AT523698A2 - DEVICE FOR ACOUSTIC MEASUREMENT OF AIR SOUND WAVES - Google Patents

Abstract

The invention relates to a device (1) for the acoustic measurement of airborne sound waves for arrangement in a vehicle test bench, the device (1) having at least one microphone (13) for recording airborne sound waves and a housing (2) surrounding the microphone (13), wherein the housing (2) has at least one opening (10) for the passage of the airborne sound waves from the outside to the microphone (13). The object is to provide a particularly robust device that reduces background noise. This object is achieved in that at least one first protective element (3) is arranged in the opening (10), which has at least a first grille that prevents particles from entering the housing (2) and that at least one second protective element (7) is arranged in the opening (10), which reduces the occurrence of interfering noises of an air flow.

Description

The invention relates to a device for the acoustic measurement of airborne sound waves for arrangement in a test bench - in particular in a vehicle test bench - the device having at least one microphone for recording airborne sound waves and a housing surrounding the microphone, the housing having at least one opening for the passage of airborne sound waves from

has outside to the microphone.

Such devices are used in EoL test stands (end-of-line test stands), which are used for quality assurance at the end of a production line. Among other things, functional tests are carried out on the workpiece (test item), for example motors, to determine whether they are fully functional. As part of this comprehensive inspection of the workpiece, airborne sound acoustical measurements are also carried out and evaluated during operation with the aid of microphones. If there are abnormalities in the sound, the workpieces - for example motors - are rejected.

For this purpose, normal commercially available microphones can be used, which are arranged in a housing that keeps coarse dirt away. However, these usual microphones are not impervious to liquids and do not meet the requirements of a test bench. This can lead to oil and cooling water leaks and high air flow speeds, for example through ventilation of the test bench. This generates noise that complicates the detection of noises from defective components. In addition, all possible noises are recorded from the environment, for example from the

Manufacturing, which can, however, contribute to the falsification of the measurement.

Existing devices for harsh environments are primarily suitable for outdoor use. Although these meet the requirements for resistance to wind and weather, they are not suitable for the action of mechanical forces by test objects on the test bench or by fitters. Ordinary devices with microphones for the outside area do not meet the high demands on test stands.

Boundary microphones, which are arranged on the floor at concerts, for example, are also not suitable for arrangement on a test stand, especially with regard to wind noise and with regard to their repellent properties against liquids, since liquids and mechanical

Influences can destroy them and make them unusable.

The object of the present invention is to provide a device which meets these requirements, is robust and reduces the noise.

According to the invention, this object is achieved by a device specified above in that at least one first protective element is arranged in the opening, that at least one first grille that prevents particles from entering the housing and that at least one second protective element is arranged in the opening that reduces the occurrence of noise in an air flow. This has the advantage that the two protective elements prevent the ingress of dirt. By providing a protective element, the background noise of the air flow is reduced and the noise is insulated or attenuated. The protective element absorbs or reflects

the airborne sound waves emanating from the air flow.

These protective elements are essentially covers of the opening. For example, these protective elements can be fastened to the housing with a fastening ring and screws. Alternatively, the protective elements can be glued to the housing or with the housing using another joining method

get connected.

For particularly simple and inexpensive production and to ensure that coarse dirt particles cannot damage the microphone, it is advantageous if the first protective element has a perforated plate.

Acoustically neutral perforated sheet metal is particularly advantageous as a cover.

In order to provide a further barrier for dirt particles, which can have larger or smaller mesh sizes for the respective requirement, it is provided in a favorable embodiment that the first protective element has at least one layer of textile fibers.

A protection against dirt particles created in this way can be applied particularly easily if the at least one layer of textile fibers forms a coating.

This coating can, for example, form a coating over the above-mentioned perforated plate. Alternatively, a coating can be provided over the entire housing.

In order to be able to keep even the smallest dirt particles away effectively, it is

advantageous if the textile fibers are formed into a fleece.

In order to achieve particularly favorable acoustic properties of the device, the first protective element is a perforated plate glued with fleece, which swirls the

Air and thus noise are completely or at least largely prevented.

