In a speaker's motor section, the space between the top plate and the pole piece. This is where the magnetic flux field is concentrated and where the voice coil interacts with it.
Ampere is a unit measurement of current of electrical energy equal to one coulomb of charge per second. Most DC applications refer to positive current - current which flows from a positive potential to a more negative potential, with respect to a reference point which is designated as zero or neutral potential (usually ground). The electrons in a circuit flow in the opposite direction as the current itself. Ampere is commonly abbreviated as "amp", not to be confused with amplifiers, of course, which are also commonly abbreviated "amp". In computation, the abbreviation for amperes is commonly, "I".
All sound is a sinosoidial waveform. It has alternating peaks and valleys. The center point of each wave is the zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave. When a tube or transistor amplifier operates in Class A, the output tubes or transistors amplify the entire waveform without splitting it into positive and negative halves. In Class AB, used in the overwhelming majority of amplifier designs, the signal is split into two halves, positive and negative, and each half is sent to a tube or transistor circuit for amplification. Both sides work in tandem, and the two halves are recombined at the output section to reconstruct the whole signal. This technique increases the amount of power that can be applied, but increases distortion. Class A amps usually provide lower, often imperceptable distortion, but at the expense of reduced power output.Class D or High Current operation is essentially rapid switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Theoretically, since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero; and when the device is off, the voltage is large, but the current is zero. Consequently, class D operation (often, but not necessarrily digital) is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product yet to be made; meanwhile designs do exist with efficiencies approaching 90%. This is a design that is increasimgly popular for use in bass systems, where maximum power is necessary, and slightly elevated levels of distortion are easily tolerated.
A device, either a single stage or a large scale circuit with mutiple stages for creating gain, ie. making small signals larger.
A flat panel that divides the front and rear sound waves produced by a woofer. Sometimes baffle is used to mean an enclosure or the front panel on which the speaker is mounted.
|Bandpass (box or enclosure)|
An enclosure that is specifically tuned to give maximum energy to a very limited range of frequencies, usually the lowest. In this arrangement, the woofers are fully enclosed in the box with the sound pressure being vented through one or more ports.
A filter that has a finite passband, neither of the cutoff frequencies being zero or infinite. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, the Midrange driver may be fed by a bandpass filter.
The increase (or decrease) in efficiency of loudspeakers, due to the enclosure size and tuning. This is measured by the midband sensitivity of the speaker as a whole.
The metal frame structure of a standard dynamic loudspeaker. In larger, heavier speakers, this may be made of cast metal for extra strength and rigidity. All the other elements of the speaker are mounted on this structure.
The portion of the audible sound spectrum that contains the lowest frequencies. These frequencies have the longest wavelength and require considerably greater electrical power to render them at their original strength. In a good modern speaker system, the bass portion of the response curve extends from as high as 500 hertz, down to 20 Hz.
|Bass Boost/Enhancer Circuit|
An active low pass amplifier section added to some receivers, equalizers, and amplifiers that allows as much as an 18 decibel boost to be applied to an audio signal in the low frequency 35 to 90 Hertz range.
|Bass Reflex (box or enclosure)|
A speaker box design that makes use of a port or Passive Radiator which allows the energy derived from the motion of the back of speaker cone to be redirected in such a way as to reinforce the front radiation. This smooths and extends the low frequency response, but the effect is sharply Rolled Off on the low end, as the port signal goes back out of phase with the front. The overall effect of this is to tune the bass response to a particular point on the lower end of the spectrum, below which it rolls off sharply.
The part of the woofers metal Basket or frame on which the Magnet structure is mounted.
Bridging an amplifier, combines the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Because of this high power output, bridging is the best way to drive a single subwoofer.
|Capacitor (Power audio)|
Power stabilizing capacitors store the necessary power amplifiers need to punch larger bass notes while limiting clipping. They store energy during intervals when it is not required, which is most of the time, and release it when demand exceeds what is available from the car's power system. The amount of capacitance to be used is half (.5) farad per 500 watts of available RMS power. Capacitors are not used with amplifiers that supply less than 300 watts RMS in total.
