A loudspeaker generates sounds by causing some part of the reproducing unit to vibrate at frequencies corresponding to those in the microphone diaphragm. This vibration in the speaker unit can be imparted to the surrounding air in two ways, thus separating loudspeakers into two general classes depending on the method used.

The first and oldest is the horn type, in which a driver unit equipped with a diaphragm capable of reproducing sound of high intensity is coupled to the surrounding air through a speaker horn or trumpet. This horn, to be efficient, must be designed so that the sound waves expand uniformly as they pass through the horn, without reflections or compressions.

This type of speaker offers a sound conversion efficiency of 15 to 25% and is an excellent reproducer for large outdoor gatherings. At first these horns were used chiefly for outside permanent installations on account of their ability to cover large areas. Because of their length of 5 to 6 feet, they were not well adapted to portable hookups.

Later folded or reflex horns are much shorter in length, but offer about the same air column. The air waves travel out from the reproducer unit about, one-third the way and are then returned by an inside reflecting chamber back to the reproducer end of the horn and then through the horn flare. This gives about the same result as the long horns, with about one-third the length.

The second general class of speakers consists of those in which sound waves are produced by a large vibrating cone known as a direct radiator, instead of by a small diaphragm. This type is most generally used today where the sound demands are not too great. It is much less efficient than the horn-type radiator (5-15%), depending on cone and magnet size and type of baffling. Used for indoor installations.

As both the horn and direct-radiator speakers operate on the dynamic principle, a strong magnet field is required in their design. Formerly, this field was obtained by a field coil through which direct current passed, either from the amplifier or a separate power supply.

However with the advent of new alloys capable of being magnetized to a much higher degree than steel, the , electromagnetic dynamic speaker is fast giving way to the permanent-magnet type. The PM dynamic speaker offers the following advantages: It requires less space, needs no electrical energy source, is free from hum and requires but 2 conductor cable to connect it to the amplifier.

MOUSEHOLD AERODROME 1938 - MARCONI OCTAGONS

VITAVOX 75" HORN

VITAVOX 20 WATT DRIVER UNIT

Marconi Sound Projectors

The Small Sized S.P.G.I. has sufficient power to fill a fair-sized dance hall or to address an audience of 5.000 people. It is fitted with a moving coil of approximately 2 cms diameter. The moving coil will carry for a considerable period an alternating current of o.6 ampere-about 4 watts.

Sound Projector installed on board ship enabling 3rd Class passengers to listen to the orchestra.

The Large Sized S.P.G.2. is sufficiently powerful to reach an audience of 20,000 people in the open air. It is fitted with a moving coil of approximately 5 cms. diameter. The moving coil will carry for a considerable period an alternating current of I ampere- about 10 watts.

The field coil of S.P.G.I. is connected to a 6-volt battery, and takes about 1.8 amperes. The field coil of S.P.G.2. is connected to a 6-volt battery, and takes about 3 amperes. The magnetic flux is approximately 9,500 lines per square centimetre.

Valerie Hobson at the Carlton Cinema Norwich 1960's

It supplied the Roxy speakers for the first talking pictures in cinemas and the speakers for the cinema in the liner 'lle de France'. Its speakers were used at the British Empire Games, the Aldershot Tattoo, and
Kidbrooke Park. They were used for the Coronation of King George V1 and Queen Elizabeth in Westminister Abbey and also at the wedding of the late Duke and Duchess of Kent when the Duke of Windsor, then Prince of Wales, was best man. Sir Alan Cobham used Vitavox speakers at his Flying Circus displays throughout the country.

Each of these venues presented the problems peculiar to large areas, either open or enclosed, with a paramount need to overcome distortion and provide a true and clear sound. It is to solving these sort of problems that Vitavox has devoted much research and continues to do so.

ROXY HORN

Roxy Cinema Horns

Folded Exponential Horn Type M Specification Air Column, 11 feet 1 inch long Height, 5 feet, 2 inches Length, 6 feet, 2 inches Depth (front to back), 2 feet, 6 inches Flare Opening, 5 feet x 3 feet, 4 inches This Horn is designed for Cinemas, Seating up to 700 (1931).

