Handbook for Sound Engineers

Computer Aided Sound System Design 1339

Introduction

For more than 2000 years acoustic phenomena have
been perceived and manipulated subjectively. Reference
can be made in this context to Marcus Vitruvius, the
ancient Roman architect who described at this early
time the application of acoustic laws in theatrical
spaces. But only since the end of the medieval times and
particularly during the last century acoustics has devel-
oped into an independent science.
Highlights on the way to a scientifically calculated
design:

• Roman/Greek times, medieval times: knowledge
  based on experience and first trial and error
  reports—e.g., by the Roman architect Vitruvius, 15
  BC.


• Since the end of 18th^ century: Theoretical investiga-
  tions—e.g., Chladni, 1810, or in 1875, Lord
  Rayleigh, Professor Helmholtz.


• Since 1900: room acoustical basics, Professor
  Sabine/United States 1923; radiation of sound, H.
  Stenzel/ Germany 1930, and H. F. Olson/United
  States 1947.


• By 1935: measurement in models and “auralization”
  in physical models, Professor Spandöck München,
  Professor Reichardt, Dresden/Germany.


• Since 1965: computer-model investigations, Pro-
  fessor Krokstad, in Trondheim/Norway, afterwards
  many similar works have been done.


• Since 1995: auralization by means of computer
  models has been introduced.

A measured sound-field structure in 3D, so-called
waterfall form (decay of sound energy as a function of
time and frequency) is shown in Fig. 35-1. The sound
level is marked on the ordinate, the frequency (range of
frequency 63 Hz–8 kHz) on the abscissa, and the time
on the third axis (0 ms–direct sound to 3.5 s reverbera-
tion).
These sound-field structures are depending on
listener locations. In the old days a wanted sound decay
for concerts or for speech transmission was generated
by changing the primary or secondary structure of a
room, see Chapter 7.3.2. Now with sound systems it is
possible to generate any sound fields subjectively
desired.
Today we can derive the basic items in sound design.
Listening comfort and intelligibility are influenced by:

• Reverberation time and volume.


• Early and late reflections.


• Ambient noise level.
  
  
  • Directivity of the loudspeakers or new array
    constructions.
  
  
  • New loudspeaker types.
  
  
  • Interference effects.
  
  
  
  

Some basic measures of the performance of a sound

system are:

• Intelligibility Alcons, Ct, RASTI, etc.


• Loudness in dB (SPLtot).


• Direct sound in dB (SPLdir).


• Frequency response in ±dB from flat.


• Coverage in ±dB from even.

The goal of modern sound design is to calculate in

advance the complete sound field structure in a hall or

in open spaces by means of Computer-Aided Acoustic

Design (CAAD) programs enabling you to prevent any

surprises that become evident after a sound system has

been installed. You just describe in advance the

expected properties of your sound system and the

overall acoustic properties of your room using the new

sound system.

The following considerations include personal expe-

riences of the authors, especially with the CAAD

program EASE,^1 but features of other programs are also

explained.

35.1 Sound Design Basics for Acoustic Simulation

Application of physical or computer models for acoustic

and sound system design:

Prior to 1965. Physical models since the 1930s and

after WWII mainly in selected cases in research centers

by means of huge computers.

Figure 35-1. Typical waterfall presentation.