Re: PA Powered Amp Gain Settings Question

<[email protected]> wrote in message
news:[email protected]
> So I've been trying to look around the Internet for
> information on how I should have my powered amplifier set
> for my PA which I'm using for singing in a rock band.
>
> I found this video:
> http://www.youtube.com/watch?v=tornRFVtGxI

> Which suggests turning down the powered amp gain and
> settings all volume knobs to unity (0) and turning my
> mixer preamp gain up until clipping occurs while the mic
> is in use (someone singing loudly into it, basically).

You need some headroom, because you want to avoid clipping due to its
seriously bad effects on sound quality. Therefore, lacking metering, it is
advisable to turn mic preamp gain up until there is a clipping indication on
loud sounds, and then back it off a certain amount. You want from 10 to 20
dB of so-called headroom, or added gain before clipping.

You can estimate how far to back off the microphone gain control by the
following means:

(1) Consult the specifications for the mic preamp or console to determine
its gain range. For example, a mic preamp might have from 10 to 50 dB of
gain, per its spec sheet. This preamp has a gain range of 40 dB.

(2) Count the calibrations on your mic preamp's gain control. For example,
there might be 11 black marks around the knob/ Subtract one, and divide that
into the gain range by this number. Continuing the example above, divide
the gain range of 40 dB by 10 to give 4 dB per black mark.

(3) If you want to have 12 dB worth of headroom, crank the mic preamp gain
control up until you have clipping (clip light flashing slightly) on the
loudest sound, and then back off by 3 black marks.

> After following this advice I only turn my powered amp up
> to about 25% before I start getting feedback.

Feedback happens when your mic picks up too much sound from your
loudspeakers. Reposition your mic and speakers for less feedback. Get your
mic out of the sound field that the speakers generate. Put your speakers
between the mic and the listeners.

Feedback also happens when the sensitivity of your mic and speakers is
greater at some frequencies than others. Feedback first happens at the
frequency where your mic and speakers have maximum gain. That's why the
feedback happens at a certain frequency, and not some other frequency. The
frequency where your mic and your speakers have maximum gain can vary
depending on the positioning of your mic and your speakers. So, the feedback
frequency can be different for every mic and every location and orientation
of the mic and every location and orientation of the speakers.

Once you have optimized the location and orientation of your mic(s) and
speaker(s) for maximum sound and minimum feedback, you can further improve
the situation by using an equalizer to reduce the gain of your speakers and
microphones at the frequency where the feedback takes place.

Thanks for the replies and info,

I'll checkout that handbook to see more about eliminating the
feedback. Currently it's a very basic setup and it's worked for years
but I recently started wondering if it would be possible to get more
sound and better quality with less feedback.

We are practicing in a converted garage so it's a fairly small space
which makes 'placing the mics' and all such things rather difficult.
Currently the mics are in the center of the room because that's where
we have space and because besides myself the two guitar players and
singing backup.

There is currently no EQ, compressor's, limiters, etc on the system
just a mixer, power amp and two loudspeakers. I've been thinking about
getting an EQ or compressor but money is limited so I'm trying to
maximaze what I can before buying more gear.

On Fri, 18 Jul 2008 06:17:41 -0700 (PDT), [email protected] wrote:

>Thanks for the replies and info,
>
>I'll checkout that handbook to see more about eliminating the
>feedback. Currently it's a very basic setup and it's worked for years
>but I recently started wondering if it would be possible to get more
>sound and better quality with less feedback.
>
>We are practicing in a converted garage so it's a fairly small space
>which makes 'placing the mics' and all such things rather difficult.
>Currently the mics are in the center of the room because that's where
>we have space and because besides myself the two guitar players and
>singing backup.
>
>There is currently no EQ, compressor's, limiters, etc on the system
>just a mixer, power amp and two loudspeakers. I've been thinking about
>getting an EQ or compressor but money is limited so I'm trying to
>maximaze what I can before buying more gear.

OK. Well, you're talking PA - there's no-one out front to hear it!
You just need monitors. You need the speakers to be pointing at the
performers, as close to their ears as possible while still keeping all
microphones pointing AWAY from the speakers. The classic position to
achieve this is placing them on the floor in front of the mic stands,
angled up. If the drummer complains he can't hear give him one of the
speakers all to himself, aimed straight at his face.

If you have trouble getting guitars etc. to turn down to a realistic
level make sure THEIR personal amps are aimed straight into their
faces. It's only the guitarist who wants to hear himself THAT loud
:-)

<[email protected]> wrote:
>
>I'll checkout that handbook to see more about eliminating the
>feedback. Currently it's a very basic setup and it's worked for years
>but I recently started wondering if it would be possible to get more
>sound and better quality with less feedback.

Feedback is caused by sound from the speakers going into the microphones.
It can be reduced by using more directional speakers and microphones, by
careful placement of speakers (and that includes monitors) and microphones,
and by avoiding reflective surfaces around the stage area (like big cement
walls behind the band that take the sound from the monitors and reflect
it right into the mikes).

>We are practicing in a converted garage so it's a fairly small space
>which makes 'placing the mics' and all such things rather difficult.
>Currently the mics are in the center of the room because that's where
>we have space and because besides myself the two guitar players and
>singing backup.

Your goal, then, becomes to keep the backline levels down, so the PA
doesn't need to be up very high.

>There is currently no EQ, compressor's, limiters, etc on the system
>just a mixer, power amp and two loudspeakers. I've been thinking about
>getting an EQ or compressor but money is limited so I'm trying to
>maximaze what I can before buying more gear.

If your problem is feedback, an EQ with real notch filters (not a cheap
graphic) will help you a lot. There are a bunch of automatic feedback
eliminator boxes out there that are basically just automated notch filters...
they find the frequency where the feedback takes place and drop a notch
there. As long as you don't move anything around, the feedback frequencies
stay in the same place, but move a mike a foot and they can change. So
the equalization is something you want to use only AFTER you have done
everything else to reduce feedback.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."