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Absorption (Surfaces)
Absorbs energy because sound can enter its porous surface to be dissipated by being reflected
off the material's fibers. In this mechanism, sound energy is converted into a minute amount
of heat within the absorbing material.
Amplitude-Frequency Response (Magnitude Response)
The variation of gain, loss, amplification, or attenuation a function of frequency.
Amplitudue Moduation
The amplitude of the carrier voltage is caused to vary directly with the modulating voltage.
Acoustic Power Level (PWL)
The total sound energy radiated by a source per unit time. The unit of measure is the
acoustic watt. Also known as sound power.
Bottoming
At extreme volumes, when the voice coil smacks into the back of the pole plate it creates
a very unpleasant sound — similar to the sound of snow crunching under foot only much,
much louder.
Capacitor
An electric circuit element composed of two metallic plates separated by a dielectric, used
to store energy. Note: Capacitance also reacts to AC. While an inductor becomes more reactive
at high frequencies, the capacitor becomes more reactive at low frequencies.
Class A
By definition, Class A operation provides collector (output) current during the complete signal
cycle (over a 360-degree interval). Because the device is always turned on, the theoretical maximum efficiency is only 50%.
Class B
In Class B operation, the bias point is set at cutoff, the output current varying for only
about 180 degrees of the cycle. The device is biased with no collector current and therefore
no power dissipated by the transistor. Only when a signal is applied does the transistor handle
an average current, which increases for larger input signals. Theoretical efficiency is about
78.5%.
Class AB
In between class A and class B operation is class AB. The collector current occurs for more
than 180 degrees of the signal cycle but less than 360 degrees. The theoretical efficiency
falls in between class A and class B (50 -78.5%).
Clipping
The occurrence of short term overload in an amplifier. (Geek version: The deformation of the
oscilloscope waveform characterizing the output of an amplifier.
Comb Filtering
Comb filtering is the constructive and destructive interference between two similar sounds,
but one being delayed relative to the other.
Crossover
The crossover is a circuit that divides, shapes and allocates the high and low frequencies
to different drivers. A crossover is used when a speaker system has more than one driver. It
keeps the drivers operating in their most accurate frequency range.
Current
Is the electron charge moving through a conductor. The electrons travel through the conductor
from the negative charge to the positive charge. Current is measured in amperes, or amps for
short. Note: current flow is analogous to water moving through a hose.
Decibel (dB)
Decibel notation is a convenient way to express very large numbers, but also corresponds
closely with our perception of sound. A figure in decibels can describe quantities that are
proportional to power. Examples of quantities that qualify are; power, voltage squared, sound
pressure squared (sound pressure level), sound intensity and sound energy density. If two powers
PI and P2 differ, their difference can be expressed in decibels as D"= 10 log (P I/P2).
It is meaningless to state absolute values of power in decibels. The decibel represents a ratio,
and therefore a reference level must also be stated if absolute values are required.
For example "a power of 20 dB" is meaningless, but "20 dB relative to 1 watt" means 100 watts. In
most cases the reference level is implicitly understood. A good example would be sound pressure
level where the reference level is always understood to be the threshold of hearing.
Note: Fundamentally, the Bel (after Alexander Graham Bell) is defined as the logarithm to the base
10 of a power ratio. However, the Decibel is a more convenient unit to use, and is defined as 10
times the logarithm to the base 10 of a power ratio (I Bel = 10 decibels).
Diffraction
Diffraction is the bending of sound waves around an object and the re-radiation of energy through
an opening. Diffraction makes it possible to hear sounds around comers and behind walls, or through
a small opening in an obstruction.
Diffusion (Surfaces)
Diffusion is a scattering of sound. A diffuser converts a sound traveling in one direction into
many lower-amplitude sounds moving in many directions. Note: An irregularly shaped surface tends
to diffuse sound, provided that the irregular structures are similar in size to the wavelength of
the sound striking them.
Directivity Pattern
Usually presented graphically, it is a function of the radiation of the transmitted or incident
sound wave in a specified plane and at a specified frequency.
Dynamic Range
The difference, in decibels, between the overload level and the minimum acceptable signal level in
a system or transducer. Note: The minimum acceptable signal level of a system of transducer
is ordinarily fixed by one or more of the following: noise level, low-Ievel distortion,
or interference.
Efficiency
Efficiency is the percentage of electrical power converted by the loudspeaker into acoustical
power. Note: it is incorrect to use the term efficiency in place of sensitivity.
Frequency
The time rate of repetition of a periodic phenomenon. The frequency is the reciprocal of the
period. The unit of measure is cycles per second, or Hertz.
Frequency Modulation
A process of changing the frequency of a tone (called a carrier tone). The difference
frequency relative to the carrier tone varies directly with the information signal (or
modulating voltage).
Harmonic
Frequency components which are an integral multiple (1,2,3,4,etc., times) of the
fundamental frequency.
Hertz (Hz)
A standard unit of frequency that equals one cycle per second.
Impedance
Parameter used by speaker engineers to characterize how much current the speaker will draw from
an amplifier. Low impedance means correspondingly higher current. Impedance is the opposition
to current flow in an AC circuit, specified in ohms. Impedance is to an AC signal what resistance
is to DC. Impedance differs from resistance in that impedance implies that the load is not a
simple resistance, but a combination of resistance, inductive reactance, and capacitive reactance.
Inductor
A circuit element, i.e., a coil of wire, in which electromagnetic induction generates
electromotive force. Note: This induced voltage opposes the applied voltage, reducing current
flow (i.e. a frequency-dependent resistor". The higher the alternating current frequency, the
greater the induced voltage and the greater the opposition to the applied voltage.
