Page 124 - The Master Handbook Of Acoustics

99
SPEECH, MUSIC, AND NOISE

This is to be expected because the head is
small compared to wavelengths of 4.5 to 9 0
feet associated with this frequency band.
5 dB
There are significant directional effects,
however, for the 1,400- to 2,000-Hz band. 10 dB
For this band, which contains important
speech frequencies, the front-to-back dif-
90 270
ference is about 12 dB.
In the vertical plane, Fig. 5-8B, the 125- 1400–2000 Hz
to 250-Hz band shows about 5 dB front-to-
125–250 Hz
back difference again. For the 1,400- to
2,000-Hz band, the front-to-back difference
is also about the same as the horizontal 180
plane, except for the torso effect. The dis- A
crimination against high speech frequen-
cies picked up on a lapel microphone
90
becomes obvious in Fig. 5-8B, although the
measurements were not carried to angles
closer to 270 degrees.

Music 10 dB
5 dB
180 0
Musical sounds are extremely variable in
their complexity and can range from a near 1400–2000 Hz
sine-wave form of a single instrument or
125–250 Hz
voice to the highly complex mixed sound
of a symphony orchestra. Each instrument
and each voice has a different tonal texture 270
for each note. Many musical instruments, B
such as the violin, viola, cello, or bass, pro- FIGURE 5-8
duce their tones by vibration of strings. On Human voice directionality measured using the voice
a stretched string, the overtones are all as a sound source. (A) Front-to-back directional
exact multiples of the fundamental, the effects of about 12 dB are found for the important
speech frequencies. (B) In the vertical plane, the
lowest tone produced. These overtones
front-to-back directional effects for the 1,400- to
may thus be called harmonics. If the string 2,000-Hz band are about the same as for the hori-
is bowed in the middle, odd harmonics are zontal plane. By permission of Heinrich Kuttruff and
emphasized because the fundamental and Applied Science Publishers Ltd., London.
odd harmonics have maximum amplitude