Acousta-Stuf™:
Acousta-Stuf™ is a sound absorption
and dampening fiber typically used in sealed box enclosures. Acousta-Stuf™
is a crimped polymer fiber that was designed to offer a similar performance to long
hair wool. This non-volatile synthetic fiber is superior to other materials because
it is safe to handle and will not decay with age.
Acoustic Suspension:
A type of loudspeaker
enclosure that uses a sealed rear
chamber to contain the back wave and provide damping of the cone motion. To qualify
as an acoustic suspension system, the enclosure must literally be airtight.
Active Crossover:
An electronic high or
low-pass filter that is placed between
the pre-amplifier or source and the amplifier. The benefits of an active filter
include removing components from within the speaker, removing the complexities of
driver impedances from the equation, and greater flexibility with regard to crossover
slopes and points.
Air, Airy, Airiness:
A subjective term often
used to describe a speaker's
ability to reproduce very high frequencies with detail and low distortion. Airiness
helps provide an ambient soundfield and is very important to producing a "live"
sound.
Amplifier:
An electronic device responsible for
increasing signal levels.
A power amplifier produces the high currents necessary for driving speakers. A
pre-amplifier
is responsible for increasing the low voltages associated with turntables, microphones,
or other low-voltage devices.
Anechoic Chamber:
A room that is designed such
that the walls absorb all
incoming sound waves and reflect nothing back. An anechoic chamber is useful for
measuring speakers without the negative influences of the typical listening room.
Using an anechoic chamber can provide a superior picture of the theoretical output
of a system, however real-world factors such as room gain and floor bounce cannot
be measured.
Anechoic Response:
The frequency response of a
driver or system measured
in an anechoic environment. As above, this response does not include any room effects
such as room gain, floor, or wall reflections.
Attenuate (attenuation):
The reduction in
output of a signal. In speakers,
a tweeter is oftentimes attenuated to match the level of a woofer. This attenuation
can be achieved with series or parallel resistors, but often an L-pad is used to
maintain a constant impedance load to the crossover.
Back plate:
A steel plate that is on the back
of a loudspeaker driver's magnet
structure that transmits the negative magnetic pole into the pole piece. A bumped
back plate has a raised central portion that helps prevent the voice coil from hitting
the plate on the down stroke.
Baffle:
The front panel of a speaker where the
drivers are mounted. A baffle
can either be the front wall of an enclosure, or a two-dimensional plane where a
driver is mounted. A baffle is used to separate the radiated front and back waves
of a driver.
Baffle Step:
An increase in the high frequency
output of a loudspeaker as
the radiation pattern changes from 4-pi space to 2-pi space. At wavelengths shorter
than half the width of a baffle, the waves "bounce" off the front baffle and are
reinforced due to reduced acoustic impedance. At wavelengths longer than half the
baffle width, the waves no longer are reinforced off of the front baffle and radiate
in all directions. The result is a 6dB increase (step) in the output above the baffle
step frequency.
Baffle Step Compensation:
A circuit that is
used in a speaker crossover to
"compensate" for the increase in output at higher frequencies due to the baffle
step. Typically the change in output across the baffle step is 6 dB. Baffle step
compensation can be achieved by using a low-pass filter at or near the baffle step
frequency to counter the natural rise. However, this will only be successful in
speakers that have relatively low crossover points where excessive attenuation above
the baffle step is not a problem. Baffle step compensation can also be achieved
by using an inductor and resistor in parallel with a second resistor shunting to
ground. Resistor values are generally on the order of the nominal impedance of the
driver and the inductor is generally in the .5-1.0 mH range.
Bandpass:
A combination of high-pass and
low-pass filters that yield a section
of flat response with a roll-off on either end. In the acoustic realm, a bandpass
can be achieved by using a single driver within a front and back enclosure tuned
to different frequencies. In the electronic realm, a bandpass filter is usually
used on the midrange of a three-or-more-way speaker to allow only a narrow band
to be reproduced.
Bandpass gain:
A phenomenon that occurs in
electrical and acoustic systems
when the high-pass and low-pass sections of a bandpass filter interact with each
other. As the passband region of the filter narrows, the amount of bandpass gain
also increases.
Bass:
The lowest portion of the audio frequency
spectrum, generally from
20 Hz to 160 Hz.
Bessel Filter:
A type of crossover filter that
has a small peak in the response
at the crossover frequency. The Q of the filter is slightly higher than average,
and phase characteristics are average.
Bi-amp(ing):
The ability of a single speaker to
be driven by two separate
amplifiers. Generally this is accomplished by having two sets of inputs on the back
of the speaker, one going to the tweeter high-pass filter and one going to the woofer
low-pass filter. It is also possible in 3 or more-way systems by combining the tweeter
and midrange into one section, etc. This method can be used to allow separately
adjustable levels for the treble and bass, but is not guaranteed to produce positive
results.
Bi-pole:
A speaker using two drivers facing
opposite directions and operating
in phase with each other. In home theater setups, bipolar speakers produce a somewhat
diffuse sound field, but there is still some direct radiation at the listener.
Biscuit:
A small spline of wood that is used to
help reinforce a joint. The
biscuit is placed into a slot and glued, where it absorbs moisture and swells up.
The swelling action along with the increased gluing surface area yields a very secure
joint.
Bi-wiring:
Bi-wiring uses the same internal
layout as bi-amping, but is accomplished
by using one amplifier channel with two separate runs of wire to the speaker. There
are many claims about the sonic improvements of this technique, but very little
scientific evidence to back them up.
Binding Post:
The most widely used method of
accepting speaker-level connections
on mid to high-end speakers. A binding post consists of a metal shoulder with a
protruding threaded rod on which a nut tightens down.
Bondo®:
An epoxy-based filler traditionally
used in autobody repair.
Makes an excellent wood filler for speaker building because of its great adhesion
to MDF, fast curing time, and ease of sand-ability.
Bucking Magnet:
A charged ring-type magnet that
can be used to help shield
a driver. The bucking magnet is secured to the rear of the motor structure with
the like magnetic poles together. This will reduce the stray magnetic field, but
will also affect the T/S parameters of the driver.
