Glossary
1 Bit
A reference to the way a digital-to-analog converter processes the 16 bits of information that make up a "word" on most digital recordings. 1-bit processors read one bit at a time (very quickly), rather than all 16 at once.
Air gap
The space between the top plate and the pole piece. This is where the voice coil sits.
Air space
Refers to the internal volume of a subwoofer box and is measured in cubic feet. Every subwoofer has been designed to fit in a box of a certain size for optimum performance, so if you're planning to build your own box be sure you're making it to the exact specifications recommended by the manufacturer.
Alternator
A device that is turned by a motor to produce AC voltage, which is then rectified (turned into DC) and used to supply voltage to the vehicle's electrical system.
Amplifier Power
Measured in watts, this is the measure of an amplifier's power output. All things being equal, the more power you have, the louder you'll be able to play music without distortion. Note: when comparing power specifications, make sure you're looking at continuous or RMS ratings and not peak.
Baffle
A board or other plane sirface used to mount a loudspeaker.
Basket
The basket is the metal frame of a speaker and is the thing that holds everything together. Some baskets are made of stamped steel, while others are die-cast aluminum. Either way, the best baskets will be very rigid and will not resonate. Cast baskets often offer better rigidity.
Bass Boost Adjustment
Some amplifiers offer a circuit that boosts the bass so you can make your system sound more full without adding a subwoofer. The most flexible kind of bass boost circuits will provide a boost at a low bass frequency- -around 45Hz- -and give you the ability to vary it so that it blends well with your system.
Bass reflex
Also called ported or vented, these boxes come in several configurations. Although ported enclosures aren't typically as good at playing the lowest frequencies, they tend to have higher-than-average efficiency and therefore require less power to achieve a given volume.
Box/Tube Interior Volume (cu. ft.)
Every subwoofer is designed to sound its best when "loaded" into an enclosure of a very specific volume (air space) inside. Although the size of the enclosure is critical to the performance of a subwoofer, the shape is less critical. Therefore, subwoofer enclosures can be tubes, cubes, trapezoids- -whatever. This fact has opened up a whole new market for "vehicle-specific" enclosures designed to fit perfectly in specific makes and models of cars.
Brigeable
In a multi-channel amplifier, the connection of two channels to drive a single load. The input signal is split, and then the phase of one of the signals is inverted. The non-inverted signal is sent to the left amplifier and the inverted signal is sent to the right amplifier (L+R-). The load is connected between the two outputs so it receives twice the voltage at a given input level. The resultant power is much greater than the two 4-ohm channels combined.
Capacitor
An electronic device which stores energy and releases it when needed. Also used to direct high frequency energy to tweeters. Rated in Farads.
CD changer controls
Many headunits have buttons that will control a CD changer of the same brand. The nice thing about this is that you can add a changer to your system invisibly; there is no way anyone can tell you have a changer trunk.
Channels
Refers to the number of speakers an amplifier is designed to power; four-channel amplifiers will power four speakers, two-channel amplifiers will drive two speakers, etc. While a two-channel amplifier can drive more than two speakers, each speaker will get less power and use of the fader control will be sacrificed. Note that all radios have either two or four channels of amplification as well and this should be considered when you plan to purchase one.
Chassis size
Refers to the size of the entire radio. The most common sizes are DIN, DIN and a half, and double DIN. While single-DIN headunits will fit in virtually any car, some cars (many GM and Chrysler vehicles) have dashboard openings designed for a larger unit. Older cars may have "two-knob" chassis'. With the use of vehicle-specific trim kits, most radios can look perfect in your car.
Coaxial Speaker
TA coaxial speaker has a large cone for the low range, and a smaller tweeter for the high spectrum. There is a cross-over network which divides and routes the signal to the correct driver.
Crossover
A network of electrical components that sends frequency ranges to the appropriate speaker drivers. High frequencies go to tweeters, midrange frequencies go to midrange drivers, and low frequencies go to woofers or subwoofers. If the music is sent to two drivers (like a tweeter and a combination midrange/woofer) the crossover is called a "two-way".
DAC
Digital-to-analog converter. This is the circuit found in all digital sources (CD, MiniDisc) that translates information from binary code (0s and 1s) to analog signals that can be used by your amplifier and speakers to make music.
