Laboratory Jottings

Radio Record, Volume II, Issue 53, 19 July 1929, Page 30

Laboratory Jottings

Af A. SMYTH, Ltd., Victoria Street, ° Wellington, have in hand -units for the linen diaphragm speaker described in our column last week. These are the original units that were used with .the speaker, They have one made up, and the writer was able to hear this'performing. «It proved to be an excellent speaker, reproducing. the bass with pnusual fidelity, while the top notes were very clear. A wide range of frequencies ‘are covered in this manner,’ and the, speaker being very simple to’ constr uct, should appeal widely to amateur constructors. : Electrolytic Condensers. HE: greatest number of electrodynamic speakers at present ‘on the market and operated from a sixvolt source require approximately 4 ampere of current. If this is drawn directly from an accumulator, a fairly. heavy drain is placed. upon it and constant recharging is necessary, Most battery operated -sets’ have as an acCessOry a trickle charger supplying about 4 ampere. This is an admirable source of current for thé dynamic speaker,-and when not in use ¢harging the battery, the charger can be applied to the field winding of, _the speaker,

In most cases a strong hum will be noticeable, but this can be very easily eliminated by connecting an electrolytic condenser between the two terminals of the charger which are connected to the field windings. Johns, Limited, Auckland, have sent us one of these for test, ‘and wé are able to _Say definitely that it. will. eut out dynamic hum. For some considerable time now .we have’ been working "a speaker: ‘under these conditiqns, ‘with perfect results. Ferranti Speakers. WE have received from A.. D. Riley, Ltd., one of their latest Ferranti ‘ speakers,. and have been -able. to test this under all conditions. The speaker is‘of English make and of the -smull curled ‘exponential type. It is finished in a dark brown crystalline and ‘is provided ‘with a large unit with’ an adjustable screen. The tone is quite good for this type of Speaker, dnd the range of frequencies covered causes it to compare favourably with our standard horn speaker. It is very sensitive- and: will. stand- ample volume for the average household.