Bumped Back Plate:
A back plate that has a
protruding central portion that
helps prevent the voice coil from hitting it on the down stroke.
Butt Joint or Lap Joint:
In woodworking, a type
of joint that connects two
pieces of wood by fastening the end-grain of one piece to the face of another. The
weakest type of joint, due to the lack of lateral support and the limited gluing
surface area.
Butterworth Filter:
A crossover filter slope
that yields a maximally flat
frequency response in the passband with minimal phase shift. Drawback is a shallower
slope than other filter topologies.
Capacitance:
A measure of the ability of a
device to store electric charge
and resist changes in voltage. Capacitance is measured in Farads.
Capacitor:
An electronic component composed of
two metallic plates separated
by a dielectric. Stores electric charge and opposes changes in voltage. In speaker
building and all AC circuits, a capacitor acts as a high pass filter. Typical values
in crossover networks are in uF, or 1/1,000,000th of a Farad.
Center Channel:
The speaker used in a
surround-sound setup that is responsible
for reproducing vocals and other centrally located sounds. The speaker is generally
magnetically shielded to prevent interference with CRT based screens. While many
will argue that a center channel speaker is not necessary, in cases with a lot of
off-axis movie watching, it greatly helps keep dialogue centered on the screen.
Care should be taken to keep the center channel timbre matched to that of the front
speakers, which is important to provide a smooth transition as sounds move from
one speaker to the next.
Clipping:
A type of distortion that occurs when
the tops of the sine wave
are cut-off or "clipped". This generally occurs in amplifiers when they exceed output
voltage, and can be very detrimental to a speaker due to the non-linear motion that
is created.
Closed Box:
A completely sealed loudspeaker
enclosure. See Sealed Box
Coaxial:
A type of loudspeaker transducer that
has separate high-frequency
and low-frequency drive units together in one driver. In most situations, a tweeter
is suspended in front of the woofer cone, but it can also be located on top of the
pole piece where a dustcap is normally found. Coaxial arrangements can create a
"point-source" where the acoustic centers of both drivers are on the same axis.
Comb Filtering:
An artifact seen in
multi-driver systems that is the result
of constructive and destructive interference from multiple point sources. The addition
or subtraction of multiple sources will vary with location relative to the speaker.
Comb filtering becomes more of a concern at higher frequencies due to the shorter
wavelengths involved. Most often used when talking about line arrays where spacing
between tweeters can be problematic.
Compliance:
The overall stiffness of a speaker
driver's suspension. Represented
in the Thiel-Small parameters by the figure Vas, the equivalent air volume with
the same springiness.
Compression (power):
A condition in loudspeaker
transducers that is a result
of high temperatures in the voice coil, causing an increase in resistance and overall
impedance. Symptoms of compression include a decrease in sound output, unpredictable
spectral changes, and other audible distortions. This term is most commonly used
when referring to a speaker's ability to remove heat from the voice coil at high
powers.
Compression (driver):
A type of driver that
forces a larger radiating surface
area through a small opening. This is then usually attached to a horn loading system
that provides greater directivity and better acoustic coupling with the surrounding
air mass. The advantage of compression drivers is their very high efficiency and
ability to produce very high output.
Cone:
The portion of a driver that is attached
to the voice coil and excites
the air as the coil moves. The main function of a cone is to increase the radiating
area of the voice coil while maintaining a rigid form. The traditional conical shape
is most often used because it yields excellent strength to weight ratio when force
is applied from the vertex.
Conjugate Network:
Another name for impedance
compensation or Zobel networks.
A circuit consisting of a capacitor and resistor in series, in turn paralleled to
the driver. Is used to counter the rising impedance found in most drivers above
their resonance point. This enables more ideal functioning of a crossover.
Copper Cap:
A copper ring that is placed on top
of the pole piece in order
to reduce eddy currents. Helps reduce distortion and improve high-frequency performance.
Counter- EMF:
A voltage generated in the
opposite direction of the input
signal as a result of the voice coil moving back through the magnetic gap. The harmful
effects of counter-EMF can be reduced by having an amplifier with a high damping
factor. Also called Back-EMF
Curvilinear Cone:
A type of cone that is
flatter towards the surround and
curves progressively steeper towards the voice coil. Benefits of a curvilinear cone
can include better high-frequency performance and better off-axis response.
Crossover:
An electrical filter within a
loudspeaker responsible for dividing
up the frequency spectrum and sending portions to the appropriate drivers.
Coil:
In crossover construction, a simplified
name for an inductor. Used
because most inductors look like a large coil of magnet wire.
Cutoff:
The frequency where useful output can
no longer be produced. Usually
this is the F3 of a speaker, the frequency where the response is 3 dB down.
Dado:
In woodworking, a groove that is machined
into a piece of wood to accept
another board for making T-shaped joints. A joint formed by using a dado is strong
because of the increased gluing surface area, and the presence of some lateral
stability.
D'Appolito Configuration:
An arrangement of two
woofers and a tweeter such
that the tweeter is placed vertically between the two woofers. A D'Appolito
configuration
yields a narrower high-frequency vertical dispersion that in turn reduces floor
and ceiling reflections. A superior vertical symmetry is achieved compared to
traditional
two-way speakers. One thing to consider when building D'Appolito style systems is
the increased distance between the acoustic centers of the woofers. This may cause
comb filtering problems when crossed at high frequencies.
Damping (or Dampening):
The ability of a
material to reduce vibrations. On
a driver, a cone coating or surround material can minimize vibrations within the
cone, yielding flatter frequency response. Overall movement of the cone can be damped
electrically or mechanically through the voice coil and suspension. In speaker cabinets,
damping materials can reduce wall vibrations when applied directly to the walls,
or can absorb acoustic energy from within the enclosure itself.
Damping Factor:
A measurement of an amplifier's
ability to control the motion
of a speaker at the stop of transient impulses. Technically defined as the ratio
of the load impedance to the amplifier's output impedance. The high output impedance
of the amplifier enables it to absorb the back EMF generated by the voice coil.
