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 M.A.T.T.: The room was now completely built and the speakers had been installed. It was time for the acoustic treatments. As you may have already surmised, that proved a little more complex than just buying Tube Traps and placing them randomly around the perimeter. First, we needed several on-site meetings both prior to and during the rough-in construction to take exact measurements with photos. In my case, this also meant special attention paid to the unique room elements of soffit and rear bump out.

Finally we discussed the brand of speakers, doors and equipment orientation. The room had been built according to ASC’s IsoDamp specifications so I had a functional room shell. Visually it was an ordinary room. And without any treatment or furniture it was an acoustical nightmare - utterly reflective and with an echo that was much like that of a large cave or possibly a cavernous dungeon. The echo made normal conversation difficult to understand. Bass was boomy and completely out of proportion. Imaging was zero. The sound was nothing more than organized noise. For ASC of course, that's their normal starting point.

As part of the design process, the Overture Audio technicians once again showed up with a CD, computer, specialized software and an Audyssey-calibrated microphone for the Music Articulation Test Tone (M.A.T.T.) testing. Art Noxon designed M.A.T.T. to measure the articulation and intelligibility of music in a listening room.

It tests the speakers and room as a complete acoustic whole or system to determine what Art calls "the fast-tracking ability of the listening room"The test measures the loudness of transient bursts and the quietness of the silent sections alternating in rapid succession.

The test setup is relatively simple. In my case a dedicated room was destined for complete treatment. We removed all of my temporary acoustic treatments from the walls, floors and ceilings, then readjusted the speakers for their best sound in the untreated room. The M.A.T.T test tone signals played through the system with a microphone feeding a computer placed at the listening position to capture the resultant sound.

The graph at left is a sample of the original signal direct from the oscillator. The triangle below the response curve represents frequency vs. time. It starts off at 28Hz and rises linearly up to 780Hz in 8Hz increments, then decreases back to 28Hz at the same rate. This works out to 1/16 seconds of signal followed by 1/16 seconds of silence.

This on/off process is key to your room’s (and ultimately your system’s) articulation. The progression continues up and down the frequency scale. A recording process measures the signal bursts and following silences of the room response at the listening position. While the recorded sound has a machine-gun type rhythmically distinct tatt tatt quality, the untreated room mangled it pretty badly.

The test itself only took about a minute and half but with set up, stripping the room and multiple takes at various volume levels, the entire process took several hours. Unfortunately we suffered a glitch during the original test so Overture had to return for additional MATT tests – no big deal. One might question the point of this exercise. ASC has determined that a room’s ability to cleanly and quickly track the music’s instantaneous transients across the frequency spectrum is key to the room’s articulation. Art defines articulation as "…the ability of the room to distinctly sound out each audio event."  The recording of the room's behavior is sent to ASC. Their analysis determines among other things how much energy the room stores and at what frequencies. This along with the room's measurements and structure guides the treatment plan.

Let’s examine the test itself. To hear the actual signal without the deleterious room effects, you really must listen through headphones. Each transient has a distinct beginning and end. For those old enough to remember 50’s B movies, the test sounded like flying saucers invading the listening room. I was half expecting Gort to appear between my speakers. Yet the raw sound is only a baseline. The true test are the changes the room imposes on its playback. Since my room had been stripped bare, the sole remaining treatment was carpet. Thus playback of the test tones bore little resemblance to the original. Listening to the MATT test signal in a bare room produced almost no discrete sounds. They all blended together fitting Art Nixon’s untreated room description. What started off as individual sounds was transformed by my room into an almost continuous warble. The transients were lost and there were no indications of the silences between the tones. Individual blips became a homogeneous jelly of sound.

It’s hard enough to describe the sound of music in a listening room. To describe mutated test tones is probably beyond my ability so I offer ASC’s descriptions along with their meanings.
    • Ta-Ta-Ta-Ta, the sound of an articulate group of tone bursts. There will be usually some 8 to 10 clean bursts in such a group, lasting about one second. A typical room will only have a few articulate groups of signals in the 75-second test.
    • Tattle-Tattle-Tattle-Tattle, the telltale sound of the room's double-tongue response. Large spans of the track will sound like this. Notice that the tonal pulse rate is really twice that of the real signal. Too much energy occupies the dwell period of the test signal.
    • Toodle-oodle-oodle-oodle, the sound of the garbled room. Notice that it is a softer, less impacted sound. It's close to a slurred double-tongue response.
    • Tathump-Tathump-Tathump is a more accurate presentation of the Ta-Ta. The thumps are the turn-on and turn-off transient effects. This subtle transient coloration becomes totally inaudible with anything but articulate room playback. The thump is a damped 45Hz ringing with only 2 oscillations of presence following each burst transition.

For those curious, the M.A.T.T. mp3 can be downloaded from the ASC website. Let’s look at the response graphs of a typical room.  When I completed the room, I did not have Overture return to perform an additional M.A.T.T. test. Hence these graphs are ASC examples. Figure 1 shows the original signal as output by the oscillator; Figure 2 an untreated room; and finally Figure 3 the measured response of a treated room.

The test measures the loudness of a transient burst and the quietness of the subsequent silence and can track an up to 20db drop in 1/16th of a second. As I learned early in this process, the size, design and construction of the room alter the frequency response to boost certain frequencies while canceling others. The room alters the original Figure 1 signal and prevents individual tones from rising during the tone burst. Likewise it limits the tone drop-offs during the interim silent periods. Areas of poor articulation are evidenced by sections of small amplitude zigzags in Figure 2. Key to this test are the periods of audible silences after the tone bursts. The frequency bursts represent a musical transient. Post attack, the periods of silence (or lack thereof) define the room's residual energy.

The M.A.T.T. graph of untreated rooms shows that some tone levels do not rise to the recorded peaks and do not fall during the periods of silence. This excess energy in the room destroys subtle decay clues and interferes with the following transient. The music is blurred and fuzzy without any clarity of focus and no imaging. The other interesting effect is the room’s effect on the overall level. The original signal is flat (figure 1). When played in an untreated room, a level graph show a humped response (figure 2). According to ASC, smoothing of the jagged plots yields a classic slow sine wave room response. The room’s inherent resonances alter the frequency response of the music. A tube-trapped room flattens out the response levels and increases the vertical swings of the response graph’s zigzags. (Figure 3)

We forwarded the audio file of the MATT test along with the dimensions, photos and speaker orientation to ASC for analysis. They in turn proposed multiple treatment options. The final treatment plan with the intended acoustic improvements is presented in the diagram below. While the MATT testing was part of the comprehensive Overture Audio treatment process, ASC does also offer it as a DIY test. You can download the test tones from ACS. Play back and record them and return the file to ASC. Their website has plenty of information and for a nominal fee, they will analyse your room and report suggestions for improvements. I have not seen the end result of such a DIY test but considering the wealth of acoustic knowledge at ASC, I would certainly recommend to contact them. We’re now getting close to the end of my journey. The next chapter will show the Tube Trap installation and discuss their setup and tuning.

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