WO2006047048A2 - Acoustic ribbon transducer arrangements - Google Patents

Abstract

A ribbonned microphone assembly, for adjustable sound receiving capabilities, including a transducer (60) having a surrounding flux frame (61) for positioning at least two magnets (62) adjacent a suspended ribbon (66) between the magnets. An array of receiving apertures (68) is arranged in the flux frame. At least one curved return ring positioned in the receiving apertures to create a return path for magnetic flux in the transducer.

Description

PCT PATENT APPLICATION

Title: Acoustic Ribbon Transducer Arrangements

Background of the Invention

Field of the Invention

This invention relates to acoustic transducers and more particularly to ribbon

and thin film transducers and composite membranes fabricated with thin film

techniques that operate at various sound wavelengths, and is based upon U.S.

Provisional Application serial no. 60/620,934, filed 21 October 2004, and

corresponding U.S. applications, incorporated herein by reference in their entirety.

Prior Art

Designers and manufacturers of microphones used for vocal and instrument

recording in studio environments look for improved ways to provide accurate

sound reproduction. It would be desirable to provide characteristics to favor

particular types of sounds, such as voices, grand pianos, or woodwinds as well as

general designs having lower noise, higher and less distorted output, and greater

consistency and longevity. Microphones generally use transducers that are configured either as the

electrodynamic type, or more simply "dynamic", and ribbon, and condenser

varieties. Of these three major transducer types used in microphones, the ribbon

type is the focus of this invention, however certain improvements and principles

that apply to microphones in general are also incorporated. Such transducers,

which may include those utilized for medical imaging, may also be fabricated,

used or improved utilizing the principles of the present invention.

Advancement of the microphone art could proceed more quickly if better

materials and methods of fabrication could be employed, and if the microphones

were assembled and tested using techniques adapted from advanced techniques

developed by the semiconductor and medical device industry. Precise positioning

of the moving element, closed loop feedback control of the tuning of that element,

and statistical process control techniques that reduce piece to piece variability

would improve device characteristics and quality and consistency. Close control of

microphone characteristics allow artists and studio engineers to quickly arrive and

maintain optimal settings for recording, which saves time and production costs by

reducing the number of sound checks and retakes required.

Microphones that are suitable for use on sound stages and in other film and television production settings must be sensitive, robust, and reliable, but not

sensitive to positioning or swinging on a boom arm. Such motion may cause wind

damage or noise to the delicate ribbon that is suspended within a magnetic gap.

Improvements to the strength and durability of that ribbon structure would permit

greater application and use of this type of microphone. It would further be

desirable to increase the ribbon conductivity, decrease the overall mass and

strength of the ribbon without making it excessively stiff, thus improving output

efficiency while adding toughness. Output efficiency should be high since that

improves the signal to noise ratio and overall sensitivity of the microphone.

Microphones utilized for recording purposes must be accurate. Each

microphone built in a series should ideally perform in an identical manner. This is

not always the case with current microphone manufacture inasmuch there are

certain variations in the assembly and tuning of such microphones that affect their

ability to reproduce sound consistently. It would be desirable to overcome

irregularities that produce these variations and have precise assembly and tuning

methods that would result in more exact piece-to-piece performance consistency.

External air currents and wind, including airflow from a performer's voice or a

musical instrument or an amplified speaker may be of high enough intensity to damage or distort the delicate internal ribbon used in the current art. It would be

desirable to permit normal airflow and sounds to freely circulate within the

microphone, which then would permit more accurate sound reproduction without

attenuation, while at the same time limiting damaging air blasts that exceed a

certain intensity level. Such an improvement would allow wider use of the ribbon

type microphone.

It is an object of the present invention to overcome the disadvantages of the

prior art.

It is a further object of the present invention to provide a ribbon microphone

arrangement which has superior functional characteristics.

It is a further object of the present invention to provide a microphone

manufacture arrangement capable of consistent performance characteristics.

The invention thus comprises a ribbonned microphone assembly, having

adjustable sound receiving capabilities, including: a transducer having a

surrounding flux frame for positioning at least two magnets adjacent a suspended

ribbon between said magnets; an array of receiving apertures arranged in the flux frame; and at least one curved return ring positioned in the receiving apertures to

create a return path for magnetic flux in the transducer. The flux frame may have

parallel sides. The flux frame may have tapered sides. The flux frame preferably

has side apertures thereon. The side apertures may be non-circular. The side

apertures may be elongated and curvilinear.

