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Section 4. - MATCHING TRANSDUCERS TO POWER AMPLIFIERS
Transducers used in JBL’s HLA system are conservatively rated. Each transducer in an HLA system has
been tested with pink noise with a crest factor of 6 dB, over its intended range, simulating realistic operating
conditions with music program peaks of four times the RMS power.
Power is calculated based on a minimum impedance (when the driver is cold) and the RMS voltage of
the noise input signal. The AES specification used by JBL requires the transducer to operate at this level for 2
hours with no degradation in performance.
It is recommended that amplifiers have a peak output capacity of double the RMS power rating at full
power, taking amplifier dynamic headroom into account, to avoid clipping the signal. For this reason maximum
Recommended Power Levels per Transducer (RPL/T) exceed the AES power rating of individual drivers.
Transducer specifications and power levels:
Frequency HLA Frequency, Impedance AES power RPL/T Sensitivity,
Band Driver in Hz rating 1w/1m
SUB 2242HPL 35-120 8 ohms 800 W 1,000 W 98 dB
LF 2254J 120-297 16 ohms 600 W 700 W 107 dB
MF 2251J 297-1.14k 16 ohms 400 W 500 W 107 dB
HF 2451SLJ 1.14-16k 16 ohms 75 W 200 W 116dB
Power amplifier requirements for HLA system
Four 4895 three-way speaker systems need only three channels of amplification, one for each output
band. Each band uses 16-ohm transducers, and four paralleled transducers represent a 4-ohm load.
A 4897 subwoofer requires a single channel of amplifier power. 4897 subwoofers use two 8-ohm
transducers with separate Speakon circuit connections. One 4897 subwoofer presents a 4-ohm load to a power
amplifier, with its two transducers in parallel.
Choosing the correct amplifier for each bandpass.
The 4897 subwoofer uses two 8-ohm transducers with separate pin-outs for maximum energy transfer.
The subwoofer amp should be capable of 1,600 to 2,400 watts output into four ohms. The use of 16-ohm
transducers in the 4895 speakers allows four drivers in each band pass to be driven in parallel from an amplifier
running at 4 ohms, for efficient use of amplifiers.
The suggested minimum number of HLA units recommended by JBL to be used together in a system
are qty. four HLA-4895’s and qty. two HLA-4897’s. This quantity of loudspeakers is called an “Array Module”. A
minimum of two array modules would be used for a stereo (left/right) system. Four 4895 three-way speakers will
need three channels of four-ohm power at these power ratings:
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