Ampeg 6x10 speakers have buzz when turned up

[soulpurpose]

I bought a SVT610 speaker cabinet, but the seller reported a buzz at top volume. Turns out is buzzes bad at even medium levels, especially at low tones. I originally used a Behringer amp head 125 W, and thought it may be overloading the amp. I bought a SVT PRO 3 and it does even worse. It sounds like some speakers are worse than others...but hard to tell. My question is...can I bench test the speakers, or ohm test them? Is is possible the crossover network is bad? Who has expereience with this, before I take it to a shop and spend more than I paid already, or start replacing parts blindly.

[Enzo]

All the speakers work, even if they buzz, right? SO ohm tests will tell you nothing. You could pull each speaner and mount it to something and test drive it, sure. If the speaker buzzes bad enough, you could even sit it on the bench alone and drive it.

Crossover? usually any crossover in a bass cab only serves the tweeter. The woofers run full range. In any case, the woofers would be wired together, so anything affecting one will affect them all.

But you need to determine just what is buzzing. Are you sure it is a driver buzzing and not the cab itself?

Apply a signal that makes the buzz. Just loud enough. Now roll up a magazine or use the tube from paper towels. Hold it up to your ear and aim ot around the speakers. It will work like a stethoscope to pinpoint the sounds. When you find which speaker/speakers is buzzing, then you can deal with it.

Male sure the wires are not touching the rear of the cones inside.

You can remove individual drivers, but they have to come out. Just removing the wires is not enough. The acoustic pressures from the other drivers will move the unwired ones. So they can still buzz with the wires off.

If it is not a driver, try pressing hard on various surfaces of the cab. Put your hand on the side panel and push in. Push down on the top. Remove the grille. Rock the cabinet up on one edge, now the other, even balance it on a corner. DOing this lets the cab flex a little, alters stresses in it. If doing this affects the buzz, it points to a cab buzz, not a driver.

Make sure the handles are tight and not buzzing. Check the jack plate.

[soulpurpose]

Good things to check out

All good and reasonable things for me to check. Yes all the drivers work. I will get back to the cabinet this afternoon to check these things out. As far as crossover, I was thinking that the woofers may have an induction coil to block hi frquencies, but have not opened the cabinet back yet. It does have one mid range horn. I'll post by discoveries later. Thanks.

[Steve Conner]

Argg, I feel your pain, I hate bass cabinets that buzz and rattle.

If I was in your place, as well as all the stuff Enzo recommended, I'd remove all six woofers, check each one for voice coil rub (move the cone in and out gently by hand, make sure that it moves smoothly and silently, any scraping noise means the voice coil is damaged) as well as using an ohm-meter to make sure they aren't burnt out. While the woofers were out, I'd look carefully inside the cabinet for loose nuts and bolts, things that got in there that shouldn't, or wires that might be rattling around.

As a shortcut to see if any of the drivers are burnt out, measure the resistance across the speaker jack with an ohm meter. It should read a bit less than the nameplate, eg, if it says 4 ohms you should read about 3.5. A burnt-out driver will make it considerably higher.

I can't see how the crossover would cause buzzing, unless it had fallen off its mountings and was rattling around the cabinet.

[Enzo]

Most instrument cabs run the woofer full range, the crossover is only for the horn. So the crossover would only affect said horn.

It is hard sometimes to press the cone in evenly.

A better rubbing voice coil test is to pull the driver and hold it up in front of your face. Hold it by a frame rib, facing away. DO not touch the cone. Now ball up your fist and whack the back of the magnet with the meaty part opposite your thumb. Like you are banging on a door. Officially we would use a rubber mallet, but God gave you a rubber mallet with fingers.

A good speaker makes a little TUMP sound or no sound at all. A rubbing voice coil will make a little flapping sound or a quick rattle sound.

[soulpurpose]

First results are good

Brought amp and speaker home to check out. Had definite buzz. Seemed to be from lower two speakers. I pulled them and checked these two, seemed OK. While reinstalling them I checked again to find that when I thumped a guitar string, the upper four pushed out, but the lower two pulled in! I reversed the phasing on the bottom two and reassembled. Also added two missing speaker screws. All seems well now. Hard to tell for sure, because our living room windows, curio cabinet and assorted knick knacks rattle in the room. Some ended up on the floor. I think the speaker sound is fairly clean. I will test back at our church tomorrow. Thanks to all responses....Mark.

[Enzo]

Missing speaker screws? That alone can cause buzzes.

[Steve Conner]

As far as I know, that thing is really two cabinets in one: a 4x10" sealed cabinet stuck on top of a 2x10" with ports. I'd expect the two sections to respond differently to a transient such as a thump on the strings, so it might look like they were wired out of phase even if they weren't. So you might now have it wired backwards.

For an unambiguous answer you need to use DC: Try applying a 1.5 volt battery (borrow one from a flashlight or whatever) to the speaker jack and make sure all six cones move the same way.

[soulpurpose]

Your correct about the cabinet config. I will test this weekend with DC. It has been used @ 3 live venues this week and seems to sound good. Still bears checking out. Thanks.

[soulpurpose]

Possible out of phase speakers

One reason I also suspect speaker wiring, is that when I got the cabinet, it had an aoutomotive sub woofer in one hole, nothing in the other, and was handed two Ampeg 10" speaker loose, (along with some 10" monitor speakers) I gave th auto woofer to my son (He said it was worth $150) and r-installed the original speakers myself.