(Last Updated On: January 18, 2020)
abampere The unit of current in the cgs electromagnetic system. One abampere equals 10 amperes and corresponds to 1 abcoulomb per second.
Abbe condenser 1.In microscopy, a special two piece lens that has enhanced light-gathering power. 2. A similar focusing device in an electromagnetic antenna.
abbreviated dialing In telephone systems, special circuits requiring fewer-than-normal dialing operations to connect subscribers.
abcoulomb The unit of electrical quantity in the cgs electromagnetic system. One abcoulomb equals 10 coulombs and is the quantity of electricity that flows past any point in a circuit in one second when the current is one abampere.
aberration 1. Distortion from perfect shape in a lens or reflecting mirror or antenna dish. 2. A small error in the determination of the direction of a source of electromagnetic energy, on account of the motion of the source and/or the detecting apparatus. 3. A small displacement in the apparent positions of the stars from month to month on account of the earth’s orbital motion.
abfarad The unit of capacitance in the cgs electromagnetic system. One abfarad equals 109 farads and is the capacitance across which a charge of 1 abcoulomb produces a potential of 1 abvolt.
abhenry The unit of inductance in the cgs electromagnetic system. One abhenry equals 10–9 henry and is the inductance across which a current that changes at the rate of 1 abampere per second induces a potential of 1 abvolt.
abmho The obsolete unit of conductance and of conductivity in the cgs electromagnetic system. Replaced with ABSIEMENS.
abnormal dissipation Power dissipation higher or lower than the customary level, usually an overload.
abnormal oscillation 1. Oscillation where none is desired or expected, as in an amplifier. 2. Oscillation at two or more frequencies simultaneously when single-frequency operation is expected. 3.Oscillation at an incorrect frequency. 4. Parasitic oscillation.
abnormal propagation 1.The chance shifting of the normal path of a radio wave, as by displacements in the ionosphere, so that reception is degraded. 2. Unintentional radiation of energy from some point other than the transmitting antenna. 3. Propagation over a path or in a direction not expected.
abnormal reflections Sharp, intense reflections at frequencies higher than the critical frequency of the ionosphere’s ionized layer.
abnormal termination The shutdown of a running computer program or other process. Caused by the detection of an error by the associated hardware that indicates that some ongoing series of actions cannot be executed correctly.
abnormal triggering The false triggering or switching of a circuit or device, such as a flip-flop, by some undesirable source instead of the true trigger signal. Electrical noise pulses often cause abnormal triggering.
abohm The unit of resistance and of resistivity in the cgs electromagnetic system. One abohm equals 10–9 ohms and is the resistance across which a steady current of 1 abampere produces a potential difference of 1 abvolt.
AB power pack 1.A portable dry-cell or wet-cell array containing both A and B batteries in one package. 2. An ac-operated unit in one package for supplying A and B voltages to equipment normally operated from batteries.
abrasion machine An instrument for determining the abrasive resistance of a wire or cable.
abrasion resistance A measure of the ability of a wire or wire covering to resist mechanical damage.
abscissa 1.The independent variable in a function. 2.The axis (usually horizontal) on the graph of a function that indicates the independent variable.
absence-of-ground searching selector A rotary switch that searches for an ungrounded contact in a dial telephone system.
absiemens The unit of conductance or conductivity in the cgs electromagnetic system. One absiemens equals 109 siemens and is the conductance through which a potential of 1 abvolt forces a current of 1 abampere.
absolute 1. A temperature scale in which zero represents the complete absence of heat. Units of measure are same as units on Celsius and Fahrenheit scales. See ABSOLUTE SCALE. 2. Independent of any arbitrarily assigned units of measure or value.
absolute accuracy The full-scale accuracy of a meter with respect to a primary (absolute) standard.
absolute address In a digital computer program, the location of a word in memory, as opposed to location of the word in the program.
absolute code A computer code in which the exact address is given for storing or locating the reference operand.
absolute coding In computer practice, coding that uses absolute addresses.
absolute constant A mathematical constant that has the same value wherever it is used.
absolute delay The time elapsing between the transmission of two synchronized signals from the same station or from different stations, as in radio, radar, or loran. By extension, the time interval between two such signals from any source, as from a generator.
absolute digital position transducer A digital position transducer whose output signal indicates absolute position. (See ENCODER.)
