Ribbon support system for electrodynamic microphone

Abstract

A ribbon microphone having a housing made of wood, a wood laminate, or another suitable composite material having a characteristic impedance and density and a ribbon transducer assembly with metal support chassis having a higher characteristic impedance and density. By engineering a body housing and the ribbon support chassis having a similar or equal total weight but differing greatly in density, a rapid attenuation of internal harmonics is achieved, particularly reducing the undesirable metallic resonance of the metal bodies of conventional microphones. The improved tonal quality is achieved, not by uncoupling the acoustic mass of the housing, but rather, by tightly coupling the wood housing to a slender chassis on rails that support the ribbon. Advantageously, this cooperative effect also acts to dampen unwanted rumble and external shock outputs, and in a preferred embodiment, magnetic pole pieces are eliminated by designing air gaps between the chassis and the magnets. The chassis is a conductor and electrically connects the ribbon to a transformer, eliminating the need for solder connections. Thus the ribbon support system of the invention achieves a synergy of function by eliminating unneeded parts, simplifying assembly, and improving the tonal quality of the microphone.

Claims

1. An improved ribbon microphone having tonal qualities derived from a wood housing, which comprises a wood housing configured with center cavity to enclosingly receive a conductive, metallic chassis, said metallic chassis having contralateral rails for acoustically coupling to said wood housing, said wood housing having acoustic windows for receiving a sound and guide slots for receiving said lateral rails, wherein said metallic chassis is configured to support (a) a ribbon-magnet transducer combination in a cradle between said lateral rails, wherein said transducer is defined by a conductive ribbon suspended in a magnetic field having parallel flux lines between two permanent magnets such that an electrical potential is generated by sound-driven oscillation of said conductive ribbon, and (b) an electrical transformer mounted between said lateral rails, wherein said transformer is configured to receive said potential from said transducer through said chassis and to convey said potential to an amplifier; and, further characterized by a low impedance housing acoustically coupled by said lateral rails to a high impedance metal chassis, said housing having a mass that is similar to or greater than the mass of said chassis.

2. The improved ribbon microphone of claim 1, wherein said lateral rails extend from a base of the housing to a top of said acoustic windows in said guide slots, said glide slots and lateral rails having a compression fit effective in acoustically coupling said housing to said chassis.

3. The improved ribbon microphone of claim 2, wherein said magnets are precision mounted in slots in said chassis, requiring no additional fixtures or adhesive.

4. The improved ribbon microphone of claim 1, wherein said wood housing is composed of a wood body, a wood laminate body, or a composite body, and said wood of said housing is selected from ash, birch, basswood, hickory, ebony, lignum vitae, walnut, rosewood, koa, spruce, mahogany, or other woods and wood laminates effective in imparting an overtone or color to the microphone output.

5. The improved ribbon microphone of claim 4, wherein said wood body is oriented with transverse isotropy, having a grain orientation essentially normal to a ribbon of said ribbon-magnet transducer combination.

6. An improved ribbon microphone, which comprises a conductive ribbon having two ends, lateral edges, a front face and a back face, a length and a thickness supported in a magnetic field by a hoop chassis; a housing body with hollow center cavity and acoustic windows open thereto, said cavity for receiving said hoop chassis in an interference fit; and, wherein said hoop chassis, said housing body and said hollow center cavity define an acoustic cavity, said acoustic cavity having an impedance mismatch between a higher impedance of said chassis acoustically coupled by said chassis to a lower impedance of said housing body, said housing body having a mass that is similar to or greater than the mass of said chassis.

7. The improved ribbon microphone of claim 6, wherein said housing body of said acoustic cavity is made of a dampening material and is configured to act as an acoustic sink thereof so as to add a tonal quality characteristic of the dampening material.

8. The improved ribbon microphone of claim 7, wherein said dampening material is a wood, a composite, or a material having a lower acoustic impedance relative to said chassis.

9. The improved ribbon microphone of claim 8, wherein said wood of said housing body is selected from ash, birch, basswood, hickory, ebony, lignum vitae, walnut, rosewood, koa, spruce, mahogany, or other woods and wood laminates effective in imparting a desirable overtone or color to the microphone output.

10. The improved ribbon microphone of claim 8, wherein said dampening material comprises laminations having an oriented grain structure for defining a signature tonal quality to the microphone output.

11. The improved ribbon microphone of claim 6, wherein said chassis is selected from a steel, a plastic, or a ceramic.

12. The improved ribbon microphone of claim 11, wherein said chassis is composed of a high density material having precision machinable or formable properties.

13. The improved ribbon microphone of claim 6, wherein said chassis is a conductive or non-conductive high density material.

14. The improved ribbon microphone of claim 6, wherein said chassis comprises a ribbon-magnet transducer subassembly having a pair of magnets disposed contralaterally next to said ribbon, said pair of magnets defining lines of magnetic flux over said front and back faces of said ribbon, each magnet having two ends, a length, and a circumference, said circumference having a path length L from said front face of said ribbon to said back face thereof, wherein said path length L defines a treble roll-off frequency having a frequency greater than 12 KHz, preferably greater than 15 KHz, and more preferably greater than 17 KHz.

