The most common type of driver uses a lightweight diaphragm connected to a rigid basket, or frame, via flexible suspension which constrains a coil of fine wire to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the coil which thus becomes an electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force which causes the coil, and so the attached cone, to move back and forth and so reproduce sound under the control of the applied electrical signal coming from the amplifier. The following is a brief discussion of the individual components of this most common type of loudspeaker.

The diaphragm is usually manufactured in a cone or dome shaped profile. Numerous materials may be used, but the most common are paper, plastic and metal. The ideal material would be stiff, light and well damped. In practice, all three of these criteria cannot be met, and thus driver design involves tradeoffs. Paper is light and well damped, but not stiff. Metal can be made stiff and light, but it is not well damped. Plastic can be light, but typically the stiffer it is made, the less well-damped it is. As a result, many cones are made of some sort of composite. This can either be a sandwich construction or simply a coating to stiffen or damp a cone.

The basket or frame must be designed for rigidity to avoid deformation which could cause the voice coil to rub against the magnet structure. Baskets are typically cast or stamped metal, although molded plastic baskets are becoming common, especially for inexpensive drivers. The frame plays a secondary role in conducting heat away from the coil.

The suspension system keeps the coil centered in the gap and provides a restoring force to make the speaker cone return to a neutral position after moving. A typical suspension system consists of two parts: the "spider", which connects the diaphragm or voice coil to the frame and provides the majority of the restoring force; and the "surround", which helps center the coil and allows free movement. The spider is usually made of a corrugated fabric disk. The surround can be a roll of rubber or foam or a corrugated fabric, attached to the outer circumference of the cone and to the frame.

The voice coil wire is usually copper, though aluminum, or rarely silver, may be used. Voice coil wire can be round, rectangular, or hexagonal, giving varying amounts of wire volume coverage in the available magnetic gap. The coil is oriented coaxially inside the gap, a small circular volume (a hole, slot, or groove) in the magnetic structure within which it can move back and forth. The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside of the gap being one pole and the center post (a.k.a. pole-piece) being the other. The center post and back-plate are sometimes a single piece called the yoke.

Modern driver magnets are almost always permanent and made of ceramic, ferrite, Alnico, or, more recently, rare earth. The size and type of magnet and the magnetic circuit differ depending on design goals. A current trend in design, due to increases in transportation costs and a desire for smaller, lighter devices (as in many home theater multi-speaker installations), is the use of rare earth magnet instead of ferrite types.

Driver design, and the combination of one or more drivers into an enclosure to make a speaker system, is both an art and science. Adjusting a design to improve performance is done using magnetic and material science theory, high precision measurements, as well as experienced listeners. Designers can use an anechoic chamber to ensure the speaker can be measured independently of room effects, or any of several electronic techniques. Some developers eschew anechoic chambers in favor of specific standardized room set-ups intended to simulate real-life listening conditions. Some of the issues speaker designers must confront are lobing, phase effects, off axis response, crossover complications, and psychoacoustics.

Most loudspeaker drivers are currently manufactured in China. The fabrication of finished loudspeaker systems is segmented, depending largely on price point. High-end speaker systems are usually made in the same region as their target markets and can command prices of $10,000 per pair and up. The lowest-priced speaker systems are mostly manufactured in China or other low-cost manufacturing locations. Although the manufacture of drivers has become essentially commoditized, the fabrication and subsequent sale of finished speaker systems still carry high profit margins. Partly for this reason, manufacturers are increasingly combining power amplifier electronics (a typically lower profit item) with finished speaker systems to create "powered speakers" with an overall higher market value.


Woofer, tweeter, midrange

A woofer is a driver capable of reproducing low (bass) frequencies. The usable frequency range varies widely according to design. Some woofers can cover the audio band from lowest bass to 3 kHz, while others only work up to 1 kHz or less. Some woofers are capable of very deep bass performance in an enclosure that is large enough and properly braced. Other woofers become unusable or highly distorting below 50 or 60 Hz, and so listeners who want to listen to music with very deep bass may need a subwoofer (see below).

A tweeter is a driver capable of reproducing the higher end of the audio spectrum, usually from around 3-5 kHz up to 20 kHz and beyond.

A mid-range speaker, also called a squawker, is designed to cover the middle of the audio spectrum, typically from a few hundred hertz to about 4-5 kHz. Midranges are used when the other drivers are incapable of adequately covering the full audio range without them and/or to increase maximum output, as tweeters in 3-way systems can be spared the difficult requirement to reproduce lower frequencies.