This term is used in relation to speaker systems, to indicate a system in which separate mounting arrangements are provided for each component of the system. In a typical car system you might see a woofer in a box in the rear, midranges at the side and tweeters mounted on the dash panel. This compares to the typical integrated speaker enclosure in which all the Drivers are mounted in the same box.
Compression drivers are usually dynamic; that is, with a magnet and interacting coil arrangement, and a small diaphragm as the main transducer. These are the motor parts, also known as the driver, of a compression horn tweeter or compression horn general-purpose speaker, such as those used for Public Address (PA) purposes. These drivers are usually coupled to the throat of an exponential horn. Such an arrangement enables this type of tweeter to have very high directional characteristics, which allows them to be especially effective in situations requiring a very wide sound field. In typical home and car stereo near-field applications, large horns can be a bit too narrowly directional to be practical. For this reason, compression horn systems are usually found only in special purpose speakers used in mid and wide field applications such as PA systems or the sound systems installed in large theaters. However, some specialized horns have small apertures and very shallow horns, and can be quite suitable for close spaces.
A type of dynamic range processor which reduces the gain of audio signals which are over an adjustable 'threshold' level, therefore reducing the dynamic range. Generally allows the operator control over threshold, ratio, attack and release times. Both analogue and digital types are available.
A device or passive circuit used in systems with separate tweeter and/or midrange Drivers. It Rolls Off frequencies above and below certain points in the range, to allow the sound to be tailored for the specific driver to which it is sent. Most speakers have crossovers that consist of passive elements such as capacitors, coils, and resistors to separate the various frequencies. In a bi-amped or multi-amped system, the crossover is an active device that feeds the various frequency bands to the inputs of the amplifiers that operate the individual drivers.
The frequencies at which a passive or electronic crossover network divides the audio signals, which are then routed to the appropriate amplifiers or speakers.
|Cutoff Frequency Filters|
The frequency at which a signal falls off by 3 dB (the half power point) from it's maximum value. Also referred to as the -3 dB points, or the corner frequencies.
|Decibel or dB (see also Efficiency and Sensitivity)|
One tenth of a Bel. This is a measurement of the comparative strength of two powers, and can be applied when measuring any signal in the audio, video, and electromagnetic spectrum. If two powers differ by one Bel, there is a difference of 10 times the power. If comparing amplifiers, where one is rated at 10 watts while the other is 100 watts, then we have a difference of 10 decibels, or one Bel. Decibels should be understood as ratios, not fixed quantities. smallest difference in volume that can be heard by the average person. The term is derived as an honor to Alexander Graham Bell, who invented the telephone, and did much of the preliminary work in the modern science of acoustics.
This term describes the sound-producing element in a tweeter, or Horn. This is the surface that produces the sound you actually hear. The motor that drives it can be any of several technologies including Piezo, conventional dynamic, or ribbon types. Diaphragms do not produce low and low midrange frequencies well, so they are not usually found in that application.
|Die Cast (basket)|
A type of speaker basket or frame that is cast as a single piece of relatively thick, rigid metal. This contrasts with a Stamped frame that is shaped by pressure, much like a car body fender. Cast metal is heavier and more rigid, and thus less likely to "ring" at certain frequencies, and will hold its shape somewhat longer against the pull of gravity. This is mainly advantageous in the larger woofers of 12" or greater. Smaller drivers will likely not benefit perceptibly from being cast.
The extent to which a sound emitter yields acoustic radiation over a given area. This is a particular concern in tweeters and midranges whose portion of the audio spectrum has a much more directional character than woofers. Many Horn tweeters, while very energetic, have a more limited area of dispersion within which their effect can be fully perceived. Generally, Dome tweeters can be heard over a much wider area, all other factors being equal. But each particular example must be assessed individually for this factor. Some radiator designs are better than others.
The measurement of cubic volume that an item (such as a speaker or port) takes away from the internal volume of an enclosure. When designing an enclosure, this figure must be added to the enclosure volume .
