You seem to be suffering from trying to convert Audio Engineering into Electrical Engineering.
Basically I don't get it either.

Impedance is a combination of resistance and reactance. On an X/Y graph, resistance is the X axis and reactance is the Y axis and 90 degrees out of phase with resistance. When you do the math for any given audio circuit, you get an impedance value on the X/Y graph, and it has a phase angle. Whether you want impedances between input and output to match or not depends on which end of the signal chain you're on. At the microphone end, you want the input of the preamp to have an impedance at least 10 times higher than the output impedance of the mic. This sets up a substantial gain stage. Resistance and voltage are kissin' cousins, so the voltage increase from the higher impedance of the preamp translates into higher voltage for a gain increase. At the monitor end, you want the amplifier impedance and monitor impedance to match so that you get maximum current and power transfer. Power (watts) and current (amperage) are also kissin' cousins, so by keeping the imepdances matched on this end, you get maximum power transfer from amp to speakers. Sidenote: reactive components (capacitors and coils) in circuits are frequency sensitive, this is why impedance causes a phase shift, and where most gear related translation issues arise from. If the net phase angle of a signal chain from one studio is drastically different than the net phase angle of another studio's chain, stuff will sound drastically different out of each set of monitors. Gear manufacturors have never gotten together to standardize this, unfortunately.

so now that, that is clear
we are all happy now

:)

to begin to understand
it might be better to take one specific situation at a time
and discuss some of the concepts
with cause and effect scenarios

" I've come to a conclusion that the impedance of the output must be higher or equal to that of the input it's being wired to, "
completely wrong

although I get where Jon is coming from,
it might be easier for audio people to view impedance as resistance again frequency

in the world of electronics many consider audio to be near DC
this is incorrect but for people that work in Radio Frequencies in either analog or digital
you can see why they think this way

impedance(resistance) can change with frequency

SO
lets take one situation and look deeper

Codemonkey
we can talk about the headphones
but first
get a look at the RANE notes on driving headphones

"Resistance and voltage are kissin' cousins"

Is it just me or is it gettin' warm in here :)

not without current nearby
so that would make it a threesome

Something between my ears is swelling badly. Fireworks will follow shortly.

I'll have a look at the rane thing.

I was hoping for a general guideline of say, plugging line outs into line ins on different devices although i suspect the whole -10dbV and +4dBu comes into it here?

yes it does

and there are times when the dbv makes sense
and times when dBu makes more sense

it's all about available current/power and the load presented

these specifications we like so much don't tell the whole story in isolation
and it requires many specs to begin to tell the story

ALL the spec in the world don't tell how it will sound
that is NOT to say that specs are useless

it's complicated BUT it can be simplified
and
always beware that a little knowledge is dangerous

knowledge ... persure you must

Is it just me or is it gettin' warm in here?

Must be you, the thunderstorms just cooled it down up here in Nashville!

Codemonkey, didn't mean to make your head explode. Impedance is a very abstract concept, I'm still working on wrapping my noggin around it completely. My source on theory is Al Grundy, who was AES President for many years, and made my head spin on a regular basis (had him as a professor).

Codemonkey wrote: OK, I've spent a bit of time searching here and on wiki, etc. but I can't find anything to sum up the whole concept of impedance in audio gear.

I've come to a conclusion that the impedance of the output must be higher or equal to that of the input it's being wired to, or you get buzzing and noise etc.
eg My headphone jack is 300 ohm and I have no problems with 64 ohm HPs but putting this into a Line In at say, 10Kohm causes noise.

BUT I have no faith in that statement unless someone confirms or denies this.

Basically, what's the rule of impedance? Input = output, input output or what?

There's some misunderstanding here.

Firstly, I think your headphone/line in noise difference has nothing to do with impedance. Headphones are inherently isolated (not grounded) whereas single-ended line inputs are referenced to ground. I suggest the noise is due to a ground problem.

Secondly, the matter of input and output impedance. Generally speaking, for signal transfer, the output impedance should be lower than the driven input impedance. There are several common situations:

(1) bridging: the output impedance is low and the input impedance high. This causes the lowest attenuation of the signal and also allows many inputs to be connected to one output without interaction or signal degradation.

