We recently made the trip to London’s Southbank Centre to remove our Giant Feedback Organ. It had been installed there since early March as part of the Pull Out All The Stops organ festival. This is the story of how it came about and what our plans are for it now…


Giant Feedback Organ demo – in Southbank rehearsal space
[decent headphones or very decent speakers required for a full fundamental experience]

In the beginning…

Sometime last year we saw this video. It was the best implementation of such a system we had seen and it provoked our usual response: Bigger, louder, bassier. At the time we were searching for something we might develop further. We added this to the list.

We always start testing with what we have lying around. In this case we used a powered monitor speaker and a standard vocal mic at opposite ends of some old carpet tubes we found in the shed. Initial results showed promise: we were able to make a decent racket in the 150-300hz range and by sliding one pipe inside another we could even “swanee” the feedback. Huge smiles all round.

Now we needed a better test rig. We replaced the vocal mic with one with a much extended low-frequency response, got a decent power amp and some bass driver loudspeakers. Then we approached our kindly local farmer who lent us some lengths of grain blowing pipe and joining clamps.

Test rig
Early test rig

To give us maximum space and flexibility, and as near to a free field as possible, we set this arrangement up in the garden. We soon discovered that the system resonated most willingly at higher order harmonics, since these take less power to start sounding. We added a combination of low pass and notch filters to alter the system’s frequency response in favour of the fundamental pitches. We also discovered the extent to which the efficiency and pitch of the system were dictated by the way we coupled the speaker to the end of the pipe. Our most successful experiments used a large round bung (made from a plastic bucket) fitted with a speaker and pushed into one end of the pipe. In the course of these experiments we burnt out several cheap loudspeakers and one expensive power amplifier (another victim of our “More Power Igor” bent).

Despite these teething troubles we were getting some pleasing results at quite low frequencies, so we added more length to the pipe. This provided some interesting results; counter intuitively, an increase in pipe length would often result in an increase in pitch. We had our theories for why this might be and decided the system was interesting enough to demonstrate at our first ever If Wet – a monthly sonic exploration event we run in Sam’s village hall.

If Wet
The first ever photograph of If Wet, featuring the Giant Feedback Organ test rig [by Pete Ashton]

If Wet is a place to demonstrate work in progress, a place for discussion and development of ideas. Luckily, local recorder maker Tim Cranmore had read about our first event in the local paper and was present at it. When we explained our prototype’s reluctance to resonate at the fundamental frequency Tim was quick to offer a complete explanation: for the notes we sought our bore-to-length-ratio was wrong. We had been increasing the length of our tube by adding more grain pipes of the same diameter. Each time we did this the bore became narrower as a proportion of the total length. We should have increased the pipe’s diameter as we increased its length. That is what If Wet is about! Onward.

Pull Out All The Stops

Well, not immediately. Our development of the Giant Feedback Organ had been driven in part by our aim to present it at the inaugural If Wet. That had now passed. To develop this project further we needed someone to commission an instrument based on our prototyping work. Luckily for us that is just what the team at Southbank Centre had in mind. They put out a call for instrument makers who could help them create four unique instruments, inspired by pipe organs, as part of a festival to celebrate the refurbishment of the organ in the Royal Festival Hall. We were selected, and after a couple of meetings and discussions it was agreed that we would be in charge of the very lowest notes: F0, B♭0 and C1. To put this in context: that low F is off the bottom of the range of a piano, contrabass tuba and contra-bassoon…we had our work cut out.

We needed larger diameter pipes. We knew we would save time if we could re-purpose standard pipes since everything is easier: they interlock, have tried and tested fixtures and fittings and they’re cheaper than any bespoke system. We visited some yards, spoke again with the local farmer and a few other contacts, and finally chose air ducting, supplied by the wonderful Ductmann in Bilston. The first fully-laden van trip was, um, interesting…

Pipes on van
Ducting pipes on van

With the “pipe system” sorted, what followed was a period of intense testing. We had our ups and downs; or rather they were all ups as negative results are clearly still very useful. The most interesting part of our testing for some time was the development of large “reed microphones” that we would place in the centre of the tube. These were really effective in chopping the top off the frequency response. As we do at MortonUnderwood, Sam was running around building lots of test stuff, whilst David was pondering the outcomes and suggesting the next course of action. The split isn’t as clear as that really but in broad terms that about sums up our working process.

Come the end of 2013, we were still struggling to get the pipes to go off at their fundamental frequencies. In fact we were struggling to alter the frequency of the note at all. Most odd. At one point we suspected the room effects were greater than those of the pipes, so we took them up to the village hall but that didn’t seem to alter much either. We did however have much of the system well established with custom built speaker couplings, a powerful PA amplifier, a suitable desk and filtering system, but it was clear that it wasn’t responding as you’d expect from blowing air up an organ pipe; we hadn’t yet achieved a proper resonant system.

