Anthem Room Correction and Martin Logan Renaissance ESL 15A
Perfect Bass Kit supplied by LookenListen, distributor for the Benelux
For the longest time, I’ve had mixed results when using Room Correction software. Of course, most of the time this meant using an extra digital device with analog inputs and outputs and no matter how good the built-in A-D and D-A converters are, this process is not likely to be 100% transparent. Things are different when the correction software is an inherent part of the hardware design of an existing component such as the Anthem STR preamp. In that review, I have detailed the differences in sound between the fully analog path and the path following A-D and D-A conversion as well as the switching on and off of the ARC process. While the former had an impact on some aspects of the reproduction, the ARC process itself was actually transparent. And that brings us to the Martin Logan ESL 15A electrostatic loudspeakers. Their bass sections contain active amplification and use DSP by default and as such, uploading curves that have been optimized by Room Correction software should not have adverse effects. But here, the plot thickens. But before I dive into the precise effects, room-related issues, and solutions, let me explain some more about the Room Correction software at hand: ARC.
Above: ARC on Windows, below: ARC on iOS
Anthem Room Correction
To use Anthem Room Correction (ARC) with Martin Logans, one needs to purchase a PBK (MartinLogan Perfect Bass Kit) consisting of a microphone with calibration file, a stand and all the required cables for 149 euros. The Martin Logan microphones are fully compatible with Anthem Room Correction for MartinLogan speakers and the ARC software can be freely downloaded from The Anthem website. Note that the software only works with Anthem-, Paradigm- & Martin Logan products that are PBK of ARC ready. For example, I tried using a MiniDSP Umik-1 but, alas, it was not recognized.
The software runs on Windows and Mac and also on Android and iOS, although the latter implementations either work only with the built-in (not calibrated-) microphone or require special USB adapters and offer less functionality than the desktop solutions. The measurement process is simple and painless and works by connecting the PBK microphone and one of the speakers via two USB cables to a computer and interconnecting the speakers using a LAN cable.
The software plays a number of frequency sweeps for each speaker and then calculates the optimum curves. These curves can either be manually adjusted using a range of settings or uploaded to the speakers as they are. After that, ARC can always be switched off and back on using a button on the rear of the speakers. There are two things to keep in mind. First, USB cables are limited to a certain length and this mandates the use of a laptop or a nearby desktop computer. Second, the effect cannot be heard (ARC won’t be active) until the USB cable has been pulled from the speaker.
Above: clean setup with only the Logans in place
Above: Logans as well as Kroma Audio Carmens. Although this setup may seem cramped, the Kroma’s are almost in their ideal positions and the Logans are actually set up ideally. The Kromas can have wider soundstaging and become more transparent when set up ideally without the Logans but, still, they sound highly involving. Interestingly, the Logans’ performance is altered only moderately by the presence of the Kromas. The imaging perspective does change but this does not affect the soundstage size or the focus. Neither does it have any negative impact on the bass, rather the opposite, as the columns reduce the reflected HF energy from the Logans’ rear sides and also tame the standing wave between floor and ceiling. Interesting, isn’t it, how counter-intuitive things can sometimes work out in the wonderful world of audio?
Above and below: Magico S1MkII’s positioned between the Logans. This is the setup that I used when performing the measurements and corrections for this article. The Magicos are relatively tiny resulting in a negligible impact on the sound. Fortunately, like the Kromas, the Magicos seem to be happy in these spots. I’m sure that they can sound even better when spaced a little wider apart and with the Logans out of the way but I love those panels with their big butts too much to even want to try this.
ARC is arguably most beneficial when the speakers are set up in non-ideal positions but even when the setup is as perfect as is possible, using ARC still results in very audible improvements, most notably an even more linear and cleaner bass. When I reviewed the ESL 11A’s, ARC indicated that there was a bump down below which can be flattened very effectively, but with that version of the software, I found the adjusted sound to be a little lean, even if it was more accurate. Re-adjusting the bass level on the rear of the speakers did not really make it better so, for that review, I chose to use the speakers with no correction. When I got the ESL 15A’s, they sounded so great with default settings that I did not feel the urge to use ARC.
