Martin Poulin
Sealed vs bass-reflex? The eternal debate, what about a great trade off between both systems?
Almost a Win-Win
May 2018
This is the kitchen system as it currently stands with four S&B Acoustic 12" subwoofers and two 15" sealed woofers.
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.
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!
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
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.
The subs are about 3 meters away from microphone.
The measurements were done in Mono, with all four subs playing (same EQ on all)
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.
Sealed configuration would easily win on both subjective and measured performance vs a standard 32 Liters BR tuning.
Interesting things happen when you don’t use standard calculated "optimal" boxes and go much bigger size.
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.
Have a look at the measurements at the listening position, and see how close they are.
Try to predict which one you think sounds best :)
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.
Results will impress you. (efficiency gain of a reflex system, deep extension and no subjective boominess like smaller BR tuning)
Very great compromise, at the same size as a sealed system.