EP3206414A1 - Microphone array - Google Patents

Abstract

Microphone arrangement with at least one microphone for measuring airborne sound and an evaluation unit for storing the measured microphone signals, characterized in that an acceleration sensor is provided, which detects a structure-borne noise for the microphone, wherein the evaluation unit is designed to return to the structure-borne sound portion of the microphone signals herauszurechnen.

Description

The invention relates to a microphone arrangement, in particular a multi-channel, synchronous measurement technique for airborne and structure-borne noise. Can be used, the microphone assembly for the realization of an acoustic camera with a distributed multi-sensor microphone system. Moreover, the invention also makes it possible to realize adaptive systems, e.g. for noise reduction.

The document " Listening with the eyes - acustic camera ", GFAI / Society for Applied Computer Science, Berl in describes different applications for an acoustic camera. It explicitly deals with spatially resolved investigations of noise emissions from wind turbines, construction vehicles, automobiles, aircraft, industrial plants and sewing machines.

The DE10304215A1 - "Method and apparatus for imaging of acoustic objects and a corresponding computer program product and a corresponding computer-readable storage medium" describes the construction of an acoustic camera with a central data recorder, a calibration tester and a PC with different analysis and visualization options.

The US2014 / 0241548 - "Acoustic Sensor Apparatus and acoustic camera for using MEMS microphone array" describes an acoustic camera made of MEMS microphones in an arrangement on a printed circuit board.

The US 5193117 - "Microphone Apparatus" describes a construction with two microphones each with a ball characteristic, which are used by temporal shift and overlay to reduce background noise.

Out DE 10 2013 005 405 A1 For example, a method and a device for determining acoustic properties of a vehicle interior are known. The method combines structure-borne sound information with simultaneously determined sound pressure information of the vehicle interior, wherein the sound pressure information is detected by means of a beam-forming microphone array in the far field and / or by means of an intensity measuring device in the near field. A very high degree of detection in the determination of a sound radiation distribution in the vehicle interior is realized over a broad medium frequency range with simultaneous knowledge of a body sound introduction. The aim of this linkage is a three-dimensional sound pressure mapping, which allows to carry out a transmission path analysis.

The invention has for its object to provide a microphone assembly, which is particularly suitable to achieve undisturbed results in the measurement of airborne sound.

According to the invention the object is achieved by a microphone arrangement with the features of claim 1. The subclaims correspond to advantageous embodiments.

The measurement of airborne sound is carried out according to the prior art with microphones. These convert airborne sound into an electrical signal, typically into an electrical voltage. According to the prior art, this signal is amplified and then further processed or digitized directly in the microphone and transmitted digitally. In addition to the airborne sound to be measured, microphones also convert structure-borne noise into an electrical signal which is superimposed on the actual measured variable as a disturbance. In order to minimize these disturbances, microphones are usually built up isolated against structure-borne noise, eg by integration into one vibration-damping mount or by suspension on the ceiling (eg concert halls).

The microphone arrangement according to the invention has at least one microphone for measuring airborne sound and an evaluation unit for storing the measured microphone signals. The storage of the microphone signals is important for applications in which, for example, a spatial resolution of sound sources is to take place. In the microphone arrangement according to the invention, an acceleration sensor is provided which detects a structure-borne noise for the microphone. According to the invention, the evaluation unit is designed to eliminate a component of the microphone signals that goes back to the structure-borne noise. When calculating, the recorded microphone signals are scaled and subtracted from the structure-borne noise. The aim of the calculation is to reduce the influence of structure-borne noise on the microphone signals. Preferably, a field (array) of microphones is provided, the microphone signals are evaluated in a conventional manner by the evaluation to an acoustic image. The microphones may, for example, be a microphone according to MEMS technology (microelectromechanical system). In addition, MEMS microphones may be a small distance apart that is small relative to a mean wavelength of the incoming airborne sound. So information about the intensity of airborne sound can be recorded very accurately.

