AT523698B1 - DEVICE FOR ACOUSTIC MEASUREMENT OF AIR SOUND WAVES - Google Patents

Abstract

The invention relates to a device (1) for acoustically measuring 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 housing (2) having at least one opening (10) for the passage of the airborne sound waves from the outside to the microphone (13), wherein at least one first protective element (3) is arranged in the opening (10), which has at least one first grid which prevents particles from entering the housing (2) and at least one second protective element (7) is arranged in the opening (10). , which reduces the generation of noise of an air flow. The task is to specify a particularly robust device that reduces background noise. This object is achieved in that the housing (2) tapers in a funnel shape towards the microphone (13), the microphone (13) being arranged in an interior (6) of the housing (2).

Description

description

The invention relates to a device for the acoustic measurement of airborne sound waves for arrangement in a test stand - in particular in a vehicle test stand - 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 passage which has airborne sound waves from the outside to the microphone, with at least one first protective element being arranged in the opening, which has at least one first grid which prevents particles from entering the housing and at least one second protective element being arranged in the opening, which prevents the occurrence of background noise an air flow is reduced.

[0002] Devices of this type are used in EoL test benches (end-of-line test benches), 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 engines, in which it is to be determined whether the full functionality is given. As part of this comprehensive inspection of the workpiece, airborne acoustic 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 engines - are discarded.

For this purpose, normal commercially available microphones can be used, which are arranged in a housing that keeps dirt away. However, these conventional microphones are not impervious to liquids and do not meet the requirements of a test stand. This can lead to oil and cooling water leaks and high air flow speeds, for example due to ventilation of the test bench. This generates background noise, which complicates the detection of noise from defective components. In addition, all sorts of noises are also picked up from the environment, which originate, for example, from production, but which can contribute to the falsification of the measurement.

WO 2015/0115646 A1 discloses a protective element for a microphone, which has the task of protecting the microphone against the effects of water, dust and wind. The microphone is arranged in the interior of a closable rotary body, with the protective element against dirt and to dampen noise being arranged in a cover part.

[0005] US 2008/0159558 A1 discloses a protective housing with a cuboid base made of rubber as protection against vibrations, with a receiving space for several microphones, which can be protected by various covers.

Another dustproof microphone is known from EP 1 691 570 A2.

Existing devices for harsh environments are mainly suitable for outdoor use. Although these meet the requirements for resistance to wind and weather, they are not suitable for the effects of mechanical forces from test specimens on the test bench or fitters. Conventional devices with microphones for outdoor use therefore do not meet the high demands placed on test benches.

Boundary microphones, which are arranged on the floor at concerts, for example, are also not suitable for arrangement on a test bench, especially with regard to wind noise and with regard to their repellent properties towards liquids, since liquids and mechanical influences destroy them and make them unusable be able.

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

This object is achieved according to the invention by a device as specified above in that the housing tapers in a funnel shape towards the microphone, the microphone being arranged in an interior space of the housing. This significantly increases the quality of the recording.

The ingress of dirt can be prevented by the two protective elements. By providing a protective element, the disturbing noise of the air flow is reduced, the noise is insulated or muffled. The protective element absorbs or reflects the airborne sound waves originating from the air flow.

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

For a 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.

[0014] It is particularly advantageous to use acoustically neutral perforated metal 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.

[0016] Protection against dirt particles created in this way can be attached 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 cover may 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 covered with fleece, which completely or at least largely prevents turbulence in the air and thus noise.

The perforated plate is particularly advantageous because sound waves are hardly reflected in the desired acoustic frequency range. The perforated plate is chosen in such a way that there are no disturbing reflections and interferences.

It when the second protective element consists of a substantially acoustically neutral material is particularly favorable.

In order to achieve particularly good properties for preventing noise from the air flow or to provide the best possible barrier against dirt particles, it is favorable if the second protective element has a thickness that is greater than 2 mm. The air flow is thus kept away from the microphone by the second protective element and the disturbing influence of the air flow on the microphone is reduced.

[0023] Particularly favorable properties for reducing disturbing 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 the ideal prerequisites for preventing background noise.

If the second protective element has at least one foam layer and preferably consists of foam, the influence of the air currents around the device can be prevented in a particularly simple manner.

