NOISE CRITERION LEVEL

A set of NC criterion curves drawn on graph is used to find the NC level. At first we measure the sound pressure level of each octave band of the noise spectrum and them plot every octave band level on the graph. The NC level is the label attached to the lowest curve which is not exceeded by the spectrum.

The NC level is used to help set design goals that will ensure a maximum acceptable indoor noise, dependent on the purpose of the room. International standards organizations (ISO, ANSI and ASA) recognize the need to objectify judgements on the amount of ambient noise in enclosed spaces, and provide us with definitions for various Noise Curves. The ANSI/ASA S12.2-2008 standard, for example, NC-40 is the limit that workers can endure in the office, while noise lower than NC-25 is desirable in the concert hall.

The standard ANSI/ASA S12.2-2008 recommends the following criterias:
 

Due to International standards and recommendation of WHO, the Government of Vietnam has made great strides in awareness of the noise impact on human health. Therefore, a system of National Standards for Noise and Noise Level in Vietnam has been issued:

• TCVN 5964-1995: Acoustics: Description and measurement of environmental noise.
• TCVN 5949: Acoustics - Noise in public and residental areas Maximum permited noise level.
• TCVN 3985-1999: Acoustics – Allowable noise level at workplace.
• TCVN 5948-1999: Acoustic - Noise emitted by accelerating road vehicles - Permitted maximum noise level.
• TCVN 7878-1:2008: Acoustics – Desription, measurement and assessment of environmental noise.
• TCVN 8018:2008: Acoustics - Noise control design procedures for open plant.
• QCVN 26:2010/BTNMT: National Technical Regulation on Noise. 

Source: TECOTEC HCM