A damping factor greater than 10 is usually adequate, however amplifiers with damping
factors up to several thousand are available. Note that damping factor varies with
frequency as the load's impedance changes.
DC resistance:
A measure of the pure resistance
of a driver's voice coil
at rest. Is used to help calculate crossover networks and determine nominal impedances.
Delay Network
A ladder delay network or a lattice delay network is a compensation network that doesn’t
affect the amplitude response, but alters the phase and group delay response.
The main purpose of a ladder delay network is to align the acoustic centers of the
drivers on the horizontal plane. Let’s consider a 2 way setup. Even though the speakers
are placed flush on the baffle, the tweeter is actually in front of the woofer,
acoustically. Implementing a lattice delay network will delay the tweeter, and the two
drivers will be phase coherent.
Decibel (dB):
A logarithmic scale used to
measure relative acoustic output
levels. Zero Decibels is defined as the quietest sound the average human is capable
of hearing. Traditionally, a difference of 3 dB is considered the smallest change
in loudness that the average human can detect. A doubling of perceived loudness
is equivalent to a 10dB change in acoustic output. A 3dB increase in acoustic output
requires double the amplifier power, while a 10dB increase in acoustic output requires
a one-hundred-fold increase in amplifier power.
Detail:
A subjective term used to characterize
a speaker's ability to reproduce
and separate small variations in input. Usually used to describe a tweeter's ability
to play intricate overtones and nuances.
Diffraction:
A series of constructive and
destructive interferences that
occur as waves change directions or go around obstacles. Typically, main diffraction
concerns are at the edges of the front baffle and around the frames of drivers.
A typical diffraction will look like a series of dips followed by peaks in the response.
Dipole:
A loudspeaker type that features one or
two drivers that emanate
sound in opposite directions out of phase with each other. A benefit of a dipole
speaker is the cancellation of the sound at 90 degrees to the listening axis, which
helps reduce side-wall room interactions. In home theater, dipoles are often used
to create a "diffuse" soundfield where there is minimal sound radiated directly
at the listener.
Directivity:
The tendency of a loudspeaker
transducer to radiate sound in
a particular direction. Typically used to describe the dispersion patterns in
horn-loaded
drivers. A very directive driver will project sound only to a small portion of
three-dimensional
space. This can be very helpful in sound reinforcement where coverage needs to be
tightly controlled.
Dispersion:
The characteristic pattern of how a
loudspeaker radiates sound
in a three-dimensional space. Horizontal dispersion describes the amount of sound
output at various angles side-to-side from the listening axis. Vertical dispersion
describes sound output at various angles up and down from the listening axis. Many
times controlled dispersion is used to reduce unwanted reflections from floors,
ceilings or other obstructions in the sound field.
Distortion:
Any type of error in the
reproduction of an audio signal. Distortions
can be produced at any point in the music chain, and can be caused by analog, digital,
or mechanical errors.
Dome:
A type of loudspeaker driver that uses a
convex, dome-shaped diaphragm.
Traditionally only used for mid-to-high-frequency drivers due to the limited structural
integrity of this shape. It does have the advantage of generally improved dispersion
with less diffraction compared to cone-shaped drivers.
Doping:
A thin layer of viscous material that
is added to the surface of
drivers to dampen resonances within the diaphragm.
Driver:
A term for a loudspeaker transducer in
its raw state without an enclosure.
Driver types are woofers, tweeters, midranges, compression drivers, domes, etc.
Dual Voice Coil:
A speaker driver, usually a
woofer or subwoofer, that has
two voice coil windings on one former. There are actually two sets of terminals
on the woofer for hooking an amplifier to each coil. A dual voice coil woofer allows
stereo signals to be summed and produced from one driver. Other benefits include
additional wiring flexibility (series or parallel combinations) and the ability
to use one coil to change the electrical damping characteristics of the woofer.
Dynamic Range or Dynamics:
A measure of a
system's abilities to produce very
quiet and very loud sounds. In digital devices, dynamic range measures the difference
between the largest and smallest possible signals produced. In loudspeakers, dynamic
range is a somewhat subjective term used to describe a speaker's ability to produce
quiet sounds and very loud sounds with good intelligibility and low distortion.
Early reflections:
The first reverberated
sounds to reach the listening position
generated by direct reflections from floors, ceilings, and walls. These are the
most harmful to sound reproduction because they arrive very soon after the original
signal and at fairly large magnitudes.
EBP:
Efficiency Bandwidth Product, equal to the
Fs divided by Qes. The EBP
is used to help determine what type of enclosure a woofer is suitable for. The general
rule of thumb is that EBP's less than 50 are better for sealed enclosures and EBP's
>50 are better for vented enclosures. However, this is only a general rule of
thumb, successful designs can be achieved that do not follow it.
Efficiency:
A rating of how much acoustic
output a driver or system will
produce with a given amount of input power.
Electrostatic Speaker:
A loudspeaker type that
uses a thin dielectric film
suspended between two electrically charged panels. The motion of the diaphragm is
the result of electrostatic charges pulling or pushing on it. This arrangement is
unique because there is no voice coil; the signal is applied by changing the voltage
on the electric panels.
Enclosure:
A cabinet that entraps the rear wave
from a loudspeaker transducer
to keep the front and back waves separate. Also serves to enhance bass response
due to the physical properties of the air enclosed.
Even Order:
Any of the crossover slopes that
are of an even order, usually
2nd or 4th.
Excursion:
The distance a driver's diaphragm is
capable of moving from the
at-rest position. Maximum linear excursion (Xmax) refers to how far a driver cone
can move while the still under control of the motor. Mechanical excursion is how
far the cone can physically move including portions where the voice coil is out
of the magnetic gap. Typically, excursion figures represent the amount of movement
in one direction from the at-rest position. However, movement in both directions
is sometimes given with a peak-to-peak rating.
