E2S demystifies decibel levels

How loud is very loud? The signal company tries to explain
Publish date:
Updated on

E2S Warning Signals, a manufacturer of “high-performance audible and visual signals for commercial, industrial, marine, onshore and offshore hazardous locations” with offices in the UK and US, has published an educational guide that seeks to ‘de-mystify’ the dB (decibel), one of the most common units in engineering, “yet also one of the most confusing”.

“The main difficulty in comprehending dB measurements,” says E2S, “is that it is a log-linear scale, which, while it is very useful in representing very large differences in a more user-friendly scale, also compresses the scale. Sound is defined as any pressure variation that can be heard by the human ear.

“The threshold of hearing is defined as 0dB [SPL]; the threshold of pain is around 130dB [SPL], a scale that can be readily understood. However, as the power difference between the two levels is 1013 : 1, or, to spell it out in full, 10,000,000,000,000 or ten million million to one, expressing it in these terms suddenly gives a much better idea of the change.”

The guide is all based around the company’s products, of course, but nevertheless it’s an interesting read for the curious or the concerned. For example, the A151 disaster warning sounder is rated at 150dB SPL, the same as a jet engine at 1m. It also discusses the effect of frequency on perceived loudness and includes some rules of thumb for system designers who are specifying the output and location of warning sounders to provide the desired sound levels as part of a warning system.



Headphone level control - monitoring versus limiting

Technology has allowed higher and higher sound levels to be produced at better and better quality over the past 20 years but more recently there has been a realisation of what this can do to people's hearing. The European Commission acted on this in 2003 by issuing a Directive to harmonise noise control legislation across Europe, which led employers in broadcasting, live music and industry to consider how to protect both staff and the public. In broadcasting, limiter circuits on headphones have been a first line of defence but, as Kevin Hilton reports, a new approach is being taken for location filming.


Loudness or level?

In this week's feature the Prof looks at normalising and maximising, and how 'loudness wars' are having a negative effect on reproduced sound