Noise acronyms and terminology

Noise terminology and acronyms

Us noise people are fragile souls with a pitifully small sense of self-worth, so to build our egos up a little we like to use loads of terminology and acronyms and other gubbins to make it look like we know stuff that normal people don't and this makes us feel good. What we don't admit is that normal people don't actually want to know this stuff anyway as they have a life. Anyway, as noise assessments are littered with jargon, here is a page explaining what the various bits mean.

APV - Assumed Protection Factor

This is a term used when deciding how much of a noise reduction you can expect the wearer of hearing protection to experience. This takes some account of the user not wearing the protection properly, so for example the plugs may not be all the way in or they may have glasses breaking the seal of over-ear ear muffs. When you see 'APV' being used it gives you a more realistic idea of what users will experience.


This is what is meant by the 'health surveillance' part of the Noise Regs and just means hearing tests. The 'chat about hearing health then hear beep press button' test. Audiometry is the proper term, whereas most people just call it a hearing test.


Decibel. Or a tenth of a bel for the unusually obsessive. It's what we measure noise in and more information on it can be found on the dB(A) and dB(C) page. It's a weird logarithmic scale meaning parts of a dB are tiny so in a noise assessment I always round up or down to the nearest dB as it makes no difference at all to the result, is well within the standard deviation of the measurement and keeps things much easier. 


This is one of your two main limits and the A version relates to the magic 85dB(A) limit. dB(A) measurements mimic how the human ear works - it measures the frequencies which are audible to you. You need to measure this in a noise assessment.


This is t'other main measurement for a noise assessment. As noise levels get louder the way the ear responds to it changes and dB(C) replicates this in the noise meter. dB(C) measurement mostly relates to peak or impact noise, short term stuff where time isn't really a factor so fractions of a second, and it is also for hearing protection calculations. dB(C) relates to the 137dB(C) limit in the noise regs so you also need to measure this in a noise assessment. In a noise assessment dB(C) levels are almost always higher than dB(A).


If you see this one ignore it as it is not for the likes of you. It is an unweighted result and we don't use it in noise assessments.

Integrating meter

You will often see the word 'integrating' given, for example 'integrating noise meter'. To be compliant with the Regs the meter used in a noise assessment must be an integrating one. The 'integrating' bit means it can measure the noise level over time and give you an average, the Leq. Non-integrating ones just give you an instantaneous result of the noise at that precise point in time and are no good for noise assessments.

Leq, (Sometimes La,eq)

This is how you measure the dB(A) limit and is the average over the duration of the measurement. For example, on you noise meter screen you may see 88dB(A) Leq which means this the average over the time you have been doing that measurement. You must have a meter which gives an Leq for measuring dB(A) in a noise assessment. During the assessment you usually keep measuring until the Leq (the average) has settled and is not changing which may take anything from a minute to several hours depending on the work, although more often than not it's at the 'few minutes' end of the scale.

Lep,d (or sometimes written as Lepd, LEP,d, etc.)

This is the eight hour average and is calculated using the Leq you measured. This is the actual result you need from your noise assessment and is what you are calculating for an eight hour exposure. Or to be more precise, what you will use a tool to calculate for you (such as this one at Noisemeters) as only someone brimming with self-loathing would manually do the noise calculations themselves where multiple Leq results are needing to be combined for one day's exposure level. The limit in the noise regs of 85dB(A) relates to the Lep'd.

Noise assessment vs noise survey

Noise assessments good, noise surveys bad. Can't make it any simpler than that. A noise assessment is what the regs ask for while a noise survey is usually a plan of a site with some dB levels noted on it.

Octave band

This is a way of not just measuring the total noise level but breaks the sound down into several frequency bands and gives you the noise level for each band, which can be very useful for assessing the effectiveness of hearing protection. It is not compulsory to do an Octave Band measurement for a noise assessment, but is useful.

Peak vs max noise level

Your noise meter may show Min and Max levels which are the minimum and maximum dB(A) figures recorded in the duration of that individual measurement. Peak is different as this has no time or duration weighting and means the dB(C) figure. Use peak.

Sound Pressure Level (SPL) vs Volume

This is where noise geeks differ from normal people. Human ears hear pressure, not volume, so technically a noise meter is measuring the 'sound pressure level' and noise obsessives often refer to this, whereas people who can go out in daylight and don't sleep with their favourite noise meter under their pillow just call it 'volume'. Generally volume does increase with increasing SPL so when we say something has a noise level of 80dB that's technically a SPL of 80 dB and not a volume of 80dB. But, taking popular understanding and common use of the terminology then it may as well be 'volume' as this is what everyone else understands it as. Throughout the site I've tried to sound normal and just use 'volume', or 'noise level'. For the purposes of this it makes no difference at all to treat the words as meaning the same thing.


This means Time Weighted Average. It relates to the 8-hour 85dB(A) limit and is how Lep,d results are calculated. In effect, Lep,d is synonymous with TWA. Hey, why have one acronym for something when you can have two?

Types or Classes

These relate to how accurate noise meters are, with 'class' now replacing 'type' as the way they are grouped but unless you sleep with your favourite noise meter in bed next to you at night it is perfectly fine if you treat the two as synonymous. There is a page which includes classes of noise meter on this FAQ, but to summarise, you need a Class 2 or Class 1 meter for a noise assessment.