I worked on a show last month where I decided to face the subwoofers at the wall. People were looking at me funny and asking questions…and that was before they even saw the subs. 🥁
So I made a video to investigate the effects of path length differences in this binary scenario. One result is not necessarily better than another, but it’s good to make an informed choice.
You can use this formula to estimate the frequency of the first dip of the comb filter.
c / d / 2 = 1st dip
speed of sound / distance (aka total path length difference) / 2 = first dip of comb filter
Subs facing audience
1130ft/s / 13ft / 2 = 43.5Hz
345m/s / 3.96m / 2 = 43.5Hz
Subs facing wall
1130ft/s / 6ft / 2 = 94.2Hz
345m/s / 1.83m / 2 = 94.2Hz
Pick your poison.
Taking a look at the field measurements, it looks like the subs were probably closer to 5ft from the wall because of the dip at 112.8hz, indicating a 10ft round trip distance for the reflection.
One side benefit that I forgot to include in the video is that the QSC subs were polarity inverted compared to the Kara mains. Facing them away from the audience meant that I didn’t need the polarity inversion. Tiny victory. 👏
Check out Merlijn’s Low-frequency Acoustic Center Calculator.
Have you tried facing your subs at the wall? What were your results?
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