Woofer is the term commonly used to designate the speaker designed to produce low frequency sounds, often from 40 Hertz to 1000 Hertz or more. The word came from English onomatopoeia barking of a dog, “woof” (in contrast to the name used for high frequency speakers, tweeter).
The woofer is an electromagnetic device. Use a cone, attached by adhesives to a voice coil surrounded, in turn, by the magnetic field of a permanent magnet. The voice coil and magnet in the base form a linear electric motor. When electric current flows through the coil, it moves respecting the right hand rule, causing the rise or fall of the cone, resulting in a movement similar to a piston. The movement created in the cone produces sound waves output.
There are many challenges in the design and production of a woofer, mainly related to the mechanics. Most searched for is that the cone movement faithfully reproduces the electrical impulses applied to the coil, as it is to handle high-volume sound without distortion. In relation to the impedance, it should allow the use of low-cost electronic amplifiers.
Designing a maximum performance woofer involves transforming the output signal of an amplifier with high fidelity sound waves and is a bit complicated with the use of an enclosure or infinite baffle sound. If done correctly, mechanical problems are diminished.
The bass reflex (bass reflex cabinet) most used was patented in the United States by Albert L. Thura, Bell Laboratories in 1932.
Before this date, the speakers were built just another surface and low frequencies are lost in the back of the device.
A. N. Thiele, in Australia, and later Richard Small, in America, adapted at the beginning the crossovers for the design of enclosures, particularly at low frequencies, which is the operating range of the woofer.
This was a breakthrough in the design of interconnections with woofers and now is practiced almost universally, without exception, by acoustical engineers.
The resonant frequency is one of these parameters. This is defined as the frequency of vibration and material is determined by moving the speaker (coil, cone, Dust Cover).
All woofers have electrical and mechanical properties that determine the most suitable cabinet for each device.
The baskets are the most widely used metal, preferably aluminum, to make low cost, the disadvantage with these is that with strong pressure, high volume or strokes may lose their shape.