Handbook for Sound Engineers

Computer Aided Sound System Design 1343

35.1.3 Acoustic Sources and Loudspeaker Systems

35.1.3.1 Natural Sources

Sound reinforcement quite often has to deal with rein-

forcing natural sources like human voices or natural

music instruments. Therefore to know the amount of

reinforcing required, we have to know the quality of the

reference sources and the following aspects:

• Loudness.


• Frequency response.


• Directivity.

Fig. 35-6 shows the level and frequency range of
natural sources and instruments perceived by human
beings. In this range natural sources develop their sound
power and produce level components in the mentioned
frequency range. Everything outside this range is on one
side masked by noise (lower 30 dB in the midrange) or
dangerous for our health—pain threshold |120 dB.
Frequency components lower than 25 Hz are becoming
inaudible as well as frequency parts higher than
15–20 kHz—depending on age and health.

Natural sound sources like human voices or musical

instruments do not radiate sound in an omnidirectional

way. It comes close in case of a human voice, but the

higher the frequencies, the more the head becomes an

obstacle to the sound radiation backward. Fig. 35-7A

shows the directivity balloon curves of a female voice

in the vertical domain. Below 1000 Hz the pattern is

almost an omnidirectional radiation pattern, but for

higher frequencies the radiation dominates more and

more in front of the head. This is also the reason that in

such concert halls where the audience is behind the

orchestra, people sometimes complain about the

singer’s clarity.

The radiation behavior of musical instruments is

much more complex. Here a lot of investigations have

been done, especially by Meyer.^6 Fig. 35-7B shows the

3D presentation of the directivity balloon of a horn

instrument including the player. According to Meyer the

shadow effect of the player himself is also considered.

We observe with increasing frequencies a reduced radia-

tion into the front domain of the player.

To model all these different natural sources correctly,

their radiation behavior has to be known and this not

only as single instruments but also in groups. Here a

lack of corresponding data is still evident.

Figure 35-5. Same room model in four different views.

A. Wireframe model. B. Rendered view.

C. AutoCad presentation. D. SketchUp view.