A sound level meter is used for acoustic measurements. The word "acoustic" means "sound that travels through air". This is opposed to the word "audio", a term that is also often used in the field of sound measurement. "Audio" refers to sound that travels electronically through cables and audio components. That having being said, let's get back to acoustic measurements.
A sound level meter needs a microphone to measure the changes in air pressure produced by the sound source. The better quality the microphone, the more accurate the measurements will be. Such measurement microphones are categorized as Class 1 or Class 2. For many applications a Class 2 microphone, which is slightly less accurate and less pricey than a Class 1 microphone, is more than sufficient. Class 1 microphones are usually only required when the law prescribes. Whichever microphone you use, it is important for accuracy that the microphone is correctly calibrated.
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The single value measured by a sound level meter is referred to as the "broadband value" as it uses all values across the audio frequency bands (20 Hz to 20 kHz) to calculate the level. It is typically measured in decibels (dB), which is a logarithmic unit. This means, for example, that doubling the sound level would correspond to a 10 dB higher measurement value.
The spectrum of frequencies provided by an RTA measurement suits tasks such as optimization of sound systems and rooms. An RTA typically measures with a resolution of 1/1 or 1/3 octave. To conceptualize this, one can think of a piano. 1/1 gives us a single measurement value for each octave (12 semi-tones), 1/3 provides a single value for groups of 4 semi-tones, 1/6 represents 1 semi-tones, while 1/12 is a separate level measurement for every key on the piano.
Sound Level Meter Functions
A sound level meter can be used for measuring sound or noise* for Community Noise Analysis, Building Acoustics, Industrial Noise Control, Machinery Noise Analysis, and further applications.
* the definition of "noise" is simply "unwanted sound"; one person's sound may be another person's noise
In this video, Philipp Schwizer tells us about the XL2 Sound Level Meter
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