DE19710414C2 - Method for determining the airborne sound component of a sound field in the passenger compartment of a motor vehicle - Google Patents

Description

The invention relates to a method for determining the proportion of airborne noise of a sound field in the passenger compartment arising during driving operation Motor vehicle.

When driving, a total is created in the passenger compartment of a motor vehicle. Sound field that ver audible noise in particular in the passenger compartment causes. This overall sound field is created by superimposing one Large number of individual sound components, which in particular result in two effects Classify, namely in the airborne sound component and the body sound component. The structure-borne noise component is particularly caused by vibrations of the drive train, while the airborne sound component is the component of the total Sound field is that from outside the motor vehicle in the driving guest room penetrates. The measures for the insulation of structure-borne noise therefore differ from the measures for insulating the air sound components. For example, the structure-borne noise components are changed mechanical transmission behavior of the drive train or insulated by changing the bearing stiffness. The insulation of the  Airborne noise is prevented in particular by insulating materials of leaks or to reduce the transmissibility of the body reached. To see the impact of each measure on each The structure-borne noise must be able to examine sound components in a more targeted manner parts and the airborne sound components can be recorded separately.

In particular the determination of the proportion of airborne sound during driving resulting sound field in the passenger compartment is in known methods only achieved with a great deal of effort. In a known method the determination of the airborne sound component by eliminating the body sound component achieved by storing the drive train externally. This However, the process is not only very complex, it also carries the risk serious measurement error in itself, since the original vibration behavior the vehicle is significantly affected.

It is an object of the invention to ensure that the procedure is as accurate and simple as possible Ren to determine the airborne sound component of a while driving to create the sound field in the passenger compartment of a motor vehicle.

This task is ge by the features of the only claim solves.

The procedure according to the invention is as follows:

In a first step, the sound field, in particular, is at least one microphone, but generally several microphones especially in the form of sound pressure spectra, outside the vehicle in Driving operations measured. For this purpose, the microphones, preferably by means of a measuring scaffold that can be adapted to the size of the vehicle, evenly around the Vehicle arranged distributed. The necessary number of microphones for that The inventive method depends in particular on the highest Fre sequence of the measuring range. During tests, it was found that  the measuring range is preferably selected below 1000 Hz, since this is the case the strongest superposition of airborne noise and structure-borne noise lies. For this measuring range, approximately 80 microphones have been empirically shown to be turned out to be particularly advantageous. Preferably, the measurement of the Sound field in driving operation in a largely free of noise ten measuring hall carried out in which the vehicle operated on a roll can be. The method can also be used to determine wind noise be used by measuring in an acoustic wind tunnel.

In a second step, the sound field is amplified using the same microphones outside the vehicle when the vehicle is stationary, d. H. when the Vehicle and with the engine switched off, with sound excitation at least one loudspeaker installed outside the vehicle measured.

In a third step, the sound field is measured while driving guest room also when the vehicle is stationary by at least one in the driving microphone attached to the guest room with sound excitation by the same Speakers as in the second step instead.

For both the second and the third step, the same applies with the sound excitation of the loudspeaker, its membrane acceleration is also measured. Should be a sound excitation with several speakers the measurements of the sound fields can be provided one after the other sound excitation by each individual loudspeaker become. Instead of using a variety of speakers however, the same speaker is used in different positions become.  

With steps 1 to 3, those for the method according to the invention are required measurements completed. The following are the inventions The method according to the invention is only used for calculations.

In a fourth and a fifth step, the Transfer function between everyone outside the vehicle microphone and any loudspeaker placed outside the vehicle cher and on the other hand the transfer function between everyone in the driving attached microphone and everyone outside the vehicle speakers brought up by calculation.

In a final step, the airborne sound component of the sound field, which is in the Passenger compartment would exist when driving, calculated from the two Transfer functions or from the two sets of calculated Transfer functions and the ge outside of the vehicle while driving measured sound field.

In addition, it is pointed out that the spatial resolution is mainly from the number of microphones outside, preferably 80-100, and the number number of speaker measurements, preferably about 10, depends.