Preferably, a first group evaluation unit is provided for a first group of microphones and a second group evaluation unit for a second group of microphones. First and second group evaluation unit provide the received microphone signals each with time stamps and cause a further evaluation. The core idea for the use of group evaluation units is that which is necessary for signal processing Already apply computational power to subgroups of data, not the entirety of the data. Furthermore, the amount of data exchanged between the group evaluation units and a central unit can be reduced, for example by lossless compression. Expediently, further group evaluation units can be provided for further groups of microphones. The assignment of the signals of the acceleration sensors is preferably carried out here for the microphones grouped in the groups. For a better evaluation of the signals, the group evaluation units are preferably synchronized with each other with the evaluation unit of the microphone arrangement. The evaluation unit may be a microcontroller and / or an FPGA unit as well as a memory for the microphone signals and for the signals of the acceleration sensors to the structure-borne sound. Conveniently, each of the microphones is equipped with an acceleration sensor, which is installed together with the microphone. Depending on the design of the microphone, the acceleration sensor may be integrated in the housing or even on a circuit board of the microphone. In a further preferred embodiment, further sensors are provided for the microphone arrangements, which allow a position determination or a determination of the orientation for the microphone arrangement. The position determination can help with an evaluation of the sound signals.

An important idea of this invention is to integrate a pick-up for structure-borne noise (ie an acceleration sensor) together with the acoustic microphone in a mechanical unit and so perform an electronic compensation, ie removal of the structure-borne sound signal. For this purpose, an arithmetic unit (ie a microcontroller or an FPGA) is further integrated, which receives both signals synchronously and preferably subtracts each other digitally. Alternatively, an analog circuit, such as a differential amplifier, may be used. The acceleration sensor may be single or multi-axis. Especially Advantageous is the invention described using micromechanical sensors that offer advantages over precision mechanical sensors by their small size, low weight, high robustness and low price. The preferably integrated in the microphone arithmetic unit can also compress these signals in addition to the compensation of interference signals and provided with time stamps, so that they can be synchronized with the signals of other microphone units in the aftermath. In addition, the additional recording of the signal of an acceleration sensor can also record very low frequencies that an acoustic microphone can no longer detect (infrasound).

The integration of at least one acoustic microphone with at least one single- or multi-axis acceleration sensor and a programmable arithmetic logic unit with non-volatile memory in the microphone arrangement is envisaged. Here, the use of highly integrated sensors, which is usually realized as a microelectromechanical system (MEMS), advantageous. In principle, the microphone and the acceleration sensor can also be produced in a MEMS process. This is in illustration 1 shown.

The advantage of the use of highly integrated sensors lies in particular in the increased robustness of the sensors and the measuring method, lower sensitivity to external disturbances and a simplified performance of acoustic measurements. In addition, the sensor modules according to the invention offer a considerable potential to reduce costs for this measurement technology by a factor of 100 to 1000 and to realize adaptive systems.

For certain applications, such as the use in an acoustic camera or other multi-channel measuring method, it is advantageous to position or Alignment of the respective microphone exactly and simultaneously to capture the measurement. Beyond the position, variables measured locally on the microphone, such as the temperature or the absolute pressure, may be advantageous.

According to the prior art (example acoustic camera) for this purpose the measuring microphones are set up stationary and generates an acoustic reference pulse at a known position. By means of an algorithm it is concluded from the arrival of the pulse at each microphone or from the phase position of the acoustic oscillations to the position of the microphones, which are usually arranged in a fixed arrangement, e.g. circular or arranged on a tripod.

Another embodiment of this invention integrates further sensors in the microphone array: The integration of a compass allows the measurement of the exact orientation in space during the measurement. This allows the orientation of the microphones to be recorded during the measurement. This allows acoustic measurements on a non-stationary platform, such as on a ship (at sea). In a further embodiment, the integration of a rotation rate sensor allows an improved determination of the orientation of the microphone.

Another measure that is advantageously integrated in the described microphone arrangement is a rangefinder, which determines the distance to the examined, sound-emitting object, for example by transit time measurement of a time-modulated laser beam.

Preferably, the integration of at least one acoustic microphone with at least one single or multi-axis acceleration sensor and a programmable arithmetic unit with non-volatile memory and other, Independent sensors, for example, to determine the rate of rotation, the orientation (compass), the pressure, the temperature or the distance to the measurement object provided.

