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How To Make PA System Louder Without The Feedback

Discussion in 'Sound, Music, and Intercom' started by YdoIevenTry, Feb 19, 2004.

  1. YdoIevenTry

    YdoIevenTry Member

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    I have the B-52 1000 Martix and the Ub2222FX mixer and its all hooked up and works but doesn't seem to be as loud as it can.When we turn it up it we get too much feed back.I was hoping i could buy a mic preamp or something to make the mic a louder so we can be loud with out the feedback.
     
  2. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Ok - I have not done any major sound work for some years now but as a DJ I do use mics. I am not familiar with the system you are using but in principle, this shouldn't make all that difference.

    First thing that I would do is start off with just one mic plugged in and all the other channels turned down/off or muted (depending on your desk). Check that the mic if giving a good strong signal. The desk that I have has an attenuation (or gain) control with a level LED that indicates when a strong signal is being received. It also has a –20db pad switch, which cuts the level. Check that this is not one of the problems as if the mic signal is weak you will have problems.

    Next I would set ALL the EQ settings to flat on the desk (ie the middle setting so as not to cut or boost any frequency ranges).

    Assuming that your speakers are matched to the amp that you are using, turn the amp on and dial the volume up to the level that you would usually use. Personally, I always run my amps flat out and drive them from the desk as most times the amps are at or near the stage and I am a good 30m away. HOWEVER, you should probably not do this when first testing. I am sure one of the other guys who do this day in, day out will discuss this more.

    Ensure that the person who is going to speak into the mic is not too close to the speakers when testing and ask them to speak normally into the mic as you bring up the channel level. Does this make any difference? If not, repeat the procedure on a different channel and also with a different mic. If using a radio mic, ensure that the batteries are good and that the gains on the radio mic and receiver levels are suitably adjusted.

    If this doesn’t change the results that you are getting, try adjusting your EQ to cut some of the frequencies. Common feedback frequencies are around the 600Hz and 1.2KHz ranges.

    The other thing to do is check cables and the gain/tone settings on any other equipment that is inline between the desk and the amp. It may be a good idea to remove all of them and then introduce one-by-one as you sole the problem.

    That is really all that I can suggest and I hope that it is a starting point for you and perhaps reduces the problem. I was always taught that by sending the strongest signal (without clipping it) from the source to the amp is an essential key to success. I would really welcome any comments from the sound guys out there. As I said, I have only done a handful of live gigs in the past 5 years or so and they were not of any huge magnitude. However, having said that, these steps have worked for me.

    Good luck,
     
  3. The_Terg

    The_Terg Active Member

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    Good points mayhem!

    If most of your microphones are not handheld, headset of lavalier microphones, then you may want to consider moving your microphones around a bit. What kind of mics ARE you using?

    If you use floor or bounday microphones like the Crown PCC 160's, double check that they are well behind your speakers. You want your speakers to be no further back than the edge of the stage, or whatever.

    If you are using hanging microphones, try to lower them a little. Their pickup range will decrease, but you will have a larger amount of gain-before-feedback.

    If you are using shotgun mics.... well, they may not be the best if you are having severe feedback problems. It would be advisible to just not use em, attach a longer or more solid barrel, and/or move them closer to the stage.

    If you have more than 1 pair of speaker arrays (IE, if you also have side-fill speakers) consider adding more volume in the rear of the auditorium/theatre. Take the weight off of the main mix or music program speakers at the front of the theatre, and boost the side fills. I often need to constantly monitor my speaker mix, because people are always messing with my damn levels.. (Grrrrr.)

    As mayhem said, it is also very important to mind your EQ settings when you are working with a system with low gain-before-feedback. You may need to cut the highs a bit. This will get the most gain out of your microphones, but be aware that it also degrades the overall bandwith or sound of the system. An EQ for just your main mix is often helpful in this kind of situation.

    When I am mixing for, say, the fourth grade play, I know that Im gonna be fighting feedback desperately. I like to do a little 'feedback check,' and get a good sense for how much gain I can get out of the system before feeding back. Then, I either tape off the faders so they won't accidentally go too high, or just turn down the trim so that they wont feedback.

    Also look into the acoustics of whatever you are operating in. If you are surronded by hard, uncovered walls, then that may be your problem right there. Keep in mind that feedback is often the result of reverb gone amiss. If you are in the position to do so, you may need to consider asking about mild soundproofing like carpeting on the floor, or sound panels on the walls.
     