The invention also includes a method of manufacturing a ribbon for a ribbon

microphone, comprising one or more of the following steps comprising: providing

a first form having an irregular predetermined ribbon engaging surface thereon;

depositing a ribbon forming material on the ribbon engaging surface; and forming

the microphone ribbon on the first form. The method may include as steps:

providing a second form having an irregular predetermined ribbon engaging

surface thereon which corresponds matingly to the irregular predetermined ribbon

engaging surface of the first form; and sandwiching the ribbon forming material

between the ribbon engaging surfaces of the first and second forms. The form

may have its temperature controlled. The ribbon may be comprised of more than

one material. The form may be comprised of a vapor deposition supportable

material selected from the group comprised of aluminum, wax and a dissolvable

material. The invention also includes a method of tuning a ribbon for subsequent

utilization of said ribbon in a ribbon microphone comprising one or more of the following steps: arranging a calibration member for adjustable supporting and

calibrating of a microphone ribbon therewith; attaching a microphone ribbon to

the calibration member, the ribbon having a predetermined pattern formed

thereon; activating a variable frequency oscillator connected to a loudspeaker, the

oscillator being set to a desired resonant frequency of the ribbon; adjusting the

calibration member to tension the ribbon; and observing a maximum excursion of

the ribbon which indicates a resonant peak. The ribbon may be installed into a

transducer assembly in a ribbonned microphone.

The invention also includes a method for reducing sound propagation from a

microphone support, comprising one or more of the following steps: arranging a

plurality of ring-like spacer members as a support for a ribbonned microphone;

interposing acoustically lossy material between adjacent spacer members;

attaching a first end of the plurality of spacer members to a ribbonned microphone

housing; and attaching a second end of the spacer members to a microphone stand.

The spacer members are preferably of annular shape.

The invention also includes a case for the safe enclosure and un-pressurized

transport and removal/loading of a ribbonned microphone therewith, the case

comprising: an enclosure housing; an openable door on the case; a spring loaded valve connected to the door which valve opens the case to the outside ambient

atmosphere during opening and closing of the door. A casing for a ribbonned

microphone, the casing enclosing a ribbon therewithin, the casing comprising: a

plurality of sound propagating apertures arranged through said casing enclosing

the ribbon therewithin, the apertures being comprised of curved, non-cylindrical

shape openings. The apertures are preferably arranged so as to be curved away

from the ribbon enclosed within the casing.

The invention also included a modular ribbon microphone assembly

comprised of a top ribbon transducer; an intermediate matching transformer

section; and a bottom amplification and electronics control section, to permit

various combinations of sub-assemblies to be easily interchangeable in the

assembly. Each of the sub-assemblies may have a bus bar with interconnecting

pins thereon to facilitate interconnection of the sub-assemblies to one another.

The invention also includes a ribbon transducer for the detection of energy

waves, the ribbon transducer comprising: an elongate ribbon structure comprised

of electrically conductive carbon nanotube filaments, the ribbon structure arranged

adjacent to a magnetic field, and wherein the ribbon structure is in electrical

communication with a control circuit. The ribbon structure of carbon nanotube filaments comprises a ribbon element of a ribbon microphone. A ribbon

microphone having a moving carbon-fiber-material ribbon element therein, the

ribbon element comprising: an elongated layer of carbon filaments; and an

elongated layer of conductive metal attached to the carbon filaments.

The invention also comprises: a ribbon transducer for the detection of sound

waves. The ribbon transducer comprising an elongated ribbon structure comprised

of electrically conductive carbon nanotube filaments arranged adjacent to a

magnetic field, wherein the ribbon structure is connected to a further circuit; a

ribbon microphone having a movable ribbon element comprised of a carbon

nanotube material integrated therein; a ribbon microphone having a movable

ribbon element comprised of a carbon fiber material integrated therein, said ribbon

element comprising a layer of carbon filaments, and a layer of a conductive metal

attached onto the layer of carbon filament material.

The invention also comprises a composite membrane acoustic transducer

structure arranged adjacent a magnet assembly, the transducer structure and the

magnet assembly arranged to produce a flux field; the transducer structure

comprising a first layer of thin, elongate composite membrane material held under

tension; a second conductive layer of membrane material attached to the first layer of composite material, wherein the first and second layers of membrane material

are arranged adjacent to, generally parallel and offset from the magnet assembly, to

produce the flux field through at least part of the first layer and the second layer of

composite material. The first layer may be comprised of a carbon fiber. The first

layer may be a polymeric material. The carbon fiber may be comprised of carbon

nanotubes. The first layer is preferably electrically conductive. The second

conductive layer is preferably a deposited metal. The second conductive layer may

be an electroplated layer. The second conductive layer may be an electrodeposited

layer.