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

For easier production, a preferred embodiment provides that the

Housing is designed essentially as a body of revolution and has an axis of rotation. For example, the robust housing can also be manufactured as a turned part from a metallic material.

[0027] Particularly good acoustic recording properties are achieved when a pick-up of the microphone is arranged eccentrically to the axis of rotation.

It is advantageous if a pick-up of the microphone is arranged eccentrically to the axis of rotation and is preferably arranged in the immediate vicinity of a bottom of the housing. This means that interference effects such as the comb filter effect can be almost completely eliminated.

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

It when edges of the housing are rounded is particularly advantageous. This avoids turbulence such as flow separation and turbulence at the edges. The resulting noise is reduced. The achievement of an almost completely laminar flow around the device is particularly advantageous.

In order to save space and to reduce the height of the device, it is advantageous if the microphone is arranged within a recess in the housing.

In order to achieve a device that is as unobtrusive and less disruptive 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 leads to a Width has a ratio of less than 1/3.

It is advantageous to use an acoustically reverberant material for the housing. Here, reverberant means a material that reflects sound waves and does not absorb them. Materials with a stiff surface, such as metals, for example, are suitable for this purpose.

The combination of a round outer shape of the housing, the rounded edges, the gluing of the perforated plate of the first protective element with fleece and a layer of acoustically neutral foam as the second protective element avoids the wind noise caused by test bench ventilation or other strong air currents.

In an advantageous arrangement, the second protective element is located between the first protective element and the microphone in the opening.

The enclosing of 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. In this way, the desired recording area can be selected by the orientation of the device.

The invention will be explained in more detail below with reference to the non-limiting embodiment in the figures. Show it:

[0038] FIG. 1 shows a device according to the invention in a first view; Figure 2 shows the device in an exploded view; and [0040] FIG. 3 shows the device in a section.

In Fig. 1 a device 1 for the acoustic measurement of airborne noise is shown. The device 1 has a housing 2, which is designed as a solid turned part and is made of a metallic material, for example.

The housing 2 is closed here with a first protective element 3, the first protective element 3 having a perforated plate with a coating of textile fibers. In alternatives

Embodiments, the first protective element 3 can also be a layer of textile fibers, for example a woven fabric, a knitted fabric or a fleece, or just a fine grid.

In an advantageous embodiment, the covering of the perforated plate consists of an oil- and water-repellent fleece. Various 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 noise caused by air flow over the perforated plate. An acoustic fleece or a glass fiber fleece, for example, which is produced using the wet fleece method, are suitable for this purpose.

The coating is provided here as a layer on the perforated plate on the surface to the outside and is glued to 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 noise caused by air flow at the perforated plate.

The first protective element 3 is with a fastening ring 4 on the housing 2 with several screws 5 - in the embodiment shown there are four screws 5 - attached. A connection A is provided on the housing 2 and is used to connect the device 1 to other measurement technology components.

The housing 2 has a plurality of edges K. These edges K are rounded to avoid turbulence in the flow and to avoid the resulting noise.

A second protective element 7 is also arranged between the first protective element 3 and an interior space 6 of the housing 2, as can be seen from FIG.

In this embodiment, the second protective element 7 is advantageously made of acoustically neutral foam. This second protective element 7 serves to protect against air currents. For example, the air flow from the room ventilation cannot reach a microphone 13 .

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

In an alternative embodiment it is provided that each protective element 3, 7 is provided with a paragraph. In a further embodiment, not shown, the two protective elements 3 and 7 are in direct contact with one another at a shoulder.

In the interior 6 of the housing 2, the microphone 13, not shown in this view, is provided. For this purpose, the microphone 13 is arranged in a recess 11 .

Here, this recess 11 is designed as a bore, which is visible as an ellipse on a funnel-shaped wall 12 of the housing 2 .

The wall 12 of the housing 2 has a pitch angle 5 of about 22°. In preferred alternative embodiments, the pitch angle δ can be up to about 45°. The pitch angle is favorably between 5° and 30°.

Fig. 3 shows a section across the device 1 through a plane that is laid through an axis of rotation D, wherein the axis of rotation D is the axis of rotation D of the body 2 of rotation. 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 being in contact with the rubber, the microphone 13 is isolated from vibration and electrical noise. As a result, interference from this side can also be largely prevented.

