Induction Loop Disadvantages
Installation costs may be high
Installation may not be possible in historic buildings
Can’t assume everyone will have a T-coil
Susceptible to electrical interference and spill over
Must sit around looped area
May be dead areas within loop
Notes:
Installation in classrooms may be high if put in after the building has gone up. For example, carpet may be torn up to cover the wire so that it will not be a mobility hazard. It can actually be installed in the concrete floors or walls of a building. (In fact, because distance makes a difference, if possible it is best to install the wires about 3 ft. above the floor. This is about ear level when you are seated.) Obviously this is much less expensive if done while the building is first being constructed. This type of installation may not be possible in historic buildings, where the structure cannot be altered.
Induction loops (and therefore T-coils, by the way) are susceptible to spillover and interference of other objects that create EMF. (Induction loops would not be the system of choice in a computer lab!) Sometimes simply changing seats will help reduce the interference.
There may be some instances where only an area of a room is looped. This may be because of the size of the area. Large areas require carefully placed multiple loops in order to avoid dead spots in the center of the looped area. In any case, the individual must sit within the looped area.
Finally, not everyone will have a T-coil. Some receivers must still be kept on hand. (It is a good idea for service providers to have these receivers on hand, anyway, as a way to hook in headphones and test the loop system to see if it is working.)