Phon

The Phon (according to new German spelling also Fon ) is the unit of psychoacoustic variable volume level. In addition to the loudness in sone of the volume level is used in phon to describe the perceived loudness, a human being perceives a sound event as a listening event with the. Was first introduced in 1925 by Heinrich Barkhausen the unit.

The value in Phon indicates which sound pressure level ( in dB ) has a sine wave at a frequency of 1000 Hz, which is as loud as the sound event, which has a different frequency, perceived. Through this comparison, the perceived loudness of an arbitrary sound signal with the sound level of a reference signal ( a sine wave at 1000 Hz), it is possible to describe the aural sensation of a level value that is independent of the spectrum of the signal.

For pure sine waves, the dependence of the perceived loudness of the frequency curves in the same volume level ( isophones ) is described (see chart with the old standard - new standard is ISO 226:2003 ). The lowest of these curves describes the course of the hearing threshold and is 3 phon since a 1000 Hz tone ( the reference signal for the phon - definition) can be perceived only from a sound pressure level of 3 dB. The pain threshold is around 130 phon. Louder sounds are perceived as pain and can cause hearing loss even with brief exposure.

Volume versus loudness

The size of the volume level in Phon is the link between perceived volume levels with level values ​​. A quantitative comparison of different volumes, however, is only restricted by the phon scale possible:

• On the one hand the Phonwert is not proportional to perceived loudness: A noise with 80 phon is not twice as loud as a sound of 40 phon, but 16 times as loud. The volume level is mathematically expressed, " non-proportional scaling ".
• On the other hand leads an equal change of Phonwertes not the entire level range to an equal change in the perceived loudness. Thus, results in an increase of Phonwerts from 10 to 20 phon, a sixfold increase in the perceived loudness. An increase in the Phonwerts from 50 to 60 phon, however, only leads to a doubling of perceived loudness.

In this respect, a further quantity of psychoacoustic evaluation of the volume is still necessary, which has a largely linear relationship between objective value and psychoacoustic effect. This is done by the psychoacoustic variable loudness with their unit Sone: A sound that has the volume level of 40 phons, the loudness " 1 sone " is assigned by definition. A noise which is perceived twice as loud, has double the loudness ( ie 2 sone ), etc. Above 40 phon, there is a logarithmic relationship between Sone and Phon (see picture); an increase in the volume level by 10 phon here corresponds to a doubling of perceived loudness. For example, a sound volume is 100 phon 64 times as loud as a sound perceived with 40 phon.

Noise measurement technology

In the noise measurement technology that Phon has little significance. For noise measurement, either the sound pressure level is measured ( in most legal guidelines is a measurement requires the A-weighting filter), where the systematic error of this method to be accepted, or from the sound event, the loudness is determined in sone.

But then The Phon plays a role in sound pressure level and loudness to be compared. Thus, for example, offers the loudness measurement method according to Zwicker the ability to determine both the loudness in sone, as well as the volume level in Phon. The volume level in Phon then allows a direct comparison with weighted sound pressure level measurements in dB ( A) and an easier evaluation of differences.

Difference threshold

A volume difference of about 1 phon is measured as the difference threshold just at the limit of detectability. Therefore, it is neither necessary nor useful to specify a fraction of a phon.