Any departure from a true and accurate reproduction of the original waveform. It can include Noise, Clipping Distortion, Harmonic, and Intermodulation Distortion. These last two forms are fairly common in loudspeaker reproduction and can be reduced but not entirely eliminated in the existing technology. It would be fair to say that modern amplifier design fairly eliminates nearly all forms of inherent perceived distortion, leaving only that caused by inappropriate user settings and overloading. Distortion is the name given to anything that alters a pure input signal in any way other than changing its size. The most common forms of distortion are unwanted components or artifacts added to the original signal, including random and hum-related noise. Distortion measures a system's linearity - or nonlinearity. Anything unwanted added to the input signal changes its shape (skews, flattens, spikes, alters symmetry or asymmetry). A spectral analysis of the output shows these unwanted components. If a circuit is perfect, it does not add distortion of any kind. The spectrum of the output shows only the original signal - nothing else - no added components, no added noise - nothing but the original signal.
An alternate term for: speaker, transducer, or radiator. Properly speaking, the term speaker should refer to an entire sound producing system with whatever combination of woofer, midrange and tweeter; in whatever enclosure type it is housed.
The amount of enclosure airspace that is displaced by the speaker itself.
|DSP (digital signal processing)|
A technology for signal processing that combines algorithms and fast number-crunching digital hardware, and is capable of high-performance and flexibility.
|Dual Channel or Dual Voice Coil (speaker)|
A woofer with two voice coils mounted to a common cone, which can be connected to separate amplifiers, to produce a common bass output. Since bass has a non-directional character, this still permits the optimum reproduction of the stereo image via other speakers. Care should be taken in making connection, to observe proper polarities, however. Failure to do so can result in the quick extinction of the Driver if the amplifiers are pulling the cone in different directions at once.
Many factory installed auto speakers are of the dual cone type. Sometimes also referred to as a "full-range" speaker, it uses an inexpensive, efficient design. The small "whizzer" cone in the center of the woofer reproduces high frequencies, but not with the dispersion, range, or intensity of a separate tweeter.
The ratio of the loudest (undistorted) signal to that of the quietest (discernible) signal in a unit or system as expressed in decibels (dB). Dynamic range is another way of stating the maximum S/N ratio. With reference to signal processing equipment, the maximum output signal is restricted by the size of the power supplies, i.e., it cannot swing more voltage than is available. While the minimum output signal is determined by the noise floor of the unit, i.e., it cannot put out a discernible signal smaller than the noise. Professional-grade analog signal processing equipment can output maximum levels of +26 dBu, with the best noise floors being down around -94 dBu. This gives a maximum dynamic range of 120 dB - pretty impressive numbers, which coincide nicely with the 120 dB dynamic range of normal human hearing (from just audible to uncomfortably loud).
|Dynamic Range Suppression|
A signal compression technique which raises the level of lower passages without affecting overall volume. Especially useful with high noise levels, such as a moving vehicle.
|Efficiency (see Sensitivity)|
The ability of an audio system to convert electrical energy (watts) into mechanical energy (Decibels of acoustical energy). This ratio is usually given as the amount of energy measured in Decibels at a distance of one meter from the input of one watt of electrical energy. In most speakers, the greater the efficiency rating, the louder the unit will play in response to the same setting of the volume control, in comparison to less efficient types. The overall efficiency for most speakers systems is under 20 percent. Typical speakers can be rated at anywhere from 85 to 110 dB. Keep in mind, of course, that efficiency is only one parameter of a speaker's overall quality.
A polarized capacitor with a negative and a positive terminal that is commonly used for DC power filtration and energy storage. As with all capacitors, the dielectic insulator separates two plates and holds a charge. In this case the dielectric is a form of chemical electrolyte that is polarized. Smaller types are mesured in microfarads while the large ones used for amplifier stabilization are measured in farads. Values in the range of .5 to 3 farads are typical for use with car audio amplifiers.
|Enclosure, or Box|
A cabinet in which the various Drivers are housed. This arrangement is absolutely essential if bass response is desired from the woofer, which by itself in the open air, will produce very little low frequency response. This is so because of an effect called phase cancellation. This means that the sound wave coming from the back of the speaker at low frequencies is identical in form and intensity to the one coming from the front of the cone. When they meet, as in the open air, they are exactly 180 degrees out of phase and thus cancel each other out. An enclosure either prevents this from occurring or modifies the interaction so that the backwave actually reinforces the front wave. Tweeters and midranges are less severly effected by the phase cancellation effects, and are not in need of enclosures.
