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hobbyists's
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Page created September 19th, 2000.
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A Particular
Loudspeaker |
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Do you use the DECCA London Ribbon horn tweeters or super tweeters? Or do you still have a set of the original Stanley Kelly ribbon tweeters? Or, maybe you are just curious about these products? At left the original Decca London Ribbon with the metal horn. |
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Read about how these ribbon speakers work and about the possibility to make new ribbons of aluminum household foil and repair these extraordinary ribbon speakers yourself. At left the Decca Super Tweeter |
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PRINCIPLE
The ribbon loudspeaker consists of a small aluminum ribbon that is placed between two pole plates which are attached to a magnet. A current is fed through the ribbon and thus the ribbon functions like the coil in a dynamic loudspeaker. At the same time the ribbon has the function of a cone (though it does not look like it) because it moves and thus brings the air into motion. It's efficiency (maximum sound level) depends mainly on the strength of the magnet. The first application of the electro-mechanic principle of a ribbon moving in a magnetic field, was not a loudspeaker but a microphone. It was "das Band Mikrophon" and was developped in 1924 by E. Gerlach and (according to Jean Hiraga in his outstandig book "Les Haut-Parleur", Paris) was modified and adapted by W. Schottky, C.A. Hartmann and H.F. Olson. The first commercialisation was by Stanley Kelly. |
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MICROPHONE
The ribbon loudspeaker is a dynamic loudspeaker. It was derived from the beautiful and at the same time fragile ribbon microphone which is still used in some studios and is loved by many a sound technician. Famous is the LEM ribbon microphone. |
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STANLEY
KELLY Stanley Kelly's design was taken over by DECCA who manufactured the DK 30 (=Decca Kelly 30) as pictured on the left. From there the bigger Decca London Ribbon tweeter was developed. |
| Square
Wave |
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HARMONICA
POWER
HANDLING |
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ADAPTATION
The secondary coil connects to the ribbon and this coil is wound of very thick and flat wire. Efficiency, frequency response and distortion levels depend on the quality of the transformer, the magnet and the way the ribbon is combined with other units. |
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I have owned loudspeaker systems that incorporated the London Ribbon high frequency loudspeaker and the sound reproduction is exceptional because the Decca Ribbon was for a long time one of the two existing high frequency transducers which can reproduce a square wave. The other one is the AUDAX TW8 with aluminum diaphragm well protected by a grid. The maximum power handling is 20 Watt connected via a 2.2 uF capacitor, crossover frequency:8 kHz.(Image and curves taken from the AUDAX catalog of 1973.) Both the Decca and the Audax produce a very precise and correct sound which is achieved nowadays by tweeters which have a metal coated membrane/diaphragm. If compared to a soft dome tweeter, the soft dome is less precise. All depends of course if correct phase is achieved.
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VINTAGE
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HORN
Measurements (left) as given in the original Decca brochure.
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| Decca
'Vintage' Horn Loudspeaker |

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Decca + McIntosh + Thorens The
image above is of a true vintage audiophile set. Vintage because of the McIntosh
integrated amplifier and the use of the Decca London Ribbon horn tweeter and Decca
Bass chassis in a DIY cabinet. The records are played on a simple Thorens TD-160
with original Thorens arm. The set is owned by Ralf Löffler from Germany
who sent several images to me.
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| EXTENDED
Loudspeaker systems perform more naturally if the tweeter has an extended frequency band. The DECCA literature of the nineteen seventies mentions a response that is practically flat up to 40.000 Hz. after which the response weakens a few dB and continues to 80.000 Hz. The dimensions of the horn determine the lower cutoff frequency. The mouth opening of the DECCA horn measures 14.9 by 28.1 cm (the surface of the mouth opening is 418 cm2) and makes it possible to use the London Ribbon from 1000 Hz. on. So essentially it is suitable for use in a 2 way system. But generally a higher crossover frequency of about 3000 or even higher is recommended to avoid coloration. | ![]() |
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SOURCES
Technical specifications and filter design as given in the original Decca brochure. |
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| Decca
Kardioid |
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Another Decca Special Product loudspeaker system is the Decca Kardioid. Jason Clark from geat Britain sent images and details about this 2-way loudspeaker.
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Jason Clark: "I have them on the end of a Leak Stereo 30 Plus amplifier (from around 1970), Leak Stereofetic FM tuner, Pioneer PL-41A turntable and Technics SL-PS770A CD player." There
is an archived review in Gramophone magazine here: |
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| Mordaunt
Short and The Decca Volt |
| MORDAUNT
SHORT |
Mordaunt Short MS 737 and filter. |
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PASSIVE
FILTERING | ![]() |

| Frequency
Characteristics and Polar Diagram |
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Engasound
3KF: Kelly, London Ribbon, Fane |
EFFECTIVE COMBINATION | ||||||||||||||
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| An
example of a High End system of the nineteen sixties: (1) AR turntable, the first floating (suspended) sub chassis turntable constructed along the principle devised by Mitch Cotter, (2) Rogers Master preamplifier, (3) Rogers Master main amplifier, and (4) the first version of the 3KF. | ||||||||||||||
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The
original London Ribbon was a development of DECCA Special Products. |
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Ribbon
Repair |
| It is possible to repair the ribbons.
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© Rudolf A. Bruil - Page created and first published September 19th, 2000.
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Bulletin - Rudolf A. Bruil, Editor - Copyright 1999-2012
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