Adrian C wrote:

Marnok.com wrote:

These are Pro-Luxe IR-650ST.

They were pretty cheap, and they make me look a bit like a cyberman

I tried shutting the curtains, turning the lights out and switching my
monitor off in case any of that was an IR source, none of it seemed to make
any difference.

You need to pipe cold liquid nitrogen into the IR receiver modules to
reduce the noise floor. Looking like a cyberman does help ;-)

You just reminded me of something.

When I was at (St Albans) School there was an almost 'spare' lab in the Science
Block. It rarely got used for lectures, so enthusiasts like the Radio Society had
use of it. At that time they downloading weather maps ! Together with 2 friends I
was working on an organic dye laser but were knackered by the impossibility of
getting optically flat mirrors. We still did some 'interesting stuff' there some
of which is utterly hilarious but since you mention LN2, we went and bought some.
Or at least 2 of us did. They went to the local 'British Oxygen' depot with a
crate full of thermos flasks and were asked on admittance if they wanted oxygen
or nitrogen !

So they went to the nitrogen section which they described as being like a petrol
pump and filled up all the thermos flasks. It wasn't even that expensive.

So we had fun trying the effects of extreme cold on many things like ICs for
example.

Then my friend Nick and I had a mischievious idea. Our next lesson was Computing,
and the teacher was well known to be rather poor with discipline, so each of us
took a boiler tube of LN2 in our jacket pockets (well insulated with several
layers of simple paper), made sure we were last into class, and before entering
poured the LN2 over our suits !

So the 2 of us entered looking like something from Dr Who, white fumes smoking
all over us and totally straight faced.. One of the guys knew we we were up to
something and unfortunately for him, was leaning back in his chair. He was so
surprised that the chair slid from under him and he got put on report.

Not a word to Nick or myself, as the 'smoke' gradually dissipated. I'm glad you
reminded me of that.

Graham

"Marnok.com"

I just bought some (fairly cheap) IR stereo headphones. They work ok, but
with a very audible hiss even at very low volume when there is no sound
from the source (PC). This could quickly get annoying. I wondered if anyone
could tell me, is it that I just have a poor quality product or is this
sort of noise somehow inherent in the technology?


** Seems you have bought these:

http://tiranossaurus.com/product.asp?id=055253

The specs reveal it uses twin carriers ( 2.3 and 2.8 MHz) and FM modulation
of the pulsed IR light.

The receiver ICs are generally the same as those in FM demodulators - so
will hiss loudly in the absence of signal.

The claimed 55dB s/n is probably optimistic or heavily weighted or both.

Similar IR phones from Sennheiser claim only 46 dB s/n.

Good enough for low dynamic range stuff like TV listening.



...... Phil

Eeyore wrote:

Adrian C wrote:

Marnok.com wrote:
These are Pro-Luxe IR-650ST.

They were pretty cheap, and they make me look a bit like a cyberman

I tried shutting the curtains, turning the lights out and switching my
monitor off in case any of that was an IR source, none of it seemed to make
any difference.
You need to pipe cold liquid nitrogen into the IR receiver modules to
reduce the noise floor. Looking like a cyberman does help ;-)

You just reminded me of something.

When I was at (St Albans) School there was an almost 'spare' lab in the Science
Block. It rarely got used for lectures, so enthusiasts like the Radio Society had
use of it. At that time they downloading weather maps ! Together with 2 friends I
was working on an organic dye laser but were knackered by the impossibility of
getting optically flat mirrors. We still did some 'interesting stuff' there some
of which is utterly hilarious but since you mention LN2, we went and bought some.
Or at least 2 of us did. They went to the local 'British Oxygen' depot with a
crate full of thermos flasks and were asked on admittance if they wanted oxygen
or nitrogen !

So they went to the nitrogen section which they described as being like a petrol
pump and filled up all the thermos flasks. It wasn't even that expensive.

So we had fun trying the effects of extreme cold on many things like ICs for
example.

Then my friend Nick and I had a mischievious idea. Our next lesson was Computing,
and the teacher was well known to be rather poor with discipline, so each of us
took a boiler tube of LN2 in our jacket pockets (well insulated with several
layers of simple paper), made sure we were last into class, and before entering
poured the LN2 over our suits !

When was this?
Presumably a long time ago, before your '37 years as a pro-audio designer'.
So how did 'downloading weather maps' work then?
I remember some physics students at college doing silly things with
liquid nitrogen,
such as pouring it over their hands. It apparently didn't feel too cold
because of the layer of gaseous nitrogen that acted as an insulator.

--
Eiron.

Eiron wrote:

Eeyore wrote:
Adrian C wrote:
Marnok.com wrote:
These are Pro-Luxe IR-650ST.

They were pretty cheap, and they make me look a bit like a cyberman

I tried shutting the curtains, turning the lights out and switching my
monitor off in case any of that was an IR source, none of it seemed to make
any difference.
You need to pipe cold liquid nitrogen into the IR receiver modules to
reduce the noise floor. Looking like a cyberman does help ;-)

You just reminded me of something.

