I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Thanks (I am aware of the professionally priced reflectors from Sweden.)
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Malcolm Stewart wrote:
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Old (solid) satellite dish.

For 7Khz song, you need surface accuracy of 1/4 * 340m/s /7000Hz = 1.25cm.
One way of cheating is to take a strip of plywood.
Now, form it into a curve.
Yes, it's flat, but as long as it's only a small strip, it can fairly well
approximate a strip of a parabola.

In article , Ian
Stirling writes
Malcolm Stewart wrote:
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Old (solid) satellite dish.


There are some plastic lightweight transparent dishes around., Have a
Google for them....

--
Tony Sayer

In message , Malcolm Stewart
writes
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Thanks (I am aware of the professionally priced reflectors from Sweden.)

I'm sure I've seen el cheapo ones somewhere, maybe maplin
--
geoff

"Malcolm Stewart" wrote in
message ...
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I
could
cannibalise for their parabolic shape. Any ideas would be welcome.
Best
I've thought of so far is an old radiant heater with the cylindrical
heating
element at the centre of a spun reflector.

I had ideas about this years ago and considered taking a papier mache
mould of the round end of a spacehopper.

In message , OG
writes

"Malcolm Stewart" wrote in
message ...
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I
could
cannibalise for their parabolic shape. Any ideas would be welcome.
Best
I've thought of so far is an old radiant heater with the cylindrical
heating
element at the centre of a spun reflector.

I had ideas about this years ago and considered taking a papier mache
mould of the round end of a spacehopper.

Not a parabola though, is it

--
geoff

"raden" wrote in message
...
In message , OG
writes

I had ideas about this years ago and considered taking a papier mache
mould of the round end of a spacehopper.

Not a parabola though, is it

True, but I'm not sure how important it is for sound.
Spherical Aberration is a problem for optical systems were the reflected
wavefront has to have pixel sharp focus; but so long as all (or most
of) the sound falls on the front of the microphone you won't lose much
information.

I'm happy to be corrected though.

"OG" wrote in message
...

"raden" wrote in message
...
In message , OG
writes

I had ideas about this years ago and considered taking a papier mache
mould of the round end of a spacehopper.

Not a parabola though, is it

True, but I'm not sure how important it is for sound.
Spherical Aberration is a problem for optical systems were the reflected
wavefront has to have pixel sharp focus; but so long as all (or most
of) the sound falls on the front of the microphone you won't lose much
information.

I'm happy to be corrected though.


Spherical aberration doesn't apply to a parabola. Spherical aberrations is
normally associated with a crude simple lens where the focal point depends
on its distance from the optic axis.

In message , OG
writes

"raden" wrote in message
...
In message , OG
writes

I had ideas about this years ago and considered taking a papier mache
mould of the round end of a spacehopper.

Not a parabola though, is it

True, but I'm not sure how important it is for sound.
Spherical Aberration is a problem for optical systems were the reflected
wavefront has to have pixel sharp focus; but so long as all (or most
of) the sound falls on the front of the microphone you won't lose much
information.

I'm happy to be corrected though.

A parabola will take parallel (which anything from any reasonable
distance approximates to) waves and focus them on a single point at the
locus - which is where you stick the microphone

A trepanned sphere (I can't remember the correct term offhand either)
won't focus on a point which is important if you have a small microphone


--
geoff

On Sat, 19 Mar 2005 23:59:21 -0000, "Malcolm Stewart"
babbled like a waterfall
and said:

I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Thanks (I am aware of the professionally priced reflectors from Sweden.)

Blow up a balloon. Coat it with wax polish and then cover a suitable
end in glass fibre to the shape you require.

They are better if you also have a tube on the front to prevent side
noise.

Malcolm Stewart wrote:

I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Thanks (I am aware of the professionally priced reflectors from Sweden.)

What I would do is glue chunks of blue foam together, then make a
parabilic shaped template, and use a wire brush and maybe spinnin the
lot and sand a parabola on that.

