OK so you’re a mobile DJ who wants more bass, how do you do it?
Buy some sub speakers (bass bins), but how do you connect them?
Three methods exist.
a) Just daisy chain them from your existing tops. This works providing you don’t exceed the load your amp can manage, in most cases 4 ohms. It will increase your music output power, but uses the sub speakers to produce a full range signal for which they were not designed. Anyway it is an improvement.
b) Use the passive crossovers which are built into some sub speakers. An example of this type of speaker is the Peavey Hysis 115xt. The crossover in the speaker splits the output music power of the amp into two parts, one driving the sub speakers, the other fed from the subs to the top speakers. Normally the split or crossover frequency is around 150Hz.
c) The ultimate solution is to use an active crossover to split the music output from the mixer into two parts at line level prior to amplification. Two amps can then be used with a variable crossover point enabling the optimization of music output power. A cost effective example of such a crossover is the Behringer CX2310 (http://www.behringer.com/EN/Products/CX2310.aspx). It is not necessary to use two amps, one can be used, one channel driving the sub speakers, the other driving the top speakers, which produces a mono musicoutput.