A/s Bruel & Kjaer

Aktieselskabet Bruel & Kjaer

Aktieselskabet Bruel & Kjar

Aktieselskabet Bruel & Kajaer

A/s Bruel & Kjar

Erling Frederiksen

Ole Schultz

A method and a system for testing one or more transducers, preferably acoustic transducers, from a central control unit. The transducers are individually connected to the inlet of a preamplifier (4) having a relatively high input resistance (6). A test conduit extends from the central control unit to each transducer. The test conduit communicates with the joint between the transducer and the inlet of the preamplifier (4) through a relatively small capacity (10). In this manner a method is obtained for testing the transducer, said testing being highly sensitive to the condition of the transducer and relatively insensitive to external fields.

Method and a system for testing capacitive, acoustic transducers

A probe microphone comprising an acoustic transducer with a cavity, to which a probe tube and a matching tube are connected. The matching tube is divided into several small tubes of a total internal transverse cross sectional area substantially corresponding to the internal transverse cross sectional area of the probe tube. The small matching tubes improve the frequency response because of their acoustic loss. Moreover, a further improvement is achieved when the matching tubes are of different lengths, the already reflected signals thereby outbalancing each other. As a result, a probe microphone with a more uniform frequency response than previously known is achieved.

Probe microphone

A dual cavity pressure microphone comprising a microphone housing and an oscillating element mounted in or on said housing. The oscillating element including a membrane which is in principle only sensitive to a sound field on one side, the second side forming part of a closed cavity in the microphone housing, said cavity being connected to the ambient atmosphere through a narrow pressure equalizing channel. The microphone comprises an additional cavity representing an additional acoustic capacitance and an additional pressure equalizing channel located in series therewith and representing an additional acoustic resistance, the second capacitance and the second resistane being located in series with the capacitance and resistance, respectively, of the first cavity and the first channel in such a manner, that the pressure equalization of the microphone is also effected through the additional pressure equalizing channel and the additional cavity. According to the invention the additional pressure equalizing channel is dimensioned in such a manner that it substantially only provides a static pressure equalization.

Dual cavity pressure microphones

An acoustic calibration device for intensity measuring systems comprising at least two pressure microphones to be calibrated without using an anechoic chamber. The calibration device comprises at least two cavities interconnected by means of one or several acoustic resistance elements. One of the pressure microphones is to be inserted into one of the cavities and the second pressure microphones is to be inserted into the second cavities. A sound source is connected to one of the cavities. In connection with the subsequent cavity the acoustic resistance thus forms an acoustic RC-link providing a phase shift proportional to the frequency corresponding to the conditions in the free field. By a suitable dimensioning of the RC-link a phase shift corresponds to the phase shift over a distance of e.g. 50 mm in the free field. The sound source is able to generate either white noise or pink noise depending on whether measurements are performed over fixed frequency intervals or relative frequency intervals.

Acoustic calibration device

A capacitor transducer, for instance a condenser microphone, is so designed that the stationary electrode can be mounted relatively quickly and in a relatively simple manner in the microphone housing. The transducer is provided with an inner cylindrical supporting wall spaced from the inner surface of the transducer housing. One end of the supporting wall is fixedly connected to the transducer housing through a transverse wall while the other end is remote from the transverse wall and constitutes a seat for the insulating body. The supporting wall in the insulating body are so dimensioned that the body can be mounted into its seat either by a pressing action or by insertion and subsequent retention by means of frictional forces or by means of an adhesive.

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Holte, Denmark

Erling Frederiksen