Electronic Shock Protection. An electronic circuit that stores the audio data stream from a CD or MD in a memory buffer. If the laser pick-up mistracks, audio still flows from the buffer preventing an interruption.
Mounting a speaker in such a way that the speaker and its Grill do not protrude above the surrounding surface. Usually, this means mounting it at the back of the baffle board (the board the speaker is mounted on).
The cylindrical portion of a speaker's voice coil section. A wire is wound around this cylinder to form a coil such that when current interacts with the magnetic field it produces a pumping motion that alternatively compresses and rarifies air, and creates the velocity for such air masses to reach our ears as sound.
The range of frequencies that a speaker will reproduce (lowest frequency to the highest). While the optimal normal is 20 - 20,000 Hz (Hertz), the range of human hearing for individuals is often much more restricted. A good full-range speaker system however, will reproduce as much of this range as possible in order to cover all variations. Individual Drivers are limited to reproducing only that part of the spectrum for which they were made, so their response will be limited, but still a necessary point to consider when designing a complete sound system.
An increase in volume or amplitude, usually measured in dB.
A barrier meant to prevent damage to the Driver that it covers, or that creates a more attractive appearance.
A term that describes anything having an electrical potential of zero relative to other points in a circuit. Most modern vehicles are designed around a negative ground system, with the metal frame being the vehicle's ground.
The term given to the condition that occurs when a voltage potential exists between two separate ground points.
The function of transfering heat away from a component into the air to prevent damage to the output section of an amplifier or the voice coil of a speaker.
Parts of an amplifier, typically heavy metal "fins," and a section of the frame of the speaker used to conduct and radiate heat away from the ponit of electrical consumption, or motor assembly.
The measurement of frequency. One hertz is equal to one cycle per second, or the complete cycle of an alternating (AC) waveform. Higher frequencies are measured in kilohertz, (thousands of cycles per second) Megahertz, (millions of cycles per second), etc.
The totality measured in Ohms of all electrical opposition to current flow: resistance, reactance, capacitance, as well as all mechanical factors inhibiting the completion of energy transfer in a contained system. In practical terms, this means that most Drivers are assigned a certain nominal impedance based on their DC voice coil resistance and mechanical stiffness. For car audio this is usually 4 ohms; for home stereo, 8 ohms is the standard.
Is the SPL (sound pressure level) a speaker will produce given one watt of power as measured from one meter away given a typical input frequency (usually 1kHz unless otherwise noted on the speaker). Typical sensitivities for car audio speakers are around 90dB/Wm. Some subwoofers and piezo horns claim over 100dB/Wm. However, some manufacturers do not use true 1W tests, especially on low impedance subwoofers. Rather, they use a constant voltage test which produces more impressive sensitivity ratings.
The power voltage provided to an amplifier. While most cars can be expect to reliably produce 12 volts, amplifiers are sometimes measured at higher voltages; up to 15 volts. In this way, higher power can be developed, albeit at the expense of longevity. It is a practice that allows higher power figures to be claimed.
The resistance or impedance to which energy is being supplied. In amplifiers, the speaker or speakers connected to the output of the amplifier.
Refers to radio frequencies within the 30-300 kHz band. In audio it usually refers to frequencies in the 20-160 Hz band.
|Low Pass Filter|
A network of components which attenuate all frequencies above a predetermined frequency selected by the designer. Frequencies below cut-off are passed without any effect.
A rubber or plastic cover for the magnet housing for protection or appearance, mostly the latter.
A combination of magnetic material and connected field concentrators that creates the magnetic field within which the voice coil interacts to produce sound. Magnetic materials have changed greatly over the years to produce much higher concentrations of magnetic fields (rated in gauss) with lighter and smaller volumes of material. In marketing speakers, a great deal of hype is often applied to the question of magnet weight. But many of these claims should be treated with skepticism. With greater and greater concentrations of gauss fields being developed from ever lighter and smaller mass metallurgical materials, the only good measure of adequate power handling is the manufacturer's RMS Wattage rating. Hefty magnets may look impressive, but while capable,they are no longer an essential index to a speaker's power capacity.
A Driver that is usually much smaller than a woofer, but with a surface area greater than the typical tweeter. It reproduces the mid frequency range from approximately 300 to 5000 Hertz. This optimum range can vary considerably from one driver to the next, thus giving the system designer more flexibility in choosing Crossover points for the other drivers.