Directional Tweeter
This refers to the ability of a tweeter to be aimed where desired. Most speakers have fixed tweeters, but the ones that have tweeters that can be aimed will allow you to make the speakers sound their best no matter where they're mounted in the car.
Dolby noise reduction
By far the most common type of noise reduction is Dolby B, which can be found on virtually any store-bought prerecorded cassette. When used on a tape that has been encoded with Dolby B, tape hiss is cut in half. It is a common misconception that Dolby noise reduction removes high frequencies, when in fact it is merely returning them to their proper levels.
Electronic Shock Protection
Known by a variety of names, these electronic buffers hold a few seconds of the music in memory so that when a CD skips the player has a few seconds to get back on track. The effect is that you may never hear a CD skip.
Enclosure Type
- Box/unloaded: Subwoofer cabinet without subwoofer
- Box/loaded: Subwoofer cabinet with subwoofer included.
- Box/Amplified/Loaded: Subwoofer cabinet with built-in amplifier and subwoofer included.
- Tube/Loaded: Subwoofer cabinet in the shape of a cylinder with subwoofer included
- Tube/Amplified/Loaded: Subwoofer cabinet in the shape of a cylinder with built-in amplifier and subwoofer included.
Farad
The basic unit of capacitance. A capacitor has a capacitance of 1F when a charge of 1 Volt across the capacitor produces a current of 1 Ampere through it. Named after Michael Faraday.
FM Modulator
Also known as an RF modulator, this device converts signals from a CD changer to radio frequency and allows you to receive the music from your CD changer on a "radio station." Although CD changers that interface with a headunit using an FM modulator don't sound quite as good as those directly connected, they can be added to any existing car stereo; even factory systems.
Free-air resonance (Fs)
The natural resonance point of a subwoofer. The lower the Fs, the greater the bass potential when placed in the appropriate enclosure.
Frequency range
The range of frequencies the subwoofer is capable of reproducing. Because the performance of a subwoofer is highly dependent on being placed in the right enclosure, this specification should be used as a guideline rather than an absolute.
Frequency Response
This specification is designed to indicate the range of frequencies a speaker will reproduce. This specification is only meaningful if accompanied by a tolerance specification, expressed as +/- x dB, that indicates the amount of deviation within the rated range. For a speaker to accurately reproduce, say, a 40Hz tone, it must be able to do it at the same volume as all the other frequencies. Ideally, you'll want your speakers to reproduce the widest range of frequencies possible so you can hear all the music. Because no single speaker can play all frequencies accurately, many people choose to add separate subwoofers and tweeters to existing systems.
For a subwoofer, the important part of the frequency range is the deep bass. Generally, the closer a subwoofer can get to reproducing 20Hz, the better.
The tricky thing about frequency response is making sure it's playing all the sounds it claims to play at a similar volume, which is indicated with a tolerance specification of +/- x (usually 3 or 6) dB. Frequency response specifications without a tolerance notation cannot be taken very seriously.
Fuse
A device designed to provide protection for a given circuit or device by physically opening the circuit. Fuses are rated by their amperage and are designed to blow or open when the current being drawn through it exceeds its design rating.
Gold Plated
In addition to being a great electrical conductor, gold also will not corrode. This is especially important in car audio, where the components of a car audio system are constantly exposed to humidity. Gold contacts give you more reliable, better sounding connections.
Harmonic Distortion
The type of distortion most often rated and listed with power specifications and is considered a very good measure of an amplifier's ability to accurately reproduce the tonal quality of the components of music. Most people can detect harmonic distortion greater than 1%, so lower percentages are better.
High Level Inputs
Also known as speaker level inputs, these terminals allow you to add an amplifier to virtually any system, even if the radio doesn't have preamplifier outputs.
High-pass filter
Unlike a crossover network, filters allow some frequencies to pass while simply blocking others. As the name implies, a high-pass filter allows the high frequencies to pass to the appropriate driver or amplifier. In better car stereo systems, separate amplifiers may be used for each type of speaker driver, so a high pass filter would be used to send signals to the amplifier that drives the tweeters or perhaps the tweeters and midrange drivers.