Folded Exponential Horn Type R Specification 2 Air Columns, each 11 feet, 6 inches long Height, 5 feet, 6 inches Depth, 2 feet, 4 inches Flare, opening, 5 feet x 4 feet, 3 inches This Super Horn is designed to Cover 2,500 seats

One sector which has always demanded the highest possible standard of design and manufacture is the Royal Navy. The Company carried out its first work for them in 1933. designing and manufacturing microphones and loudspeakers. The Navy has been one of its largest and most consistent customers ever since that time, reaching such high proportions in the war years of 1939-45 that company staff were working twenty hours a day, seven days a week with a greatly increased staff, in order to supply them with thousands of microphones and loudspeakers they required.

Len Young's belief that there was a big future for sound reproduction equipment in the world of popular music has proved to be very true, The popular music boom began in the pre-war night clubs, the first to use Vitavox microphones and amplifiers was the famous Kit Kat Club, where the Joe Loss band was resident.

After the war, the Company set out to establish itself internationally in the new growing 'Hi Fi' market and succeeded in doing so at the upper end of the quality market. At this time the Company also achieved one of the biggest 'hi fi's' in its history, supplying loudspeakers for the great Todd-AO cinema installations.

The Services, the railways, coastal authorities, industry generally-all requiring more perfect sound reproduction and loudspeaker facilities with a greater range of increasingly complex units.

Since the nineteen fifties the Navy, Army, and Air Force have needed increasing power and experimentation in the production of more robust and powerful speaker systems for their use is continuous . The requirements range from very powerful loudspeakers for the RAF for laboratory sound vibration tests on components, to speaker developments for the latest naval frigates, command cruisers, destroyers and mine hunters.

Len Young, worked as Chairman of the Company until his death in 1974 having seen his sons, Neil Young and David Young appointed respectively as Managing Director and Technical Director in 1969. This was no case of nepotism, as both sons worked up through the Company since 1961.

BOAC Hanger 1960's

TYPE 550 SERIES MULTICEL HORNS FOR USE WITH 20 WATT PRESSURE UNIT 1960'S

Throughout its history, Vitavox has attracted the Finest brains in the industry-Bill Beresford, Works Manager for the first twenty years; Tom Mogdridge, Technical Manager from 1937 to 1969; John Maunder, who established Vitavox at the upper end of the international quality 'hi-fi' market in the nineteen fifties and Harold Blunden, who joined in 1937 and who was still leading the Company further into the
European music and entertainments industry when he died in 1973, are but four of the many who have guided Vitavox forward through the years.

K15/40 CONE TYPE LOUDSPEAKER 40 WATTS 1960's

The whole range of Vitavox naval loudspeakers are for upper or lower deck use and designed to meet the most stringent requirements of the maritime defence industry. They are fully watertight and shockproof.

Type 220 series Cell Combinations

TYPE 220 SERIES MULTICEL HORNS FOR USE WITH GP.1 20 WATT PRESSURE UNIT

Naval Loudspeakers.

Two 10 watt and 1 1watt loudspeakers for main broadcast,and intercom as well as a 150 watt power column, all proof against weather, gun-blast, and shock.

VITAVOX HAILER LOUDSPEAKER HEAVY DUTY NAVAL PATTERN 10 WATTS 1960'S

Royal visit to South Africa 1947

In connection with the Royal visit to South Africa, special loudspeakers have been installed in the Royal suite in H.M.S. Vanguard. These loudspeakers have been manufactured by Vitavox Ltd., and the photograph shows the cabinet, in light oak, which has been made to match the panelling in the sun lounge. The speakers are arranged for bulkhead mounting, the moving-coil loudspeaker units are of the Vitavox K12/10 type.

THE VITAVOX CABINET LOUDSPEAKERS MADE FOR THE ROYAL VOYAGE

H.M.S. Albion Prepares for Far East 1962

First pictures of H.M.S. Albion since commissioning as Royal Navy's second Commando Ship. They were taken during her recent Trials and work-up before leaving for the Far East Station to relieve H.M.S. Bulwark in November. Flight Deck scene as Royal Marines of 41 Commando dash to their helicopters .

