But when a passing motorist has his stereo turned up, you cannot even hear what the person next to you in your car is saying. After settling into bed, you may hear your blood pulsing through your ears. In a quiet forest, you can sometimes hear a single leaf fall to the ground. Noise on crowded roadways like this one in Delhi makes it hard to hear others unless they shout. Pictured is a decibel chart displaying a range of common sounds and their relative dB(A) measurements.Figure 1. Noise levels above 140 dBA can cause damage after just one exposure. In general, the louder the noise, the less time is required to cause damage to one’s hearing. According to the National Institute for Occupational Safety and Health (OSHA), the maximum exposure time at 85 dBA is eight hours. It is generally recognized that continued exposure to any sound measured at 85 dBA can be harmful to the human ear. Overexposure to noise over time can create hearing loss. While there are other weighting scales (e.g., dB(B) or dB(C)), dBA is easy to measure and therefore the most widely used.
When a weighting filter is turned on (using the A-scale), the SPL read out is given in units of dBA. To account for sensitivity range of the ear, sound meters contain a filter with a frequency response similar to that of the human ear. While efforts have been made to develop a sound meter that will simulate the equal loudness contours, the complexity of manufacturing such a device would not be economically viable. a phon is a unit of sound sensation and.There is an important distinction to note between the phon and the dB: The resulting numbers assigned to each curve is a unit known as the phon.
Each contour gives the sound level necessary to produce the same loudness at different frequencies. Unequal sensitivity can be represented in the charting of equal loudness curves. This is due to the ear’s abilities to hear sound differently depending on the frequency, a phenomenon referred to as unequal sensitivity. The SPL measurements gathered from a sound level meter refer to the physical phenomenon of sound, however, this number does not correlate simply to the sensation of loudness human ears interpret. Despite all the complexities that go into formulating and measuring the sound pressure level, it still lacks a direct correlation with how the human ear actually perceives the loudness of sound. Not all sound pressures are equally loud. Filters can be used by the meters to measure specific bands of sound wave pressure by honing in on specific frequencies within a larger soundscape. Finally, the read out panel displays the average sound pressure levels for the environment being analyzed. The output amplifier then converts the weak sound signal to a level adequate to display on the read out panel. That electrical charge is then converted by the input amplifier into a voltage that, once processed by the electrical circuitry, is converted into a sound pressure level (SPL). The microphone converts fluctuating air pressure produced by a sound source into a fluctuating electrical charge. However, all meters consist of four basic components: microphone, input amplifier, output amplifier, and a read out device. There are various types of Sound Level Meters available, some with more precision and versatility. In more detailed terms, the decibel is a logarithmic way of expressing a ratio between sound pressure or intensity, though it may measure other factors such as power or voltage.ĭecibel measurements are obtained by using an instrument called the Sound Level Meter. Today, the decibel is the most convenient way to convey the intensity of a sound level in the environment. In 1928, Bell Telephone Laboratories coined the new unit of measurement, calling it the bel, in honor of telecommunications pioneer Alexander Graham Bell. The unit of measure was derived from the methods used to quantify signal loss in telegraph and telephone circuits. The decibel (abbreviated dB) is an expression of the loudness or intensity of sound.