Is summarized by the invention for determining the air sound component in the passenger compartment when the vehicle is at rest, d. H. if no body sound component is generated, a sound field outside the passenger compartment generated, which corresponds to that when driving. Through this fiction According to the procedure, no intervention in the construction of the vehicle is required such. As a result, both costs and development times for the investigation of measures for the insulation of airborne noise saved.

In the drawing, an embodiment of the invention is shown. It shows

Fig. 1.1 the definition of a number and the locations of the microphones and speakers or speaker positions used

Fig. 1.2 to Fig. 1.5 an example of the inventive method in matrix representation, with three microphones outside the vehicle, with two microphones in the passenger compartment and with two loudspeaker positions or two loudspeakers outside the vehicle in four essential steps.

Sound fields are usually determined in the form of sound pressure spectra. In Fig. 1.1 the frequency f = 300 Hz is given as an example instead of a frequency range. Instead of the sound field p (f) in the form of a sound pressure spectrum, the sound pressure p at a fixed frequency of (e.g.) f = 300 Hz is used to simplify the representation of a sound field. Likewise, the membrane deflection is only for the Schallan excitation with a single frequency, for. B. also 300 Hz, who is shown, while in practice white noise is preferably used as sound excitation.

In FIG. 1.1, the microphones arranged outside the vehicle are denoted by K, the microphones arranged in the passenger compartment by L and the loudspeakers or loudspeaker positions arranged outside the vehicle by J. According to the exemplary embodiment, three microphones, namely top, right and left, are arranged outside the vehicle. The sound fields or sound pressure values p assigned to these three microphones are therefore identified by the indices K _o , K _r , and K _l . Inside the vehicle, ie in the passenger compartment, two microphones are provided, preferably on the headrests of the driver and the front passenger. The sound fields or sound pressure values p assigned to these microphones are given the indices L _f and L _b . The two speakers outside the vehicle are provided by a loudspeaker in two positions, namely in relation to the direction of travel in front of and behind the motor vehicle. The sound fields or sound pressure values te p, which are determined on the basis of the sound excitation by the loudspeaker J at one of these two positions, are given the indices J _v and J _h .

In a first step in FIG. 1.2, the sound field is measured in the form of sound pressure values p outside the vehicle while driving, preferably on a roller in a measuring room, with the microphones at the top, right and left in relation to the vehicle in the direction of travel. In a computer not shown here, the result of this measurement (p _fahr , _Ko , p _fahr , _Kr , p _fahr , _Kl ,) is displayed in a "matrix" which has one column and three rows. In addition, it is pointed out that only the sound fields penetrating into the passenger compartment from outside are determined during driving operation. There is no sound excitation by the loudspeaker or the loudspeaker at the various positions yet.

According to Fig. 1.3, in a second step the sound field in the form of sound pressure values p outside the vehicle with the microphones above, right and left when the vehicle is stationary or when the engine is not running twice, namely firstly on the sound excitation by the loudspeaker in the rear position (p _{still, Jh, Ko} , p _{still, Jh, Kr} , p _{still, Jh, Kl} ,) and secondly to the sound excitation through the loudspeaker in the position in front (p _{still, Jv, Ko} , p _{still, Jv, Kr} , p _{still, Jv, Kl} ,) towards, measured. At the same time, the diaphragm deflections of the loudspeaker are also measured during sound excitation (a _{still, Jh} ; a _{still, Jv} ).

From the quotient of the respectively measured sound pressure values p and membrane deflection values a, the transfer function T _{outside is formed} in the form of a matrix which, according to the number of speakers or speaker positions, has two columns and, according to the number of microphones, has three lines outside the vehicle.

In Fig. 1.4, analogous to the second step, the sound field inside the vehicle is measured in a third step using the microphones on the driver and front passenger seats when the vehicle is stationary or when the engine is stopped. Here, too, two measurements are carried out on the sound excitations of the speaker at the two positions in front (p _{still, Jv, Lf} , p _{still, Jv, Lb} ) and in the back (p _{still, Jh, Lf} , p _{still, Jh, Lb)} . Again, the membrane deflections of the loudspeaker (a _{still, Jh} ; a _{still, Jv} ) are also recorded.

