PA question...

Insouciance · #1 11-16-2010, 01:15 PM

Hello TB!

Got a quick question about my PA...

Like a lot of bass players, I am the one in the band that has the PA (pays the most for the practice space, I could go forever) and though we don't play THAT loud, I have an incredibly hard time hearing myself and my guitar player sing. My mixer/head is a generic Madison/some-cheap-ebay buy and it doesn't have that many watts to it. I have two huge 2x15 mains and when I turn the mics up, I get bad feedback. My question is if I could just get a power amp to beef up the wattage of the mixer (those 2x15 mains are rated at 800 watts), and if so, if there are any power amps you would recommend? And if not a power amp, what should I do?

Thanks all!

Blasto · #2 11-16-2010, 05:58 PM

First off, positioning of your cabs relative to your microphones is an important consideration. You mentioned having feedback. A lot of inexperienced players will set speakers behind the microphones, mostly because they do not have monitors.

Secondly, it isn't always a safe thing, (and some will disagree I am sure) to run a "head" (pre AND power amp) without some type of load on it. Meaning, if you buy an additional power amp and use it to power your speakers, then the head is sitting there (trying) to put out power that has no where to go. Not good.

You may want to invest in a coupla small wedges! Let the head push the wedges, and THEN buy a power amp for your 2x15s. But remember, headroom is damn near everything, so buy enough amp!

staindbass · #3 11-16-2010, 06:12 PM

you mentioned mains, but i think you are using them for vocal monitors? you need a 31 band eq to notch(filter or turn down) out the frequencies that are feeding back. johnny a/ staind

t bake · #4 11-16-2010, 06:16 PM

+ 1 above buy all the amp you can afford pwr amps have come down in the watt per dollar way Lots of good amps are being produced at verry good price. I would stay away from the one off brands and series , A name brand with a good rep . Ive had verry good luck with crown and pv . REMBER!! feadback is about frequancy as much as voulme.Some low budget mics will allmost allways have a crappy feedback to gain ratio (for lack of a better way to put it ) get ya some monitors a 2nd amp and a couple of shure 58s or equivlent and you will be on your way. set your stuff up and work with it mic placement and gain struchure is some thing that takes practice and time to learn God Bless and GIG ON!!!!

modulusman · #5 11-16-2010, 09:11 PM

What are the speakers you are using?

Insouciance · #6 11-16-2010, 11:26 PM

Quote:

Originally Posted by modulusman

What are the speakers you are using?

Also generic speakers.

Do you buy power amps for speakers, mixers or both?

**Rune Bivrin** · #7 11-17-2010, 01:29 AM

It's not unheard of that feedback is the result of sound going from the mic stands into the mic housing and then into the actual mics. We had a few not so good AKG mics with that problem. It was evident that they had a problem with handling noise and the feedback was a secondary consequence of that.

You need too think about mic placement in relation to speaker placement, and notching out frequencies can often help. Sound treatment of the room can often do wonders, if that's an option.

A new amp won't do anything with regards too feedback.

However, there is one fundamental tenet of amplification:

If you get feedback, something is too loud. Turn everything down!

greenboy · #8 11-17-2010, 01:45 AM

Yep, box and mic placement really matters. On crappy smaller stages it also pays to limit the number of mics in use (each one increases feedback potential quite a bit) and stick with a known pattern and matched mics where possible. Know your hypercardioids and cardioids etc and use them for the type of monitor setup and stage space that you typically encounter.

I've found that placing mic stands on foam or mats can even help at times.

modulusman · #9 11-17-2010, 07:20 AM

Quote:

Originally Posted by Insouciance

Also generic speakers.

Do you buy power amps for speakers, mixers or both?

