The peak of 52 ohms at 53Hz in the impedance plot suggests that this is the tuning frequency for the SCM 11's woofer, which will be the frequency at which the response lies 6dB down from the midband reference. As I've written before, all things being equal, a sealed-box design will give a more extended low-frequency performance in-room than a reflex (ported) design, due to the former's slower rolloff below resonance: 12dB/octave rather than 24dB/octave. The SCM 11 is somewhat unusual in having for its woofer a sealed-box alignment. It's possible that these modes are high enough in frequency to have no subjective consequencesJM certainly didn't remark on any midrange congestion that might have been laid at the door of this behavior.įig.2 ATC SCM 11, 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). There is a slight discontinuity between 500 and 600Hz in the impedance-magnitude trace, and an investigation of the enclosure panels' vibrational behavior with an accelerometer did uncover two fairly strong resonant modes on the sidewall in this region (fig.2). Though there is a rather demanding combination of 5.5 ohms magnitude and ≤2° electrical phase angle at 3.3kHz, this shouldn't overtax well-designed amplifiers.įig.1 ATC SCM 11, electrical impedance (solid) and phase (dashed). This was probably owing to the fact that the SCM 11's impedance remains above 8 ohms for most of the audioband, with a dip to 6 ohms between 100 and 300Hz, and to 4.8 ohms in the mid-treble (fig.1). I estimated the ATC's sensitivity as being a low 82dB(B)/2.83V/mthis speaker should work best with higher-power amplifiers, though I note that JM had no drive difficulties with the Arcam Mini or Carat I57 receivers he used, and was impressed by the speaker's dynamic capabilities when he drove it with the Peachtree Nova. I will at some point move to class A/B amplification with more headroom as I feel there is more to come from these speakers.The SCM 11's voltage sensitivity is specified as a fairly low 85.0dB/2.83V/m this seemed a touch optimistic, as the ATC didn't seem to play any louder than the sample of the BBC LS3/5a that I routinely include when I'm set up to measure a bunch of loudspeakers. I have a PS Audio Stella Gain Dac and S300 Power Amp. They also allegedly need plenty of power. If they have limitations, it's that they have limited bass, not as limited as some i have tested, but limited.
They are also good for low level listening, although they do benefit from being given a bit of power and they open up more. For nearfield and very nearfield, highly recommended. I have a very small room where i work and chill (2.5m x 2.2m) and they sound just a good sat at my desk 60cm away from the speakers as on my couch 1.5m away. I'm hearing things in my music i never heard before. They have a great amount of detail and the way they reproduce music is just lovely. Only my journey i've been through Dynaudio, Buchardt and PMC bookshelf speakers and i've finally settled on these. What can i say about these speakers that has not already been written.
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