Question 1

What is A-weighting and when should I use it?

Accepted Answer

A-weighting is a frequency-dependent filter defined in IEC 61672-1 that approximates the sensitivity of human hearing at moderate loudness levels. It heavily attenuates frequencies below 500 Hz and slightly attenuates frequencies above 6 kHz. The resulting measurement in dBA correlates well with perceived loudness for broadband noise. Use A-weighting for: occupational noise assessment (OSHA requires dBA), environmental noise surveys, general noise level documentation, and comparing noise sources. Nearly all noise regulations worldwide specify A-weighted levels. SonaVyx applies the A-weighting filter digitally using an IIR biquad cascade that matches the IEC standard tolerance curves. You can switch between A, C, and Z weighting in real time to see how different weightings affect your readings.

Question 2

What is C-weighting and when is it preferred over A-weighting?

Accepted Answer

C-weighting is a nearly flat frequency response filter with only slight roll-off below 31.5 Hz and above 8 kHz. Measurements in dBC capture the full frequency spectrum including low-frequency energy that A-weighting suppresses. Use C-weighting for: peak sound pressure measurements (LCpeak), assessing low-frequency noise from HVAC, machinery, or subwoofers, checking hearing protector adequacy (C-A difference indicates low-frequency dominance), and live sound where bass energy matters. A large difference between dBC and dBA readings (more than 10 dB) indicates significant low-frequency content that A-weighting is hiding. SonaVyx displays both A and C weighted readings simultaneously so you can monitor this difference in real time.

Question 3

What is Z-weighting and why was it introduced?

Accepted Answer

Z-weighting (Zero-weighting) was introduced in the 2002 revision of IEC 61672 to replace the older Linear or Flat weighting. Z-weighting applies no frequency correction, providing a flat response from 10 Hz to 20 kHz within ±1.5 dB. It was standardized because different manufacturers previously had different definitions of Linear weighting, causing inconsistencies. Use Z-weighting when you need raw, unfiltered sound pressure levels, such as for scientific research, loudspeaker measurements, or when applying custom weighting post-measurement. SonaVyx implements Z-weighting as the bypass mode of the weighting filter chain, giving you the true broadband SPL without any frequency shaping.

Question 4

Why does A-weighting underestimate the impact of bass-heavy noise?

Accepted Answer

A-weighting was designed based on the 40-phon equal-loudness contour, which represents moderate listening levels. At these levels, human hearing is less sensitive to low frequencies. However, at high SPL (above 80 dB), hearing sensitivity becomes more uniform across frequencies, and low-frequency sound produces physical sensations (vibration, pressure) that A-weighting ignores. Concert and club sound systems producing 100+ dBC at sub-bass frequencies may read only 85-90 dBA, severely underestimating the physiological impact. This is why some jurisdictions use C-weighting or combined criteria (e.g., 85 dBA AND 100 dBC) for entertainment noise. Monitor both dBA and dBC in SonaVyx to get the complete picture.

Question 5

What is the C-A difference and what does it tell me?

Accepted Answer

The C-A difference (also called C minus A or LCeq minus LAeq) indicates how much low-frequency energy is present relative to the overall spectrum. A C-A difference of less than 3 dB means the noise is dominated by mid and high frequencies. A difference of 3-10 dB indicates moderate low-frequency content. A difference greater than 10 dB signals strong low-frequency dominance. This metric is useful for: selecting hearing protection (high C-A means you need protectors with good low-frequency attenuation), diagnosing HVAC rumble, evaluating subwoofer contribution, and identifying masking noise character. SonaVyx calculates and displays C-A difference automatically when both weightings are active.

Question 6

Which weighting should I use for measuring music and live events?

Accepted Answer

For live events, use both A-weighting and C-weighting simultaneously. A-weighted levels (dBA) correlate with perceived loudness and are required by most venue noise ordinances. C-weighted levels (dBC) capture the full bass energy that can cause hearing damage and structural vibration complaints from neighbors. Many European regulations now specify dual criteria such as 96 dBA Leq and 110 dBC Leq for music venues. For sound system tuning purposes, Z-weighting gives you the uncolored frequency response. SonaVyx lets you monitor all three weightings in parallel, with the SPL meter showing the primary weighting prominently and secondary weightings in smaller displays.

Question 7

How does frequency weighting affect octave band analysis?

Accepted Answer

Frequency weighting is applied to the broadband signal before computing the single-number SPL value. Octave band analysis, by contrast, splits the signal into frequency bands first and shows the energy in each band separately. You can apply weighting to octave band data by adding the weighting correction for each band center frequency. For example, A-weighting subtracts 26.2 dB at 125 Hz but only 0.0 dB at 1 kHz. This lets you see which bands contribute most to the weighted total. SonaVyx displays octave bands with optional A or C weighting overlay, helping you identify which frequency ranges are driving your overall SPL reading and where to focus treatment or EQ efforts.

Question 8

What are the B and D weightings and are they still used?

Accepted Answer

B-weighting was designed for moderate sound levels (70-phon contour) and D-weighting for aircraft noise assessment. Both were removed from the IEC 61672 standard in 2003. B-weighting is no longer used in any current standard. D-weighting is occasionally referenced in older aircraft noise studies but has been superseded by the EPNL (Effective Perceived Noise Level) metric in modern aviation noise assessment. The current IEC 61672-1 standard defines only A, C, and Z weightings. SonaVyx implements these three standard weightings. If you encounter legacy data in B or D weighting, you can convert it to modern weightings using published correction tables, though this introduces some uncertainty.

A-Weighting, C-Weighting, and Z-Weighting: Which One Should You Use?

Frequently Asked Questions