Australia's Science Forum

Hi
One of the teachers here wants to do a prac where two sound waves cross so cancel each other out, the noise fades in and out. Does that make sense? any ideas how I could set this up?
Krysia

We use the wave machine to demonstrate that concept visually. Do you have one of those? They sit over an OHP so you can project it onto the big screen or if only a small group you can attach a light over the top and watch the waves on a white surface.

Hi Krysia Lee
You can use 2 speakers emitting the same frequency (from a sound box or signal generator)but placed in different corners of the room so the sound waves "overlap" slightly out of phase. This will produce area where it is louder (added) or softer/ none (cancelled). I found this website that has an explanation of the theory
http://www.school-for-champions.com/sci ... lation.htm
Our physics teacher has done it here with hearable (if not brilliant) results.
Regards
Sue G

Yep, two speakers from a wave lab or audio generator. Opposite corners of the room, but angled in so that the sound waves "cross" each other as they travel. Works really well.

Our Physics teacher does the same one, but performs the experiment outdoors, in the playground so as to reduce reflection from the internal classroom walls. The idea is that you have the speakers about 10 - 20 feet apart (3 - 6 metres for you "young ones"!) and then, standing in front of the speakers (maybe 20ft, 6m or more away) you walk across from on speaker to the other. You should hear a change in volume several times as you walk across.
If you type "Interference of waves" or similar into Google, you will come up with explanations and demonstrations, similar to this one http://www.5min.com/Video/Sound-Waves-a ... -174070562

Cheers
Ian

The other option is if you have a matched pair of tuning forks set on the wooden sound boxes
set them up with opening facing each other dong one and the other will ring with resonance then put a rubber band round one fork of one tuner this alters the freq. slightly then dong both and they will set up beat freq. getting loud and soft for when they match
Does that make sense, I know what I mean

I must say that sounds alot easier. Cheers

Hey thanks for all the ideas!!!!!!!!!
I just followed your instructions Ocker and its works just beautifully. Knew I could rely on you guys (my saviours).
Thanks a mill.
Krysia

Try this website for any type of wave. We have not used the "Ripple Tank" from IEC since finding this site.
http://www.falstad.com/ripple/

That looks like a useful site, Tim - Thanks! I'll pass it on to our physics teacher.