Martin Poulin
Sealed vs bass-reflex? The eternal debate, what about a great trade off between both systems?
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Almost a Win-Win
May 2018
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This is the kitchen system as it currently stands with four S&B Acoustic 12" subwoofers and two 15" sealed woofers.
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When I build those four subs, I calculated the enclosure volume so they’d work as well as a sealed or a "EBR" bass reflex system.
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Sealed:
Box volume = 80 liters
System Q= 0.5 (critically damped, my favorite tuning) Quite a good place to start for a sealed config.
-6 dB @ 28 Hz, and with EQ can do 20 Hz flat!
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Bass reflex:
80 Liters over-sized box allows much lower tuning
Almost in EBR tuning category. (Extended Bass Reflex)
Box volume = 80 liters (ideal EBR @-3 dB would require 91 liters)
Box tuning = 19 Hz
-3 dB @19 Hz
-6 dB @ 17 Hz
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Both systems have strong merits and perform satisfactory to reasonable outputs. (within limits of the four 12" subs)
small size bass reflex have high group delay, a 80liter box pay good benefit.
Measurements above are at the listening position, at about 90 dB.
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The subs are about 3 meters away from microphone.
The measurements were done in Mono, with all four subs playing (same EQ on all)
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Both alignments have almost the same frequency response after EQ is done, yet sound very different.
Note: Normal bass reflex size would be ~32 liters (~60% smaller) but would behave quite worse, have bad behavior in time domain area, distort more and would not reach as low as my under-damped over-sized design.
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Sealed configuration would easily win on both subjective and measured performance vs a standard 32 Liters BR tuning.
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Interesting things happen when you don’t use standard calculated "optimal" boxes and go much bigger size.
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With an over-sized bass reflex box tuning, things are not this simple, and the BR box almost acts as a hybrid between sealed and BR.
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Have a look at the measurements at the listening position, and see how close they are.
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Try to predict which one you think sounds best :)
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The lesson is that: If you do a bass reflex sub-woofer, don’t use a simple calculator. (I use winLSD. Free and powerful software)
Use a bigger than normal enclosure and tune lower than normal.
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Results will impress you. (efficiency gain of a reflex system, deep extension and no subjective boominess like smaller BR tuning)
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Very great compromise, at the same size as a sealed system.