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A New Way of Looking at Speakers and Rooms - Review of APL TDA
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<blockquote data-quote="Jack Regula" data-source="post: 205232" data-attributes="member: 11500"><p>[h=2]The Speaker Measured at the LP[/h] When the mic is moved out to the primary LP, 4m from the corner speakers, the room dominates the measurement, especially in the lower registers. The TDA display isn’t as pretty a picture there but then it’s an untreated room. Nevertheless, the direct response stands out down into the modal region.</p><p></p><p>[ATTACH]205233[/ATTACH]</p><p>Figure 6 TDA 3D display of the measurement at the LP in the untreated room</p><p></p><p>To diagnose the room modes and reflections evident above, we again look at the TDA PL display and at the AFR graph to see their effect on the frequency response. The pl display in Figure 6 is configured to high dynamic range mode with a 20dB logarithmic scale.</p><p></p><p>[ATTACH]205234[/ATTACH]</p><p>Figure 7TDA PL and AFR displays of the measurement at the LP</p><p></p><p>In this room, modal effects dominate below 200 Hz and a general lack of bass damping is evident. Without TDA, seeing nulls in the 100-200 Hz region in conventional frequency response measurements and misled by SBIR and room mode calculators that assumed a rectangular room, I initially believed those frequency response nulls were due to ceiling reflections. With TDA, I at first thought it was a more distant reflection. Gradually, I came to understand that it was a longitudinal room mode and that the listening position just happened to be sitting in a null of the mode’s standing wave. Moving the microphone just 2’ forward and out of the null gave a cleaner measurement, confirming the diagnosis. </p><p></p><p>Several reflections and resonances in Figure 6 were annotated and traced back to their sources by iteratively moving absorber panels and re-measuring. Marker 1 shows the impact of the longitudinal room mode just discussed. In general, the bass is elevated in part due to the modes and floor support but also as part of a house curve. That voicing needs to be redone based on a set of measurements taken over the listening window. Marker 2 points at reflections from objects on the front wall between the speakers, the flat panel TV and audio equipment rack. Marker 3 points at reflections from the unterminated conical horn mouth itself. Marker 4 shows multiple reflections or modes between 400 and 500 Hz, where floor bounce nulls occur.</p><p></p><p>Eventually, I placed bass traps in the corners above the speakers, which reduced the room modes dramatically. Using the AFR as a guide, I attenuated the modal peaks at 80 Hz and 180 Hz and obtained the vastly improved measurement below in which the direct response stands out well down into the bass. </p><p></p><p>[ATTACH]205235[/ATTACH]</p><p>Figure 8 Measurement with bass traps in place and attenuation of remaining modal peaks</p><p></p><p>Prior to TDA, I found even windowed measurement data taken at the LP in room overwhelming – too many frequency response nulls and impulse response peaks to make sense of easily. TDA helped me distinguish between room modes and reflections, to locate the sources of reflections, and immediately showed me the effectiveness of treatments I applied. With the speaker’s direct response now prominent in the measurements taken at the listening positions, I’m confident the room equalization process will result in a more than satisfactory listening experience.</p><p></p><p>(continued in next post)</p></blockquote><p></p>
[QUOTE="Jack Regula, post: 205232, member: 11500"] [h=2]The Speaker Measured at the LP[/h] When the mic is moved out to the primary LP, 4m from the corner speakers, the room dominates the measurement, especially in the lower registers. The TDA display isn’t as pretty a picture there but then it’s an untreated room. Nevertheless, the direct response stands out down into the modal region. [ATTACH=JSON]205233.vB5-nodeid=205233[/ATTACH] Figure 6 TDA 3D display of the measurement at the LP in the untreated room To diagnose the room modes and reflections evident above, we again look at the TDA PL display and at the AFR graph to see their effect on the frequency response. The pl display in Figure 6 is configured to high dynamic range mode with a 20dB logarithmic scale. [ATTACH=JSON]205234.vB5-nodeid=205234[/ATTACH] Figure 7TDA PL and AFR displays of the measurement at the LP In this room, modal effects dominate below 200 Hz and a general lack of bass damping is evident. Without TDA, seeing nulls in the 100-200 Hz region in conventional frequency response measurements and misled by SBIR and room mode calculators that assumed a rectangular room, I initially believed those frequency response nulls were due to ceiling reflections. With TDA, I at first thought it was a more distant reflection. Gradually, I came to understand that it was a longitudinal room mode and that the listening position just happened to be sitting in a null of the mode’s standing wave. Moving the microphone just 2’ forward and out of the null gave a cleaner measurement, confirming the diagnosis. Several reflections and resonances in Figure 6 were annotated and traced back to their sources by iteratively moving absorber panels and re-measuring. Marker 1 shows the impact of the longitudinal room mode just discussed. In general, the bass is elevated in part due to the modes and floor support but also as part of a house curve. That voicing needs to be redone based on a set of measurements taken over the listening window. Marker 2 points at reflections from objects on the front wall between the speakers, the flat panel TV and audio equipment rack. Marker 3 points at reflections from the unterminated conical horn mouth itself. Marker 4 shows multiple reflections or modes between 400 and 500 Hz, where floor bounce nulls occur. Eventually, I placed bass traps in the corners above the speakers, which reduced the room modes dramatically. Using the AFR as a guide, I attenuated the modal peaks at 80 Hz and 180 Hz and obtained the vastly improved measurement below in which the direct response stands out well down into the bass. [ATTACH=JSON]205235.vB5-nodeid=205235[/ATTACH] Figure 8 Measurement with bass traps in place and attenuation of remaining modal peaks Prior to TDA, I found even windowed measurement data taken at the LP in room overwhelming – too many frequency response nulls and impulse response peaks to make sense of easily. TDA helped me distinguish between room modes and reflections, to locate the sources of reflections, and immediately showed me the effectiveness of treatments I applied. With the speaker’s direct response now prominent in the measurements taken at the listening positions, I’m confident the room equalization process will result in a more than satisfactory listening experience. (continued in next post) [/QUOTE]
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