absolute efficiency The ratio Xx/Xs, where Xx is the output of a given device, and Xsis the output of an ideal device of the same kind under the same operating conditions.
absolute encoder system A system that permits the encoding of any function (linear, nonlinear, continuous, step, and so on) and supplies a non-ambiguous output.
absolute error The difference indicated by the approximate value of a quantity minus the actual value. This difference is positive when the approximate value is higher than the exact value, and it is negative when the approximate value is lower than the exact value. Compare RELATIVE ERROR.
absolute gain Antenna gain for a given orientation when the reference antenna is isolated in space and has no main axis of propagation.
absolute humidity The mass of water vapor per unit volume of air. Compare RELATIVE HUMIDITY.
absolute instruction A computer instruction that states explicitly and causes the execution of a specific operation.
absolute magnitude For a complex number quantity, the vector sum of the real and imaginary components (i.e., the square root of the sum of the squares of those components). Also see ABSOLUTE VALUE and IMPEDANCE.
absolute maximum rating The highest value a quantity can have before malfunction or damage occurs.
absolute maximum supply voltage The highest supply voltage that can be applied to a circuit without permanently altering its characteristics.
absolute measurement of current Measurement of a current directly in terms of defining quantities. 1.TANGENT GALVANOMETER method: Current is proportional to the tangent of the angle of deflection of the needle of this instrument. Deflection depends on torque, resulting from the magnetic field produced by current in the galvanometer coil acting against the horizontal component of the earth’s magnetic field. 2. ELECTRODYNAMOMETER method: With this 2-coil instrument, current is determined from the observed deflection, the torque of the suspension fiber of the movable coil, and the coil dimensions.
absolute measurement of voltage Measurement of a voltage directly in terms of defining quantities. 1. CALORIMETRIC method: A current carrying coil immersed in water raises the temperature of the water. The difference of potential that forces the current through the coil then is determined in terms of the equivalent heat energy. 2. Disk-electrometer method: In this setup, a metal disk attached to one end of a balance beam is attracted by a stationary disk mounted below it, the voltage being applied to the two disks. The other end of the beam carries a pan into which accurate weights are placed. At balance, the voltage is determined in terms of the weight required to restore balance, the upper-disk area, and the disk separation.
absolute minimum resistance The resistance between the wiper and the nearer terminal of a potentiometer, when the wiper is as close to that terminal as physically possible. All potentiometers have two such specifications, one for each end terminal.
absolute Peltier coefficient The product of the absolute Seebeck coefficient and absolute temperature of a material.
absolute pitch A tone in a standard scale, determined according to the rate of vibration, independent of other tones in the range of pitch.
absolute pressure Pressure (force per unit area) of a gas or liquid determined with respect to that of a vacuum (taken as zero).
absolute-pressure transducer A transducer actuated by pressure from the outputs of two different pressure sources, and whose own output is proportional to the difference between the two applied pressures.
absolute scale 1. A scale in which the zero value indicates the lowest physically possible value that a parameter can attain. 2. A standard scale for measurement of a quantity. 3.A universally agreed-upon scale for the determination of a variable quantity. 4.The Kelvin temperature scale. 5.The Rankine temperature scale.
absolute Seebeck coefficient The quotient, as an integral from absolute zero to the given temperature, of the Thomson coefficient of a material divided by its absolute temperature.
absolute spectral response The frequency output or response of a device in absolute power units (such as milliwatts) as opposed to relative units (such as decibels).
absolute system of units A system of units in which the fundamental (ABSOLUTE) units are those expressing length (l), mass (m), charge (q), and time (t). All other physical units, including practical ones, are then derived from these absolute units.
absolute temperature Temperature measured on either the Kelvin or Rankine scales, where zero represents the total absence of heat energy.
absolute temperature scale 1. The Kelvin temperature scale, in which the divisions are equal in size to 1°Celsius, and the zero point is absolute zero, the coldest possible temperature, approximately –273.16°Celsius. 2.The Rankine temperature scale, in which the divisions are equal in size to 1°Fahrenheit, and the zero point is absolute zero or approximately –459.7°Fahrenheit.
absolute tolerance The value of a component as it deviates from the specified or nominal value. It is usually expressed as a percentage of the specified value.
absolute units Fundamental physical units (see ABSOLUTE SYSTEM OF UNITS) from which all others are derived. See, for example, AMPERE, OHM, VOLT, and WATT.
