Reg, G4FGQ wrote:
"I would like to know, crudely, the audio input level to 2000-ohm, non
diaphragm head phones for a nice, comfortable, not too difficult
intensity level."

First problem is sensitivity of the phones. These vary widely.

Satisfactory reception also depends on competing noise in addition to
signal strength. According to the FCC in the U.S.A., you may need 1/2
millivolt for satisfactory reception.

A kilowatt radiated by a medium wave transmitter may produce about 200
millivolts/m at one mile. It depends on antenna and path. Field strength
is proportional to the square root of the watts per square meter times
377.

I used to live about 15 mile4s from a 50 KW station. The signal strength
at a mile from the station could have been 1.5 volts/ m, and at 15 miles
could have been 0.1 V/m. Point is, my crystal set drove a dynamic
loudspeaker directly through the output transformer mounted on the
speaker. It was clearly audible. Impedance presented to the crystal set
was closer to 10,000 ohms at 1 KHz than to 2000 ohms. The speaker and
its cabinet were from a battery vacuum-tube set. The audio power may
have been less than a microwatt, but as a kid my ears were acute.

My 2nd edition GE "Transistor Manual" has 2000-ohm headphone amplifiers
with 2 milliwatts maximum power output.

Chinese stereo headphones claim 20-20KHz response, 32-ohms impedance,
100dB/1mW sensitivity, 140 mW rated input, 400 mW max. etc. Much of this
spec. is target and untrue. Wide variations exist between samples of
these phones claiming similar specs.

The GE book is believable. Class A power output is from the familiar.
First formula says maximum power is 1/2 the product of the peak voltage
and peak current. Load resistance is then the peak voltage divided by
the peak current. So, Load resistance=Epk squared/2Po

When GE prints the circuit of a 2 milliwatt amplifier driving 2000-ohm
phones, I believe it works.

Best regards, Richard Harrison, KB5WZI

On Fri, 2 Jul 2004 16:45:12 +0000 (UTC), "Reg Edwards"
wrote:

What if I said 43?

==========================

If you had also mentioned the measurement units, such as femto-Watts, that
would have been the ideal, even perfect, reply to my enquiry and would have
deserved the congratulations of all and sundry.
----
Punchinello, G4FGQ


Ah Shirley!

You jest. Thanks uttered by Punchinello? Time and tide wait for no
such unlikely occasion. Lord Kelvinator wouldn't be very proud of
you, old son, if I had to lead you by the hand through ALL of the
work, much less spoon fed you the answer. It is only a matter of
simple junior high math employing conversions (all the numbers are
already there). About as demanding as chinese checker strategy.

88's
Richard Clark, KB7QHC

On Fri, 2 Jul 2004 16:45:12 +0000 (UTC), "Reg Edwards"
wrote:

What if I said 43?

==========================

If you had also mentioned the measurement units, such as femto-Watts, that
would have been the ideal, even perfect, reply to my enquiry and would have
deserved the congratulations of all and sundry.
----
Punchinello, G4FGQ


Ah Shirley!

You jest. Thanks uttered by Punchinello? Time and tide wait for no
such unlikely occasion. Lord Kelvinator wouldn't be very proud of
you, old son, if I had to lead you by the hand through ALL of the
work, much less spoon fed you the answer. It is only a matter of
simple junior high math employing conversions (all the numbers are
already there). About as demanding as chinese checker strategy.

88's
Richard Clark, KB7QHC

Dear Rich, in your own best interests you should merely have said "I don't
know.".

Or better still - - - silence.
----
Punch, G4FGQ

Dear Rich, in your own best interests you should merely have said "I don't
know.".

Or better still - - - silence.
----
Punch, G4FGQ

On Fri, 2 Jul 2004 22:09:13 +0000 (UTC), "Reg Edwards"
wrote:

Dear Rich, in your own best interests you should merely have said "I don't
know.".

Oh the ravage of age upon you - here it is again
On Thu, 01 Jul 2004 20:43:37 GMT, Richard Clark
wrote:
I don't know


Or better still - - - silence.
----
Punch, G4FGQ

My own best interests? Somehow I don't see you in the confessional
offering Ave Marias to me (now there is an image, Punchinello with a
Mitre - the pope and you both like funny hats).

I'm still not going to spoon feed you, you know. Do you have a number
yet? Or is this the better, silence? ;-0

73's
Richard Clark, KB7QHC

On Fri, 2 Jul 2004 22:09:13 +0000 (UTC), "Reg Edwards"
wrote:

Dear Rich, in your own best interests you should merely have said "I don't
know.".

