Mic2+

Mic2-

Mic1+

Mic1-

470 nF

470 nF

470 nF

470 nF

OUT-

LPF

LMV1089

OUT+

Osc2

Osc1

AC Voltmeter

LMV1089

www.ti.com

SNAS441H – SEPTEMBER 2008 – REVISED MAY 2010

TEST METHODS

For optimum noise suppression the far field noise should be in a broadside array configuration from the two

microphones (see Figure 34). Which means the far field sound source is equidistance from the two microphones.

This configuration allows the amplitude of the far field signal to be equal at the two microphone inputs, however a

slight phase difference may still exist. To simulate a real world application a slight phase delay was added to the

generator, the phase of Mic 2 is delayed by 1.1° when compared with Mic1.

2. Measure the output level in dBV (X)

3. Mute the signal from Mic2

4. Measure the output level in dBV (Y)

For optimum near field speech preservation, the sound source should be in an endfire array configuration from

the two microphones (see Figure 34). In this configuration the speech signal at the microphone closest to the

sound source will have greater amplitude than the microphone further away. Additionally the signal at

microphone further away will experience a phase lag when compared with the closer microphone. To simulate

a signal generator is used to delay the phase of Mic2 by 15.9° when compared with Mic1.

2. Measure the output level in dBV (X)

3. Mute the signal from Mic2

4. Measure the output level in dBV (Y)

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