We connect this microphone to the microphone input on a mixer. The microphone emits 10 millivolts of voltage when we speak into it. It can also be used to study the vibrations of structures such as bridges or buildings that are caused by sound waves. Pressure amplitude is often used to evaluate speaker performance or the impact of noise on the environment. However, the pressure amplitude of a sound wave decreases along with the increasing distance from the sound source because some sound energy is lost due to absorption and attenuation by the environment. A higher pressure amplitude means the sound wave has more energy and is therefore louder. The pressure amplitude of a sound wave is proportional to the sound intensity and the acoustic power. The pressure amplitude of a sound wave is measured in pascals (Pa) and is a direct measure of the sound energy emitted by a sound source. Atmospheric pressure is the pressure exerted on the earth by the weight force of air. It indicates how much the pressure of sound waves deviates from atmospheric pressure.

Pressure amplitude is a measurement of the strength (amplitude) of sound waves. In this case, the measured sound pressure amplitude P is determined relative to the value P0. This shows once again that decibels are a relative measurement scale. Note that the equation still has one undefined variable in the equation, namely P0. The sound pressure level in decibels for a sound of pressure amplitude P is given by the following relation: The sound pressure level is therefore also a logarithmic variable with a fixed reference value (so we're back to the human hearing limit, 20 µPa at a frequency of 1000 Hz). The sound pressure level, which is a very complicated value on closer inspection, can be translated into the more easily processed decibel scale in acoustics and electrical engineering. At this point, we will save ourselves the in-depth side trip to the realm of atmospheric background and different frequencies. Sound pressure is the difference between the pressure of a sound wave and the ambient pressure of the room through which the sound is propagating (usually atmospheric pressure). It basically boils down to nothing more than measured pressure fluctuations. The sound pressure level is measured using a (measuring) microphone in Pascal (Pa). To understand this, we need to define the term sound pressure level (SPL for short, sometimes just: sound level). Because most dance clubs are around 100 decibels loud. This is however subjective and is also a matter of (unhealthy) habits. That's roughly the threshold of discomfort – things get unpleasant from here on. Most vacuum cleaners are about that loud as well.ġ00 decibels is the approximate volume of chainsaws or trucks driving close by. The noise coming from most refrigerators are between 35 and 45 decibels.Ĩ0 decibels is loud screaming from this level on, continuous sound exposure becomes unhealthy. We have the following exemplary orientation values for “volume”, as measured on the decibel scale:Ģ0 decibels is approximately a ticking clock.ģ0 decibels are sounds of breathing and soft whispering.Ĥ0 decibels is a quiet yet not whispered conversation. The decibel was first used as a scientific unit of measurement in 1924 when Bell Laboratories developed the “Bel Scale,” now colloquially known as the decibel scale.Īn increase in the sound level by 3 dB usually corresponds to a doubling of the sound pressure (i.e. That is why a tenth of a bel has prevailed as the unit, indicated by the prefix deci (Latin for tenth). However, the bel unit is very large for measurement purposes and accordingly too broad and imprecise. The unit is named after Alexander Graham Bell.

Sound decibel scale