[arya202]

I doubt this question has ever come up but if it has sorry for not looking. Anyway this year I have my eigth grade science fair project and I've gotten really in to home theatre lately and I wanted to do my project on something related to home theatre so what are some suggestions?


I was thinking comparing different cables and seeing if "better" cable makes a difference. And if external radio signals actually goes into your cables and distorts your image. Any other suggestions realating to home theatre?


The old volcanoe just won't cut it this year.

 

[hedrick]

There's nothing wrong in principle with your suggestion, although I'm going to suggest some other possibilities. The key is that you need to come up with something specific you can test. The real issue with cables is whether differences are audible. Ideally you'd like to try a range of different cables and test physical parameters and do AB tests with a variety of people. You'd then say things like "with really thin wire, you can see that the resistance or capacitance is high, and people see it as weak treble or a diffuse image." That's fairly complex, because it's going to require you to have pretty good test equipment and also to do AB tests with a reasonable sample of people. The tests that excite people here are to see whether $10,000/ft cables actually do anything. But (1) your audience isn't even going to know that there are people selling such cables, and may find the whole idea absurd, and (2) you may find it hard to get hold of such cables to test (though possibly other subscribers could help). Of course you don't have to test super-expensive cable. But if you're going to show the effects of too much resistance or capacitance, you're going to have to find or make cables that are bad enough have measurable effects. I'm not sure how easy that is. Does anyone here know how hard it is to find or make test equipment to detect the levels of resistance or capacitance required? (Can you get someone from a nearby university EE department to help?)


As for other ideas, it depends upon what areas of science are acceptable. If psychology is allowed, there are things you could do with AB testing to show what kind of biases people have and how careful testing can deal with them. However that would require you to find other people to be test subjects. Would you family, friends, and classmates help? (Also, be aware that any experiment involving human subjects may require a human subjects review. You would need to check with your school.)


I can think of various projects to check either people's preferences (in a blind test do they prefer flat response or something else? Can you identify any reasons?) or perception (what factors influence imaging?) Without doing preliminary tests I'm not sure which of these would be easy enough to show results on to be practical.


If you like to build things, you could learn lots about acoustics by building a speaker and describing the design process. I don't have the URLs handy, but I've seen online sources.


Another acoustics project would be to look at room effects, e.g. setup of subwoofers. You'll learn lots about waves and modelling.


Both of these involve a bit of math, though I don't think it would be beyond an 8th grader (at least not if you can get any help).


Another human subjects project would be to check peoples' hearing. It would be interesting to see how it varies with age and (if you think you can get people to answer a brief questionaire) exposure to rock concerts and other noise sources. For this you would probably want to work with your school nurse or someone else with a health background. If done properly this could combine electronics, acoustics, medicine and statistics. However like any experience with people, the risk is that you may find it hard to get interesting results. You'd at least want to make sure you included people with varying ages.

 

[arya202]

its pretty much open to all kinds of science I'm pretty sure. I'm also pretty sure I can have test subjects.

 

[Mr.Poindexter]

Show standing waves by playing a mid-bass frequency for an extended period while people walk towards and away from the speaker, hearing the volume go up and down as they pass from peaks to nulls. You could even get a sound meter and show how it gets louder as you move AWAY from the speaker because you are leaving a node and going to a peak. It is pretty trippy, since you know it is a constant volume but it doesn't sound that way. Don't use something too high, as the wavelength is too short and too low just makes it hard to hear and disturbs the projects next to you, as well as requiring more wattage and beefier speakers.


You can then show sound cancellation by sending a mono signal into two speakers with one out of phase. Point them towards eachother and bring them close in and show how the volume drops as the majority of the sound is cancelled out.


Don't try and do imaging and soundstaging effects, since you will likely be in an environment with lots of background noise and horrible acoustics. Stick with the hard science of sound and you should be fine.


One other possibility is to get an underwater speaker and play that in a tub of water to show how sound travels through water, but I don't know who would want to stick their head in the water to hear it - VERY few people would do that at a science fair, plus the underwater speaker is something you would need to order. Clark Synthesis makes it, but not many people have one and it is several hundred dollars. If you did that, you would probably want to get a tube that is full of water and has some sort of earpiece attached to it so they can hear the sound transmitted through the water, which will be much louder than the sound transmitted through the air since water is a better conductor of sound (and the speaker is in the water, too).

