.. Rather ironically, some of the speakers I have liked have had less good specifications than some of the competition that I liked less well. For example, when the Ohm Walsh 2 speaker came out, I liked it very much for a speaker at its price point (which was about $750 in the early 1980's, if my memory is right). But as I recall, their frequency response specification was with a worse tolerance than usual (+/-4dB), and even so, they did not go out to 20kHz (not that there is much musically at such a high frequency, even if one is able to hear that high). The Ohm website lists the frequency response as 42 - 17,000 Hz, but without a tolerance specified (which, again, if my memory is correct, was originally specified +/-4dB). But I have not seen comprehensive tests of this speaker, nor have I seen anything for off-axis response (which, for frequencies below the crossover point for the tweeter, should be identical to on-axis response, until one gets behind or nearly behind them, given the Walsh driver and the blocking of the sound to the rear).
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