Difference between revisions of "Determination of the Speed of Sound"
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The purpose of this experiment is to determine the speed of sound. | The purpose of this experiment is to determine the speed of sound. | ||
| − | + | =Experimental Apparatus= | |
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The apparatus is a PVC tube (sometimes refered to as "Kundt's tube"), with 1458 millimiters in length. On one end there is a fixed speaker that can produce an audio sine, triangular or a single pulse wave. On the opposite side there is a movable piston, changing the effective lenght of the tube. Along the tube there are several microphones to register the sound intensity at fixed points. | The apparatus is a PVC tube (sometimes refered to as "Kundt's tube"), with 1458 millimiters in length. On one end there is a fixed speaker that can produce an audio sine, triangular or a single pulse wave. On the opposite side there is a movable piston, changing the effective lenght of the tube. Along the tube there are several microphones to register the sound intensity at fixed points. | ||
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The sound is aqquired through 2 channels of a sound card: the left channel (CH 1) is always bounded to the reference microphone (Mic 1); the other channel (CH 2) can be connected to one of the other three microphones. | The sound is aqquired through 2 channels of a sound card: the left channel (CH 1) is always bounded to the reference microphone (Mic 1); the other channel (CH 2) can be connected to one of the other three microphones. | ||
| − | The experimental data is captured by the soundcard and processed online (normalization). | + | The experimental data is captured by the soundcard and processed online (normalization). |
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| − | + | =Protocol= | |
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This assembly is also used for the stationary wave experiment, and thus has two modes of operation: in the "Speed of sound" mode, the amplitude of the wave is registered over time. | This assembly is also used for the stationary wave experiment, and thus has two modes of operation: in the "Speed of sound" mode, the amplitude of the wave is registered over time. | ||
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where \(s\) is the distance between the selected microphones. | where \(s\) is the distance between the selected microphones. | ||
| − | Of course other waveforms could be used but a | + | Of course other waveforms could be used but this will require a close look at the phase. |
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| − | + | =Advanced Protocol= | |
| − | + | The correlation from the acquired signals can improve with great accuracy the determination of the phase among the diferent microphones. Using an appropriate software package in mathlab or octave for instance, this phase is easily determined. Noise is very suitable for that end as it won't exhibits any phase indetermination. | |
| − | The correlation from the acquired signals can improve with great accuracy the determination of the phase among the diferent microphones. Using an appropriate software package in mathlab or octave for instance, this phase is easily determined. Noise is very suitable for that end as it won't exhibits any phase indetermination | ||
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Revision as of 18:59, 20 May 2012
Description of the Experiment
The purpose of this experiment is to determine the speed of sound.
Experimental Apparatus
The apparatus is a PVC tube (sometimes refered to as "Kundt's tube"), with 1458 millimiters in length. On one end there is a fixed speaker that can produce an audio sine, triangular or a single pulse wave. On the opposite side there is a movable piston, changing the effective lenght of the tube. Along the tube there are several microphones to register the sound intensity at fixed points.
The following table shows the positions of the microphones in relation to the speaker:
Referência Distância à fonte (altifalante) Mic 1 (referência) 250 mm Mic 2 (centro do tubo) 750 mm Mic 3 (extremidade do tubo) 1250 mm Mic 4 (superfície do êmbolo) Entre 1260 e 1480 mm Extremidade do tubo 1450 mm Table 1 – Microphones distance to the sond source (speakers membrane)
The reference mic (Mic 1) should be used to verify that the emitted sound is the disered on (i.e., there is no distortion caused by the speaker). On the piston surface is another microphone (Mic 4) capable of moving between 1269mm and 1475mm. The sound is aqquired through 2 channels of a sound card: the left channel (CH 1) is always bounded to the reference microphone (Mic 1); the other channel (CH 2) can be connected to one of the other three microphones.
The experimental data is captured by the soundcard and processed online (normalization).
Protocol
This assembly is also used for the stationary wave experiment, and thus has two modes of operation: in the "Speed of sound" mode, the amplitude of the wave is registered over time.
To determine \( v_{sound} \), the user must choose a "pulse" type of stimullus and measure the "time-of-flight" taken by the wave from Mic 1 and any other microphone. The speed can be determined with data from table 1 and the formula for speed determination:
\[ v_{sound} = \frac{\Delta s}{\Delta t} \] where \(s\) is the distance between the selected microphones. Of course other waveforms could be used but this will require a close look at the phase.
Advanced Protocol
The correlation from the acquired signals can improve with great accuracy the determination of the phase among the diferent microphones. Using an appropriate software package in mathlab or octave for instance, this phase is easily determined. Noise is very suitable for that end as it won't exhibits any phase indetermination.
