Acoustical measurements and instrumentation
Encyclopedia
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
, IEC
, and 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. Most of the acoustical measurement and instrumentation systems can be broken down into three components:
1) Sensors
2) Data Acquisition
3) Analysis
. Measurement-grade microphones are different than typical recording-studio microphones because they can provide a detailed calibration for their response and sensitivity. Other sensors include hydrophones for measuring sound in water or accelerometers 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
and Brüel & Kjær
.
s (ADCs), anti-aliasing
filters, 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
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. Some well known vendors include HEAD acoustics, Norsonic, Brüel & Kjær
, National Instruments
, and LMS International
has a selection guide detailing the difference between microphones., Prosig, and OROS.
American National Standards Institute
The American National Standards Institute 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 organization also coordinates U.S. standards with international...
, IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
, and ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
. 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. Most of the acoustical measurement and instrumentation systems can be broken down into three components:
1) Sensors
2) Data Acquisition
3) Analysis
Sensors
The most common sensor used for acoustic measurement is the microphoneMicrophone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
. Measurement-grade microphones are different than typical recording-studio microphones because they can provide a detailed calibration for their response and sensitivity. Other sensors include hydrophones for measuring sound in water or accelerometers 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
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. "Piezotronics" combines the science of Piezoelectricity and...
and Brüel & Kjær
Brüel & Kjær
Brüel & Kjær is a subsidiary of UK-based Spectris plc. Brüel & Kjær is a manufacturer and supplier of sound and vibration measurement apparatus. The company headquarters is based in Nærum, Denmark...
.
Data Acquisition
Data acquisition hardware for acoustic measurements typically utilizes 24-bit analog-to-digital converterAnalog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
s (ADCs), anti-aliasing
Anti-aliasing
In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...
filters, 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
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
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. Some well known vendors include HEAD acoustics, Norsonic, Brüel & Kjær
Brüel & Kjær
Brüel & Kjær is a subsidiary of UK-based Spectris plc. Brüel & Kjær is a manufacturer and supplier of sound and vibration measurement apparatus. The company headquarters is based in Nærum, Denmark...
, National Instruments
National Instruments
National Instruments Corporation, or NI , is an American company with over 5,000 employees and direct operations in 41 countries. Headquartered in Austin, Texas, it is a producer of automated test equipment and virtual instrumentation software...
, and LMS International
LMS International
LMS International is an engineering services and software company, headquartered in Leuven, Belgium. The company employs about 890 people in 31 offices across the world....
has a selection guide detailing the difference between microphones., Prosig, and OROS.