Warning about cheap TVs currently on sale

"Richard Tobin" wrote in message
...
In article ,
Bill Wright wrote:

A 100W bulb runs at 100W all the time. A speaker rated at 100W runs at
whatever power the amp provides. In this case the '100W' refers to the
maximum the speaker can handle. So the comparision is worthless.

Quite true, and in any case amplifier power ratings are generally
entirely specious. But if it did produce 100W, it would heat things
up just as much as a 100W bulb.

But in the real world a domestic 100W speaker will not be dissipating 100W,
whereas a 100W light bulb will be. Practicality and reality are what matter.

Bill

In article ,
Bill Wright wrote:

Quite true, and in any case amplifier power ratings are generally
entirely specious. But if it did produce 100W, it would heat things
up just as much as a 100W bulb.

But in the real world a domestic 100W speaker will not be dissipating 100W,
whereas a 100W light bulb will be. Practicality and reality are what matter.

I'm not disputing that. I just want to dispel this idea that some
energy, such as sound, doesn't end up as heat.

-- Richard
--
Please remember to mention me / in tapes you leave behind.

"Richard Tobin" wrote in message
...
In article ,
Bill Wright wrote:

Quite true, and in any case amplifier power ratings are generally
entirely specious. But if it did produce 100W, it would heat things
up just as much as a 100W bulb.

But in the real world a domestic 100W speaker will not be dissipating
100W,
whereas a 100W light bulb will be. Practicality and reality are what
matter.

I'm not disputing that. I just want to dispel this idea that some
energy, such as sound, doesn't end up as heat.

Yes. As a matter of fact I suppose audio systems are highly inefficient. I
doubt if the energy that's actually in the form of air pressure amounts to
much at all.

Bill

John Rumm wrote:
Agamemnon wrote:

"Richard Tobin" wrote in message
...
In article ,
Agamemnon wrote:

And if I can't have a cheep power hungry TV heating up the room then I
will
have to pay more for the central hearting.

Electricity: 11.518 p/kWh
Gas: 3.398 p/kWh

[snip]

Your TV may be nearly 100% efficient at turning electricity into heat,
but electricity is a secondary energy source, with less than 60%
efficiency when you include the generation and distribution elements.

So with such a difference in price for electricity and gas these days, are we
not better off with each house having its own mini gas-fired generator?
There's a lot of scope for inefficiency before you end up back at 11 and a
half pee per kWh...

In article ,
chunkyoldcortina wrote:
So with such a difference in price for electricity and gas these days,
are we not better off with each house having its own mini gas-fired
generator? There's a lot of scope for inefficiency before you end up
back at 11 and a half pee per kWh...

Most engines that could be used will only have a decent efficiency at a
set load. So when it starts up when you go to the loo in the middle of the
night, not too high.

--
*The longest recorded flightof a chicken is thirteen seconds *

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

In article ,
Bill Wright wrote:
Yes. As a matter of fact I suppose audio systems are highly inefficient. I
doubt if the energy that's actually in the form of air pressure amounts to
much at all.

According to Wikipedia, the efficiency of the loudspeakers alone is
about 1%.

The efficiency of various classes of amplifiers is well-known
(1/sqrt(2) = 71% for class B IIRC).

-- Richard
--
Please remember to mention me / in tapes you leave behind.

In article ,
wrote:
On 22 Jan,
"Dave Plowman (News)" wrote:

Most engines that could be used will only have a decent efficiency at
a set load. So when it starts up when you go to the loo in the middle
of the night, not too high.

But you could use the waste heat to heat the bog. That would increase the
efficiency.

You could use the waste from the bog to drive the engine. That would
increase efficiency.

--
*A chicken crossing the road is poultry in motion.*

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

chunkyoldcortina wrote:
John Rumm wrote:
Agamemnon wrote:

"Richard Tobin" wrote in message
...
In article ,
Agamemnon wrote:

And if I can't have a cheep power hungry TV heating up the room then I
will
have to pay more for the central hearting.

Electricity: 11.518 p/kWh
Gas: 3.398 p/kWh

[snip]

Your TV may be nearly 100% efficient at turning electricity into heat,
but electricity is a secondary energy source, with less than 60%
efficiency when you include the generation and distribution elements.

So with such a difference in price for electricity and gas these days,
are we not better off with each house having its own mini gas-fired
generator? There's a lot of scope for inefficiency before you end up
back at 11 and a half pee per kWh...

If you can organise combined heat and power micro generation such that
you can share enough of the energy liberated locally to keep it all
ticking along in a nice steady state, then yes. Its one of those ideas
that is nice in theory, but requires quit a bit of work to get working
in reality. There have been some trial schemes run IIRC.

--
Cheers,

John.

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DM wrote:

In some situations this type of reasoning has a small element of truth.

And in this one it has a large element of truth.

However, jsut becasuse tv a uses more power than TV B, does not mean
that the differece between them is given off as heat. In fact that sort

Erm , I think you will find that is largely true.

of reasoning of really very poor and does not apply to electronics design.

Might I suggest some background reading on the second law of thermodynamics?

If TV A consumes 100W and TV B 200W, then that is largely the heating
effect you will observe in the room. A very very small proportion of
that energy may escape the room as vibration or light passing through
windows etc. However ultimately even that will ultimately end up heating
up something.


(you may be getting confused with the differences between real an
imaginary (or reactive) "power" - a concept that can exist with
electrical systems).

--
Cheers,

John.

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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Richard Tobin
writes
In article ,
Bill Wright wrote:
Yes. As a matter of fact I suppose audio systems are highly inefficient. I
doubt if the energy that's actually in the form of air pressure amounts to
much at all.

According to Wikipedia, the efficiency of the loudspeakers alone is
about 1%.

The efficiency of various classes of amplifiers is well-known
(1/sqrt(2) = 71% for class B IIRC).

-- Richard

But surely no one runs audio amplifiers in class-B?
--
Ian