F3 (6,8, etc.):
The point in an acoustic
roll-off where the output is 3 Decibels
down from the baseline level. The 3dB figure is used because this is the point where
a decrease in output will be noticeable to the average human.
F10:
The point in an acoustic roll-off where
the output is 10 Decibels down
from the baseline level. The 10dB figure is important because this is where the
average human will perceive a loudness of one-half of the baseline level.
Farad:
The unit of measure of capacitance. The
ability to store one coulomb
of energy at one volt is equivalent to 1 Farad. In most loudspeaker applications,
the values commonly used are in the uF range, or 1/1,000,000th of a Farad.
Far-Field:
The far-field can be defined as any
distance from a loudspeaker
at which inter-driver integration is complete. Typically set at 1m. Far-field
measurements
are useful because they usually take baffle step and driver-to-driver spacing into
account. In studio monitoring situations, near-field and far-field listening techniques
are used to evaluate a mix.
Fc:
The resonant frequency of a box system.
Ferrofluid:
A fluid that has magnetic
properties that allow it to be attracted
to magnetic fields. Often used in tweeter magnetic gaps to provide mechanical damping
and to help conduct heat away from the voice coil.
Fiberglass:
Fiberglass is a material often used
in speakers as a damping
material. Fiberglass has excellent thermodynamic characteristics useful for speaker
building, but is considered less safe than polymer based damping materials. Fiberglass
can be used as general stuffing in sealed enclosures, or used to damp walls in vented
cabinets.
Film and Foil Capacitor:
A type of capacitor
that uses two separate layers
of a solid metal and dielectric film. This type of capacitor generally has superior
audio characteristics than other types of capacitors.
First-Order Crossover Network:
A crossover
network that uses a single component
as a filter, yielding a cutoff slope of 6 dB per octave.
Five-way Binding Post:
A type of connection
usually found on speakers and
amplifiers used for connecting speaker wire. The term five-way comes from its ability
to connect to multiple wire termination methods: bare wire (compressed under the
nut), bare wire (through-hole), speaker pin, spade plug, banana plug, and banana
plug (through-hole). Used very often on high-end speakers for its flexibility and
ease of use.
Floor Bounce:
Typically, the first of the early
reflections to reach the
listening position from a loudspeaker. The negative effects of this reflection are
the greatest due to the close relative lengths of the original signal and reflected
signal. The usual result of floor bounce is a large dip and hump in the frequency
response between 100 Hz and 200 Hz.
Fourth Order Bandpass:
A type of bandpass
enclosure that uses a sealed rear
chamber and a vented front chamber.
Fourth Order Crossover Network:
A filter type
that uses four components to
produce a roughly 24 dB per octave rolloff.
Flush Mounting:
A process of recessing a driver
in its baffle so that the
faceplate of the driver is even with the surrounding baffle. Flush mounting will
prevent diffraction effects that occur as the waves go around the edge of a mounting
flange.
Frequency:
The number of cycles of a wave that
pass a given point in a given
time. Most often measured in Hz (cycles/second).
Frequency Response:
A measurement of a
loudspeaker driver or system's output
over a large range of frequencies. A typical frequency response curve plots loudness
in dB vs. frequency. This information is useful because the overall tonal
characteristics
of a speaker can be determined from this plot. Also, the useful operating range
of a speaker can be measured.
Fs:
The resonant frequency of a loudspeaker
driver in free-air.
Full-range driver:
A driver that is designed to
produce a wide range of frequencies.
There are no set limits to what frequencies must be covered in order to qualify
as a full-range driver. It is very difficult to produce a driver that is capable
of producing both ends of the frequency spectrum simultaneously, in most cases either
top-end or bottom-end response will be sacrificed to a certain extent.
Fundamental:
The lowest or primary tone
produced in the spectrum of a given
sound.
Golden Ratio:
A ratio often used in calculating
the internal dimensions of
a speaker enclosure. The ratio is 0.62 :1.0 : 1.62 and is used because it spreads
the internal resonances of the cabinet over the broadest frequency range.
Grill:
A screen or mesh that covers the front
of a speaker or driver to protect
it from damage. Despite using acoustically transparent grill cloth, the grill frame
may cause some negative effects because of diffraction problems.
Group Delay:
A measurement of the amount of
phase delay induced by a filter
at various frequencies. Ideally, a filter would pass or attenuate all signals without
any changes in the phase of the input signal. In the real world this is not the
case, and differing amounts of delay will be induced at varying frequencies. By
examination of a group delay plot we can see how phase has been affected, and we
can detect problems that may cause phase distortion or "smearing" of the signal.
Harmonic:
A multiple of the fundamental
frequency that is found in many locations
within the sound reproduction chain. Each higher harmonic is produced at a smaller
output than the last. In speakers, harmonics are detrimental to the accurate
reproduction
of a signal and are one of the primary forms of distortion. Naturally occurring
harmonics are responsible for the unique sound characteristics of varying instruments
and voices.
Helmholtz Resonance:
Resonances that occur when
air or other fluids are excited
and form standing waves within a fixed volume. The traditional examples of Helmholtz
resonance are organ pipes and "blowing over the top of a bottle." As can be imagined,
Helmholtz resonance produces extremely detrimental frequency response problems.
When designing ports for vented enclosure, helmholtz resonance must be considered
in situations where port length is much greater than port diameter. Helmholtz resonance
can also be found in long, narrow enclosures of any shape.
High-Pass Filter:
A filter that allows high
frequencies to pass, but cuts
off lower frequencies. Used on tweeters and midranges to limit low frequency production,
thus reducing excursion and distortion.
Impedance:
A complex calculation of the
resistance of electron flow in alternating
current circuits. Impedance is calculated from a combination of resistive, capacitive,
and inductive elements in a circuit. Measured in ohms.
Impedance Curve:
A plot of the impedance of a
loudspeaker across the entire
frequency spectrum. An impedance plot is useful in determining many key parameters
in loudspeaker design. Most driver T/S parameters can be derived from the impedance
plot, as well as most in-box performance parameters.
Inductance:
A device's ability to resist
changes in current, measured in
Henries.
