix with some epoxy.

 

[elitopus]

Yes 1 center vent in the 2240/2245 and three smaller vents in the 2241/2242.

Does the 2241 have any kind of mass ring under the dustcap?

Have you PM'd GordonW about this? I'm sure in his years of fixing speakers he has seen something similar. He rebuilt my 2242's for me.

 

[whoaru99]

Checked around (as locally as possible) and was quoted about $180 parts and labor for a recone using genuine JBL kit installed by a JBL Service Center. It's a chunk, but probably not bad all in all since even an aftermarket recone kit eats up almost 70% of that for just the parts.

 

[elitopus]

Thats actually pretty cheap for a genuine JBL recone. I called around for some 2225 woofers and it was much more than 180$ each

 

[GordonW]

It is possible that the cone may have slightly warped/sagged due to humidity. If so, then it's time for a recone.

These don't have the foam filters like the earlier model (2240, etc), so that's not the issue, unfortunately. However, that doesn't mean that something else isn't going on inside the dust cap (foreign matter in the coil gap). It might be worth cutting out the dust cap, to see if there's anything obvious going on. Sometimes a careful wipe-down inside the gap with a piece of masking tape, can remove debris. All it would take then, is to acquire and install another dust cap (should be available from any speaker reconer, pretty much).

Regards,
Gordon.

 

[whoaru99]

In consideration of sag, this morning I rotated the driver 180 degrees. Previously, even tapping on the cone of the other driver in the sub caused the noise to occur in the suspect driver. With the suspect driver now rotated 180 degrees that does not happen. I can even tap on the cone of the suspect driver most of the way around and not have the noise, except when tapping firmly in the bottom quadrant.

So, I'm headed back over now to play a bit of music and see what happens.

 

[whoaru99]

After a brief, relatively low output test the noise is not present playing some tunes with the driver rotated 180 degrees. Prior to rotating the driver, it would have made the noise at the level I used in the short test.

So, for now, I think I'm going to put the driver back the way it was then rotate both sub cabinets 180 degrees. The subs have been laying in the current orientation for many years and did not get exercised much at all over that time. Thinking 180 degree rotation for all involved may be a good thing.

Sound like a reasonable course of action?

 

[donprice]

Rotation is very cost effective compared to the alternatives

Hope it works!

 

[whoaru99]

Update.

After the one driver has been rotated 180-deg for about a week now it's still playing clean, without the noise. And, in the tap test described in post #11 re. the lower quadrant, that's nearly all gone too now. Again, don't know that I'd consider it a "fix" but it has restored function at least for the time being.