MultEQ XT Test Report (cont)

Figure 3 is a collection of pre-MultEQ XT amplitude response plots as measured at M1 – M6. (Note: the M dots in Figure 1 are color-coded to coincide with the plot colors in Figure 3, along with all other graphs where individual response plots are featured). The room’s modal structure, evidenced in the individual plots, had its anticipated effect; made up of both peaks & dips, the picture presented indicated a formidable challenge for the MultEQ XT! I was especially curious to see what the MultEQ XT system would do with the peak at ~ 25Hz as well as the dip at ~ 50Hz that persisted across each of the 6 measurements.

Figure 3: Pre-MultEQ dB spl Amplitude Response plots (1/12th Octave Smoothed) As

Measured At Listening Positions M1, 2, 3, 4, 5, & 6

Figure 4 is the response plot resulting from averaging all 6 pre-MultEQ measurements together. This will be used later for comparison with both the averaged post-MultEQ XT plots, as well as the hard-coded MultEQ XT target function. Doing so will clearly illustrate the effect MultEQ XT has on the system’s amplitude response.

Figure 4: Vector RMS Average of Pre-MultEQ XT dB spl Response Plots As Measured At

Listening Positions M1, 2, 3, 4, 5, 6

Figure 5: Post-MultEQ XT dB spl Amplitude Response Plots (1/12th Octave Smoothed) As

Measured At Listening Positions M1, 2, 3, 4, 5, & 6

The MultEQ XT process was then run to completion and the post measurements were made.

In Figure 5 we see the post-MultEQ XT amplitude response plots generated measuring, once again, at positions M1 – M6, color coded as before. Figure 6 is the result of averaging all 6 measurements together. Cursory examination of Figs. 3 – 6 shows changes have indeed occurred.

Overall, it would appear the individual post-MultEQ XT plots have tightened, becoming more alike or similar in appearance than their pre-MultEQ XT counterparts. In fact, they now more closely resemble the hard-coded target function mentioned earlier.

As well, it can be seen that the LF peak at ~ 25 Hz remains, but has been somewhat tamed. So too has the dip: frequency-wise shifted downward a bit, but otherwise largely remains untouched. The fact the LF dip remains is important as it indicates the MultEQ system wisely did not attempt to pointlessly fill it with extravagant amounts of LF acoustical energy. There are other means to deal with the dip; experiment with sub placement prior to running MultEQ XT for best results.

Given the practical constraints arising from packing FIR filters with sufficient numbers of taps (necessary for dealing with low frequency signals) into a DSP already running other processes, an approach whereby resolution varies continuously with frequency was employed. The net result is that at low frequencies (say, below 100 Hz) MultEQ XT could more effectively deal with .5 Octave wide peaks than a .083 Octave wide peak.

Another interesting feature is the appearance of an upswing at approximately 25kHz in both post-MultEQ XT plots. It’s the LMS system picking up the acoustic output of a motion-detection system that happened to be operating nearby. Its actually been part of all the measurements taken, though not until the MultEQ XT system took over was it visible in the amplitude response curves.

Where it comes to background noise, it pays to heed all warnings relating to keeping things quiet while the MultEQ XT system is progressing through its measurement sequence. Because a substantial signal to noise ratio is required to successfully complete the sequence, the overall background noise floor must be kept low otherwise the process stops and MultEQ XT throws an error message

It appears the nature of the noise may have some bearing on how MultEQ XT deals with it. When I first put the system through its paces, quite a lot of LF acoustic energy from the air-handling system bled through, convincing MultEQ XT that a large segment of the subwoofer’s output was at a significantly higher amplitude than it actually was. The end result was MultEQ XT applied the brakes and pretty much wiped out much of the lower portion of the sub’s output. For this sequence of measurements, steps were taken to ensure air handler noise did not intrude. No further problems were encountered.

Figure 6: Vector RMS Average of Post-MultEQ XT dB spl Response Plots As Measured At

Listening Positions M1, 2, 3, 4, 5, 6

As mentioned earlier, MultEQ XT calculates speaker-mic distance for each of the individual system components during the initial calibration stage of the setup sequence. Figure 7 compares the actual measured distance (from the center of each loudspeaker’s faceplate to mic tip center) with that calculated by MultEQ XT. The figures are in fairly good agreement, in each case the MultEQ XT distance is longer than the measured distance, in part owing to driver voice coil-to-faceplate offset. The voice coils are, of course, recessed relative to the respective cabinet’s faceplate and are thus slightly more distant from the mic than the faceplate.

