LOUDSPEAKER HORNS

Radio Record, Volume I, Issue 25, 6 January 1928, Page 14

LOUDSPEAKER HORNS

THE EXPONENTIAL TYPH. A correctly designed horn makes a very good type of loudspeaker. ‘Ihe best horn is oue which radiates most uniformly over the required range of frequency, and it has been proved mathematically that the expouentially shaped horn conforms closely to this requirement. A horn is of the exponential type .when its cross section arca doubles at equal intetvals along | its length. For example, a liorn would would be of the exponential type if at the orifice it had an area of 4 square inches and an aieu of $ sqnare inches, 1 square inch,~-and 2 square inches, at distauces of 1, 2,.and 8 feet respectively from the orifice, ‘The rate of expansion determines the lowest frequency of which the horn will be a good sound producer. A horn which doubles in area every foot will reprofluce down to about 6! cycles, and a horn which expands twice as rapidly will only renrodnce weil down to 198 cycles. : Correct Measurements. ‘A properly designed born should be free from noticeable resonance, and to prevent this the month of the horn should be made large enough to transmit the sounds coming from it without auy gréat amount of back pressure. In the design of loudspeaker horns it has been found that, if the mouth is made coinparable io + of the wave-length corresponding to the low fiequency cutoff point of the liorn, the resonance in the horn wil! be negligible. The wave-length in feet is determined by dividing the velocity of enund in fect per second, which is 1120, by the frequency. Vor example, a horn whose cut-off frequency is to be 82 cycles, corresponding to a wave-length of 39 feet, should have a month of 89 divided by 4, or 94 féet, These facts indicate dcfinitely that a horn, to he a good one, must. be large, Small horns, whether they are or are not exponential, cannot radiate the low frequencies. The horn makes it possible for a comparatively small diaphragin 1o get a good grip on the air and thereby produce a large volume of sound. The small diaphragm and the large liorn nay be replaced by a large diapliragin, as is done in a cone type loudspeaker. The material of which the horn is made is important. Although a liorn may be well designed, and constructed to the correct size, total length «nd expansion per unit length, it inay still fail to give really good results because’ of resonant effects in the material used in the construction. The material used should have no maiked reasouant ‘reyuency unless it is very low, where it might help to increase the low note radiation. ©