Question 1

What is Leq and why is it the most important SPL metric?

Accepted Answer

Leq (equivalent continuous sound level) is the energy-averaged sound level over a measurement period. It represents the steady sound level that would deliver the same total acoustic energy as the actual fluctuating sound. Leq is the most important metric because it correlates with both hearing damage risk and annoyance better than any instantaneous reading. Nearly all occupational and environmental noise standards use Leq as the primary metric. For example, OSHA bases its 90 dBA permissible exposure limit on an 8-hour Leq (using 5 dB exchange rate). SonaVyx computes Leq continuously from the moment you start measuring, using true energy integration rather than simple arithmetic averaging of dB values.

Question 2

What is the difference between Lmax and Lpeak?

Accepted Answer

Lmax is the maximum time-weighted (Fast, Slow, or Impulse) sound level recorded during a measurement. Lpeak is the maximum instantaneous sound pressure without any time weighting. Lpeak is always higher than Lmax because time weighting smooths out short transients. For example, a snare drum hit might produce Lpeak of 135 dB but Lmax (Fast) of only 115 dB. Lpeak is critical for hearing protection because the ear can be damaged by a single extreme pressure peak. OSHA sets a ceiling of 140 dBC peak, and the EU Directive sets action values at 135 and 137 dBC peak. SonaVyx tracks both metrics separately, with Lpeak sampled at the full audio sample rate (48 kHz) for accurate capture of transients.

Question 3

What do L10, L50, and L90 percentiles mean?

Accepted Answer

Statistical noise levels (Ln) represent the SPL exceeded for n percent of the measurement time. L10 is exceeded 10% of the time, representing the louder events. L50 is the median level, exceeded 50% of the time. L90 is exceeded 90% of the time, representing the background or residual noise level. The L10-L90 difference indicates how much the noise fluctuates: less than 5 dB for steady noise, 10-20 dB for traffic, and 20+ dB for intermittent noise. Environmental assessments commonly use L90 as the background noise level and L10 to characterize event noise. SonaVyx computes percentiles using a 0.1 dB resolution histogram updated every 100ms, giving accurate statistical distributions even for short measurement periods.

Question 4

What is SEL (Sound Exposure Level) and how is it different from Leq?

Accepted Answer

SEL (Sound Exposure Level, also called LAE) normalizes the total sound energy of an event to a reference duration of one second. If you measure a 10-second event with Leq of 80 dBA, the SEL would be 80 + 10*log10(10) = 90 dBA. SEL is useful for comparing events of different durations on an equal footing. A short, loud event and a long, quiet event can have the same SEL if they deliver the same total energy. SEL is commonly used in: aircraft noise assessment (single flyover events), sleep disturbance studies, construction noise impact assessment, and noise dose calculations. SonaVyx calculates SEL continuously alongside Leq so you can assess both the average level and total energy exposure.

Question 5

How is TWA (Time-Weighted Average) calculated for OSHA compliance?

Accepted Answer

OSHA TWA uses a 5 dB exchange rate (doubling rate), meaning that for every 5 dB increase above 90 dBA, the permissible exposure time is halved. The formula is TWA = 16.61 × log10(D/100) + 90, where D is the noise dose percentage. Dose accumulates as D = 100 × sum(Cn/Tn), where Cn is actual exposure time at each level and Tn is the permissible time at that level. At 90 dBA, Tn = 8 hours. At 95 dBA, Tn = 4 hours. At 100 dBA, Tn = 2 hours. NIOSH and ISO use a 3 dB exchange rate instead, which is more scientifically accurate. SonaVyx calculates TWA using both OSHA (5 dB) and ISO (3 dB) exchange rates simultaneously so you can assess compliance under both standards.

Question 6

What is Ldn and how does it differ from Leq?

Accepted Answer

Ldn (Day-Night Average Sound Level) is a 24-hour Leq with a 10 dB penalty applied to nighttime hours (10 PM to 7 AM). This penalty accounts for the increased annoyance and sleep disturbance caused by nighttime noise. An Ldn of 65 dB is commonly used as the threshold for residential land use compatibility in the US. The European equivalent is Lden, which adds a 5 dB penalty for evening hours (7 PM to 11 PM) and a 10 dB penalty for nighttime (11 PM to 7 AM). SonaVyx environmental monitoring mode computes both Ldn and Lden automatically, applying the correct time period penalties based on your selected standard (US or EU).

Question 7

What does the NC (Noise Criteria) rating mean?

Accepted Answer

NC (Noise Criteria) curves are a set of octave band spectral shapes used to rate background noise in occupied spaces. The NC rating is determined by the lowest NC curve that is not exceeded by any octave band measurement. For example, NC-25 is typical for concert halls and recording studios, NC-30 for private offices, NC-35 for conference rooms, NC-40 for open offices, and NC-45 for corridors. NC ratings account for both the level and spectral character of noise, making them more informative than a single dBA number. A room can have acceptable dBA levels but fail NC criteria if there is excessive low-frequency rumble. SonaVyx overlays NC curves on octave band displays and automatically calculates the NC rating.

Question 8

How do I interpret the difference between LAeq and LCeq readings?

Accepted Answer

When LAeq and LCeq are close (within 3 dB), the noise spectrum is dominated by mid and high frequencies, typical of speech, HVAC hiss, or electronic noise. When LCeq is significantly higher than LAeq (difference greater than 10 dB), there is substantial low-frequency energy that A-weighting is filtering out. This matters because: low-frequency noise travels farther through building structures, standard hearing protection is less effective at low frequencies, and low-frequency noise causes more annoyance per unit of A-weighted level. Common sources of high LCeq-LAeq difference include subwoofers, diesel generators, industrial fans, and HVAC compressors. SonaVyx highlights this difference automatically and flags when it exceeds 10 dB as a potential concern.

SPL Metrics Explained: Leq, Lmax, Lpeak, SEL, TWA, and Statistical Noise Levels

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