A Novel Loud-Speaker

Radio Record, Volume II, Issue 27, 18 January 1929, Page 28

A Novel Loud-Speaker

For the "Omniphone" Unit.

By

Meghom

H2kn is an easily-built loudspeaker that gives fine quality reproduction, with prominence to bass notes without losing the higher tones, and eliminating any tendency to "scratchiness’ in the latter. This speaker has been designed by the writer to give good volume and quality from any decent amplifier that will give not less than full volume on a good power valve in the last stage. Only the wood case has to be constructed, and in this work there is ample scope for the amateur cabinetmaker, the finished appearance depending chiefly upon his skill and patience. The novel character of the speaker is in doing away with any kind of paper diaphragm, and making the case as a whole do the duty of a cone. The Cabinet. HE accompanying diagrams give all necessary dimensions, the whole being constructed from a piece of seasoned rimu five feet long by 114 inches

wide, obtainable from any timber yard. The dressed thickness should be exactly 8-8in. Solid construction is to be aimed at if good tone is required, and all joints should be fastened with fin. No. 6 brass screws, and also glued in order to make an airtight joint. Constructors who do not possess a glue-pot can use seccotine. It will be seen that the body of the speaker is merely a box of correct dimensions, in the front of which is placed an ornamental grille, The sides

are spaced about 3-16in. from the front edges of the box because the front is to be removeable, and the space is left in order to eliminate any chance of rattle from a loose joint. The front is secured to the top and bottom by projecting strips jin. wide, behind it. The bars of the grille are cut from the 8-8in. board, and are planed up to a width of fin. They should be cut just short of the inside height of the box, and are secured to the inside of the front with a brad at each end. Put on the middle bar first in the exact centre, then carefully measure the spacing of the next two, nailing them in position.

The spacing is 7-8in. The front aperture is a half-circle at top and bottom, joined by a straight line each side. The total height of aperture is sufficiently

less than inside of box to allow roont to fasten the bars (107-8). The back is the same width as the Yr top and bottom pieces, 8} inches, and 4 the height must be made an exact fit after the top, bottom and sides are put together. Glue is applied to the inside edges of case, the back is then pushed in and secured by screws. A. neat effect is obtained by rounding off the edge of the front aperture. It should be noted that the front of the speaker projects beyond the box about jin. each side. Finishing the Speaker. HE outside of the speaker is finished according to taste, with Leonart walnut stain, shellac, or other medium, whilst the interior should be painted black. When all is dry, the Omniphg, unit is hung inside the back of the b so that the end of driving spindle rests against the centre. The shaped "foot" is secured to the wood by means of a small piece of coarse cloth, or webbing folded to two or three thicknesses and secured at each end by a 4in. screw and washer, leaving the unit free to find its level, resting against the back. The best effect is obtained when this speaker is hung on the wall, the projecting pieces at the back leaving a clear inch space in order not to deaden the vibrations. Its appearance is similar to that of the familiar boxedin cones, and its performance is equal to some and better than many. If quality is not produced by this speaker, it is a sure sign that the amplifier needs improvement, as the utmost clarity of speech is obtainable if the amplifier can supply it. If constructors have any difficulty » in procuring an "Omniphone"’ unit! locally, they should write direct to the Rodger Importing Co., Ltd., 159 Manchester Street, Christchurch, the price being 30/-, plus postage.