15. The improved ribbon microphone of claim 14, further comprising a mounting system for said magnets, wherein said ends of said magnets are mounted in slots at the top and the bottom of said center cavity, one slot proximate to each said lateral edge at each of said two ends of said ribbon; the depth of said slots and the end-to-end length of said magnets are dimensioned so that said magnets are longer than an effective ribbon length between a pair of clamps configured for securing said ribbon in said transducer subassembly; thereby exposing said ribbon to a magnetic field having essentially parallel lines of magnetic flux over said effective ribbon length thereof, said magnetic field having a strength equal to or greater than 42 MOSe.

16. The improved ribbon microphone of claim 15, wherein said lines of magnetic flux are not modified by a pole piece.

17. The improved ribbon microphone of claim 14, wherein said magnets are precision mounted in top and bottom slots in said chassis, requiring no additional fixtures or adhesive, and said magnets have a length greater than the effective ribbon length.

18. The improved ribbon microphone of claim 6, wherein said hoop chassis comprises contralateral guide rails, and said contralateral guide rails of said chassis are configured to be slideably received in internal mating contralateral guide slots inside said cavity of said housing, and, wherein said guide rails are in a compression fit in said guide slots so as to be effective in acoustically coupling said housing to said chassis.

19. The improved ribbon microphone of claim 6, wherein said ribbon is tensioned in clamps affixed to said chassis.

20. The improved ribbon microphone of claim 6, comprising a transformer having a primary coil with electrical connections for closing a circuit path through said ribbon and a secondary coil having an electrical output, said transformer having a seat in said chassis proximate to said ribbon.

21. The improved ribbon microphone of claim 6, wherein said housing comprises a guide sound flat externally disposed parallel to and co-axial with a front face of said ribbon, thereby directionally demarcating the orientation of the ribbon inside the housing.

22. The improved ribbon microphone of claim 6, wherein said housing comprises a multihedral array of external sound flats disposed externally thereon, said array having a guide sound flat configured to be parallel to and co-axial with a front face of said ribbon, thereby directionally demarcating the orientation of the ribbon inside the housing.

23. An improved ribbon microphone, which comprises a housing, a chassis in said housing, a conductive ribbon having two ends, lateral edges, a front face and a back face, a length and a thickness; a) wherein said ribbon is supported in a magnetic field by said chassis and is affixed at said two ends by clamps thereto, said distance between said clamps defining an effective ribbon length; b) wherein said chassis comprises: a ribbon-magnet transducer subassembly having a mounting system for mounting a pair of magnets contralaterally beside said ribbon, said pair of magnets defining lines of magnetic flux across said ribbon, each magnet having two ends, a length, inside and outside magnetic faces, said outside magnetic faces defining an air gap on either side thereof, and a circumference, said circumference having a path length L through said air gaps from said front face to said back face of said ribbon; and, c) wherein said mounting system comprises: mounting slots in the top and the bottom of said chassis for receiving said ends of said magnets without any fasteners or adhesives, one slot proximate to each said lateral edge at both of said two ends of said ribbon.

24. The improved ribbon microphone of claim 23, wherein the depth of said slots and the end-to-end length of said magnets are dimensioned so that said magnets are longer than said effective ribbon length when mounted in the transducer subassembly; thereby exposing said ribbon therebetween to a magnetic field having essentially parallel lines of magnetic flux over said effective ribbon length thereof.

25. The improved ribbon microphone of claim 24, wherein said magnetic field is configured with a strength equal to or greater than 42 MOSe and said path length L is configured so as to define a treble roll-off frequency having a frequency greater than 12 KHz, preferably greater than 15 KHz, and more preferably greater than 17 KHz.

26. The improved ribbon microphone of claim 23, wherein said chassis is a hoop chassis having contralateral guide rails, and said contralateral guide rails of said chassis are configured to be slideably received into internal mating contralateral guide slots inside a cavity of said housing.

27. The improved ribbon microphone of claim 26, wherein said guide rails are in a compression fit in said guide slots so as to be effective in acoustically coupling said chassis to said housing.

28. The improved ribbon microphone of claim 26, wherein said chassis is electrically conductive and said transformer coil is electrically connected to said conductive ribbon through said chassis.

29. The improved ribbon microphone of claim 26, wherein said magnets are dampened by a finger tab extending from said chassis to said magnet at about a middle of said magnet.

30. The improved ribbon microphone of claim 23, wherein said chassis comprises a seat adapted to mount a transformer coil, said transformer coil having operative electrical connections with said conductive ribbon through said clamps, said chassis, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The teachings of the present invention are more readily understood by considering the drawings, in which:

(2) FIG. 1A is a schematic of a ribbon microphone transducer with support housing.

(3) FIG. 1B shows a field of sound around ribbon microphone components.

(4) FIG. 2 is an exploded view of a ribbon support system of the invention.

(5) FIG. 3A is a detail view of a ribbon support system assembly.

(6) FIG. 3B is a plan view at section A-A of a ribbon support system assembly FIG. 4A is a perspective view of an internal ribbon support system assembly.

(7) FIG. 4B is a basic schematic showing the electrical connection from the ribbon (R) through a transformer to an amplifier. A three-pin adaptor includes an electrical ground to the transformer shield or can.

