When I'm singing in the toilet at work

[blinkyblinky]

and I hit a middle C, the whole room echoes and reverberates deeply. Can anyone explain in layman's terms why this happens?

[fo3nix]

what you're experiencing is probably resonance.

http://en.wikipedia.org/wiki/Resonance

if you don't understand the stuff there, post back. but it seems to explain it fairly well...

basically, consider something that can move up and down or left and right; a pendulum may be ideal here. if you shake it back and forth, with a steady rhythm, then it'll move back and forth. nothing cutting edge here. by the way, this moving back and forth is called oscillating to those in the trade. but if i tell you that all things that oscillate have a natural frequency (the frequency is the speed at which you make it go back and forth), then you may be interested to know that there is a phenomenon known as "resonance" that makes the osciallations/vibrations increase quite a lot if you move it back and forth at its natural frequency.

that's basically what you're doing... if the cause is resonance, then the natural frequency is likely to be around midde C (the scale of a piano etc. is really just a scale of frequency).

[hopalong]

Could be wind

[mibn2cweus]

Sound travels at ~1000 (340 meters) feet per second at sea level.
The frequency of middle C is about 262 cycles per second.
1000 / 262 = 44 inch wavelength or
340 / 262 = 1.3 meter wavelength

Sound waves are compressions and decompressions of air. If you�ve ever see a large speaker working you can probably visualize this. This is also similar to the waves in a still pond when you toss a stone into it.
When we here sound typically about 90% is reflected sound from walls or other smooth hard surfaces.
If reflected sound waves (echoes) arrive in sync with the original wave they reinforce each other. This can provide an intensified sustained echo of the original (source) sound.

If the dimensions of a reflective room coincide with multiples of the wavelength of a tone (1.3 meters for middle C in this case) this will augment this effect.

[Piper-AK]

Where do you work?!

[blinkyblinky]

Thanks for your replies.

I'm currently working in an old church hall which contains a piano (which is how I know that the magic note is middle c).
There is also a tape measure there, so today I'm going to measure the dimensions of the toilet to see if mib's theory is right.

Science is fun! ;o}

[mibn2cweus]

Ah oh, better check me math. Dependin on yur ellivashun (air pressure) sound may be wizzin along about 1100 fps makin it closer to 50 inches. . . hope ta hell Im rite bout this. Shiver me timbers matey.

[Calvesy]

The speed of sound varies with pressure, so you could use your toilet as a barometer, and calibrate your voice with the pips or the beeps on a Nokia, which are 256 Hz or middle C. If you get someone in the loo with you to hum this pitch, and you hum the pitch that resonates, you will be able to tell from the the frequency of 'beats' fron the interference of the dischord just how much the ambient pressure is higher or lower than normal. There is nothing gay or silly about two grown men making noises in the toilet together. Probably.

[blinkyblinky]

LOL


Ok, I measured it and it was 90 cm by 148 cm.

Before deciding to jettison all of Newtonian physics I thought I'd better check the note again, and today it was B (ie a semitone below middle C).

This can be explained by the fact that I have to walk quite a way to get from the toilet to the piano, so even though I'm constantly humming the note, it obviously moved up or down slightly during the journey. So I'd say it is somewhere between B and C.

So where does this leave your theory mib? Does this spell the end for science?

(In case you need to know, my elevation is about 10 metres above sea level.)

[mibn2cweus]

[So where does this leave your theory mib? Does this spell the end for science?]
So much for the layman approach, nevertheless, I�m glad you�re able to find humor in this, even if it is largely at my expense.
I�ve done some experimentation with my �theory�, and one thing I�ve found is that standing waves are hard to pin down. Several factors need to be taken into consideration including but not limited to the placement of both the sound source and the point at with the effect is being measured. Fortunately in this case both of these are in fairly close proximity; however the relationship of these to the reflective surfaces must also be taken into account. Also it�s typical to find several different resonant frequencies often not far removed from one another and these can change as you move to different points in the room. I realize this is getting a little more complicated the more we delve into this but perhaps there is still hope if you�re willing to continue with this pursuit, (no promises).

Here�s what we have so far: (frequency of resonance) = B adjacent to Middle C. For a piano tuned to A440, this would correspond to a frequency of 247cps. yielding a wave-length at sea level of about 138cm. This is not so far from the second dimension you gave for the room that I would exclude this as the culprit; as a matter of fact it is not that uncommon for a piano to be tuned a semi-tone flat in which case the frequency would correspond to a wavelength of 146cm. And this would be within 2% of your measurement (148cm) for the longer dimension of the room. So maybe all is not lost after all. But let�s hold off on counting our chickens just yet. I think that under the circumstances a more precise measurement of the pitch of the suspected note is in order. But even if I turn out to be right about this I won�t be applying for an acoustic engineers license.

[mibn2cweus]

Incidentally if you happen to know someone with a tuned guitar the second smallest (5th) string should correspond to B below middle C. Lots of luck. Let me know what you come up with.

[blinkyblinky]

After all the talk in the faith v science threads, I just want to point out that this is a good example of evidence not really backing up science. The conclusion? The evidence must somehow be wrong, or other factors must be coming into play.... It's easy to see how faith can play a big part in science too, isn't it?

(Ok ok, I'm being provocative mib, I have a lot of faith in science myself ;o) and I appreciate your replies.)

I forgot to measure the height of the ceiling - I suppose this measurement is going to be just as important. Obviously it will be higher than 1.3ish m, but I guess if one dimension is exactly double or triple the wavelength then the waves are still going to reinforce eachother in a similar way.

I'm not going to take my guitar into work, I think a harmonica will be easier. I will try from different points in the room to see if it makes a difference. I will make sure all my measurements are spot on this time, and we shall see if science can withstand the might of blinky's evidence.

I will let you know the results, I'm sure the AB community awaits with baited breath!

[mibn2cweus]

I personally eschew faith and I doubt that my simple formula and our rather simplistic experimental methods would hold-up well against the rigors of science. I am confident however that you are aware of and understand this. But I do believe we can still have a little fun and provided we see the evidence in the proper light we might even learn something in the process; even if it is that we are not considering enough of the physical properties involved to come to an informed decision concerning this exploration of what is certainly a real phenomenon. Therefore I�m all for this but please don�t impugn me for the downfall of science, I am neither a scientist nor a credible spokesperson for science. Nevertheless please excuse me if I find all of this somewhat fascinating, and if hopalong turns out to be right and it�s just the wind that�s cool too.

[rojash]

I think you'll find that relationship between the main resonance and the room size is a lot more complicated than just a simple correspondence with 1 or 2 of the dimensions, especially in a small (semi) sealed room like a toilet, where standing waves will arise in the body of air within the room (like blowing on milk bottle).

You can download a spreadsheet to perform the calculations from the address below, but you really need to read and understand the article as well.

http://www.ultimateavmag.com/news/10388/

[blinkyblinky]

Hmmm, maybe things are getting a bit complicated.

Well, the exact measurements of the room are:

H = 274 cm
L = 156 cm
W = 91 cm

The note is halfway between a B and a C (about 252 Hz I think)

It doesn't matter where the note is sung and it's the only note that produces the "magic" effect.

340 / 252 = 1.35m

135 cm doesn't really correspond to any of the room's dimensions, but double it and you get 270cm, very close to the height of the room. Not that I'm qualified, but I declare science the winner!

Well, my maths isn't very good. If anyone's interested enough to check it/correct it, feel free.

[mibn2cweus]

Got to say, I wasn't holding out much hope for a nine foot ceiling. Since this is such a dominant and pronounced effect that's where I'm putting my money!

I'm ready to celebrate success.