I have seen a lot of discussion about horizontally positioned MTM centers, with many consumers pointing to off-axis lobing issues that are clearly revealed in contour plots.
Contour plots, as generated by the Kippel NFS, are true anechoic measurements. They display each *individual* off-axis angle and indicate the amount of amplitude change using colors. They are a useful tool for a quick examination of the overall directivity of a speaker.
The problem is that they do not represent what we hear. We do not hear individual off-axis responses. For example, at 20 degrees off-axis, we do not just hear the response at 20-degrees, we hear a weighted summation of all of the off-axis angles.
Below is the vertical contour plot of the 340SE2, which would be the horizontal contour plot of the same speaker when positioned horizontally.
You will note the frequency range of lobing is mostly between 800Hz to 2.8kHz. The contour plot shows this area being quite messy - to the inexperienced, it simply looks horrible.
But how does this translate into what we are hearing? As I mentioned above, we hear a summation of all off-axis angles, we do not hear a single angle.
Below is a comparison between the on-axis in-room response of our CMT-340SE2 center and in-room response of the same speaker with the mic at 20 degrees to the right. Microphone is at ear-level, positioned 8 ½ feet back from the center, with the center speaker positioned as most would place it. The mic was then moved over to the right by exactly 3 feet (which translates to an off-axis horizontal angle of 20 degrees)
I could not move the mic further to the right, as it gets much too close to that sidewall, which has a far more dramatic effect on the response than lobing would ever cause.
Blue trace is on-axis, brown trace is the 20-degree measurement. BTW, that on-axis in-room response for a center looks fantastic and does indeed closely mirror the predicted in-room response of the 340SE2 center.
*Ignore the response below 300Hz as below this frequency, the response is dominated by room modes.
You will note that the frequency range of the off-axis lobing was well represented in the contour plot, as the off-axis response shows a dip in that same range. That dip is ~ 3dB. When you factor in that most rooms will create +/- 10 dB peaks and dips, actual audibility of this 3dB dip is suspect.
Is it ideal? Certainly not, however, all center speakers have major compromises and many simply can not fit a properly designed 3-way center due to the significant increase in speaker height.
Is this anywhere near as bad as many would conclude by looking at just the contour plot? That is a firm no. We are fast approaching nearly 10,000 CMT-340 centers out there, I honestly can’t recall even a single complaint about off-axis issues.
There have been questions thrown our way (and towards other manufacturers as well) as to why we don’t post a horizontal contour plot for the 340SE2 center. The reason is simple enough, contour plots are generally misunderstood – and, with regard to Ascend, we don’t need to.
Why don't we need to?
We post far more critical data as to the off-axis performance of the 340SE2 center, data that actually represents what a listener would hear in a listening environment. This data is both peer-reviewed and accepted and we spent a ton of time developing this unique measurement with some assistance from the designer of the NFS himself.
Below is our published CMT-340SE2 center Off-Axis Estimated In-Room Response:
Note just how closely this unique measurement mirrors the actual on- and off-axis in-room measurements I took of the 340SE2 center using REW.
The green trace (20 degs off-axis) is 3dB down from the on-axis (black trace) in the exact same frequency range. Rather remarkable how closely they compare with one being anechoic and the other in what I would call a typical listening environment.
This measurement is quite difficult to generate though, I do not think it even possible to do without an NFS, and even with the NFS, it is complex. However, it is a FAR MORE accurate representation of off-axis performance compared to a contour plot, as I have just proven.
Once again, a quick look at just how accurate our predicted off-axis measurement is to actual:
It is my hope that our off-axis EIR measurement will eventually become the standard to evaluate off-axis performance, as it is indeed a properly weighted summation of all of the off-axis angles we hear, with the listener being seated at different off-axis angles.