You can then lay upo a fibergallss one obver teh top, nd when set, rip
the foam away and use acetone to clen it all off.

Voila! a parbolic reflctor.

Or just nick someones sky dish instead.

Malcolm Stewart wrote:

I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

How about printing yourself a parabola on a graph (using excel or
something), use that to cut some templates from ply which you then
assemble into a star pattern. Finally lay it up with firbreglass tissue
and resin....

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Malcolm Stewart" wrote in
message ...
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical
heating
element at the centre of a spun reflector.


Be aware that most satellite dishes are offset and the dish axis doesn't
point directly at the satellite. Given a dish (eg Sky) which is nominally
vertical and the satellite is at approx 36 deg. elevation or so (from
London) the offset is 36 deg and the LNB is 36 deg below the dish parabolic
axis. Dishes which are true parabolic have the LNB on the central axis
usually on a tripod arrangement and the dish is pointed up directly at the
satellite.

john

"John" wrote in message
...

"Malcolm Stewart" wrote in
message ...
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical
heating
element at the centre of a spun reflector.


Be aware that most satellite dishes are offset and the dish axis doesn't
point directly at the satellite. Given a dish (eg Sky) which is nominally
vertical and the satellite is at approx 36 deg. elevation or so (from
London) the offset is 36 deg and the LNB is 36 deg below the dish
parabolic axis. Dishes which are true parabolic have the LNB on the
central axis usually on a tripod arrangement and the dish is pointed up
directly at the satellite.

john


Anybody want to buy a 1.8m centre lnb dish on a tripod mount?

On Sun, 20 Mar 2005 13:21:31 +0000 (UTC), "John"
wrote:

Anybody want to buy a 1.8m centre lnb dish on a tripod mount?

I think he was wondering about how to listen to tweeting noises at the
end of his garden, not the lower crested twit on the surface of Mars


Andrew

In article ,
Andrew McKay wrote:
Anybody want to buy a 1.8m centre lnb dish on a tripod mount?

I think he was wondering about how to listen to tweeting noises at the
end of his garden, not the lower crested twit on the surface of Mars

The one I used for ball being kicked FX at Wembley was IIRC about 2 metres
in diameter.

--
*If a mute swears, does his mother wash his hands with soap?

Dave Plowman London SW
To e-mail, change noise into sound.

In message , Andrew McKay
writes
On Sun, 20 Mar 2005 13:21:31 +0000 (UTC), "John"
wrote:

Anybody want to buy a 1.8m centre lnb dish on a tripod mount?

I think he was wondering about how to listen to tweeting noises at the
end of his garden, not the lower crested twit on the surface of Mars


Earth calling Beagle II, Earth calling beagle II ...

--
geoff

On Sun, 20 Mar 2005 22:37:32 GMT, raden wrote:

Earth calling Beagle II, Earth calling beagle II ...

I tried selling Beagle II on ebay with an instruction "buyer must
collect". Didn't get any takers for some reason

Andrew

In message , John
writes

"John" wrote in message
...

"Malcolm Stewart" wrote in
message ...
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical
heating
element at the centre of a spun reflector.


Be aware that most satellite dishes are offset and the dish axis doesn't
point directly at the satellite. Given a dish (eg Sky) which is nominally
vertical and the satellite is at approx 36 deg. elevation or so (from
London) the offset is 36 deg and the LNB is 36 deg below the dish
parabolic axis. Dishes which are true parabolic have the LNB on the
central axis usually on a tripod arrangement and the dish is pointed up
directly at the satellite.

john


Anybody want to buy a 1.8m centre lnb dish on a tripod mount?

Put it in an envelope and post it down ...

Put it aside in the pigsty for me

--
geoff

On Sat, 19 Mar 2005 23:59:21 -0000, Malcolm Stewart wrote:

I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Thanks (I am aware of the professionally priced reflectors from Sweden.)

Not a domestic item but ...

