Woofer

Woofer is the term commonly used for a loudspeaker driver designed to produce low frequency sounds, typically from around 40 hertz up to about a kilohertz or higher. The name is from the onomatopoeic English word for a dog's bark, "woof" (in contrast to the name used for speakers designed to reproduce high-frequency sounds, tweeter). The most common design for a woofer is the electrodynamic driver, which typically uses a stiff paper cone, driven by a voice coil which is surrounded by a magnetic field. The voice coil is attached by adhesives to the back of the speaker cone. The voice coil and magnet form a linear electric motor. When current flows through the voice coil, the coil moves in relation to the frame according to Fleming's left hand rule, causing the coil to push or pull on the driver cone in a piston-like way. The resulting motion of the cone creates sound waves as it moves in and out.


The frame, or basket, is the structure holding the cone, voice coil and magnet in the proper alignment, and must be as rigid as possible. Cast metal baskets are the most expensive and the most rigid in all directions. Stamped steel baskets are cheaper but less rigid, and cast plastic is cheaper still and has come into common use.


An important woofer specification is its power rating, the amount of power the woofer can handle without damage. The power rating is not easily characterized (see below) and many manufacturers cite momentary peak power ratings which would damage the speaker if maintained.


At ordinary sound pressure levels (SPL), most humans can hear down to about 20 Hz. Woofers are generally used to cover the lowest octaves of the system's frequency range. In two-way loudspeaker systems, the drivers handling the lower frequencies are also obliged to cover a substantial part of the midrange, often as high as 1000 or 2000Hz; such drivers are commonly termed mid woofers. Since the 1990s, a sub-type of woofer (termed subwoofer), which is designed for very low frequencies, has come to be commonly used in home theater systems and PA systems to augment the bass response; they usually handle the very lowest two or three octaves (i.e., from as low as 20 to perhaps 80 or 120 Hz).

Loudspeaker

A loudspeaker is an electroacoustical transducer that converts an electrical signal to sound. The speaker pushes a medium in accord with the pulsations of an electrical signal, thus causing sound waves to propagate to where they can then be received by the ear. Loudspeakers (and other electroacoustic transducers) are the most variable elements in a modern audio system and are usually responsible for most audible differences when comparing systems.

The term 'loudspeaker' can refer to individual transducers (known as 'drivers'), or to complete systems consisting of an enclosure incorporating one or more drivers and electrical filter components. To adequately reproduce a wide range of frequencies, most loudspeaker systems require more than one driver, particularly for high sound pressure level or high accuracy. Individual drivers are used to reproduce different frequency ranges. The drivers are named subwoofers (very low frequencies), woofers (low frequencies), mid-range speakers (middle frequencies), tweeters (high frequencies) and sometimes supertweeters optimized for the highest audible frequencies. The terms for different speaker drivers differ depending on the application. In 2-way loudspeakers, there is no "mid-range" driver, so the task of reproducing the midrange sounds falls upon the woofer and tweeter. Home stereos use the designation "tweeter" for high frequencies whereas professional audio systems for concerts may designate high frequency drivers as "HF" or "highs" or "horns". When multiple drivers are used in a system, a "filter network", called a crossover, separates the incoming signal into different frequency ranges, and routes them to the appropriate driver. A loudspeaker system with n separate frequency bands is described as "n-way speakers": a 2-way system will have woofer and tweeter speakers; a 3-way system is either a combination of woofer, mid-range and tweeter or subwoofer, woofer and tweeter.

Capacitors
Capacitors are used to store energy for the amplifier to draw on demand. They come in many different sizes ranging from .5 Farads to well over 100 and their intended function is to temporarily cover the short-burst electrical demands of a car audio system that have exceeded the general electrical capabilities of the vehicle.

Rattle-reduction

Sound deadening is often used in the door cavities and boot/trunk area to provide less rattling of the metal in the car, especially the boot/trunk. The most common type of deadening is either Butyl or rubberized asphalt which has an adhesive quality and can be applied by simply pressing it into place with a roller and use of a heat gun (or hair dryer) if needed. Other types of deadening can be sprayed on, but they're less common because of the additional difficulty in their installation. The most popular sound deadening brand would be Dynamat, with others that are not as well known but offer sound deadening products in which some have been proven to be superior in performance such as Second Skin's Damplifier Pro, FatMat, and RAAMat to name a few other companies.

Subwoofer

A subwoofer is a woofer, or a complete loudspeaker dedicated to the reproduction of bass audio frequencies, from 150 Hz down as far as 20 Hz, or in rare cases lower. Also known as "subs", these are used to augment the low frequency performance of main loudspeakers. Subwoofers are constructed by mounting one or more woofers in a well-braced wood or plastic enclosure. Subwoofers have been designed using a number of speaker enclosure designs, including bass reflex (with a port or tube in the enclosure), infinite baffle, horn-loaded, and bandpass designs, each of which has advantages and disadvantages in efficiency, size, distortion, cost, and power handling. Passive subwoofers have a subwoofer driver and enclosure and they are powered by an external amplifier. Active subwoofers include a built-in amplifier.