While according to FIG. 1.3, the transfer function T _outside au between each ßerhalb of the vehicle-mounted microphone and each mounted outside the vehicle speaker is made, the transfer function T is shown in FIG. 1.4 _internally mounted between each of the passenger compartment is interrupted th microphone and each outside of the vehicle loudspeaker cher formed. This results in a matrix which has two columns in accordance with the number of loudspeakers and two lines in accordance with the number of microphones in the passenger compartment.

In Fig. 1.5, the actual determination of the airborne sound component of the sound field generated during driving takes place in the passenger compartment of a vehicle. This airborne sound component is calculated in the form of a sound field, in the special exemplary embodiment in the form of sound pressure values p _{fahr, Lf} and p _{fahr, Lb.} Here, the product of the transfer function T _inside , the inverted transfer function T _outside ^-1 and the sound field shown outside in the vehicle in driving mode shown in the form of a column in FIG. 1.2 is formed. In addition, it is pointed out that the transfer function T _outside is overdetermined in the form of the matrix according to FIG. 1.3, so that it must be inverted according to the known method of pseudo inverses.

According to the exemplary embodiment, this calculation yields a Sound field in the form of two pressure values that are spatially resolved to the air Noise level in the passenger compartment on the driver and front passenger seats during operation corresponds.

This embodiment is not an embodiment example in the strict sense, but rather a description of the basic approach based on a greatly reduced model. In the Reality is K ≧ 80 and J ≧ 10.

Claims (1)

Method for determining the proportion of airborne sound in an airborne sound field in the passenger compartment of a motor vehicle, which is due to sound entering the motor vehicle from outside, with the following steps:

• - Measurement of the sound field (p _{fahr, Ko} , p _{fahr, Kr} , p _{fahr, Kl} ) outside the motor vehicle in driving mode ("fahr") by at least one microphone (K _o , K _r , K _l ) mounted outside the motor vehicle,
• - Measurement of the sound field (p _{still, Jv, Ko,} p _{still, Jv, Kr} , p _{still, Jv, Kl} ; p _{still, Jh, Ko} , p _{still, Jh, Kr} , p _{still, Jh, Kl} ) outside the vehicle when the motor vehicle is at rest ("still") through the same microphone (K _o , K _r , K _l ) when the sound is excited by at least one loudspeaker (J _v , J _h ) mounted outside the motor vehicle, whose membrane _acceleration (a _{still, Jv} ; a _{still, century} ) is measured at the same time and
• - Measurement of the sound field (p _{still, Jv, Lf} , p _{still, Jv, Lb} ; p _{still, Jh, Lf} , p _{still, Jh, Lb} ) in the passenger compartment when the motor vehicle is at rest ("still") by at least one installed in the passenger compartment Microphone (L _f , L _b ) in the event of sound excitation through the loudspeaker mounted outside the motor vehicle (J _v , J _h ), whose membrane acceleration (a _{still, Jv} ; a _{still, Jh} ) is measured at the same time, so that
• - The frequency-dependent transmission function (T _outside ) between each microphone attached outside the motor vehicle (K _o , K _r , K _l ) and each loudspeaker outside the vehicle (J _v , J _h ) and
• - The frequency-dependent transfer function (T _inside ) between each microphone installed in the passenger compartment (L _f , L _b ) and each loudspeaker outside the vehicle (J _v , J _h ) can be determined and
• - The sound field (p _{fahr, Lf} , p _{fahr, Lb} ), which is present as the above-defined airborne sound component in the passenger compartment when driving ("fahr"), from the two transmission functions (T _inside, T _outside ) and the outside of the motor vehicle in Driving operation ("fahr") measured sound field (p _{fahr, Ko} , p _{fahr, Kr} , p _{fahr, Kl} ) can be calculated.