• 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

    inMusic acquires ArKaos

    Fort Lauderdale, FL USA (October 27, 2020) inMusic, the has announced the acquisition of ArKaos.

    Founded in 1996, ArKaos specializes in video processing technologies,... Read more

    Meyer Sound launches Spacemap Go, a tool for spatial sound design and mixing

    Meyer Sound has officially released Spacemap® Go for spatial sound design and mixing. Available now as a free app for Apple iPad (any iPad capable of running the latest iPadOS), Spacemap... Read more

    Bose unveils L1 Pro family


    These three new portable Bose PA systems are designed to give artists choices, suit different styles and audiences, and provide an solution for creators reintroducing live music and sound experiences into venues and online platforms across... Read more

    ClearOne BMA 360 beamforming microphone array ceiling tile

    ClearOne (NASDAQ:CLRO), provider of audio and visual communication solutions, has announced its new BMA 360, reportedly the world’s most technologically advanced Beamforming Microphone Array Ceiling Tile.

    The ClearOne BMA 360 is the world’s first truly wideband,... Read more
  • Recent articles

    Power amplifier modes : stereo, parallel and bridge mono

    In general, two-channel power amplifiers for professional use default to stereo mode. That is, each amplifier channel receives a signal from its input connector and its volume is controlled by... Read more

    Basic electricity formulas

    Although it not specific to sound, we include this document with some basic electricity formulas. They can be found in any electricity textbook, but we have added them to the DoPA Library for reference.

    Ohm's law

    The most basic formulas derive from Ohm's law, which specifies that the electric current between two points is proportional to the potential difference (voltage) between them and inversely proportional to the resistance between them. The formula is:
    V
    I = ———
    Z


    where I is the current (intensity) in amps and V is the voltage in volts. Since we use alternating current in audio, we have replaced resistance with impedance (Z, and this could also be resistance R), measured in ohms. Clearing Z and V we have these other two formulas:

    V
    Z = ———
    ... Read more

    Y-cables, looping audio signals through

    This article will explain loop-though connections and "y-cables" for analog audio signals.

    To obtain one or more copies of a signal (for example, to distribute the signal from a mixer to various self-powered speakers or power amplifiers) we use parallel connections. To do this we simply connect each terminal (pin) of the connectors in parallel. That is, 1 to 1, 2 to 2 and 3 to 3 (or tip to tip, ring to ring and sleeve to sleeve in a TRS connector). When we split a signal in two in this way, we refer to a "Y-cable" or "Y" connection, since the division of a signal in two looks like letter "y". Contrary to what it may seem, a y-cable is not a technically incorrect solution, but a correct way of splitting the audio signal. In fact, when a self-powered loudspeaker system or one channel of... Read more
  • PAcalculate app