The invention also comprises a method of manufacturing a membrane

transducer element, comprising one or more of the following steps of: providing a

form having a predetermined pattern thereon; depositing a layer of metal upon the

pattern on the form to create a continuous, separate metal transducer element on

the form; removing the deposited metal transducer element from the pattern, and

installing the membrane transducer element adjacent to a magnetic field. The

predetermined pattern may be a periodic pattern. The predetermined pattern may

be aperiodic. The metal may be aluminum. The invention also comprises a method of manufacturing a ribbon type

acoustic element to a specific frequency comprising: one or more of the following

steps: axially mounting an acoustic element in a holder having a movable

mounting point for supporting the acoustic element; moving the mounting point to

vary the tension of the acoustic element, and resonating the acoustic element to a

predetermined frequency. The acoustic element may be a metal element. The

acoustic element preferably comprises a transducer assembly.

Brief Description of the drawings

The objects and advantages of the present invention will become more

apparent when viewed in conjunction with the following drawings, in which:

Figure 1 represents a prior art ribbon microphone transducer showing a

corrugated ribbon suspended between ferrous poles extending from an

electromagnet;

Figure 2 represents a prior art ribbon microphone transducer showing its

corrugated ribbon suspended between tapered, ferrous pole pieces extending from

a permanent magnet;

Figure 3 is a side elevational view of the present invention showing a

microphone casing having a suspension system therewith;

Figure 4 is a cutaway view of the microphone casing shown in figure 3;

Figure 5 is an enlarged sectional view of the casing of the present Invention

showing an aperture arrangement therewith;

Figure 6 is an exploded, sectional view from the side of a modular ribbon

microphone assembly constructed according to the principles of the present

invention;

Figure 7 represents a side elevational view of an assembled stack of

transducer, transformer, and electronics modules represented in the exploded view

of figure 6;

1 ! Figure 8 is a side elevational view of a tapered transducer featuring a

surrounding flux frame that positions two or more adjacent magnets in proximity

to a suspended ribbon mounted therebetween;

Figure 9 is a perspective view of a non-tapered (parallel sided-walls)

transducer of the present invention showing installed return rings;

Figure 9 A is a view taken along the lines 9A-9A of figure 9;

Figure 10 is a side elevational view of a flux frame of the preset invention

showing features of both the tapered and non-tapered embodiments;

Figure 11a is a cross-sectional view of a ribbon form of the present

invention, having a predetermined "ribbon-forming" pattern on that form;

Figure l ib is a cross-sectional view of a ribbon form shown in figure 11a,

having a deposited layer of metal thereon, such as for example, aluminum;

Figure 1 Ic is a side elevational view of the completed ribbon after removal

of that metal ribbon from the form shown in figure 11a;

Figure 1 Id is a cross-sectional view of a completed ribbon produced by the

process of deposition, the ribbon having a predetermined pattern thereon;

Figure l ie shows a side efevationaϊ view of a graduated fixture having a

scale, movable slides, and clips to hold a microphone ribbon therebetween;

Figure Hf is a schematic representation of a tuning system to be used with

the graduated ribbon-holding fixture shown in figure 1 Ie; Figure 12a is a plan view of a series of filaments suspended between a pair

of filament holders useful in the manufacture of microphone ribbons;

Figure 12b is a side elevational view of the series of ribbon filaments shown

in figure 12a;

Figure 12c is a side elevational view of the series of filaments in spaced

proximity between a pair of forms which may be utilized to apply pressure, heat, or

both;

Figure 12d is a side view of the series of filaments after being impressed

with the shape of the forms shown in figure 12c;

Figure 13a is a plan view of a ribbon assembly with a sound absorbing

wedge placed a spaced distance from one side, in this case the rear of the ribbon;

Figure 13 b is a detailed side elevational view of the sound absorbing wedge

as shown in figure 13 a;

Figure 14 is a side elevational view, in section, of a microphone assembly

having back lobe suppression therewith;

Figure 15a shows an electrical schematic diagram of a pair of identical

ribbons of the present invention arranged in a parallel circuit configuration;

Figure 15b shows a plan view of the pair of identical ribbons in proximity to

each other and each within gaps of adjacent magnets; Figure 15c is a perspective view of a practical holder for a pair of adjacent

magnets;

Figure 16a shows a perspective view of a storage and travel case for a

pressure sensitive device such as a ribbon microphone;

Figure 16b is a cross sectional view of an air escape valve utilizable in the

travel case represented in figure 16a; and

Figure 17 is a side elevational view, in cross section, of a sound absorbing

structure integrated into the body of a microphone.