Inductor:
An electronic device that resists
changes in current due to the
production of a magnetic field around itself. In crossovers, an inductor is a coil
of insulated magnet wire that acts as a low-pass filter. Inductors come in several
types, air-core, iron-core, and ferrite core. Air-core inductors are considered
the best for audio applications, followed by iron core, and then ferrite core. When
large inductance values are needed, iron or air core inductors may be used. An inductor
should have the lowest possible DC resistance to allow maximum power throughput
and minimal negative effects on the crossover. Values typically seen in crossover
networks are in mH, or 1/1000th of a Henry.
Infinite Baffle:
A loudspeaker enclosure type
that theoretically uses an
infinitely large rear chamber to contain the back wave. Since an infinitely large
volume is not possible in many situations, traditionally any volume roughly 5 times
the Vas of the driver is considered infinite. Woofers to be used in infinite baffle
situations must have a high Qts, giving them adequate damping in a free-air situation,
and allowing them to operate effectively. Benefits of an infinite baffle enclosure
are extremely clean and uncolored sound with very low bass output capabilities.
In home construction, infinite baffle woofers are often installed in ceilings or
floors, using an attic or basement to contain the back wave.
Isobaric:
A loudspeaker configuration in which
two woofers are sealed together
with a very small airspace in between. The two drivers can be facing each other
in a "clamshell" arrangement, or placed very close together with the magnet of one
woofer near the cone of the other. An isobaric configuration yields an overall Vas
which is half that of a single woofer. When the two woofers are wired in parallel
an increase in efficiency results, but the maximum SPL is not increased since it
is still excursion-limited. In a clamshell arrangement, some distortion can be reduced
due to the cancellation of odd-order non-linearities.
Jasper Circle Jig:
A jig that mounts to the
base of a router to allow easy
machining of circular holes and recesses. Pre-drilled with all of the holes and
labels necessary to create any diameter circle.
Kevlar®:
A synthetic fiber produced by
DuPont® that is sometimes
used in loudspeaker driver cones because of its high strength to weight ratio.
L-Pad:
A means of attenuating the output of a
tweeter or midrange using a
combination of series and parallel resistors. An L-pad can provide variable levels
of attenuation without changing the impedance that the crossover sees.
Labyrinth:
A type of loudspeaker enclosure that
is similar to a transmission
line. A labyrinth features a constant cross-sectional area that has damping material
lining the walls only. The typical length is 1/4 wavelength.
Le:
Abbreviation for voice coil inductance.
Linkwitz-Riley Crossover:
A type of crossover
popularized by Siegfried Linkwitz,
of a second or fourth order classification. Both drivers are 6dB down at the crossover
frequency and sum to zero to yield a flat frequency response on axis. L-R crossovers
also produce a main lobe that is perpendicular to the drivers' central axis.
Listening Room:
A dedicated room designed
specifically for listening to hi-fidelity
sound reproduction. A listening room typically has dimensions conducive to good
listening and is well damped to reduce room reflections.
Lobing:
The three-dimensional shape of how
sound radiates from a multiple-point-source
speaker. The sound will vary with different angles relative to the listening axis
due to the separation of the acoustic centers. At some angles, there will be
cancellations
at certain frequencies. Lobing occurs vertically in vertically aligned speakers
and horizontally in horizontally aligned speakers.
Low-pass:
A filter type that allows low
frequencies to pass, while rolling
off higher frequencies. A low-pass filter is used on woofers to reduce their output
at frequencies where they experience cone breakup or poor off-axis response.
Magnetic Gap:
The round opening in the top of
the motor between the pole
piece and the top plate. The magnet's entire field is concentrated into this small
gap where the voice coil sits. Having a narrow magnetic gap contributes to a
high-efficiency
speaker, but care must be taken to ensure that the voice coil will not rub on either
side.
MDF:
Medium Density Fiberboard. A type of
engineered wood product that is
used extensively in the loudspeaker industry. It is used because of its relatively
high mass and good damping characteristics. MDF is made from glued and pressed wood
pulp fibers; the process is very similar to the paper making process. MDF can be
either a very light brownish-yellow color or a darker brown, depending on what type
of sawdust is used in its making. This mainly varies by what part of the country
the MDF is coming from. MDF machines very well, it will hold sharp edges and complex
forms very well. Care should be taken in securing MDF due its layered nature that
tends to separate when inserting screws. Most glues will work with MDF, though the
suggested types are standard "yellow" carpenters glue or polyurethane-based glue.
Metallized Film:
A method of constructing
capacitors using a non-conductive
dielectric with a thin layer of metal deposited on one side. The very thin layers
of film are then rolled up to produce a large surface area of alternating layers
of metal and dielectric. Most relatively inexpensive capacitors are constructed
using this method.
Midrange:
The central portion of the audible
frequency spectrum. The midrange
is considered one of the most critical areas in speaker performance due to the location
of human vocals and many instruments in this area. Midrange frequencies can range
from as low as 200 Hz up to 4000 Hz, though the traditional range does not extend
quite as high.
Miter Joint:
A joint type in which both pieces
of wood are beveled and glued
together. Miter joints exhibit improved strength compared to butt joints because
of the greater gluing surface area and the securing of end-grain to end-grain. Miter
joints are most often used in situations where odd angles are being joined, or the
builder does not want any exposed end grain. In MDF, miter joints are far superior
to butt joints, because they join end-grain to end-grain and will not de-laminate
the material when stressed.
Motor:
The motor consists of the top plate,
back plate, magnet, and pole
piece. The motor contains the parts that are responsible for the motion of a loudspeaker
diaphragm. The strength of the control over the voice coil and cone are determined
by the motor design.
Mono-pole:
The traditional type of loudspeaker
in which sound is radiated
in one direction. As opposed to a di-pole or bi-pole type speaker that radiates
sound in multiple directions.
Mylar Capacitor:
A capacitor type that uses
mylar as a dielectric. Considered
superior to electrolytic capacitors, but not as good as polypropylene or film-and-foil
capacitor types.