 

[arya202]

I'm doing this with a partner that doesnt know too much about home theatre. But he can learn quick enough. I'll ask him which ideas he likes.


The one about the sound getting louder as you step away sounds really cool. The one about peoples biases sounds cool too. But can you explain more about that one?


I have to submit and an idea to the teacher probably in the next couple of weeks. Howbout something about the tendency of high and low frequencies? could that be possible? like lower frequencies seem to be less monodirectional while highs only go in one direction usually. could that work? or possibly how we use two senses(not just one) to examin sound?


Well the possibilites are endless. I am excited.

 

[BobL]

Is the science fair going to be in a classroom or a large auditorium or gymnasium type space? That could definitely have an impact on choosing a project.


Bob

 

[Quill]

A couple more ideas:


The eye's reaction to watching television in a darkened room, and the increase in perception that occurs with bias lighting...?


The science of bass...the relationship between enclosure size, driver size, port size, wattage...? You could have samples of a few extremes constructed, then one set up correctly....press the button in front of each sub and listen...

 

[ChrisWiggles]

A really cool thing to do would be some physics demos about waves maybe.


I was in an acoustics class, and one very cool visual demo was a simple bass driver and a signal generator to create the frequency, and a stretched circle diapragm (like a drum). With the lights off, and a strobe light, you can adjust the signal generator to frequencies that excite resonant modes of the diaphram (more interesting than the same thing done with just strings), and when you get a resonant mode (pretty easy to hear it), you adjust the strobe light, and you can watch a very cool slow motion like movement of the modes of vibration.


Very nifty. And then you have all the materials you need for a rave when you're done .

 

[audiofirst]

Another idea: explain sound perception and the decibel. Did you know it takes a ten-fold power increase for the ear to subjectively hear the sound as being twice as loud? This is expressed as a 10 decibel (or one bel) increase in loudness. Likewise, a two-decibel change is typically the smallest change a human can perceive. The decibel is a logarithmic scale, as are many effects in nature.


To measure this, you would need a signal source (any one of the many such discks out there), a power amplifier, a speaker, and a sound-pressure meter ($35 at radio shack). You also need a way to measure the power being output by the amplifier. If you have or can find one with a built-in power meter that might be sufficient, although they are typically not that accurate.


Then, set up a double-blind experiment where your subjects are simply remarking about the relative loudness of the sound. You might need to do some research on the techique of a double-blind test.


This experiment would involve discussion of the logarithmic scale, decibels, and the physiological perception of sound. Could be a pretty neat presentation.


Good luck.

 

[Tex-amp]

Here is a link to sound ramp that decends 6dBs and then 3dBs per tone to get an ideal for the difference. This is a good site to learn more about hearing and the terminology used.

 

[apg]

One area where it is difficult to get solid numbers is "The Rainbow Effect". (Search on rainbow and DLP projectors.) If you can borrow a DLP and an LCD projector and get a good crowd, you can draw up a simple questionnaire, something along the lines of "I'm going to show some images. Please indicate which ones seem to have color fringes or some other odd color effect." Create images and clips that both show and diminish the "Rainbow Effect". Include images that are _deliberately_ altered. There are ways of making this "Double Blind"; I'll leave that to you.


Or you can always do a classic- how loud do you have to play The Ramones before it causes laboratory mice to explode?

 

[Bigus]

A visual demonstration of standing waves and modal interaction would make for a fairly nifty science fair project. Something like a plexiglass box filled with water, perhaps a touch of food coloring, and a light from the right angle should highlight peaks and troughs of waves enough to see clearly. The analogy between longitudinal and transverse waves (i.e., the analogy between surface waves in water and sound waves in air) is strong enough to really make the point. In fact, you could even show the effect of "room treatments" by modifying the conditions at the edges of the container, emphasizing how a peak or null in one area can be moved or eliminated through proper treatment.


I like some of the other ideas as well, particularly bias in testing (which really isn't specific to home theater), the way the eye is biased by background light level, and whether people prefer flat or modified frequency response etc.