(8) FIG. 5A views a housing body member in perspective

(9) FIGS. 5B, 5C and 5D are alternative housing body member shapes in plan view. FIG. 5E is a sec ond view of an octagonal housing body showing the internal cavity for receiving the chassis and a pair of guide slots for receiving the rails. FIG. 5F shows the base in plan view.

(10) FIGS. 6A and 6B are views of a microphone assembly including octagonal housing with internal ribbon support system. FIG. 6B is at cross-section A-A, showing a cutaway lateral view.

(11) FIG. 7A is a side view of an octagonal housing. FIG. 7B is at cross-section B-B, showing a cutaway view of an internal ribbon support system.

(12) FIG. 8A and FIG. 8B are views of alternative housing bodies of the invention.

(13) FIG. 9 is a summary overview of a ribbon microphone assembly and procedure.

(14) The drawing figures are not necessarily to scale. Certain features or components herein may be shown in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity, explanation, and conciseness. The drawing figures are hereby made part of the specification, written description and teachings disclosed herein.

Glossary

(15) Certain terms are used throughout the following description to refer to particular features, steps or components, and are used as terms of description and not of limitation. As one skilled in the art will appreciate, different persons may refer to the same feature, step or component by different names. Components, steps or features that differ in name but not in structure, function or action are considered equivalent and not distinguishable, and may be substituted herein without departure from the invention. Certain meanings are defined here as intended by the inventors, i.e., they are intrinsic meanings. Other words and phrases used herein take their meaning as consistent with usage as would be apparent to one skilled in the relevant arts. The following definitions supplement those set forth elsewhere in this specification.

(16) Acoustic impedance Z is the ratio of amplitude p to volumetric flow U in a medium. Formally, Z=p/U (where p is the applied acoustic pressure and U is the acoustic volumetric flow rate. Impedance is typically given in Pa.Math.m.sup.3/s and is a measure of the opposition that a system presents to an acoustic flow when an acoustic pressure is applied to it. Acoustic impedance may vary strongly with frequency.

(17) Also more relevant to the present invention, characteristic acoustic impedance (Z) of a material is defined as the product of its density (p) and acoustic velocity (V) and is measured in Rayleighs (Rayl). Thus for example the acoustic impedance of a softwood across the grain is on the order of 1.6 Rayl; selected stainless steels on the order of 46 Rayl, some brasses about 41 Rayl, and TEFLON is 2.97 Rayl. The characteristic impedance Z of wood is very much dependent on grain orientation, a property termed transverse isotropy, and is important in that the grain orientation may be used to absorb sound from a high impedance material rather than reflect it at the interface.

(18) Acoustic attenuation Q is a measure of the energy loss of sound propagation in media, and is the sum of thermal conversion of sound energy plus acoustic scattering. Acoustic attenuation in a lossy medium promotes dampening and noise reduction but by selection of interfacial materials and masses may instead be used to add color to a tone. Wood on metal for example absorbs sound by both its elasticity and by acoustic scattering, and adds a tonality that is complementary to the properties that make ribbon microphones attractive to audiences.

(19) Composite materials refer to materials made from two or a plurality of constituent materials having significantly differing physical or chemical properties, such that when combined, the resultant composite has characteristics that are recognizable distinct from the individual components. These materials are also sometimes termed composition materials or simply, composites. Composites include such materials as micarta (http://en.wikipedia.org/wiki/Micarta, incorporated herein in full by reference), fiber-reinforced phenolics, and laminated materials, where particularly preferred are lower density materials and layered materials having mixed densities enabled to dampen undesirable resonances. Given that the speed of sound in wood varies according to the grain, laminations having variably oriented grain may also be useful composites for dampening undesired resonances. Useful laminating resins include epoxy and polyester, while not limited thereto.

(20) A pole piece is a structure composed of material of high magnetic permeability that serves to direct the magnetic field produced by a magnet. A pole piece attaches to and in a sense extends a pole of the magnet, hence the name.

(21) Pitch: Pitch describes a sound as heard by the ear, and is interchangeable with the wavelength or frequency of a sound wave in air.

(22) Color: One of the basic elements of music is called color, or timbre. Color includes higher harmonics and overtones. A guitar and a flute, for example, have differences in sound; it is these differences that are the color of the sound. The harmonics at the beginning of each notethe attackare especially important for color. The invention realizes a microphone that has color, much like a musical instrument.

(23) Vibe: is a term used by musicians to describe the responsiveness and liveliness of an instrument. Good vibe means that the microphone responds quickly, and develops a rich harmonic overtone spectrum.

(24) Reverberation: A note played in a small space will reverberate. Reverberation, also termed verb, is nothing more than lots and lots of little echoes, but also can be produced electronically.

(25) Dynamic level: The loudness or softness of a sound.

(26) Resonance: refers to the sympathetic vibration of two structural elements sharing a natural resonance frequency. Natural resonance frequencies are determined by the vibrational modes of the material and its dimensions or mass.

(27) Harmonics: refers to standing waves or overtones at integer multiples of a fundamental frequency.

