Owner's manual

Home THX Equalization Manual Rev. 1.5

NOTE: CHECK THE OVERALL SPLs AT EACH MICROPHONE LOCATION. IF THESE VARY BY

MORE THAN ± 1 dB, ADJUST THE MASTER VOLUME ON THE CONTROLLER TO COMPENSATE

THE SPL AT EACH LOCATION TO APPROXIMATE THE SPL AT THE REFERENCE POSITION

(Microphone 1). FAILURE TO DO SO MAY RESULT IN SKEWED SPATIAL AVERAGES.

With the four positions stored in memory, now average to obtain the spatial response for the

entire listening area. Notice that we have used the method of obtaining several samples for each

microphone position to smooth out the stochastic effects of the pink noise.

NOTE: DISPERSION AND AIR ABSORPTION AT HIGHER FREQUENCIES WILL CAUSE A

GENTLE ROLL OFF IN RESPONSE BEGINNING AROUND 6 kHz. THIS IS NORMAL AND DOES

NOT REQUIRE EQUALIZATION. (Fig. 10)

Typical Unequalized LCR Room Response

Frequency Hz

SPL

100

160

250

400

630

1000

1600

2500

4000

6300

10000

16000

Fig 10

2.5) Equalize:

The resulting spatial average will approximate the inverse of the correct EQ curve. As a starting

point, assume that a dip of -3 dB on the analyzer calls for an increase at the appropriate EQ frequency

of +3 dB. Since we will re measure a number of times, any over correction or under correction will be

caught. When analyzing the averaged RTA curve try to look for the mean SPL for all frequencies and

adjust the peaks and dips to that mean.

Remember that we are trying to achieve a response in the LCR channels of ± 1 to 2 dB, from 100

Hz to 1 kHZ, without drastic EQ shifts. A boost of 6 dB places many demands on both amplifiers and

loudspeakers.