Supplementary Regulations
Table 1: WECS Noise Limits at Residential Receivers | ||
|---|---|---|
(1-Hour LEQ Derived per ANSI S12.9 Part 4 and S12.100) | ||
Daytime (7:00 a.m. to 8:00 p.m.) | Nighttime (8:00 p.m. to 7:00 a.m.) | |
A-weighted level (dB) | 45 | 35 |
C-weighted level (dB) | 63 | 50 |
NOTES: |
|---|
1. In relatively quiet areas, insect noise, especially during summer months, can easily dominate the A-weighted ambient sound level. This domination occurs partly because the primary frequencies or tones of many, if not most, insect noises are in the range of frequencies where the A-weighting is a maximum, whereas, most mechanical and WECS noises primarily occur at the lower frequencies where the A-weighting significantly attenuates the sound. Also, insect noise and bird song do not mask WECS noise at all because of the large differences in frequencies or tones between them. |
2. Schomer, Paul D. et al., "Proposed 'Ai'-Weighting; a weighting to remove insect noise from A-weighted field measurements," InterNoise 2010, Lisbon Portugal, 13-16 June 2010. |
Table II Correction in dB that shall be subtracted from the WECS sound level measurement (which always includes the background sound level) because of the background sound so that the result is just the sound level of the WECS alone. (See Note 1 below.) | |||||||
|---|---|---|---|---|---|---|---|
Δ, difference (dB) | < 3 | 3 — 4 | 5 — 6 | 7 — 10 | >10 | ||
K, correction (dB) | Notes 2,3 | 3 | 2 | 1 | 0 | ||
Notes: | |||||||
|---|---|---|---|---|---|---|---|
1. This table provides a simple correction to measurements of WECS sound in the presence of the background. For example, the sound of a WECS (along with the background sound, which is always present) is measured as 40 dBA, and the background sound level alone (without the WECS) is measured as 34 dBA. Then Δ, the difference in decibels is six dB (first row, third column), and the corresponding correction shall be two dB (second row, third column). That is, two dB shall be subtracted from the measured 40 dBA level, and it is adjusted to and reported as 38 dBA. The same procedure is followed in each band for one-third-octave-band data. | |||||||
2. When using directly measured A-weighted levels, if the difference between the WECS sound level (plus background sound level) and the background sound level alone is less than three dB, then it shall not constitute a violation of this section. | |||||||
3. When using measured one-third-octave-band data, if the difference between the WECS sound-pressure level (plus background sound-pressure level) and the background sound-pressure level alone, each in the same one-third-octave band, is less than three dB, then the WECS level for that one-third-octave band shall be set to zero. The report shall include a sketch of the site showing distances to the structure(s), to the property line, etc., and several photographs showing the structure(s), the property, and the acoustical instrumentation. All instrumentation shall be listed by manufacturer, model, and serial number. This instrumentation listing also shall include the A-weighted noise floor and the one-third-octave band noise floors, if utilized, for each sound level meter used. |
Supplementary Regulations
Table 1: WECS Noise Limits at Residential Receivers | ||
|---|---|---|
(1-Hour LEQ Derived per ANSI S12.9 Part 4 and S12.100) | ||
Daytime (7:00 a.m. to 8:00 p.m.) | Nighttime (8:00 p.m. to 7:00 a.m.) | |
A-weighted level (dB) | 45 | 35 |
C-weighted level (dB) | 63 | 50 |
NOTES: |
|---|
1. In relatively quiet areas, insect noise, especially during summer months, can easily dominate the A-weighted ambient sound level. This domination occurs partly because the primary frequencies or tones of many, if not most, insect noises are in the range of frequencies where the A-weighting is a maximum, whereas, most mechanical and WECS noises primarily occur at the lower frequencies where the A-weighting significantly attenuates the sound. Also, insect noise and bird song do not mask WECS noise at all because of the large differences in frequencies or tones between them. |
2. Schomer, Paul D. et al., "Proposed 'Ai'-Weighting; a weighting to remove insect noise from A-weighted field measurements," InterNoise 2010, Lisbon Portugal, 13-16 June 2010. |
Table II Correction in dB that shall be subtracted from the WECS sound level measurement (which always includes the background sound level) because of the background sound so that the result is just the sound level of the WECS alone. (See Note 1 below.) | |||||||
|---|---|---|---|---|---|---|---|
Δ, difference (dB) | < 3 | 3 — 4 | 5 — 6 | 7 — 10 | >10 | ||
K, correction (dB) | Notes 2,3 | 3 | 2 | 1 | 0 | ||
Notes: | |||||||
|---|---|---|---|---|---|---|---|
1. This table provides a simple correction to measurements of WECS sound in the presence of the background. For example, the sound of a WECS (along with the background sound, which is always present) is measured as 40 dBA, and the background sound level alone (without the WECS) is measured as 34 dBA. Then Δ, the difference in decibels is six dB (first row, third column), and the corresponding correction shall be two dB (second row, third column). That is, two dB shall be subtracted from the measured 40 dBA level, and it is adjusted to and reported as 38 dBA. The same procedure is followed in each band for one-third-octave-band data. | |||||||
2. When using directly measured A-weighted levels, if the difference between the WECS sound level (plus background sound level) and the background sound level alone is less than three dB, then it shall not constitute a violation of this section. | |||||||
3. When using measured one-third-octave-band data, if the difference between the WECS sound-pressure level (plus background sound-pressure level) and the background sound-pressure level alone, each in the same one-third-octave band, is less than three dB, then the WECS level for that one-third-octave band shall be set to zero. The report shall include a sketch of the site showing distances to the structure(s), to the property line, etc., and several photographs showing the structure(s), the property, and the acoustical instrumentation. All instrumentation shall be listed by manufacturer, model, and serial number. This instrumentation listing also shall include the A-weighted noise floor and the one-third-octave band noise floors, if utilized, for each sound level meter used. |