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Month: August 2014

Gervais Currie: Sun 31st Aug. 2014

People entered the classroom, and while waiting, spontaneously picked up the objects we’ve laid on the table, and started playing them. Suddenly, each corner of the London Hackspace Classroom was filled with the echoing sound waves of mbira, bowls, and the percussive rhythms of the tables and metal bits. It was truly surreal, and rather entertaining to witness.

Unpredictability has always been a thrilling aspect of our meetups, as the tone of the meeting widely varies between one to another. In this one, we’ve have somehow managed to create an ideal environment for experimentation and true self-expression.

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This meetup, we had the pleasure of meeting Gervais Currie; an instrument repair expert at Portobello Music. Gervais has been repairing amplifiers, fixing instruments and installing pickups for over 20 years [ link ].

To summarise, here are some tips and the most discussed points of the evening:

  • When designing a pickup system for a stringed and bridged instrument, use two Piezo discs instead of one. One is placed under the bridge and another is placed over the bridge. The two Piezo Discs must be wired in the same polarity (to avoid phase cancellation). This would provide an extra 6dB of gain, and among other benefits this can be used as a ‘differential’ setup as described here [ Wikipedia ]
  • The popular Panasonic WM-61A capsules have been very well known all over the internet, and you don’t have to dig deep to find out why. These beautiful little omnidirectional electret condensers have brilliant flat frequency response [ as claimed in the datasheet ], cheap as chips [ eBay ], and their tiny size factor means you can make them fit virtually anywhere.

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The main idea is to use one of these capsules to mount directly onto the top plate of an instrument, in this case Gervais’s Banjo, and here this tiny creature really comes alive.

These capsules obviously have to be phantom powered or plugin powered ( Here is an example of such setup on Wildlife Sound ) – if you don’t have a mixer with phantom power. Although among us, we have yet to test these out.

Note, most handheld recorders provide Plugin Power.

  • The Art of Electronics is highly recommended [ Buy ]
  • Class D Amplifiers crept up in our discussions, and the reason is because they don’t require much power, and are very musical sounding. Therefore they would make for a great portable general purpose amplifier for use on the go.If interested in reading, here are Class D Amplifiers explained in Detail [ Link ]
  • Vaguely touched on what’s called ‘Acoustic Transformers’ which deals almost exclusively with matching ‘Acoustical Impedance’ rather than Electronic Impedance. This can take the form of for example, a horn [ Horn Loudspeakers and Acoustic Impedance ].If interested, have a read this Audio Express Horn Theory Paper from our resources folder [ link ].
  • Gervais recommended to trace Harvey Gerst’s tips around the internet for thorough understanding of the technology and history of microphones. [ his profile ] Harvey Gerst has 50+ years of experience as a gold record songwriter, studio musician, recording engineer, producer, musical instrument designer, and manufacturer.Make sure to browse the stickies by Harvey Gerst on the Home Recording Forum [ link here ].

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These photographs mark the end of this megapost. Warm thanks to everyone who attended, and our special guest for making this meetup truly fun memorable. This one has definitely been the most ‘musical’ meetup we’ve had!

We’re encouraging people to participate in our friendly discussions on our own forums [ link ]. Hop over there, and you can click join to enter the Acoustic Hacking circle, and you’d also receive latest updates of our discussions. We’re also constantly adding resources such as papers and links to the Goodies Folder, so have a browse if you fancy doing some general research or even solve some mathematic equations [ link ].

Join us next time on Sunday 28th September 2014 7 pm at the London Hackspace. Agenda will be uploaded soon! See you.

Any queries, please email acoustichacking@gmail.com

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