absolute value The magnitude of a quantity without regard to sign or direction. The absolute value of a is written |a|. The absolute value of a positive number is the number itself; thus, |12| equals 12. The absolute value of a negative number is the number with its sign changed: |-12| equals 12.
absolute-value circuit A circuit that produces a unipolar signal in response to a bipolar input and in proportion to the absolute value of the magnitude of the input.
absolute-value computer A computer in which data is processed in its absolute form; i.e., every variable maintains its full value. (Compare to INCREMENTAL COMPUTER.)
absolute-value device In computer practice, a device that delivers a constant-polarity output signal equal in amplitude to that of the input signal. Thus, the output signal always has the same sign.
absolute zero The temperature –273.16°C ( 459.7°F and 0 Kelvin). The coldest possible
temperature, representing the complete absence of heat energy.
absorbed wave A radio wave that dissipates in the ionosphere as a result of molecular agitation. This effect is most pronounced at low and medium frequencies.
absorptance The amount of radiant energy absorbed in a material; equal to 1 minus the transmittance.
absorption The taking up of one material or medium by another into itself, as by sucking or soaking up. Also, the retention of one medium (or a part of it) by another medium, through which the first one attempts to pass. See, for example,
ABSORBED WAVE, ABSORPTION COEFFICIENT, DIELECTRIC ABSORPTION. Compare ADSORPTION.
absorption band See ABSORPTION SPECTRUM.
absorption circuit A circuit that absorbs energy from another circuit or from a signal source—especially a resonant circuit, such as a wavemeter or wavetrap.
absorption current In a capacitor, the current resulting from absorption of energy by the dielectric material.
absorption dynamometer A power-measuring instrument in which a brake absorbs energy from a revolving shaft or wheel.
absorption fading Fading of a radio wave, resulting from (usually) slow changes in the absorption of the wave in the line of propagation.
absorption frequency meter See WAVEMETER.
absorption line See ABSORPTION SPECTRUM.
absorption loss 1.Transmission loss caused by dissipation of electrical energy, or conversion of it into heat or other forms of energy. 2. Loss of all or part of a skywave because of absorption by the ionosphere. Also called ionospheric absorption or atmospheric absorption.
absorption marker A small blip introduced onto an oscilloscope trace to indicate a frequency point. It is so called because it is produced by the action of a frequency-calibrated tuned trap, similar to an absorption wavemeter.
absorption modulation Amplitude modulation of a transmitter or oscillator by means of an audio frequency-actuated absorber circuit. In its simplest form, the modulator consists of a few turns of wire coupled to the transmitter tank coil and connected to a carbon microphone. The arrangement absorbs energy from the transmitter at a varying rate as the microphone changes its resistance in accordance with the sound waves it receives.
absorption spectrum For electromagnetic waves, a plot of absorption coefficient (of the medium of propagation) versus frequency. Also called EMISSION SPECTRUM.
absorption trap See WAVETRAP.
absorption wavemeter A resonant-frequency indicating instrument that is inductively coupled to the device under test.
absorptivity In audio and microwave technologies, a measure of the energy absorbed by a given volume of material.
A-B test Comparison of two sounds by reproducing them in alternating succession.
abvolt The unit of potential difference in the cgs electromagnetic system. One abvolt equals 10–8V and is the difference of potential between any two points when 1 erg of work is required to move 1 abcoulomb of electricity between them.
abwatt The unit of power in the cgs electromagnetic system. One abwatt equals 10-7 W and is the power corresponding to 1 erg of work per second.
ac base current Symbol, IB(ac). The ac component of base current in a bipolar transistor.
ac base resistance Symbol, RB(ac). The dynamic base resistance in a bipolar transistor.
ac base voltage Symbol, VB(ac). The ac component of base voltage in a bipolar transistor. It is the ac input signal voltage in a common-emitter amplifier or emitter-follower amplifier.
ac bias In a tape recorder, the high-frequency current that passes through the recording head to linearize operation.
ac cathode current Symbol, IK(ac). The ac component of cathode current in an electron tube.
ac cathode resistance Symbol, RK(ac). The dynamic cathode resistance in an electron tube. RK(ac) equals dVK/dIK for a constant value of VG.
