Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-09-20
2002-08-13
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S431000, C381S176000
Reexamination Certificate
active
06434252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ribbon microphone. More particularly, the present invention relates to a ribbon microphone that produces absolutely realistic sound performance, free of coloration and distortion and that provides an electrical equivalent of the acoustic information so that digital converters can read the acoustic information very accurately in digital audio conversion.
2. Description of the Prior Art
Ribbon microphones have been around for many years, and reached their peak of popularity in the 1950's. Condenser microphones and dynamic microphones, which were smaller and more sensitive replaced the ribbon microphone. Ribbon microphone rely on tapered pole-pieces that concentrate a magnetic field to a narrow point, with a ribbon suspended exactly in the middle of that point, between an air gap. The tapered pole pieces were utilized to maximize the sensitivity of the microphones. Cobalt steel and later Alnico 5 and 7 were the best magnetic materials available to microphone designers in the 1930's. Because of the rather large pole pieces and the relatively weak magnets it was common to taper the pole pieces to provide a sufficiently strong field at the ribbon and thereby provide acceptable sensitivity. The foregoing was the accepted design for ribbon microphones.
Due to the shallow area in front of and behind the ribbon, where the magnetic flux was uniform, the motion of the ribbon was restricted, for example by damping screens. The restriction of motion of the ribbon was to minimize distortion. Furthermore, the assembly process required precise alignment of the ribbon in order to minimize the distortion. The ribbon had to be perfectly positioned to perform properly.
The ribbons themselves were very thin. As a result, a blast of air would often deform the ribbon to such an extent that the ribbon no longer was positioned in the gap, thus creating the undesired distortion. Although conventional ribbon microphones are sensitive at low and moderate levels, when very high pressure waves strike the ribbon microphone, the ribbon is pushed away from the narrow gap causing decreased efficiency. The early ribbon microphones were adequate for recording at the lower volume levels prevalent at that time, however, modern day recording environments involve high volume levels for which such ribbon microphones are inadequate.
A ribbon microphone consists of a strip of aluminum foil, of approximately one ten-thousandth of an inch thick, {fraction (3/16)}″ wide and 1.5″ long. The ribbon is suspended between the poles of a powerful magnet. Sound waves force the ribbon to vibrate in a direction perpendicular to its length, and as the ribbon moves an electrical voltage is induced in the ribbon. With most ribbon microphone designs the impedance of the ribbon is a small fraction of an ohm, so that a suitable transformer is connected between the ribbon and a following pre-amplifier, to step up the impedance to a value on the order of 250 ohms. The use of a transformer also provides a voltage step up on the order of 30 dB.
The most common types of microphones in use today are condenser microphones and dynamic microphones, primarily because they are more robust than conventional ribbon microphones, and because they are well suited to recording for television. However, such conventional condenser and dynamic microphones are poorly suited to burgeoning digital recording field. Digital conversion in audio recording needs to be as accurate as possible. Conventional microphones produce too many high-frequency dips and/or phase distortions, that incorrectly are interpreted as data in the digital recording process.
SUMMARY OF THE INVENTION
From the foregoing, it is an object of the present invention to provide a ribbon microphone that produces absolutely realistic sound performance, free from coloration and distortion.
Still another object of the present invention is to provide a ribbon microphone that is well suited to digital audio recording.
Another object of the present invention is to provide a ribbon microphone that requires no external power supply.
Yet another object of the present invention is to provide a ribbon microphone having a compact size.
Still another object of the present invention is to provide a ribbon microphone that is not affected by changes in temperature and/or humidity.
Another object of the present invention is to provide a ribbon microphone that is durable and easily repaired.
These and other deficiencies of the prior art are addressed by the present invention which is directed to a ribbon microphone. The ribbon microphone utilizes magnets positioned adjacent north and south pole pieces. The magnets are of uniform thickness along their lengths, and do not taper. The pole pieces are substantially the same width and the magnets. An offset ribbon is disposed in an air gap between the pole pieces. The offset ribbon is not centered in the air gap, but rather is offset front a center line which bisects the magnets and pole pieces. The offset ribbon is located closer to the front of the microphone than the back of the microphone. The flux area is uniform and corresponds to the area of the air gap between the pole pieces.
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Perrotta Richard T.
Royer David E.
Dabney P.
Gitler Stewart L.
Kent Evan M.
Kuntz Curtis
Royer Labs
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