The perforated plate is particularly advantageous because sound waves are hardly reflected in the desired acoustic frequency range. The perforated plate is like this

chosen so that there are no annoying reflections and interference.

It is particularly favorable if the second protective element consists essentially of

acoustically neutral material.

In order to achieve particularly good properties for preventing interfering noises from the air flow or to provide the best possible barrier against dirt particles, it is advantageous if the second protective element has a thickness that is greater than 2 mm. The second protective element thus keeps the air flow away from the microphone and reduces the disruptive influence of the air flow on the microphone.

Particularly favorable properties for reducing interfering noises caused by air flow can be achieved if the second protective element is designed to be compressible and preferably has a cellular structure. As a result, this protective element has ideal conditions for preventing

Noise.

If the second protective element has at least one foam layer and is preferably made of foam, the influence of the air currents can around

the device can be prevented in a particularly simple manner.

To increase the quality of the recording, it is advantageous if the housing tapers in the shape of a funnel towards the microphone, with the microphone in an interior space

of the housing is arranged.

An embodiment in which the housing has a flat funnel shape in an interior space is particularly advantageous, an angle of inclination of this funnel shape being less than 45 ° and advantageously between 5 ° and 30 °. This very flat funnel ensures that no large reflective surfaces with the same distance are created. This largely avoids comb filter effects (non-linear behavior due to reflections).

To simplify production, a preferred embodiment provides that the housing is essentially designed as a body of revolution and has an axis of rotation. For example, the robust housing can also be used as a turned part

be made of a metallic material.

Particularly good acoustic recording properties are achieved when a

The pickup of the microphone is arranged eccentrically to the axis of rotation.

It is advantageous if a pickup of the microphone is arranged eccentrically to the axis of rotation and is preferably arranged in the immediate vicinity of a base of the housing. As a result, interference effects such as the comb filter effect can almost be avoided

be eliminated.

In an advantageous embodiment it is provided that the microphone rests against a rubber insert, which in the embodiment shown is, for example, 2 mm thick, and / or is fastened to the bottom of the housing by a rubberized clamp. The rubber insert is thus located between the microphone and the floor. By providing the rubber insert or the rubberized clamp, vibrations are passed on from the housing to the microphone. In addition, electrical insulation is achieved as a result. This also prevents interfering signals.

It when edges of the housing are rounded is particularly advantageous. This creates turbulence such as flow separation and eddies at the edges

avoided. The resulting noise is reduced. Particularly

it is advantageous to achieve an almost completely laminar flow around the

Contraption.

In order to save space and reduce the height of the device, it is advantageous to

when the microphone is arranged within a recess in the housing.

In order to achieve a device that is as inconspicuous as possible and that is as inconspicuous as possible, which can be arranged on any type of test stand, a special variant of the invention provides that the device has a maximum extension in the direction of the axis of rotation of the housing, which corresponds to a width

Has a ratio of less than 1/3.

It is advantageous to use an acoustically reverberant material for the housing. In this context, reverberant means a material that reflects and does not absorb sound waves. For example, materials with a stiff one are suitable for this purpose

Surface, such as metals.

Due to the combination of a round outer shape of the housing, the rounded edges, the gluing of the perforated sheet of the first protective element with fleece and a layer of acoustically neutral foam as the second protective element, the wind noise caused by test bench ventilation

or other strong air currents avoided.

The second protective element is in an advantageous arrangement between the first

Protective element and the microphone located in the opening.

Enclosing the interior of the housing in the radial direction around the axis of rotation and on one side of the axis of rotation leads to a directional effect when recording the sound waves. So can a selection of the desired

Recording area can be carried out by the orientation of the device.

In the following, the invention will be based on the non-restrictive

Embodiment explained in more detail in the figures. Show it:

1 shows a device according to the invention in a first view;

2 shows the device in an exploded view; and

In Fig. 1 a device 1 for the acoustic measurement of airborne sound is shown. The device 1 has a housing 2 which is designed as a solid rotating part

and is made, for example, of a metallic material.

The housing 2 is closed here with a first protective element 3, the first protective element 3 having a perforated plate with a covering made of textile fibers. In alternative embodiments, the first protective element 3 can also represent a layer of textile fibers, for example a woven fabric, a knitted fabric or a fleece, or it can also be just a fine lattice.