In a particular embodiment, an integrated microphone unit allows an improvement of the frequency and phase response: A first microphone is combined with a second, different type of microphone. For example, a microphone for measuring audible sound (f <20kHz) can be combined with a second microphone for measuring ultrasound (f> 20kHz). In the arithmetic unit, both signals are superimposed time synchronously, so that a particularly broadband microphone unit is created. By using the second, closely spaced microphone, it is also possible to measure the pressure gradient and the sound intensity.

• Die Daten von mindestens zwei bis typisch 30 Mikrofonen werden in einer autark arbeitenden Recheneinheit B zeitsynchron zusammengeführt und mit Zeitstempeln versehen sowie zwischengespeichert. Mehrere dieser Recheneinheiten B synchronisieren sich wiederum vor Beginn einer Messung, z.B. über ein Netzwerk. Alle Messdaten werden mit einem Zeitstempel entweder zu Beginn einer Messung (bei Abtastung mit konstanter Abtastrate) oder mit jedem aufgenommenen Messwert (bei variabler Abtastrate) aufgezeichnet und zwischengespeichert.

Another technical challenge is the time-synchronized recording of a large number of individual microphones. According to the state of the art of acoustic cameras, typically 30 .... 100 analog signals are fed in parallel with a data recorder which digitizes these signals and records them synchronously. Here another aspect of this invention provides significant benefits through significantly reduced cabling and cost overhead:

• The data from at least two to typically 30 microphones are combined in a self-sufficient computing unit B time synchronized and provided with time stamps and cached. Several of these arithmetic units B are in turn synchronized before starting a measurement, for example via a network. All measurement data is recorded with a time stamp either at the beginning of a measurement (in the case of sampling with constant sampling rate) or with each recorded measured value (with variable sampling rate) and buffered.

• Entfernung von Störungen durch Filterung
• Entfernung von Offsets der aufgezeichneten Sensordaten
• Mathematische Operationen (z.B. Addieren, Subtrahieren, Multiplizieren, Dividieren, Korrelation) der Sensorsignale untereinander
• Bestimmung von Laufzeitunterschieden (d.h. Unterschieden im Zeitpunkt der Aufnahme einer bestimmten akustischen Signatur zwischen unterschiedlichen Multisensor-Mikrofonen)
• Korrektur des Phasengangs der Mikrofone
• Korrektur des Frequenzgangs der Mikrofone
• Verzögerung und Addition ("Delay and Sum") der Messdaten der einzelnen Mikrofone

Figure 2 shows the structure according to this invention.
The arithmetic units B can perform a preprocessing of the measured data beyond the recording, such as

• Removal of disturbances by filtering
• Removal of offsets of recorded sensor data
• Mathematical operations (eg adding, subtracting, multiplying, dividing, correlation) of the sensor signals with each other
• Determination of transit time differences (ie differences in the time of recording a specific acoustic signature between different multisensor microphones)
• Correction of the phase response of the microphones
• Correction of the frequency response of the microphones
• Delay and Sum ("Delay and Sum") of the measurement data of the individual microphones

At the end of a measurement cycle, all computing units B transfer their measured data with a time stamp to a central processing unit C, on which the overall measurement is then evaluated. The structure can be extended modularly by adding further arithmetic units B or possibly supplemented by cascading. A key advantage lies in the fact that the merging of all channels can take place offline in the arithmetic unit C at the end. The difficult technical task of synchronizing a measuring system with several hundred channels is thus reduced to the synchronization of the computing units B with each other.

The arithmetic units B can continue to pre-process the measured signals, for example by compensation, correction of offsets or even compression, in order to then only process the preprocessed data to the central processor To transfer arithmetic unit C. For the realization of an acoustic camera, the arithmetic units B can already perform a preprocessing of the measured data of the microphones. The computing units B are group evaluation units which evaluate signals of a group of microphones.

LIST OF REFERENCE NUMBERS

(1)

Microphone 1

(2)

Optional: different microphone 2

(3)

accelerometer

(4)

optional: additional sensor elements (compass, yaw rate, pressure, ...)

