PA feedback issue

jazzbender · December 17th, 2007, 09:43 AM

I rehearse with a small group in a 15 x 20 basement that has painted block walls. The problem we're having is that if we turn the Yorkville 100W mixer amp up loud enough to hear the vocals, we get terrible feedback. We're not playing our guitars excessively loud, so we don't want to turn down. The mikes we use are Shure CL588 Unisphere B and a Radio Shack uni 33-3002. One of the guys suggests we hang carpet on the wall, and another says that won't help.

Any suggestions?

woodman · December 17th, 2007, 11:01 AM

any sort of acoustic treatment will keep sound from bouncing around into mikes where it doesn't belong. but have you tried EQing?

Tim Armstrong · December 17th, 2007, 11:27 AM

Headphones. Run your mics into a mixer, run the mixer into a headphone amp, wear headphones.

Or, reconsider turning down your amps and if you have a drummer, have him use bundle sticks rather than drumsticks. Band rehearsal is a time to really listen, to work on the little things, and lots of volume is the enemy of actual hearing.

Putting up some blankets on the walls might help deaden all the reflections...

Tim

mark norwine · December 17th, 2007, 11:52 AM

Take the PA speakers off the stands & put them at your feet as if they were monitors......in reality, that's what you are using them for, anyway. They won't need to be as loud, and your problems will diminish.

Been there...done that.

Schnauzer · December 17th, 2007, 03:07 PM

Woodman nailed it. You must use a multi band EQ and "ring out" your sound for a given room. This proceedure will identify the offending frequencies. As a room fills with bodies things may change so you may have to adjust.

Good luck,

Jim

jazzbender · December 17th, 2007, 04:37 PM

Thanks to all for your useful advice.

emu! · December 17th, 2007, 04:44 PM

Some things I have learned:

Make sure you are using XLR balanced cables and not Hi-Z unbalanced cables for the mics. Use 16 guage or smaller for the speaker cables. Also, those small mixer/amps are a pain because they usually don't have a mic input/pad control. That means using 2 different kind of mics with different gain structures can cause havoc. And, match the speaker impeadance to the lowest possible ohms the amp can handle. For example: if the amp can go down to 4 ohm load, use a 4 ohm speaker or add enough speakers to bring it down to 4 ohm. (assuming parrallel inputs)

BoB/335 · December 17th, 2007, 06:08 PM

Getting an amp down to its lowest ohm rating will reduce feedback??? Never heard that one.

16 gauge or smaller cables for speakers??? Reducing feedback??? Point me an article on that one please.

IMHO 16 gauge is the smallest I would ever use for speakers. My cables are 14 and up.

I would go with putting something soundabsorbing on the walls first. Carpet should do the trick of stopping that sound from bouncing around.
If it continues, I would try AFTER that to place the speakers on the floor as monitors.
I think the carpet on the walls will be more effective. Chances are the sound will still bounce off those walls using the speakers as monitors without the carpet on the wall.

I agree that using the same mics will help.

emu! · December 17th, 2007, 09:33 PM

Quote:

Originally Posted by BoB/335

Getting an amp down to its lowest ohm rating will reduce feedback??? Never heard that one.

16 gauge or smaller cables for speakers??? Reducing feedback??? Point me an article on that one please.

IMHO 16 gauge is the smallest I would ever use for speakers. My cables are 14 and up.

I would go with putting something soundabsorbing on the walls first. Carpet should do the trick of stopping that sound from bouncing around.
If it continues, I would try AFTER that to place the speakers on the floor as monitors.
I think the carpet on the walls will be more effective. Chances are the sound will still bounce off those walls using the speakers as monitors without the carpet on the wall.

I agree that using the same mics will help.

Well, it worked for me. Go figure. I think the reason I got feedback at 8 ohms is because the amp puts out a weaker signal at 8 than at 4. Therefore we were turning the volume knob WAY too high. Keep in mind this was not real expensive, high-tech gear. 14 guage IS smaller than 16, right??? We, at one time were using regular old guitar cables for speaker cable...something like 22 guage...it was way to high of a guage to handle the speaker connection. The 22 guage cables were ACTUALLY GETTING WARM TO THE TOUCH!

studio1087 · December 17th, 2007, 10:02 PM

You need an EQ. Can you find a small powered mixer with even a 7 band EQ?

I have a small Yamaha Powered PA head with a simple 7 band EQ. I can pull the feedback out of the speakers in any small room.

Will a rackmount EQ work with your PA unit? If not, upgrade the powered mixer.

An EQ is great for playing CD's through your PA....you can tweak an OK sound.

jazzbender · December 18th, 2007, 08:44 AM

It looks like there are many options. I guess we should start with the easiest and least expensive ones and work our way through them until the problem is solved. Thanks again to everybody.

