Equaliser

NOTES ON ADJUSTMENTS

1.Turn the EQ controls on the mixing desk to a central position (linear setting).

2.Switch any third-octave or octave equalisers to “Bypass” or set the equaliser controls to a central position.

3.Connect a microphone and use the SUB and TOP control of the power amplifier to set the signal in such a way that the human voice sounds “natural”.

4.This concludes the basic system setup.

5.Using the EQ controls, a wide variety of microphone and instrument inputs can now be adjusted on the mixing desk to match personal preference.

Third-octave or octave equalisers should be set very carefully, if at all. With many third-octave or oc- tave equalisers, even slight alterations in Lo or Mid range lead to unacceptable sound falsifications which cannot be eliminated via other EQ controls.

ADJUSTMENTS WITH REAL TIME ANALYSER AND EQUALIZER

“Fine tuning” of amplifier and loudspeaker systems with real time analysers and third-octave or octave equalisers is not normally advisable. Depending on the setting in question, third-octave equalisers in particular cause phase and group time distortions which falsify the sound considerably. The measuring microphone evaluates both the cabinet direct sound field and the reflections simultaneously, thus pre- venting any proper interpretation of the readings from a sound point of view.

If particularly unfavourable acoustic conditions make fine tuning seem necessary, the following princip- les should be adhered to when tuning amplifier and speaker systems:

1.Only measure in the direct speaker sound field, normally at a distance of 3 - 5 metres maximum. If the measuring microphone is set up further away, (e.g. in the middle of the hall), both direct and room sound is measured. Any attempt to linearize this “blend” with EQ normally produces an extremely mid-, tinny- sounding, obtrusive sound image.

2.When measuring in the “critical” range between ca. 250 Hz - 5 kHz, only cut with the EQ - do not boost on any account! A “gap” in the spectrum is not considered so obtrusive as a “hump”. It is essential to avoid substantial increases in the bass range as this would drastically impair the transient response of the entire system.

3.When measuring, only work with 5 W maximum capacity (pink noise). This prevents

amplifier clipping and related distortions. With conventional noise generators the peak value of the noise voltage is approximately 10 dB higher than the RMS value, meaning that even 5 W amplified power can lead to short-term peaks of up to 50 W.

4.Dominant acoustic feedback can sometimes be suppressed somewhat by third-octave equalisers or parametric EQ’s. In applications of this nature, great care should be taken to ensure that the gain in volume does not mean reduced clarity and naturalness.