Meanwhile, Anthem released ARC Genesis which is much-improved from the previous version. The new interface looks great and the software now offers many settings that can be used to further tweak the sound before or after the measurements. It was while using this version of the software that I was able to achieve an even better sound from my 15A’s but it did take me some time to make it work perfectly.
As with many rooms, my room has some resonances that work out differently for the left and right speaker but ARC can very effectively counteract these, resulting in a much more linear bass response from each speaker. Audibly, the ARC-corrected sound results in a faster and more nimble bass that is considerably more articulate and unveils overtones much more distinctly. A very welcome side effect of this is that individual instruments are also better separated and considerably easier to follow. While some upgrades have a subtle effect, these improvements are anything but. Actually, when switching back to the non-linearized sound it is baffling to realize how the comparatively blurry sound was interpreted as being great up until the ARC measurement process.
However, when playing a certain Janet Jackson track, I noticed that the lowest note of a repetitive riff was no longer audible. Not just softer than the higher ones but just completely absent. Moreover, as Anthem already warned for, with many tracks, the sound had also become leaner and less impactful. Sure enough, when switching off the ARC on the back of the speakers, the low note was back! The ESL15A’s extend to 22Hz -3dB which is considerably deeper than this particular note so it could not be a limitation of the speakers themselves. Now, I am aware of the commonly made mistake of misinterpreting an accurate bass for being too lean and that is not what was happening here. My speakers are positioned almost in the middle of the room and, if anything, my room is detracting bass energy, certainly not adding any. So, why would the corrected sound result in the loss of low notes?
Above and below: Left and Right speaker ARC measurement results using the Curve Viewer section. Red = measured curve, Purple = corrected curve, Green = equalization curve.
The answer to this is as annoying as it is interesting. When inspecting the measured curves for each speaker I noticed that in two bands below 100 Herz they had almost opposite behavior. Where one would spike up, the other would dip. Although one would expect this to not sound very good, the net result at the listening position is a seemingly linear bass all the way down to the deepest notes that my music collection contains.
Above: optional ARC Settings
In an effort to find the precise point of the cutting off of the aforementioned note, I started moving up the “minimum correction frequency” in the ARC settings. Initially at 15Hz, I incremented it in steps of 5dB until I reached 40dB and the low note was back! 5 more Herz made it even fuller while another 5 more Herz did not help. I settled at 45Hz. This way, I could see that the left and right speaker had very different responses below that frequency but that they were still corrected for bumps and valleys above that.
Above: ARC with minimum correction frequency at 45Hz, leaving the bumps below that untouched. These curves can be uploaded to the speakers with the click of a button.
With this setting, the sound was fabulous. Granted, there was slightly less clarity in the lowest bass compared to the full-range correction but at least all the bass notes were now played at full strength. Lacking specific measurement software I can only guess as to what causes this but the problem is probably two-fold. First, it is a fact that the left and right speaker have opposing behavior in the very low bass. Second, I know from experience that my room has some nulling at the listening position. Apparently, the discrepancy between the untreated left and right speakers is such that it counteracts the nulling at the listening position. That being the case, the ARC-corrected sound may make each individual speaker more linear but it cannot predict the combined effect of both speakers in my room. Thus, the corrected sound effectively allows the nulling to take place and in the process removing the lowest bass notes.
As this exercise shows, the measurements and auto-corrections that are done by ARC can make a profound impact on the quality of the bass. What’s more: even when the speakers have already been positioned ideally, the ARC results are still far from subtle. However, it remains important to assess the measured results and apply manual corrections where required. Fortunately, ARC Genesis provides all the handles to do this in a simple and intuitive manner. If you have a Martin Logan speaker or subwoofer, I strongly recommend the use of ARC software. You may need to purchase the Perfect Bass Kit but the ARC software can be downloaded for free.