Detailed Description of the Preferred Embodiments

Referring now to the drawings in detail, and particularly to figure 1, there is

represented a typical prior art ribbon microphone transducer 20, from U.S. Patent

1,885,001 to Olson, incorporated herein by reference, shows a corrugated ribbon

22 suspended between ferrous poles 24 extending from an electromagnet 26. The

electromagnet 26 establishes the magnetic field, which is carried through the pole

pieces 24 and into proximity with the sound-responsive ribbon 22. When the

ribbon 22 is vibrated by incoming sound waves, an electrical current is generated

in the ribbon 22 which may then be amplified, recorded or transmitted. A typical

prior ait ribbon microphone transducer 30 shown in figure 2, as may be seen more

completely in U.S. Patent 3,435,143 to Fisher, incorporated herein by reference,

illustrates the corrugated ribbon 32 suspended between tapered, ferrous pole pieces

34 extending from a permanent magnet 36. The tapered pole pieces 34 reduce the

path length between the front of the ribbon and the back of the ribbon, which

improves high frequency response. The ribbon is suspended in an adjustable trains

38 with screw and nut adjustments that may be used for fine tuning the position of

the ribbon 32.

Improvements in such prior microphone art are however, represented in

Figure 3, wherein a microphone casing 40 is shown having a suspension system 41 consisting of a zig-zag arrangement of elastomeric cords or cables 42, a tapered

body shell arrangement 44, and a sound screen 46 having a multiplicity of

apertures 48 for sound to propagate through, while preventing ingress of foreign

objects, dirt, and the like. The cutaway view of figure 4 shows the microphone

casing 46 showing a plurality of spaced-apart apertures 48 therethrough, each

aperture 48 having an axially curved, non-cylindrical, non-linear shape. Figure 5

shows an enlarged view of the apertures 48, representing how air blasts "W" may

be directed away from a nearby ribbon "R" under conditions of a high velocity

wind. Such redirection of strong fluid currents may be attributed to the Coanda

effect whereby laminar flow of fluids over curved surfaces is effective to change

the direction of flow to conform to those surfaces. Apertures 48 shaped with non

linear profiles as shown in Figure 5 may allow ordinary vibratory sound waves to

enter relatively unimpeded while potentially destructive air blasts are however,

directed away from a delicate sound pickup device such as the ribbon 'R", or other

transducer.

Figure 6 displays an exploded representation of a modular ribbon

microphone assembly 50 comprised of a top ribbon transducer 52, an intermediate

matching transformer section 54, and a bottom amplification and electronics

control section 56, thus allowing different varieties of ribbon microphone systems io oe uspr-cυmigureα. uirect interconnecting pins 58 extending from bus bars 57

are used to interconnect each section 52, 54, and 56 to one another. Users of

microphones often wish to interchange components in the audio chain to adjust

different sonic and electronic attributes such as gain, frequency response, timbre,

distortion and the like. The use of a matched, modular setup has been used in prior

art condenser microphones but not in ribbon microphones, because ribbon

microphone construction prior to the present invention has not been consistent in

gain, frequency response, timbre or distortion. Figure 7 represents the assembled

stack of transducer, transformer, and electronics modules 52, 54 and 56. Straight

bus bars 57 are utilized connect the motor to transformer unit, and transformer unit

to amplifier/connector unit. The straight, preferably in-line fixed position

interconnects afford a greater degree of control of hum pickup from external fields,

in contrast to circuitous wired connections, Wire connections are often

manipulated for lowest hum pickup due to the variable nature of flexible wires.

The use of rigid interconnecting members 58 virtually eliminates this variable,

while at the same time assuring a low resistance, low noise connection. The use of

silver bars or copper plated with silver provides low resistance and low noise.

Thermal noise generated within the conductor is also minimized by the use of thick

conductors and silver metal. Generally there are three sections of prior art ribbon

microphones that contribute to the overall thermal noise and other noise floor produced by the completed microphone assembly. These include the ribbon, the

interconnections, and the transformer sections. The use of heavy conductors in

both the transformer and the interconnecting sections is desirable. The ribbon must

be a light conductor out of necessity, yet improvements to that portion are also

possible.

One preferred embodiment of a transducer 60 is shown in figure 8. It is a

tapered transducer 60 featuring a surrounding flux frame 61 that positions two or

more adjacent magnets 62 in proximity to an elongated, formed, preferably

multilayered, suspended ribbon 66 mounted therebetween. The tapered flux frame

61 shortens the acoustic distance from the front to the back of the ribbon 66 to

improve high frequency response in the shortened area, and reduces the abruptness

of any high frequency cutoff effect that is characteristic of "parallel" sided flux

frames. The flux frame 61 is equipped with ring-receiving apertures 68 near the

position of the magnets 62 extending through the flux frame 61. The apertures 68

are positioned to receive curved return rings, (shown for example, as members 72

in figures 9 and 9A) which are used to create a return path for the magnetic flux.

