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Two great inventions formed the basis of our modern sound technology.
Alexander Bell famously invented the telephone, but what was more significant is that in doing so he invented the microphone, and so converted audible sounds to electrical signals for the first time. In applying these signals to the telephone's earpiece he was also the first to convert them back to sound again. The patent for the telephone was granted on 7th March 1876.
We are now so accustomed to modern sound technology that we almost regard a sound, and the electrical signals which represent a sound, as being much the same thing. For the time being the telephone technology played no part in sound recording but the invention was there waiting to be developed later.
Edison invented the phonograph around 1877, but the great thing about this is that it was the first time anyone had recorded sound to make it playable again. In fact the phonograph was entirely mechanical and did not involve representing sounds electrically. It did not even use a motor to turn the mechanism. It was hand wound.
The first viable electric motor was designed in the early 1870's but not used in sound recording for some time.
Around 1887 German born Emil Berliner, now living in the USA, invented the phonograph disk as an improvement to Edison's drum phonograph. He called the apparatus the Gramophone. One big advantage of a disc over a drum was that it facilitated the duplication of disks from a single master and Berliner pioneered this technique. Another advantage of discs is the compactness of the storage medium, which may have contributed to its greater popularity.
The very first disks were still recorded entirely mechanically from the vibrations of the sound, and the resulting manufactured disks were also played back entirely acoustically. There was still no such thing as electronic amplification and the small electrical signals used in the telephone were of no use in recording. At this time there was really no connection between the two technologies.
The 78 rpm disk became standard. It was 10 inches in diameter made initially of shellac and later a hard plastic material was used. The discs were brittle and fragile.
Around 1900 Danish engineer Valdemar Poulsen
invented a type of recorder to record speech on steel wire which was called
the telegraphone. This was quite an achievement because it was done before electronic
amplification was available. It basically used the type of technology used in
telephones. Sound was picked up by a microphone, and an electromagnet was used
to magnetise a thin steel wire (approx 0.01 inches in diameter) which moved
at high speed (7 feet, or 84 inches, per second). It could record 30 minutes
of sound. Its potential was for use as a telephone answering machine. It was
an alternative to the phonograph and said to have higher sound quality with
less noise. The telegraphone was not a commercial success.
Amplification of the small electrical signals representing sound only became possible with the development of the thermionic valve or vacuum tube, and even then only with the later developments particularly by Lee de Forest.
Edison was one of the first to notice the phenomenon that under certain conditions a current would pass between electrodes in a vacuum tube, but did not develop it further. This is known as the Edison effect.
English physicist Sir J. J. Thomson (Joseph John) did some work on this around 1897. English electrical engineer (Sir) John Ambrose Fleming designed a tube called a diode which could rectify an alternating current and hence had application in detection of radio waves. It was patented in 1904.
The great breakthrough which made amplification possible was when the American Lee De Forest developed the diode further in 1906 by adding a third electrode (later called the grid). This was the first triode and was patented in 1907. He called it the Audion.
Picture of an Audion.
Note the similarity with an electric light bulb and the Edison screw fit for the connections to the filament.
It seems that de Forest was not seeking to achieve amplification. He was experimenting on ways of improving the detection of radio waves.
The diode had been applied in radio receivers and initially the audion was used similarly, but as a kind of enhanced detector. One account says "For some years the audion was used only as a detector for radio telegraphy".
Later De Forest realised the potential of the audion as an amplifier. A small electrical signal on the grid could control a larger signal through the valve. One of the first applications was as a repeater for long distance communications.
The next important step was made by Fritz Lowenstein (USA). He found that
adding a negative bias to the grid improved the performance significantly. It
was probably Lowenstein who developed the first audio amplifier as a result
of this in about 1911. Early electrical engineer Lloyd Espanchied said in 1973,
"Fritz Lowenstein, here in New York, had early in 1911 made De Forest's
audion into an amplifier before De Forest ever did".
Click here to see the circuit diagram of an early audio amplifier
Various loudspeakers had existed before amplification, usually using a horn to get the maximum sound from the very small audio signals available.
Sound amplification developed further and together with developments in loudspeakers and microphones early public address systems were developed.
In the early 1920s amplification was used to improve the recording of gramophone discs. The sound was picked up by a microphone and then amplified to a level which could drive a transducer to cut the disc. This made it possible to record quieter sound sources, and without the need to play sounds very close to the recording machine.
There was probably a simultaneous development of technology which could replay discs with amplification but notably these were not used by the ordinary buyer of gramophone records. One use of amplification for playback was in the cinema and much work was done in trying to develop methods of playing sound for use in conjunction with cinema films. Early experiments were done with discs and wire recorders but were impractical. The eventual method which lasted many years was to record a sound track on the film itself, optically.
