Anthem STR Operating Manual - Anthem Room Correction (Arc)
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For anyone reading this, the experience of walking into a room and being struck by the dramatic change in its sound
after carpet and furnishings have been moved out is probably a familiar one. It may also bring to mind the varying sound
character from one room to the next according to its size and structural qualities.
By the same token, even when the finest speakers are optimally positioned, the room impacts sound quality
considerably. The walls, floor, ceiling, and windows add unwanted resonance and coloration making bass less
impactful, voices less natural, and dialogue less intelligible. The effect on frequency response is typically ±6 dB in
the midrange and ±10 dB at low frequencies. To compensate for this and to optimize the in-room response of your
speakers, Anthem Room Correction measures the output of each one relative to the listening area then through a
special series of calculations adjusts the output accordingly. Its target responses have a psychoacoustic basis from
research results, not just theoretically ideal curves.
While removing resonances and modal peaks common to the measurement positions, ARC also distinguishes and
preserves the positive effects imparted by the room by detecting how much the room’s boundaries and pressurization
reinforce low frequencies. This effect, known as room gain, appears as a bump in the target response. ARC does not
remove it because if flattened, bass sounds thin. Our ear/brain mechanism expects to hear this characteristic when
indoors. Ideal anechoic speaker response, as measured in a special non-reverberant facility, is not the same as ideal
in-room response, which normally includes this room gain to varying degree. It is one reason that a speaker sounds
different outdoors when in fact it is the same speaker. If a speaker indoors was forced to sound like it’s positioned
outdoors, it just wouldn’t sound right.
Sample curves:
The red curves represent the in-room response before correction, as an average from five measurement positions,
whereas the green ones show response with equalization applied. In this case a subwoofer and bass management are
also in use. In the subwoofer graph, which is on the left, the difference between the level of the red and purple curves
shows the amount of room gain.
In addition, ARC senses where each speaker’s low-frequency response naturally declines, and sets the high-pass filters to
match this natural limit.
The default correction range is 5 kHz. Although it can be changed to a lower frequency if desired, raising it is not
recommended. At higher frequencies the microphone becomes directional thus affecting measurement accuracy.
Note that the subwoofer graph may imply that the subwoofer plays up to the highest frequency shown, but what it plays
depends on what the other channels send to it as determined by their crossover setting. The subwoofer graph shows the
available correction range, which is not necessarily the range that other channels send to it through bass management.