This increases the strength of the magnetic field in the gap where the ribbon 66 is

positioned and results in a more efficient conversion of sound energy into electrical

energy. This efficiency improvement increases overall output and sensitivity, which is a desirable attribute of high quality microphones. The return rings 72 are

shaped, with a cross-section that is small with respect to incoming sound waves at

any angle. This shape reduces reflections and undesired internal resonance. The

overall small cross-section of the return rings 72 reduces blocking or attenuation of

the sound energy yet permits sound energy to arrive unhindered at the ribbon 66,

while performing flux carrying duty.

Figures 9 and 9a show a non-tapered, generally parallel-walled transducer 70

with the installed arrangement of return rings 72. There may be as few as one

return ring 72, or many, depending upon the length of the transducer and the

amount of magnetic reinforcement/recirculation that is desired. The return rings

72 may be inserted via press fit into the thickness of the flux frame 73 to enhance

coupling of the magnetic field thereto, or they may be attached to the flux frame 73

by welding.

A further transducer embodiment is shown in Figure 10 with a flux frame

76 having the features of both the tapered and non-tapered styles, having further

side apertures 80 to shorten the distance from the front to the back of the ribbon.

The use of side apertures 80 is known to improve high frequency response in

ribbon microphones. The use of large, elongated curvilinear/circular side apertures 80 in conjunction with the use of tapered assemblies allows magnetic field strength

to be preserved.

Figure 11a represents a cross section view of a ribbon form 90 having a

predetermined ribbon-shaping surface pattern 92. The form 90 may be made from

a wax or dissolvable material which may support vapor deposition of metals, such

as aluminum thereon, or the plating of such metals. Figure l ib represents a cross

section view of a ribbon form 90 having a deposited layer of aluminum 94. The

aluminum thickness may generally be from about ¹A micron to up to about 4

microns. More than one layer (not shown) may be deposited on the surface 92 of

the form 90, The layers may be of the same materials or of different materials

having different mechanical and electrical properties. For instance, a first layer of

gold may be deposited, followed by a second layer of thicker aluminum and then a

third gold layer or mixed combinations thereof. The gold layers may be very thin,

in the order of a few hundred nanometers. Hie aluminum layer may be from

500nm to about 3000nm, more or less, depending upon the size required, the

amount of conductivity desired, and the total mass allowed in the design.

Generally, high mass ribbons require greater amounts of sound energy to be

vibrated within the magnet gap, while lower mass ribbons require less, so it is desirable to keep mass to a minimum. However, too-thin materials, such as

aluminum, become increasingly resistive however, as the cross section decreases.

The tradeoff between resistance and mass has long been a limiting factor in ribbon

microphone design, as has the tradeoff between strength and mass. The use of

composite materials, layered materials and highly conductive materials as taught

herein affords a greater design latitude and improved performance.

Figure 1 Ic represents, for example, an edge view of a completed ribbon 100

after removal from the form 90. The pre-formed metal ribbon 100 is thus stronger

and does not have fractures or stresses, nor will it tend to relax. Prior art ribbons

are made of formed by bending and/or distorting a flat sheet, which compromises

the tensile strength and leaves residual forces which may cause the ribbon to relax

over time. Figure 1 Id represents an edge view of a completed ribbon 102 produced

by the process of deposition on a form, having a predetermined pattern. The

pattern may be periodic, aperiodic, or graduated so that smaller, shorter waves

portions or undulations 104 are placed near the ends of the ribbon 102, and the

flatter portions 106 are arranged near the middle of the ribbon 102. Due to the

precise and confoπnal nature of the deposition process, fine details such as letters

(not shown) or features such as longitudinal ribs (not shown) may be produced to

mark or stiffen certain planar or surface portions of the ribbon 102. Figure l ie shows an example of a graduated fixture 110 having a scale 112,

movable slides 114, and clips 116 to hold a ribbon 118 to be adjusted. The figure

1 If discloses a schematic representation of a tuning system 120 to be utilized with

the graduated fixture 110 of figure l ie. A variable frequency oscillator 122 may

be connected to an amplifier 124 which drives a loudspeaker 126 and triggers a

strobe light 128 in synchronization with the oscillator 122. The oscillator 122 is

set to the desired resonant frequency of the ribbon 118 and the clips 116 are moved

until maximum excursion of the ribbon 118 is observed, indicating a resonance

peak of the ribbon 118, shown in figure l ie. The strobe light 128 aids in the

observation of the peak and also any other resonant modes, including out-of-phase

modes, which may lead to distortion. The ribbon 118 may be precisely tensioned

using the combination of the apparatus 110 shown in figure lie and the apparatus

120 and procedure therewith, represented by figure Hf, and then installed into a

transducer assembly when properly tuned. The ribbon 118 may then be connected

to a load, such as a transformer, and subsequent amplifier, during the tuning

process if desired. This fine and precise adjustment of the ribbon 118 improves the

unit-to-unit consistency of assemblies which is very desirable.