(28) General connection terms including, but not limited to connected, attached, conjoined, coupled, secured, and affixed are not meant to be limiting, such that structures so associated may have more than one way of being associated. Acoustically coupled indicates a connection for conveying a sound pressure therethrough.

(29) Relative terms should be construed as such. For example, the term front is meant to be relative to the term back, the term upper is meant to be relative to the term lower, the term vertical is meant to be relative to the term horizontal, the term top is meant to be relative to the term bottom, and the term inside is meant to be relative to the term outside, and so forth. Unless specifically stated otherwise, the terms first, second, third, and fourth are meant solely for purposes of designation and not for order or for limitation. Reference to one embodiment, an embodiment, or an aspect, means that a particular feature, structure, step, combination or characteristic described in connection with the embodiment or aspect is included in at least one realization of the present invention. Thus, the appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment and may apply to multiple embodiments.

(30) Furthermore, particular features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments.

(31) It should be noted that the terms may, can, and might are used to indicate alternatives and optional features and only should be construed as a limitation if specifically included in the claims. The various components, features, steps, or embodiments thereof are all preferred whether or not specifically so indicated. Claims not including a specific limitation should not be construed to include that limitation. For example, the term a or an as used in the claims does not exclude a plurality.

(32) Conventional refers to a term or method designating that which is known and commonly understood in the technology to which this invention relates.

(33) Unless the context requires otherwise, throughout the specification and claims that follow, the term comprise and variations thereof, such as, comprises and comprising are to be construed in an open, inclusive senseas in including, but not limited to.

(34) The appended claims are not to be interpreted as including means-plus-function limitations, unless a given claim explicitly evokes the means-plus-function clause of 35 USC 112 para (f) by using the phrase means for followed by a verb in gerund form.

(35) A method as disclosed herein refers to one or more steps or actions for achieving the described end. Unless a specific order of steps or actions is required for proper operation of the embodiment, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the present invention.

DETAILED DESCRIPTION

(36) A general structure of a ribbon microphone of the invention is shown schematically in FIG. 1A. As seen in plan view, the structure includes a pair of magnets positioned at opposite edges of a ribbon such that a magnetic flux is disposed generally crosswise between the magnets and parallel to the faces of the ribbon. The ribbon is depicted as if in section and is perpendicular to the plane of the drawing. The heart of a ribbon transducer assembly is defined by the ribbon and its paired magnets. Magnetic flux lines are shown sweeping across the ribbon and are generally parallel between the magnets. A chassis supports the transducer assembly and is acoustically coupled to an external body or housing by a compression (alternatively termed interference) fit. An air gap separates the magnets and the chassis; the air gap allowing sound waves (figuratively wavelets) to encircle and envelop the ribbon from either side.

(37) An analysis of the motion of individual wavelets on a ribbon transducer of the invention is shown in FIG. 1B. The wavelets may indicate a continuous propagation of a single frequency or may indicate a progression of a single pulse as it encircles the ribbon. Each wavelet shown here will strike the front of the ribbon first. Wavelets admitted through the air gaps on either side of the ribbon-magnet assembly will propagate so as to strike the back side of the ribbon a short time later. Because the ribbon is generally flaccid and of low mass, it will be displaced by as little as a whisper of a sound wave according to any pressure differential across the ribbon. As the ribbon moves, it intersects and cuts magnetic flux lines, and because the ribbon is electrically conductive, a potential is generated in a circuit attached to the ends of the ribbon that can be picked up by a transformer and passed to an amplifier.

(38) The response curve for a ribbon microphone is relatively flat at lower and mid-range but tends to diminish at a frequency that is characteristic of the path length L, where L is a free path distance (not in a straight line) between the front of the ribbon and the back, the distance covered by a sound wave between first striking the front of the ribbon and then striking the back, as described in detail by Olson in U.S. Pat. No. 1,885,001, which is incorporated by reference for all it teaches.

(39) As shown in FIG. 1A, the path length L is equal to a partial circumference of a magnet and passes through an air gap between the magnet elements and a chassis element, shown here figuratively. Note that no accessory pole pieces are shown: only the permanent magnets. The magnets are suspended between a top aspect and a bottom aspect of the chassis as will be described in more detail in FIG. 2, and are seated next to the ribbon.

(40) Other than a gradual treble roll-off, the frequency response of ribbons tends to be very flat especially in the mid-rangedue to the lack of resonances within the ribbon element. Ribbon microphones, in comparison to condenser microphones, tend to be superb at bringing out the body and size of voices and instruments. They are particularly suited to sources that may sound strident or shrill and tinny when recorded with a condenser microphone.

(41) Integral to the transducers of the invention is a low impedance housing that is acoustically coupled to the chassis. This will be discussed in more detail with reference to FIG. 5A, where a fully assembled microphone with representative housing is drawn.

(42) Referring to FIG. 2, in broad overview, the ribbon transducer assembly, shown here without housing, includes a ribbon, a pair of magnets, a chassis, a transformer, and a base mount with adaptor for connecting the microphone to an external amplifier. The ribbon transducer assembly is fitted into a housing body that receives the chassis under compression. Thus the chassis engages both the ribbon transducer and the external housing and serves as an acoustic coupling between the two. A transformer is cradled at the base of the chassis and is electrically connected to the ribbon transducer. The base also includes standard XLR pins for making connections to an external amplifier as shown in FIG. 4B. More structural details will be described below.