H.M.S. Raleigh 1975

This year the sound of Vitavox will ring out from Tor Point in Cornwall, where Vitavox loudspeakers are being installed to relay recorded martial music for the drilling of the ratings at this famous Royal Navy training Base. The installation is a sophisticated combination of the static and mobile, incorporating Lightweight Hailers, Bass Bins, and Multicell Horns.

DRILLING AT FAMOUS NAVY BASE

WEATHERPROOF LOUDSPEAKER

VITAVOX HAILER LOUDSPEAKER

Heavy duty universal microphone support

Dynamic Microphone Inset

AK 120 Loudspeaker

BP.28 10 watt Beam projector loudspeaker

A friend and colleague - Bob Henderson of Henderson PA, 1947

Before the days of Broadcasting, good wireless telephones were very sensitive and comparatively expensive. The high-resistance type were wound with an enormous number of turns and depended for their remarkable sensitivity on a certain amount of mechanical and electrical resonance in the neighbourhood of 1.000 cycles per second.

On the introduction of Broadcasting, the same telephones were used, and they were obviously unsuitable. The modern headphones are much improved acoustically, but whether sufficient attention has been given to the response/frequency curve in every case is open to question. No doubt the necessity for a low price is largely responsible for this.

Recently, a capacity type of telephone earpiece has been developed on the Continent, which gives excellent reproduction of the extreme ends of the frequency scale, but suffers commercially from the fact that the necessary input is many times that required for the ordinary type of headphone.

The design of loud-speakers has presented more difficulties than perhaps any other part of the broadcast receiver. The most outstanding difficulties have been the suppression of strong mechanical resonance effects, and the accurate reproduction of frequencies below about 200 cycles per second, especially when they have, as is usual, a complex wave shape.

The necessary mechanical displacement of a diaphragm for accurate reproduction increases with a reduction of frequency. This fact in itself makes the design of the conventional type of loud-speaker with steel armatures and wound magnets difficult owing to the large movement necessary for the lower frequencies.

Again, if a high frequency is superimposed on a low, the former may be distorted owing to the fact that the armature is not at a constant mean distance from the magnets so far as the superimposed higher frequency oscillations are concerned.

Marconi Energized 1933

Diaphragm and Horn

Nevertheless , the vast majority of loud-speakers in use by the public are of the diaphragm and horn type, but most of these lack the lower frequencies to some extent

A diaphragm of the type used in loud-speakers is bound in itself to have one or more resonant frequencies, but the damping effect of the air column contained in the horn reduces the resonant effects to a large extent if the whole instrument is carefully designed. Howeve,r a large amount of compromise in the design of the models sold to the public.

There is, however, an entirely different type, which is very widely used in America. This loud-speaker consists of a magnet system, which may be of the "permanent" variety, or it may be energised by a special winding. The air gap is annular, and in this coil of wire is suspended with freedom to move backwards and forwards along its own axis. To this coil is rigidly attached a cone-shaped diaphragm.

These moving parts are held in position by a circular strip of some very flexible material, such as rubber, one edge of which is attached to the outer edge of the cone, and the other to the inside edge of a circular metal flange. The coil and cone move together, and the only resistance to movement, apart from air damping, is that exercised by the rubber strip, but this should be negligible. The input is applied to the moving coil by flexible leads.

In general, this arrangement has several advantages over the metallic diaphragm or reed type apart from commercial considerations. In the first place, the force exercised by the magnetic field on the coil does not vary largely with the exact position of the coil in the air gap. Again, the resonant frequency of the moving parts as a whole can be made very low, in fact in the neighbourhood of the lower limit of audibility, while the mechanical construction allows the diaphragm to move through the large amplitudes necessary for the reproduction of the lower frequencies.

In general all loud-speakers are extremely inefficient from the power point of view, and it is interesting to note that if an instrument could be devised which converted all the electrical energy supplied to it into sound-wave energy, the effects of resonance would disappear.

It would seem, however, that the essentials of design of loud-speakers as well as receivers are being realised more generally, so that in the future we may hear much less frequently the too common remark that "loud-speaker" reception gives too much distortion.

Marconi with matching transfomer 1935

Pickup arms 1930's

Early Philips loop system receiver and earpiece 1960's