Bell
Technical Support
System
Tel 0845 121 4008
(Telephones) Ltd
Fax 0845 121 4009
Web
www.bellsystem.co.uk
Speech Problems
Acoustic feedback:
Loud tone/howl at the
entrance speaker and
phone, whenever the
handset is taken off
hook. Sometimes this
effect is continuous and
sometimes it will vary
with the position of the
handset or appear only
whilst talking.
1. Either or both volume controls are adjusted too
high. Normally both A and B should be adjusted
to between one third and one half of full rotation
to achieve good speech volume without
feedback.
2. The
>
O
=
connection is not properly made. Mis-
connection of the O-line between the speech unit
and the telephone will dramatically reduce the
feedback threshold. Check your wiring for this
fault. If the phone rings or the lock button works
this cause is unlikely (they also use the O).
3. There is an air gap between the speech unit and
the grill. The speech unit must be placed firmly
against the rear of the grill of the entrance panel;
if necessary use packing materials to achieve
this.
4. The Entrance Panel and Telephone are located
too closely together. If the caller can be heard
directly (i.e. without the use of the entry phone
system) then the units are too close!
5. The environment is too noisy. If the entrance
panel is placed in a noisy environment such as
on a busy high street, it may be difficult to obtain
satisfactory volume levels. Try sacrificing the
volume in one direction to the benefit of the other.
6. The entrance panel is placed in an
>
acoustic well
=
.
If the entrance panel is surrounded by reflecting
walls e.g. a basement flat then acoustic feedback
may occur at lower volume levels. Try changing
the position or orientation of the panel.
7. Twisted-pair cable has not been used. The
maximum volume achievable can be reduced
with other types of cable, especially when the
amount of cable or length of runs become
significant.