ac cathode voltage Symbol, VK(ac). The ac component of cathode voltage in an electron tube. It is the ac output signal voltage in cathode-follower and grounded-grid amplifiers.
accelerated life test A test program that simulates the effects of time on devices or apparatus, by artificially speeding up the aging process.
accelerated service test A service or bench test in which equipment or a circuit is subjected to an extreme condition in an attempt to simulate the effects of average use over a long time.
accelerating conductor or relay A conductor or relay that prompts the operation of a succeeding device in a starting mode according to established conditions.
accelerating electrode In a cathode-ray tube or klystron, the electrode to which the accelerating voltage is applied.
accelerating time The elapsed time that starts when voltage is applied to a motor, and ends when the motor shaft reaches maximum speed.
accelerating voltage A positive high voltage applied to the accelerating electrode of a cathode-ray tube to increase the velocity of electrons in the beam.
acceleration at stall The angular acceleration of a servomotor at stall, determined from the stall torque and the moment of inertia of the motor’s rotor.
acceleration derivative Acceleration (a) expressed as the second derivative of distance (s) with respect to time (t): a equals d2s/dt2.
acceleration potential See ACCELERATING VOLTAGE.
acceleration switch A switch that operates automatically when the acceleration of a body to which it is attached exceeds a predetermined rate in a given direction.
acceleration time The time required by a computer to take in or deliver information after interpreting instructions. Compare ACCESS TIME.
acceleration torque During the accelerating period of a motor, the difference between the torque demanded and the torque actually produced by the motor.
acceleration voltage The potential between accelerating elements in a vacuum tube, the value of which determines average electron velocity.
accelerometer A transducer whose output voltage is proportional to the acceleration of the moving body to which it is attached.
accentuation The emphasis of a desired band of frequencies, usually in the audio-frequency spectrum.
accentuator A circuit or device, such as a filter, tone control, or equalizer, used to emphasize a band of frequencies, usually in the audio frequency spectrum. Also see ACCENTUATION.
acceptable-environmental-range test A test to disclose the environmental conditions that equipment can endure while maintaining at least the minimum desired reliability.
acceptable quality level Abbreviation, AQL. A percentage that represents an acceptable average of defective components allowable for a process, or the lowest quality that a supplier is permitted to regularly present for acceptance.
acceptance sampling plan A probabilistic method of sampling a quantity of units from a lot, and determining from the sample whether to accept the lot, reject the lot, or perform another sampling.
acceptance test A test performed on incoming equipment or on submitted samples to determine if they meet tester’s or supplier’s specifications.
acceptor 1. Any device or circuit, such as a series resonant circuit, that provides relatively easy transmission of a signal, in effect accepting the signal. 2. A hole-rich impurity added to a semiconductor to make the latter p-type. It is so called because its holes can accept electrons. Compare DONOR.
access 1.To gain entrance to something, such as the interior of the cabinet of a high-fidelity amplifier. 2. In a computer, the action of going to a specific memory location for the purpose of data retrieval. 3. A port or opening into a piece of equipment, placed there to make the equipment easy to maintain and repair.
access arm A mechanical device that positions the read/write mechanism in a computer storage unit.
access control register A register that is part of a computer protection system that prevents interference between different software modules.
access method A method of transferring information or data from main storage to an input/output unit.
access right The access status given to computer system users that indicates the method of access permitted (e.g., read a file only or write to a file).
access time The time required by a computer to begin delivering information after the memory or storage has been interrogated.
accidental error An unintentional error committed by a person making measurements and recording data.
accidental triggering The undesired chance operation of a flip-flop or other switching circuit caused by a noise pulse or other extraneous signal.
ac collector current Symbol, IC(ac). The ac component of collector current in a bipolar transistor.
ac collector resistance Symbol, RC(ac). The dynamic collector resistance of a bipolar transistor. RC(ac) equals dVC/dIC for a constant value of base current IB (in a common-emitter circuit) or emitter current IE (in a common-base circuit).
ac collector voltage Symbol, VC(ac). The ac component of collector voltage in a bipolar transistor. The ac output signal voltage in a common-emitter or common-base amplifier.
accompanying audio channel The RF signal that supplies television sound. Also called Co-channel sound frequency.
ac component In a complex wave (i.e., one containing both ac and dc), the alternating, fluctuating, or pulsating part of the combination. Compare DC COMPONENT.
