Page 77 - The Master Handbook Of Acoustics
P. 77
52 CHAPTER THREE
120
32 dB
100 90 Phons
Sound-pressure level - dB 80 58 dB
60
40
20 30 Phons
0
20 50 100 300 1 kHz 3 kHz 10 kHz 20 kHz
Frequency - Hz
FIGURE 3-7
A comparison of the ear’s response at 20 Hz compared to that at 1,000 Hz. At a loud-
ness level of 30 phons, the sound-pressure level of a 20-Hz tone must be 58 dB higher
than that at 1,000 Hz to have the same loudness. At 90 phons loudness level, an
increase of only 32 dB is required. The ear’s response is somewhat flatter at high loud-
ness levels. Loudness level is only an intermediate step to true subjective loudness as
explained in the text.
about 60 phons). As the passage was played at something like an 80-
phon loudness level in the concert hall, something needs to be done to
give the bass and treble of the music the proper balance at the lower-
than-concert-hall level. Our enthusiast would find it necessary to
increase both bass and treble for good balance.
The loudness control found on many amplifiers adjusts electrical net-
works to compensate for the change in frequency response of the ear for
different loudness levels. But the curve corresponding to a given setting
of the loudness control applies only to a specific loudness level of repro-
duced sound. The loudness control is far from a complete solution to the
problem. Think of all the things that affect the volume-control setting in
a particular situation. The loudspeakers vary in acoustic output for a
given input power. The gain of preamplifiers, power amplifiers, tuners,