(2) matched: the output (driving) and input (receiving) impedances should be equal. Maximum signal power is transferred in this case, half being lost in the driver and half in the receiver. An example of this case is 600 Ohm working. The signal amplitude is exactly halved at each interconnection, and the open-circuit gain of the equipment has an extra x2 to allow for this. It is important that the equipment is designed for this use, as putting a 600 Ohm load on outputs that expect higher impedance loads can cause clipping and distortion due to current limiting.

(3) power transfer: this is the case when for example you are driving loudspeakers from a power amplifier. The amplifier has a very low output impedance (often lower than the cables in use), and for current-limiting reasons is specified to drive loads of not lower than a certain impedance. You want as much power as possible to be transferred to the load.

In the case of your headphone jack, it would be unusual for it to have a 300 Ohm output impedance. It's more likely that it is specified to drive 300 Ohm phones, but that in itself would be unusual, as the majority of phones are nearer 30 Ohm.

:-? :-? :shock: :x :-? :shock:

Ok. Im going to start freaking out!

Why can't we just keep this simple ????

Mic's need to go into 10x heir output impidence. Amps need o drive a speaker the same as or less than their output impedince etc....

Every i have tried to understand it any better I :-?

You see, I don't question it. For the same reason I dont question why 'But' is but, and 'Put' is put... gettting it ?

English and electronics are both funny languages....

I eed to have another beer....

:lol:

So basically my noise problem is not resistance, but ground issues, and plugging into onboard crap? I kinda let that slip past because I've had good results (relatively speaking) in the past with said line input.

Something tells me I should just plug it in and turn it up, and forget about the fine electrical details?

this is why I didn't want to give an explanation like Boswell did
take a specific situation and we can discuss the cause and effects

Boswell's power transfer description doesn't seem right to me but does make sense in the context that it followed the description for matched.

Matched is a bit historic and probably doesn't help younger people with new bridging interfaces who may never own a transformer coupled tubed circuit
It IS important to know this stuff if you get into the retro gear.

most of the interconnects need some degree of power transfer ... some more then others and power amplifier and speaker combination has much in common with a bridging transfer where
" the output impedance is low and the input impedance high "

Codemonkey ... read the RANE notes on driving headphones

Space wrote: "Resistance and voltage are kissin' cousins"

Is it just me or is it gettin' warm in here :)

Wait... so making out with your cousin is bad?

[unfounded joke]
Only in some states.
[/unfounded joke]

Remember, it ain't illegal unless you get caught!

Codemonkey, you have typed impedance and you have typed resistance.

The two are different? Awww fiddlesticks. No, don't explain the difference. I'm over my head and tbh, I'll leave it at that. I see there is more to this than magic formulae.

I can grasp the difference between the two, if that helps :)

But the rest of this thread is months^2(x) down the road for me.

an impedance plot will give

resistance against frequency

audio is AC so you must not restrict your thinking to a simple DC view
V=IR as a static figure

think AC and think audio Frequencies ... not just a 50 or 60 hz power AC

to both code and space
we should go back to original items of the heaphone amp and the headphones
why and how

then to the headphone amp as a line driver
why and how

A Broadcast Practel Line Distribution Amplifier for 600ohm and bridging line levels
looks a lot like a Headphone Amp

likewise.. an old Neve desk output
( from those days that made them famous )
can drive an Auratone 8ohm speaker to usable levels

again why and how

What Kev said......impedance is kinda like weather, very dynamic situation.

Kev wrote: this is why I didn't want to give an explanation like Boswell did
take a specific situation and we can discuss the cause and effects

Boswell's power transfer description doesn't seem right to me but does make sense in the context that it followed the description for matched.

Matched is a bit historic and probably doesn't help younger people with new bridging interfaces who may never own a transformer coupled tubed circuit
It IS important to know this stuff if you get into the retro gear.

most of the interconnects need some degree of power transfer ... some more then others and power amplifier and speaker combination has much in common with a bridging transfer where
" the output impedance is low and the input impedance high "

The business of power transfer does not altogether correlate with one's own experience. Theoretically, the maximum power is transferred from a source to a load when the output resistance of the source equals the resistance of the load. Half the generated power is dissipated in the source output resistance and half in the load.

It's relatively easy to visualise this in a 600 Ohm resistive environment, but what about the case of a power amp driving a loudspeaker? If the resistive part of the output impedance of a power amp is .01 Ohm, does that mean we should be using 0.01 Ohm loudspeakers and correspondingly even lower resistance cables?

