The optional matching transformer is well worth buying to use with XLR inputs.
Expanding on my recent forays into the wonderful world of outdoor recording I am now starting to explore the possibilities of recording underwater using my newly purchased JrF D-Series Hydrophone. These are handmade to order in the North of England by the acclaimed sound artist Jez Riley French. I was looking for a high quality, lightweight device that is quick and easy to deploy. It is also very reasonably priced!
Hydrophones and the world underwater.
Hydrophones utilise piezoelectric transducers to detect underwater vibrations and pressure differences. A piezoelectric transducer is a device that produces an electric current when a mechanical force is applied to it. No external power source is required. Piezoelectric materials are able to flex under pressure, converting mechanical energy into electrical energy. Because sound is a form of pressure wave that physically moves particles, it produces a mechanical force as it comes in contact with a hydrophone. The first widespread use of hydrophones was during WW1 when they were used to detect enemy submarines. This 100 year old technology is still alive and well! Today they also have wide ranging use in underwater exploration, seismology, aquatic research, and deep sea recording. Apart from these important scientific functions, hydrophones can also simply be used to capture fascinating and unusual sounds with which to delight the ear!
My first Hydrophone Recording
Some friends of ours have a pond in their garden and this seemed like a good place to start. Dropping the hydrophone into clear open water the initial results fell somewhat short of the whales and dolphins I had been imagining……………. absolute silence!!
However, we persevered. Moving the hydrophone into a patch of water weed suddenly produced this strange sound! Perhaps some alien life form sending code? CLICK On Photo
This next recording features a delivery van driving through a shallow ford across a stream. The hydrophone is positioned in the middle of the weir about 2 feet out into the stream. As the van passes we hear the initial waves caused by the wheels followed by a strange ‘phasing’ sound produced by the reflected waves bouncing back off the wall on the opposite bank.
This final recording is a strange one from another local pond. I dropped the hydrophone into the water close to a large rock just below the surface about 3 feet out from the bank. Along came a duck and started to rub it’s beak on the stone only inches from the hydrophone. I thought at first it was sharpening it’s beak but I am informed by knowledgeable folk that this is in fact a sort of conditioning that ducks carry out. Who knew?
The JrF D-Series hydrophone is a great addition to my microphone collection and has opened up a whole new world of sound exploration. Thoroughly recommended.
Found in a garden shed where it had been for at least the last thirty years, this WW2 British military throat mic looks a bit sad and dilapidated. The paint is falling off and the steel fittings are rusting, the elastic is past its best, and a hungry woodworm has been drilling into the crumbling leather. So imagine my surprise when I plugged it in and it immediately burst into life!
The M.T.L.L. No 2 was used by the RAF and by the army. The mic was worn around the neck and was designed to pick up vibrations direct from the voice box. The two leather covered sensors were pressed against either side of the throat. The great advantage of the throat mic was that it could be used effectively in very noisy environments, such as inside a tank or an aircraft in combat. Even loud sounds around the wearer would be largely rejected. Although the audio quality is not fabulous, speech has a high degree of intelligibility.
This view below is of the back of one of the sensors with the plastic cover removed. Inside there is a magnet, the polarity of which is marked on the metal case ‘N’ and ‘S’. The wires are identified with red and blue cotton thread. (Hot and cold?)
Below, (pinched from an ebay listing) is a photo of the front side of the mic, without its leather covering. Here there appear to be a couple of coils.
Below, the strip of steel which picks up vibrations from the throat is sitting on top of the coils and magnet. This assembly is held in place by the leather covering. The result of this ingenious arrangement is a small electrical (audio) output signal appearing at the red and blue wires.
The notion of using a parabolic reflector to pick up sounds from afar has been around for many years.
With the advent of aerial warfare in the First World War, the British military started developing acoustical devices to provide early warning of incoming enemy aircraft. The first ‘sound mirror’ was erected in Maidstone in April 1915. During the 1930s, in the run-up to World War 2, a number of these enormous concrete parabolic reflectors appeared along the South coast of England and at other strategic locations. The largest of these structures could detect aircraft at a distance of 25 miles. However, the whole project was abruptly abandoned in 1938 with the invention of Radar!
The listening ‘trumpet’ seen on this dish could be rotated to find the strongest signal. This would enable the listener in the control room beneath the dish to calculate the direction of the incoming aircraft. The information could then be relayed to anti-aircraft batteries.
A ‘stereo’ device like this could be used to pick up activity in enemy positions and provide early warning of attack. (That is if you could hear anything above the sound of your mates laughing their heads off!)
The Parabolic Microphone
In the post war years with the rise of television and the increasing popularity natural history broadcasts on both wireless and TV, sound recordists were quick to adopt the parabolic microphone i.e. an omni or a cardioid microphone, mounted facing inwards, at the central focal point of a portable parabolic dish.
A parabolic reflector has one significant advantage over other sound pick-up devices: it is a noiseless acoustic amplifier. The frequency response and polar pattern are a function of the size of the dish used. The enormous concrete military dishes of the 1930’s were often 30ft in diameter or more, enabling them to detect the lowest frequencies of an aircraft engine over huge distances. For the modern wildlife recordist a somewhat smaller portable dish is something of a compromise! For a narrow forward beam of 10 degrees a 60cm diameter dish gives around 14db (x5) gain to frequencies above 500Hz. A 1m dish will give 20db (x10) gain to frequencies above 300Hz. The forward gain of a reflector is defined as the difference in output level between a microphone which is reflector-mounted compared to the same microphone unmounted. Even with a modest sized reflector, the on-axis sound of the chosen subject is greatly magnified without adding any of the hiss and hum associated with electronic amplification. However, given the narrow beam characteristics of the dish, one thing that the recordist should bear in mind is that if the subject moves off axis the tonal quality of the sound will change. This can be difficult if for instance the subject is moving around in a group of birds. For that reason I would suggest that the parabolic dish is at its best when recording an isolated single subject.