accordion A printed-circuit connector contact with a Z-shaped spring that allows high deflection with low fatigue.
ac-coupled flip-flop A flip-flop that is operated by the rise or fall of a clock pulse.
ac coupling Transformer coupling or capacitive coupling, which transmit ac, but not dc. Compare DIRECT COUPLING.
accumulator 1. In a digital computer, a circuit or register device that receives numbers, totals them, and stores them. 2. Storage battery.
accuracy 1. Precision in the measurement of quantities and in the statement of physical characteristics. 2. Degree of precision. Usually expressed, in terms of error, as a percentage of the specified value (e.g., 10 V plus or minus 1%), as a percentage of a range (e.g., 2% of full scale), or as parts (e.g., 100 parts per million).
accuracy rating The maximum error in an instrument, given as a percentage of the full-scale value.
ac/dc Abbreviation of ALTERNATING CURRENT/DIRECT CURRENT. Pertains to equipment that will operate from either ac utility power or a dc power source. A notebook computer is a good example.
ac directional overcurrent relay A relay that works on a specific value of alternating overcurrent that is rectified for a desired polarity.
ac drain current Symbol, ID(ac). The ac component of drain current in a field-effect transistor.
ac drain resistance Symbol, RD(ac). The dynamic drain resistance in a field-effect transistor; RD(ac) equals dVD/dIDfor a constant value of gate voltage VG.
ac drain voltage Symbol, VD(ac). The ac component of drain voltage in a field-effect transistor. The ac output signal voltage in a common-source FET amplifier.
ac dump The removal of all ac power from a system or component.
ac emitter current Symbol, IE(ac). The ac component of emitter current in a bipolar transistor.
ac emitter resistance Symbol, RE(ac). The dynamic emitter resistance of a bipolar transistor; RE(ac) equals dVE/dIEfor a constant value of base current IB(in an emitter-follower circuit) or collector voltage VCC(in a common-base circuit).
ac emitter voltage Symbol, VE(ac). The ac component of emitter voltage in a bipolar transistor. The ac input signal voltage in a common-base amplifier; the ac output signal voltage in an emitter-follower amplifier.
ac equipment An apparatus designed for operation from an ac power source only. Compare DC EQUIPMENT and AC/DC.
ac erasing In tape recording, the technique of using an alternating magnetic field to erase material already recorded on the tape.
ac erasing head Also called ac erase head. In tape and wire recording, a head that carries alternating current to erase material already recorded on the tape or wire. Also see AC ERASING.
acetate Cellulose acetate, a tough thermoplastic material that is an acetic acid ester of cellulose. It is used as a dielectric and in the manufacture of photographic films.
acetate base 1. The cellulose acetate film that served as the base for the magnetic oxide coating in early recording tape. Most such tapes today are of polyester base. 2.The cellulose acetate substrate onto which certain photosensitive materials are deposited for lithographic reproduction. Also see ACETATE and ANCHORAGE.
acetate tape Recording tape consisting of a magnetic oxide coating on a cellulose acetate film. Also see ACETATE BASE.
ac gate voltage Symbol, VG(ac). The ac component of gate voltage in a field-effect transistor. The ac input signal voltage.
ac generator 1. A rotating electromagnetic machine that produces alternating current (e.g., a dynamo or alternator). 2. An oscillator or combination of an oscillator and an output amplifier.
ac grid voltage Symbol, VG(ac). The ac component of control grid voltage in an electron tube. The ac input signal voltage in a common-cathode amplifier or cathode follower.
A channel The left channel of a two-channel stereo system.
achieved reliability A statement of reliability based on the performance of mass-produced parts or systems under similar environmental conditions. Also called OPERATIONAL RELIABILITY.
achromatic 1.Without color. In a TV image, the tones from black through gray to white. The term occasionally refers to black-and-white television, although MONOCHROMATIC is more often used in this sense.
achromatic locus Also called achromatic region. An area on a chromaticity diagram that contains all points, representing acceptable reference white standards.
achromatic scale A musical scale without accidentals.
