Big Sound Waves – getting the measure!

The Pipe

My idea was to show a large-scale resonator (pipe) that would describe how long the LIVE sound

wave   actually was, and we would hear and experience the vibrations of the sound wave as it

resonated  in the pipe.  I was aiming to play a 16 meter long sound wave!

I set up a geophone that played live sound from the ground into a speaker at the end of a pipe.

A 4 m  sewage down pipe was the largest I could get my hands on at this time. The geophone

was  picking upthe sound of the traffic 80 m away, across Headington House Gardens at

Oxford Brookes  University.

I found out that sealing the end of a pipe would create a lower frequency, in fact a quarter of the length of a sound wave in a sealed pipe.  So our 4m sealed pipe resonated the same as the whole 16m length of sound wave in an open or un sealed pipe, amongst other frequencies. Ours was not an exact science as far as the sealing up of the pipe went. (With an outside setting there were not exact workings regarding end correction etc.)  I had some helpful advice from musician and electroacoustician, Sarah Angliss and artist and technologist Mike Blow, who played a sine wave into a carefully sealed pipe and had the maths to prove it.

Open 16m pipe at  21Hz (Just audible)

4m long sound wave resonates best in an open 4m pipe at 85Hz (You can hear this)

A 4m sealed pipe resonates ¼ of a 16m sound wave at 21Hz  (Just audible again)

So what were we listening to? Here’s some of the sound and vibration if you have good bass speakers or a sub.

[audio:|titles=pipe blog sound]

Revealing-   Showing –   Illustrating –   Demonstrating –   Informing –   Illuminating –   Amplifying

So, did it work? It played sound, and different frequencies were resonated. It didn’t work in the way I had imagined, because these details, in my head, were not obvious to the observing audience. The feedback was varied: it had encouraged some people to think to of the space under their feet, to imagine a massive inaudible sound in the earth, to question the trickery of the equipment, think of the ‘ground as a vibrating surface’, and importantly question the need to standardize the equipment in order to understand what I was listening to.

It posed the question: When is an event a demonstration of science, and when is it art?  Is there a difference and does it matter? Sound artist Alvin Lucier, in an interview with Chris Buck in the Wire (issue 245 2004) states, ‘Scientists often miss the poetic beauty of nature and the sensual experience of natural forces…. I understand the (scientific) principals more because I’ve used them in a piece experientially rather than theoretically’. With that in mind it’s definitely worth checking out these works:

Katie Patterson – Moon

Mark Bain – Live Room:Transducing Resonant Architecture

Bill Fontana – Speeds of Time

Roberta Gigante  OrgOOn in  Ghent Docks

I was sorry to miss this festival in Ghent last year, where Roberta Gigante was playing sound into 30m long pipes. Open at one end they would be resonating at a frequency of 11.43 Hz.   Given the pipes could be sealed frequency would be =3.81Hz and the sound wave 90m long. That is some length of sound wave!

If anyone knows the whereabouts of some monster sized pipes in the UK, then let me know as I ‘d be delighted to use them for some sound experiments.

Roberta Gigante  OrgOOn          photo: Reinout Hiel for Vooruit

Sizing up Seismometers

I drove down to North Devon to Hartland Point with a friend Charlotte, to see a seismometer in action.

I wanted to find out what I was hearing with the microphones I had put in the ground in Bristol? (Piezo and AKG pick-ups and a geophone).

What was I hearing from them? How could I find out where the sound was coming from? The understanding of this long distance low frequency microphone would help me find out.

Hartland  Magnetic Observatory

The seismometer in it's case in the ground

The seismometer in it’s case in the ground 6 feet down on bedded on solid rock

I was right about seismometers picking up sound waves traveling long distances from other continents, which was mind blowing, but surprisingly even thelocal dog walkers had an effect on the seismometer. This was strange, but of course they were making their own mini tremors with their foot -falls.

Here’s the data read from the seismometer – showing a blob on the left

I stamped my foot and the seismometer reacted instantly even though it was out side the building 60 METERS AWAY!!

This clever instrument could pick up the quieter range of sounds in the ground. It would be capable of monitoring 0.01Hz-100Hz, and the (inaudible to human ear –which hears from approx 20Hz) natural Hum of the earth (0.02Hz- 7 Hz).

And this being lower than the cultural man made sounds from cities and trains (in particular) that start at approximately 1Hz.

Look here for more pictures :

While I was getting my head round the image of a sound wave making it’s way to effect this instrument, in a box 6 foot under the ground, from several thousands of miles away, I felt the mighty physicality of the sound wave traveling over such a distance was certainly a planetary scale event.

I start to think of earth as a lump of humming, quaking, vibrating buzzing rock.

The work by artist Floriain Dombois, puts this global phenomena into context with pictures of measuring devices in sheds and compounds and seismic stations from different 60 countries. (Seismic Stations   Global seismographic Network (GSN) 59 of them. )

Up in the Edinburgh the British Geological Society monitor the signals that get picked up from round the UK, those from the UK and those that have traveled from other continents. With data from different station’s the origin of the tremor can be plotted. Primary, Secondary and surface waves, and their different trajectories through and round the planet are compiled and compared with data from other countries. We hear the effects of these forces more often on the news, from places that suffer human tragedy from the destruction caused by the planet.

Here’s pictures of sound through the earth’s mantle:

Here’s some big tremors:

Here are some recent tremors:

Here are seismograms at different stations:

That afternoon we learnt that forces effect our planet -not only vibration working from the middle of the planet: from the movement of tectonic plates (making quakes and tremors), but also the geomagnetic forces from round the outside of the ionosphere working in.

It was described to me recently that we, on the surface of our planet, are like innocent children or kittens, to whom things happen. In this case vibrations and forces from outside our local view.

We noticed the amazing display of Heath Robinson looking gadgets/instruments all over the station.

Although we came to see the seismometer, the observation station mainly monitors geomagnetic forces, measuring slight changes in the earth’s magnetic field, and has done for over 100 years (I found a bound record book dated1865). They moved from near Kew Gardens / London in 1957 when the train line was built and started to interfere with the instruments.

Records were meticulously kept for posterity, hand drawn in dusty volumes reminding me of nautical maps of uncharted seas.

On the head land with the on shore breeze, Steve, the manager who kindly showed us around the Observatory, describes how the latest magnetometer no longer needs a whole building, being small, digital and self heating.

I felt inspired to use the geophone we had brought, and was advised by Steve, that a good place to listen to natural sound, was through rock, and the ancient granite rock of the cliffs and harbour wall down the road at Hartland Quay.

Our geophone is an SM24 that picks up signals from 10Hz-240Hz.Like the seismometer has a capability of 2D and and 3D surveys, picking up sounds from all directions, and has a different mechanism to the seismometer. Have a look at it

It turned out we would have heard the sound of the sea, pounding on the ocean floor off Hartland Point, as it added to the natural din of sound in the ground. I never had thought of the sound of the sea emanating INTO the ground before, and even, I fancy, mixing with the earth’s natural low hum, and maybe the sound of more localised quarries and train lines, and low frequency signals from much further a-field, but unfortunately we found we had run out of time to make some good recordings and had to return home, so leaving our recording for another day.