The view shown in Figure 12a is a plan view of a series of filaments or

fibers 130 suspended between a set of fiber holders 132. The fibers 130 may be made of a high tensile strength polymeric material such as Kevlar which does not

stretch or shrink. The fibers 130 may also be comprised of a carbon nanotube

fiber, ribbon or composite having high tensile strength and low mass. For

example, such a carbon nanotube ribbon may be conductive or super-conductive.

Figure 12b is a side view of the series of filaments 130 shown in figure 12a.

Figure 12c shows a side view of the series of filaments in proximity to a pair of

patterned forms 134 which may apply pressure, heat, or both. The view of Figure

12d is a side view of the series of filaments 130 after being impressed with the

shape of the forms 134. The series of filaments 130 may be further coated, plated

or covered using a deposition process, such as a vapor deposition process, not

shown for clarity. The deposited material may be aluminum or other conductive

material such as gold. Multiple materials may be used including alloys having

superconducting properties. Such alloys are generally stiff and hard to form into

wire, yet may be suitably formed in a practical manner by the method described.

The advantage of using such a superconducting or very highly conducting alloy is

an ability to produce a strong, low mass ribbon without reducing the conductivity

to the point where microphone output drops to an unacceptable degree.

Superconducting alloys may have sufficient tensile strength to be used alone in this

application. Carbon nanotubes or carbon fibers, or ribbons, may have sufficient

conductivity, strength, and low enough mass, to be used in this application with the advantage of improved toughness, resistance to long term distortion, sagging, or

damage. Very strong, low mass, and highly conductive ribbons may now be

constructed using these new techniques, (such multi-layering done, for example, by

bonding, adhesives, deposition or various interactive or adhesion processes).

In Figure 13 a, there is shown is a top view of a ribbon assembly 140 with a

sound absorbing wedge 142 placed a spaced distance from one side, in this case the

rear of the ribbon 143. The sound absorbing wedge 142 is effective to absorb and

attenuate sound energy arriving from the rear of the microphone. Ribbon

microphones without sound absorbers exhibit a dipolar, "figure 8" reception

pattern. Monopolar, or unidirectional ribbon operation is sometimes desired. The

back of the ribbon is sealed so that sound energy does not arrive at the ribbon from

the rear. The wedge 142 absorbs reradiated sound produced by the moving ribbon.

The shape of the wedge 142 reduces specular reflection back to the ribbon, which

is undesirable. Multiple wedges may be used. The wedges may be enclosed to

define a chamber 145 having one opening facing the ribbon 143. In Figure 13b

there is shown a detailed view of the sound absorbing wedge 142 showing a

heterogeneous structure. The heterogeneous structure is comprised of filaments,

open cell foams, and closed cell foams 144, each having a directionally- formed

increasing density and acoustic impedance to sound, which increase in loss in the form of heat without producing reflections from the front surface, which is at or

near the acoustic impedance of air. This construction allows lower frequencies to

be absorbed at a greater rate than would otherwise be possible with homogeneous

materials such as common foams.

Figure 14 is an example, in a cross section view, of a microphone assembly-

ISO having "back lobe" suppression. An acoustic labyrinth 152 may be produced

using rolled or coiled tubing 153 such as plastic tubing, Tygon TM, or other

coilable, formable generally tubular materials. The formable tubular materials may

be arranged in any formation so as to fit within the housing of the microphone 150.

Back chamber (as described partially in figure 13a) may be connected to the

acoustic labyrinth which may be positioned at or below the transducer assembly

154, or around internal structures or components such as a transformer. The tubing

153 may be filled with a lossy, sound absorbing material such as injected, open cell

foam of urethane, or filled with a loose, sound absorbing fibrous material such as

nylon, or aerogels. The length of the tube is generally about 30" as described in

the prior art for acoustic labyrinth construction using machined ports or chambers

which are more difficult to produce and do not offer positioning options of a

flexible tube. One end of the tube may be attached to the chamber of figure 13a so

that a continuous seal of air from the back of the ribbon 143 through the entire length of the tube 153 may be maintained. Such an arrangement provides a

convenient and repeatable construction of a unidirectional ribbon microphone

system which works as a pressure transducer.

