Note in Table 1.1 that the dB values are the same regardless of whether they were calculated from intensity (power) or pressure however, a 100-fold increase in intensity is equal to a 10-fold increase in pressure.įig. As a result, it is cumbersome to measure the incredibly small amounts of power associated with the enormous range of intensities that the human ear can hear. According to Gulick, Gescheider, and Frisina (1989), “a dangerously intense sound would represent a power of only about 0.0024 watt” ( p. The reference for dB IL is 10 –16 W/cm 2. A less common method to express sound intensity is in acoustic power by using decibels intensity level, or dB IL. What Is the Difference between dB IL and dB SPL?Īs stated in the previous section, a common method to express the magnitude of a sound is in decibels sound pressure level or dB SPL, for which the reference is 0.0002 dynes/cm 2. Because it is easy to measure dB SPL with a condenser or free-field microphone coupled to a sound level meter, sound measurements are often expressed in dB SPL. The reference for dB SPL is 20 micropascals (20 μPa) or 0.0002 dynes/cm 2. 1.1, is equal to 0 dB HL on the audiometer for the corresponding frequency.ĭecibels in sound pressure level, or dB SPL, refers to the magnitude of the displacement of molecules in the air. Each threshold in dB SPL, which is noted in the table at the bottom of Fig. 1.1, the solid black line represents the average auditory threshold in dB SPL at each audiometric frequency. The reference level for dB HL is “10,” which is related to the average threshold in decibels sound pressure level (dB SPL) for the average, normal-hearing listener. Decibels in hearing level, or dB HL, is commonly used in audiology because it refers to the decibel level on the audiometer. The decibel ( dB) is a logarithmic unit of measurement used to express the magnitude of a sound relative to some reference level. Sounds on the same equal loudness curve have the same number of phons.What Is the Difference between dB HL and dB SPL? The phon is an attempt to put a unit on human perception of loudness of pure tones. Notice that the ear is especially sensitive to sounds near 3,500 Hz- this is due to resonance of air in the ear canal.Įqual loudness curves are the basis of a unit of loudness called the phon. By contrast, the center of the graph shows that sounds near 1000 Hz don’t have to have be very intense to be heard. Similarly, sounds above 10 kHz must be quite intense to be noticed. Barely noticeable sounds at low frequency must have a high sound level to be heard (70 dB for 20 Hz). Points along this trace are barely perceptible for most people. The bottom curve represents all sounds at the threshold of human hearing. Each curve on the graph represents sounds with equal perceived loudness. Frequency is plotted along the x-axis and sound level is plotted on the y-axis. This frequency plot and ones like it are sometimes called equal loudness contoursor Fletcher-Munson curves(after the researchers who did groundbreaking research on the perception of loudness). The figure at the right (taken from ) shows the typical frequency response of the human ear. For best results, you will need good quality over-the-ear headphones. To see how it’s done, take your own hearing test using the tool on the “Music Acoustics” website at the University of New South Wales. The listener compares tones at different frequencies and is asked to adjust the amplitude of one of the tones until the two tones sound equally loud. Hearing tests can be used to construct equal loudness contours. Our ears are far less efficient at frequencies outside this band. This is fortunate- most human speech takes place in this frequency band. Our ears are especially sensitive to sounds with frequencies between 300 Hz to 3000 Hz. (For most people, the 1000 Hz version will seem much louder). However, frequency also plays a role in loudness perception- a 70 dB tone at 1000 Hz and a 70 dB tone at 16,000 Hz will not be perceived as equally loud, even though the intensities are the same. If a sound is played at 50 dB and then the same sound is played at 70 dB, our brains interpret the 70 dB sound as louder. Loudness perception 44 Frequency and loudness perception Loudness perception (and frequency)Īmplitude plays the dominant role in loudness perception.
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