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Need help to isolate/eliminate speaker cab buzz

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Postby katmetal » January 5th, 2009, 4:46 am

On my 2 x 10 bass speaker cab, (The speakers are 4 ohm ea., wired in series) I am getting buzzing when I am playing the lower notes. (5 string bass) I can go thru the "trial & error" of locating the source myself, by isolating 1 speaker, making sure they are tight, etc. But I figured some of you guys may have already dealt with this & could point me in a direction to save some time.

Questions;

1. The speakers are mounted directly to the mdf board on the outside of the cab; that is, they drop in from the outside. There is no foam under the speaker, to act as a cushion between the speaker & the board. Should there be?

2. The speakers are just mounted w/ wood screws; is that sufficient, or should they be securely bolted in? I don't know how the "pro" cabs are set up.

It is my gut feeling that the speakers are vibrating against the board that they are mounted to, but as you well know, these things can be hard to pinpoint sometimes. I hadn't really gave it much thought before, since I mostly worked w/ combo amps in the past, but it looks funny to watch series wired speakers in action, as 1 is "pushing", while the other is "pulling".

Makes me feel that they are out of phase...
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Postby Moonrider » January 5th, 2009, 6:11 am

katmetal wrote:
1. The speakers are mounted directly to the mdf board on the outside of the cab; that is, they drop in from the outside. There is no foam under the speaker, to act as a cushion between the speaker & the board. Should there be?

2. The speakers are just mounted w/ wood screws; is that sufficient, or should they be securely bolted in? I don't know how the "pro" cabs are set up.

It is my gut feeling that the speakers are vibrating against the board that they are mounted to, but as you well know, these things can be hard to pinpoint sometimes. I hadn't really gave it much thought before, since I mostly worked w/ combo amps in the past, but it looks funny to watch series wired speakers in action, as 1 is "pushing", while the other is "pulling".

Makes me feel that they are out of phase...


1) The speakers ARE out of phase. They should be going in the same direction. Revers the leads on one of 'em.

2) The baffle's MDF? Check the mounting screws to make sure they're tight. If any of them seem "stripped" and won't tighten, you may need to dismount that speaker and rotate it a bit so you can make new screw holes for a short term repair. Then look at replacing the baffle with plywood or some type of appropriately sized solid wood board for the long term repair. The combination of vibration, loose screws, and relatively soft MDF can "wallow" out a screw hole amazingly fast.
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Postby katmetal » January 5th, 2009, 11:03 am

1) The speakers ARE out of phase. They should be going in the same direction. Revers the leads on one of 'em.

I thought that as well, but they are wired in Series, remember.Pos. of one speaker goes to the Neg. term. of the other. It I switched them, they would then be out of phase, according to the wiring websites; Look at this site, go down the page to the heading -
2 Speakers - Series Wiring; In Phase
It shows the wiring pos. to neg. as being correct.

http://colomar.com/Shavano/spkr_wiring.html

) The baffle's MDF? Check the mounting screws to make sure they're tight. If any of them seem "stripped" and won't tighten, you may need to dismount that speaker and rotate it a bit so you can make new screw holes for a short term repair. Then look at replacing the baffle with plywood or some type of appropriately sized solid wood board for the long term repair.
The cab. is prebuilt, covered. Are you saying to remove the front & screw/glue plywood to the front for the speaker to mount into?

Sorry, I don't quite understand, maybe a bit more clarification.

Thanks for the reply.
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Postby Moonrider » January 5th, 2009, 6:56 pm

katmetal wrote:
1) The speakers ARE out of phase. They should be going in the same direction. Revers the leads on one of 'em.

I thought that as well, but they are wired in Series, remember.Pos. of one speaker goes to the Neg. term. of the other. It I switched them, they would then be out of phase, according to the wiring websites; Look at this site, go down the page to the heading -
2 Speakers - Series Wiring; In Phase
It shows the wiring pos. to neg. as being correct.

http://colomar.com/Shavano/spkr_wiring.html


Have opened the cabinet up and verified the wiring is correct? It's also entirely possible that one speaker may have the terminals marked wrong. I've run across that more than once.

One thing I know for a certainty is that all speakers in a multiple speaker configuration should be excursing and recursing ( moving ) in the same direction. If one is NOT, then that speaker is 180 degrees OUT OF PHASE with the other. Being wired in series or parallel shouldn't have any effect on the phase if it's done properly.

katmetal wrote:
) The baffle's MDF? Check the mounting screws to make sure they're tight. If any of them seem "stripped" and won't tighten, you may need to dismount that speaker and rotate it a bit so you can make new screw holes for a short term repair. Then look at replacing the baffle with plywood or some type of appropriately sized solid wood board for the long term repair.
The cab. is prebuilt, covered. Are you saying to remove the front & screw/glue plywood to the front for the speaker to mount into?

Sorry, I don't quite understand, maybe a bit more clarification.

Thanks for the reply.


It surprised me that the baffle would be MDF rather than sturdier plywood or solid wood. Most cabs I'm familiar with use that .
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Postby katmetal » January 6th, 2009, 12:49 pm

Have opened the cabinet up and verified the wiring is correct? It's also entirely possible that one speaker may have the terminals marked wrong. I've run across that more than once.
Well, you were correct; the speaker terms. were labeled wrong! I tested polarity w/ a "C" cell, & 1 of the speakers was incorrectly marked.

Guess that took care of that problem anyway. Now to track down the buzz.
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Postby Moonrider » January 7th, 2009, 6:38 am

katmetal wrote:
Have opened the cabinet up and verified the wiring is correct? It's also entirely possible that one speaker may have the terminals marked wrong. I've run across that more than once.
Well, you were correct; the speaker terms. were labeled wrong! I tested polarity w/ a "C" cell, & 1 of the speakers was incorrectly marked.

Guess that took care of that problem anyway. Now to track down the buzz.


If fortune smiles on you, correcting the wiring took care of he buzz. If not, check and make sure all the screws are snug. The baffle itself may be screw mounted. If there's casters on the cabinet, make sure they're firmly attached and not rattling in their mounts. Even check the jack plate and jacks. In short, put a screwdriver or a wrench on anything that could possibly loosen up.
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