dBA - Calculating weighting filter frequency to dBA and dBC DIN IEC 651 calculator equal-loudness contours

Sound measuring (Noise measuring)

Weighting filter after DIN EN 61672-1 2003-10 (DIN-IEC 651)
Calculation: Frequency f → dBA and dBC - The difference

Notice: Sound level meters measure the sound pressure level in dBSPL.
Sound pressure is a sound field quantity.

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At sound level analyzers the display (attack time t_in) is time weighted. There are different settings:

Slow (S):	t_in	=	1000 ms
Fast (F):	t_in	=	125 ms
Pulse (I):	t_in	=	35 ms,	t_out	=	1500 ms

Formulas to calculate the weighting filter curves A, B und C

Note - Comparing dBSPL and dBA:
                There is no conversion formula for measured dBA
                values to sound pressure level dBSPL or vice versa.
                That is only possible measuring one single frequency.

There is no "dBA" curve given as threshold of human hearing.

Readings of a pure 1 kHz tone should be identical, whether weighted or not.

The A-weighting filter curve is defined from 20 Hz to 20 kHz.
This is intended as a rough replica of the 30 dB loudness of the
curve of "equal-loudness contours" for low frequencies.
That means, the cutoff low frequencies are not measured.

Because of the complexity of the equal loudness contour curves one was looking for an easy
simple evaluation scale and chose the A weighted curve, which reflects the course of the
hearing curve for bass frequencies of the low loudness level L_N = 30 phon approximately.
From the noise spectrum one gets a single number, which corresponds to the real loudness at
higher levels lesser and lesser. Because of the easy measuring possibility and the ease of use
of this single number the industry marketing took the dBA sound pressure level measurement.

dBA: The decibel A filter is widely used. dBA roughly corresponds to the inverse of the
30 dBSPL curve at 1 kHz equal-loudness curve for the human hearing.
An A curve always provides for "nice" values when low frequency noise signals are included.
An A filter of a measured motorcycle noise must show untrue values. You should know that.
From a dBA measurement no accurate description of the expected volume is possible.

The weighted sound level is neither a physiological nor a physical parameter.

Words to the wise: Always wonder what a manufacturer
is hiding when they use A-weighting. *)

*) http://www.google.com/search?q=Always+wonder+what+a+manufacturer+Rane&filter=0

dBC: The decibel C filter is practically linear over several octaves and is
suitable for subjective measurements at higher sound pressure levels.

Notice:
The sound pressure p as a sound field quantity
moves the diaphragms of the microphones
and the ear drums of our sense of hearing.
And what operates the sound level meters?

Why should our ears need the sound intensity?

Comparing dBA and dBC

Relative Response (dB)	Frequency f in Hz
Relative Response (dB)	31.5	63	125	250	500	1000	2000	4000	8000	16000
dB(A)	−39.4	−26.2	−16.1	−8.6	−3.2	0	+1.2	+1.0	−1.1	−6.6
dB(C)	−3.0	−0.8	−0.2	0	0	0	−0.2	−0.8	−3.0	−8.5

The B-weighting curves and the D-weighting curves disappeared
ages ago from the standards. Don't use that anymore.

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