Just curious but, what size subwoofer do you have in this 12x11 room? What are the size of the woofers in your main speakers and what do you typically cross them over at.
The reason I ask is, the often prescribed generalizations with subwoofer displacement ratios with regard to main speaker size/power, is absolutely backwards in some situations. In my room, I can get a 5" subwoofer to make believable bass in here and 4" midrange speakers of sufficient power to fill the room in that range.
I have a 10” sub and two small Polk owm3s mounted on the wall crossed over at 120hz.
In my main room, I have a 15” Dayton sub 1500, which has an f3 of 23hz. I have it about a foot out from the wall and around 2’ from the corner. I get a relatively flat response down to 25hz. My seating position is 9’ from the sub, the room is 20x12. With this sub, I can achieve a maximum of 108dB at 25hz and 105 dB from 31hz-60hz. The reason I can achieve a higher spl at 25hz is because the port is tuned to 23hz, so there is very little motion of the woofer and impedance is high, so little power is required. Above 105dB, I run out of xmax.
My situation is a bit different. I only get about 3dB of reinforcement from my room, because the room opens up to two split-level staircases at the back, essentially behaving as if there is little to no boundary in the rear. The plus side to this is a very flat bass response through most of the room without the need for eq.
All five of my floor level speakers have 5.25” drivers with a box tuning of 63hz, since 1/2 wavelength of 47hz is 12’ (24’ wavelength), I get reinforcement along the width of the room (12’) at 47hz, extending the floor channels to 50hz -3dB, my ceiling mounted speakers have a response of 92hz anechoic, my room is about 8’ tall, 70hz has a wavelength of about 16’, therefore at 8’, 70hz is reinforced along the height dimension of the room, extending the response to 80hz. While I should technically receive reinforcement along the length dimensions of the room at 28hz, the openings in the rear hamper that.
Like I said, depending on the speakers relative to the room modes, some rooms can be perfect, essentially extending the response of your system, mine just happens to have exactly the right dimensions to receive an extra 10hz of extension from my speakers.
Whether or not you need a big subwoofer depends entirely on the seating distance and room dimensions. Placing a sub in a corner in a well sealed room nets an extra 6dB, however, depending on the room dimensions this boost could be an ugly 1 note boomy boost. Placing a sub along a wall out of a corner, where response will likely be flatter, should net 3dB.
Getting enough spl at sub bass frequencies is no joke of a task. In order to make a driver have a lower resonant frequency, and therefore response, you must make it heavier. This reduces efficiency. Low frequencies are substantially larger than even the biggest sub drivers, and therefore drivers have very poor coupling to the air at those frequencies. It’s not uncommon for sub drivers to have an efficiency as low as 83dB at 1w. To achieve normal levels of bass for the average ht requires about 100-110dB of output at the mlp, for an 85dB driver placed 10’ away requires about 500-1000 watts. Since excursion quadruples with each octave decrease, a 12” driver would need 70 inches of xmax just to reach 105dB at 25hz at a distance of 10’. As you can see most consumer subs fail to truly be capable of reference output. A port cuts the xmax in half, and the room adds 3dB of reinforcement, but that’s still 24mm of xmax, very few subs can handle that.
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