  4. YdoIevenTry

    YdoIevenTry Member

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    Thanks. Im not exactly sure if what you told me is going to work because (me being the drummer)the exuipment isnt at my house so i cant do what u guys tole me to do but i will try once i get over to my guitar players house.I also want to thank you for going into such detail....i was expecting"Yea ummmmm try turning up your PA system"so again thank you for taking your time.If anyone else has any more information to help feel free to post.Anything u can tell me would be great.We spent 1300+ bux on this bad boy and i would like to get every thing out of it that i can.



    THANX
     
  5. The_Terg

    The_Terg Active Member

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    If that is the case, then Mayhem's points are probably a little bit more accurate... to clarify-

    A - Keep the speakers WELL away from the mics, and pointed well away.

    B - Make sure that you are spaking close into the mic, but not slobbering on it. (I'd say a good 3-6 inches would suffice)

    C - Keep the mics pointed backwards - IE, aways away from the audience, and from where the sound comes from.

    D - If you are still having feedback problems, turn down the high frequencies, or treble.

    And lastly, always get a mix that is a half-notch or more lower than the point of feedback. Don't run the system Riiiight on the edge of feeding back, because it will, and someone will have to go running for the mixer.
     
  6. fishyswishy

    fishyswishy Member

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    I have ran into this problem less then a few months ago. the threshold level before feedback came was raised by changing the speakers. for some reason with our newer speakers feedback is hit at a much higher level
     
  7. dj_illusions

    dj_illusions Active Member

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    just out of curioisity... do you guys work of the VU Meters or the LED's on the desk when mixing the sound.

    I was taught sound ages ago, and the guy that taught me said that it doesnt really matter what your main LED's are peaking at just so long as your single channels dont peak.

    I have always tried to make sure that the main LED's on the desk arnt peaking... but then again he used to run the desk with the Main L+R up full..... but meh, how do others do it?
     
  8. Nephilim

    Nephilim Active Member

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    VU meters are evil, but that's an opinion. They react far too slowly.

    ANYWAY. You need to watch both individual channel levels (if you can) and the overall mix output level. If your desk as a whole is clipping at the mix amp (the fancy device that actually combines all your channels into the one LR send, or whatever) then it will register on the main meters, and it will still sound terrible. If you have a whole bunch of very hot signals coming through at one time, it's quite possible to clip your desk; it depends on what the mix amp's headroom is. Mackie CFX series clip at +22dBu, their VLZs generally at +28dBu or so. Other desks generally let you know when they're clipping at the mains.
     
  9. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Ok – This is what I was taught and it as Nephilim pointed out, it depends upon the equipment that you are using.

    Essentially you want to have the strongest possible signal getting to your amplifier because this will give you the best sound as amplifying a weak signal will introduce noise. However, amplifying a distorted signal will just make the distortion louder!

    If your desk has a pre-fade meter or indicator, as well as an output meter you job has just been made that little bit easier. Each channel on my mixer (both my DJ console and my 12ch mixer) has a gain control which allows me to adjust the signal coming into the mixer so that is as close to 0db as possible, without clipping.

    On my DJ console, I have a meter that I can allocate to pre-fade and one for master output. When I DJ, I have the channel masters set to full and use the output gain to drive the amplifiers. I use the gain (pre-fade) to ensure that the signal doesn't clip. On my 12 ch mixing desk I simply have a LED for each channel which lights up when the signal is clipping. In this case I set the gain so that it flickers when signal is present.

    Most effect units will also have some sort of signal level indication, but not all so you need to be careful there. In some instances, you will not be able to get a good indication form these and this is where your ears come into play.

    So what I am looking for is a signal that causes the clip LED to flicker but not stay on at the input/pre-fade stage, and of course at the amplifier. I always run my amps flat out as I find it gives better base response and so the master output on my desk is used to control the volume. Plus, most of the time the amp rack is on side of stage and I don't want to be running back and forth.

    I have been using this method for many years now and never had any problems. Although, having said that, I use compressor/limiters for live shows and will adjust the output accordingly to get the sound just right. Like anything, it comes down to your equipment, application and own preferences but at the end of the day the RED LED’s are BAD and you should be concerned with preventing them from staying lit.

    Hope this is helpful,
     

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