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.
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.
The amplitude of the carrier voltage is caused to vary directly with the modulating voltage.
Amplitude-Frequency Response (Magnitude Response)
The variation of gain, loss, amplification, or attenuation a function of frequency.
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.
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.
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%.
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%).
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%.
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 is the constructive and destructive interference between two similar sounds, but one being delayed relative to the other.
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.
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 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 of20 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 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 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.
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.
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 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.
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.
A process of changing the frequency of atone (called a carrier tone). The difference frequency relative to the carrier tone varies directly with the information signal (or modulating voltage).
Frequency components which are an integral multiple (1,2,3,4,etc., times) of the fundamental frequency.
A standard unit of frequency that equals one cycle per second.
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.
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 (another words, l'afrequency-dependent resistor". The higher the alternating current frequency, the greater the induced voltage and the greater the opposition to the applied voltage.
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.
To regulate some parameter of a high-frequency carrier wave by means of the lower-frequency information signal.
The interval between two frequencies having a ratio of 2: 1.
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.
Circuits provide multiple path 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 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 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.
The variation of sound power as a function of frequency.
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 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.
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 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.
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.
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 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.
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 (C)
The speed of sound in air is approximately 1132 ft/sec (c=1052+1.106F ft/sec).
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.