Subwoofers can be a reference to woofers or a set of loudspeakers that produce audio in base frequencies somewhere between 150 Hz and 20 Hz. If a rotary woofer is being used then the bass audio frequency can even be reproduced at 1Hz. It is generally not easy to produce bass frequencies below 80Hz from run-of-the-mill bookshelf loudspeakers because their drivers are not big enough to create the requisite amount of air displacement. This is the reason that subwoofers are used to support main speakers since they are capable of producing really low frequencies at loud volumes.
Ken Kreisel created the first subwoofers in the 1960s because he saw customers complaining about the poor bass frequencies in high end speakers. He realised there would be a ready market for specialty speakers that could produce frequencies which other electrostatic speakers were not capable of emitting. This key concept saw the birth of the first subwoofer and subsequently, design modifications were implemented continuously in order to improve the initial subwoofer.
It was only about a decade later that subwoofers got noticed by the masses primarily because it was used, with great commercial success, for the film “Earthquake”. Now, with the increasing popularity of newer media like CDs, DVDs, DTS and Dolby, there is a keener requirement for frequencies that can produce deep and loud bass audio. This has necessitated the production of special effects using subwoofers.
Subwoofers are now available in many different formats. You might find subwoofers that specialize in acoustic suspension, tapped horn, or bass reflex, or infinite baffle or bandpass types. All these enclosure topology designs come with their own set of pros and cons vis-à-vis the size and dimensions of the cabinet, for example, or perhaps the bass extension and so on but by far, the bass reflex enclosures are the most popular for the home user as well as for the professional sound artist. Essentially, each subwoofer tries to do the following balancing act – cool the voice coil without distorting the sound too much, try to improve the results and yet keep the cone excursions within limits and so on.
Subwoofers use drivers that can be anywhere between 4” and 60” in diameter, even so, the drivers, the amplifier and the enclosure must be able to work together in tandem. Some are known as active subwoofers when they have an amplifier built into the system and passive subwoofers don’t have an in-built amplifier but they do have a driver as well as an enclosure. Some types of active subwoofers are servo controlled which reduces sound distortion to a large degree but they add to the cost of the purchase. The primary aim of the Servodrive subwoofers is to improve the power and reduce distortion, amongst other things. Subwoofers are used in some form or another almost everywhere these days, in churches, at home, in parks, discos and clubs, movie halls, live shows.
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