Loudspeaker acoustics is a subfield of acoustical engineering concerned with the design of loudspeakers. It focuses on the reproduction of sound and the parameters involved in doing so in actual equipment.
Engineers measure the performance of drivers and complete speaker systems to characterize their behavior, often in an
anechoic chamber
An anechoic chamber (''an-echoic'' meaning "non-reflective" or "without echoes") is a room designed to stop reflection (physics), reflections or Echo (phenomenon), echoes of either sound or electromagnetic waves. They are also often isolate ...
, outdoors, or using time windowed measurement systems -- all to avoid including room effects (e.g.,
reverberation
In acoustics, reverberation (commonly shortened to reverb) is a persistence of sound after it is produced. It is often created when a sound is reflection (physics), reflected on surfaces, causing multiple reflections that build up and then de ...
) in the measurements.
Designers use models (from electrical filter theory) to predict the performance of drive units in different enclosures, now almost always based on the work of
A N Thiele and Richard Small.
Important driver characteristics are:
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Frequency response
In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...
*Off-axis response
dispersion pattern,
lobing
*Sensitivity (dB SPL for 1 watt input)
*Maximum power handling
*
Non-linear distortion
*
Colouration (i.e., more or less, delayed
resonance
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...
).
It is the performance of a loudspeaker/listening room combination that really matters, as the two interact in multiple ways. There are two approaches to high-quality reproduction. One ensures the listening room is reasonably 'alive' with reverberant sound at all frequencies, in which case the speakers should ideally have equal dispersion at all frequencies in order to equally excite the reverberant fields created by reflections off room surfaces. The other attempts to arrange the listening room to be 'dead' acoustically, leaving indirect sound to the dispersion of the speakers need only be sufficient to cover the listening positions.
A dead or inert acoustic may be best, especially if properly filled with 'surround' reproduction, so that the reverberant field of the original space is reproduced realistically. This is currently quite hard to achieve, and so the ideal loudspeaker systems for stereo reproduction would have a uniform dispersion at all frequencies. Listening to sound in an anechoic "dead" room is quite different from listening in a conventional room, and, while revealing about loudspeaker behaviour it has an unnatural sonic character that some listeners find uncomfortable. Conventional stereo reproduction is more natural if the listening environment has some acoustically reflective surfaces.
It is in large part the directional properties of speaker systems, which vary with frequency that make them sound different, even when they measure similarly well on-axis. Acoustical engineering in this instance is concerned with adapting these variations to each other.
Notable experts
In the 1930s, one of the leading experts on loudspeaker acoustics was N. W. McLachlan, author of ''Loud Speakers: Theory, Performance, Testing and Design''.
See also
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Audio quality measurement
Audio system measurements are used to quantify audio system performance. These measurements are made for several purposes. Designers take measurements to specify the performance of a piece of equipment. Maintenance engineers make them to ens ...
*
Acoustic lobing
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Loudspeaker time alignment
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Digital room correction
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Directional Sound
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Impulse response
In signal processing and control theory, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse (). More generally, an impulse response is the reac ...
*
Loudspeaker
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...
*
Loudspeaker measurement
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...
*
MLSSA
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Sound quality
Sound quality is typically an assessment of the accuracy, fidelity, or Intelligibility (communication), intelligibility of sound, audio output from an electronic device. Quality can be measured objectively, such as when tools are used to gau ...
*
Spectrogram
A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time.
When applied to an audio signal, spectrograms are sometimes called sonographs, voiceprints, or voicegrams. When the data are represen ...
References
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External links
Conversion of sensitivity in dB per watt and meter to energy efficiency in percent of passive loudspeakers
Acoustics
Loudspeaker technology
Sound