UNISource Corporation FG-8102, Operation Manual

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FIG 8. TESTING SPEAKER SYSTEMS AND IMPEDANCE NETWORKS.
5-6. Testing Speakers and Impedance Networks
This instrument can be used to provide information regarding the input impedance
of a speaker or any other impedance network vs. frequency. In addition, the
resonant frequency of the network can be determined.
A. Connect equipment as shown in Test Set-Up in FIG. 8 for frequency
response measurement except that the signal input to the speaker or
impedance network is monitored. The oscilloscope may be used to verify that
this instrument is not in a clipping condition.
B. If the voltmeter method is used, vary the range over the full range of interest
and log the voltage measured at the speaker terminals vs. Frequency. The
dB scales of the AC voltmeter are convenient for converting this information
to standard response units.
C. If the oscilloscope method is used, use sweep operation as for frequency
response measurement.
D. In speaker testing, a pronounced increase of voltage will occur at some low
frequency. This is the resonance frequency of the speaker systems(FIG. 8).
The speaker enclosure will modify the results obtained from the same
speaker without an enclosure. A properly designed enclosure will produce a
small peak on each side of the peak obtained without an enclosure. the
enclosure designer can use the response characteristics to evaluate the
effects of varying port sizes, damping materials and other basic enclosure
factors.
E. In testing other impedance networks resonance will not necessarily occur at
low frequency. However, as resonance is approached the signal level will
increase. The impedance of the network can be measured at resonance, or
at other frequencies if desired as follows:
1) Connect a variable resistor in series with the impedance network as
shown in FIG. 8
2) Measure the voltage at points E1 and E2 respectively and adjust variable
resistor R1 so that voltage E2 equals one half of voltage E1