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=75020720 78

How about a Wok

On Sun, 20 Mar 2005 09:31:30 +0000 (UTC), Alex wrote:

How about a Wok

Mine's more a section of a sphere (must be a name for that) raher than a
parabola. The particular property of a parabola he needs to exploit is that
there's a point of focus.

nog wrote in
:


How about a Wok

on the wild side?

mike

On 20 Mar 2005 10:13:52 GMT, mike ring wrote:

nog wrote in
:


How about a Wok

on the wild side?

You haven't quoted anything of what I said - you're actually responding to
Alex's posting. Not such a big deal in this instance but it's not hard to
envisage cases where it could lead to serious misunderstandings.

"Alex" wrote in message
...
How about a Wok

That is not a bad idea at all. I have seen really big woks for sale at Wing
Yips Chinese super markets. I estimate the largest available in store are
about a metre in diameter. They are pretty deep though probably not a true
parabola I am sure they would concentrate the sound and cut out unwanted
noise quite well.

Unfortunately the largest ones they sell on line are only 14" dia. So give
them a call to find out the sizes and prices. I was not looking for a big
wok when I saw them so I did not note the prices but they were remarkably
cheap. IFIRC about £35 for the really big ones.

At the worst you could use one at a large scale barbeque ! They are
definitely bigger than the domed BBQ cooking kettles that I have seen and
are a lot less expensive.

Happy recording and/or stir-fries :-)

Richard.

In article ,
Malcolm Stewart wrote:
I'd like to try recording birdsong using a microphone at the
focus of parabolic reflector. Currently, I'm having difficulty
thinking of domestic items which I could cannibalise for their
parabolic shape. Any ideas would be welcome. Best I've thought
of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

How about a big torch, the sort that takes a
lantern battery?

Enough room in there also to do a small battery
powered preamplifier.

--
Tony Williams.

Tony Williams wrote:

How about a big torch, the sort that takes a
lantern battery?

Enough room in there also to do a small battery
powered preamplifier.


Similar idea was suggested in an issue of Everyday Electronics, many
years ago...or was that the infrared torch link? Was a long time ago

Lee
--
Email address is valid, but is unlikely to be read.

In article ,
Malcolm Stewart wrote:
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector. Currently, I'm having difficulty thinking of
domestic items which I could cannibalise for their parabolic shape. Any
ideas would be welcome. Best I've thought of so far is an old radiant
heater with the cylindrical heating element at the centre of a spun
reflector.

Don't think metal is a good idea - too much 'ring' to it. Glass fibre
would be my choice.

As others have said, an old satellite dish of the large type you plonked
in the garden?

IMHO, you'll need something larger than a metre or so for decent results.

--
*A hangover is the wrath of grapes.

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 20 Mar 2005 11:11:57 +0000 (GMT), Dave Plowman (News) wrote:

IMHO, you'll need something larger than a metre or so for decent
results.

Depends how much MF and LF response he wants... there is a
relationship between dish diameter and the lowest frequency that it
will focus effectively. They do have a lot of "suck" and directivity
though at the expense of frequency response. Do a UK google search on
"sound mirrors" for real parabs...

Last time I rigged a parab was at Headingly on a test match to get the
whack of leather on willow, there where also mics buried in the pitch
and cabled back, these had to be delayed.

--
Cheers
Dave. pam is missing e-mail

In article om,
Dave Liquorice wrote:
IMHO, you'll need something larger than a metre or so for decent
results.

Depends how much MF and LF response he wants... there is a
relationship between dish diameter and the lowest frequency that it
will focus effectively. They do have a lot of "suck" and directivity
though at the expense of frequency response.

Yes. I'm not sure they're exactly of the best quality, as the ones I've
seen tend to have been used with any old mic that was lying around.

Last time I rigged a parab was at Headingly on a test match to get the
whack of leather on willow, there where also mics buried in the pitch
and cabled back, these had to be delayed.

Yet another problem to add to digital this and that. But I suppose at
least that parab would have been fixed since the balls are hit only on one
axis?