(5)

computer unit

(6)

non-volatile memory

(7)

electrical interface / network interface

(8th)

Interface to the microphone module

(9)

Computing unit with microcontroller and possibly FPGA

(10)

non-volatile memory

(11)

Network Interface

(12)

opt. wireless network

(13)

(Central) arithmetic unit

(14)

Network Interface

(15)

opt. wireless network

(16)

non-volatile memory

(17)

microphone

(18)

data recorder

(19)

PC with computer program

Examples of the invention are:

1. 1. multi-sensor microphone consisting of at least one microphone, a sensor for structure-borne noise and a computing unit, a non-volatile memory and a preferably digital interface
2. 2. Multi-sensor microphone according to number 1, whereby the sensors used are structure-borne microelectromechanical systems (MEMS)
3. 3. Multi-sensor microphone according to number 1 or 2, wherein further sensors, such. Rotation rate, absolute pressure, magnetic field sensors (compass) or distance sensors are integrated into the multi-sensor microphone
4. 4. multi-sensor microphone according to number 1 or 2, wherein other different types of microphones e.g. are integrated for an extended frequency range
5. 5. Multi-sensor microphone according to number 1 or 2, whereby more identical microphones are integrated into the multi-sensor microphone
6. 6. Multi-sensor microphone according to number 4 or 5, wherein the distances between the microphones are small compared to the average wavelength of the signal to be examined
7. 7. Distributed, synchronous multi-sensor microphone system consisting of microphones numbered 1-6, with at least two multi-sensor microphones each with a self-sufficient recording unit are connected, which records all connected microphones time synchronously and with a time stamp and more Recording units connected microphones that have synchronized automatically before a measurement
8. 8. Recording unit according to number 7, wherein this is preferably constructed of a microcontroller with a Field Programmalbe gate array (FPGA) and a storage medium for the caching of larger amounts of data.
9. 9. Distributed, synchronous multi-sensor microphone system with self-sufficient recording units according to the numbers 7-8, which make a preprocessing of the recorded sensor data.
10. 10. Distributed, synchronous multi-sensor microphone system with stand-alone recording units according to the numbers 7-9, which perform an analysis of the recorded sensor data and determine transit time differences of an acoustic signal between the multi-sensor microphones
11. 11. Distributed, synchronous multi-sensor microphone system according to the numbers 7-9, wherein the recorded measurement data including their time stamp after completion of the measurement are transmitted to a central processing unit.
12. 12. Distributed, synchronous multi-sensor microphone system according to the numbers 7-11, wherein the measurement data for controlling an actuator, such. of a loudspeaker will be used to generate counter sound.

Claims (11)

Microphone arrangement with at least one microphone for measuring airborne sound and an evaluation unit for storing the measured microphone signals, characterized in that an acceleration sensor is provided, which detects a structure-borne noise for the microphone, wherein the evaluation unit is designed to return to the structure-borne sound portion of the microphone signals herauszurechnen. Microphone arrangement according to claim 1, characterized in that a field of microphones is provided, whose microphone signals are evaluated by the evaluation unit to an acoustic image. Microphone arrangement according to claim 1 or 2, characterized in that the microphones, in particular formed as MEMS microphones, have a distance from each other which is small relative to a mean wavelength of the incoming airborne sound. Microphone arrangement according to one of Claims 1 to 3, characterized in that a first group evaluation unit is assigned to a first group of microphones and a second group evaluation unit is assigned to a second group of microphones, wherein the first and second group evaluation units each time-stamp the microphone signals of the microphones to be assigned to them and evaluate. Microphone arrangement according to claim 4, characterized in that further group evaluation units and further groups of microphones are provided. Microphone arrangement according to claim 4 or 5, characterized in that the group evaluation units are designed to respectively evaluate the signals of the acceleration sensors and the microphones grouped in the group. Microphone arrangement according to one of claims 1 to 6, characterized in that the group evaluation units are synchronized with each other and with the evaluation unit. Microphone arrangement according to one of claims 1 to 7, characterized in that the evaluation unit has a microcontroller and / or an FPGA unit and a memory for the microphone signals and the signals of the acceleration sensors for structure-borne noise. Microphone arrangement according to one of claims 1 to 8, characterized in that each of the microphones has an acceleration sensor which is installed together with the microphone. Microphone arrangement according to one of claims 1 to 9, characterized in that further sensors are provided which allow a position determination for the microphone arrangement. Microphone arrangement according to one of claims 1 to 10, characterized in that further sensors are provided which measure locally the temperature or the absolute pressure.

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