It is instructive to compare the threshold of hearing value to the background air Of course the ability to hearĪlso varies from person to person so this is an average for the human population. So the value is quite different at other frequencies. This is a standard value defined for a pure sine wave at a frequency of 1000 Hz.Īs we will see later in this class, our ability to hear is a strong function of frequency The pressure amplitude for the threshold of hearing is 2 xġ0 -5 N/m 2.

This value is referred to as the threshold of hearing (for obvious reasons). Sound that is audible to the average person. Typical sounds? To answer we begin by considering the pressure amplitude for the weakest Our next concern is to address the question: how large is the pressure amplitude for Is performed by Sound Pressure Level (SPL) meters. This pressure variation can be converted into the pressure amplitude. By applying known pressure variations to the microphone the electrical signalĬan be calibrated to directly measure the air pressure variations. It is fairly simple to understand how a calibrated measurement of the pressure amplitudeĬan be made using a microphone to convert the pressure variations into an electrical The relation between amplitude of the sine wave (measuredįrom the background level to one extreme) to the pressure amplitude (average pressureĮxcursion from the background) is shown in the figure below. Is reduced from the maximum amplitude by a factor of 0.707 (equivalent to dividingīy the square root of 2). Pure tone-a pure sine wave-the averaging process leads to a pressure amplitude that The real average is a root mean squareĪverage which you might be familiar with if you have done some electronics. Goes above (positive) and below (negative) the constant atmospheric background soĪ straight average would tend to give zero. I am hiding a bit of complication in the word average the pressure Pressure variation away from the constant background level is the Pressure Amplitude On the weather map-however, we can consider it to be essentially constant on theĪ sound wave creates a variation in the normally constant air pressure that oscillatesĪbove and below the normal atmospheric level of 105 N/m2. The space of hours or days-this is what they mean by high and low pressure centers The atmospheric pressure varies a small amount over Atmospheric pressure is measured in newtons/meter2Īnd is approximately 105 N/m2. Variation in air pressure caused by a sound wave. Pressure amplitude is a measure of the size of the The most physically understandable quantity used in determining the size of a sound The question of what parameters are measured in determining sound levels. Thus, to begin our discussion I want to cover There are a variety of different definitions of the decibel scale depending upon the There are decibel scales defined for use in electronics and optics. Decibel scales are by no means confined to acoustics, Pressure Amplitude: Quantitative Measurement of SoundĪs we will discuss in this section decibels are a means of creating a logarithmic

Decibel Scales: Sound Pressure Level and Sound Intensity Level

Define decibel