December 17th, 2007, 09:43 AM	#1 (permalink)
jazzbender Tele-Meister Join Date: Sep 2007 Location: Washington DC Posts: 173	PA feedback issue I rehearse with a small group in a 15 x 20 basement that has painted block walls. The problem we're having is that if we turn the Yorkville 100W mixer amp up loud enough to hear the vocals, we get terrible feedback. We're not playing our guitars excessively loud, so we don't want to turn down. The mikes we use are Shure CL588 Unisphere B and a Radio Shack uni 33-3002. One of the guys suggests we hang carpet on the wall, and another says that won't help. Any suggestions?

December 17th, 2007, 11:01 AM	#2 (permalink)
woodman Poster Extraordinaire Join Date: Nov 2004 Location: Mint Hill, NC Age: 62 Posts: 5,968	any sort of acoustic treatment will keep sound from bouncing around into mikes where it doesn't belong. but have you tried EQing? __________________ Truth is stranger than fact ... www.myspace.com/woodymitchellmusic BAND PAGES: www.myspace.com/stragglerswing (Stragglers - Western Swing) www.myspace.com/loafersgloryband (Loafers Glory - '70s country-rock)

December 17th, 2007, 11:27 AM	#3 (permalink)
Tim Armstrong Moderator Poster Extraordinaire Join Date: Mar 2003 Location: Berlin, Maryland, USA Age: 49 Posts: 9,720	Headphones. Run your mics into a mixer, run the mixer into a headphone amp, wear headphones. Or, reconsider turning down your amps and if you have a drummer, have him use bundle sticks rather than drumsticks. Band rehearsal is a time to really listen, to work on the little things, and lots of volume is the enemy of actual hearing. Putting up some blankets on the walls might help deaden all the reflections... Tim __________________ http://www.moodswingers.org

December 17th, 2007, 11:52 AM	#4 (permalink)
mark norwine Tele-Afflicted Join Date: Mar 2003 Location: New Jersey Age: 50 Posts: 1,381	Take the PA speakers off the stands & put them at your feet as if they were monitors......in reality, that's what you are using them for, anyway. They won't need to be as loud, and your problems will diminish. Been there...done that. __________________ "Progress is not possible without deviation from the norm." Frank Zappa

December 17th, 2007, 03:07 PM	#5 (permalink)
Schnauzer Tele-Meister Join Date: Apr 2005 Location: Coeur d'Alene Idaho Age: 61 Posts: 160	Woodman nailed it. You must use a multi band EQ and "ring out" your sound for a given room. This proceedure will identify the offending frequencies. As a room fills with bodies things may change so you may have to adjust. Good luck, Jim __________________ Jim - "You boys doesn't play none of that narcotic music do ya?" The Clayton Club 1984

December 17th, 2007, 04:37 PM	#6 (permalink)
jazzbender Tele-Meister Join Date: Sep 2007 Location: Washington DC Posts: 173	Thanks to all for your useful advice.

December 17th, 2007, 04:44 PM	#7 (permalink)
emu! Tele-Afflicted Join Date: Aug 2007 Location: Location Location Posts: 1,168	Some things I have learned: Make sure you are using XLR balanced cables and not Hi-Z unbalanced cables for the mics. Use 16 guage or smaller for the speaker cables. Also, those small mixer/amps are a pain because they usually don't have a mic input/pad control. That means using 2 different kind of mics with different gain structures can cause havoc. And, match the speaker impeadance to the lowest possible ohms the amp can handle. For example: if the amp can go down to 4 ohm load, use a 4 ohm speaker or add enough speakers to bring it down to 4 ohm. (assuming parrallel inputs)

December 17th, 2007, 06:08 PM	#8 (permalink)
BoB/335 Tele-Meister Join Date: Aug 2003 Location: Long Island Posts: 476	Getting an amp down to its lowest ohm rating will reduce feedback??? Never heard that one. 16 gauge or smaller cables for speakers??? Reducing feedback??? Point me an article on that one please. IMHO 16 gauge is the smallest I would ever use for speakers. My cables are 14 and up. I would go with putting something soundabsorbing on the walls first. Carpet should do the trick of stopping that sound from bouncing around. If it continues, I would try AFTER that to place the speakers on the floor as monitors. I think the carpet on the walls will be more effective. Chances are the sound will still bounce off those walls using the speakers as monitors without the carpet on the wall. I agree that using the same mics will help. __________________ BoB/335

December 17th, 2007, 10:02 PM	#10 (permalink)
studio1087 Friend of Leo's Join Date: May 2003 Location: Near Milwaukee Age: 44 Posts: 4,009 36 Photos	You need an EQ. Can you find a small powered mixer with even a 7 band EQ? I have a small Yamaha Powered PA head with a simple 7 band EQ. I can pull the feedback out of the speakers in any small room. Will a rackmount EQ work with your PA unit? If not, upgrade the powered mixer. An EQ is great for playing CD's through your PA....you can tweak an OK sound. __________________ JLG Carry On

December 18th, 2007, 08:44 AM	#11 (permalink)
jazzbender Tele-Meister Join Date: Sep 2007 Location: Washington DC Posts: 173	It looks like there are many options. I guess we should start with the easiest and least expensive ones and work our way through them until the problem is solved. Thanks again to everybody.