The answer is yes if that were the only consideration. The voltage would be low and the currents enormous, but that would be the way of getting maximum power out of a completely linear and unconstrained source. However, amplifier designers have to work with the current and voltage limits of their output devices, so in practice, the power into the loudspeaker at the lower end of the load impedance range is limited by the maximum current available and at the higher end by the maximum voltage available.

We've got so used to the idea that power amplifiers are good at transferring power to a load that we tend to lose sight of the maximum power transfer theorem. For a practical power amp, what matters is the maximum power transfer within other constraints, which include not only current limits and voltage limits, but also distortion figures, stability and having to deal with the reactive component of the load, including lead inductance. In my day job as a professional designer, I meet this sort of multi-dimensional problem in most of the designs I get to do, audio and otherwise. But you can't get away from the underlying physics.

What I got from this:
http://www.rane.com/hc4hp.html

was...big speakers use watts and little speakers use the milliwatt.

Boswell wrote: But you can't get away from the underlying physics.

no you can't

but does this help the original post where the statement of
" I've come to a conclusion that the impedance of the output must be higher or equal to that of the input it's being wired to, or you get buzzing and noise etc.
eg My headphone jack is 300 ohm and I have no problems with 64 ohm HPs but putting this into a Line In at say, 10Kohm causes noise. "

most buy gear that already exists and then try to use it

Boswell and I get to design and make gear to our spec and for our needs
and so we can refer to formulas and laws ... like
Jacobi's Law
The law known as the maximum power theorem
The theorem applies to maximum power, and not maximum efficiency.
... not that max efficiency is required here either
The theorem is often applied to electric motors ... speakers are also often refered to as motors
The theorem is also helpful when looking at Transformer coupling ... including Microphones as they often have transformers and so do the Mic-preamps.

so
my comments where were aimed at
" ... impedance of the output must be higher or equal to that of the input it's being wired to, ... "

I don't think this is correct.

The original post had
" My headphone jack is 300 ohm and I have no problems with 64 ohm HPs but putting this into a Line In at say, 10Kohm causes noise. "

by looking at the specific situation and the gear being used we might be able to explain why you can't hear the noise on 64 ohm HPs and why a 10kohm input does hear excesive noise.

Is the output really 300 ohms ?
I think this was queried on the previous page were Boswell suggested
" In the case of your headphone jack, it would be unusual for it to have a 300 Ohm output impedance. It's more likely that it is specified to drive 300 Ohm phones, but that in itself would be unusual, as the majority of phones are nearer 30 Ohm. "

agreed
except for the comment on " majority of phones are nearer 30 Ohm "
depends were you work
many Camera Headsets and Talkback headsets are higher

so again I refer to the Rane tech pages
I think they list a number of popular Headphones and impedances.
My Headphone web pages and the Headwize pages refer to these issues and the various diferent situation from
9volt chip based
to Crown DC150 and passive distribution systems

there is a big difference from a favourite CD while jogging around the block
to tracking METAL DRUMS with the band at full throttle

http://www.headwize.com/projects/

this is a very good discussion topic and so much can be learned
and then extended to general interfacing

quote from Rane through Space
" ... big speakers use watts and little speakers use the milliwatt. "

yes
but
there are times when the watts are not the issue ... but the voltage swing

Old school grunt PA systems
ARX1200 on horns
Perreaux 9000B on Mids
Perreaux 9000 on subs

the Horns don't need the Wattage an ARX1200 can deliver
but they didn't sell an amp with 100 Volt swing and only a couple of output devices ( instead of the 5 up and 5 down )
the 9000 had 6 up and 6 down
and the B had more meat in the power transformer and more capacitance in the supply.

here comes the best bit

Levels ... dbs, volts and watts
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html

typical chip based audio gear
15 volts balanced supply ... +15V / 0V / -15V
so VPEAK = 15 V
which might lead to 22.73dbu if there were NO losses
dbu is 600 ohms
so for
600 ohms = 187.5 mW
300 ohms = 375 mW
100 ohms = 1125 mW
30 ohms = 3750 mW
8 ohms = 1.406e4 mW .... Crown DC150 ??

as Boswell said .... only IF the output devices can deliver the current required

yes it is an over use of Low Impedance High Current outputs.
Broadcast Audio Distribution Amplifiers designed for 600 ohms (dbu) employ designs to about the 100 or 30 ohm levels.

