Audio Calibration

Anthem Room Correction (ARC) System - Part 1

ARTICLE INDEX

Verification of the Functionality of the Maximum EQ Frequency Option

This is a key feature of the ARC system. The maximum frequency at which the EQ will affect the speaker's response is set by this parameter. It is unique among EQ systems in that the choice is user-dependent. Some systems may offer one option, typically at 300Hz, where the transition between the room's dominated frequency response moves to the speaker's dominated region, but ARC offers the ability to set the EQ frequency limit to any value between 200Hz and 20 kHz. Anthem sets 5 kHz as a default. This was used in all examples shown above.

In the measurements below, the Max EQ Freq was set to 1 kHz. The control panel to set the Max EQ value is below.

The reference level offset allows the amplitude of the area above the Max EQ Freq to be reduced relative to the average speaker amplitude. The reason for changing this value will be discussed in in part of the review to appear later.

In this section I want to demonstrate the feature works correctly. Recall that we saw a problem with this in the HK 990 room equalizer (Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part I).

Below, I show a curve set with the measured acoustic response before the room correction is turned on (top curve). The electrical inverse correction curve is in the middle, and the measured acoustic response with ARC room correction enabled is at the bottom. This is the same format I used in the curve sets above that included the electrical inverse correction curves.

Limiting the maximum EQ frequency to 1kHz, the electrical inverse correction curve stops equalizing beyond 1kHz and stays at 0dB beyond 1kHz. There is a transition from equalization around 500 Hz to the 0dB reference at 1kHz. This is a smooth curve attempting to mask the sonic transition. I have highlighted, in red, the area that the electrical inverse correction curve transitions from correction to flat. In this graph, the Infinity speaker was placed in a different position of the room similar, but not identical with, the position used earlier.

As expected, the pre- and post-equalized acoustic response curves are similar above 1kHz since the electrical inverse correction curve is flat above this frequency. The orange box on the pre and post-equalized curves highlights the portion of the area that does not get corrected. Note that these measurements were made with a 0.05 octave smoothing instead of the 0.1 octave smoothing used in the curve sets above. Even with this more revealing smoothing function the corrected curve is still within ± 2dB below 1 kHz, the maximum frequency ARC is correcting. Slight differences in the curves above 1kHz are the result of slight difference in the placement of the microphone for the two measurements.

You can ignore the 16kHz peak, which is an artifact of the horizontal retrace frequency off the 13- inch NTSC TV I deployed to monitor the graphic interface from the D2 Pre/Pro.

Getting the max EQ transition correct requires complex coding. The use of the many speakers and rooms for this review helped to insure that the ARC Max EQ Frequency function is indeed very robust. A pair of additional electrical inverse correction curves with the Max EQ Frequency functional enabled, but at a different frequency, will also be shown in use in the second part of this review which looks at the performance of the ARC system when a subwoofer is added.

Using the Max EQ Frequency in conjunction with the Reference Level Offset advanced control option, makes it is possible to remove voicing (variation from flat response) from some speakers. Some companies apply voicing that was just more pleasing to the staff that was designing the product or perhaps one that will more likely move the product in the showroom.

Using the Max EQ Frequency option only works if the speaker has horizontal and vertical radiation patterns that are well behaved in an anechoic chamber. No room correction system, which can only respond to the measurements at your listening chair, can correct a speaker with poor horizontal and vertical response characteristics over the frequency range above 300Hz.

You may see a significant in-room response change around crossover points in some speakers that are flat on-axis. This is a result of significant changes in the horizontal radiation patterns between the speakers at the crossover point.

Anthem ARC was a teaching tool for me with respect to voicing. Flat was not always the best option. Attempting to remove a small voicing of as little as a 1 - 2dB made the speaker sound subjectively worse. They key take away is that Anthem ARC has the advanced algorithms that let you experiment, and since you own the PC technology, you can make adjustments in the control panels over as long of period of time as you want to take.