Small Gear For Big Bands Part 4: Speaker Cabinets and Subs
In previous postings of “Big Bands” we covered gear pertaining to instruments. In this issue we’ll begin with equipment that makes up the PA system that will present your sound to the audience. In Part 2 we covered ways for the bass player to get his sound out with or without speaker cabinets. In Part 3 reviewing electronic drum kits the “Kick Drum” is replaced by digital samples. These two sources contain a lot of low frequency energy that needs to be radiated by the sound system into the performance space. All full-range PA speakers include a “woofer” designed to reproduce these tones to some extent while also supplying the mid-range frequencies. If we can remove the signals below 120-150(Hz) from the full range cabinet its output and clarity can be enhanced. This is done using a “sub-woofer”; a cabinet designed to reproduce only low tones. These cabinets usually include a “crossover”or filter that removes unwanted frequencies from the full-range mixing board output and passes the mid-range and high signal along to the PA speakers.
Sub-woofers can be either “passive” requiring a separate power amp and crossover or “powered” with an internal amp. Sub-woofers for commercial sound are offered with 12”, 15”, and 18” drivers. Internal power amps are usually in the 800-2000 watt range. A number of models are available in relatively compact cabinets, some in the 16” X 22” X 24”range weighing 70+lbs. Most cabinets are supplied with a top-mounted “socket” which will accept an optional speaker mounting pole. This mates with a similar socket on the bottom of full-range cabinets providing elevation without the higher expense of separate stands. For smaller venues a single 12” sub is usually sufficient for medium volume. Since the frequencies that a “Sub” operates at are not acoustically directional dispersion of sound is not position-critical. A single larger cabinet works just as well as additional speakers. This information should assist in building a strong “big bottom” foundation for your Big Band.