![]() The phon is a unit of loudness that represents equal loudness to a 1000Hz tone. Loudness level can be expressed in sones or phons, which are both units of loudness. This doubling is more consistent than the decibel scale where it is only a "general rule of thumb" that 10 dB is doubling in perceived sound. The sone scale is linear, so no matter the frequency or level, 2 sones is twice as loud as 1 sone, and 4 sones is twice as loud as 2 sones. A doubling of sones equates to a doubling of perceived loudness at any frequency. This can be seen in Figure 6.įigure 6: The sone scale is frequency independent. However, a doubling of sone level does correspond to a doubling of perceived loudness at all frequencies. At 30Hz a doubling in perceived loudness only requires a 5dB increase. The “rule of thumb” that a 10dB increase corresponds to a doubling in perceived loudness does not hold true at all frequencies. This means that at 1000Hz, an increase of 10dB corresponds to a doubling in perceived loudness. Both the 50 dB tone (100 Hz) and 92 dB tone (20 Hz) can be expressed as 1 sone or 40 phons.Īt 1000Hz, the curves of equal loudness are 10dB, or 10 phons, apart. This means that a 100 Hz tone at 50 dB sounds equally as loud as a 20 Hz tone at 92 dB as they both intersect the pink curve at these respective frequencies and decibels levels. In Figure 5 below, every frequency and dB level that lies on the pink curve is perceived as equally as loud.įigure 5: The curve of equal loudness represent dB and frequency values that are perceived as equally loud (Magenta is a 1 sone curve of equal loudness). This resulted in several curves of equal loudness.Ī curve of equal loudness represents all the frequencies and dB levels that are perceived as equally as loud. This jury experiment was repeated until all frequencies and 13 decibel ranges within the human hearing domain were included. The 100Hz tone would have to be playing at 52dB to sound equally as loud as the 1000Hz tone at 40dB (see Figure 4).įigure 4: To develop the curves, two tones were played and the levels adjusted until they sounded equally as loud. Then a 100Hz tone was played and the volume was adjusted until it sounded equally as loud to the jury as the 1000Hz tone. The level of the second tone would be altered until it sounded equally as loud as the 1000Hz tone.įor example, a 1000Hz tone was played at 40dB. Then, a second tone would be played at a different frequency. The jury would listen to a tone at 1000Hz and a particular dB level. To develop this metric, a jury of humans with normal hearing was gathered. As frequency changes along a curve, the dB value also must change to result in an equally loud sound.įigure 3: The curves of equal loudness originally developed by Fletcher-Munson in 1933. Thus the metric was developed with a jury of humans (unlike decibels which is simply a math equation).Įach curve shown on Figure 3 below represents a curve of equal loudness for sinusoidal tones. The loudness metric is based off of perceived loudness. Clearly dB alone is insufficient to represent the perceived loudness of a sound. The dB value is the same at both frequencies, but the perceived loudness is very different – one is audible, the other is inaudible. In general, humans can hear sounds at lower decibel levels between 3 kHz and 5 kHz than at any other frequency.įor example, humans are able to hear a 10dB sound at 5 kHz but we cannot hear a 10dB sound at 50Hz as shown in Figure 2.įigure 2: A tone at 50Hz and 10dB is inaudible. Humans can hear particularly well at these frequencies due to a resonance of the air volume in the ear canal. The threshold has different values at different frequencies. ![]() Tracing the lower limit (the hearing threshold), it is evident that the lower limit of hearing varies with frequency. The dip at about 4000 Hz is because the air volume in the ear canal goes into resonance which allows the ear to hear even low level sounds. Sounds cannot be heard at the decibel levels and frequencies outside of the grey area. The human hearing domain is shown in Figure 1.įigure 1: The human hearing domain is both frequency and level dependent. In fact, there is a separate sound quality metric called loudness (with units sones or phons) which gives a much better representation of how humans perceive the level of a sound. Decibel (dB) values accurately represent the amplitude of a sound, but they do not accurately represent the perceived loudness of a sound. The decibel value is often used to quantify sound. ![]() Calculating Loudness in Simcenter Testlabĩ.3 Calculating Loudness in Signature Throughput Processing Sones takes into account the frequency and level dependent nature of human hearing, while decibels does not fully address this dependency.Ħ.3 Stationary Loudness Spectrum (Specific Loudness)ĩ. Sones is a different unit of measure than the traditional decibel quantity. Sones is unit of measure of the loudness of a sound.
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