US3436493A - Electroacoustic transducer with unilateral directional characteristic - Google Patents
Electroacoustic transducer with unilateral directional characteristic Download PDFInfo
- Publication number
- US3436493A US3436493A US490994A US3436493DA US3436493A US 3436493 A US3436493 A US 3436493A US 490994 A US490994 A US 490994A US 3436493D A US3436493D A US 3436493DA US 3436493 A US3436493 A US 3436493A
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- US
- United States
- Prior art keywords
- phase
- sound
- shifting
- compliance
- diaphragm
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
- H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
- H04R1/38—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone
Definitions
- An electroacoustic transducer includes a diaphragm having forward and rear surfaces and a phase-shifting arrangement for transmitting sound to the rear surface of the diaphragm.
- the phase-shifting arrangement includes a first phase-shifting system consisting of a resistance and a compliance and effective in a lower sound frequency range and includes a second phase-shifting system consisting of a mass and a compliance and effective in a higher sound frequency range, the two systems being connected in series with each other between a common rear sound inlet, for both lower and higher sound frequency ranges, and the rear surface of the diaphragm.
- This invention relates to electroacoustic transducers, such as microphones, and, more particularly, to an electroacoustic transducer including a phase-shifting acoustic arrangement effective over a wide frequency range.
- phase-shifting acoustic arrangement which is disposed in the sound path from the outside air to the rear surface of the diaphragm.
- This phase-shifting acoustic arrangement serves to impart a unilateral directional pattern, such as a cardioid pattern, for example, to the microphone.
- the phase-shifting arrangement comprises acoustic elements representing masses, compliances, frictional resistances and sound lines, and the combination of these elements has a delaying or phase-shifting effect.
- the delay is equal to the time required for the sound waves to traverse, exteriorily of the microphone, the distance between the center of the forward surface of the diaphragm and the effective sound inlet of the phase-shifting arrangement. This time is almost constant up to very high sound frequencies, so that the delay which is effected by this phase-shifting arrangement disposed inside the microphone is highly independent of frequency, and the phase increases with frequency in a linear relation.
- phase-shifting arrangements are known, but all have the disadvantage that they do not have a constant transit time throughout the frequency range to be transmitted. This results in disturbances in the unilateral directional pattern, and the differences between the external and internal transit times result in phase difference. Thus, sound waves reaching the microphone from the rear are also converted into electrical oscillations within a certain frequency range, where the microphone has poor directional discriminating properties.
- An object of the invention is to provide an electroacoustic transducer including a phase-shifting arrangement in which the above-mentioned disadvantages are minimized so that the directional pattern is maintained throughout all the frequencies to be transmitted.
- Another object of the invention is to provide an electroacoustic transducer comprising a phase-shifting arrangement including a first phase-shifting system consisting of a resistance and a compliance and effective in a lower frequency range, and a second phase-shifting system consisting of a mass and a compliance and effective in a higher frequency range, the transducer having a common rear inlet for both sound frequency ranges.
- the parameters are expressed in the following units: resistance R in grams per second, compliance C in centimeters per dyne, length of sound path A in centimeters, velocity of sound in air c in centimeters per second, mass L in grams, and transit time 7- in seconds.
- resistance R is expressed in ohms
- capacitance C in farads
- inductance L in henries.
- While the invention is not restricted to a specific type of electroacoustic transducers, it is particularly suitable for condenser microphones and dynamic treble microphones. The latter may be combined with a second microphone for the bases, to constitute a so-called two-range transmitter for high requirements.
- Still another object of the invention is to provide a condenser microphone in combination with a phase-shifting arrangement and in which the resistance serving for the frictional control of the vibratory system also constitutes the resistance for a phase-shiftin system including a resistance and a capacitance.
- Still a further object of the invention is to provide an electrodynamic transducer in combination with a phaseshifting arrangement and including a gasket sealing the space accommodating a moving coil from an air chamber constituting the compliance in a phase-shifting system including a resistance and a compliance.
- Yet another object of the invention is to provide an electroacoustic diaphragm in combination with a phaseshifting arrangement, and having two phase-shifting systems as mentioned above, and in which at least one of the acoustic elements in each of the phase-shifting systems is adjustable to compensate for deviations, such as due to manufacturing tolerances.
