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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:

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