Full range drivers

A full-range driver is designed to have as wide a frequency response as possible. These drivers are small, typically 2 to 6 inches (5 to 16 cm) in diameter to permit reasonably high frequency response, but this means they often have limited low distortion sound output at low frequencies and limited power handling capacity (due to a small voice coil).

They often employ an additional cone called a whizzer, a small, light cone attached to the woofer's apex near the dust cap, to extend the high frequency response and broaden the high frequency directivity. The main cone is built so as to flex more in this region at high frequencies than the rest of the cone. The result is that the main cone delivers the low frequencies and the whizzer cone contributes most of the higher frequencies. Since the whizzer cone is smaller than the main diaphragm, dispersion at high frequencies is improved over a driver with a single larger diaphragm. Full range drivers are one approach to avoiding the possible audible effects of multiple driver systems caused by non-coincident driver location and crossover issues.

Subwoofer

A subwoofer is a woofer driver used only for the lowest part of the audio spectrum. A typical subwoofer only reproduces sounds below perhaps 120 Hz; some can go lower than 20 Hz. Because the intended range of frequencies is limited, subwoofer design is usually simpler, often consisting of a single, subwoofer enclosed in a suitable (often bass reflex) cabinet. To accurately reproduce very low bass notes without unwanted resonance, subwoofers have to be large enough and properly braced. Subwoofers are often supplied with power amplifiers and electronic filters, with additional controls relevant to low frequency reproduction, such as phase switches built directly into the cabinet. These subwoofers are known as "active subwoofers". Some subwoofer systems, often called "servo" or "motional feedback" subwoofers, also include sophisticated systems utilizing accelerometers or back EMF sensors to sense cone movement. The actual motion of the cone is compared to the input signal many times per second and the feedback circuitry applies continuous correction to the drive signal to enable the woofer to reproduce the input signal with less distortion.

Speaker specifications generally include:

Speaker or driver type (individual units only) – Full-range, woofer, tweeter or mid-range.

Rated Power – Nominal (or continuous) power, and peak (or maximum short-term) power a loudspeaker can handle (ie, maximum input power before thermally destroying the loudspeaker. It is not the power the loudspeaker produces). A driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies. Tweeters can also be damaged by amplifier clipping or by music, or sine wave input, at high frequencies. Both situations pass more energy to a tweeter than it can survive without damage.

Impedance – typically 4 Ω (ohms), 8 Ω, etc.

Baffle or enclosure type (enclosed systems only) – Sealed, bass reflex, etc.

Number of drivers (complete speaker systems only) – 2-way, 3-way, etc.



and optionally:

Crossover frequency(ies) (multi-driver systems only) – The frequency boundaries of the signal division between drivers.

Frequency response – The measured, or specified, output over a specified range of frequencies for a constant input level varied across those freqencies. it often includes a variance limit such as within "+/- 2.5 dB".

Thiele/Small parameters (individual drivers only) – these include the driver's Fs (resonance frequency), Qts (a driver's Q (or damping factor) at resonant frequency), Vas (the equivalent air compliance volume of the driver), etc.

Sensitivity – The sound pressure level produced by a loudspeaker, usually specified in dB, measured at 1 meter with an input of 1 watt or 2.83 volts, typically at one or more specified frequencies. This rating is often inflated by manufacturers.

Maximum SPL – The highest output, short of damage or not exceeding a particular distortion level, the loudspeaker can manage. This rating is often inflated by manufacturers and is commonly given without reference to frequency range or distortion level.




Crossover

Used in multi-driver speaker systems, the crossover is a device that separates the input signal into different frequency ranges for each driver. Each driver, therefore, will receive the frequency range it is designed for, so that the distortion in each driver, and interference between the drivers, is reduced. The ideal crossover would have no overlap in the signal sent to different drivers, but this is not achievable in practice with standard analog filters.

Crossover can be passive or active. A passive crossover is an electronic circuit that uses capacitors, inductors, and resistors. These parts are connected after the amplifier and divides the signal into individual frequency ranges before the speaker drivers. A passive crossover requires no external power. An active crossover is a device that uses more complex electronic circuitry and requires power from an external source. An active crossover divides the signal into individual frequency ranges before the amplifier, which necessitates one amplifier for each speaker driver.

Passive crossover are generally contained inside speaker boxes and the most common type of crossover for home use. In car audio systems passive crossovers can be contained in a separate box. Active crossovers are used mostly in professional applications, concert sound systems, for example.