Testing Head-phones

Radio Record, Volume III, Issue 12, 4 October 1929, Page 10

Testing Head-phones

Some Useful Hints thee THD usual method of testing a pair of telephones is by placing the two terminal tags on two different battery terminals, and listening for the loud double click. This is not the best way, for telephones are so extremely delicate and sensitive instruments that to place them directly across a battery in this way is like cracking a nut with a sledge hammer, A bétter test for ‘phones, and one that does not need a battery, is the following :- Place the earpieces over the ears in the ordinary manner, and then take one of the tags firmly between the lips. In one hand take the other tag, and inn, ; the other hand a key, nail, or a similar piece of metal, and rub this gently on the second tag. If the telephones are in good order, noises corresponding with this rubbing will be heard through the earpieces, ; The noises, of course. will not be very loud, for in the absence of a battery, a kind of human electricity is being utilised. So sensitive, however, are 4 good pair of telephones that if they are O.K. the noises will be absolutely distinct and unmistakable. The great advantage of this method is that not only is there no risk of damage to the windings, but by virtue of the small current used, minor faults will be discovered which would be unnoticeable if higher power were used, "Phones should be kept in a dry place, with leads neatly coiled, and if owing to constant use these latter become frayed, bind the affected place with silk or cotton to stiffen ‘and protect it. On no account throw the telephones on ¢0 a table, or drop them on the floor, as a sudden sharp shock of his kind is sufficient to impair the permanent magneto. Finally, it is a good plan to remember that after the phones have been worn for an hour or so they should be wiped carefully with a soft duster to remove perspiration from the diaphragms, which would otherwise rust.