Analysis of sound and acoustics plays a role in such engineering tasks as product design, production test, machine performance, and process control. For instance, product design can require modification of sound level or noise for compliance with standards from

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

, IEC, and

ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...

. The work might also involve design fine-tuning to meet market expectations. Here, examples include tweaking an automobile door latching mechanism to impress a consumer with a satisfying click or modifying an exhaust manifold to change the tone of an engine's rumble. Aircraft designers are also using acoustic instrumentation to reduce the noise generated on takeoff and landing. Acoustical measurements and instrumentation range from a handheld sound level meter to a 1000-microphone phased array.

Components

Most of the acoustical measurement and instrumentation systems can be broken down into three components: sensors, data acquisition and analysis.

Sensors

The most common sensor used for acoustic measurement is the

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...

. Measurement-grade microphones are different from typical recording-studio microphones because they can provide a detailed calibration for their response and sensitivity. Other sensors include

hydrophones A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potenti ...

for measuring sound in water or

accelerometers An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...

for measuring vibrations causing sound. The three main groups of microphones are pressure, free-field, and random-incidence, each with their own correction factors for different applications. Well-known microphone suppliers include

PCB Piezotronics PCB Piezotronics is a manufacturer of piezoelectric sensors. The name ''"PCB"'' is abbreviation for "PicoCoulomB" which is technical terminology defining an electrical charge of the type generated by the piezoelectric sensors they manufacture. ...

Brüel & Kjær Brüel & Kjær (Sound and Vibration Measurement A/S) was a Danish multinational engineering and electronics company headquartered in Nærum, near Copenhagen. It was the largest producer in the world of equipment for acoustic and vibrational mea ...

, GRAS and Audio Precision.Measurement Microphones & Acoustic Test Accessories
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Data acquisition

Data acquisition hardware for acoustic measurements typically utilizes 24-bit

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...

s (ADCs),

anti-aliasing filter An anti-aliasing filter (AAF) is a filter used before a signal sampler to restrict the bandwidth of a signal to satisfy the Nyquist–Shannon sampling theorem over the band of interest. Since the theorem states that unambiguous reconstruct ...

s, and other signal conditioning. This signal conditioning may include amplification, filtering, sensor excitation, and input configuration. Another consideration is the frequency range of the instrumentation. It should be large enough to cover the frequency range of signal interest, taking into account the range of the sensor. To prevent aliasing, many devices come with antialiasing filters, which cut the maximum frequency range of the device to a little less than one-half the maximum sampling rate, as prescribed by the Nyquist sampling theorem.

Dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of Signal (electrical engineering), signals, like sound and light. It is measured ...

is a common way to compare performance from one instrument to another. Dynamic range is a measure of how small you can measure a signal relative to the maximum input signal the device can measure. Expressed in decibels, the dynamic range is 20 log (Vmax/Vmin). For example, a device with an input range of ±10 V and a dynamic range of 110 dB will be able to measure a signal as small as 10 µV. Thus, the input range and the specified dynamic range are important for determining the needs of your instrumentation system.

Analysis

Audio and acoustic analysis includes: fractional-octave analysis, sound-level measurements, power spectra, frequency response measurements, and transient analysis. Results are viewed on waterfall displays, colormap displays, and octave graphs.

References

{{DEFAULTSORT:Acoustical Measurements And Instrumentation Acoustics