PA Question

[Jax]

The PA in my studio's live room can play back anything from a line level stereo source as loud as I want it to, but when I plug in a mic, there's not much headroom before feedback. The PA gear is a couple of self-powered Yamaha MSR 400's connected to a Mackie 1202.

Why can't I get a miked source a whole lot louder before feedback? Confusing!

[Jay Kahrs]

Usually those powered PA speakers have a switch to go from mic to line level... try looking on the input plate. The JBL eon's have it recessed in so you need a paperclip or small screwdriver to flip it...

Or wait, are you plugging the mic into the Smackie first? Then line in the speaker?

Sounds like a gain-staging issue as much as anything else. Could be the position of the speakers in the room as well...

[fifthcircle]

It's feeding back because you need to EQ the speaker to compensate for issues with the speaker's frequency response and room acoustics. Get a 30 band EQ and ring out the speakers and you'll be fine.

--Ben

[Roland]

In addition to what Ben said above, speaker positioning, the type of microphone you are using both effect GBF (gain before feedback). Correctly set u and eq'd you would be surprised at just how much volume you can get. Line sources don't feedback because there is no live signal.

Regards


Roland

[Jax]

Jay - the Mackie is first, then line out into the PA. I've experimented with the gain stages by keeping the preamp pot very low and cranking the channel output knob (same as a fader on the Mackie), and vice versa. I've also tried keeping both the preamp and fader knob very low and cranking the main outputs. All approaches aren't much different to the point at which it feeds back. How else could I check the gain stages?

Ben - how exactly do you ring out a PA with a 30 band eq? I know it's common practice, but I don't know how. I'll take a guess: Do you crank the PA right before it feeds back, then boost each frequency one by one, turn down the frequencies that feedback, and then turn up the PA level to compensate?

I'm a noob when it comes to live sound gear.

[waveterm]

Originally Posted by Jax

Jay - the Mackie is first, then line out into the PA. I've experimented with the gain stages by keeping the preamp pot very low and cranking the channel output knob (same as a fader on the Mackie), and vice versa. I've also tried keeping both the preamp and fader knob very low and cranking the main outputs. All approaches aren't much different to the point at which it feeds back. How else could I check the gain stages?

It doesn´t matter how you drive the Mackie vs the Speakers ( until you overdrive a stage ). Gain is gain

Originally Posted by Jax

Ben - how exactly do you ring out a PA with a 30 band eq? I know it's common practice, but I don't know how. I'll take a guess: Do you crank the PA right before it feeds back, then boost each frequency one by one, turn down the frequencies that feedback, and then turn up the PA level to compensate?

You´re not too stupid after all !!

;)

Originally Posted by Jax

I'm a noob when it comes to live sound gear.

At least you figured it out. A graphic eq is easy to use but a parametric is better for finetuning the offending frequencies.

WT

[fifthcircle]

Originally Posted by Jax

Ben - how exactly do you ring out a PA with a 30 band eq? I know it's common practice, but I don't know how. I'll take a guess: Do you crank the PA right before it feeds back, then boost each frequency one by one, turn down the frequencies that feedback, and then turn up the PA level to compensate?

I'm a noob when it comes to live sound gear.

You got the idea... Running live sound is a careful balancing act between system sound and EQ for gain before feedback. If you cut too many frequencies, it won't feed back, but it also might not sound very good. When you boost the bands, feel how fast it feeds back. If you hit a frequency and it rings hard instantly, you need to cut a lot. If a frequency takes awhile to start to ring, leave it be...

Do this and you'll get a lot more gain before feedback in your system.

--Ben

[Jay Kahrs]

Originally Posted by Jax

Ben - how exactly do you ring out a PA with a 30 band eq? I know it's common practice, but I don't know how. I'll take a guess: Do you crank the PA right before it feeds back, then boost each frequency one by one, turn down the frequencies that feedback, and then turn up the PA level to compensate?

Sort of.

Position the mics & monitors where they're gonna live for the performance, and then with the EQ flat... bring up the gain slowly until it starts to ring/feedback. Cut whichever frequency is feeding back... raise the volume again. Cut the next... rinse & repeat. Never boost. Always cut. This also works a little better with someone speaking into the mic & eeking it on...

Typically 1kHz to 3.5kHz is the first to bark followed by 5-6kHz... maybe 8 & 12kHz... you can sometimes get a muddy rumble around 150, 250 & 400-800Hz which might require some shaping... I'll also cut everything below 80Hz and roll off gently above 16kHz if it's a vocals only rig.

FWIW though... one of the bands I do a lot of FOH for, the B3 player uses the $500 Neumann KMS or a Beta 58 and a JBL eon that he carries as a personal monitor. At smaller gigs where there are only two monitor mixes we run the KMS right into the Eon and it can get frighteningly loud with NO eq on it... His vocal goes from the JBL split to FOH which we try to avoid because that split is a tone sucker. Much hipper to run a send back to it from the desk...

Having a 30band EQ for a rehearsal rig is not a requirement IMO... it's nice... but not mandatory like it is on a full-blown gig. Even a 15-band EQ or parametric will work... you're just notching whatever rings, and hopefully making the sound of the wedges more "true" to life.

Getting the null of the mic aimed at the drivers is at least 70% of the battle.