JBL VTX Series, User Manual

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VTX A12 | User Manual
13 - TESTING VTX A12
Speakers need to be periodically checked and maintained to assure long-term performance and reliability. While the VTX A12 is designed
for the utmost reliability, it is important to confirm that the system is operating within specified tolerances to ensure optimal performance
for years to come. Below are two methods that can be used to check and verify proper transducer performance in a VTX A12 system.
13.1 USING A DMM (DIGITAL MULTIMETER)
This method is best suited for when the speaker system is in the shop. A DCR (DC resistance) test with a multimeter can give a very
accurate reading of how many transducers are properly wired together and within their standard operating tolerances. This test is ap-
propriate for individual cabinets and not groups.
With the A12 speaker unconnected to any amplifiers, set a DMM to the resistance (Ω) setting and place the probes across the 1+/-, 2+/-,
3+/-, and 4+/- leads. Record the values indicated on the DMM for each pair of leads and refer to the chart below to either confirm correct
readings or investigate out-of-tolerance DCR readings.
HF Section (Pin 4)
DCR Tolerance
All drivers functioning 7.0 Ω +/- 0.2 Ω
1 x HF Driver open 10.3 Ω +/- 0.2 Ω
2 x HF Drivers open 20.5 Ω +/- 0.2 Ω
3 x HF Drivers open OL -
Any driver shorted 0.2 Ω -
MF Section (Pin 3)
DCR Tolerance
All woofers functioning 5.4 Ω +/- 0.2 Ω
1 x woofer open 10.8 Ω +/- 0.2 Ω
LF Section (Pin 1 / 2)
DCR Tolerance
Functioning woofer 5.5 Ω +/- 0.2 Ω
Shorted 0.2 Ω -
Notes:
• The DCR values listed above assume room temperature transducers. If measurements are taken right after use, when the transduc-
ers are warm, the values will vary. For best results, test the speakers cold.
• The DCR value of a transducer gives an accurate representation of its electrical state, but mechanical defects are not characterized
by this test. Refer to the VTX A12 Service Manual for instructions on performing a rub-and-buzz test with a sine wave generator.