Frequency response from speakers of different sizes
The hypothesis that reducing the size of the speaker enclosure will cause the dB of some frequencies to be higher is proven to be true. With a depth of 300mm the sound of speaker C at the 150Hz frequency was 6 times louder than the sound level of the other speakers.
This type of air tight speaker enclosure is called a sealed enclosure. When the diaphragm of the speaker moves inwards, air pressure will build up inside the speaker enclosure and push the diaphragm back out. Similarly if the diaphragm of the speaker moves outwards, the air pressure inside the enclosure will drop and pull the diaphragm back. This spring like effect will cause the sound produced to be more precise. However the audio electrical signal will require boosting by the amplifier circuit.
This science fair project may be repeated, this time,by checking the frequency response using different types and thickness of wood for the enclosure.
Modify the science project experiment, using using different sizes of speakers.
Speaker enclosure design - http://www.niksula.hut.fi/~mdobruck/siililand/mini/diy/alien/ice/speaker.html
How speakers work - http://electronics.howstuffworks.com/speaker9.htm
Basic safety requirements