Microphone no. 2485.10

18.06.14 2485.10 AE

2485.10 Microphone

Microphone for measurement of sound frequencies,the speed of sound and recording of sound signalsfor FFT displays (Fast Fourier Transform).

The sensitive area of the microphone unit is verysmall and therefore well suited for measurement ofinterference patterns.

The microphone requires an operating voltage of 5-9V DC, which is provided through the DIN plug.

The microphone is supplied including a 1 meter cable with a DIN connector which connects directlyto the electronic counter type 2002.50 and studet ti-mer 2202.60.

The microphone can be connected to an oscillo -scope, to previous electronic counters versions2000.xx or 2001.xx, to a Pasco interface or to anymeasuring instrument via the optional battery box ty-pe 2515.60.

Frequency range: 20-20.000 Hz.Supplied with holder with 10 mm diameter holdertap.Dimensions: Length 105 mm, largest diameter 30mm.

Speed of sound measurementThe traditional method of measuring the speed of sound is as follows. Two micro phones are placedone or two meters from one another and connectedto a counter. Using clapper boards placed in line withthe two microphones a sharp sound pulse is gene -rated. When the sound pulse encounters the first microphone, the counter timer starts counting. Whenthe sound pulse passes the second microphone, thecounter stops. The sound pulse must be loud andsharp to give a good result.

In order to achieve good, reproducible results we have found the following method to be helpful:

The microphones are connected to the counter in theusual manner. It is important that the microphonespoint in the same direction. Produce a loud noise using the clapper boards at a distance of at least onemeter from the closest microphone and in line withthe listening directions of the two microphones.

By taking 10-20 measurements one can find a reasonable value for the speed of sound. Divide thedistance between the microphones with the averageof the measured time values.

Problem solving:Unreasonably short time intervals can occur, typi callyaround 1% of the expected time interval. This is usually due to an excessively loud sound pulse. Move a little further away with the clapper board andtry again. This should give better measurements.

The loud sound pulse causes the microphone to saturate, probably faster than the microprocessorclock frequency in the counter. Thus the counter does not "discover" the sound before it reaches theother microphone. Here the sound pulse is less intense and it can trigger the counter.

It is also possible that the counter records a muchlonger time than the expected time. This is most often due to an unclear sound pulse which does notprovide the micro phones with clear start and stopsignals. Try again with a more precise clap with theclapper boards.

A/S Søren Frederiksen, Ølgod Tel. +45 7524 4966 info@frederiksen.euViaduktvej 35 · DK-6870 Ølgod Fax +45 7524 6282 www.frederiksen.eu

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2515.60 Battery Box (accessory)

This power supply is designed for microphones andother detectors which require a voltage to operate.

The unit is supplied with a battery compartment for a9 V alkaline battery type 6LR61 (3510.10).

Connect the microphone to input number 2 whenperforming measurements with microphone no.2485.10. The input signal can then be supplied viathe DIN-connector to previous models of the electro-nic counter, via the banana plugs to an oscillo scopeor analog instrument or via the “sensor”-con nector toa Pasco interface type 500, 750 or 850.

For measurement of the speed of sound using twomicrophones, the power supply is provided with twoinput connectors to accommodate two micro phones.

The power supply is also provided with an input connector for microphone sensor type 2515.50 aswell as sensors for light measurements.

When using microphone type no. 2485.10 in con -nection with earlier counter types (2000.xx or2001.xx), it is necessary to use the type 2515.60power supply as well as one or two adapter leads type no. 1122.20 (parallel leads).

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