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JBL 4719A noises

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Richard Rempes:
Hoping someone can help with subwoofer rattling issue. I have four 4719A cabinets loaded with original 2441 8 ohm drivers. Half are reconed, half are original. Obviously these cabinets are pretty old and I'm not the original owner, so I'll guess on the safe side and say they've seen quite a bit of use. Last year we noticed a very un-musical hard (presumably) wood-on-wood slapping sound on BD hits and full-on rattling with the lowest of bass guitar/synth notes. This is happening with all four cabinets, regardless of the original and/or re-coned 2241s loaded in them. I pulled every driver and checked for VC rubbing - all seem OK. We finally tried an unorthodox test that involved me "bear hugging" the cabinets while they were making this noise from the back and compressing my body as tight to the enclosure as possible. The hard slapping/rattling stopped. All four yielded the same result. On to tearing the drivers and the back panel insulation out to inspect the internal 2x4 bracing. Everything appeared tight - even removed every accessible wood screw to verify boards were glued to the back panel. I find nothing loose, so my decidedly uninformed conclusion is that there is insufficient bracing in these cabinets. Have any of you experienced this issue with these older 4719A cabinets and if so, what did you do to rectify the problem? Add bracing? Fix some weird thing that happens with these cabinets that is not obvious? Scrap the cabinets and put the drivers into something lighter and better sounding? I've attached a screenshot from a Sketchup drawing I made that shows the bracing with the back off.

Steve-White:
Drivers can rattle, enclosures can rattle.  Most likely the plywood in the cabinets has dried out and de-laminated over time.  Maybe from moisture as well.

Rather that try and explain how to get loose plywood lamination's back together (which I would undertake in my shop without hesitation) and then get 25 other recommendations.

I'll give you this - pull the drivers out and grills.  Rap them with a rubber mallet to be sure.  Call around to local cabinet shops and have a pro work on them for you.  No big deal to repair, maybe coat a paint on the inside when repaired.

Rock on.

Paul G. OBrien:
The removable rear panel and 2x4 bracing is a red flag to me, I don't know for certain but that doesn't sound like an OEM JBL cab to me. These things should be made from baltic birch so the cab alone should be about 100lbs.

Steve-White:

--- Quote from: Paul G. OBrien on August 07, 2021, 05:24:49 PM ---The removable rear panel and 2x4 bracing is a red flag to me, I don't know for certain but that doesn't sound like an OEM JBL cab to me. These things should be made from baltic birch so the cab alone should be about 100lbs.

--- End quote ---

You're probably right - the OEM JBL stuff is pretty bullet proof.

Helge A Bentsen:
FWIW I bought 12 subs at a auction last year, two of them made a lot of noise when I tested them.
Initially suspected the drivers, upon further investigation I found that the baffle was loose in both of them.
Tightening them up with glue and screws solved this.

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