Oh the ravage of age upon you - here it is again
On Thu, 01 Jul 2004 20:43:37 GMT, Richard Clark
wrote:
I don't know


Or better still - - - silence.
----
Punch, G4FGQ

My own best interests? Somehow I don't see you in the confessional
offering Ave Marias to me (now there is an image, Punchinello with a
Mitre - the pope and you both like funny hats).

I'm still not going to spoon feed you, you know. Do you have a number
yet? Or is this the better, silence? ;-0

73's
Richard Clark, KB7QHC

Harry Whitfield wrote:
"Sensitivity is given as 112 dB at 1 mW. I assume this means 112 dB
above the Threshold of Hearing (1pW per square metre) at 1 mW in."

That looks OK to me. My handy "Science Answer Book says:
Hearing starts at zero decibels. 10 units is a tenfold increase. The
sound made by leaves rustling is often 10 decibels. Office noise level
is typically 50 decibels. A pneumatic drill = 80 dB. A riveting machine
= 110 dB. A jet takeoff at 61 m (200 ft.) measures 120 dB. Noise above
70 decibels harms hearing. At 140 dB, noise is physically painful.

Acute hearing is sensitive. More so in some other species.

In a previous posting I may have appeared naive saying I believed GE
produced a circuit for a 2 milliwatt 2000-ohm headphone amplifier. But I
have additional evidence of the adequacy of 2 milliwatts. For many years
I worked at a radio station where we kept a pair of crystal phones near
the audio patch panel. These, because of their extremely high impedance,
could be bridged across any program line with no significant effect.
Program lines are usually adjusted to a zero VU level (1 milliwatt into
600 ohms) or 0.775 volt on program peaks. Magnetic phones produced about
the same audio output with 0.775 volts as did the crystal cans. The
difference is only in the circuit loading of the 2000-ohm magnetic
phones on a 600-ohm circuit. Point is, one milliwatt is plenty loud in
headphones. I know from listening.

Best regards, Richard Harrison, KB5WZI

Harry Whitfield wrote:
"Sensitivity is given as 112 dB at 1 mW. I assume this means 112 dB
above the Threshold of Hearing (1pW per square metre) at 1 mW in."

That looks OK to me. My handy "Science Answer Book says:
Hearing starts at zero decibels. 10 units is a tenfold increase. The
sound made by leaves rustling is often 10 decibels. Office noise level
is typically 50 decibels. A pneumatic drill = 80 dB. A riveting machine
= 110 dB. A jet takeoff at 61 m (200 ft.) measures 120 dB. Noise above
70 decibels harms hearing. At 140 dB, noise is physically painful.

Acute hearing is sensitive. More so in some other species.

In a previous posting I may have appeared naive saying I believed GE
produced a circuit for a 2 milliwatt 2000-ohm headphone amplifier. But I
have additional evidence of the adequacy of 2 milliwatts. For many years
I worked at a radio station where we kept a pair of crystal phones near
the audio patch panel. These, because of their extremely high impedance,
could be bridged across any program line with no significant effect.
Program lines are usually adjusted to a zero VU level (1 milliwatt into
600 ohms) or 0.775 volt on program peaks. Magnetic phones produced about
the same audio output with 0.775 volts as did the crystal cans. The
difference is only in the circuit loading of the 2000-ohm magnetic
phones on a 600-ohm circuit. Point is, one milliwatt is plenty loud in
headphones. I know from listening.

Best regards, Richard Harrison, KB5WZI

John, MW1FGQ wrote:
"I used to carry a pair of old military headphonees in my kit when
building broadcast installations until they were nicked by some ****."

Several models of telephone receivers were used in WW-2, including the
TS-10 (sound powered) unit. This was probably the most efficient
transducer except for the R-13 and other resonant models designed for
morse code reception. The HS-33 with its leather-covered headband is the
model I saw most often. I don`t remember it being particularly sensitive
but it did have pretty good fidelity.

I seem to recall seeing the most valuable patent ever issued by the U.
S. Patent Office. It`s the Alexander G. Bell telephone patent. The
microphone was dynamic, not carbon, so his receiver had to be sensitive
as the instrument was sound powered.

I used to carry around a surplus TS-10 unit in my kit. Although sound
powered, it is not sharply resonant. The fidelity is not too bad. Aboard
my ship in WW-2, I had a spare TS-10 unit wired with an attenuator and
connected to the ship`s entertainment and information line. There was an
almost 24-hour music feed from radio or records. We had a V-disk
transcription library too. Nobody complained and the zero dBm level was
plenty loud if I turned up the attenuator. Little electrical power is
needed for considerable acoustical power when using the right
transducer. As long as I kept the movie projector running, the skipper
would let me get away with about anything.

Best Regards, Richard Harrison, KB5WZI