Impedance
Measured in ohms, this is a measure of resistance to an amplifier's power. Most car audio speakers, including subwoofers, are rated at 4 ohms. Note: this specification has nothing to do with sound quality.
Loaded
In car audio, this term is used to describe a subwoofer/enclosure combination. A subwoofer cabinet without a subwoofer is said to be unloaded, and a cabinet with a subwoofer included is referred to as loaded.
Loudness
This circuit is designed to compensate for the insensitivity of our ears to low and high frequencies at low volumes. Engaging this feature at low volumes will make the music sound more full. Many loudness circuits will reduce their effect as the volume increases.
Low-pass filter
Unlike a crossover network, filters allow some frequencies to pass while simply blocking others. As the name implies, a low-pass filter allows the low frequencies to pass to the appropriate driver. In better car stereo systems, separate amplifiers may be used for each type of speaker driver, so a low pass filter would be used to send signals to the amplifier that drives the woofers or subwoofer.
Midrange
This is the speaker that plays the frequencies in the middle of the audible range; the sounds to which we are most sensitive. Many times midrange speaker drivers will serve double-duty as a midrange/woofer.
Nominal Impedance
The minimum impedance a loudspeaker presents to an amplifier, directly related to the power the speaker can extract from the amplifier.
Ohm
Used as a measure of resistance as well as impedance, this specification is most often associated with speakers because they offer resistance to an amplifier's power. In car audio, most speakers are rated at 4 ohms. This is simply an electrical measurement used for matching speakers to amplifiers and has no relationship to sound quality.
Oversampling
A technique designed to remove the high-frequency harshness associated with digital recordings.
Passband
Refers to the range of frequencies that will be allowed to pass through the speaker system (the frequencies you will be able to hear/feel). Any frequencies above or below the passband will be attenuated (reduced).
PMPO
Stands for Peak Momentary Performance Output. This is the specification used most often when rating the power output of head units (in-dash tape and CD players). Peak power is a measure of how much power an amplifier can produce for an instant. This should never be confused with the much more useable RMS or continuous power specification that measures the average power output of an amplifier.
Polypropylene
A type of polymer that has a good balance between stiffness and low weight, making it ideal for use as a speaker cone. The fact that it's impervious to water makes it perfect for car applications.
Port/Ported Enclosure
An enclosure can either be ported or sealed. Ported enclosures have a tube or port that allows air to move in and out of the cabinet. Compared with sealed enclosures, ported enclosures are typically more efficient (that is, they need less power for a given volume) and play bass more loudly but may not play the deepest bass notes as well.
Power Range
Usually defined as the range between the least amount of power needed to drive a speaker properly and the maximum amount of power the speaker will handle. Note: this specification has nothing to do with sound quality.
Pre-Amp Level Outputs
On an amplifier, preamplifier outputs give a lot of system flexibility by allowing you to "daisy chain" amplifiers together. Ultimately, this would allow you to create a system that had a separate amplifier for each speaker in the car. If you plan to build a system, this is a feature you should look for.
Preamp output voltage
This refers to the strength of the signal coming out of the preamplifier outputs of a headunit. Typical voltage output is around .75-1 watt, but some headunits can produce as much as 4 and even 8 volts. The advantage of these higher voltage outputs is that you don't have to turn the input gains on your amplifier as high, and that translates into lower noise.
Q
This identifies the point at which the impedance of a speaker peaks, which is vital when determining whether to "load" a subwoofer in a ported or sealed enclosure. See Qts.
Qts
This is an indication of how a subwoofer will react with the amplifier, and is very helpful in determining whether to "load" a subwoofer into a ported or sealed enclosure. As a general rule, a woofer with a high Q (.3-.9) will work best in a sealed enclosure and a woofer with a low Q (.1-.4) will work best in a ported enclosure.
RCA outputs
These outputs use RCA connectors and provide an unamplified signal that is affected by preamplifier controls like volume and tone. The most common use for these is connecting an amplifier.
Remote bass control
This is a knob that can be mounted in easy reach of the driver and can control the volume of the bass in a system with separate amplifiers. Before this feature was available, bass levels had to be set in one position and left alone because they were so inconvenient to get to. Currently, this is an option that can be added to some amplifiers and amplified subwoofers.
