When I last posted on this subject I had just finished preliminary
field testing of the prototype and had set myself the tasks of:
a) providing silent operation of the potentiometer when moving from
parabolic to boundary microphones,
b) making a lightweight version of the PRHSB, and
c) investigating the use of better capsules to replace the cheapo Rapids.
Items a and b have been completed. Thanks to the help of Scott Helmke
and Rich Peet of the Micbuilders Group a new power/matrixing
arrangement has been built which completely eliminates the noise when
operating the potentiometer. A picture of the component board is here
http://ad2004.hku.nl/naturesound/TomR/PRHSB2/P4140002.JPG
The following photo shows the lightweight PRHSB which has been made
out of 3mm foamboard. Its diameter is half an inch less than that of
the prototype and, at one and a half pounds, is half its weight. The
focal point of the new reflector is five and one half inches which is
just outside its rim. Consequently it is somewhat more prone to wind
noise. Here is a photo of the lightweight rig
http://ad2004.hku.nl/naturesound/TomR/PRHSB3/LW%20PRHSB.JPG
You will note the box at the base of the handle which contains the
potentiometer and power/matrix arrangement.
It is proving difficult to obtain a "demonstration quality" recording
of the noiseless transition from parabolic to wide stage and back
again - can't get a singing bird to stand still long enough to allow
switching back and forth. When I get one I will post it here.
This just leaves item c - finding better capsules. Posts on
Micbuilders suggest Transound capsules could provide an improvement at
reasonable cost. Similarly Primo capsules would also provide an
improvement, albeit at a much higher cost. Twelve Rapid capsules
(four sets of triplets) at 70cents each are currently used in the
PRHSB. A starting point is to find out just how bad (or good) the
Rapid triplets perform. To investigate this I made simultaneous
recordings of yesterday's dawn chorus using a Rapid triplet equipped
head spaced boundary rig, very similar to that used in the PRHSB, and
a pair of matched NT1As angled at 60 degrees and spaced 7 inches
apart. This is a photo of the two rigs
http://ad2004.hku.nl/naturesound/TomR/PRHSB3/Test%20Config.JPG
Two NH1 minidisc recorders were used. First a snippet using the head
spaced boundary mic with the Rapid triplets
http://ad2004.hku.nl/naturesound/TomR/PRHSB3/DuckFP_BoundaryAmp3.mp3
maybe a touch over modulated when the duck flys over but the triplets
are very sensitive. Now exactly the same segment of time as recorded
by the NT1As.
http://ad2004.hku.nl/naturesound/TomR/PRHSB3/DuckFP_NT1AAmp3.mp3
Although the mic setups are not the same, and there is an
omni/cardioid difference, it is clear that the NT1As are superior.
However the triplets are not too bad. Comments regarding how Primos
or Transound capsules might improve on the Rapid triplets' sound will
be welcomed.
If you have listened to the samples using headphones or speakers with
extended bass you will have noticed some booming sounds. When I was
monitoring the recording of the dawn chorus I heard these and could
not work out what they were. They were quite unlike any
neighbourhood noises I had heard before. Eventually it dawned on me
(no pun intended). The night had been good; cold, cloudless sky,
nearly full moon and no wind - ideal conditions for a pre dawn sea
mist. Sure enough when I looked out of the window the fog was
beginning to roll in from the sea.
What I had been hearing were ships foghorns. Now the main shipping
lane in the Thames Estuary is at least 20 miles away! Low frequency
sound certainly travels - especially over water.
So, here is a slightly longer sample (from the NT1As) featuring the
usual garden chorus, some argumentative gulls and assorted foghorns.
Enjoy :-)
http://ad2004.hku.nl/naturesound/TomR/PRHSB3/Dawn%20Chorus%20with%20Foghorn=
sAmp3.mp3
Cheers
Tom Robinson
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