Typical Noise Control Design Methods

                                 ~ 3-5 dB                                                   ~ 8-12 dB                                  

                             ~ 1-3 dB                                              ~ 12-30 dB                              

Absorbers and NRC values (Noise Reduction Coefficients)

Sound absorbers are soft materials like foams and fiberglass that reduce sound reflection. They are rated by an NRC value between 0-1.0 which indicates the percentage of the incident noise absorbed by the material (the higher the better.) Generally, the thicker the absorber the better it is at absorbing low frequency.

Barriers and STC values (Sound Transmission Class)

Ideal sound barriers are heavy limp masses which stop transmission through the product to the other side. Flexible mass-loaded vinyl sheeting has replaced lead sheets as the barrier of choice. STC values from 1-60 rate the ability of the product to stop sound transmission. An STC of 30 will stop about 30 dB of noise in an ideal lab setting. The higher the STC the better the product at stopping transmission.

Composites

Acoustical composites combine both absorption and barriers into one product, offering superior noise reduction. Good acoustical composites have high NRC and STC numbers.