Fixing a Rattle without starting over

[ADG]

I just completed my first project, a cabinet for my Bass guitar and I find that for notes below the low G (49 hz) the woofer rattles.

My box is made from 3/4' marine grade plywood 14.75" x 23.5" x 15.75", approximately 2.45 cuft. For the ports I have two, 3"dia 5.8" long.

I have two drivers, an eminence 12" Delta 12LFA and an eminence alph8MR with a 2 way crossover. The box is stuffed with 2 lbs of Acoustastuff.

The box is solid and the drivers held in plase with 3/4" #8 screws

Is there anything I can do short of starting over, perhaps tune the ports?

(If you read this in the Music forum sorry for the duplication, I realized after the fact it probably belongs here)

[wes-ninja250]

Have you figured out *what's* rattling?

Idea: grab a tape recorder (or a friend) and feed a bunch of low Gs at the amp. Stick some earplugs in your ears so you can get nice and close without damaging your ears. Push on things 'till the rattle goes away. Then figure out how to fix it.

If you're lucky, it might be the woofer shaking against the wood... in which case you might be able to fix it by mounting it with more pressure... either a gasket ring or maybe some machine screws with T-nuts.

Wes

[rabbitz]

Just check the ports are not chuffing severely and at times can sound like a rattle.

I'm not sure how much stuffing 2lb of Acoustastuff is, but you shouldn't need much if it's for bass. Normally you would only need some on 3 walls, say back, bottom and 1 side about 1.5" thick.

[ADG]

Thank you both. the rattle is coimg from the woofer cone itself.

The acoustic fill ultimately fills 2/3 to 3/4 of the box.

In my ignorant newbe view it sounds like there is not enough back pressure for the low notes.

[ShinOBIWAN]

Originally posted by ADG
Thank you both. the rattle is coimg from the woofer cone itself.

The acoustic fill ultimately fills 2/3 to 3/4 of the box.

In my ignorant newbe view it sounds like there is not enough back pressure for the low notes.

Sounds like the driver isn't upto the task. The knocking is almost certainly the pole piece bottoming out.

[wigginjs]

Just a thought, I didn't hear you mention glue. You may have an air leak on one of the seams of your box. If this is the case it's an easy fix, just add some caulk to the inside seams of the box. This generally doesn't sound very "rattleish", but I just thought I'd throw it out there.

[Cal Weldon]

Originally posted by ADG
My box is made from 3/4' marine grade plywood <snip>

The box is solid and the drivers held in plase with 3/4" #8 screws

What size screws?

Can you describe the rattle/buzz/hum/knocking sound a little more. If it's a kind of fuzz sound it may be the a problem with the coil rubbing.

Cal

[wintermute]

I don't have access to my normal moddeling tools, but from what you have given, and an applet I found on the web, I think the tuning freq of your box is around 43Hz..... you maybe playing notes that are at or below the box resonant freq, which is somewhat of a no no for a vented enclosure. effectively the cone will be flapping about uncontrolably going past it's excursion limits.

I'm surprised at the relatively high fs for this woofer.. 45Hz seems rather high for a 12".... note the datasheet says usable freq range is 45Hz to 3Khz you probably need to limit it to that, maybe put in a high pass filter at 45Hz or just don't play anything lower than 45Hz....... probably not what you wanted to hear

Tony.

[ScottG]

Originally posted by ADG
the rattle is coimg from the woofer cone itself.

Though it could be any number of problems I find that low freq. freq.-specific buzz/rattle is usually induced by a failure of the diaphram connection to the surround (aka a glue problem), or sometimes in the case of an acordian surround a failure of the surround itself (rubing against itself). The best way to check for this problem is playing the annoying freq. at moderate volume and listening closely to the driver to hear where the buzz is coming from.. then placing your thumb against the surround area where the problem seems to be comming from to mechanically dampen the problem. If it reduces the buzz then thats your problem. The best solution would then be to replace the driver. Alternativly you could try dampening with something like a silicone caulk in the problem area.

[ADG]

Originally posted by ScottG

. . . sometimes in the case of an acordian surround a failure of the surround itself (rubing against itself). . . .

I took a closer look and it does seem as if the sound is coming from the accordian surround rubbing itself. Does this mean I choose the wrong driver or should try and get it replaced by the manufacturer?