RMS
RMS stands for root mean square. In the world of audio it means the amount of power (watts) an amplifier can produce for an extended period. This measurement is a much better indicator of an amplifier's useful power output than the "peak" power specifications often used in car audio.
Sealed enclosure
An enclosure can either be ported or sealed. Unlike ported enclosures, which have a port that allows air to move in and out of the cabinet, sealed enclosures use the trapped air inside the cabinet as an "air spring" for the woofer. Compared with ported enclosures, sealed boxes are usually smaller and play deeper bass but need more power.
Sensitivity
The rating of a loudspeaker that indicates the level of a sound intensity that the speaker produces (in dB) at a distance of one meter when it receives one watt of input power. Also sometimes incorrectly called efficiency, sensitivity is a measure of how much volume a speaker can produce when given a 2.83 volt (1 watt) signal. Although this specification has nothing to do with sound quality, speakers with higher sensitivity numbers may help you make the most of the amplifier power you've got.
Signal to Noise Ratio
This is an expression of the mixture of music to noise. The less noise, the higher the number. A good signal-to-noise ratio specification for an amplifier is 100dB or higher.
Signal-to-Noise Ratio
This is an expression of the mixture of music to noise. The less noise, the higher the number. A good signal-to-noise ratio specification for an amplifier is 100dB or higher.
Speaker Power Handling (Continuous Watts)
This indicates how much power a speaker can take from an amplifier for an extended period of time. Although this is often interpreted as an indication of how loudly a speaker can play, speakers and subwoofers can vary widely in their efficiency (how much volume they can produce with a given amount of power). For this reason, and the fact that it is not indicative of sound quality, this specification should only be used as one of several meaningful specifications when choosing a subwoofer or speaker.
Speaker Power Handling (Peak Watts)
This indicates how much power a speaker can take from an amplifier for an instant. Although this is often interpreted as an indication of how loudly a speaker can play, speakers and subwoofers can vary widely in their efficiency (how much volume they can produce with a given amount of power). For this reason, and the fact that it is not indicative of sound quality, this specification should only be used as one of several meaningful specifications when choosing a subwoofer or speaker.
Speaker Type
In car audio terms like full-range, 2-way, and 3-way are used to describe how many different sized cones are used to reproduce the music. Full-range speakers have a single cone, 2-way speakers use a tweeter and a mid/range woofer combination, and 3-way speakers use a separate tweeter, midrange, and woofer. By far the most common speaker configuration is the 2-way, but some larger speakers can accommodate 3 and even 4 different-sized speaker cones. While it's tempting to assume that speakers with more cones will produce better sound, that's often not the case.
Spider
A flat, round, springy device that holds the vibrating cone of a dynamic loudspeaker. The spider is where the diaphragm meets the voice coil.
Strontium Magnet
A magnetic material with superior magnetic strength characteristics to that of ferrite.
Surround
The rubber or foam ring that attaches the speaker's cone to the basket while still allowing for in and out movements necessary to make sound. Given the harsh environment of a car, more durable surrounds are worth considering even though they often cost a little more.
Tuner Sensitivity
This is a way of quantifying a radio tuner's ability to receive weak stations. In this case, lower numbers are better.
Tweeter
The smallest of the speakers, tweeters are designed to play the highest frequencies. Tweeters must be small because they must move in and out 20,000 times per second to reproduce the highest frequencies we can hear.
Voice coil
This is the coil of wire through which an electrical signal is sent. When the voice coil receives a charge it becomes an electromagnet and reacts with the permanent magnet found on the back of a speaker. This reaction is what causes a speaker to move in and out. Specialized voice coil materials and winding techniques are often used to improve a speaker's efficiency and/or power handling capabilities.
Woofer
Of tweeters, midranges, and woofers, these are the largest speakers and play the low frequencies. Woofers should not be confused with subwoofers, which are specifically designed to play the lowest two octaves.
Woofer Surround Material
The surround is a flexible ring that attaches the woofer cone to the frame or basket. This ring can be made of a number of materials, including foam and rubber. Although both materials are good, the trend is toward rubber due to its durability in the worst conditions.
X-max
The distance a speaker cone can move in and out. This is specification is usually found only on subwoofers and is a pretty good indicator of the amount of volume a sub will be able to deliver.
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