(43) The side edges or rails of the chassis aid in assembly. Each vertical rail slides into a hollow center of a solid block housing (see FIG. 9). By machining mated slots inside the housing, a directional fit is ensured so that the external sound flats of the housing may be used by sound engineers and a particular flat is identifiable as being parallel to the front face of the ribbon, an orientation in use that is chosen for optimal sensitivity and pickup.

(44) The ribbon is central to the transducer and is sized for particular applications. The ribbon is typically made from nearly pure aluminum or a metal-coated Mylar and has a flexible substructure. Corrugation is preferred as was first disclosed by Olson, but variants are shown in U.S. Pat. No. 8,218,795 and Pat. No. CN 2030784 U, for example. The thickness is a tradeoff between output signal strength and durability. In typical applications, ribbons from 0.6 micron aluminum up to 4 microns are useful. A preferred thickness is about 1.8 microns when aluminum metal (99.9% pure) is used and the corrugations are typically formed by bending, such as with a toothed roller and a mating platen.

(45) The ribbon is tuned to about 15 to 20 Hz. Royer in U.S. Pat. No. 6,434,252 describes a tuning process in which the ribbon is stretched to resonant mode at about 70-90 Hz, but this overlaps the 82.4 Hz E string on a base guitar, and is expected to cause audible exaggeration at the frequency when excited.

(46) Generally the ribbon is flaccid or limp and responds to deflection without any internal restorative force or stiffness. A small level of tensioning may be applied if desired, but for maximum sensitivity, the mass of the ribbon must be small enough that even a very gentle sound wave is capable of pushing and pulling the ribbon back and forth through the magnetic flux. If the ribbon is too delicate, the ribbon may have to be periodically replaced because of breakage.

(47) U.S. Pat. No. 7,900,337 to Crowley is incorporated in full by reference and discloses vapor deposition and electrodeposition of metal ribbons having no residual bending stresses (bending can lead to microfractures and work hardening). Crowley also discloses a number of composite ribbon materials, including more highly electroconductive layers. Also incorporated by reference is expired Chinese Pat. Doc. CN 2030784 U to Zhongyi, which discloses metal-coated plastic film ribbons.

(48) Interestingly, three-dimensional printing of ribbons has become possible and may be used in place of vapor deposition to achieve an unstrained ribbon with a variety of corrugation periodicities, including diamond corrugation. Three-dimensional printing may also be used to produce combinations not previously realized, such as an aluminum ribbon having no residual bending stress, and further wherein the ribbon is coated with a nanoparticulate of a highly conductive material such as graphene or Fullerenes, or where alternating molecular layers are built up by successive passes with differing feedstocks. Advantageously, the printer may be used to form a fully integrated wire to the transformer lead, eliminating the need for a solder connection. 3D printing may also be used to form the precision chassis hoop (the supportive bracket for the ribbon), if desired.

(49) The ribbons of the inventive microphones disclosed here are bent on a jig as currently practiced, as are most ribbons in commercial and hobby use. Alternative ways to reduce bending stress include use of jigs having sinusoidal surface patterns rather than teeth, and use of materials with a plastic backing such as MYLAR, having a polyester backing and a metallized layer formed by deposition of aluminum on the plastic. Metallized polymeric films are available in many forms and may be obtained with additional electroconductive layers. Carbon black films are available. The films may be stretched if desired to form a relatively flaccid ribbon, provided care is taken to provide adequate conductivity.

(50) Aluminum may be treated with carbon black or Fullerene layers to improve conductivity. Aluminum alloys and coatings may also be used to reduce surface oxidation. Plastic layers may be fused to the aluminum to improve durability and shock resistance. Other conductive metals such as gold, titanium, and ferrous alloys may also be used to form suitable ribbons, provided the inertial mass of the ribbon is kept low and the material is resistant to work hardening.

(51) Ribbons are mounted in the transducer assembly in a variety of ways. As preferred here, clamps are used. The clamps will generally sandwich the aluminum ribbon against the chassis, and include a fastener for tightening. The clamps are either conducting or insulating according to the circuitry and the electrical connections. Each end of the ribbon is supported by a clamp affixed to the metal chassis. Generally the ribbon is tensioned lightly to a chosen resonant frequency, typically less than 50 Hz as currently practiced. The ribbon has a slight but non-zero elastic moment and hence an essentially zero restorative force. Thus clamping a ribbon onto a transducer chassis is a very delicate operation.

(52) The clamping system is part of an electrical loop that follows the ring bracket from the chassis and returns to the ribbon through the transformer. The top clamp and fasteners are electrically conductive and part of an open circuit between the ribbon and the chassis. The bottom clamping assembly includes insulative materials so that the bottom end of the ribbon may be contacted with the transformer primary winding input without shorting to the chassis. Due to the precision of the machined chassis piece, I am able to use conductive fasteners that do not contact the lower portion of the ribbon. A conductive layer on the lower clamp tab facing the ribbon is used to ensure a low resistance contact to the transformer.

