One of the common questions that I see asked often has to do with what sound system is best for a wedding and do I need a subwoofer (or two)? My standard answer is …. It Depends. For almost all sound systems, the traditional loudspeaker consists of a low frequency driver and a high frequency driver paired together in a single box. In the recent years, manufacturers have branched into many different configurations in search of the “perfect” sound system. Generally speaking, all designs have some form of trade off of sound vs size and footprint. This discussion will be primarily about subwoofers and not the design of the mid/high range loudspeakers.
It is commonly known that if you take two subwoofers and acoustically couple them (by placing them next to each other) that there is an effective increase in radiated power. This is generally in the +3DB range. However this can complicate setup structure if you choose to mount your normal top speakers on poles in the subwoofers. The bonus when dealing with low frequencies is that they are essentially omni directional. What that really means is that the positioning of the subwoofer(s) in the room is less critical than the placement of the regular loudspeakers. This does not mean that the low frequencies are mono, in fact it is totally to the contrary. Recording engineers place low frequencies in both channels of recorded music, so if you only use one subwoofer it is essential that you use a crossover device (high pass/low pass filters or an active crossover). Crossover design is not simple and almost all the time crossovers have a transition that occurs over a range of frequencies where both the subwoofer and the loudspeaker receive the same frequencies. This is referred to as polar response and can affect sound quality.
Not all subwoofers are created equal. Physics plays an important part of audio reproduction, and generally speaking physically larger cones and voice coils make for better bass reproduction. However cabinet, amplifier and speaker design are all components of a good sounding subwoofer system. The compliance (how easily the cone moves)and damping (how quickly it moves back to original position) will also affect output.
So, a single larger driver can have better sound performance and power handling, while a pair of drivers has the potential to cover the audience more effectively. There is no configuration that is superior in all contexts of performance, but engineering can make a big difference. So, one thump or two…. It depends! Personally I believe it depends more on the audience than it does the DJs personal preference. For weddings, I always use two 12” powered subwoofers with appropriate spacing to take advantage of stereo, along with line array style speakers. For high school and college events I use a passive 18” subwoofer with a large voice coil and powerful external amplifier and traditional powered loudspeakers. Let your ears and your audiences decide!