--
*Reality? Is that where the pizza delivery guy comes from?

Dave Plowman London SW
To e-mail, change noise into sound.

In article om, Dave
Liquorice writes
On Sun, 20 Mar 2005 11:11:57 +0000 (GMT), Dave Plowman (News) wrote:

IMHO, you'll need something larger than a metre or so for decent
results.

Depends how much MF and LF response he wants... there is a
relationship between dish diameter and the lowest frequency that it
will focus effectively. They do have a lot of "suck" and directivity
though at the expense of frequency response. Do a UK google search on
"sound mirrors" for real parabs...

Last time I rigged a parab was at Headingly on a test match to get the
whack of leather on willow, there where also mics buried in the pitch
and cabled back, these had to be delayed.


He's only after birds song and I don't suppose they do Baritone and
Bass)
--
Tony Sayer

Don't think metal is a good idea - too much 'ring' to it

In the 1960's Granpian used to sell a parab spun from aluminium. It was
about 2 feet in diameter and was very widely used before rifle mics
became commonplace.

In fact a parab is a particularly good solution under certain
circumstances.

A rifle mic works by cancelling out the off-axis sound, while a parab
works by magnifying the wanted sound. However it isn't directional at
all frequencies, but if you're wanting to record s quietish high
frequency sound, such as bird song, the parab has much to recommend it.

I can remember some articles about the theory, construction and usage
of parabs published in 'Wireless World' around 1970, a reference
library might have copies on file.

In article .com,
Roly wrote:
Don't think metal is a good idea - too much 'ring' to it

In the 1960's Granpian used to sell a parab spun from aluminium. It was
about 2 feet in diameter and was very widely used before rifle mics
became commonplace.

Yes. But I'd not want to use one for quality recording.

--
*Born free...Taxed to death.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman said
Yes. But I'd not want to use one for quality recording.

But the fact remains that for many years they were pretty well the only
option available and some extremely good recordings, particularly of
birdsong, have been made with them.

These days I own a number of rifle mics made by Sennheiser, AKG and
Neumann, but there are occasions when I still wish that I had kept my
old Grampian parab to try under unusual circumstances.

I owned a Grampian one and then when I joined the BBC in the 1960's I
noticed them at Kendal Avenue and also at Ealing. They were certainly
in KA until the late 1070s.

Admittedly KA also favoured much bigger parabs converted from 4 foot (
metal ) radar dishes which were lined with Sorbo rubber foam on the
reverse, to deaden any ringing.

The size of a parab governs the lowest frequency which it offers gain.
The amount of gain is governed by the size and the geometry. Anything
from 2 feet upwards will work well on birdsong and similar sounds which
have minimal low to mid frequency content. The bass response will be
that of the microphone used to pick up the sound.

As the wanted sound is being magnified by the parab, there will be less
need to boost the gain of the microphone, so the lower gain will also
mean that unwanted sound ( most likely traffic noise ) will be at a
lower level in the first place and there will be less of a need to
filter it.

Gary Cavie refers to a Gatlin mic made from varying lengths of tubing.

I wouldn't bother with 1" tubing. Imagine the diameter of a bundle of
36x 1" tubes and then imagine how you might couple a microphone to
them.

Many years ago I used to use a commercial microphone of that type. It
was made by Electrovoice and was about 7 feet long ( it broke into two
parts for less inconvenient travel than would otherwise have been the
case ). From memory, I would guess that the tubes were thin walled
brass of about 1/4" diameter. The whole thing had to be mounted on a
sturdy U shaped yoke in order to operate it.

To call it an unwieldy microphone is to be polite about it and I was
glad to see it pass, although it retained it's directionality to a much
lower frequency than rifle mics of the time did.

In article .com,
Roly wrote:
Gary Cavie refers to a Gatlin mic made from varying lengths of tubing.

I wouldn't bother with 1" tubing. Imagine the diameter of a bundle of
36x 1" tubes and then imagine how you might couple a microphone to
them.