Loudness Level
This is defined as the sound pressure level of a 1000Hz tone that sounds as loud as the sound
in question. The unit of measure is the phon. Note: Extensive measurements have been made to
determine the loudness of pure tones and narrow bands of noise as a function of frequency and
sound pressure level. The resulting equal loudness contours are known as the Fletcher-Munson curves.
Modulation
To regulate some parameter of a high-frequency carrier wave by means of the lower-frequency
information signal.
Octave
The interval between two frequencies having a ratio of 2: 1.
Ohm's Law
The amount of current flow is determined by two things: the resistor's resistance value and the
supply voltage. More resistance will decrease current flow. Conversely, a higher voltage will
increase current flow. The relationship is expressed by Ohm 's Law, which states that: V=IxR Note:
If we Know any two values, we can calculate the third using Ohm's Law.
Parallel
Circuits provide multiple paths through which current can flow. Parallel circuits differ from
series circuits in that the voltage across each branch of a parallel circuit is the same as the
applied voltage.
Phase
Phase describes how reactive a load is compared to the load's resistance. Phase angle is
introduced because capacitive reactance causes voltages to lag slightly behind current flow in
time. In an inductor, the opposite occurs, current lags voltage.
Power
Power is an expression of the amount of work done by the voltage and current. The unit of measure
is the watt. Power is the product of voltage and current, expressed by Ohm's Law as: Root Mean
Square The equivalent power-producing measure of a waveform. Defined as the square root of the
arithmetic average of a set of squared instantaneous values.
Power Response
The variation of sound power as a function of frequency.
Reflection (Surfaces)
Hard surfaces which do not allow sound to penetrate the surface; nearly all energy is reflected
back toward the source. Sound is reflected at the same angle at which it struck; i.e., "the angle
of incidence equals the angle of reflection."
Resistance
Resistance is the opposition to current flow. It reduces the number of electrons flowing through
the conductor. The higher the resistance, the less current flow in the conductor (given the
same voltage). The unit of electrical resistance is the ohm. Note: Resistance is analogous to a
kink in a water hose when water is moving through it.
Reverberation
1) The persistence of sound in an enclosed space, as a result of multiple reflections after the
sound source has stopped. 2) The sound that persists in an enclosed space, as a result of
repeated reflections or scattering, after the source of the sound has stopped.
Sensitivity
Sensitivity is expressed as the sound pressure level with 1-watt input measured 1 meter away.
Note: Technically, sensitivity should be expressed with a constant drive signal of about 2.83 V;
which corresponds to 1 watt into an 8 ohm load.
Series
In a series circuit, there is only one path through which current can flow. In a series circuit,
the current remains the same while the voltage across each resistor is different.
Simple Point Source
A source that radiates sound uniformly in all directions under free-field conditions.
Skin Effect
The non-uniform distribution of current flow in a cable. The overall effect is current tends to
flow near the surface of the conductor. Because the current is confined to a smaller cross section
of the conductor, the apparent resistance of the conductor Increases.
Sound
Sound is produced by variations in air pressure around the average steady-state barometric
pressure, caused by the physical movements of objects and the surface in the air. The
alternating variations of pressure at a sound source cause sound waves to radiate out from the
source in the same manner as waves are caused in water by a dropped stone. The waves travel with
a certain velocity of propagation, which depends on the medium through which they are traveling
(air, water, metal, etc.), and they transmit energy at a certain rate (expressed in watts).
Sound pressure levels are typically stated in terms of average pressure variations (RMS) about
the barometric level.
Sound Intensity
The average rate of sound energy transmitted in the specified direction through a unit area.
Sound Pressure Level (SPL)
The sound pressure level of a sound, in decibels, 20 times the logarithm to the base 10 of the
ratio of the measured effective sound pressure of this sound to a reference effective sound
pressure. When sound pressure levels (SPL) are stated, they are usually quoted in decibels above
the average threshold of hearing level. Therefore, Prefis equal to 0.0002 microbar.
Speed of Sound ©
The speed of sound in air is approximately 1132 ft/sec (c=1052+1.106F ft/sec).
Standing Wave
A periodic wave having a fixed distribution in space which is the result of interference
of progressive waves of the same frequency and kind. Characterized by the existence of maxima
and minima amplitudes that are fixed in space.
Timbre
In general, timbre is described as the quality of sound that allows one to discriminate one sound
from another sound when both have the same pitch, loudness, and duration. A violin and a viola
might play the same pitched note at the same loudness for the same duration, and we know that
one instrument is a violin and one he viola because the two instruments produce different timbres.
Transformer
A device that employs mutual induction to convert variations of electric current in a primary
circuit into variations of current and voltage in a secondary circuit.
Transient Distortion
The failure of system to exactly follow sudden large changes in sound level. Pulses of sound
energy tend to shock the system into oscillation at its natural frequency. The flywheel effect
of these oscillating circuits causes the oscillation to continue after the true pulse, which
has excited it has ceased. This effect is often referred to as hangover.
Transistor
A three terminal semiconductor device for amplification, switching, and detection,
typically containing two rectifying junctions and operating so that the current between one pair
of terminals controls the current between the other pair, one terminal being common to input
and output.
Vented enclosure
A method for increasing the bass response of a given speaker in which the back wave from the
woofer cone exits the cabinet through a vent or port. (In a way that would make Mr. Helmholtz
proud). Also called a bass reflex or ported enclosure.
Volt
Unit of measure for voltage; an electrical parameter indicating signal strength.
Voltage
Exists between two points when one point has an excess of electrons in relation to the other
point. This is called a potential difference, because it has the potential to do work. The volt is
the unit of measurement that expresses the magnitude of this difference. Note: Voltage is analogous
to water pressure in a faucet.
Watt
Unit of electrical power.
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