![]() The A-weighting was based on the 40-phon FletcherMunson curves, which represented an early determination of the equal-loudness contour for human hearing. These figures demonstrate just how important it is to use the correct unit. Deficiencies A-weighting is valid to represent the sensitivity of the human ear as a function of the frequency of pure tones. This unit has a sound power level of 73.8 dB(A), or 92.4 dB, or NR 72, all of which are describing the same noise, or same sound power level. To take an example, let’s look at a commercially available 100kW air conditioning unit. That’s why it’s so important to state the unit clearly and correctly. It’s important to realize that all these methods of defining a sound level are describing the same thing, but the figures themselves differ dramatically. The A-weighting is the most common rating used in industry, but we occasionally also find the Noise Rating, or NR. Both sound power and sound pressure levels can be A-weighted, that is, stated in dB(A). A-weighting adapts measured sound levels accordingly to reflect the response of the human ear. ![]() Human beings perceive tones of different frequencies as being of different loudness. Here I’ve just provided you with an introduction. We won’t go into this logarithmic addition process here - that would be too much for this blog. These individual sound levels are added together using a logarithmic scale to determine the overall sound level. More often than not, youll see A-weighted decibel limits. They both measure SPL but use different frequency curves to weight the reading. When acoustic (calibrated microphone) measurements are being referred to, then the units used will be dB SPL referenced to 20 micropascals 0 dB SPL. We also call these A-weighted and C-weighted decibels. A-weighted decibels are abbreviated dB(A) or dBA. Sound levels are mostly stated at the frequencies 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, and 8kHz. Decibel readings for music are typically done with two different measurements: dBa and dBc. Those of us who can read music or play an instrument know our way round octaves. ![]() To present this in figures, it is commonly divided up into so-called octave bands. Altogether, these make up the frequency spectrum. Sound therefore consists of tones with different frequencies. I like this! And high-frequency noise is what you experience when you’re woken from your Saturday nap by your neighbor urgently sawing wood with a buzz saw. Many of us are familiar with low-frequency sounds from good concerts where you not only hear the bass, but feel it in the pit of your stomach. This subject is somewhat complicated, but I will try to describe it in simple words without falsifying the facts.Ī noise consists of low, medium and high frequencies. We assess the quality of things, other people’s work output, car damage after an accident, and we don't shy away from assessing noise levels either. Humans are champions in the assessment of things. ![]()
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