Figure 15a discloses an electrical schematic diagram of a pair of identical

ribbons 160 and 162 produced using the teachings herein, arranged in parallel

circuit configuration. Figure 15b is a top view of the pair of identical ribbons 160

and 162 in proximity to each other and each within gaps of adjacent magnets 164.

Figure 15c shows a perspective view of a practical holder 166 for the adjacent

magnets 164 shown in figure 15b. The holder 1(J6 controls the amount of air or

sound waves from entering the space between the ribbons (160 and 162) using

sliding aperture stops 167 or other adjustable door means. The use of two identical

ribbons (i.e. 160 and.162) allows variable patterns to be produced using ribbon

elements within the space of one microphone without excessive distortion due to

the identical and repeatable nature of the ribbon elements when produced using

improved ribbon and microphone construction methods such as deposition,

synchronized tuning, and filamentous or carbon nanotube ribbon construction.

A storage and travel case 170 is shown in figure 16a, for a pressure sensitive

device such as a ribbon microphone 172. Prior art boxes generally have a lid which may be closed or opened suddenly. Such sudden unprotected operation as

the opening or closing of the case may produce undesired pressures that may

damage the contents. An air valve 174 is connected to latch (or hinge) so that there

is an escape path for air pressure during the opening and closing procedure. Figure

16b shows a cross section view of an air escape valve 174. A spring loaded

plunger 176 may be incorporated into the latch to release air through discharge

openings 177 prior to opening. The area of the valve 174 is large relative to the

case 170 so that undesired pressure cannot build up, even momentarily.

An exemplary microphone support 180 is shown in Figure 17 in a cross

sectional view of a sound absorbing structure integrated into the body of a

microphone 182. A plurality of annular rings 184 are preferably interposed with

acoustically lossy materials 186 such as filled low durometer urethanes. The

alternating series of lossy segments assures little propagation of noise from the

microphone stand 188, up into the microphone head. The flat, annular ring

arrangement allows reasonably rigid and compact microphone body to be safely

maintained while assuring a high area of sound absorbance. A clamp 190 may be

attached firmly to the microphone body base 191, but is isolated from head,

reducing or eliminating sound propagation from the stand into the microphone 182.

Claims

I Claim:

1. A ribbonned microphone assembly, having adjustable sound receiving

capabilities, including:

a transducer having a surrounding flux frame for positioning at

least two magnets adjacent a suspended ribbon between said magnets;

an array of receiving apertures arranged in said flux frame; and

at least one curved return ring positioned in said receiving

apertures to create a return path for magnetic flux in said transducer.

2. The microphone assembly as recited in claim 1, wherein said flux

frame has parallel sides.

3. The microphone assembly as recited in claim 1, wherein said flux

frame has tapered sides.

4. The microphone assembly as recited in claim 1, wherein said flux frame

has side apertures thereon.

5. The microphone assembly as recited in claim 4, wherein said side

apertures are non-circular.

6. The microphone assembly as recited in claim 4, wherein said side

apertures are elongated and curvilinear. 7. A method of manufacturing a ribbon for a ribbon microphone,

comprising:

providing a first form having an irregular predetermined ribbon

engaging surface thereon;

depositing a ribbon forming material on said ribbon engaging

surface; and

forming said microphone ribbon on said first form.

8. The method as recited in claim 7, including:

providing a second form having an irregular predetermined ribbon

engaging surface thereon which corresponds matingly to said irregular

predetermined ribbon engaging surface of said first form; and

sandwiching said ribbon forming material between said ribbon

engaging surfaces of said first and second forms.

9. The method as recited in claim 7, wherein said form has its temperature

controlled.

lO.The method as recited in claim 7, wherein said ribbon is comprised of

more than one material.

11. The method as recited in claim 7, wherein said form is comprised of a

vapor deposition supportable material selected from the group comprised

of aluminum, wax and a dissolvable material. 12. A method of tuning a ribbon for subsequent utilization of said ribbon in

a ribbon microphone comprising:

arranging a calibration member for adjustable supporting and

calibrating of a microphone ribbon therewith;

attaching a microphone ribbon to said calibration member, said

ribbon having a predetermined pattern formed thereon;

activating a variable frequency oscillator connected to a

loudspeaker, said oscillator being set to a desired resonant frequency of

said ribbon;

adjusting said calibration member to tension said ribbon; and

observing a maximum excursion of said ribbon which indicates a

resonant peak.

