More Fun with More Subs
Multiple subwoofers can be used to increase sound pressure over a single unit, and efficient use of room boundaries can additionally increase sound pressure.
Like any other type of engineering, the art and science of loudspeaker design often revolves around overcoming obstacles thrown up by nature. Every once in a while, however, physics turns out to be our friend. Subwoofers are a case in point.
At the frequencies where subwoofers operate, you can get fairly astonishing increases in maximum bass output by using multiple subwoofers, placing them
FIGURE 1
against room boundaries (walls, floor), or both. At the very lowest frequencies, you even get some boost just from having the subwoofer in a room.
This last phenomenon is known as "room gain," and you actually get more of it in small rooms than in large ones. Below a frequency determined by the room volume, a speaker’s output will be progressively reinforced at a rate close to that at which its response naturally rolls off below its lower limit. So a subwoofer that has flat response to 30 Hz outdoors would hold up strongly to below 20 Hz in a typical living room. In a typical bedroom or small office, the boost might begin at 40 or 50 Hz, which dovetails nicely with the capabilities of the smaller speakers and sub- woofers that would tend to be used in such set- tings. Make the room even smaller — well, if you have been wondering how people get so much bass out of their cars, here is your answer! A freer lunch you will not find.
FIGURE 2