Assistance with Sound Wave Reduction/Amplification Experiment

• pasomatt
In summary: Amplifier...a big stable platform to work from.In Summary, when the tone generator is placed in the box and left open, there is no discernible change in dbs. When the glass is placed on the box, the sound is increased by a range of 2 to 13 dbs.
pasomatt
I was conducting an experiment with a tone generator (330 Hz) in boxes of different sizes with a glass plate placed on top of the box. There is a receiver about .55 meters away. Without any interference, the receiver registered -41 db +/- 1 db. When the tone generator is placed in the box and left open, there is no discernible change in dbs. When the glass is placed on the box, the sound is increased by a range of 2 to 13 dbs.

Going into this, I expected the sound to be reduced, not amplified. Like rolling up a car window, or closing a window in your house to reduce the noise from outside. After realizing the sound was being amplified I was expecting this to be proportional to the amount off free space in the box. I.e. large box = more space = less of an increase in sound. This second part mostly held up.

In a space of .008 m^3 the sound amplification was 2.
In a space of .003 m^3 the sound amplification was 6.
In a space of .0005 m^3 the sound amplification was 8.
However, in a space of .0007 the sound amplification was 13.Does anyone know why the sound is not being dampened? Or can refer me to some sort of concepts/equations? I'm really struggling to model what is happening.

Let me know if you can help.

Here's an example of my setup:

It looks as if the glass plate is Matching the acoustic impedance of the generator to the air. The glass acts like a piston and just moves more air, launching more sound energy.
There would be very little damping. The glass wouldn't be absorbing much energy because it is rigid.
The spacing between generator and receiver and, it appears, the size of the glass are around a half wavelength and the effects of the geometry will be very relevant. For a very low frequency (long wavelength) the air vibrations will be fairly straightforward to describe but diffraction effects are very relevant at the scale you are working. You could be getting standing waves between the box and the generator - it's quite a complex arrangement aamof.
If you vary the height / separation you could expect to get a periodic fluctuation with distance x and / or y (standing wave effect). x would probably be easiest to vary and you could plot the received level against x. Using a linear scale might give a better graph with more obvious level changes.

pasomatt said:
Or can refer me to some sort of concepts/equations

Stephen Tashi said:
Since conservation of energy is such a reliable principle, we can look for an explanation using it as a guide.
This is actually a bit of HARD ENGINEERING. I'm afraid.
Problem is that the Energy (Power) of the sound coming out depends upon the Matching of the amplifier to the surroundings because the Power may never be generated in the first place . An audio amplifier is not a 'constant power source'. Most audio amplifiers provide a Voltage Out that's proportional to the input signal. The actual Power that's delivered will be that voltage times the Current that flows into the loudspeaker coil and the current will depend on how easy or hard it is to move the diaphragm. This is why loudspeakers have a wide rigid Cone, which gives the voice coil something to 'push against' (i.e the air) and so deliver some significant sound power. (I'm sorry if this is very Noddy approach but the point is important and it relates to the Impedance I referred to earlier) A large flat plate may just be allowing more air to be moved by the generator and, hence more Power. A 5kg slab of concrete would not give any benefit because the driver just couldn't shift it. A light sheet of aluminium might be better than the glass etc. etc.
Once the sound has been launched, there are all the propagation issues with standing waves and the spreading out of the sound power etc.
The situation has those two separate aspects which could be studied with different experiments. But that large box will interact with the sound from the source (plate) and affect the Matching as the distance is varied - until you are a reasonable distance away. As I mentioned, that spacing is around a half wavelength which is very relevant. Working further away would be favourite if the power is high enough or the receiver is sensitive enough. I think I could expect the variation with distance to be a gradual decrease with some ups and downs when in close.

BvU
sophiecentaur said:
This is actually a bit of HARD ENGINEERING. I'm afraid.
Problem is that the Energy (Power) of the sound coming out depends upon the Matching of the amplifier to the surroundings because the Power may never be generated in the first place .
Yes, from the conservation energy point of view, the physical situation may change the amount of electrical energy that is changed to sound energy. (Likewise for units of power). This could be tested by measuring the power consumption of equipment generating the sound with and without the glass on the box. I wonder how sensitive a watt-meter would have to be in order to detect a change.

1. How do sound waves travel through different mediums?

Sound waves are mechanical waves that require a medium to travel through. They can travel through solids, liquids, and gases. The speed of sound varies depending on the medium, with sound traveling faster through solids and slower through gases.

2. What is the difference between sound wave reduction and sound wave amplification?

Sound wave reduction involves decreasing the intensity or loudness of a sound wave, while sound wave amplification involves increasing the intensity or loudness of a sound wave. This can be achieved through various methods such as using soundproofing materials for reduction or using amplifiers for amplification.

3. How can I conduct an experiment to reduce sound waves?

To conduct an experiment on sound wave reduction, you can set up a controlled environment with a sound source and a sound detector. Then, introduce different soundproofing materials between the source and detector and measure the decrease in sound intensity. You can also experiment with different materials and thicknesses to determine their effectiveness in reducing sound waves.

4. What factors affect the amplification of sound waves?

The amplification of sound waves can be affected by various factors such as the distance between the sound source and the listener, the frequency and amplitude of the sound wave, and the properties of the medium through which the sound wave is traveling. Additionally, the type and quality of the amplification equipment used can also impact the amplification of sound waves.

5. How can I measure the amplitude and frequency of a sound wave in an experiment?

To measure the amplitude of a sound wave, you can use a sound level meter or an oscilloscope. These devices can measure the intensity or pressure of the sound wave. To measure the frequency of a sound wave, you can use a frequency analyzer or a spectrum analyzer. These devices can display the different frequencies present in a sound wave, allowing you to determine the dominant frequency.

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