The operation of an amplifier in one channel for both input and output. Can refer to an amplifier with only one channel of amplification or operating in bridged mode. For low frequency amplification applications, it provides better phase coherence and less distortion than stereo operation.
|MOSFET (Metal Oxide Semiconductor Field Effect Transistor)|
A type of large output transistor used in the final stages of many power amplifiers, and commonly found in most car and home amplifiers today.
|MOSFET Power Supply|
A power supply that employs MOSFET transistors to convert DC to AC. Offers superior thermal stability and more accurate switching.
In speakers, the complete sound generator or transducer that converts incoming electrical signals to mechanical/acoustic energy or sound. In a dynamic Driver, this includes the magnet, its directive field concentrators or Pole Pieces, and the voice coil that interacts with them.
The measurement of electrical resistance and system impedance. It is a measure of the degree to which electrons are limited in both velocity and quantity in passing through a circuit. In Impedance measurements, this takes into account, the mechanical resistance inherent in the motion of transducers. The standard is usually 4 ohms for car audio and 8 ohms for home and commercial audio. Some specialty woofers may be rated at 16 ohms.
The mathematical relationship between voltage, current, and resistance. It is named after George Ohm, it's discoverer. Ohm's law states that current volume in a conductor is directly proportional to the voltage flow across it and inversely proportional to its resistance. In general, this means that more voltage will produce more current, if resistance stays the same, but higher resistance will cause current to decrease if voltage stays the same. In mathmatical terms, V = I x R, where V is voltage, I is current, and R is resistance. Ohm's law is a description of electron behavior upon which virtually all understanding of electronics is based.
The high level (speaker) or line level (RCA) signals sent from one system component to another, or the high level signal from an amplifier to the system speakers.
|Peak Power Handling (MAX)|
Peak power handling refers to the amount of power a speaker is estimated to handle during a brief high-intensity musical burst. Since this can vary with both frequency and amplitude, it is a much less accurate way to judge speaker durability and performance than RMS (see RMS).
The ends or "Poles" of a magnet from which the magnetic lines of force, measured in Gauss, are at the greatest strength. In a typical speaker, this will be at the gap within which the voice coil is located.
A polymer based plastic material offering superior resistance against resonance.
A plastic based material used primarily for speaker cones due to its rigidity, damping and resistance against harsh environmental conditions.
|Power Handling (continuous or RMS)|
A rating of a Driver's ability in optimum conditions to handle a specified amount of audio power (electrical current power) on a constant basis, without damage. This is generally considered to be a conservative and reliable figure to use in judging what types of amplifier power will be most successful with a particular speaker design.
Root Mean Square is a formula that provides a reasonably accurate means of measuring and comparing continuous AC power. The use of this measure is preferred when matching system components, like amplifiers and receivers.
A graduated reduction in the strength of audio output above and below certain specified frequencies.
Sometimes known as an Acoustic suspension type, the sealed enclosure is a simple design in which each woofer is mounted in a sealed, airtight box or compartment with a specific internal volume for precisely the woofer being used. The air contained within the box or compartment then acts as a spring that allows more control over the speaker's behavior. Great care must be taken in design, as too small a box will sound "boomy," while too large a box may have hardly any bass at all. This should be remembered when replacing a woofer in such an enclosure. Best results can be expected when using woofers with a QTS between .30 to .90. These speakers offer good control, low Distortion and high power handling.
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.The Efficiency or Sensitivity rating indicates how effectively a speaker converts electrical power from the amplifier into sound pressure. This is frequently related to larger magnet sizes, larger voice coil diameters, and more compliant suspensions. Optimized enclosures are essential in achieving maximum sensitivity, overall. The higher the Decibel number, the more efficient the speaker and the louder it will play with the same input power. While usually more expensive, an efficient speaker helps maximize the potential of the available power.
