Rohde & Schwarz UPD - Page 29

1GA16_1L.DOC ROHDE & SCHWARZ28
5.3.1 Test Setup
The test setup is the same as for sound pressure measurements (see section 5.2.1), but the use of a
power amplifier is not obligatory. In a setup without power amplifier, the generator outputs are connected
in parallel to the loudspeaker and to the XLR input of the UPD/UPL analyzer (channel 1).
The standard microphone is connected to the XLR input (channel 2) of the UPD analyzer (if required via a
microphone amplifier).
FIG 13: Test setup for phase measurement
5.3.2 Frequency Response of Phase
The phase linearity should be checked in a linear frequency sweep where the phase is measured between
the loudspeaker input and the generated sound wave. In the case of a linear phase response, a line with a
negative slope would ideally be obtained. In order to obtain a continuous phase response without 360°
shifts, the sweep points displayed in the range from 0 to 360° have to be further processed. The
algorithm of the application software requires in addition that the phase values measured at two adjacent
sweep points differ by less 180°. At a defined microphone distance the signal travel time is
t s
d m
/
/
=
330
The requirement
ϕ ϕ
2 1 2 1
360 180
− = °⋅ − ⋅ < °
( )f f t
yields for the frequency increment
( )/
/
f f Hz
t s
2 1
1
2
− <
⋅