For many years the most common method of playing discs in a domestic setting was using a wind-up gramophone. These used no electricity at all, neither to amplify the sound nor to rotate the turntable. They were still used in the 1950s.
Electrically powered gramophones became available with a motor to turn the turntable and electronic amplification of the sound. In the days of the 78 rpm record these types of gramophone where often home-made by dedicated enthusiasts from separate components such as the turntable and pick-up arm. Playback was typically done through a radio (wireless) many of which were provided with an external input specially for the purpose.
The long-playing (LP) record, 12 inch diameter, with a playing speed of 33 1/3 rpm was first introduced in 1948. This was only suitable for playback on a modern record player with electrical pickup and amplification.
In the following year, 1949, the 45rpm 7 inch single was introduced and gradually through the 1950's replaced the old 78s.
Stereophonic 33 1/3 rpm LPs were introduced in 1958.
Lee de Forest tried to apply audio amplifiers using the audion to the Telegraphone but no practical system resulted.
In the early 1920s German inventor Curt Stille modified the Telegraphone to use electronic amplification. The intended application was for speech such as telephone recording and as a dictation machine.
There followed various developments to the wire recorder, such as the Dailygraph and Blattnerphone. The Blattnerphone used steel tape instead of wire. It was used to record radio programmes prior to broadcast.
In 1928 the German engineer Fritz Pfleumer demonstrated a magnetic recorder which recorded on magnetic tape consisting of paper tape coated with iron dust. AEG began manufacturing it, calling it the Magnetophon. The tape was manufactured by the company which later became BASF.
The Magnetophon was developed further and became successful (in a very limited market of professional users). It was used for broadcast purposes in Germany.
In 1941 there was a significant improvement. High frequency AC bias was used during the recording which greatly improved the sound quality. It seems to have been confined to Germany, probably because it was during the 2nd World War.
Meanwhile wire recorders continued to be developed.
During the war there seems to have been a situation that the USA had wire recorders, and Germany had tape recorders. Not surprisingly there was no collaboration between the two, in fact the technologies had military applications and would have been kept secret.
After the war, German Magnetophons were discovered in Germany. Major John T Mullin took two back to America, together with some tapes, and worked on them, making some improvements. Tape recorders based on the Magnetophon started being made in the USA. The 3M Coroporation introduced a plastic based tape as an option to existing paper tape.
The Ampex Corporation in America set the world standard tape width of 1/4 inch, and the tape speed of 30 inches per second (i.p.s.). Subsequent developments allowed lower tape speeds to be used, each one half the previous one. 15 and 7.5 i.p.s. were used for professional applications for many years until at least the 1970's. Quality tape recorders for home use used 7.5 and 3.75 i.p.s.
The modern tape recorder had arrived.
Early experiments with stereo were done in the early 1930s including some attempts to record in stereo. Work was done in the USA and by Alan Blumlein in Britain. In particular Blumlein pioneered microphone techniques for stereo. Recording may have been done initially using two disc recorders simultaneously. The idea of using two grooves in the record was considered but deemed unsatisfactory because of incompatibility with existing playback equipment. There was no practical recording system for recording stereo either on disc or tape at this time.
The term High Fidelity was used in the 1930s for loudspeakers and gramophone records. It was mainly a marketing term, but was not Hi-Fi as we know it.
The first truly successful stereo recordings were made on the magnetophon in Germany in 1942. Mullin made a stereo tape recorder in the USA in 1946.
These developments were the start of High Fidelity as we know it. It is notable that the first viable stereo recording was done on tape before it was done on disc.
Stereophonic 33 1/3 rpm LPs were introduced in 1958.
These combined left and right channels in the same groove. The groove is a V shape with the walls at 90 degrees. The inner wall of the groove contains the movements for the left channel, and the outer wall is for the right. These modulations on their own cause the pickup to move at an angle of 45 degrees. The pickup detects each of these directions of movement separately, thus giving stereo.
At this time mono records were laterally cut, that is the groove moves the pickup sideways and not vertically. The stereo pickup cartridge is wired so that horizontal movements give equal left and right signals so compatibility is achieved. That is, a stereo record player will play mono records in mono, with the same signal from each channel.
Where stereo information is present there will be some movements in the vertical direction whenever the left and right signals differ. Many mono pickups at the time did not move freely in the vertical direction and so if used to play a stereo LP they caused excessive wear to the record. As a result, for some years most L.P. records were available with a choice of mono or stereo, and people with mono record players were advised to buy the mono version. Single 45 rpm records were available only in mono. In the 1960s stereo systems became more common, and modern mono record players began to be made using a pickup which had the necessary freedom of movement to not damage stereo LPs, and around the end of the 60s most LPs were available in stereo only, and many singles were also made in stereo.
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