The human ear can distinguish sound pressure within a very large area. A special measuring scale is used to describe the strength of the sound in the working area of the ear. Please click on the demo button to hear their sounds and the difference in pitch. A loud noise usually has a larger pressure variation and a weak one has smaller pressure variation. Human ear can perceive a very wide range of sound pressure. In air, sound pressure can be measured using a microphone, and in water with a hydrophone. While 1 atm (194 dB Peak or 191 dB SPL) is the largest pressure variation an undistorted sound wave can have in Earth’s atmosphere, larger sound waves can be present in other atmospheres or other media such as under water, or through the Earth. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C.
The human ear can respond to minute pressure variations in the air if they are in the audible frequency range, roughly 20 Hz – 20 kHz. Contributing to the wide dynamic range of human hearing are protective mechanisms that reduce the ear’s response to very loud sounds. Sound intensities over this wide range are usually expressed in decibels. The normal human ear can detect the difference between 440 Hz and 441 Hz. It is hard to believe it could attain such resolution from selective peaking of the membrane vibrations. This can be compared to the human eye, which can detect light frequencies (colors) that vary by less than a factor of 2. The dynamic range– the difference between the quietest and loudest sounds we can hear– is about 130dB (decibels, we’ll get to these in a while) which corresponds to a factor of 10 12th (that’s 10,000,000,000,000). Sound pressure waves within the scala vestibuli are propagated through the Reissner’s membrane into the scala media, which contains a fluid with different properties than those in the other scala. Because the dynamic range of human hearing is very large (factor of 1,000,000), and because the frequency response of the ear is non-linear (the same ratio between two frequency stimuli is always perceived to be the same musical interval), we use the logarithmic decibel (dB) to express sound intensity level (SIL). Just as the total energy in an oscillating spring is proportional to the square of the amplitude of the oscillation, the energy in a sound wave is proportional to the square of the amplitude of the pressure difference. Just as the total energy in an oscillating spring is proportional to the square of the amplitude of the oscillation, the energy in a sound wave is proportional to the square of the amplitude of the pressure difference. The human ear can detect sound of very low intensity. Similar to a hydraulic lift, the pressure is transferred from a relatively large area (the eardrum) to a smaller area (the window to the inner ear).
Sound can generally by defined as vibrating waves in elastic media. A human ear actually perceives the effective sound pressure level. The time difference occurs when a longitudinal sound wave passes the two ears under an angle. In an open field sound is stronger near the source and weaker further away as the energy of the source is distributed over a larger area. Since pressure is equal to force divided by area, this difference in area increases the sound wave pressure by about 15 times. For example, a 200 hertz sound wave can be represented by a neuron producing 200 action potentials per second. The sensitivity of the ear is amazing; when listening to very weak sounds, the ear drum vibrates less than the diameter of a single molecule!. For example, sounds in a large auditorium will contain echoes at about 100 millisecond intervals, while 10 milliseconds is typical for a small office. A few years after writing this paragraph I found the very interesting book This is Your Brain on Music which confirms the speculation on wiring to primitive parts of the brain, but argues that music has a definite evolutionary function. Sound pressure level (SPL) is given in dB SPL. The human ear is most sensitive in a band from about 2,000-5,000 Hz. This is an important region for understanding speech, and could be construed to imply that hearing evolved to match speech. You can hear what a 3 dB difference sounds like yourself with sound files in the sound demo section.
Sensitivity Of Human Ear
We describe some fundamental auditory functions that humans perform in their everyday lives, as well as some environmental variables that may complicate the hearing task. Thus, one can describe sound as temporal fluctuations in pressure, or one can describe sounds in terms of the frequency components that compose the sound. This is a very inefficient way of hearing, in that this way of exciting the auditory nervous system represents at least a 60 dB hearing loss. This head shadow produces large interaural level differences when the sound is opposite one ear and is high frequency. When underwater objects vibrate, they create sound-pressure waves that alternately compress and decompress the water molecules as the sound wave travels through the sea. To the human ear, an increase in frequency is perceived as a higher pitched sound, while a decrease in frequency is perceived as a lower pitched sound. So when you are describing sound waves and how they behave it is very important to know whether you are describing sound in the sea or in air. When these changes in air pressure vibrate your eardrum, nerve signals are sent to your brain and are interpreted as sound. People can detect a very wide range of volumes, from the sound of a pin dropping in a quiet room to a loud rock concert. Because the human ear can handle such a large range of intensities, measuring sound pressure levels on a linear scale is inconvenient. The signal-to-noise ratio, typically measured in dB, is the difference between the nominal recording level and the noise floor of the device. These pressure fluctuations, when they occur in cycles or waves, are what we call sound. In addition to transmitting sound to the middle ear, the eardrum can be tightened to help protect the inner ear from very loud, and potentially damaging, sounds. This occurs because smaller vibrations over a larger area, the eardrum, are leveraged through the bones to create bigger vibrations over a smaller area, the oval window. However, there is large individual variability in the auditory abilities of older people, as well as substantial gender differences in auditory performance.