The decibel scale works on a logarithmic basis. You might assume that a speaker playing at 100dB is twice as loud as a speaker playing at 50dB, however, this is not the case. Logarithms (or logs for short) are simply a way of describing numbers which vary by very large amounts in a much smaller range. So, a sound that is 100dB on the scale, is louder than one that is 50dB. Just about every piece of audio equipment (microphones, loudspeakers, sound cards, amplifiers, mixers, etc) will have specifications expressed as logarithms (i.e. The Decibel Scale You may have noticed that when people talk about the loudness of a sound, they describe it in units of decibels rather than watts per meter squared. We need to get familiar with the idea of a logarithm. The decibel is a better fit to how our brains perceive sound. The relationship between perceived loudness and the decibel is a straight line. On the next graph below, a logarithmic decibel scale is used and now the curve becomes a straight line. Our ’10x’ rule means that as the overall level increases, we need increasingly large changes in intensity to get a similar change in loudness. An intensity of 1,000 is also half as loud as an intensity of 10,000. So an intensity of 1,000 is twice as loud as an intensity of 100. To make a sound twice as loud, you need to multiply its intensity by about 10. In the graphs below, the x-axis represents the perceived loudness of a sound, and the y-axis represents the acoustic intensity needed to create that loudness.

After analysis, I could offer various recommendations to rectify the issue − all distinctly individual from each other, as acoustics can be affected by nearly everything!” Rob Bungay, Acoustic Consultant, WSP What are decibels? To understand and try to reduce these causes of complaints, among other things I installed sound level meters throughout the room to record noise levels during the day and night, and used acoustic models of the space to assess changes within the room. “I recently worked on a multi-bed intensive care ward where patients and visitors were complaining about the intrusive noise made by the alarms from bedside monitors. In acoustical and audio engineering, decibels are used everywhere because knowing how loud a sound is important whether you’re assessing whether the noise from a new road is going to be a problem or setting the loudness of music in an arena. Graphic: Nick Maroulis Where are decibels used? number of decibels 10 × log(P 1 P 0) For sound we need some agreed intensity as a reference value. Instead of having a loudness scale that stretches from the threshold of hearing to a value that is one billion times greater, the decibel scale goes from 0 dB to 140 dB. When a sound is perceived to double in loudness, this corresponds to roughly an increase in 10 dB. The logarithmic scale compresses the range of loudness values. It makes things easier if a logarithmic scale is used this is what the decibel scale is.

The ratio of intensities between silence and ‘ow that hurts my ears’ is about 1:100 million million. The human ear is capable of hearing very quiet (low intensity) sounds and extremely loud (high intensity) sounds.

Loudness and decibel scale