(53) In addition to supporting the ribbon, the transducer chassis has other functions. It holds the magnets in place in an exact position next to the ribbon (see FIG. 3B) and defines air gaps on each side of the magnets. The chassis includes a hoop or hoop bracket that supports the ribbon-magnet transducer at the top and bottom, the bracket defining air gaps on either side of the magnet pair. Precision slots at top and bottom of the chassis are used to mount the magnets without any adhesive or fasteners, an advance in the art. Neodymium magnets producing an effective ribbon voltage can have a cross section as small as or smaller. Because the chassis holds the magnets in place by only supporting the ends, it eliminates the need for accessory pole pieces, immediately reducing path length L to a partial circumference of each magnet. With this improvement, high frequency roll off can be increased to around 16 KHz as currently practiced. In contrast, the magnets and pole pieces in most conventional ribbon transducers are glued to the ribbon chassis, thereby increasing the distance the sound must travel to reach the back of the microphone.

(54) There are other ways to increase the high frequency performance of ribbon microphones (such as with high frequency resonator plates) but not without other drawbacks (increased resonance that destroys the microphones ability to translate high frequency transients and increased self-noise). As shown here, using magnets without accessory pole pieces, path length L is reduced to less than 10 mm, enabling a significant extension of frequency response without treble roll off. Further improvement is achieved using magnets graded N42 or higher. Path length L in the range of 5 mm to 250 mm, more preferably about 10 mm (0.375 inches), has been found to be practical for most applications with the improved design.

(55) As can be seen in exploded view, FIG. 2, the entire effective length of the ribbon between the electrical contacts is within the parallel flux field of the magnets. Each magnet extends into a top and bottom slot in the chassis such that the depth of the slots is greater than the electrical contact points for the ribbon clamps. The contacts are shaped with a nose that extends into the magnetic field. In this way the entire effective length of the ribbon is saturated by the magnetic flux field which flows in generally parallel lines across the faces of the ribbon. This aids in charge separation to the ribbon ends and improves the overall microphone response.

(56) The magnets are held in place at their ends, allowing the audio signal to traverse the shortest path around the magnets with a cross section as small as 0.1250.125 but not limited to that size. Securing the magnets by their ends as shown above further allows the magnetic flux field to encompass the entire ribbon element. Duncan and Fisher tapered the pole pieces to allow for the short path, but this also results in a lower magnetic flux density reducing the output.

(57) As shown here, a small dampening finger or rib is inserted at the middle of the magnet to reduce any resonance node that could otherwise form. The small tabs that touch the middle of the magnet on each side exert a slight pressure on each magnet preventing it from ringing. These tabs are not necessary for the function of the microphone but follow my original design intention to reduce as much internal resonance as possible.

(58) Magnets are preferredly neodymium magnets, but samarium-cobalt and AlNiCo magnets may also be suitable if the magnetic flux density is sufficient. Higher strength magnets (for example rare earth magnets, such as neodymium magnets graded N42 or stronger) will produce a flux density that results in a usable signal output along the entire length of the ribbon. The ratio of magnet circumference at the ribbon edge to magnet flux density B* (the strength of the magnet per unit cross-sectional area in Teslas) is a compromise, but can be resolved by attention to the output signal impedance and selection of a suitable transformer. The custom magnets are magnetized through thickness, not on the long axis. The ribbon-magnet assembly is core to the transducer and may be considered without its supporting chassis as a subassembly operative as depicted broadly in FIGS. 1A and 1B. The elimination of accessory pole pieces is an advance in the art and decreases the path length L through the air gaps on either side of the transducer subassembly.

(59) The chassis also includes a separate cradle for the transformer under the ribbon. The cradle is designed to hold the transformer in compression fit to reduce axial vibration and rattling and the housing prevents radial vibration of the transformer body. Most current manufacturers either use screws to hold the transformer in place or use foam or cotton wadding to dampen vibrations. By acoustically coupling the transformer body to a housing having an impedance mismatch, sound conveyed through the transformer or resulting from transformer motion is deadened and the assembly is thus self-dampening.

(60) Custom transformers may be designed to improve performance, but in many instances, a conventional transformer may be used, where winding ratios and gain are selected according to the ribbon output and the needed impedance of the amplifier. Because the cradle is electrically conductive, one of the ribbon ends connects to the chassis ribbon cradle. The closest ribbon end is wired to the transformer directly. The signal path utilizes the ribbon transducer chassis as the return path, limiting ohmic resistance in the circuit.

(61) Advantageously, because the chassis is not needed to close magnetic flux loops, the ribs, transformer cradle and ribbon hoop bracket can be very minimal in their structural dimensions, as configured to provide only the stiffness needed to secure and support the ribbon-magnet combination in the housing under light compression. This is a technical advance in the art because a higher impedance chassis when coupled to a lower impedance housing body with a similar or greater mass will effectively dampen unwanted sound and harsh reverberations. The impedance mismatch allows residual sound to drain into the body like an acoustic sink instead of being reflected back at the ribbon as would occur if the body was uncoupled from the chassis and adds a tonal quality characteristic of the body material, thus allowing the engineer to select a tonal quality complementary to the microphone's use, such as in recording vocals, instrumental music, and the like.