The funnel-shaped wall 12 is shaped in such a way that the volume delimited by the wall 12 towards the microphone 13 becomes narrower from everywhere. To the bottom 9 of the housing 2 out

the wall has a flat which is arranged substantially parallel to the protective elements 3,7. Essentially means here that any inaccuracies and tolerances during production with regard to parallelism should be taken into account and these inaccuracies are included.

The second protective element 7 serves to protect against the disturbing influences of air currents that act on the device, for example through room ventilation and other drafts.

[0058] Knocking noises or other sound images of damage or malfunctions from a test specimen in a test stand are not dampened by this second protective element 7 due to the essentially acoustic neutrality, so that these noises are nevertheless recognized.

The device 1 is used, for example, in EoL test benches (end-of-line test benches) for recording and evaluating, ie for quality control, of engine noises. The microphone array is very robust and its acoustic properties are unaffected by liquids such as cooling water and oils, by dust, soot and other airborne contaminants, and by mechanical impact during work by fitters. The strong test stand ventilation does not affect the signal quality due to the second protective element 7 .

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 noise due to strong test bench ventilation and large gas flows.

Due to the very flat design, the device 1 does not affect the work in the test benches.

The special shape of the housing 2 avoids negative effects such as comb filter effects. In addition, the housing 2 has an advantageous behavior in relation to sound waves impinging from the side. These are recorded weakened and the sound wave coming from the test object can thus be better assessed.

The use of stiff, ductile material for the housing 2 is particularly advantageous. The housing 2 is extremely robust due to a round and thick-walled design 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, 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 designed essentially as a rotating body.

Claims (16)

patent claims 1. 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) has, 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), wherein at least one first protective element (3) is arranged in the opening (10), the at least one first grid that prevents particles from entering the housing (2) and at least one second protective element (7) is arranged in the opening (10) which reduces the occurrence of interference noise from an air flow, characterized in that the housing (2) faces the microphone (13) tapering towards a funnel, the microphone (13) being arranged in an interior space (6) of the housing (2). 2, device (1) according to claim 1, characterized in that the first protective element (3) has a perforated plate. 3. Device (1) according to claim 1 or 2, characterized in that the first protective element (3) has at least one layer of textile fibers. 4. Device (1) according to claim 3, characterized in that the at least one layer of textile fibers forms a coating. 5. Device (1) according to one of claims 3 or 4, characterized in that the textile fibers are formed into a fleece. 6. Device (1) according to any one of claims 1 to 5, characterized in that the second protective element (7) is made of essentially acoustically neutral material. 7. Device (1) according to any one of claims 1 to 6, characterized in that the second protective element (7) has a thickness which is greater than 2 mm. 8. Device (1) according to any one of claims 1 to 7, characterized in that the second protective element (7) is designed to be compressible and preferably has a cellular structure. 9. Device (1) according to any one of claims 1 to 8, characterized in that the second protective element (7) has at least one foam layer and preferably consists of foam. 10. Device (1) according to one of Claims 1 to 9, characterized in that the housing (2) has a flat funnel shape in an interior space (6), with a gradient angle (3) of this funnel shape being less than 45° and preferably between is 5° and 30°. 11. Device (1) according to any one of claims 1 to 10, characterized in that the housing (2) is designed essentially as a body of revolution and has an axis of rotation (D). 12. Device (1) according to claim 11, characterized in that a pick-up (14) of the microphone (13) is arranged eccentrically to the axis of rotation (D) and is preferably arranged in the immediate vicinity of a bottom (9) of the housing (2). . 13. Device (1) according to one of claims 1 to 12, characterized in that the microphone (13) bears against a rubber insert and/or is fastened to the bottom (9) of the housing (2) by a rubberized clamp. 14. Device (1) according to any one of claims 1 to 13, characterized in that edges (K) of the housing (2) are rounded. 15. Device (1) according to any one of claims 1 to 14, characterized in that the microphone (13) is arranged within a recess (11) in the housing (2). 16. The device (1) according to any one of claims 1 to 15, characterized in that the device (1) has a maximum extension (E) in the direction of the axis of rotation (D) of the housing (2) which leads to a width (B) has a ratio (E/B) of less than 1/3. 3 sheets of drawings