Specifications

Appendix: Acoustics
Dynaudio Professional AIR reference manual – 2014-08-28 122
Surround Sound Forum
Surround Sound Forum is a German interest group
composed of the VDT (Verband Deutscher Tonmeister;
Association of German Sound Engineers), the Institut
für Rundfunktechnik (IRT) and the Schule für Rund-
funktechnik (SRT). The SSF has prepared calibration
guidelines, which are generally accepted in Europe.
They specify three test signal, which are recorded at
-18 dBFS (RMS).
Signal (only in one channel) PPM level
t < 0,1 ms
PPM level
t < 10 ms
RMS level Sound pressure
level SLOW
Sound pressure
level SLOW
[dB] [dB] [dB] [dB] [dB(A)]
1 kHz sine -18 -18 -18
Pink noise 20 Hz to 20 kHz -9 -13 -18 82 78
Pink noise 200 Hz to 20 kHz -11 -15 -20 80 78
SMPTE
The corresponding SMPTE standard (RP155) uses
a standard of -20 dBFS for the reference level. Here,
the C-weighted sound pressure level of a 500 to 2 kHz
noise signal ends up at 83 dB.
Calibration of cinema systems
In a cinema, the listeners are sitting far from the moni-
tors. Presumably, the majority sits in the diffuse sound
eld. Attempts are made to establish a diffuse sound
eld from the surround monitors. Accordingly, when the
sound pressure is measured inside the cinema or in a
mixing theatre, it must be averaged over many differ-
ent measurement locations. The typical basis for the
majority of the standards is measuring at four or more
locations. If there are different areas for the audience
(for example main oor and balcony), measurements
should be made in at least four locations in each area.
Before these measurements can be made, the sys-
tem’s frequency response must also be in order.