A good quality Headphone Amplifier can be used as a line driver.
see Silicon Chip Magazine for a design,
currently available from Jaycar Kits.
8)

I've come to a conclusion that the impedance of the output must be higher or equal to that of the input it's being wired to, or you get buzzing and noise etc.

Buzz has nothing to do with impedance. Noise may happen if there's a large mismatch (very high output impedance into very low input impedance).

eg My headphone jack is 300 ohm and I have no problems with 64 ohm HPs

You have just hit the only case where the ISO has chosen a very specific standard. The recommended output impedance on a HiFi amp is 180 ohms (If I Remember Well) because it will provide almost uniform power to any headphone frm 8 ohms to 600 ohms.

but putting this into a Line In at say, 10Kohm causes noise.

I guees if you connect your headphone to the input of a piec of gear, the headphone may pick up sound (structurally, there's no differnce between a microphone and a loudspeaker) but it may also pick up a lot of interference, because it is probably unshielded.

Basically, what's the rule of impedance? Input = output, input output or what?

Input = output is called impedance-matching (good for old land-line telephones), input output is looking for trouble :) .
Google these expressions and you should start to see the light.

lead_ears wrote: input output is looking for trouble :

No. Read the previous posts.

Noticing a theme here: people are confused as to my posts.

I am NOT putting headphones into line ins. nor is my HP output 300ohms, I'm talking hypothetically.
IF the headphone out was 300 - or something equally low - but I put this into a line in at, per se, 10kohm...

TBH I gave up and went back to the old way of "if it doesn't blow up, that's good enough for me"

Codemonkey wrote: ... I'm talking hypothetically.
IF the headphone out was 300 - or something equally low - but I put this into a line in at, per se, 10kohm...

yeah
and I said

" A good quality Headphone Amplifier can be used as a line driver.
see Silicon Chip Magazine for a design,
currently available from Jaycar Kits. "

any of the broadcast distribution amps are build like this
often capable of driving multiple 600 ohm loads from each output
...
well
prehaps NOT all of the outputs can be loaded below the 600 ohms

and can drive headphones that aren't too low

but primary use is as a line driver
with most following input sections being high 10k+

if you have a noise issue there may be ways to solve it

So headphone jacks on say, CD players can double as line drivers without causing noise other than that caused by the fact the equipment sucks...

"if you have a noise issue there may be ways to solve it"
Block all radio stations in the area, balance all the connections and upgrade the gear?

each headphone output needs to be looked at in isolation
A simple CD player could have any thing as a headphone amp
single chip ... transistors ... monolithic low power amplifier ... dual opamp in bridge mode

just too hard to predict

but ... in theory ... yes
unbalanced stereo line driver
with 15v peak

solving noise issues could be as simple as chosing the correct interconnect method
and a termination for the source equipment
see the Rane Notes

Boswell wrote: [quote=lead_ears] input output is looking for trouble :

No. Read the previous posts.Sorry, I just meant the contrary:
input > output is called impedance-bridging, input
I got my>

>_

Impedence is when that german scientist started researching metals and found that some conducted electricity better than others. His name was (insert german first name) Ohm. That's all ohms is. A basic measurement of how much electricity will pass through a wire. How thick a wire is determines how much eletricity will pass through it, and also what type of metal.

Hi, I certainly agree with you. Your advice is really very helpful for us.
Thanks a lot!

It's a spammer, ban him!
Man, 265 posts all spam, how slow are the mods :roll::lol:

I do keep wondering...

Um... I have a job...

Sidhu wrote: Amps need to drive a speaker the same as or less than their output impedance

no, No, NO! First of all, you will never find a speaker with impedance levels that of amplifiers (way, way under 1 ohm). If you did this the overwhelming majority of the power would be dissipated in the AMP, not the speaker.

Amplifiers are VOLTAGE SOURCES - they need to have as low an output impedance as possible, and they are RATED to drive a certain amount of power into specific loads (e.g. 4 ohms, 8 ohms).

A stout power amplifier will continue to double its output power each time the speaker load is cut in half:

100 W into 8 ohms
200 W into 4 ohms
400 W into 2 ohms

Most amps can't do this for a number of reasons - insufficient power supply, insufficient current-sourcing capacity of the output devices are chief among them.

But amplifiers are NOT impedance-matched devices.

The one we have goes 90W into 8 ohms. 120W into 4 ohms :o.
Terrible.

Here's an example of how impedance relates to output power.
From L-Acoustics' LA48A owner's manual: