folks sometimes ask for tips or basic instructions for using contact mics, hydrophones, coils etc. so, here's a page that will be updated from time to time with bits of info....do get in touch if you have specific questions.
hydrophones and contact microphones - a basic guide....
input route: with most hand held / entry level audio recorders you have a series of input options:
. mini jack (3.5mm) microphone socket
- the recorder supplies plug-in-power to this input.
Connecting a single or pair of contact mics or hydrophones to this input with 3.5mm
jacks fitted or via a proper adaptor allows for the full range of the units to be recorded.
An important point here is that if you are using an adaptor make sure it’s not a signal
splitting adaptor such as those used to allow 2 headphones to be connected to one
output. You need a proper cabled stereo breakout adaptor (see the accessories page).
. 1/4 inch / XLR combination socket - the 1/4 inch input is mostly intended for ‘line level‘
inputs, such as those coming from a microphone with its own power supply, a mixer or a
separate pre-amp. Connecting 1/4 inch jack fitted contact mics or hydrophones to this
will only give you around 80% of the possible signal. To get the optimum results use a
1/4 inch to XLR impedance transforming adaptor (see the accessories page) - this gives
the best results: a higher signal level and warmer mid / low range frequency
response.
(NB. hand held recorders can be a useful introduction to field recording - if you haven’t
bought your recorder yet and would like some advice, do get in touch. I keep an eye on
new models and test units for performance with all kinds of equipment - however, they
have thier limitations. You will probably find that with hydrophones for example, you’ll
need to raise the gain and do some subtle eq-ing in post production to compensate for
the higher level of noise that the recorders pre-amps add to the recordings. For those
new to field recording, pre-amps are one of the main reasons some recorders are
cheaper than others. Getting super quiet pre-amps that don’t add additional hiss to your
recordings means looking at professional recording equipment. If you haven’t done any
post production before or are looking for a high quality editing suite then Reaper is one
of the best there is and is very low cost - $60. Audacity is a free editing suite but it has
some limitations).
Professional recording equipment will be XLR jack enabled and therefore the use of the
impedance transforming adaptors is essential.
placement: there are no ‘rules’ when it comes to placement. With both contact mics and
hydrophones it’s a case of experimenting, chance & eventually a level of intuitive skill.
. hydrophones - there are many factors that will affect the results one can get. Sometimes
the same location will produce vastly different results on different days, at different times
of the year for example. One thing that is important is that once you’ve placed your
hydrophones into the water you have to wait for a while for the environment to settle.
You have, after all, just disturbed it. Where possible try to get away from the banks of
rivers, streams, ponds & canals - look for places where you can deploy your
hydrophones so they don’t wash back against the banks / shore (jetties, fishing spots,
bridges etc are all good locations).
. contact microphones - attaching the contact mics is the first step. I use electrical tape as
it doesn’t leave any residue on the coatings of the mics, unlike gaffer tape or blu-tak style
products (which can leave residue that not only affects the look of the mic but can be
damage the coatings) If possible however, I try not to use any additional fixing agent,
preferring to look for in situ solutions to hold the mics in place. For example, a tree
might have cracks in the bark or two branches that cross each other and are taught
enough to hold the mic in place without causing additional friction sounds. The truth is
that every situation you use contact mics in is different and it might take you some time
to find the ‘sweet spot’ on the object or surface you want to hear. This is part of the fun
and the creative process - take your time and enjoy !
care: as with any audio equipment do take care of your hydrophones and contact mics.
There is no reason your mics can’t last years - I still have pairs of the original test units I constructed over 6 years ago for example - but you must handle them carefully. The cost might be reasonable but handle them as if they cost 10 times + more !
Avoid bending the elements (contact mics) or the section of the cable that is coated. If
your contact mics get wet in the rain, pat them dry carefully. Also, when you’ve taken your
hydrophones out of the water, pat them dry and make sure no water runs back along the
cable to the jack. If using hydrophones in ice, allow them to return to room temperature
before coiling the cable. Likewise, if used in high temperature liquids allow them to cool
down fully before coiling.
contact mics: . the C-series contact microphones feature a larger special element than the standard design, using the ceramic welding technique, and are coated with the unique acoustic transfer material (+ outer coatings).
. the flat surface of the microphone should be placed on the surface of the object being recorded. It can be held in place using a small clamp or electrical tape if needed. Blu- tac should be avoided as it will leave a residue on the surface of the microphone. The white foam dot is there to help protect the microphone when pressing into place - its the other side of the element that is the main surface.
. the choice of pro-cable has been determined by the need to reduce handling noise as much as possible whilst allowing for the unique AT coating to improve signal strength.
. If you have used the contact microphones in extreme low or high temperatures do allow them to return to room temperature before coiling the cable.
. remember, there are several coating employed in the design of these units so even if the edge of the outer coating begins to peel from the cable slightly it will not effect the performance of the element. You can however repair such a peel by using epoxy resin, electrical tape or heat-shrink.
hydrophones: . the d-series hydrophones feature a special element in each capsule, using the ceramic welding technique, and are coated with the unique acoustic transfer material (+ marine adhesives and outer coatings).
Unlike more expensive hydrophones that use one element but employ various baffles between the capsule and the cable, d-series units allow for the full high and mid frequency range of aquatic life to be captured.
. the choice of pro-cable has been determined by the need to reduce handling noise as much as possible whilst allowing for the unique AT coating to improve signal strength.
Anyone who has used hydrophones before will know that the key to getting great recordings is to have the hydrophones as stable as possible in the water / liquid. Whilst all JrF hydrophones come pre-weighted, if you are using them in situations where they will be subjected to strong currents it is advisable to apply additional weights in order to keep them as stable as possible (fishing weights that grip the cable are one solution). This will further reduce the possibility of handling noise.
. Always carefully dry your hydrophones after each use to prevent build up of water born pollutants.
. If you have used the hydrophones in extreme low or high temperatures do allow them to return to room temperature before coiling the cable.
. remember, there are several coating employed in the design of the capsules so even if the edge of the outer coating begins to peel from the cable slightly it will not effect the waterproof sealing of the capsule. You can however repair such a peel by using epoxy resin or various waterproof sealants.
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