Frequency/ Directional Response Plot for a typical parabolic reflector for wildlife recording
Using an unmounted microphone there are many wildlife recording situations in which it is simply not possible for the sound recordist to get close enough to achieve a good signal to noise ratio. As you creep up with your microphone the subject simply flies off or runs away! ……..Or in the case of dangerous wild animals it may be the sound recordist who does the running! The parabolic dish enables the sound recordist to record from a safe distance without risk of disturbing the subject or getting eaten!
One of the most common problems with wildlife recording is that quite often the perfect recording opportunity comes up without warning. Animals and birds are not predictable. Hence, my minimalist, rapid response kit, illustrated below is light, portable and very fast to set up. I can be in record in a matter of seconds!
Extremely light weight, flexible, 50cm plastic parabolic dish available from new UK company innercore
Aluminium handle on the back which can also be screwed on to a tripod
Simple microphone mount marked at the focal point.
HMN Sound MicroLav. N.B. to prevent wind noise a Rycote Furry windshield is recommended. (Not pictured.)
M-Audio MicroTrack II set to record in mono at 96kHz 24bit.
M-Audio in-ear headphones with industrial ear defenders over the top for isolation.
Walking by a local lake the other day I came across a small flock of Canada geese about 40ft away quietly pottering about on the grassy bank. Suddenly one of them started squawking/honking. I started recording and within a few seconds it flew high into the air and passed straight over my head. On the recording the strange creaking sound of the bird’s wings and the movement of air can be clearly heard. It sounds close up, even though the bird is at least 30ft above me. It then flies round the lake and lands back with the others and carries on honking very loudly. Definitely not a bird you would want to get close to! Would probably make a good guard dog! CLICK HERE to take a listen.
Other Uses for the Parabolic Microphone.
When listening to sporting coverage on radio or TV you may have enjoyed the additional excitement of hearing the ball striking the bat or the racket. You may hear the close-up thunder of the horse’s hooves in a race or the grunts and shouts of a rugby scrum and…… Not a microphone in sight!
My purpose in writing this post has not been to advertise the merits of a particular set of equipment but merely to suggest some of the possibilities and fun to be had recording sound using a parabolic dish.
P.S. (Nov 2019) I have just come across this fascinating patent by British Acoustic Films Ltd from 1931 ( !! ) for a Parabolic Microphone for use in film production, recording and broadcasting. Parabolic Microphone B.A.F Ltd 1931 It even includes a setup whereby sound can be recorded (and mixed) from 3 independent reflectors aimed at 3 different sound sources simultaneously using a single microphone! Wow!
P.P.S. 2020 update during COVID 19 lockdown with Sennheiser MKE2 microphone.
In 1942 after America entered World War 2, the US military estimated that only 20% of radio communications in combat were successful. Failure in the other 80% was mainly due to the voice of the radio operator being drowned out by the surrounding cacophony of war. Like no other conflict before, success on the battlefield relied on communications. Spotting a gap in the market Al Khan and Ed Burrows, the owners of Electro-Voice, came up with a brilliantly simple, ingenious and cost effective solution to this problem.
Even in 1942 the single button carbon microphone was a piece of old fashioned tried and tested technology, having been in use in telephones since the tail end of the previous century. Although the audio quality of the T45 is little better than it’s telephonic predecessors it is extremely reliable and very robust. It also has a high output making it ideal for long distance communication. Even if the microphone gets wet you can simply dry it out (as per the instructions above) and it will carry on working! However, the really clever part of this design utilises 2 small holes of equal size on the front and back of the mic.
These allow the surrounding noise to enter the microphone on both sides of the diaphragm. The sound striking the back of the diaphragm is 180 degrees out of phase with the sound at the front. This causes a very impressive cancellation of the unwanted noise whilst the speaker’s voice, which is less than a 1/4 of an inch from the front opening, dominates the transmission.
In terms of manufacturing costs it would be hard to produce a cheaper microphone. A carbon button is a very small tin of glorified coal dust (carbon granules) with a simple diaphragm attached. A bit of wire and some lightweight plastic fittings and that is it! Pure genius !
After some initial military skepticism the product was thoroughly tested and a first order came through to Khan and Burrows for 100,000 units! The T45 was soon taken up by all branches of America’s armed forces and the success rate of combat communications rose to 90%.
Rags to Riches.
Prior to World War 2 Electro-Voice was a small struggling company, with 20 employees, manufacturing a handful of dynamic and velocity microphones per week. By the latter part of the war Electro-Voice had 500 employees working in 3 shifts producing more than 2,000 T45 microphones a day! After WW2 it was also adopted by commercial aviation and remained in service for several decades. The T45 was also used on the Mercury, Gemini and Skylab space missions.
Over the entire production run more than a million were produced placing the T45 among the highest selling microphones ever made.
During the war many small firms went out of business due to a shortage of manpower and materials, but for those involved in the war effort fortunes were to be made. In 1946 Electro-Voice moved into an impressive new factory at Buchanan Michigan where they continued to manufacture innovative and exciting audio products for the next 60 years.