When I was at (St Albans) School there was an almost 'spare' lab in the Science
Block. It rarely got used for lectures, so enthusiasts like the Radio Society had
use of it. At that time they downloading weather maps ! Together with 2 friends I
was working on an organic dye laser but were knackered by the impossibility of
getting optically flat mirrors. We still did some 'interesting stuff' there some
of which is utterly hilarious but since you mention LN2, we went and bought some.
Or at least 2 of us did. They went to the local 'British Oxygen' depot with a
crate full of thermos flasks and were asked on admittance if they wanted oxygen
or nitrogen !

So they went to the nitrogen section which they described as being like a petrol
pump and filled up all the thermos flasks. It wasn't even that expensive.

So we had fun trying the effects of extreme cold on many things like ICs for
example.

Then my friend Nick and I had a mischievious idea. Our next lesson was Computing,
and the teacher was well known to be rather poor with discipline, so each of us
took a boiler tube of LN2 in our jacket pockets (well insulated with several
layers of simple paper), made sure we were last into class, and before entering
poured the LN2 over our suits !

When was this?
Presumably a long time ago, before your '37 years as a pro-audio designer'.

Comtemporaneous. I was designing my first pro-spec mixing desk at age 17. Heck, I mixed
my first band at 16.


So how did 'downloading weather maps' work then?

They had some electrochemically sensitive paper and a synchonised drum with a helical
contact.. Signal current darkened the paper. I think it was similar to how Muirhead
equipment worked.


I remember some physics students at college doing silly things with
liquid nitrogen,
such as pouring it over their hands. It apparently didn't feel too cold
because of the layer of gaseous nitrogen that acted as an insulator.

Never tried that myself.

The other stuff we got up to in that lab was brilliant too.

Graham

Eiron wrote:
Eeyore wrote:
snip
At that time they downloading weather maps !

When was this?
Presumably a long time ago, before your '37 years as a pro-audio
designer'. So how did 'downloading weather maps' work then?

I'd assume this was direct from the satellite.

"Marnok.com" wrote in message
...
I just bought some (fairly cheap) IR stereo headphones. They work ok, but
with a very audible hiss even at very low volume when there is no sound
from the source (PC). This could quickly get annoying. I wondered if anyone
could tell me, is it that I just have a poor quality product or is this
sort of noise somehow inherent in the technology?
Thanks for any help.


UPDATE

thanks to everyone for helping out.

I took them back this morning for cheery refund (after the guy in the store
played around for half an hour trying to make them sound OK)

Found a new set - Philips SHC2000 - these are MUCH better and also have a
recharging cable and rechargable batteries, and I got them from Argos for
less than £20. No hiss, sound is fine, I don't look as much like an extra on
Dr Who but I can live with that.

"Eeyore" wrote in
message
"Marnok.com" wrote:

I just bought some (fairly cheap) IR stereo headphones.
They work ok, but with a very audible hiss even at very
low volume when there is no sound from the source (PC).
This could quickly get annoying. I wondered if anyone
could tell me, is it that I just have a poor quality
product or is this sort of noise somehow inherent in the
technology?

What's the brand/model ?

IR links may well be subject to some background hiss
anyway. Think of all the IR sources in the room.

Apparently nobody is using high-quality wireless digital links.

If one were of the do-it-yourself persuasion, one might be able to cobble
together a high-quality portable listening device out of SP/DIF running over
existing wireless video technology.

I've used a laptop accessing a music server over WiFi for the general
purpose, but of course this lacked real-time broadcast source support. I
understand that there are wireless phones and PDAs that could do similar
things via a local LAN.

"Marnok.com"

UPDATE

thanks to everyone for helping out.

I took them back this morning for cheery refund (after the guy in the
store played around for half an hour trying to make them sound OK)



** Just LOVE the sight of a hi-fi salesman SQUIRMING in the morning
.....





..... Phil

Grumps wrote:

Eiron wrote:
Eeyore wrote:
snip
At that time they downloading weather maps !

When was this?
Presumably a long time ago, before your '37 years as a pro-audio
designer'. So how did 'downloading weather maps' work then?

I'd assume this was direct from the satellite.

I think it was, yes.

Graham

Eeyore wrote:

Grumps wrote:

Eiron wrote:
Eeyore wrote:
snip
At that time they downloading weather maps !
When was this?
Presumably a long time ago, before your '37 years as a pro-audio
designer'. So how did 'downloading weather maps' work then?
I'd assume this was direct from the satellite.

I think it was, yes.

Or broadcasts on HF. At my college radio shack, we used to receive and
print weather fax maps that came from Bracknell using piccolo MFSK
transmission (I googled and think - it was a long time ago, I barely
remember what I was doing at college).

--
Adrian C