Over the break we resolved to have a rest from thinking about the Giant Feedback Organ but there were these huge pipes nagging me. I had this urge to try going back to early mic tests, as a means of calibrating where we had got to. I started digging around and found some old boundary mics I had been given. Unexpectedly these provided some particularly low frequency results. Also, by moving them up and down the pipe I was able to recreate the early swanee-ness. Progress. I reported back to David and he investigated the specs of some of the omnidirectional boundary mics I had, assuring me these would provide better bass response. As ever, correct! I also found that, inexplicably, one brand of boundary mic provided much better results in this context than the other two I had. Who knows why but at this stage we didn’t care. We were moving in the right direction again.

Giant Feedback Organ
A view down the pipes

Our prototype was soon providing reliable results and we could use the mic position within the tube to vary the pitch to a small degree; sufficient that we could use one tube to deliver the B♭0 and C1 notes. The exact pitch of each note is determined by a number of factors: pipe length, mic position, low pass filter settings and the power used to drive each channel. This comes in very handy when tuning the organ within each new space because the size and shape of the room also has a great effect.

The interface

Our instrument was to be placed in a public space, for use by all comers. It was therefore important that its console was welcoming. It had to say “Play me!” to young and old, musician and non-musician alike. We concluded that big, bold push buttons were what was needed and we fabricated the console itself out of the same material as the pipes, so it was clear what you were controlling. This console was the only part of our instrument that the public could touch. The pipes were to be suspended high up in the space, not least to avoid small people climbing into them.

Console
Giant Feedback Organ console

Rounding it off

This is the aspect of instrument design you forget at your peril. Even just constructing an interface that will survive abuse by children (and their parents) over a prolonged period is no easy task. We also had to consider how the pipes would be suspended, how cables would be run, how equipment would be housed, removing sharp edges, preventing stuff falling over, constructing mic brackets etc. We had two bites at this cherry with rehearsals at the Nautical School near Southbank Centre a couple of weeks before installation. Some stuff is best left until you can meet with the people responsible, and we made some changes in response to their suggestions. The result was an instrument which didn’t require a single maintenance visit.

Rehearsals and performances

While building our instruments all four makers had engaged with Pete Flood and Andy Mellon of Bellowhead and families from Lambeth who helped us design what they needed for their performances. Visiting London with the instrument for rehearsals we got an idea of the scale of things. Together the four instruments looked great, there were more members of Bellowhead, many of the children and family members we had worked with before and a choir! What a glorious racket they made. A few minor tweaks later and we were down again for the final install, followed by the public performances.

Installation
Installation – what could possibly go wrong?

We had a great weekend at the Southbank Centre for the final performances. By this point everything seemed to be working well and we could relax. In fact, we had a bit of a proud. The tunes were great, the children were a delight and the instruments seemed to do their job very nicely. Much fun was had.

Giant Feedback Organ - Southbank
The pipes in situ

Performance
Performance day – the calm before the storm

Performance
Performance day – chatting with feedback pipes in background

If Wet at Southbank Centre

As a “cherry on the top” we were asked to host a Meet The Makers event to highlight the work of all the instrument makers on this project. This was hosted in an If Wet salon style; everyone discussed their work before makers and audience visited the Clore Ballroom to try the instruments for themselves. If Wet went from Callow End village hall to the Southbank Centre in less than a year – not bad!

Blurb
Blurb

What’s next?

On Monday we noisily moved the Giant Feedback Organ to a warehouse space in Birmingham. During our tests we found ways to extend its usefulness both as a musical instrument and as a sound installation. This is a central project for us, so developments will continue forthwith. We are exploring all facets of this instrument: How might it sound as an extension to a traditional pipe organ? How low can we go? What can we do with the burbling thunder sounds we get when forcing the sound below the fundamental of the pipes?

We welcome enquiries from anyone wishing to explore these or other aspects of the Giant Feedback Organ!

Bye Bye
Bye bye Southbank Centre

Bye bye and thank you

Lastly, we’d like to say thank you to all involved. The Southbank Centre staff and crew have been a delight to work with, as have Bellowhead and the Lambeth families. The other makers were great too. Our suppliers have been wonderful; with special thanks to Ductmann for their expertise. Thank you, as ever, to our local farmer…who is frankly amazing! Thank you to our friends and associates for their advice and support, including those who have supported If Wet throughout. And thank you to Sam’s girlfriend for, well, putting up with us.

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