4/7/2024 0 Comments Decibel loudness scaleThis is the condition which leads to the commonly used rule of thumb for loudness addition. But if the two sounds are close together in frequency, within a critical band, then the saturation effects in the organ of Corti are such that the perceived combined loudness is only slightly greater than either sound alone. Adding a second sound of equal loudness yields a total sound about twice as loud. If the second sound is widely separated in pitch from the first, then they do not compete for the same nerve endings on the basilar membrane of the inner ear. Insight into this process can be obtained from the place theory of pitch perception. When one sound is produced and another sound is added, the increase in loudness perceived depends upon its frequency relative to the first sound. While not a precise rule even for the increase of the same sound, the rule has considerable utility along with the just noticeable difference in sound intensity when judging the significance of changes in sound level. If a second sound is widely enough separated in frequency to be outside the critical band of the first, then this rule does not apply at all. One difficulty with this "rule of thumb" for loudness is that it is applicable only to adding loudness for identical sounds. This is just a model, but it seems to correlate with the general observations which suggest that something like ten times the intensity is required to double the signal from the inner ear. Nerve cells have maximum rates at which they can fire, and it appears that doubling the sound energy to the sensitive inner ear does not double the strength of the nerve signal to the brain. Why is it that doubling the sound intensity to the ear does not produce a dramatic increase in loudness? We cannot give answers with complete confidence, but it appears that there are saturation effects. Although this rule is widely used, it must be emphasized that it is an approximate general statement based upon a great deal of investigation of average human hearing but it is not to be taken as a hard and fast rule. Another way to state the rule is to say that the loudness doubles for every 10 phon increase in the sound loudness level. A common way of stating it is that it takes 10 violins to sound twice as loud as one violin. The "rule of thumb" for loudness is one way to attempt that.Ī widely used "rule of thumb" for the loudness of a particular sound is that the sound must be increased in intensity by a factor of ten for the sound to be perceived as twice as loud. But though ff is much louder than p in dynamic level, it is not 1000x louder, so one must attempt to develop a scale of loudness that comes closer to mapping your ear's perception. Since "loudness" is a subjective measurement of perception, one must be careful about how much accuracy you attribute to it. In practical sound level measurement, filter contours such as the A, B, and C contours are used to make the measuring instrument more nearly approximate the ear. The factor of ten rule of thumb can then be used to produce the sone scale of loudness. To more realistically assess sound loudness, the ear's sensitivity curves are factored in to produce a phon scale for loudness. A general " rule of thumb" for loudness is that the power must be increased by about a factor of ten to sound twice as loud. This is one of the motivations for using the decibel scale to measure sound intensity. It must also be considered that the ear's response to increasing sound intensity is a "power of ten" or logarithmic relationship. This is the kind of information contained in equal loudness curves for the human ear. The sound intensity must be factored by the ear's sensitivity to the particular frequencies contained in the sound. It is intimately related to sound intensity but can by no means be considered identical to intensity. Sound loudness is a subjective term describing the strength of the ear's perception of a sound.
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