1370 Chapter 35
taken into account when developing a fully descrip-
tive data model.- The use of combined microphones is also wide
spread. In particular, multichannel receivers, such as
dummy heads, coincidence recording microphones,
or B-format receivers, need to find an appropriate
representation in the simulation software. - Another issue of concern is the acquisition of phase
data. The impact of neglecting the phase of the loud-
speaker on the simulation of its performance is well
known. But not much research has happened in that
respect regarding microphones. Nevertheless, it is
clear that under special circumstances like in feed-
back situations or for the electronic combination of
microphone signals (e.g., two active microphones on
lecterns) phase plays an important role. - Finally, of course, it must be stated that the usability
of microphone data has its limitations depending on
the application of the particular model. Compared to
installation microphones typical handheld micro-
phones have different properties. The data that is
needed and that can be acquired may differ
accordingly.
Recently an advanced data model was proposed that
is able to resolve many of the issues listed above.^43
Basically, it suggests using a similar approach like the
loudspeaker description language (GLL) introduced
earlier, namely to describe receiver systems in a gener-
alized, object-oriented way. This means especially that:
- Microphone data files should at least include far-field
data (plane wave assumption), but can also contain
proximity data for various near-field distances. - A microphone model can consist of multiple
receivers, that is, acoustic inputs, and can have
multiple channels (electronic outputs). - A switchable microphone should be represented by a
set of corresponding data subsets. - Impulse response or complex frequency response
data should be utilized to describe the sensitivity and
the directional properties of the microphone as
appropriate.
Fig. 35-35 is an example for an import function in
the new EASE Microphone Database software.
35.3 Tools of Simulation
Today, an acoustic CAD program must be able to pre-
dict all needed acoustic measures exactly enough. A
100% forecast is certainly impossible but the results of
a computer simulation must come close to reality (errors
generally equal or less than 30%). Then it becomes pos-
sible that the acoustic behavior of a facility can be made
audible by so-called auralization. (One will listen to
sound events just performed by means of the computer.)
The following will give a short introduction of the pos-
sibilities of computer simulation today.35.3.1 Room Acoustic Simulation35.3.1.1 Statistical ApproachBased on simple room data and the associated surface
absorption coefficients, a computer program is able to
calculate the reverberation time according the Sabine
and Norris-Eyring equations, see Section 7.2.1.1. On the
other side measured values must be usable directly in
such a program. Calculation of the early decay time
(EDT) should be possible too.
A comprehensive database of country-specific and
international wall materials and their absorption coeffi-
cients is part of the program. This database should be
accessible to allow the user to import and enter data
from other textbook sources or measurements. Because
most of the needed scattering coefficients are not avail-
able in textbooks a computer program should allow
deriving values even by rules of thumb.
A set of frequency-dependent target reverberation
times should be available for entering into the simula-
tion program so that the room models, calculated (or
real-world measured) RT 60 times can be compared with
the target values. The program should then indicate (for
each selected frequency band) the calculated (or
measured) Fig. 35-35 time versus the target RT 60 time
and list the number of excess or deficient RT 60 times forFigure 35-35. Import routine in EASE Microphone Data-
base Software.