- FIGS. 1a and 1b are schematic wiring diagrams illustrating electric circuits equivalent to conventional phaseshifting arrangements
- FIG. 2 is a schematic wiring diagram of the electric circuit equivalent to the phase-shifting arrangement of the invention.
- FIGS. 3a and 3b are frequency response curves of different types of microphones with and without the phaseshifting arrangements of the invention.
- FIG. 4 is a simplified cross sectional view of a condenser microphone embodying the invention.
- FIG. is a simplified cross sectional view of an electrodynamic microphone embodying the invention.
- FIG. la shows an electrical circuit equivalent to a known system including a resistance and mass, and which meets only partially the requirement for a phase-shifting effect having a linear relation to frequency.
- FIG. 1b shows such a system including a resistance and a compliance.
- Z is the impedance of the vibratory diaphragm
- L-R in FIG. la, and R-C in FIG. lb are phase-shifting arrangements.
- C is the air chamber which is acoustically necessary to define the reference pressure.
- u and u correspond to the alternating sound pressures on the forward face of the diaphragm and at the rear end of the phase-shifting arrangement, respectively.
- phase displacement which equals the external phase angle
- w is the circular frequency Zn-f
- A is the shortest path length between the center of the forward face of the diaphragm and the effective sound inlet of the phaseshifting arrangement.
- C is the velocity of sound and 0 the angle if incidence of sound with reference to the main axis of the microphone system.
- the phase-shifting systems effect an internal phase displacement a, which is, in the ideal case, as large as the external phase displacement.
- the latter system has an effective phase-shifting effect at higher frequencies.
- FIG. 2 is an electric circuit diagram equivalent to the invention arrangement.
- the improvements due to the provision of the delay line of the invention are apparent from FIGS. 3a and 3b.
- FIG. 3a shows the frequency response curve of a condenser microphone in the case of sound coming from a source directly in front of the microphone, or zero angle of sound incidence, and in the case of sound coming from a source directly at the rear of the microphone, wherein the angle of sound incidence is 180.
- the solid line 180 represents the frequency response for sound coming from a source at the rear of an electrodynamic treble microphone embodying the invention.
- the dotted line indicates the response of a known arrangement.
- FIG. 4 is a highly simplified cross sectional view of a condenser microphone embodying the invention.
- This microphone includes a diaphragm 1 comprising, for example, a polyester sheet with a vapor-deposited gold layer.
- Diaphragm 1 is secured to a microphone housing 3 with the interposition of a spacing ring 2.
- Housing 3 defines a cavity including an air chamber C, which may be adjustable in volume by means of an annular disc 4 screw threaded in housing 3.
- the second system in accordance with the invention is formed by the mass L and the compliance C Mass L is formed by a vibratory air column in one or more tubes and which may be adjustable.
- Compliance C is formed by the air cushion enclosed between diaphragm 1 and a counter electrode 7.
- A is the sound path from the center of the forward surface of diaphragm 1 to the rear sound inlet at the entrance of resistance R.
- the frictional resistance will be chosen as the freely selectable value because it is of great importance also for the frequency response of the transmission lever at 0 sound incidence.
- FIG. 5 illustrates, in highly simplified form, an electodynamic transducer embodying the invention.
- a diaphragm 1 is secured by a retaining ring 2 to the head of the magnetic system 8.
- the magnetic system defines a housing, and the magnetic circuit is closed by magnet 9 having the pole piece 10, which defines an air gap including a moving coil.
- the frictional resistance is shown at R and an air chamber at C
- Mass L and air chamber C must be selected, in accordance with the invention, with reference to A, R and C and these constitute the additional phase-shifting system.
- Mass L may be formed, for example, by one or more tubes which may be adjustable.
- Compliance C is formed by the air chamber between diaphragm 1 and the magnet system 8.
- This air chamber is sealed by a gasget or washer 11, which in particular separates the air chamber C from the air chamber C
- mass L was formed by the mass of the air column vibratable in the air gap. This arrangement is diflicult to adjust, because the design of the air gap is determined mainly in respect to magnetic aspects.
