• Frequency weightings: A, B, C and Z

    In the loudness contours reference, we learned that the frequency response of the human ear is not flat and it also varies considerably with listening level. To try and approximate acoustical analyzers to the response of the ear, frequency weighting curves were created. These are simplified versions of the ears' frequency response at different levels. Thus, for low sound pressure levels, the A weighting is used, which provides substantial low frequency attenuation (-50 dB at 20 Hz and almost -20 dB at 100 Hz) and some high frequency attenuation (about -10 dB at 20 kHz). The A weighting is adequate for the measurement of background noise, which is low level by nature.

    The B weighting is used for intermediate levels and is similar to A, except for the fact that low frequency attenuation is a lot less extreme, though still significant (-10 dB a 60 Hz). Recent studies show this is the best weighting to use for musical listening purposes.

    The C weighting is similar to B and A as far as the high frequencies are concerned. In the low frequency range it hardly provides attenuation. This weighting is used for high level noise. The different weightings can be graphically compared on the graph above.
    These weightings are not very accurate for two reasons. Firstly, they are based on the inverse of the Fletcher & Munson contours, which are old and provide substantial error, since they were measured with the limited instrumentation of the time. Secondly, the curves are simple and do not include significant inflexions happening in the mid-range (around 3500 Hz) as well as the high frequencies. This last reason is due to the fact that the weightings were designed around practical -and hence very simple- electrical circuits for the time. For those reasons the weightings are not all that accurate as they do not reflect the exact behaviour of the ear, although they do provide basic attenuation in the low and high frequencies that approximately simulates the varying responses of the ear at different levels. Nowadays it would be possible to define new weightings based on more exact loudness contours, and they could take more complex shapes that reflected ear responses more accurately and be easily realizable with current electronics. However, decades of use of the classic standard weightings seem to be an obstacle when it comes to standardizing a new set of more exact weighting curve.

    Measurements taken using the aforementioned weightings are denoted by writing the weighting letter in parenthesis after "dB". Thus we speak of dB (A), dB (B) or dB (C). There exist other weightings for special applications such as D, for very high pressure aeronautical noise.

    On a sound level meter (SLM) we should select weighting B for measuring loudspeaker enclosures in the listening area. If B is not available and we are forced to choose between A and C, we should pick C. If only A is available, we should use not weighting. If, for environmental reasons, we are after the lowest possible sound pressure reading, we should choose A, since it is the weighting that provides the most attenuation.


    In recent years the B-weighting has been phased out from sound pressure meters (and from the 2003 edition of IEC 61672) and the 'linear' ('unweighted') position has been replaced by the Z-weighting, which is the same except that the minimum frequency band in which the response must be flat (10Hz to 20kHz, ±1.5 dB) is specified.

    In telecommunication, the term 'psophometric weighting' is used, and the CCITT and 'C-Message' curves, which are more extreme in terms of attenuation of highs and lows than the C-weighting, are utilized.



  • Ad

  • News

    Powersoft Releases Q-SYS and Crestron Plug-ins for Mezzo Series and Duecanali, Quattrocanali and Ottocanali Series Amplifiers

    Powersoft has released new plug-ins supporting Mezzo Series and its non-DSP install dedicated amplifier platforms ranges for the Q-SYS and Crestron control ecosystems. These free-to-download plug-ins allow for... Read more

    Neutrik introduces the NPS-30W PoE Injector

    Neutrik, supplier of connectivity solutions for audio, video, and data, has announced the debut of the NPS-30W PoE injector. The NPS-30W is the world’s first... Read more

    Audinate announces Authorized Implementer Program for Dante AV products

    Audinate, developer of the Dante AV networking solution, has announced a new Authorized Implementer Program for manufacturers seeking to fast-track the development... Read more

    Audinate announces Bluetooth and USB-C Dante AVIO Adapters

    Audinate, developer of the Dante AV networking technology has announced the addition of two new models to the line of Dante AVIO audio adapters, offering USB-C and Bluetooth connectivity... Read more
  • Recent articles

    Balanced and unbalanced connections

    There are two basic ways to carry an electrical audio signal.


    • The first one is unbalanced. The signal is carried on a two-conductor cable. Unbalanced signal connectors have two pins, such as the RCA (also called Phono and Cinch, commonly used by home hi-fi equipment) and the unbalanced 1/4" (used in musical instruments and semi-professional audio). Multi-pin connectors can also carry
    ... Read more

    Choosing loudspeaker cable

    The importance of cables for the connection between the amplifier and the speaker is often controversial. Hi-fi aficionados spend fortunes on cables that promise spectacular results, and our short auditory memory and subjectivity lead many to confirm these improvements in their systems.

    The truth is that there are very few serious studies on the importance of the cable in relation to the perceived sound quality. A cable has impedance (opposition to electric current as a function of frequency), capacitance (behaves to some extent like a capacitor) and inductance (behaves like a coil). However, a few years ago an AES article concluded that the differences between cables were very small in terms of capacitance and inductance, and only recognized the importance of impedance.

    Therefore I invite you to leave aside any cable with such an exaggerated price as its promises, and look only at the gauge (thickness, cross-sectional area) of the cable, as far as the electrical characteristics are concerned (then there are important... Read more

    Intelligibility and its measurement

    1. What is intelligibility?

    The state or quality of being understood. It can apply to an idea or a writing, but in our context it relates to the spoken word and, less commonly, to music.... Read more
  • PAcalculate app