A web page to accompany an educational demonstration comparing sound wave attenuation inside pipes containing bubbly water and water droplet fog

(click on logo for links)

Downloads:

Click here to see the TV show the demonstration was used in.

Click here (or email tgl@soton.ac.uk if not loaded yet) to download the article from the Journal of the Acoustical Society of America showing how the apparatus can be constructed.

Click here (or email tgl@soton.ac.uk if not loaded yet)to download the article from Acoustics Bulletin giving the wider perspective on applications of the experiment.

Click here for more stories, and here for more publications, on the topic.

Click here to see a movie showing  how effective is the mobile phone vibrator at making small bubbles, and in turn how effective they are at attenuating the sound. The movie starts showing large bubbles injected into the water column by the needle (the bubbles are large because no voltage is applied to the mobile telephone vibrator attached to the needle). The oscilloscope screen shows strong acoustic ping picked up by the hydrophone - these large bubbles do not absorb sound well. The then voltage to the vibrator is increased to 3V, the bubbles are smaller, and the acoustic signal is more attenuated. Then the voltage to the vibrator is increased to 4.5V. The same amount of gas is being injected in, but distributed amongst a greater number of smaller bubbles. The signal is strongly attenuated. After the voltage to the vibrator is turned off, it takes a long time for the hydrophone signal to return to its original level because the small bubbles take a long time to rise out of the water path between source (which is beneath the needle) and hydrophone.

Sound files form the experiment:

1. Click here for a wav file of the sound recording of the chirp, starting just before bubbles are injected into the water-filled tube (the mp3 equivalent can be found by clicking here).

2. Click here for a wav file of the sound recording of the chirp, starting just before bubbles are injected into the  water-filled tube, but with a high pass filter applied to remove the sound of bubble injection so that the effect on the chirp can be clearly heard (the mp3 equivalent can be found by clicking here).

3. Click here for a wav file of the sound recording of the chirp, starting just before fog is poured into the air-filled tube (the mp3 equivalent can be found by clicking here). 

Time-frequency spectrograms of sound file (1) (above)

Time-frequency spectrograms of sound file (3) (above)

This is the poem, entitled "Half Term", written by Rhiannon Leighton (aged 11), following the filming of the demonstration for TV

This half term was like no other.

No aliens snatching my mother.

No Paddington Bears from Darkest Peru,

In fact I didn’t even see a kangaroo.

Though in the end the experience was great.

I actually wasn’t ten minutes late (that’s something!)

It started off in a farm near

Even though the snow was sheer.

I saw a TV programme being made,

The memory of this will never fade.

My Dad made an experiment, cool

(Much more educational than school)

He made it with the cameras on

A leak came from tube one

But that got sorted real quick

And the filming was quite slick.

He used ice to make a fog

And put it in the tube shaped like a log.

I directed Richard Hammond, presenter, to the loo

And he said back, ‘thank you’

We then had to pack up and go

The equipment we had to tow.

I said bye to everyone nice

And they offered my a cake slice

I refused

And they said it should be used

And then the day was done

And that was my half term.

I had so much fun.