Why is it that the lower the impedance for headphones, the harder it is
to drive????

Thinking about speakers ..... say connected to an 8ohm rated amp. If
they were 32 ohms, then the amp's possible power would be was less
(than if the speakers were 8 ohm)....

So why is it so?

"andrew_h" wrote in message
oups.com...
Why is it that the lower the impedance for headphones, the harder it is
to drive????

Thinking about speakers ..... say connected to an 8ohm rated amp. If
they were 32 ohms, then the amp's possible power would be was less
(than if the speakers were 8 ohm)....

So why is it so?

For a given power (which more or less + SPL) :

Lower impedence = lower voltage = more current

Higher impedence = higher voltage = lower current

So you choose higher current or higher voltage. Inherently low voltage
devices such as discman, mp3, etc, are less happy to supply higher current.

geoff

Amplifiers have an internal series resistor for each side to limit the
current to the headphones. Lower impedance headphones will have a greater
load after the limit resistor, thus reducing the voltage across the drivers.
This will force the user to turn up the volume higher in order to listen to
them.

Most amplifiers that work from the AC power for operation were designed for
8 ohm headphones. Portable devices that run on batteries are usually
designed to use headphones of at least 32 ohms or greater. This will offer
less load on the output circuits, and thus save some battery energy. The
internal bias resistor value was chosen to allow for a lower current drive.
This is why an 8 ohms headphones will be lower sounding on most portable
devices.

--

JANA
_____


"andrew_h" wrote in message
oups.com...
Why is it that the lower the impedance for headphones, the harder it is
to drive????

Thinking about speakers ..... say connected to an 8ohm rated amp. If
they were 32 ohms, then the amp's possible power would be was less
(than if the speakers were 8 ohm)....

So why is it so?

"Geoff@home" wrote in message
...

"andrew_h" wrote in message
oups.com...
Why is it that the lower the impedance for headphones, the harder it is
to drive????

Thinking about speakers ..... say connected to an 8ohm rated amp. If
they were 32 ohms, then the amp's possible power would be was less
(than if the speakers were 8 ohm)....

So why is it so?

For a given power (which more or less + SPL) :

Lower impedence = lower voltage = more current

Higher impedence = higher voltage = lower current

So you choose higher current or higher voltage. Inherently low voltage
devices such as discman, mp3, etc, are less happy to supply higher
current.

OTOH, unless they use DC-DC voltage boost circuits,
they are incapable of supplying higher voltage, which is
why high-impedance headphones are generally a poor
match for most battery-operated equipment.

"andrew_h" wrote ...
Why is it that the lower the impedance for headphones,
the harder it is to drive????

It isn't.
Unless you wish to more carefully define "harder".

Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....

25% of the power, to be exact.

So why is it so?

Ohms law. Any amplifier is limited in the amount of
voltage it can put out. The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load.

For example, if your theoretical amplifier were rated
for 100W into 8 ohms, that would mean it was capable
of putting out 28.3V (3.5A into 8 ohms) But if you
raise the load impedance to 32 ohms, that same 28.3V
would produce only 25W (0.8 Amps of current)

Here, you can calculate it for yourself...
http://www.sengpielaudio.com/calculator-ohm.htm

Thanks heaps to all who replied ... the question = understood!

Its great that there are so many helpful people here in this group....
I'm learning so much now - and once something is understood, you wonder
why you didnt get it in the first place. All a case of building and
layering up knowledge I think.

Thanks again!
Andrew

"Richard Crowley" wrote in message
...
"andrew_h" wrote ...
Why is it that the lower the impedance for headphones,
the harder it is to drive????

It isn't.
Unless you wish to more carefully define "harder".

Agreed. It's usually harder for most portable ipod style players to drive
anything higher impedance *OR* lower impedance than the design value.


Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....

25% of the power, to be exact.

Only if you ignore Current limitations.


So why is it so?

Ohms law. Any amplifier is limited in the amount of
voltage it can put out.

What amplifier has infinite current capability? Any amplifier has both
voltage *AND* current limits.

The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load.

Not necessarily. Many amplifiers will provide higher power into a four ohm
load than a two ohm load for example.
Some even provide higher power into 8 ohms than four, due to low current
capability.
(Of course their aren't too many 4 ohm headphones, but your comment
specifically mentions "speakers, incandecent lamps etc.")

MrT.

"Mr.T" MrT@home wrote in message
...

"Richard Crowley" wrote in message
...
"andrew_h" wrote ...
Why is it that the lower the impedance for headphones,
the harder it is to drive????

It isn't.
Unless you wish to more carefully define "harder".

Agreed. It's usually harder for most portable ipod style players to
drive
anything higher impedance *OR* lower impedance than the design value.


Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....

25% of the power, to be exact.

Only if you ignore Current limitations.

Actually, no I;m not. In this scenario, the power is
typically voltage limited. Doesn't matter if the amp
can source 1000 amps, if it's got only twenty-whatever
volts, it's gonna run outa gas into 32 ohms.


So why is it so?

Ohms law. Any amplifier is limited in the amount of
voltage it can put out.

What amplifier has infinite current capability? Any amplifier has both
voltage *AND* current limits.

The presenting scenario was a 32 ohm load.
Try to concentrate on the topic at hand.

Mr.T wrote:
Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....
25% of the power, to be exact.
Only if you ignore Current limitations.

Say you had yourself an amplifier that was rated at 100 watts
into 8 ohms. That means that it could swing 28.3 volts RMS
into that load. Let's say 30 volts to make life easy.

At 100 watts, it would be putting about 3.5 amps into that 8 ohm
load.