ACIA Abbreviation of asynchronous communications interface adapter.
acicular Pertaining to the shape of magnetic particles on recording tape. Under magnification, these particles look like thin rods.
acid A substance that dissociates in water solution and forms hydrogen (H) ions (e.g., sulfuric acid). Compare BASE, 2.
acid depolarizer Also called acidic depolarizer. An acid, in addition to the electrolyte, used in some primary cells to slow the process of polarization.
ac line A power line that delivers alternating current only.
ac line filter A filter designed to remove extraneous signals or electrical noise from an ac power line, while causing virtually no reduction of the power-line voltage or power.
ac line voltage The voltage commonly delivered by the commercial power line to consumers. In the United States, the two standards are 117 V and 234 V (~ about 5 percent). The lower voltage is used by most appliances; the higher voltage is
intended for appliances and equipment that draws high power, such as electric ovens, cooking ranges, clothes dryers, and amateur-radio amplifiers. In Europe, 220 V is the common standard.
aclinic line Also called magnetic equator. An imaginary line drawn on a map of the world or of an area that connects points of zero inclination (dip) of the needle of a magnetic compass.
ac meter A meter that is intended to work only on alternating current or voltage. Such meters include iron-vane and rectifier types.
ac noise 1.Electromagnetic interference originating in the ac power lines. 2. Electrical noise of a rapidly alternating or pulsating nature.
ac noise immunity In computer practice, the ability of a logic circuit to maintain its state, despite excitation by ac noise.
acoustic Pertaining to audible sound disturbances, usually in air (versus audio-frequency
currents or voltages).
acoustic absorption The assimilation of energy from sound waves passing through or reflected by a given medium.
acoustic absorption loss That portion of sound energy lost (as by dissipation in the form of heat) because of ACOUSTIC ABSORPTION.
acoustic absorptivity The ratio of sound energy absorbed by a material to sound energy striking the surface of the material.
acoustic attenuation constant The real-number component of the complex acoustical propagation constant, expressed in nepers per unit distance.
acoustic burglar alarm An alarm that receives the noise made by an intruder. The alarm device responds to the impulses from concealed microphones.
acoustic capacitance The acoustic equivalent of electrical capacitance.
acoustic clarifier In a loudspeaker system, a set of cones attached to the baffle that vibrate to absorb and suppress sound energy during loud bursts.
acoustic communication Communications by means of sound waves. This can be through the atmosphere, or it can be through solids or liquids, such as a taut wire, a body of water, or the earth.
acoustic compliance COMPLIANCE in acoustic transducers, especially loudspeakers. It is equivalent to electrical capacitive reactance.
acoustic consonance An effect that occurs when two objects are near each other but not in physical contact, and both have identical or harmonically related resonant frequencies. An example is shown by two tuning forks with identical fundamental frequencies. If one fork is struck and then brought near the other, the second fork will begin vibrating. If the second fork has a fundamental frequency that is a harmonic of the frequency of the first fork, the second fork will vibrate at its own resonant frequency. See HARMONIC, RESONANCE.
acoustic coupling Data transfer via a sound link between a telephone and a pickup/reproducer. It was once common in computer terminals and facsimile machines. This scheme has been largely replaced by hard wiring and optical coupling.
acoustic damping The deadening or reduction of the vibration of a body to eliminate (or cause to die out quickly) sound waves arising from it.
acoustic delay line Any equivalent of a special transmission line that introduces a useful time delay between input and output signals. In one form, it consists of a crystal block or bar with an input transducer at one end and an output transducer at the other. An electrical input signal in the first transducer sets up sound waves that travel through the interior of the crystal; the piezoelectric reaction of the crystal to sound vibrations sets up an output voltage in the second transducer. The delay is caused by the time required for the acoustic energy to travel the length of the crystal bar.
acoustic depth finder A direct-reading device for determining the depth of a body of water, or for locating underwater objects via sonic or ultrasonic waves transmitted downward and reflected back to the instrument.
acoustic dispersion Variation of the velocity of sound waves, depending on their frequency.
acoustic elasticity 1. In a loudspeaker enclosure, the compressibility of air behind the vibrating cone of the speaker. 2. In general, the compressibility of any medium through which sound passes.
acoustic electric transducer A transducer, such as a microphone or hydrophone, that converts sound energy into electrical energy. Compare ELECTRICAL/ACOUSTIC TRANSDUCER. Also see ACOUSTIC TRANSDUCER.
acoustic feedback A usually undesirable effect that occurs when sound waves from a loudspeaker (or other reproducer) reach a microphone (or other input transducer) in the same system. This can cause an amplifier to oscillate, with a resultant rumbling, howling, or whistling.