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Archive for April, 2014

Despite the unusually mild winter I don’t seem to have done as much walking recently as I had hoped. So it was great to get out at the weekend and go tramping up some Pennine Hills.

This week’s walk was down in the South Pennines (West Yorkshire) from Haworth. I’m doing a piece near there later in the year and wanted to get a feel for the landscape. I also wanted to get the whole Brontë thing out of my system so I could look beyond that literary baggage the area wears. So my destination was ‘Top Withins’ – a ruined farmhouse on Haworth Moor.

‘Top Withins’ must be the most visited non-place on the Pennines. A former hill farm, it was reputed to be the inspiration behind ‘Wuthering Heights’ – a lonely, remote farmhouse high on the hills although there’s no evidence to suggest Emily Brontë ever went there or even knew of it. I’ve never read the book – I’ve tried a couple of times and not got very far. I’ve even resorted to an audiobook version too, but I just end up falling asleep with no idea how far I got each time. Still, it’s big in Japan – the Pennine Way even has footpath signs in Japanese:

japanese signpost

I first encountered Top Withins on the cover of ‘Literary Britain’ by Bill Brandt. I got ‘Literary Britain’ when I was about 15 and was the first photographic book I ever had. My early years of photography were heavily influenced by his dark, high contrast, grainy pictures of desolate landscapes and hauntingly empty buildings.

'Top Withins' by Bill Brandt

‘Top Withins’ by Bill Brandt. From ‘Literary Britain’ 1951.

The farmhouse doesn’t look like that anymore. Brandt visited sometime in the 30’s or 40’s. By the 60’s the windows had been blocked in and the roof started to collapse. I expected to find a beautiful ruin of crumbling walls and maybe a standing fireplace – they’re always built stronger. Instead, the powers that be have decided to restore the walls with fresh pointing and remove the unstable gables. The result is a stone box with all the romance of a nuclear power station. Did Ruskin mean nothing to these heritage folk? Ah well…

top withins 2014

I’ve become very familiar with my own existence on a windswept hill farmhouse over the past six years. As my adventure in this wilderness is drawing to an end I’ve been more conscious to witness and record the essence of life up here on my hill.

This spring the lapwings and curlews are back in much greater numbers than last year. Their eerie calls echo around the hills and bring a very distinctive upland dawn chorus.

Last year, as part of the ‘Gods Bridge’ project, I proposed a machine to make the sound of a curlew. The idea was to fill the painting galleries in the Bowes Museum with the sound of curlews. I had already looked at dissecting its distinctive ‘bubbling’ call earlier so while on paper I knew what was needed, making that a reality was a whole different thing.

flock of curlews

First up was just getting the right notes and tone. I scoured the internet looking for the lazy way of doing things in the hope I’d find just the right bird call. I bought the only one which claimed to do a curlew sound – and it was rubbish! So back to the drawing board and after numerous attempts with varying sized brass tube I built a slide whistle which came close. The hundreds of curlews gathering on the field outside my window gave me plenty of reference material to check it by.

Next was the problem of the trilling notes.

The spectral analysis pointed to a two-note rapid trill. I tried a sine wave swoop at the same speed as the curlew to see if it was an even up and down slide:


Obviously it’s not that.

Another whistle build revealed a closer possibility. Whistles are on the surface simple things – a narrow flow of air is passed over a hole where it is split and the reverberated air makes the note. By increasing the length of the whistle tube the note is lowered, shortening it raises he pitch. The diameter of the whistle determines tone and the size of the air hole controls the volume. Only it’s not quite that simple. Subtle changes to the shape of the hole can make huge differences to both the tone and the note. Then there’s the scale. Blowing more air can increase the pitch, considerably more air can change the scale completely raising the pitch to the next step of harmonics. By chance rather than design I ended up with a whistle which when tuned to the lower note of the call would switch to the upper note by changing the air pressure blowing through it. Could this be how the curlew is making its two note trill? A bit like yodelling. The difficulty was that I just couldn’t change the air pressure I was blowing at fast enough to even get close the speed (about 9Hz). Birds don’t have a diaphragm to control their breathing and air flow when singing. Instead their entire ribcage squeezes their lungs and is far more efficient at controlling fast speed changes than we are.

bellows

This led to the realisation of significant design flaws in my simple birdsong machine. I had anticipated that a slide whistle would control the pitch (notes) of the call, while bellows would provide the air with the whole thing powered by two simple cams – one for pitch and one for phrase. However, while the bellows method works well for cuckoo clocks and chirping mechanical birds, the longer notes of the curlew trills are just too much for moderately sized bellows. Even by rebuilding several paper bellows to increase the volume of air they move, and switching to airtight plastic-coated nylon bellows skins, getting a long enough note to do all the trills was going to take bellows much larger than the scale I wanted to use.

The whole trilling thing was looking to be far far trickier to achieve using pure mechanics alone. However, curlews have a wide range of calls. The bubbling sounds are so complicated for the bird that they can only do them while gliding and not flapping their wings. While in flight they have another distinctive two-note call.

Besides, I was getting far too hung up on the ‘Machine’ bit of the piece and losing track of the original audio experience.

So, here’s the final piece as installed in the opulent painting galleries in the Bowes Museum:

 

The sound is that of the flying call of the curlew made by the brass whistle and powered by bellows. It’s a recorded sound played through an induction speaker on the machine itself. The overall effect is what I wanted even if the method of making it isn’t as hoped.

Still, it was always going to be an attempt to recreate the sound. As it stands it’s not an entirely successful one, but as a first step it’s a good one. The bug has finally bitten though – the Curlew Machine #2 is a real possibility in the future. The next version will use fans to power the ‘breaths’, a butterfly valve will oscillate between high and low pressure notes, a step motor would change the lead pitch and the whole thing controlled by a micro processor. But that’s for another day.

For now the painting galleries echo to the sound of a mechanical curlew overhead and a small essence of the big wide North Pennines is brought inside for a bit.

 

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