1614 Chapter 46
time information can’t be observed on a magni-
tude/phase plot. Any attempt to view both simultane-
ously will obscure some of the detail of both. Modern
analyzers allow the measurer to switch between the time
and frequency perspectives to extract information from
the data.
46.3.4 Testing Methods
Compared to other components in the sound system, the
basic design of loudspeakers and compression drivers
has changed relatively little in the last 50 years. At over
a half-century since their invention, we are still pushing
air with pistons driven by voice coils suspended in mag-
netic fields. But the methods for measuring their perfor-
mance have improved steadily since computers can now
efficiently perform digital sampling and signal process-
ing, and execute transforms in fractions of a second.
Extremely capable measurement systems are now
accessible and affordable to even the smallest manufac-
turers and individual audio practitioners. A common
attribute of systems suitable for loudspeaker testing is
the ability to make reflection-free measurements
indoors, without the need for an anechoic chamber.
Anechoic measurements in live spaces can be accom-
plished by the use of a time window that allows the ana-
lyzer to collect the direct field response of the
loudspeaker while ignoring room reflections. Conceptu-
ally, a time window can be thought of as an accurate
switch that can be closed as the desired waves pass the
microphone and opened prior to the arrival of undesir-
able reflections from the environment. A number of
implementations exist, each with its own set of advan-
tages and drawbacks. The potential buyer must under-
stand the trade-offs and choose a system that offers the
best set of compromises for the intended application.
Parameters of interest include signal-to-noise ratios,
speed, resolution, and price.Figure 46-13. The domain chart provides a map between various representations of a system response. Courtesy Brüel and
Kjaer.