Electronic devices which alter sound either to achieve a particular effect or to solve a problem with that sound (e.g. delays, compressors, reverbs, noise gates, equalizers).
|Signal To Noise Ratio|
A measurement of noise level in a device compared to the level of the signal. Higher numbers signify a greater difference, which is better. In technical terms, it is the ratio, expressed in dB, of signal power at a reference point in a circuit, to the noise information that would exist if the signal were removed (the noise floor). The maximum signal to noise ratio (equivalent to dynamic range) of a given piece of equipment can be seen as a measure of functional fidelity. This ratio is how much absolute noise it produces, compared to the highest signal voltage it can pass without distortion.
|Sound Pressure Level (SPL)|
An acoustic measurement of sound energy. 1 dB SPL is the smallest increment in sound level to which the average human is sensitive. Theoretically, 0 dB SPL is the threshold of human hearing while approximately 120 dB is the threshold of pain.
The rear suspension element on the cone of a loudspeaker. All the moving parts of the speaker are suspended by the spider in the rear and the Surround in the front. The spider is so named because of its resemblance to an arachnid, especially in the way in which flexion is obtained in the design of the concentric pleats that allow back and forth motion.
Total harmonic distortion is a measure of the how much a given audio device may distort a signal through the introduction of added harmonics or overtones. These figures are usually given as percentages. THD figures below approximately 1% are inaudible to most people. However, distortion is a cumulative phenomenon, so that if a receiver, equalizer, signal processor, crossover, and amplifier are all rated at "no greater than 1%THD", together, they could produce 5%THD, which may well be noticeable in the perceived sound.
|Two-way (car speaker)|
Music's high frequencies are reproduced accurately by two-way, or coaxial, designs. These speakers use a separate tweeter to deliver high frequency reproduction that surpasses that of dual-cone "extended range" models with whizzer cones. This tweeter, usually a cone or a Dome, is either on a post or bridge inside the woofer.
|Variable LP/HP Filter|
Crossover components which provide adjustable cut-off frequencies, and levels.
A type of speaker system also known as Tuned, Tuned Port, Ported, or Bass Reflex. They are basically Acoustic Suspension enclosures with the addition of a port or opening with a specific length. This allows a portion of the lower range to be coupled to the front wave produced by the woofer, in order to enhance the low frequency response. The portion of the range below the tuned point (Fb) is essentially a Free Air Driver that subjects the unloaded woofer to the possibility of severe, even catastrophic damage if the energy below this point is highly amplified. The best results for a vented speaker come when using woofers with a QTS in the range of .10 to .40.
The voice coil is the coil of wire fixed to a cylinder at the apex of the loudspeaker cone that interacts with a magnetic field. With the help of other speaker components, the voice coil is the active transducer that converts electrical signals from the amplifier or receiver into mechanical energy, which we hear as sound. The voice coil cylinder is the part of the speaker around which the voice coil is wound. More advanced speakers offer a heat-resistant voice coil to prolong speaker life.
Voltage is an electrical charge, or potential difference, between two points, one being of higher relative voltage than the other is. A 1.5-volt 'C' battery has 1.5 volts of difference between the positive and negative terminals, for example. The unit of voltage is called the "volt," named after Allesandro Volta. Voltage can be thought of metaphorically as a pressure, such as water pressure in plumbing, that is available to initiate action or work. It, however, cannot do any work until a circuit is complete so that current (measured in amperes) can flow.
A measurement of power. In speakers, wattage is a term that indicates power-handling characteristics in dealing with electrical voltage inputs from the amplifier. RMS or continuous power handling is the only accurate basis for comparing the capabilities of Drivers. In determining the proper power input for a speaker, use this measure only. So-called Peak Power handling is often only the manufacturers best guess at the power dissipation point, beyond which the unit will fail.
The bass and lower midrange sounds are reproduced by the woofer. To operate efficiently, a woofer's cone should be made of material that is stiff, yet lightweight. Cones made of polymers, polypropylene, light metals, or poly mixed with other materials including carbon strands and metals, provide excellent sound, and stand up to the heat, cold and moisture that car speakers face daily. Paper cones treated for moisture resistance also do a good job, and are usually very efficient. For car usage, untreated cones should be avoided.
A measure of a speaker cone's maximum Excursion (back and forth motion) in one direction while still maintaining a linear behavior (moving in a straight line with high precision). This factor is measured in inches or millimeters. Xmax is more precisely defined as the width of the voice coil that extends beyond the front plate plus 15%. This relates to how far the speaker can move in either direction without appreciable distortion.