Under Health and Safety regulations, employers are required to reduce the risk of damage to the hearing of employees from exposure to noise to the lowest level reasonably practicable. Noise is generally defined as unwanted sound and regulations concentrate on the control of noise. There are, however, sounds which are not unwanted but can be at such a level, sometimes unwittingly, as to present a risk of exceeding an individual’s daily personal noise exposure recommended level. Such a situation can arise from the use of headphones worn for long continuous spells whilst generating high sound levels. One BBC designed solution to this problem is the Headphone Limiter.
The small units are designed to protect headphone users from the effects of harmful sound levels. The units are powered from the incoming audio signal and are available in several different versions, to suit a wide range of different headphone impedance/sensitivity combinations. They may usually be set to limit the SPL in the range 85–110dBA.
The limiters are manufactured for Canford Audio under a BBC licence and are supplied fitted to a chosen pair of headphones and calibrated to a defined SPL. They are not available separately, due to the requirement for specialised calibration equipment.
Technical Specification:
| Input: |
Audio frequency signal balanced or unbalanced, maximum 17V rms. |
| Output: |
As input, undistorted until onset of limiting. Insertion loss varies with calibration conditions. |
| Sound limiting level: |
Typically 85–110dBA, tolerance ±2dB. (Note: Not all levels are achievable with some headphone types). |
Notes:
Headphones need to be individually type assessed to see which limiter is best suited. Assessment of a headphone not previously investigated and documented by Canford is undertaken subject to a fee. There is no charge where the headphone or headset has previously been assessed for the fitting of a limiter set to the limiting level specified. The limiter is fitted 200mm from the plug, unless otherwise specified. The fitting and calibration charge does not include changing or fitting a plug (other than that normally supplied under the stock code) on the headphone or headset; if this service is required, a quotation will be offered against a specific enquiry. Orders are required in writing, work cannot proceed until written confirmation of specification is received.
A range of headphones and headsets are available as standard products with limiters fitted inside the earcups, see CANFORD LEVEL LIMITED HEADPHONES. Please contact Canford’s Tech Support team ( techsupport@canford.co.uk ) for further information on fitting limiters not covered in the standard product range.