Community ENTASYS Application Manual page 36

AC O U ST I C A L M O D E L I N G P R O G R A M S
Data Files for Modeling
Acoustical prediction programs handle loudspeakers' maximum SPL output data in different ways. Due to the inherent
radiation characteristics of ENTASYS, Community recommends the use of EASE and EASE Focus for best results. EASE data is
provided in GLL (Generic Loudspeaker Library) format. Data is also available as an EFO file for use in EASE Focus.
These data files allow for accurate calculation of the SPL and directivity of ENTASYS systems at any distance greater than
approximately 8 ft (2.4 m). Other methods of acoustical prediction cannot accurately model the radiation of ENTASYS due to
its extended near-field to far-field transition distance (line array behavior).
Maximum SPL and Crest Factor
The maximum achievable SPL for any loudspeaker is dependent on both the loudspeaker itself and on the signal it is
reproducing. Specifically, signals with higher crest factors will generally produce lower SPL output from a loudspeaker. This is
because the RMS level of the signal is lower than its peak level.
The predicted maximum SPL in EASE and EASE Focus are based on a signal with a 6 dB crest factor (*refer to the box below
for more information.) This is a standard signal for testing the maximum input and output capabilities of loudspeaker systems.
The sounds generated by live sources typically have crest factors greater than 6 dB. The sound system designer should take
this into account when determining the maximum achievable SPL for a particular design.
A quick determination of this can be reached by subtracting 6 dB from the crest factor of the program material to be
reproduced by the sound system. The result will be the value by which the predicted SPL should then be reduced to yield a
more accurate maximum SPL when using the recommended 3,600 W into 4 ohm amplifier to power ENTASYS.
As an example, an EASE model predicts the maximum SPL in the audience area to be approximately 104 dB. The anticipated
program material is estimated to have a crest factor of 15 dB. Using this program material, a more realistic maximum SPL in
the audience area would be 95 dB (15 dB - 6 dB = 9 dB, 104 dB - 9 dB = 95 dB).
* Crest Factor
The crest factor of a signal is the difference between the RMS voltage level and the peak level of the signal. This is
illustrated in the graphs shown in Figures 31 - 32. In each figure the actual waveform of the signal is shown at the top
(green trace). Below that, the graph shows the RMS level as a solid purple area, above which is a yellow trace of the
instantaneous peak level of the signal. The space between the purple RMS voltage level and the yellow peak level
represents the crest factor of the signal at that particular instant.
The signal shown in Figure 31 is a typical pink-noise signal with a 6 dB crest factor used to test loudspeakers. The
difference between the RMS voltage level and the peak level is not 6 dB at every instant of the signal, but when averaged
over several periods of the lowest frequency component in the signal, this difference will be approximately 6 dB.
The signal shown in Figure 32 is a slightly compressed speech. The difference between the RMS voltage level and the
peak level varies from about 10 - 15 dB.
For additional information on a signal's crest factor and how it may affect SPL please refer to the Maximum SPL and
Crest Factor section above.
SYSTEM DESIGN GUIDELINES
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Community ENTASYS Application Guide - Page 36