JBL claims an output of 117dB for 30mW for the S700 but offers no specification of nominal impedance to allow this to be converted into a voltage sensitivity. Our measurements indicate that a nominal impedance of 35ohm is appropriate, which would make 117dB/30mW equivalent to 116.8dB for 1 Vrms -close to our measured value of 115.9dB at 1 kHz, averaged for the two capsules. In fact the impedance varies from 32.4ohm to 38.2ohm across the audible spectrum (20Hz-20kHz), a modest variation that introduces a frequency response change of only 0.32dB with a 10ohm source impedance, rising to 0.66dB for 30ohm - small variations that are unlikely to be noticed in practice. This is for the S700 in passive mode, with the LiveStage DSP switched off; with it engaged, input impedance rises to an almost constant 1.9kHz.
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