Near-Field:
The near-field can be defined as
any distance relative to a speaker
at which driver integration is not fully complete. Typically the near-field of a
speaker is distances less than 1 meter. Near-field measurements are useful because
they can measure the response of a driver without the effects of the room. Near-field
measurements are only good up to several hundred Hz however, since interactions
with cabinet edges and across the driver itself are not taken into account. In studio
monitoring situations, near-field and far-field listening techniques are used to
evaluate a mix.
Non-Polar Electrolytic Capacitor:
A type of
capacitor that uses a thin layer
of oxidized metal as the dielectric between layers. Non-polar refers to its ability
to be used in either direction in a circuit.
Notch Filter - Parallel:
A filter used in
crossover construction that attenuates
the signal only at a specific frequency. The "notch" can be adjusted to a specific
frequency, depth and width. The most versatile type of notch filter is the "parallel
notch filter" or "parallel trap circuit"; these are two different names for a
combination
of a resistor, inductor, and capacitor in parallel. By adjusting the values of these
components, the location, width, and depth of the notch can be manipulated. These
filters are very difficult to design, due to the complex interactions of the non-ideal
portions of each component. A notch filter like this is usually designed using formulae
to calculate approximate values and then trial-and-error to get the exact desired
result. The advantages of a parallel notch filter are that they work independently
from the impedance of the driver, and can be added to an existing crossover network.
Notch Filter - Series:
The series notch filter
is used primarily on tweeters
and dome midranges to reduce the magnitude of the impedance peak at the resonant
frequency. The large impedance peak on non-ferrofluid enhanced domes can cause erratic
performance of the crossover near the resonant frequency. An inductor, capacitor,
and resistor are connected in series to each other, all of which are connected in
across the terminals of the driver.
Octave:
An interval in the audio frequency
spectrum equal to one-half or
double of the starting value. One octave above 400 Hz is 800 Hz, one octave below
400 Hz is 200 Hz.
Odd-order:
Any of the crossover slopes that are
of an odd order, usually
1st or 3rd order.
Padding:
A term used synonymously with
attenuation, usually referring to
reducing the output of a tweeter, i.e. padding down a tweeter.
Parallel:
A method of connecting electrical
components such that the voltage
drop across each component is the same. In speaker building, this is accomplished
by connecting the terminals such that "positive is to positive" and "negative is
to negative." In a speaker, using two drivers in parallel causes an arguable 6dB
increase in output. This is due to the halving of the system impedance and a doubling
of radiating area. Two drivers in parallel in the same enclosure require a doubling
of cabinet space. It is important to note that the total system impedance of two
speakers in parallel will be half that of one driver.
Passive Crossover:
An electrical filter within
a loudspeaker responsible
for dividing up the frequency spectrum and sending portions to the appropriate drivers.
Most passive crossovers consist of a combination of resistors, capacitors, and
inductors.
They do not require any external power and are performed to the signal at the
speaker-level.
Passive Radiator:
A moveable piston often
constructed like a woofer without
a motor structure, which is used to tune a box to a certain frequency. The frequency
at which a passive radiator (of a fixed diameter and compliance) is tuned is controlled
by the moving mass of the diaphragm. Some benefits of a passive radiator enclosure
are the elimination of extremely long ports, the non-existence of port noise, and
higher frequencies will not leak out through the port.
Phase:
Phase is a relative measurement of the
difference between "where"
periodic waveforms are at a given time. Two waves are "out of phase" (180 degrees)
when the crest and trough of both waves occur at the same time. This will cause
a cancellation of the two waves. When two separate speakers are connected "out of
phase" a de-localized sound field will be created with a dramatic reduction of bass
output. In crossover design, phase is used to measure the relative output of multiple
drivers at a certain frequency. Some crossovers exhibit excellent phase response,
meaning that inter-driver destructive interference is kept to a minimum. Phase can
vary anywhere from 0 to 360 degrees and varies with frequency as well.
Piezo Tweeter:
A type of tweeter that used a
simple piezoelectric crystal
as the diaphragm. These piezoelectric crystals mechanically vibrate as current passes
through them. The advantage of this type of tweeter is that no crossover is needed
due to their high internal impedance.
Planar Transducer:
A loudspeaker drive unit
that uses a thin film suspended
between two magnets as the diaphragm. The voice coil itself is etched onto the
diaphragm,
and as current flow through it, the diaphragm moves back and forth. In a planar
transducer, the diaphragm is attached along the length of the driver. Most planar
transducers are dipolar by nature, though a rear chamber may be used to contain
the back wave. Due to the limited excursion capabilities of most planar transducers,
it is difficult to produce low bass frequencies.
Pole Piece:
The portion of a loudspeaker
transducer that provides the negative
magnetic pole on the inside of a voice coil. In the most general sense, the pole
piece is a cylinder of metal that is on the inside of the voice coil. A T-shaped
pole piece has a smaller diameter towards the bottom, and is wider at the top, yielding
a T-shaped profile. The widest portion of the T is directly across from the top
plate of the magnet structure. A vented pole piece has a hole through it to allow
air to enter the magnetic gap to increase cooling abilities.
Port:
A cutout or tube in a vented box that
"tunes" the box to a certain
frequency. The port provides an additional air mass that is excited at its own
frequency,
enabling extended bass response. A port can be anything from a hole in a cabinet
to a 4" diameter by 20" long piece of PVC. In a given box, a longer port corresponds
to a lower tuning frequency.
Port Noise:
An occurrence in vented box systems
where erratic "wind noise"
is created by the movement of air through the port. Port noise is generally described
as a "chuffing" sound that will occur at maximum excursions of the driver. By increasing
the diameter of a port, the speed at which air moves through the port will be reduced,
in turn reducing port noise. Port noise can also be reduced by using flared ends
on the port tubes, which provide a superior airflow across the transition from the
port to the outside air.
Power Handling:
The amount of electrical power
that can flow through a loudspeaker
driver before functioning ceases. Most often, the thermal power handling is quoted.
