Integrated Amp Reviews

Sidebar 3: ARC Measurements

While ARC's own computer-screen results show the performance of the system before and after running the room EQ, I also measured the results with an independent system: the Parts Express OmniMic. While this system isn't as sophisticated as the gear John Atkinson uses to measure loudspeakers for Stereophile, it does use a calibrated microphone, and can reveal what ARC is doing to the response.

While the actual equalized responses were performed by ARC using an average of eight or nine microphone positions, the OmniMic plots shown here (all were 1/6-octave averaged) represent a single listening position. In my room, the differences between a single and multiple points were trivial, though multiple positions did smooth out the dip in the equalized response at 43Hz. The use of multiple mike positions also adds uncertainty where the goal is to document multiple before-and-after tests: precise mike positions can be difficult to reproduce, possibly skewing the results.

To save space, fig.1 shows only the right channel, the worse of the two pre-EQ measurements. (The left channel, post-EQ, did eliminate a similar dip at around 43Hz, meaning that that dip was indeed correctible, and not one of the black-hole frequency dips.) Note the significant peaks and dips below 300Hz, which are not rare in room responses. Surprisingly, they don't sound as bad as these response curves might suggest—we do adapt to the quirks of our own rooms. But ARC's smoothing of the response between 80 and 200Hz is clearly visible, as is the improvement in that 43Hz dip. The overall response is still elevated from the bass to the upper bass compared to the midrange and treble, but that's desirable in a room response taken at the seating position.—Thomas J. Norton