Acoustics and Sound Technology, Instruments

Acoustics is the branch of physics concerned with the generation, propagation and reception of sound. Sound consists of mechanical pressure variations travelling through a medium such as air, where each cycle of compression and rarefaction moves outward as a longitudinal wave. The audible range for humans spans roughly 20 Hz to 20 kHz, and a wave's frequency determines its perceived pitch while its amplitude relates to loudness. In air at room temperature sound travels at about 343 metres per second, a figure that rises with temperature.

Sound levels and signal ratios are almost always expressed in decibels, a logarithmic unit. A decibel describes a ratio between two quantities, so related units carry a reference: dBm is referenced to one milliwatt of power, while dBV is referenced to one volt. The logarithmic scale matches the very wide range of intensities the ear can detect and the way perceived loudness grows. The signal-to-noise ratio (SNR), also stated in decibels, compares a wanted signal against background noise and is a key measure of audio quality.

A practical audio system forms a chain. A microphone converts acoustic pressure into an electrical signal; amplifiers raise that signal's level; filters shape its frequency content; and a loudspeaker converts electrical energy back into sound. Modern systems digitise the signal so it can be processed by digital signal processing (DSP), and surround formats such as Dolby Digital (AC-3) encode several channels using codecs. Artefacts such as jitter, hum and quantisation noise can degrade the result, which is why bandwidth, headroom and clean signal handling matter throughout the chain.

Frequently asked questions

Why are sound levels measured in decibels?: The ear responds to an enormous range of intensities, and the logarithmic decibel scale compresses that range into manageable numbers that also track perceived loudness more closely than linear units.
What is the difference between dBm and dBV?: Both are decibel units referenced to a fixed value: dBm is referenced to one milliwatt of power, and dBV is referenced to one volt. They describe power and voltage levels respectively.
What does signal-to-noise ratio tell you?: SNR compares the level of a wanted signal to the background noise. A higher SNR means a cleaner signal with less audible hiss or hum.

Acoustics:
Acoustics: topics	General overview	Speech technology
Dolby system	Instruments	Summary of surround sound systems	Surround sound systems

Audio - Instruments related subject: Physics: sound animations, Physics: sound

Accoustics for violin and guitar makers Sound and hearing, Resonance and Resonators, Sound and the Room, Properties of the Violin and the Guitar String, Vibration Properties of the Wood and Tuning of Violin Plates, The Function, Tone, and Tonal Quality of the Guitar, The Function of the Violin, The Tone and Tonal Quality of the Violin

ATLAS of Plucked Instruments an encyclopedia of all the world's plucked instruments of lute, guitar, banjo and mandolin type

Music acoustics acoustics, flute, violin, guitar, wind instruments, decibel, physics, science, music, acoustic impedance

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Audio - Instruments related subjects: Audio Tools, Physics: sound animations, Physics: sound

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Flute materials

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Musical Instruments

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Piano: How a Piano Works How a Piano Works

Guitar Play Guitar, swf file

Piano play the piano and study the corresponding notes and frequencies

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Schwebungen- oder im Reich der Klavierstimmer in German

Sound files piano Sound files

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Standing Waves, Medium Fixed At Both Ends Here is an animation showing the standing wave patterns that are produced on a medium such as a string on a musical instrument. This type of medium would be said to be fixed at both ends, that is, held motionless at both ends

Strings, standing waves and harmonics

The Physics of the Acoustic Guitar

The String Plucker This time animation is constructed from the exact Fourier series for an ideal plucked string, vibrating in a plane, with uniform tension and initial triangular profile as set by the user

Tuning Forks and Longitudinal Waves

Violin acoustics also: flute acoustics, guitar acoustics, speech acoustics, clarinet acoustics

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