This is a measure of how much power a driver can take before the voice coil insulation
melts or other joints come apart and the driver fails. In reality, most drivers
will reach a point of maximum excursion before their thermal power-handling limit
is reached.
Push-Pull:
A method of using two woofers in the
same box. A push-pull enclosure
uses two woofers on opposite sides of the box operating out of phase with each other.
Overall performance will be roughly the same as in a traditional two-woofer format,
except for a potential decrease in some forms of distortion. This occurs because
some distortions may now be present out of phase thus canceling out.
PVC Pipe:
The typical plastic pipe that is used
for plumbing in homes. It
is very useful for making ports in loudspeakers due to its availability in a variety
of lengths and diameters.
Quasi-Anechoic:
A method of making loudspeaker
measurements that can produce
results similar to those found in a full-blown anechoic chamber, but in a standard
room. These measurements can be taken by "gating" out the reflections from the
boundaries
within the room. Quasi-anechoic responses will be very accurate above a certain
frequency, but will have invalid results below that point.
Q:
The losses or relative damping (ratio of
stored to dissipated energy or
ratio of reactive to resistive energy) of a system. In an impedance plot, a driver
Q can be determined by how high and narrow the resonance peak is. A high, narrow
peak indicates a high Q, while a lower, wide peak indicates a low Q.
Qes:
The losses or relative damping (ratio of
stored to dissipated energy
or ratio of reactive to resistive energy) of a driver at Fs, considering only its
electrical (non-mechanical) resistances.
QL:
The Q of a vented speaker cabinet resulting
from all of the box losses
(acoustic weaknesses).
Qmc:
The Q of a sealed loudspeaker cabinet at Fc, considering only
its mechanical (non-electrical) resistances.
Qms:
The losses or relative damping (ratio of
stored to dissipated energy
or ratio of reactive to resistive energy) of a driver at Fs, considering only its
mechanical (non-electrical) resistances.
Qtc:
The Q of a sealed loudspeaker considering
both mechanical and electrical
resistances.
Qts:
The losses or relative damping (ratio of
stored to dissipated energy
or ratio of reactive to resistive energy) of a driver, considering both mechanical
and electrical resistances.
Rabbet:
In woodworking, a groove or recess that
is placed along the edge
of a board to improve joint quality. Using rabbets to make a joint provides increased
strength because of the increased gluing surface area, and the bonding of both end-grain
and side-grain fibers.
Re:
The DC resistance of a loudspeaker
transducer, measured in ohms.
Resistance:
A material's ability to resist the
flow of electrons, measured
in ohms.
Resistor:
An electrical component that provides
resistance to current flow.
In crossovers, resistors are used in conjunction with other elements to produce
various filters, and to attenuate output.
Resonant (Resonance) Frequency:
The frequency
at which an object will naturally
mechanically vibrate.
Ribbon Driver:
A type of loudspeaker transducer
that uses a thin metallic
film suspended between two magnets as the diaphragm. A true ribbon driver differs
from a standard planar transducer in that the diaphragm is attached only at the
ends. Thus, a true ribbon driver is very delicate, but is able to move very quickly
and can produce high frequencies very accurately.
Ringing:
A type of distortion found in
loudspeakers that is usually caused
by the natural resonances within a driver's cone material. It can also be used to
refer to the poor transient performance of a driver or system.
Rms:
The mechanical resistance of a loudspeaker's suspension
losses.
Satellite Speaker:
A typically small speaker
designed to reproduce frequencies
above a certain point. A satellite speaker is used in conjunction with a subwoofer
to fill in the lower octaves. Advantages of satellites are the ability to use small
enclosures that can be more discreet in a room. The disadvantage of them is the
difficulty integrating the lower and higher frequencies.
Sd:
The radiating surface area of a loudspeaker
driver.
Sealed Enclosure:
A type of loudspeaker
enclosure in which the rear of the
woofer fires into a tightly sealed chamber that is completely separate from the
surrounding air space. Sealed boxes have a higher F3 than a vented box with the
same woofer, but the low-end response rolls off at a shallower rate. Sealed boxes
exhibit superior transient response and group delay characteristics than ported
boxes.
Second Order Filter:
A filter that uses a
combination of two components to
yield an approximate 12 dB per octave roll-off.
Sensitivity:
A measure of the acoustic output
of a loudspeaker resulting
from the application of a fixed input power. Most often, sensitivity is measured
in decibels at a distance of 1 meter from the source with 1 watt of input power
(dB 1W/1m). It is also seen as dB at 2.83V/1m, which allows a better comparison
of sensitivities regardless of load impedance. 2.83V is the amount of voltage necessary
to deliver 1 watt of power into an 8-ohm load.
Series:
A method of connecting multiple
electrical components such that there
is the same current through each. In loudspeakers, connecting woofers in series
is accomplished by connecting the woofers "positive to negative." Putting two woofers
in series will double the system impedance and system radiating area. The net result
of using two woofers in series is no gain in efficiency. However, the increase in
surface area will reduce the amount of excursion required to produce a given SPL,
and a higher overall SPL can be produced.
Series Notch Filter:
The series notch filter is
used primarily on tweeters
and dome midranges to reduce the magnitude of the impedance peak at the resonant
frequency. The large impedance peak on non-ferrofluid enhanced domes can cause erratic
performance of the crossover near the resonant frequency. An inductor, capacitor,
and resistor are connected in series to each other, all of which are connected in
parallel across the driver.
Shielded:
A loudspeaker driver or system that
has a very small stray magnetic
field making it acceptable for use near CRT-based screens. To shield a driver, a
magnet of the opposite polarity is attached to the rear of the motor structure.
This reduces the stray magnetic field considerably, but to further improve shielding
a ferrous cup is placed over the entire magnet assembly. When done properly, the
combination of the second magnet and the metal cup will reduce the stray field to
almost nothing. Also, many drivers that use neodymium magnets are inherently shielded
very well due to the smaller stray magnetic field.
Snake Oil:
A term used in the audio community
to describe ideas or technologies
that claim to give large improvements in performance, but there is little or no
scientific evidence to back these claims.