The suggestions of turning down and mic placement might help. The speakers may be junk. Without knowing the model it is hard to tell. As staindbass mentioned a 31 band EQ might help. If you want to spend money buy one instead of a poweramp and learn how to use it. Later on when you get better gear it will still be a useful tool.

derrico1 · #10 11-17-2010, 08:04 AM

Feedback is putting a ceiling on your practice PA's volume, not the amp section of your powered mixer. Adding a bigger amp will just give you louder feedback.

The advice below is pretty basic, so apologies if you know all this already. I've also simplified in a few spots, to avoid complications it won't likely be useful to consider at this stage.

To control mic feedback in a rehearsal room, start by placing whatever PA speakers you are using as monitors--close to the singers and in the null spot of their vocal mics. Different mics have different sensitivity patterns, but the most common spots are directly behind the capsule or else 45-60% on either side of the rear axis.

Now flatten out the system as best you can with the gear you have (or can afford). A typical cheap rehearsal PA will have peaks and dips in its eq response at almost every stage--the cheap mics will be strongly colored, as will the pre-amps, the eq and built-in effects, and whatever is passing as the monitor wedges. Chances are, some of the components are hyping the same bits of the spectrum. To try to get the system closer to flat, start with eq flat and effects off. Playing recordings through the system gives you a controlled context for making this first pass. If you have huge woofing lows or ice-pick highs, adjust the system eq to tame them. Note that different spots in your room will sound different, and what matters for taming vocal mic feedback is how the system sounds at the spots where the vocal mics are placed.

Make sure your vocal mics are in their rehearsal positions. If possible, make sure that the marks for the singers' mics aren't right by a wall or reflective surface. Ideally, they'd be in a relatively quiet part of the rehearsal space, and in a part of the room not afflicted by huge nodes--but for now, just avoid putting them right in front of a reflective surface or putting your singer's ear right in the drums. Either of those conditions will make it difficult to give the singers enough monitors.

Got recorded music sounding reasonably flat? Great. Now mute playback of your recorded music and work on the mics. Mute all channels except your vocal mics. Bring up your vocal mics, one at a time and still w/o effects or channel eq. Set the channel gain for a hot signal with no clipping, and bring the PA volume up. You might find that one of the mics has a very peaky response curve and/or terrible off-axis rejection. Sometimes, one of the mics has decent gain-before-feedback and the other is a pig. If so, consider replacing the pig.

If your vocal mics are decent and your PA/monitor rig is as flat and clean as you can get it, the maximum vocal mic volume you can get before feedback will dictate the volume level for the room. If the musicians can play under that ceiling, then you're good to go.

If the drummer can only bash or the guitarist(s) insist on swamping the vocals, then you could bring in more/better gear to raise the volume of the vocals before feedback. (Stage-quality mics, monitors with flatter response and tighter dispersion patterns, and better mic pre-amps are first candidates. After that, a graphic eq or feedback suppressor could be useful. (W/o someone in the band who can set that gear though, it's easy to cause more problems than you fix.)

Flattening out your system will help you get more out of it, but there are limits. In the same room, a well tuned system with flat pre-amps and even sounding monitors will get a lot louder before feedback than a peaky or badly tuned system. Still, the best system in the world can get only so loud in a small room before live mics feed back. If you've tuned your rehearsal monitor PA and feedback still keeps the ceiling lower than the musicians can play under, you'll either need to get new musicians (seriously), or learn to live w/o hearing the vocals at rehearsals that become social get-togethers, or go a different route--such as running the vocals through a headphone amp and give closed-ear phones to whoever in the band is actually listening to the vocals.

**Rune Bivrin** · #11 11-17-2010, 08:33 AM

There is another factor which affects feedback. It's harder to control and somewhat random:

The singer...

I rarely get feedback from my own mic because I sing really loud, thus requiring low gain. I also use no compressor or limiter. Those can be a truly excellent reason for feedback. Singers who whisper in the mic will need high gain which causes feedback more easily. Singers with great variance in loudness or distance from the mic often have an agressive compressor to smooth the differences in level, which can also lead to feedback.