The total magnitude variation (around 14 Ohms) would suggest that an amplifier with a low damping factor could drive the SCM40 without some serious deviation in its frequency response. Minimum impedance magnitude at low frequencies is about 5.95 Ohm (at 90Hz), therefore the loudspeaker could be classified as an 8-ohm design. Impedance measurements shows that the SCM40 is a well cared loudspeaker in terms of its behavior as a load to the amplifier. On-axis (green curve) and averaged on/off axis response (red curve). Summed near-field frequency response (dBSPL/2.83V/m), far field/near field splicing, with 0.33oct smoothing. The two curves seems to differ significantly only above 7kHz and only in level terms, a finding that leaves some promises for a quite smooth off-axis behavior and is consistent with ATC's statements about their new tweeter. Of particular interest, finally, is the comparison between the on-axis and the off-axis horizontally and vertically averaged response. Based on this graph and the average sensitivity, -6dB points are close to 35Hz and 22kHz for the low and high frequency part respectively. Cut-off behavior at both ends of the spectrum is smooth with no visible acute dome resonance, at least up to 40kHz. Bass alignment appears to be towards an accurate and neutral character with the region between 50 and 150Hz being just 1.5dB above the average sensitivity. This graph also gives a somewhat more general idea about the behavior between 2 and 7kHz as well as about the behavior of the tweeter. This is lower than the 85dBSPL given by ATC, but keep in mind that the average method tends, more often than not, towards lower results anyway. Average sensitivity, as calculated using values between 125Hz and 16kHz in one octave steps, is approximately 81dBSPL. Summed near-field response of the SCM40, obtained by splicing near field and far field quasi-anechoic measurements (including a 0.33oct smoothing), confirms the initial impression of a good pass band behavior. Although one can see that there is some coloration introduced, of about 1dB (maximum) in the region between 5 and 10kHz, the choice of ATC is proved a correct one since this is a much better behavior compared to most grills. The same graph (that does not include any smoothing) clearly shows that the role of the protective grill is significantly limited. The bigger increase in sensitivity appears a little over the 11kHz point (3.4dB). Compared with the calculated average sensitivity the largest decrease occurs just above the 5.5kHz point (about -6.5dB) with a bandwidth clearly narrower than 1kHz. The most interesting findings in the relevant graph are a decrease in sensitivity in the 2-7kHz region and an increase trend towards very high frequencies above 10kHz or so. SCM40 quasi-anechoic frequency response (down to 500Hz) shows a loudspeaker with good pass band behavior, with only small amplitude deviations.
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