madzombieguy

Generally, our threshold of hearing lies within the 20Hz to 20kHz range. A series of tests were conducted to determine our sensitivity to different frequencies, which in turn, effect our perception of where the sound may be located. “Out of these tests, it was found that the human ear is most sensitive to frequency's between 2kHz – 4kHz” (Baert, 1995). The average person is said not to hear below 2kHz, so sounds around this level are known to seem quiet and often we feel that the softness of a sound psychologically means that it is further away from us. However, as Chowning (1999) states; “before speculating about the answer, we should consider the effect of distance on intensity.” To experiment, we can position a subject at a distance of roughly 1 metre from the listener and position another subject at a distance of 30 metres (Figure 4.0). The closer subject would speak softly as he/she would be closest and the further away subject would obviously have to speak loudly. This is made obvious by the fact that sound disperses through distance. This experiment reveals more than one single dimension to our perception of loudness. It is known that sound disperses over distance, however, as the pressure in the sound wave moves away from the subject, the actual surface area gains in size. As the surface area in a spherical context would increase alongside the square of its radius, its intensity makes up for this increase by decreasing in accordance with time and distance travelled using the inverse square law (1/d², seen in Fig 5.1). As the distance we are using is set at 30 metres then the intensity must decrease at 1/30² or 1/900 of the intensity of the sound provided by the subject at just 1 metre (Chowning, 1999). As this suggests, the distance we perceive alongside our actual auditory perspective means that the amplitude in relation to both of the subjects at different distances could be identical. To work this out, lets just assume that the sound being produced by the subject at 1 metre is of an intensity 1/144 of that of the further intensity. It seems obvious that the closer intensity is much greater and perceived as louder. This is not always the case, as the listener would most often state that the softly spoken person at 1 metre sounded more quiet than the shouting person at 30 metres, despite the softly spoken person having a tone of much greater intensity. We can work this out by calculating the intensity so that I (Intensity from source, at culminating point) can be found by following the equation S ÷ 4πr² where: S = the source strength, and 4πr² = the spherical area. Scientists often just refer to the majority average which is depicted by the famous Fletcher-Munson curves. Fletcher-Munson graph: . These curves on the graph represent equal loudness contours for sounds created using sine waves. A range varying from below 20Hz (the average understanding of our lowest noticeable level of hearing) up to more than 10kHz is displayed. The vertical axis represents the intensity (sound pressure level) in dB, where as the horizontal axis displays the range of frequencies. The curves display a great deal of variation which help us to understand how sensitive our ears are to different frequencies. For example, “in order for a soft sound at 50Hz to sound as loud as one at 2000Hz, the 50Hz sound has to be about 50dB more intense than the 2000Hz sound” (Matthews, 1999). This means that the human ear is more sensitive to sounds at 2Khz than at 50Hz. With these curves, tests carried out to simulate the results shown are usually using tones rather than other sounds. The main reason is that everyday sounds have a variety of natural harmonics in them which can often cloud our perspective, especially at higher pitch's where the loudness is often added to by the contribution of these harmonics. We often perceive everyday sounds as particularly loud because dB is logarithmic, therefore, the sound build up is quite intense. We also have to think about aspects such as cultural conditioning. By the term ‘cultural conditioning’, I am referring to the way in which the human body and more importantly here - the human ear, works. When we are brought into the world or even just before it, we are not familiar with our surroundings and it takes time for us to adjust and become comfortable in remembering where we are and what people look like. The human ear allows us to become comfortable first with sounds. For example, it is said that a baby can always tell who it’s mother is, by sound alone. It has also been known, though not yet 100% proven, that a baby can remember and associate sounds it has heard coming from someone, whilst still within the womb. “Audiotapes were played to 60 pregnant women to see how the developing child responded to the voice of either its mother or a female stranger. The scientists found the baby's heart-rate speeded up when it heard its mother but slowed down in response to a stranger's voice” (BBC News, 2003)