Many years ago I used to use a commercial microphone of that type. It
was made by Electrovoice and was about 7 feet long ( it broke into two
parts for less inconvenient travel than would otherwise have been the
case ). From memory, I would guess that the tubes were thin walled
brass of about 1/4" diameter. The whole thing had to be mounted on a
sturdy U shaped yoke in order to operate it.

I well remember a trial of that mic in TV Theatre. Something that could
pick up - say - tap dancing, while keeping well out of shot, would have
been useful. But it just didn't work. It required so much gain to get any
useful level that the end result was noisy. And so much bass cut that it
sounded like a telephone, because without that it was omni-directional at
high bass frequencies.

The first practical rifle mic IMHO was the Sennheiser 805. Which provided
the gain makeup through clever internal electronics.

--
*Everyone has a photographic memory. Some don't have film *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 19 Mar 2005 23:59:21 -0000, "Malcolm Stewart"
wrote:

I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.

Some good suggestions have been made in this thread.

However, have you thought about putting the microphone close to where
the birdies are tweeting? You could run an extension cable for the
microphone etc. Or maybe set up a tiny radio microphone like this one:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...14955 08&rd=1

My knowledge of parabolic reflectors is very limited, but I thought
the general idea was to focus everything coming in from one specific
direction into a focal point (where your microphone would be). So
wouldn't it be the case that if the birdies weren't in line with
wherever the parabola is pointing then their enthusiastic singing
would be missed, or at best subdued?

Andrew

In article ,
Andrew McKay wrote:
My knowledge of parabolic reflectors is very limited, but I thought
the general idea was to focus everything coming in from one specific
direction into a focal point (where your microphone would be). So
wouldn't it be the case that if the birdies weren't in line with
wherever the parabola is pointing then their enthusiastic singing
would be missed, or at best subdued?

If you just wanted general bird song, then any mic would do. But if trying
for one specific bird - and not getting close enough to scare it off -
parabola is a very good way of doing it. You listen to the output of the
mic and point it to get best results.

The beauty of a parabola is it adds gain and directionality to the chosen
mic 'for free'.

Rifle type mics work by rejecting unwanted sounds so sort of lose gain.

Of course a rifle mic is easy to carry and handle - not so a large
parabola.

Last time I actually used a parabola was on a cup final at Wembley
(mutter) years ago. The idea was to get close up sound of the ball being
kicked - from the top of the grandstand.;-) Worked much better than rifle
mics on the touchline.

Must have been about the most boring job ever - panning it around after
that ball.

--
*If at first you don't succeed, avoid skydiving.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 20 Mar 2005 12:29:59 +0000 (GMT), "Dave Plowman (News)"
wrote:

Must have been about the most boring job ever - panning it around after
that ball.

In this day and age you'd think they'd put a little something into the
ball so that it was self-tracking.

Alternatively, pass a bung to all the other players to ensure they
give the ball to Michael Owen. That way it won't be going anywhere

Andrew

In article ,
Andrew McKay wrote:
Must have been about the most boring job ever - panning it around after
that ball.

In this day and age you'd think they'd put a little something into the
ball so that it was self-tracking.

Wasn't this day and age, though. ;-)

--
*Why doesn't Tarzan have a beard? *

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
In article ,
Andrew McKay wrote:
My knowledge of parabolic reflectors is very limited, but I thought
the general idea was to focus everything coming in from one specific
direction into a focal point (where your microphone would be). So
wouldn't it be the case that if the birdies weren't in line with
wherever the parabola is pointing then their enthusiastic singing
would be missed, or at best subdued?

If you just wanted general bird song, then any mic would do. But if trying
for one specific bird - and not getting close enough to scare it off -
parabola is a very good way of doing it. You listen to the output of the
mic and point it to get best results.

Of course, you (not Dave) could always buy a bird song cassette and fake
it

or ....

Contact the RSPB in Sandy Beds and ask them for suggestions


--
geoff