J12L Rattles and Buzzes

[nola50]

I built a pair of J12Ls with Melded Piezos so I could use them for PA and Bass. Last night I took one to a gig and it buzzed and rattled. I was using a Gallien Krueger RB400 bass amp, which is 200W RMS, running it half open with a Gibson Thunderbird. We were perfroming outside and had the cabinet on the floor. On low certain notes, it was bad. It's got a Eminence Kappalite 3012HO Neo for the woofer.

Whatever ideas you have are appreciated. We are playing again tonight at a local spot for Cinco de Mayo event.

Thank you, in advance, for your contributions.

[Bill Fitzmaurice]

Buzzes can come from a number of sources, ranging from a damaged woofer to loose woofer mounting screws to a loose joint to unsecured grille and a dozen others. To track it down sweep a sine wave tone, which will reveal whatever is doing the vibrating.

[Seth]

Firstly, does the other cab buzz too? If not, use that one tonight. If it also buzzes, do you have another cab you can play through to verify the issue isn't the bass or amp? You may shrug it off, but many many many times it's not the speaker itself and I'd hate to send you on a goose chase in the cab when the issue lies elsewhere. Definitely verify this first. You wouldn't be the first around here that thought there was something wrong with the speaker, when there wasn't. Keep in mind, even a dirty 1/4" plug in the guitar/amp can make noise at certain frequencies. If you wiggle the guitar cord and it crackles, clean the jack... guitar end, amp end, or both. If both cabs buzz, I'd be leaning toward it not being the cabs.

Once you've verified it isn't the bass guitar, amp, or cord, play a sinewave through the cab and change frequencies until it makes noise. It can help to find the frequency if you know what notes it buzzed on last night. Google the fundamental frequency of that note, start there then change the frequency to the next harmonic until it buzzes. Example: If it was Open E String, play 41Hz, 82Hz, 123Hz,164Hz, 205Hz... just keep adding the fundamental to the frequency last played until it buzzes. Otherwise, just do a frequency sweep. Then, while it's buzzing, listen through a piece of tubing/hose. One end to your ear and move the other end around the cab listening for where it's loudest. You might not even need to tubing, might just be able to put your ear to the cab and locate where the noise is coming from. Once you get the general location, investigate. If you can't locate a hot spot, turn the volume down to where the noise is just barely present and pull the access panel. Is the noise still present or did it go away? Double check all the driver fasteners, give all the wood parts in there a wiggle. Anything loose?

If you can't get the noise to occur with the sinewaves, go back and double triple check everything that isn't the cab.

[Seth]

Here's a sweep generator. I'd sweep 40-400Hz over 60 or more seconds to help find the frequency.
https://onlinetonegenerator.com/frequen ... rator.html

[nola50]

Using an iPad app, f generator, has been a boon. Here's what I've found.

The entire back is vibrating at low frequencies. It's better if I hold my hand on it.

I'm checking the mounting frame and the 1/8" back panel itself to see what's up!

[Bill Fitzmaurice]

1/8" back panel?

[nola50]

Yes.

[Bill Fitzmaurice]

It's supposed to be 1/4", as are all the parts except the bent horn sheaths.

[nola50]

I'll make the change. The flat pack I got had all pieces 1/8".

Also the center post in the melded array is what is also buzzing. Wherever I press it, it will stop. What to do about that picke?

[Bill Fitzmaurice]

Whoa. That's not right.
As for the post it can only buzz it it's not fully glued in place. BTW, outdoors is a bit much for bass with one cab. I'd use both of them.

[Seth]

My guess is it's 1/4", there's no way that cab could be made of 1/8".

How many screws are holding the access panel on and did you use gasket tape all the way around the flange?

You can dribble a little thin hobby cement on all points where the diffuser ("center post" as you put it) contacts the piezos. Then hold it tightly in place for a minute or two while the glue does it's thing.

Tamiya extra thin cement

Alternately, you can try using acetone or MEK if you have some already, might do the job. Just a drop on all the connection points.

[nola50]

Yes, the cabinet is 1/4 inch. There are 8 bolts on the back panel with gasket tape. No air comes out the back when testing.

Using it last night was not much better. Just about any note on the low E string farts out running at half volume. Other than that, the cab sparkles with great punch.

I wonder if I should put it in in a different cab?

[Bill Fitzmaurice]

Eight bolts isn't enough. There should be a fastener every four inches or so, which comes out to fourteen to sixteen fasteners. Another potential place for buzzing is inadequate fastening of the braces to the back panel. Gaps in the adhesive can result in the braces buzzing. I use a J12 Lite with my bass, there's no buzz whatsoever.

[nola50]

I have obviously made a mistake on rear panel bolts! I’ll make new back panels for both to accommodate more bolts.

I’ll patch the buzz in the meld diffuser.

What about the farting on the “E” string? I’d certainly like it stop. I’m hoping for a tighter sound there as well as the other strings are.

Thanx for the feedback, gentlemen!

[Bill Fitzmaurice]

If the E string farting is from the driver that indicates over-excursion, which is caused by too much bass EQ. As for using bolts on the rear panels, I never use bolts, always screws. I don't see the need to replace the panels.