(62) Being under compression from the wood/composite body of the microphone, the chassis is acoustically coupled to the body. Most manufacturers attempt to decouple the transducer chassis from the body due to the un-tuned metallic construction of microphone bodies on the market today. By coupling, under pressure, the microphone transducer to a wooden or composite body, an effect is achieved that is analogous to the way a wooden string instrument is coupled to its strings. The housing body and the ribbon chassis assembly are similar in total weight but differ greatly in their densities; allowing for a rapid bidirectional attenuation of harmonic frequencies native to each part (body and transducer chassis) so that the ribbon output is not affected. This unlikely combination acts to dampen unwanted rumble, shocks, or the undesired internal metallic resonances of the metal bodies of other microphones. Furthermore, since the body is made of wood (or another dampening material), any undamped reverberation or vibration that are left un-attenuated will have the sonic characteristics of the material that is made of, in this case, wood or another suitable composite material, a highly satisfying complement to the warm resonance produced by a well-crafted ribbon microphone.

(63) A preferred chassis material is electroconductive, stainless steel 416 for example. Stainless 416 is conductive, paramagnetic and precision machinable. It is a common misconception that stainless steels are non-magnetic. The misconception arises because the type of stainless most commonly in use is austenitic (such as SS types 304 and 310L), having a grain structure that is magnetically inert. But other stainless steels, including ferritic, martensitic, duplex, and precipitate-hardened stainless types are magnetic and may be used for the invention. Stainless 416 was chosen for the preferred embodiment because of its stiffness, machinability and corrosion resistance. It is a high-chromium Martensitic steel.

(64) Within the open chassis, two air gaps are defined on either side of the ribbon-magnet transducer. These open windows allow sound to pass unimpeded from the front to the back of the ribbon. No pole pieces are used besides the magnets themselves. Thus an acoustic cavity is formed between the ribbon and the less dense and lower impedance body.

(65) More details of the ribbon support system assembly are shown in FIGS. 3A and 3B. Section A-A in FIG. 3B illustrates the close apposition of the magnets to the ribbon in the center and the air gaps defined by the outside face of each magnet and the corresponding vertical rib of the chassis frame. The ribbon is assembled in place with threaded fasteners inserted through small clamping members at the top and bottom ends of the ribbon. The bottom ribbon clamps (there are two) are generally insulative so that a direct connection may be made to the transformer. The top ribbon clamp is conductive and aids in connecting the ribbon electrically to the chassis, which serves as a return path for the electrical circuit joining the two ends of the ribbon.

(66) FIG. 4B is a basic schematic showing the electrical connection from the ribbon (R) through a transformer to an amplifier. The three-pin XLR plug includes an electrical ground to the transformer.

(67) A fully assembled transducer subassembly and supporting chassis is depicted in FIG. 4A. This is a sub-assembly and inserts under light compression into a hollow wooden body (or wood laminate or composite body) as shown in FIG. 5A and FIG. 9. A hoop bracket of the chassis supports the ribbon transducer with ribbon and magnets and a stands on two legs on an annular base configured to accept a standard microphone 3-pin jack. The jack is wired to the secondary winding output of the transformer, which is typically shielded and grounded. The base is attached to the ribbon transducer frame with 2 screws. The base serves as a stop when inserting the assembly into the housing, 4 screws around the base are used to secure the housing to the base. The annularity in the base serves as a universal adaptor plate, enabling the microphone to be connected to most standard cable receptacles no matter the shape of the exterior housing. The annularity houses an XLR (3 pronged) connector for electrically connecting the microphone to the pre-amp, typically via a cable receptacle. The XLR plug is held in place with an internal stop within the base and a left hand threaded screw that protrudes from the XLR into a larger hole in the side of the base.

(68) FIG. 5A is a view of a first wooden body. Preferred woods include ash, basswood, hickory, and more exotic woods like cocobolo, ebony, koa, or lignum vitae. Both hardwoods and softwoods may be used. Thin veneers may be layered up by a process of lamination to produce composite materials having either an axial or a radial layer structure. Laminations allow for the inclusion of more materials with dissimilar densities (epoxy and other materials) which result on more active dampening while modifying the tonal qualities of the wood. The raw block is then shaped to have a hollow center dimensioned for receiving the ribbon support chassis under light compression and exterior faces are formed with flats characteristic of preferred embodiments. The purpose of the exterior flats is explained below. Also needed are acoustic windows to admit sound. These are generally styled to be effective and aesthetically pleasing when cut or milled through the wood body.

(69) Instead of producing the microphone housing or body of metal as conventional bodies are made, the body is made of wood or another suitable composite material. The wood or composite body are acoustically coupled similar to the way a wooden string instrument is coupled to its strings, but by using impedance mismatch, using masses such that the body is greater or about equal to the ribbon chassis and materials such that the body is a lower impedance material and the chassis is a higher impedance material, a rapid attenuation of harmonic frequencies native to each part (body and transducer) is achieved. This acts to dampen unwanted rumble, shocks, or the undesired internal metallic resonances of the metal bodies characteristic of other microphones. Furthermore, since the body is made of wood (or another dampening composite material), any undamped reverberation or vibration that is left un-attenuated will have the sonic characteristics of the material that is made of, in this case, wood or another suitable low impedance material.