The cover of the perforated sheet consists in an advantageous embodiment of an oil and water-repellent fleece. Different types of fleece were tested and one of them was selected that meets the liquid-repellent requirements but also does not affect the acoustic properties of the microphone recording. This fleece also prevents the noise caused by the air flowing over the perforated plate. For example, an acoustic fleece or a glass fiber fleece, which is produced using the wet fleece method, is suitable for this purpose.

The coating is provided here as a layer on the perforated plate on the surface facing outwards and is glued onto the perforated plate. It thus forms the outermost layer of the device 1. The fleece is liquid-repellent and thus protects the penetration of liquid into the housing 2. In addition, the fleece prevents the noise caused by air flow on the perforated plate.

The first protective element 3 is fastened to the housing 2 with a fastening ring 4 with a plurality of screws 5 - in the embodiment shown there are four screws 5 fastened. A connection A is provided on the housing 2, which is used to connect the device 1 to further measurement technology components.

The housing 2 has several edges K. These edges K are to avoid turbulence in the flow and to avoid the resulting turbulence

Noise rounded off.

Between the first protective element 3 and an interior 6 of the housing 2 is still

a second protective element 7 is arranged, as can be seen from FIG.

In this embodiment, the second protective element 7 is advantageously made from acoustically neutral foam. This second protective element 7 serves as protection against air currents. For example, the air flow of the room ventilation

cannot reach a microphone 13.

The first protective element 3 rests on a shoulder 8 and the second protective element 7 rests on a floor 9 in an opening 10 for the passage of the sound waves of the housing 2.

In an alternative embodiment it is provided that a shoulder is provided for each protective element 3, 7. In a further embodiment, not shown, are the

two protective elements 3 and 7 on a paragraph directly to one another.

The microphone 13, not shown in this view, is provided in the interior 6 of the housing 2. For this purpose, the microphone 13 is arranged in a recess 11. This recess 11 is designed here as a bore that is visible as an ellipse on a funnel-shaped wall 12 of the housing 2.

The wall 12 of the housing 2 has an incline angle 5 which is approximately 22 °. In preferred alternative embodiments, the pitch angle can assume 56 to approximately 45 °. The angle of inclination is favorably between 5 ° and 30 °.

3 shows a section transversely through the device 1 through a plane which is laid through an axis of rotation D, the axis of rotation D being the axis of rotation D of the rotating body of the housing 2. The microphone 13 is arranged in the recess 11 in such a way that a pickup 14 of the microphone 13 is arranged eccentrically from the axis of rotation D of the housing 2.

The microphone 13 is arranged here on an approximately 2 mm thick rubber insert. Alternatively, the microphone 13 can be attached to the floor 9 with a rubberized clamp. By resting against the rubber, the microphone 13 is isolated from vibrations and electrical interference. This can also be used by

this side interference is largely prevented.

The funnel-shaped wall 12 is shaped in such a way that the volume that is delimited by the wall 12 towards the microphone 13 becomes narrower from everywhere. To the floor 9

of the housing 2, the wall has a flat point that is essentially parallel! to the protective elements 3, 7 is arranged. Essentially, this means that due to any inaccuracies and tolerances during manufacture, consideration should be given to parallelism and that these inaccuracies are included.

The second protective element 7 serves as protection against disruptive influences of air currents that act on the device, for example through

Room ventilation and other drafts.

Knocking noises or other sound images of damage or malfunctions from a test object in a test stand are not attenuated by this second protective element 7 due to the essentially acoustic neutrality, so that they are

Noises can still be recognized.

The device 1 is used, for example, EoL test stands (end-of-line test stands) for recording and evaluating, that is to say for quality control, of engine noises. The microphone arrangement is very robust and its acoustic properties are not influenced by liquids such as cooling water and oils, by dust, soot and other air pollutants, as well as by mechanical effects during work by fitters. The strong test bench ventilation influenced by the

second protection element 7 does not affect the signal quality.

Even the action of massive tools such as hammers or pipe wrenches

does not change the geometry and thus the acoustic behavior of the device.