The first subwoofers were developed in the 1960s to add bass response to home stereo systems. Subwoofers came into greater popular consciousness in the 1970s with the introduction of Sensurround in movies such as Earthquake, which produced loud low-frequency sounds through large subwoofers. With the advent of the compact cassette and the compact disc in the 1980s, the reproduction of deep, loud bass was no longer limited by the ability of a phonograph record stylus to track a groove. and producers could add more low frequency content to recordings. As well, during the 1990s, DVDs were increasingly recorded with "surround sound" processes that included a Low Frequency Effects (LFE) channel, which could be heard using the subwoofer in home theater systems. During the 1990s, subwoofers also became increasingly popular in home stereo systems, custom car audio installations, and in PA systems. By the 2000s, subwoofers became almost universal in sound reinforcement systems in nightclubs and concert venues.

Amplifiers

Blaupunkt Class T amplifier

Basically a mobile Audio amplifier, a car 'amp' is a term used to refer to a dedicated electronic amplifier separated from the other components of the system. Though most head units have an amplifier, some do not, or lack desired features. External amplification is available and most often used when existing amplification is insufficient. This is usually the case when powering a subwoofer, where desired wattage may be several multiples more compared to other
cabin speakers.

A car audio amplifier.

Though less common, OEM external amplification can be found in 'premium' audio packages, or in luxury cars. More common is aftermarket amplification installed later to satisfy the expansion of an existing system in some way.

During operation, it is common for a vehicle's charging system fluctuate, so a regulated amplifier will maintain its power output regardless of voltage fluctuation. Amplifiers rated at 100 watts @14.4 volts can not be regarded equal as to an amplifier that can maintain 100 watts @ 12 volts. Outside of certain standards, it is not uncommon for manufacturers to list a 14.4 rating & not post a 12 volt value.

Speakers

A set of speaker drivers removed from a passenger vehicle.

Car speakers are largely functionally identical to any other loudspeaker design with key components specialized for use in mobile environments, and generally serve an identical purpose. One major key design difference is mult-axial mounting of different types of loudspeakers in the same footprint, such as a tweeter directly mounted over a woofer. Another key difference is non-circular cone shapes, such as square, oval, or even triangular. Both of these features reflect a significant reduction in space and size that a speaker may occupy in a vehicle cabin.

Material construction may also include more exotic and hearty components more suitable to mobile use. Marine speakers may have plating for corrosion resistance. Cones may be coated with a substance to resist expansion and contraction under high vehicle cabin temps, known to reach 140 F in the sun.

Subwoofers may also be found in mobile audio applications where a cabin speaker make lack the desired low frequency response on its own.

Before stereo radio was introduced, the most common speaker location was in the middle of the dashboard pointing through perforations towards the front windshield. In most modern applications, speakers are mounted certain common locations including the front deck (or dash), the rear deck (or parcel shelf), the kick panel (located in the footwell below the A-pillar,) or the doors. In the case of subwoofers, mountings are usually under the seat or in the trunk. Each position has certain strengths and limitations from both a quality of sound, and a vehicle manufacturing perspective.

5.1 and even 7.1 channel surround sound systems, as well as THX II Certified, are now being integrated into some cars by both aftermarket enthusiasts and car manufacturers themselves. These systems include the full complement of front left, right and center speakers along with rear right and left surround speakers.

Head Unit

In modern cars, the primary control device for an audio system is commonly referred to as a head unit, and is installed in the center of the dash panel between the driver and the passenger. In older vehicles that had audio components as an option, such devices were mounted externally to the top of or underneath the dash.

The headunit itself is usually a multi-purpose device that houses multiple types of components in its housing. The most common components are a radio receiver/tuner usually with AM and FM bands, and a small amplifier for driving an audio signal to speakers. Other possible components include various media devices, such as (in older vehicles) a tape player (either 8-track or cassette), CD player, DVD player, Minidisc, USB flash memory, and even a hard disk drive typically used in notebook computing. Many head units also feature a DSP component, and equalization component (such as bass and treble controls), or a control interface for another feature on the car (such as a back-up/parking camera, navigation system, trip odometer, etc).

Due to auto manufacturing differences over the years, aftermarket headunit products are manufactured in multiple form factors. The primarily used size is mostly referred to by its legacy name of DIN, which refers to ISO 7736. DIN headunits come as single DIN or double DIN. A third less common standard is used mostly by Chrysler group and for a time Mitsubishi in their OEM devices.