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Sound system equalizing advice

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					Sound system equalizing advice
Why equalizing is needed
Equalization is needed in PA systems because the PA spakers do not have flat frequency
response. Another thing is that the room acoustics have a great deal of effect on the sound
what is heard by the listener. With right equalization you can get the best sound out of
your PA system.

How to do equalizing of PA system
By ear equalizing

This is really cheap equalizing method because you don't need any measuring
equipments. Because the quality of the sound is subjective and varies by listener, there is
no one correct setting.

How to do the adjusting:

      Listen the sound source acoustically and try to make your PA system to sound
       natural.
      Play a familar CD through the sound system and try to get the sound you are used
       to hear.

Avoid any excessive boosting or cutting.

Feedback tuning

You need a flat response omnidirectional microphone (electret measurement microphone
is perfect for this). Set you grpahic equalizer to flat position. Plug the microphone to
unequalized mixer channel. Turn up the gain and volume of that channel. Slowly bring up
the overall system level until your system starts to ring (do not let your system to ring too
loudly or you will damage your spakers and/or your hearing). Pull down the EQ slider
that makes the feedback to stop (pull only few dB). Turn the volume up again and
another frequency will begin to feedback. Pull down the corresponding EQ down again
(only few dB again). Repeat this procedure three or four times (not more).

After that, go to the sliders that you have not yet adjusted. Bring up their levels until that
frequency feeds back. Continue the procedure to all sliders you have not yet adjusted.
When you have completed this you have the equalized the spakers to flatter response for
the room.

Now you must add some subjective equalization to improve the overall sound.
Real time equalization

A ral-time analyzer uses pink-noise signal to fill the room with sound and records the
audio spectrum in graphical format using measurement microphone (omnidirectional
measurement microphone). Pink noise signal has equal energy between each octave (or
1/3 octave whatever you like). The graphic analyzer has 1/3 octave bandpass filters and it
records the energy it get's at every frequency band. Ideal frequency response should be
flat on the graph. Any peaks and valleys should be removed by adjusting your equalizer.

Today there are digital equalizers with built-in analyzer and those equipments can do the
equaling to flat response automatically. Be warned to over-use the automatic equalization
systems and measurements done only in one place. The frequency response you get from
different measurement locations varies always some amount. If you equalize the
frequency response maximally flat to one position then the frequency response can
become worse at some other location. It is best to measure the frequency response from
few locations and then equalize away those problems you see in all locations.

Channel equalization
Tone controls on the channel are used to to adjust the subjective sound quantities of the
source. There are lots of different types of sound equalizing circuits in use in channel
equalization.

                        Frequency ranges and effect of sound quality
Frequency                                    Effect to sound
             Those sounds are more felt than really heard. Lost of sound in this area
20-150 Hz
             gives sense of power. Too much sound produces muddy sound.
  150-300    The rhytm section is here. Either a fat or thin sound can be heard by mis-EQ
    Hz       here. Too much here makes sound boomy. (Bass guitar, snare, toms)
             This is propably the most important frequency range. Most instruments
  300Hz-     contain important harmonics here. Too much boosting at 300 Hz can cause
   2kHz      horn like sound. 1kHz and 2kHz sound tinny. Too much here sounds like
             telephone.
             This is upper vocal region. Too much here will cause great hearing fatigue
  2-5kHz     and loose speech intelligence. Reducing 3kHz in musical instruments brings
             vocals on top.
             This is presence range. This area has grat achievement in overall sound. Too
 5-10kHz
             little sound here causes a "far away" sound.
             Silibance levels can be containded here. This area gives bright clean
 10-15kHz
             definition.


Sources
   Sound Check, Hal Leonard Corporation, Milwaukee 1994, 104 pages

				
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