Page 185 - Master Handbook of Acoustics

FIGURE 10-1 Tonal signals and time delay. (A) A sine wave having a frequency of 500 Hz. (B)
Another sine wave of 500 Hz that is delayed 0.5 msec from A. (C) The summation of A and B. The
500-Hz signal and its delayed counterpart reach their peaks at slightly different times, but adding

them together simply yields another sine wave; there is no comb filtering. A linear frequency scale is
used.

Because signals A and B are 500-Hz sine tones, both vary from a positive peak to a negative peak
500 times per second. Because of the 0.5-msec delay, these two tonal signals will not reach their
positive or negative peaks at the same instant. Often along the time axis, both are positive or both are
negative, and at times one is positive while the other is negative. When the sine wave of sound

pressure representing signal A and the sine wave of sound pressure representing signal B combine,
they produce another sine wave of the same frequency, but of different amplitude; this shown in Fig.
10-1C.
Figure 10-1 shows the two 500-Hz tones as lines in the frequency domain. Figure 10-2 shows the
same 500-Hz direct tone and delayed tones in the time domain. The delay is accomplished by
applying the second tone to a delay device with different delays settings, and combining the original

and the delayed tones.