Ben Freeth 
 
Artist-in-Residence at Digital Artist Residency 
Zombie Media Residency 
 
== 19th October - 14th December 2015 == 
 
Whilst in residence, Freeth will create a series of workshops as practice, which investigate the media archaeology of the hydrophone through three incarnations: contemporary sound art / bio-acoustics, WW1 early detection listening networks, and Lucien Blake's speculative but never built hydrophone designs. DIY hydrophones will be built and recordings made near the Farne Isles, South Shetland, and Newcastle, UK. These will be used to generate a set of audio compositions and a third (de)composition made through algorithmic subtraction in the spectral and temporal domains based on material from the earlier pieces. The audio will be presented in a gallery setting and online. 
 
 
 
“If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.” 
Leonardo da Vinci, 1490 
Hydrophones originate in the speculative, but never built, underwater signalling systems first proposed by Lucien Blake (1889) [1], they were then followed by the fully realised water proof telephone systems developed by Elisha Grey (1901) [2]. Falling out of use once more, interest in these died but they were brought back to life by deployments during both world wars as passive sonar listening and detection devices. 
The first hydrophones, invented during World War I by British, American and French scientists, were used to locate submarines and icebergs. These were passive listening devices. The committee was named the ASDICS (for Anti-Submarine Detection Investigation Committee). R.W. Boyle In 1912 returned to Canada from the University of Manchester and took up the position of the first head of the department of physics at the University of Alberta where he began his ground-breaking research on ultrasonics. With the outbreak of World War I, Boyle joined the staff of Britain’s Board of Invention and Research, working for the Royal Navy at Parkeston Quay. In 1916 he was placed in charge of top secret research on ASDICS. The first known sinking of a submarine detected by hydrophone was the German U-Boat UC-3, in the Atlantic during World War I on April 23rd, 1916. [3] 
 
[1] [2] Beyer. R. T. “Sounds of Our Times: Two Hundred Years of Acoustics” (1999) Springer-Verlag New York. 
[3] http://www.ob-ultrasound.net/hydrophone.html 
 
1 // Overview 
A type of microphone that works underwater. 
 
2 // What are they? 
“A hydrophone (Ancient Greek water and sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change. [..} The acoustic impedance of piezoelectric materials facilitates their use as underwater transducers “ [1]. 
 
 
 
 
 
5 // In Use 
As the hydrophone is lowered deeper in water, water pressure pushes the two perspex discs together making the seal even more water tight. The peizo element effectively transduces pressure from sound waves in the water converting them to electrical pulses that can be reconstituted as sound. 
 
4 // Design 
A peizo based design has been built and tested, effectively picking up underwater sound with clear resolution. It is made from two laser cut discs of 5mm perspex, an O-ring with silicone grease sits in between the two perspex discs, creating a water tight seal when the bolted nuts are tightened creating compression. A piezo element is glued to one of the discs on the inside face. It is soldered onto a cable and the cable exists the other disc through a compression gland featuring a second o-ring, creating a water tight seal on this side. 
 
 
 
 
References 
[1] https://en.wikipedia.org/wiki/Hydrophone [2] https://en.wikipedia.org/wiki/Fessenden_oscillator [3] http://muse.jhu.edu/journals/tech/summary/v042 
/42.3frost01.html 
Building A DIY Hydrophone. 
4/ Use two part epoxy to glue the piezo to the disc. 
8/ Leave the resin to cure for five minutes 
1/ Gather tools and components. 
5/ Mix one part epoxy to one part hardener. 
9/ Feed the audio cable through the hole in the back section of the perspex disc 
12/ Crimp the jack onto the cable to provide strain relief 
13/ Screw the sleeve onto the plug. 
16/ Smear silicon lubricant onto both edges of the o-ring to improve water resistance. 
17/ Bring the two halves together and pull the audio cable through the hole in the rear perspex disc. 
20/ Hydrophone is nearly finished. 
21/ Test it through a practice amp to stay safe. 
2/ Back and front laser cut perspex.  
3/ Locate the peizo disc at the centre of the front disc  
6/ Spread the resin on the brass side of the peizo 
10/ To the other end of the cable,  
push the jack cover onto the cable. 
7/ Press the peixo down gently to avoid cracking the peizo 
11/ Solder the Ground wire (black wire on the peizo, audio cable with black mark on its side) onto the longer side of the audio jack connector. 
14/ Trim the peizo wires and strip the tips to expose fresh wire. Place the o-ring around the peizo 
15/ Tin the wires with solder and solder onto the audio cable - red to the unmarked side and black to the side with the black stripe. 
18/ Begin screwing the bolts, washer and nuts through the holes in the perspex discs. Add bolts opposite to create even compression. Fasten finger tight. 
19/ Mix up more epoxy and cover the hole in the rear perspex disc. 
22/ Make sure all of the nuts are screwed on finger tight then try the hydrophone in some water. 
 
Listening To The Inaccessible:  
Searching For  
WW1 Hydrophones 
 

   Bioacoustics // Diseased Dolphins 

Situated at the top of the food chain, White Beaked Dolphins (Lagenorhynchus albirostris) absorb high levels of pollutants. Acting as concentrators they have high levels of heavy metals and pcbs dissolved in their fatty tissue. Ultimately this manifests in reproductive problems and secondary effects, for example, the dolphin equivalent of the pox which causes tattoo skin disease. 
Frequency-Modulation Sensitivity In Bottlenose Dolphins, Tursiops truncatus: Evoked-Potential Study. 
A. Ya. Supin and V. V. Popov. (2000) 
Evoked-potential responses to rhythmic frequency modulations at carrier frequencies from 32 to 128 kHz were recorded in two bottlenose dolphins. The envelope-following response appeared at modulation rates up to 2000 Hz, with the best responses appearing at rates of 600–650 Hz and around 1000 Hz. Frequency-modulation thresholds were measured at a modulation rate of 625 Hz. 
Hydrophone Recording // Bergen, Piksel15 
 
Anthropogenic sound dominates these hydrophone recordings of ferry infrastructure (unseen at time of recording) made in Bergen near 
"Norled AS - Kundesenter Strandkaiterminalen, Hordaland, 5013, Norway" during Piksel15 
www.15.piksel.no/ 
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