(70) The body housing can be made in many different styles and shapes. Examples are shown in FIGS. 5B through 5D, which include octagonal, hexagonal, and triangular plan shapes. The current arrangement of the microphone is that of an octagonal tube. Thus the inventive microphones are not intended to be limited to 8 sides and in fact may be circular, rounded or ovoid in section. The housing design may use only 3 sides, or as many as 30, while not limited thereto and the flats need not be equally spaced. The broader flats of the microphone will allow artists and sound engineers to easily position and maintain optimal positioning relative to the sound source for recordings. This saves time and production costs by reducing the number of sound checks and retakes due to misplaced or poor microphone positioning relative to the source. The flats further give artists or sound engineers the ability to place a flat side of the microphone normal to the sound source for the highest output and for more of the wood body character to be present in the transducer. Alternatively, they may position the flats away (not normal) from the sound source, thereby increasing high frequency response, but lowering the output and tone produced by the wood or composite body. These external sound flats on the wooden body may be used to establish directionality of the ribbon front face during use.

(71) The sound output from the fully assembled microphone of FIG. 5A is in the form of an electrical signal. The transformer takes a very small electrical signal that is developed from sound moving the ribbon within the magnetic flux field, and increases its output in voltage by a ratio of turns on a primary vs the turns on a secondary winding. There are many different types of step up transformers that could perform this job adequately. While a standard off the shelf transformer may be used to practice the invention, custom transformers may be designed. Of particular interest is the electrical impedance of the output signal, which must be mated to a suitably matched impedance of a pre-amplifier or a series of pre-amplifiers as described by Royer in US Pat. Doc. No. 20060078152, which is incorporated herein in full for all it teaches. Further evolution of transformers specifically adapted to ribbon microphones is needed and work is in progress.

(72) FIGS. 6A and 6B are elevation views of a microphone assembly including octagonal housing with internal ribbon support system. FIG. 6B is at cross-section A-A, showing a cutaway view to emphasis the slots that form acoustic windows.

(73) FIG. 7A is a side view of an octagonal housing. FIG. 7B is at cross-section B-B, showing a cutaway view of an internal ribbon support system and ribbon front face.

(74) FIG. 8A and FIG. 8B are views of alternative housing bodies of the invention. While both are octagonal, the left figure depicts a housing with multiple fenestrations; the right figure depicts a housing with a single large window. The microphone in its current development is a bidirectional microphone. It has a very strong tendency to reject sounds from the sides and above.

(75) Assembly methods are described pictorially in FIG. 9. Of interest is the role of the vertical rails forming the side edges of the chassis. These enable installation of the ribbon transducer subassembly into the internal voidspace of the housing with controlled orientation by a sliding process under light compression. When boring out the housing, additional machining may be performed to provide matching slots to receive the chassis side rails (and hence the ribbon) in a preferred orientation relative to any flats or acoustic windows in the body.

(76) While the ribbon shown is corrugated before assembly and mounted in place using threaded fasteners, the magnets are simply inserted into corresponding top and bottom slots in the chassis and held by a combination of magnetic attraction and interference fit at the ends and further by an optional center rib or finger that protrudes centerwise from the ring bracket where the ribbon-magnet subassembly is mounted. The rib or finger is not necessary to fit the magnet in place, but acts as a dampening mechanism for the suspended magnet by applying slight pressure against the magnet focused at a point on the magnet that divides it into two harmonically unbalanced halves ensuring that any harmonics produced from the magnet itself will be limited by the new effective vibrating length of each side of the magnet from the rib. This is an optional feature for high SPL environments that may induce harmonic oscillation of the magnet at its resonant frequency as an independent component.

(77) The transformer is also snug fit into its cradle in the chassis, which is then mounted by two legs on a base. An acoustic screen or mesh cup may be fitted over the transducer before the completed assembly is inserted into to the hollow housing and secured in place with a few screws or other detent mechanism. Thus the assembly process is very simple and is accomplished with fewer parts than most microphones on the market today.

INCORPORATION BY REFERENCE

(78) All of the U.S. Patents, U.S. Patent application publications, U.S. Patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and related filings are incorporated herein by reference in their entirety for all purposes.

SCOPE OF THE CLAIMS

(79) The disclosure set forth herein of certain exemplary embodiments, including all text, drawings, annotations, and graphs, is sufficient to enable one of ordinary skill in the art to practice the invention. Various alternatives, modifications and equivalents are possible, as will readily occur to those skilled in the art in practice of the invention. The inventions, examples, and embodiments described herein are not limited to particularly exemplified materials, methods, and/or structures and various changes may be made in the size, shape, type, number and arrangement of parts described herein. All embodiments, alternatives, modifications and equivalents may be combined to provide further embodiments of the present invention without departing from the true spirit and scope of the invention.

(80) In general, in the following claims, the terms used in the written description should not be construed to limit the claims to specific embodiments described herein for illustration, but should be construed to include all possible embodiments, both specific and generic, along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited in haec verba by the disclosure.