This may well be related to the discontinuity in the impedance traces noted earlier, and also appears in the SCM7's farfield response, averaged across a 30° horizontal window centered on the tweeter axis (fig.4).
ATC SCM45 DRIVER
Overall, each driver has a fairly flat output within its passband, but the woofer's response is disturbed by a small peak and dip between 500 and 700Hz.
ATC SCM45 DRIVERS
This measured behavior suggests that the little ATC will benefit from some boundary reinforcement otherwise, the speaker's bass will sound, as JM found, "'respectable' rather than 'convincing.'"įig.3 ATC SCM7 v.3, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield response of woofer (blue) plotted below 355Hz.įig.3 also indicates that the crossover between the two drivers occurs just above 2kHz, and that each rolls out with an initial 12dB/octave slope, though the tweeter's slope steepens an octave below crossover. The SCM7's output is down by 6dB at the cabinet/woofer tuning frequency, as anticipated from the impedance graph. There is virtually none of the rise in the upper-bass response that usually results from measuring in the nearfieldthe assumption behind a nearfield measurement is that the speaker baffle extends to infinity in all directions, which boosts the measured low-frequency output below a frequency related to the actual baffle dimensions. Below 350Hz, the blue trace shows the woofer's output measured in the nearfield. Though the electrical phase angle (fig.1, dotted trace) reaches ≦1° at 73Hz, the impedance magnitude is high at that frequency the ATC won't present any drive difficulty to the partnering amplifier.įig.2 ATC SCM7 v.3, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of side panel (MLS driving voltage to speaker, 7.55V measurement bandwidth, 2kHz).įig.3 shows the individual responses of the woofer (blue trace) and tweeter (red). The impedance averages 6 ohms in the midrange and low treble, with a minimum value of 5.25 ohms at 1100Hz.
The sole peak in the bass, reaching 48 ohms at 57Hz, indicates that that is the tuning frequency of the woofer in the sealed enclosure, which in turn implies only modest low-frequency extension. The speaker's electrical impedance, specified as 8 ohms, is shown as the solid trace in fig.1. All measurements were taken without the grille.Īs expected from its diminutive size, the SCM7 v.3 is not very sensitive my estimate of its voltage sensitivity came in at 82dB(B)/2.83V/m, which is 2dB below the specified 84dB.
ATC SCM45 SERIAL
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the ATC's frequency response in the farfield (I measured serial no.1002), and an Earthworks QTC-40 for the nearfield responses. John Marks sent me the review pair of this elegant British, sealed-box minimonitor to run through my loudspeaker test regime.
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