7
2
Background Noise
PURPOSE – check that the level of background magnetic noise is
acceptable throughout the intended volume of use.
•
Ensure the loop system is switched off, and all other building systems
and services (e.g. lights) are operational.
•
On the FSM: Select ‘Background noise’ mode.
•
Locate and note maximum reading levels / positions on the Certificate
ensuring the FSM pick-up coil is orientated the same as the hearing aid
telecoils (usually vertical).
If a noisy zone is found a minimum of 30 sec should be taken to
establish a maximum reading. Depending on the electrical environment
and systems in use the noise may be transient in nature and an
extended measurement period may be necessary (e.g. local electric
transport services).
•
Evaluate these levels against the following recommendations:
o
Below -42dB (off scale) is excellent performance for any
installation.
o
Report levels greater than -32dB. Above this level the interference
may be a problem for hearing-aid users. The character of the
noise needs to be assessed before a loop system can be
commissioned or ideally before is even installed.
o
Report and investigate levels greater than -22dB: This is an
unacceptable level and remedial action will be required to provide
coverage in this area.
•
Outline and shade any problematic areas on the floor plan sketch of the
Certificate of Conformity.
•
The
useful magnetic field volume
can be reduced if background noise
can not be controlled sufficiently in particular areas. If coverage of only a
small number of seats is considered to be unacceptable, then an
investigation of the noise source, and possible remedial action may be
required.