Toa FB-100 - Manual (Page 6)

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8.2. Level Balance and Polarity
When using the FB-100 in combination with TOA's F or H Series Full-Range Speakers, adjust their level
balance or polarity depending on the conditions of the installation location.
8.2.1. Level balance adjustment
Adjust the level of the sub-woofer or full-range speaker depending on the number of units to be installed or
installation conditions.
8.2.2. Polarity adjustment
• Acoustic energy increases at the crossover band for the sub-woofer and full-range speaker if the two
speakers are in phase with each other, and decreases if out of phase. Because the phase characteristics of
both the sub-woofer and the full-range speaker vary continuously depending on frequency, simply matching
the connector polarities of the sub-woofer is not always the best procedure.
• To confirm how much the acoustic energy increases or decreases, reverse the polarity of the sub-woofer's
"+" and "–" connectors and select the connection polarity that results in the largest output of acoustic energy.
(The use of a real-time spectrum analyzer to check the degree of energy increase is highly recommended.)
9. CAUTIONS CONCERNING HIGH-IMPEDANCE APPLICATIONS
To avoid damaging the FB-100 speaker in high-impedance applications (with the MT-S0601 matching
transformer installed), be sure to observe the following conditions.
1. Do not limit the input signal band using such devices as a low-pass filter, but instead drive the speaker with
the full-range signal.
2. Use a high-impedance amplifier with a power rating higher than the wattage tap selected on the matching
transformer.
Tip
There is a low-frequency threshold for both the speaker matching transformer and the high-impedance
amplifier output transformer.
[Matching transformer low-frequency threshold]
If a signal with the frequencies lower than the low-frequency threshold is applied at rated power, the
transformer's primary impedance (input impedance) decreases abruptly due to core magnetic saturation. With
the MT-S0601, the impedance begins to decrease at approximately 40 Hz for the rated input power of 60 W,
and is almost halved at 30 Hz. If the speaker is used under this condition, an increased load is put on the
power amplifier as well as the matching transformer, causing potential equipment damage.
The low-frequency threshold varies depending on the selected transformer tap, and the smaller the tap-
selected wattage, the lower the threshold.
[High-impedance amplifier low-frequency threshold]
When a full-range signal (not band-limited) is applied, the amplifier is not adversely affected.
However, if the signal is band-limited with a low-pass filter and driven with rated power, an increased load is
put on the output stage, causing potential amplifier damage.