13. The method as recited in claim 12, wherein said ribbon is installed into

a transducer assembly in a ribbonned microphone.

14. A method for reducing sound propagation from a microphone support,

comprising:

arranging a plurality of ring-like spacer members as a support for

a ribbonned microphone;

interposing acoustically lossy material between adjacent spacer

members;

attaching a first end of said plurality of spacer members to a

ribbonned microphone housing; and

attaching a second end of said spacer members to a microphone

stand.

15. The method as recited in claim 14, wherein said spacer members are

of annular shape.

16. A case for the safe enclosure and un-pressurized transport and

removal and loading of a ribbonned microphone therewith, said case

comprising:

an enclosure housing;

an openable door on said case;

a spring loaded valve connected to said door which valve

opens said case to the outside ambient atmosphere during opening

and closing of said door. 17.A casing for a ribbonned microphone, said casing enclosing a ribbon

therewithin, said casing comprising:

a plurality of sound propagating apertures arranged through said

casing enclosing said ribbon therewithin, said apertures being

comprised of curved, non-cylindrical shape.

18. The casing as recited in claim 16, wherein apertures are arranged so as to

be curved away from said ribbon enclosed within said casing.

19. A modular ribbon microphone assembly comprised of;

a top ribbon transducer;

an intermediate matching transformer section; and

a bottom amplification and electronics control section, to

permit various combinations of sub-assemblies to be easily

interchangeable in said assembly.

20. The modular ribbon microphone assembly as recited in claim 19,

wherein each of said sub-assemblies have a bus bar with

interconnecting pins thereon to facilitate interconnection of said sub-

assemblies to one another.

21. A ribbon transducer for the detection of sound waves comprising:

an elongated ribbon structure comprised of electrically conductive carbon

nanotube filaments arranged adjacent to a magnetic field, wherein said ribbon

structure is connected to a further circuit.

22. A ribbon microphone having a movable ribbon element comprised of a

carbon nanotube material integrated therein.

23. A ribbon microphone having a movable ribbon element comprised of a

carbon fiber material integrated therein, said ribbon element comprising

a layer of carbon filaments, and,

a layer of a conductive metal attached onto said layer of carbon filament

material.

24. A composite membrane acoustic transducer structure arranged adjacent a

magnet assembly, said transducer structure and said magnet assembly arranged to

produce a flux field;

said transducer structure comprising a first layer of thin, elongate composite

membrane material held under tension;

a second conductive layer of membrane material attached to said first layer

of composite material, wherein said first and second layers of membrane material

are arranged adjacent to, generally parallel and offset from said magnet assembly, to produce said flux field through at least part of said first layer and said second

layer of composite material.

25. The composite membrane acoustic transducer structure of claim 24, wherein

said first layer is comprised of a carbon fiber.

26. The composite membrane acoustic transducer structure of claim 24, wherein

said first layer is a polymeric material.

27. The composite membrane acoustic transducer structure of claim 25, wherein

said carbon fiber is comprised of carbon nanotubes.

28. The composite membrane acoustic transducer structure of claim 24, wherein

said first layer is electrically conductive.

29. The composite membrane acoustic transducer structure of claim 24, wherein

said second conductive layer is a deposited metal.

30. The composite membrane acoustic transducer structure of claim 24, wherein

said second conductive layer is an electroplated layer.

31. The composite membrane acoustic transducer structure of claim 24, wherein

said second conductive layer is an electrodeposited layer.

32. A method of manufacturing a membrane transducer element, comprising:

providing a form having a predetermined pattern thereon;

depositing a layer of metal upon said pattern on said form to create a

continuous, separate metal transducer element on said form;

removing said deposited metal transducer element from said pattern, and

installing said membrane transducer element adjacent to a magnetic field.

33. The method of manufacturing a membrane transducer element as recited in

claim 32, wherein said predetermined pattern is a periodic pattern.

34. The method of manufacturing a membrane transducer element as recited in

claim 32, wherein said predetermined pattern is aperiodic.

35. The method of manufacturing a membrane transducer element as recited in

claim 32, wherein said metal is aluminum.

36. A method of manufacturing a ribbon type acoustic element to a specific

frequency comprising:

axially mounting an acoustic element in a holder having a movable

mounting point for supporting said acoustic element;

moving said mounting point to vary the tension of said acoustic element, and

resonating said acoustic element to a predetermined frequency.

37. The method of manufacturing a ribbon type acoustic element to a specific

frequency as recited in claim 16, where said acoustic element is a metal element. 38. The method of manufacturing a ribbon type acoustic element to a specific

frequency as recited in claim 36, where the acoustic element comprises a

transducer assembly.