Lowther-Hegeman

INTRODUCTION Horns have been in use in one form or another for the distribution of speech and music for many centuries: for instance, Alexander the Great had enormous horns to summon his vast armies, whilst today horns are invariably used in Public Address systems to marshal! crowds of many thousands. 

In the earliest days of the phonograph, horns were used for recording and reproduction purposes and now with the electroacoustic era, horns are once again in evidence, and most schools of thought agree that they are ideal for the reproduction and distribution of speech and music. 

Lowther-Hegeman front


Horns were further called upon by Acoustic Engineers for domestic use, but due to their large dimensions were considered impracticable: full use, however, is made of them in cinemas and auditoriums. 

The Acoustic Engineer has always sought for ways and means to use this principle for speech and music; for example, Voigt and Klipsch have excellent loudspeakers of their kind (descriptions of these speakers are dealt with in other literature), but though these two particular systems, as well as a few others, arc successful, there seems to be a great gap between their reproduction and the original, inasmuch as these may have a "distant" or heavy effect (unbalanced). 
 

Lowther-Hegeman rear


The Lowther Company used the Voigt Domestic Horns as a standard loudspeaker for a great many years, but realize that with new materials and techniques now known and available, greater realism can be attained. 

In 1947/48 the introduction by Lowther's of the P.M. 1 (19,000 gauss), closely followed and superseded by the now famous P.M. 2 drive unit (19,500 gauss) for horn loading, marked a great step "towards perfection", the electro-magnet drive unit having been eclipsed in its class by the permanent magnet unit with increased efficiency and improved overall performance. 

Lowther Drive Unit PM2 or PM4

Drive Unit Type P.M. 2 or 4


The P.M. Units are robust in construction, employ anisotropic magnet alloy (Ticonal G); diaphragm and cradle are cast aluminum, detachable as one unit; body housing stand affords short circuit protection for the magnet, mounts the moulded two-pin socket for speech connecting plug. The special shape of the magnet (patented) is of considerable importance, enabling such magnetic force to be derived from so small a mass. Another important feature is that the pole faces are run at magnetic saturation, important because the speech coil does not move in a field of unequal density which would otherwise cause distortion. 

The diaphragm is of 6 in. twin cone aluminum speech coil design, having compliances throughout its system, i.e. major cone, inner cone and speech coil, in enable a wider frequency range to be obtained with one assembly. 

THE DRIVE UNIT (P.M. 4) The development, also in 1948, of the prototype Lowther P.M. 4 driver with 23,5OO gauss, and now its release at 24,000 gauss establishes an all world record of performance and at the same time a further step "towards perfection". This increased magnetic efficiency, affording greater damping, together with a change of speech coil construction, gives improved frequency response, transient and decay factor performance combining to form the heart of a hi-fi reproducer of unequalled characteristics. 

THE HORN There yet remains the problem of utilizing the remarkable performance and high efficiency of the Lowther P.M. 4 drive unit to its full advantage. 

In conjunction with Hegeman Laboratories, N.J., U.S.A., a very ingenious compound manifold horn system was designed. 

Lowther-Hegeman top


Based upon orthodox principles, offering horn loading lo the Lowther P.M. 4 drive unit from the highest overtones to the lowest notes, broadcast or recorded, a further remarkable achievement is made, culminating in the reproducer known as the Lowther-Hegeman. 

This reproducer type "W" gives sound distribution over 180 degree and can be positioned where desired. 

Lowther-Hegeman plaster horn


By careful choice in parameters of the horn sections high efficiency has been attained over the audio range, phase differences are at a minimum and for all practical purposes time constants is zero, wide angle distribution without beam effect is a material and a pleasant feature. 

The middle end higher frequencies are covered by dual outlet double rate flare horns, the mouth acoustical impedance of the small horn is the throat acoustical impedance of the second section. 

The bass folded horn is operated by the rear of the diaphragm, special steps being taken in both design and construction to give freedom from resonance over the lower octaves.

Lowther Lowther-Hegeman horn


PERFORMANCE OF THE LOWTHER-HEGEMAN REPRODUCER To describe the differences between any two hi-fi system is, we believe, beyond the scope of man; factors alone involved in attempting to form such an opinion are too numerous in themselves and too complicated to know where to begin; we will therefore confine our remarks to the principle and achievements of the Lowther-Hegeman Reproducer. 

Design features mentioned above seem to have covered the salient and desirable points, but there remains a feature more necessary for "towards perfection" reproduction if an illusion of the original is to be attained. This is to maintain correct relationship between fundamental and harmonics of the original sound. 

Instruments of the orchestra are recognized for their tonal qualities by the various degrees of their harmonics or overtones, similar instruments are distinguished by yet a further minute change of this relationship or percentage variation. 

Employing only one Lowther P.M.4 drive unit this objective is possible. When two or more units are used the complex wave-form is dealt with by more than one section or units having entirely different time constants, quite apart from frequency characteristic deviations, including possibly a cross-over network, the relationship is therefore changed, retarded, emphasized or even advanced at different points, besides being changed yet again at various volume levels. 

Ribbon or pressure type units are commonly used to improve the "hi's"; this is similar to requesting a "sprint cyclist" to assist a penny-farthing cyclist in making his performance more spectacular, they neither start nor finish together! 

The Lowther-Hegeman Reproducer has only one basic time constant and covers the entire audio range, thus giving a remarkably live, forward and natural performance. The efficiency of the overall system being such that even at a few milliwatt input level complete balance is maintained. 

As one critic remarked „it is usual to listen in a darkened room for ethic illusion, but with the Lowther-Hegeman Reproducer in broad daylight the feeling of presence is there all the time." 

PM4a



Christine von Langa - Roedlas 54 - D - 91077 Neunkirchen a. Br. - Phone +49 (0)9192 996926 - E-Mail: listen(at)wolfvonlanga.com -
WOLFVONLANGA produces unique field coil loudspeakers and drive units. As a manufacturer we solely use the highest quality materials.
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