Speaker:
A driver or combination of drivers
that is used as a system to convert
electrical signals into acoustic output.
Spider:
The corrugated cloth ring that attaches
the voice coil to the frame
of a speaker. The typical accordion spider is used because it allows forward and
backward motion without allowing the voice coil to move side-to-side.
SPL:
The measured loudness of a sound. Often measured in decibels
(dB) from one meter (1m) away from a speaker driver while it is playing a test tone that
is being driven by one watt (1W) of power from the amplifier.
Also measured from a speaker that is being driven with 2.83 volts @ 8 ohm of audio
voltage.
(Example: 90 dB 2.83V/1m)
Step Response:
A measurement of how a speaker
responds to a theoretically
infinitely fast transition from zero output to a finite output. An ideal step response
will look like a triangle without any extra zigs in it.
Subwoofer:
A loudspeaker transducer
specifically designed to produce extremely
low frequencies. A subwoofer will generally only be capable of output up to several
hundred Hz. In home theater, a separate track is recorded for the subwoofer. These
are typically powered by their own amplifier, separate from the main speaker amplifiers.
Surface Mounting:
The installation of
loudspeaker drivers such that the frame
of them mounts on top of the baffle. This should generally be avoided to reduce
diffraction around the driver frame, and is more important at higher frequencies.
Thiele-Small parameters:
Thiele-Small
parameters are a set of data characterizing
the electrical and mechanical properties of a loudspeaker transducer. This data
can be used to help design enclosures and predict the driver performance within
them.
Third Order Crossover Network:
A filter that
uses three components to produce
a roughly 18 dB per octave rolloff.
Three-Way Speaker:
A speaker system that uses
three separate drivers to cover
the entire audio spectrum. Usually a large woofer, a smaller midrange and a tweeter
are used together.
Toe(in):
A slight angle placed on a pair of
speakers so that the drivers
are facing at an angle other than perpendicular to the wall. This is helpful to
make sure that the listening seat is at the proper axis relative to the speakers.
Top Plate:
A steel plate that is on top of the
magnet that transmits the
positive magnetic pole to the outside of the voice coil. The frame is also attached
to the motor structure through the top plate.
TQWT or TQWVP:
Tapered Quarter Wave Tube or
Voight Pipe. A type of transmission
line enclosure where the driver is placed at the 1/3 point of the length of the
line. The tapering of the line produces a slight horn-loading effect on the bass
frequencies, which can help boost bass response.
Transient Response:
A transient is a sudden
change in signal amplitude, experienced
in fast transitions from quiet to loud. In a speaker system, the transient response
describes a speaker's ability to tightly control its cone motion. The cone will
start and stop quickly to match the input signal with a minimal amount of distortion
and time smearing.
Transmission Line:
A type of loudspeaker
enclosure that routs the back-wave
of a speaker through a long tunnel that eventually exits via the front of the speaker.
The theory of the transmission line is to make a line length equal to 1/4 or 3/4
of a wavelength, therefore the front and rear waves will add to each other upon
exiting the front of the line. Because of the long, narrow rear enclosure, Helmholtz
resonances tend to be a problem and produce significant ripples in the low frequency
response. Line stuffing is generally used to increase the apparent length of the
tube and distribute the Helmholtz resonance frequencies. However, getting exact
line lengths tends to be difficult, and will often result in poor performance. There
have been several very successful transmission line designs, however they are much
more difficult to perfect than the traditional sealed and ported enclosures.
Treble:
The highest frequencies in the audio
spectrum. Generally from 4 kHz
up to beyond audibility.
Tweeter:
A type of loudspeaker transducer that
is responsible for producing
the top of the frequency range. There are several traditional styles of tweeters:
ribbons, domes, and cones. The key feature of a tweeter is its low moving mass,
enabling it to produce the fast vibrations necessary for high frequency reproduction.
Another advantage of a tweeter is its ability to produce high frequencies well off-axis.
Two-Way Speaker:
A speaker system that uses two
drivers to cover the entire
audio range. In most standard speakers, the crossover occurs in the 2 kHz to 4 kHz
range.
Vas:
The Thiele-Small parameter that measures
the overall compliance of a
loudspeaker transducer. The Vas is defined as the volume of air that has the same
compliance as the driver.
Vented Enclosure:
A type of loudspeaker
enclosure where the woofer is mounted
in an enclosed box except for one vent or port connecting to the outside air space.
Vented enclosures feature a lower F3 point than a sealed box for the same woofer.
The lower F3 comes at the expense of a steeper low-frequency roll-off. In a vented
enclosure, the driver excursion is at a minimum at the box tuning frequency, and
increases dramatically below this. Care must be taken to prevent over-excursion
(unloading) of the woofer at frequencies below the tuning frequency.
Voice Coil:
The coil of magnetic wire that
moves within the magnetic gap
of a loudspeaker transducer. The voice coil is the portion of a driver that directly
transforms electrical energy into mechanical energy.
Voice Coil Former:
A cylindrical tube of paper,
aluminum, or Kapton®
that the voice coil is wound on. A former must be very strong and have excellent
thermal properties to prevent deformation of the voice coil at high power levels.
A vented voice coil former has holes in it, through which hot air can escape to
help cool the motor structure.
Woofer:
A loudspeaker transducer that is
responsible for producing sound
in the 40 Hz to 200 Hz range. To produce a given SPL at lower frequencies, increased
radiating area and increased excursion capabilities are needed. These increases
are necessary for low frequency production, however they inhibit the driver's ability
to produce high frequencies.
Xmax:
The measurement of how far a diaphragm
can move while still maintaining
linear behavior. Traditionally it was defined as the voice coil length minus the
air gap height. With the current high-strength motors, significant control over
the cone is still possible even without the entire voice coil in the gap.
Z:
Abbreviation for impedance. In T/S
parameters, Z represents the nominal
impedance of a speaker.
Zobel Network:
Another name for a conjugate
network, which is used to flatten
the impedance rise found in woofers at increasing frequencies.
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