Acoustics+Vocabulary



**Absorption coefficient ** **: ** The fraction of sound energy that is absorbed at any surface. It has a value between 0 and 1 and varies with the frequency and angle of incidence of the sound. **Acoustic material ** **: ** Any material considered in terms of its acoustical properties. Commonly and especially, a material designed to absorb sound. **Ambient noise ** **: ** The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest. **Artificial reverberation ** **: ** Reverberation generated by electrical or acoustical means to simulate that of concert halls, etc., added to a signal to make it sound more lifelike. **Background noise ** **: ** Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structureborne, and instrument noise. **Coherence ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Listening term. Refers to how well integrated the sound of the system is. **<span style="font-family: "Calibri","sans-serif";">Compression ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload. It is also the portion of a sound wave in which molecules are pushed together, forming a region with higher-than-normal atmospheric pressure. **<span style="font-family: "Calibri","sans-serif";">Decibel ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The term used to identify ten times the common logarithm of the ratio of two like quantities proportional to power or energy. (See level, sound transmission loss.) Thus, one decibel corresponds to a power ratio of 100.1. **<span style="font-family: "Calibri","sans-serif";">Distortion ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Anything that alters the musical signal. There are many forms of distortion, some of which are more audible than others. **<span style="font-family: "Calibri","sans-serif";">Divergence ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The spreading of sound waves which, in a free field, causes sound pressure levels in the far field of a source to decrease with increasing distance from the source. **<span style="font-family: "Calibri","sans-serif";">Equalizer ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A device for adjusting the frequency response of a device or system. **<span style="font-family: "Calibri","sans-serif";">Feedback, acoustic ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Unwanted interaction between the output and input of an acoustical system, e.g., between the loudspeaker and the microphone of a system. **<span style="font-family: "Calibri","sans-serif";">Fidelity ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> As applied to sound quality, the faithfulness to the original. **<span style="font-family: "Calibri","sans-serif";">Flutter ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A repetitive echo set up by parallel reflecting surfaces. **<span style="font-family: "Calibri","sans-serif";">Headroom ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design. **<span style="font-family: "Calibri","sans-serif";">Intensity ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Acoustic intensity is sound energy flux per unit area. The average rate of sound energy transmitted through a unit area normal to the direction of sound transmission. **<span style="font-family: "Calibri","sans-serif";">Mass law ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> An approximation that describes the Sound Transmission Loss (TL) of a limp, flexible barrier in terms of mass density and frequency. For each doubling of the weight or frequency of a partition, mass law predicts a 6 dB increase in TL. **<span style="font-family: "Calibri","sans-serif";">Noise ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Interference of an electrical or acoustical nature. Random noise is a desirable signal used in acoustical measurements. Pink noise is random noise whose spectrum falls at 3 dB per octave: it is useful for use with sound analyzers with constant percentage bandwidths. **<span style="font-family: "Calibri","sans-serif";">Octave ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> An octave is a doubling or halving of frequency. 20Hz-40Hz is often considered the bottom octave. **<span style="font-family: "Calibri","sans-serif";">Phase ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> Phase is the measure of progression of a periodic wave. Phase identifies the position at any instant which a periodic wave occupies in its cycle. It can also be discribed as the time relationship between two signals. **<span style="font-family: "Calibri","sans-serif";">Pressure zone ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface. **<span style="font-family: "Calibri","sans-serif";">Rarefaction ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The portion of a sound wave in which molecules are spread apart, forming a region with lower-than-normal atmospheric pressure. The opposite of compression. **<span style="font-family: "Calibri","sans-serif";">Reflection ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> For large surfaces compared to the wavelength of impinging sound, sound is reflected much as light is reflected, with the angle of incidence equaling the angle of reflection. **<span style="font-family: "Calibri","sans-serif";">Refraction ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The bending of sound waves traveling through layered media with different sound velocities. **<span style="font-family: "Calibri","sans-serif";">Resonance ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A natural periodicity, or the reinforcement associated with this periodicity. **<span style="font-family: "Calibri","sans-serif";">Reverberation ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The persistence of sound in an enclosed or partially enclosed space after the source of sound has stopped; by extension, in some contexts, the sound that so persists. **<span style="font-family: "Calibri","sans-serif";">Soundstage ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A listening term that refers to the placement of a stereo image in a fashion that replicates the original performance. A realistic soundstage has proportional width, depth and height. **<span style="font-family: "Calibri","sans-serif";">Subwoofer ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). There are many "subwoofers" on the market that would be more accurately termed "woofers". **<span style="font-family: "Calibri","sans-serif";">Timbre ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The quality of a sound that distinguishes it from other sounds of the same pitch and volume. The distinctive tone of an instrument or a singing voice. **<span style="font-family: "Calibri","sans-serif";">Vibration isolation ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> A reduction, attained by the use of a resilient coupling, in the capacity of a system to vibrate in response to mechanical excitation. **<span style="font-family: "Calibri","sans-serif";">Wavelength ** **<span style="font-family: "Calibri","sans-serif"; font-weight: normal;">: **<span style="font-family: "Calibri","sans-serif";"> The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelenth of any frequency may be found by dividing the speed of sound by the frequency. (speed of sound at sea level is 331.4 meters/second or 1087.42 feet/second). <span style="font-family: "Calibri","sans-serif";"> <span style="font-family: "Calibri","sans-serif";">