Page 140 - The Master Handbook Of Acoustics

115
SPEECH, MUSIC, AND NOISE

1.00
1.0

0.8

Voltage 0.6

0.4
0.30
0.20
0.2
0.10
0.05
0.025
0
f o 2f o 3f o 4f o 5f o 6f o
Frequency
FIGURE 5-20

A distorted periodic wave is measured with a constant bandwidth wave analyzer. The
fundamental, f , is set for some reference voltage, taken here as 1.00 volt. Tuning the
o
wave analyzer to 2f the second harmonic amplitude is measured as 0.10 volt. The wave
o
analyzer is tuned successively to 3f , 4f and other harmonics yielding amplitudes of
o o
each harmonic as shown. The root-mean-square of the harmonic voltages is then com-
pared to the 1.00 volt fundamental to find the total harmonic distortion expressed in
percentage.

Table 5-2 Harmonic Distortion Products.

Harmonic Volts (Volts) 2
2nd Harmonic 2f 0.10 0.01
o
3rd Harmonic 3f 0.30 0.09
o
4th Harmonic 4f 0.05 0.0025
o
5th Harmonic 5f 0.20 0.04
o
6th Harmonic 6f 0.025 0.000625
o
7th and higher (negligible)
Sum 0.143125
Fundamental f 1 kHz, 1.00 volt amplitude
o