Speaker/ Amp impdeance

There was a question about speaker impedances (8 Ohms vs. 4 Ohms.). On a list server that I follow. Several reponders mumbled about matching of the speaker impedance to the amplifier impedance. To me this sounded like a lot of hooey. I assume modern audio amps have very low output impedance. And that the 4 or 8 ohms is more about the maximum voltage and current that the amp can produce. But I wanted to check with any experts here first. (Phil Allison?) Before gently correcting them. And what about tube amplifiers? Do they have higher output impedances?

Thanks, George H.

Reply to
George Herold
Loading thread data ...

"George Herold"

** Fact:

Matching an amp's RATED load impedance to a speaker's NOMINAL impedance is what is meant.

Only the dumbest of jerks confuse * actual source impedance* with the former.

The two are simply NOT RELATED in value at all.

.... Phil

Reply to
Phil Allison

pedance

Thanks Phil, These are physics people. One of the freshman physics problems that everyone does is finding the load resistance that gives the maximum power from a battery with some internal resistance. This then becomes the 'model' for all impedance matching questions. I'll try posting a gentle correction...

George H.

Reply to
George Herold

Point out that half the total power is lost inside the battery, reducing available watt-hours in half... maybe worse. Batteries and power plants shouldn't operate that way.

John

Reply to
John Larkin

e

Yeah, I can try. There are other silly comments about reflections for the speaker that isn't 'matched' properly to the amp! Gawd, one misconception at a time. (It's very hard to change someones mind though.)

George H.

Reply to
George Herold

=mesnews_0_0428111011 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: quoted-printable

Of course there are several factors missing from these problems. Not your fault George. Reflections are not a consideration at audio frequencies as the wave lengths are very long compared to the connection length. Power loss in the source is relativley insignificant although mearsurable in Power Sytems because any individual load is miniscule. There are all sorts of variations to these generalisations but the point I (you) might need to make is that there is more to it than just source and load resistance even though the simple schoolboy battery and load problem is correct.

--
John G


------=mesnews_0_0428111011
 Click to see the full signature
Reply to
John G

Tell them that power and energy aren't the same thing. Perhaps they heard something to that effect somewhere back in high school physics.

How long *are* their speaker wires?

Reply to
krw

Modern audio transistor/fet/opamp amplifiers have low impedances 0.1 or less. An amplifier has a max output power, this does not change. Only with an amp calculated for driving 4 ohm with 8 ohm speakers can possibly not deliver the max power.

One other point is damping. When the cone of a speaker is moving it generates electricity. To dead stop the cone after a pulse the total impedance of the circuit should be as low as possible. Total impedance is amp impedance, wiring impedance, AND speaker impedance.

So 4 ohm is better for damping.

Tube amplifiers have high impedances. Usually there is an output transformer. This reduces the amplifier impedance.

--
pim.
Reply to
tuinkabouter

pedance

Well here is where at least some of them get their information,

formatting link

Was there ever a time in audio when 'electronic'* impedance matching was important?

George H.

*There was certainly acoustic impedance matching in the old horns attached to a needle... no electronics.
Reply to
George Herold

If you had an old-fashioned no-feedback class A tube amp, like in an old radio, you'd get maximum volume, which you'd probably want, if the amp and speaker impedances were equal.

John

Reply to
John Larkin

"John Larkin"

** Not even then - cos the source impedance of such a stage is much higher then the optimum load impedance. Where a beam tube or power pentode output stage is used, Z source is around 10 times the optimum load.

Makes the speaker effectively current driven, providing the characteristic sound of a tube radio and also many tube guitar amps.

..... Phil

Reply to
Phil Allison

ps

=A0impedance

he

Oh, So if I was making just a class A emmitter follower to drive the speaker, I'd want the DC idle current equal to the max at full volume... I'd then have equal impedances.... Still it seems wrong to call it "impedance matching".

George H.

Reply to
George Herold

=A0higher

t
c

Thanks Phil, is that without an output transformer? Seems like a very wasteful way to make sound.

George H.

Reply to
George Herold

"George Herold" ...

Thanks Phil, is that without an output transformer? Seems like a very wasteful way to make sound.

** My god you are a colossal f****it.
Reply to
Phil Allison

Gee Phil, What did I say wrong now? I don't know anything about tube audio amps. I thought the output transformer was there to 'transform' the relative impedances. So it doesn't make sense to compare impedances on each side of transformer. (unless it's a one to one transformer)

George H.

Reply to
George Herold

--
You're missing the point, which is that if you have a tube-based
amplifier with, say, a 250VPP swing in plate voltage and an 8 ohm
 Click to see the full signature
Reply to
John Fields

--
Of course.

Take a look at almost any tubed radio or audio amplifier and you'll
 Click to see the full signature
Reply to
John Fields

--
Why not?

After all, what the transformer is doing is making the tube think that
 Click to see the full signature
Reply to
John Fields

).

t

amps

re

=A0impedance

h the

Thanks for the nice explanation John, You use the turns ratio of the transformer to match the impedances. Do you need to specify the resistance of the load/source too? I'm pretty much an idiot when it comes to tube amps. (If you couldn't tell.)

George H.

Reply to
George Herold

ry

I meant that a transformer with a one to one turns ratio doesn't change the impedance.

George H.

Reply to
George Herold

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.