The first protective element 3 provides good splash protection against liquids such as oils and cooling water. The second protective element 7 serves as a further barrier. To better prevent the ingress of liquids, the second protective element 7 can seal the interior 6 of the housing 2 from the environment.

Furthermore, the second protective element 7 prevents the occurrence of strong wind noises due to strong test stand ventilation and large gas flows.

Due to the very flat design, the device 1 influences the work in the

Test stands not.

The special shape of the housing 2 avoids negative effects such as comb filter effects. In addition, the housing 2 has an advantageous behavior with respect to sound waves impinging on the side. These are absorbed in a weakened manner and thus the sound wave emitted by the test object

come to be judged better.

The use of stiff, ductile material for the housing 2 is particularly advantageous. The housing 2 is extremely robust thanks to a round and thick-walled one

Execution on the outer contours.

The device 1 has a maximum extension E in the direction of the axis of rotation D, which is small compared to a maximum extension normal to the direction of the axis of rotation D, which is denoted by a width B. The ratio H / B is less than 1/3. In the embodiment shown, the width B corresponds to the diameter of the housing 2, since the housing 2 is essentially designed as a body of revolution.

Claims (1)

PATENT CLAIMS Device (1) for the acoustic measurement of airborne sound waves for arrangement in a test stand - in particular in a vehicle test stand - the device (1) having at least one microphone (13) for recording airborne sound waves and a housing (2) surrounding the microphone (13), wherein the housing (2) has at least one opening (10) for the passage of the airborne sound waves from the outside to the microphone (13), characterized in that at least one first protective element (3) is arranged in the opening (10), the at least one first grille which prevents particles from entering the housing (2) and that at least one second protective element (7) is arranged in the opening (10), which reduces the occurrence of interfering noises in an air flow. Device (1) according to Claim 1, characterized in that the first protective element (3) has a perforated plate. Device (1) according to claim 1 or 2, characterized in that the first protective element (3) has at least one layer made of textile fibers having. Device (1) according to claim 3, characterized in that the at least one layer of textile fibers forms a coating. Device (1) according to one of Claims 3 or 4, characterized in that the textile fibers are formed into a fleece. Device (1) according to one of claims 1 to 5, characterized in that the second protective element (7) consists essentially of acoustically neutral material. Device (1) according to one of Claims 1 to 6, characterized in that the second protective element (7) has a thickness which is greater than 2 mm. 11. 12th 13th 14th 15th 11 Device (1) according to one of claims 1 to 7, characterized in that the second protective element (7) is compressible is executed and preferably has a cellular structure. Device (1) according to one of claims 1 to 8, characterized in that the second protective element (7) at least one Has foam layer and preferably consists of foam. Device (1) according to one of claims 1 to 9, characterized in that the housing (2) tapers in the shape of a funnel towards the microphone (13), the microphone (13) in an interior (6) of the Housing (2) is arranged. Device (1) according to claim 10, characterized in that the housing (2) has a flat funnel shape in an interior space (6), a slope angle (3) of this funnel shape being less than 45 ° and preferably between 5 ° and 30 ° . Device (1) according to one of claims 1 to 11, characterized in that the housing (2) is essentially a body of revolution is executed and has an axis of rotation (D). Device (1) according to claim 12, characterized in that a pickup (14) of the microphone (13) is arranged eccentrically to the axis of rotation (D) and is preferably arranged in the immediate vicinity of a base (9) of the housing (2). Device (1) according to one of Claims 1 to 13, characterized in that the microphone (13) rests against a rubber insert and / or is attached to the bottom (9) of the housing (2) by a rubberized clamp. Device (1) according to one of Claims 1 to 14, characterized in that edges (K) of the housing (2) are rounded. 16. Device (1) according to one of claims 1 to 15, characterized in that the microphone (13) is arranged within a recess (11) in the housing (2). 17. Device (1) according to one of claims 1 to 16, characterized in that the device (1) in the direction of the axis of rotation (D) of the housing (2) has a maximum extension (E) which leads to a width (B) has a ratio (E / B) of less than 1/3. 01/27/2021 AP