Now, let's say said amplifer has an ultimate current capability of,
20 amps continuous. That would mean that it could easily do
7 amps into 4 ohms, which could be 200 watts, and it could do
14 amps into 2 ohms, corresponding to 400 watts.

Let's go in the other direction: how much current could said
amplifier put into, say, 32 ohms (just to pick a random number)?

Given that its output voltage is limited to 30 volts, the ABSOLUTE
MAXIMUM it could put out is 1 amp. 1 measely ampere. That's it.
Doesn't make any difference what it OCULD put out, 32 ohms
ain't gonna let it put out any more. None. Zip. Nadda.

But, what if you REALLY wanted the full 20 amps into 32 ohms?
Herr Ohm tells us how:

E = I * R

E = 20 amps * 32 Ohms

E = 640 volts.

Do you know any amplifiers that can swing 640 volts RMS?

What about current limitations?

The voltage limit imposes the current limitations at high impedances.

So why is it so?

Ohms law. Any amplifier is limited in the amount of
voltage it can put out.

What amplifier has infinite current capability? Any amplifier has both
voltage *AND* current limits.

Yup.

At high impedance, your voltage limit dominates. At low
impedance, you current limit dominates.

The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load.

Not necessarily. Many amplifiers will provide higher power
into a four ohm load than a two ohm load for example.
Some even provide higher power into 8 ohms than four,
due to low current capability.

Are we having fun?

(Of course their aren't too many 4 ohm headphones, but your comment
specifically mentions "speakers, incandecent lamps etc.")

Nor is there anyone on this planet that would want to dump the entire
power of their amplifier , whether it's at current limiting or voltage
limiting, into their headphones. Our hypothetical 100 watt amplifier,
which we know can produce 30 volts across 32 ohms, would generate
a nice sound pressure level of well over 140 dB SPL into your typical
headphone.

Given the context of the discussion, which I agree is only weakly
hinted at by the word "headphone" in the subject line, does your
particular thesis make a lot of sense?

"Richard Crowley" wrote in message
...
Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....

25% of the power, to be exact.

Only if you ignore Current limitations.

Actually, no I;m not. In this scenario, the power is
typically voltage limited. Doesn't matter if the amp
can source 1000 amps, if it's got only twenty-whatever
volts, it's gonna run outa gas into 32 ohms.

Since you used the word "typically", you actually agreed. Doesn't matter if
it's got a 1000V if it runs out of current.

What amplifier has infinite current capability? Any amplifier has both
voltage *AND* current limits.

The presenting scenario was a 32 ohm load.
Try to concentrate on the topic at hand.

*YOU* were the one who wrote :

" The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load."

Are incandescent lamps always a 32 ohm load? NO!
Maybe you shouldn't generalise IF you actually want to be specific in
future.

MrT.

wrote in message
oups.com...

Mr.T wrote:
Thinking about speakers ..... say connected to an 8ohm
rated amp. If they were 32 ohms, then the amp's possible
power would be was less (than if the speakers were 8 ohm)....
25% of the power, to be exact.
Only if you ignore Current limitations.

Say you had yourself an amplifier that was rated at 100 watts
into 8 ohms. That means that it could swing 28.3 volts RMS
into that load. Let's say 30 volts to make life easy.

At 100 watts, it would be putting about 3.5 amps into that 8 ohm
load.

Now, let's say said amplifer has an ultimate current capability of,
20 amps continuous. That would mean that it could easily do
7 amps into 4 ohms, which could be 200 watts, and it could do
14 amps into 2 ohms, corresponding to 400 watts.

Let's go in the other direction: how much current could said
amplifier put into, say, 32 ohms (just to pick a random number)?

Given that its output voltage is limited to 30 volts, the ABSOLUTE
MAXIMUM it could put out is 1 amp. 1 measely ampere. That's it.
Doesn't make any difference what it OCULD put out, 32 ohms
ain't gonna let it put out any more. None. Zip. Nadda.

But, what if you REALLY wanted the full 20 amps into 32 ohms?
Herr Ohm tells us how:

E = I * R

E = 20 amps * 32 Ohms

E = 640 volts.

Do you know any amplifiers that can swing 640 volts RMS?

What about current limitations?

The voltage limit imposes the current limitations at high impedances.

So why is it so?

Ohms law. Any amplifier is limited in the amount of
voltage it can put out.

What amplifier has infinite current capability? Any amplifier has both
voltage *AND* current limits.

Yup.

At high impedance, your voltage limit dominates. At low
impedance, you current limit dominates.

The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load.

Not necessarily. Many amplifiers will provide higher power
into a four ohm load than a two ohm load for example.
Some even provide higher power into 8 ohms than four,
due to low current capability.

Are we having fun?

(Of course their aren't too many 4 ohm headphones, but your comment
specifically mentions "speakers, incandecent lamps etc.")

Nor is there anyone on this planet that would want to dump the entire
power of their amplifier , whether it's at current limiting or voltage
limiting, into their headphones. Our hypothetical 100 watt amplifier,
which we know can produce 30 volts across 32 ohms, would generate
a nice sound pressure level of well over 140 dB SPL into your typical
headphone.

Given the context of the discussion, which I agree is only weakly
hinted at by the word "headphone" in the subject line, does your
particular thesis make a lot of sense?


I totally agree with you Dick. You could have saved yourself a lot of
unnecessary typing.
However I was not the one who claimed :

" The higher the impedance of the
load (speaker, headphones, incandescent lamp, etc.,)
the less power the amplifier can source into the load."

This is a very broad statement is it not? (Note it is not constrained to 32
ohm headphones)
That was what made me point out the laws of physics in more general terms.

MrT.