- FIG. 5 elements of FIG. 5 are adjusted in the same manner as in FIG. 4.
- the phase-shifting arrangement comprises a mass element which is nearest to the rear surface of the diaphragm, and a friction element which is nearest to the sound inlet of the phase-shifting arrangement in the sound path from such inlet to the rear surface.
- An electroacoustic transducer comprising, in combination, a diaphragm having forward and rear surfaces; a phase-shifting arrangement for transmitting sound to said rear surface of said diaphragm to impart a unilateral directional pattern to said transducer; said phase-shifting arrangement including a first phase-shifting system consisting of a resistance and a compliance and effective in a lower sound frequency range, and a second phaseshifting system consisting of a mass and a compliance and effective in a higher sound frequency range; and means defining a common rear sound inlet, for both lower and higher sound frequency ranges, to said phase shifting arrangement.
- transducer is an electrostatic transducer having friction-controlled vibratory system including said diaphragm; said resistance being included in said vibratory system and effecting friction control thereof.
- transducer is an electrodynamic transducer including means defining an air space; a moving coil disposed in said air space; and means defining an air chamber separated from said air space and constituting a compliance of said first phase-shifting system.
- transducer is an e'lectrodynamic transducer including means defining an air gap; a moving coil disposed in said air gap; means defining an air chamber constituting said compliance of said first phase-shifting system; and a gasket separating said air gap from said air chamber.
- An electroacoustic transducer as claimed in claim 1, in which one element of each of said first and second phase-shifting systems in an adjustable acoustic element.
- An electroacoustic transducer as claimed in claim 6, in which the adjustable acoustic element of said first phase-shifting system comprises the compliance thereof.
- said last-named compliance comprises an air chamber defined, in part, by a disc adjustable to change the volume of said air chamber.
- An electroacoustic transducer as claimed in claim 6, in which one of said adjustable acoustic elements comprises the rnass of said second phase-shifting system.
- An electroacoustic transducer as claimed in claim 10, in which said mass comprises adjustable tube means.
- phase-shifting arrangement includes a mass in the sound path between said common rear sound inlet and said diaphragm, and nearer said rear surface of said diaphragm.
- phase-shifting arrangement includes a friction acoustic element adjacent the sound inlet of said phase-shifting arrangement and in the sound path from said inlet to said rear surface of said diaphragm.
- phase-shifting arrangement comprises a mass acoustic element and a friction acoustic element in series in the sound path from said inlet to said rear surface of said diaphragm; said mass acoustic element being nearer said rear surface of said diaphragm, and said friction acoustic element being adjacent said sound inlet.
Landscapes
- Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
- Apparatuses For Generation Of Mechanical Vibrations (AREA)
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT881964A AT251668B (de) | 1964-10-16 | 1964-10-16 | Elektroakusticher Wandler |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US3436493A true US3436493A (en) | 1969-04-01 |
Family
ID=3608803
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US490994A Expired - Lifetime US3436493A (en) | 1964-10-16 | 1965-09-28 | Electroacoustic transducer with unilateral directional characteristic |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US3436493A (de) |
| AT (1) | AT251668B (de) |
| DE (1) | DE1462123A1 (de) |
| GB (1) | GB1122413A (de) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT410741B (de) * | 2002-02-26 | 2003-07-25 | Akg Acoustics Gmbh | Druckgradienten-mikrofonkapsel |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3115207A (en) * | 1954-01-11 | 1963-12-24 | Electro Voice | Unidirectional microphone |
-
1964
- 1964-10-16 AT AT881964A patent/AT251668B/de active
-
1965
- 1965-07-23 DE DE19651462123 patent/DE1462123A1/de active Pending
- 1965-09-28 US US490994A patent/US3436493A/en not_active Expired - Lifetime
- 1965-10-04 GB GB42044/65A patent/GB1122413A/en not_active Expired
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3115207A (en) * | 1954-01-11 | 1963-12-24 | Electro Voice | Unidirectional microphone |
Also Published As
| Publication number | Publication date |
|---|---|
| AT251668B (de) | 1967-01-10 |
| GB1122413A (en) | 1968-08-07 |
| DE1462123A1 (de) | 1969-02-27 |
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