Figure 7: Component distance (m) Measured vs. MultEQ XT-determined

MultEQ XT also configures speaker size and crossover frequencies. Any speaker, exhibiting a -3dB point measured at or above 80 Hz is designated as “Small”. Conversely, those measuring a -3dB point below 80 Hz are designated as “Large”. Occasionally, boundary gain can result in a “Small” being designated as “Large”. Figure 7b is a screen capture showing MultEQ XT's crossover frequency speaker size choices.

Figures 7b: MultEQ XT-determined Crossover Frequencies

Audyssey determines speaker size based on whether a particular speaker’s -3dB point falls above or below 79 Hz. (Should MultEQ XT estimate speaker size, speaker distance, crossover frequency or channel trim wrong, the settings can be manually tweaked later, if needed).

Finally, Figs. 8 & 9 give us a look at just what the MultEQ XT system did for the overall system amplitude response, as measured across the listening area.

Figure 8 shows the pre- & post-MultEQ XT averaged response plots. Its clear the MultEQ XT system has had an effect on the amplitude response, particularly in the 200Hz – 2kHz range. Figure 9 is Figure 8 repeated but with 1/3rd Octave smoothing employed to enhance visual clarity and the hard-coded target function overlaid, giving a better visual sense of how successful the MultEQ XT was in pulling the system’s overall response closer to that of the target function. Once again, it can be seen that the MultEQ XT system did manage to polish the response.  This can best be seen in the blue trace below in the smoothing out of the 60 Hz and 150 Hz regions, as well as cutting a peak at around 250 Hz, filling a hole at 1.2 kHz and lowered the nasty peak at 30 Hz. The MultEQ XT correction helped to bring the response in line as something closer to the target function than the pre-MultEQ XT amplitude response.

Figure 8: Vector RMS Average of Pre- (Red) and Post- (Blue) MultEQ XT dB spl Response Plots

As Measured At Listening Positions M1, 2, 3, 4, 5, 6. Data 1/12th Oct Smoothed

Figure 9: Vector RMS Average of Pre- (Red) and Post- (Blue) MultEQ XT dB spl Response Plots

As Measured At Listening Positions M1, 2, 3, 4, 5, 6. With MultEQ XT Target

Function (Purple) Overlay Data. 1/3rd Oct. Smoothed

So how did it sound?

The overall tonal balance of the system did change, but only modestly so. There were, however, other much more noticeable changes that had occurred. Foremost was a widened sweet-spot with enhanced clarity, imaging and localization across the now seamless, 3D soundstage. In effect, it appeared the center of the original sweet-spot had spread to cover 6 different listener positions! Not bad.

The Denon 3806 AVR offers four room EQ options, Audyssey (MultEQ XT), Front, Flat, and Manual.

• “Audyssey”:  we already know about.

• “Front”: was included to satisfy an early licensee’s requirement that while the MultEQ XT process was applied, the front L & R speakers would otherwise remain untouched, filterwise. (The idea being that people with very expensive, high-end fronts wouldn’t want them touched by any equalization). In this case MultEQ XT averages the amplitude response of the fronts and uses the resulting curve as the target function applied to equalizing the remaining speakers.

• “Flat”: essentially identical in form & function to “Audyssey”, with the exception being there is no high end roll-off (as seen in the purple target curve appearing in Figure 9.) “Audyssey” and “Flat” are likely the most commonly chosen options. Good first choice for listening to music.

• “Manual”: isn’t part of the Audyssey MultEQ XT process and is a final option that provides for a simple, manually-operated graphic EQ. (See figure below).

The degree to which the MultEQ XT system will enhance a system’s performance depends on a number of factors and any particular listener’s experience will likely be different from that of another’s. The overall intrinsic quality of the AVR/loudspeaker components as well as the location of the loudspeakers themselves are probably the leading factors determining just how and to what degree MultEQ XT will effect the system’s overall performance. All in all the inclusion of the MultEQ XT system within an AVR destined for home use is a worthwhile addition and a successful step forward in bringing audio nirvana to the home theatre.

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