APPLICATION NOTES
FREEFIELD vs. DIFFUSEFIELD USE
Only a small percentage of all acousti-
cal measurements are performed in a
well defined and/or well controlled
environment of an e.g. acoustical labo-
ratory – on the contrary most acousti-
cal measurements are done under not
really controlled conditions. Here are
some hints on how to use our micro-
phone.
Sound Fields:
Free field:
There are no reflec
ting objects, only the
microphone
influen
ces the sound field.
Diffuse field:
There are many re
flecting surfaces or
sound sources so that
the sound waves arri
ve from all directions.
Pressure field: This is found in small
confined spaces like
sound calibrators.
Depending on the nature of the sound
field an appropriate microphone, which
is optimized for the sound field could
be selected. Unfortunately there are
many practical situations where the
sound field is not really of a well de-
fined type. This application note should
give you an idea on how to measure
with a free field response microphone.
The free field microphone is the most
common in use, chosen on tradition
but we should know about the sound
field.
The following picture shows both the
free field and the diffuse field response
of a free field microphone.
