The Maker Profile segment in this past weekend’s episode of Make: television featured the talented Makers and musicians of CCRMA. Chris Warren of CCRMA sent us his instructions on how you can build your own Feedback Piano, as seen in the beginning of the segment. The Feedback Piano uses the strings and soundboard of a hacked upright piano, as well as a laptop & sound interface to allow you to play any note or combination or notes in any timbre and have it come out through the piano. Chris writes:
I kept the first feedback piano I ever built sitting in the living room of my house for several months. I was amazed at the way every visitor took to it so quickly, singing into it and marveling at the result. Playing it takes no particular musical skill and yields beautiful sonic results. It’s a fairly simple project and can be completed in a single afternoon for relatively little cost.
piano – Just about any piano will work, as long as the soundboard (the large, flat wooden panel on the back) is not cracked. A free piano can generally be found on Craigslist as long as you are willing to haul it away. Heck, for that price get two!
microphone – Since you’ll be creating a feedback loop, the sound will be passing through the mic repeatedly. Any reasonable mic will do the job, but a decent condenser mic will sound significantly better.
laptop with sound interface – You can use the onboard 1/8″ jacks but, as with the microphone, a better interface will yield better results. Even a $100 external sound interface will sound noticeably better than the 1/8″ jacks.
amplifier – Any home stereo amp that is rated for at least 30 watts will work (although 50 is recommended).
transducers – I use four Vidsonix Ghost electro-mechanical transducers. These total about $70-100 on their site or on eBay.
wiring – You will need the appropriate audio cables to connect the microphone to the audio interface and the interface to the amplifier. You will also need a dozen feet or so of speaker cable.
Tools: screwdrivers, wire strippers, small drill, mallet hammer
Software: you can download the feedback piano software at www.alloyelectric.com
Disassembling the piano is not truly necessary to make this instrument. You can create a completely functional feedback piano that is still playable as a regular piano without taking the instrument apart at all – just install the transducers and put a weight on the rightmost (damper) pedal. Personally I prefer the disassembled piano because it gives the player better access to the strings.
Move the piano to a space where you can freely access all sides. Block the wheels or raise the piano off them slightly (four bricks will usually do the trick). If you have a vacuum cleaner handy, use the wand attachment to clean out the piano. It’s amazing what collects inside these things.
2) Remove the panels
The front top and bottom panels should come off without removing any screws. However, the lid (the hinged top panel) has dozens of tiny screws.
3) Remove the action
The action is the large assembly of hammers and felts. This is much easier to remove than it looks. You will see four bolts about chest high that attach the assembly to the frame. Remove these and the whole action will lift out in one piece. Donate this to your local sculptor.
4) Remove the keybed and legs
This is by far the most difficult part. Unfortunately, this is also where all piano makes and models are slightly different. Basically, you will need to remove a pair of enormous screws from each side where the keybed attaches to the rest of the piano. These are usually much easier to access once you remove the top panel of the keybed. There may also be several other, smaller screws. Once all of these are removed the keybed will slide out, bringing the legs (which may still be attached to the feet) with it. Use a mallet hammer to loosen the legs if necessary.
5) Remove the pedals
These unscrew pretty easily.
6) Install the transducers
Tap the soundboard and listen. When you find a nice resonant spot, set one of the transducer mounts on it and trace the screw holes to mark it. I’ve usually had good luck installing at least two of the transducers immediately behind the bridge (the curved part where the strings terminate) and placing the rest in nice deep resonant spots. Once you’ve chosen your locations, drill guide holes to make sure the screws don’t split the wood. For an extra-secure connection, add a few drops of glue before you screw the mounts to the soundboard.
7) Wire it up
Use the speaker wire to connect the transducers to the amplifier. Depending on the ohmage of your amp and transducers, you may want to wire them in series pairs. Plug the mic into the sound interface and plug the interface into the amp.
8) Load the software.
Click on the “help” tag in the lower right corner to reveal the menu. This is where you can select your audio device or view the instruction manual.
Sing into the piano. Play saxophone. Yell poetry. Strum the strings. Have fun!
If you make any recordings with your feedback piano, I’d love to hear/see them. Please send them to firstname.lastname@example.org
Special thanks to Jonathan Abel for his great help with signal processing, to Bill Calhoun for his encyclopedic knowledge about pianos and to everyone at CCRMA for tolerating piano carcasses strewn everywhere.