1GA16_1L.DOC
ROHDE & SCHWARZ
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5.1.9 Equivalent Volume
The equivalent volume Veq of a loudspeaker array defines the air volume, the compliance of which is
equal to that of the loudspeaker array.
First the impedance measurement is carried out with the loudspeaker array open. The loudspeaker is then
accommodated in a small, rigid housing without any further openings and additional insulation and a new
measurement is started with the V
eq
/V
b
softkey (F11, level 4). With the newly determined resonance
frequency Fb (>Fr) the equivalent volume Veq/Vb referred to Vb is obtained with the formula
V
V
f
f
eq
b
b
r
=
−
2
1
V
b
being the internal volume of the loudspeaker housing less the volume of the loudspeaker array.
5.1.10 Go/Nogo Test
At the end of a sweep the impedance characteristic of a reference loudspeaker can be stored as a
reference trace (softkey STO REF) and is then available as a "golden unit" for further measurements. To
measure further DUTS, the stored reference characteristic is loaded with softkey REF SPK and the
tolerance range specified. One of three display modes can be selected:
•
TRACE A: the relative impedance characteristic is displayed.
•
TRACE B: the relative impedance characteristic is displayed as trace B while the absolute impedance
characteristic is displayed as trace A (see Fig. 7).
•
OFF switches the reference off so that only the absolute impedance characteristic is displayed.
5
5.2
.2 Sound Pressure Measurements
Sound Pressure Measurements
Sound pressure variations versus frequency allow conclusions to be drawn on the tone quality of a
loudspeaker. Without this information dimensioning of crossover units is not possible. Furthermore, the
sound pressure characteristic of a system provides information on possible polarity reversals in the
loudspeaker system provided the sound pressure curve of a correctly poled reference system is available
(see section 5.4.3, Polarity Check by Comparison to Reference Sound Pressure Characteristic).
With sound pressure measurements at a fixed frequency, the maximum sound pressure of a loudspeaker
(at nominal power) and the sensitivity (at 1 W) can be measured at a distance of 1 m. The measured
sensitivity (in dBspl at 1 W and 1 m distance from the microphone) may be stored as a reference value in
the measurement of frequency response (see section 5.2.5, Sensitivity Measurement and Radiation
Angle).
Sound pressure measurements (measurement of sensitivity and sound-pressure frequency response) are
selected by means of the SOUND softkey (F7).
Summary of Contents for UPD
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