Speaker/ Amp impdeance

G

George Herold

Guest
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.
 
"George Herold"
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.
Click to expand...
** 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
 
On Wed, 27 Apr 2011 06:50:17 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"



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.

** 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

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.
Click to expand...
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
 
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"



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.

** 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
Click to expand...
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.
 
On Apr 27, 10:46 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 27 Apr 2011 06:50:17 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"

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.

** 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

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.

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- Hide quoted text -

- Show quoted text -
Click to expand...
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.
 
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
 
On Wed, 27 Apr 2011 08:11:13 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 27, 10:46 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 27 Apr 2011 06:50:17 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"

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.

** 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

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.

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- Hide quoted text -

- Show quoted text -

Yeah, I can try.
Click to expand...
Tell them that power and energy aren't the same thing. Perhaps they heard
something to that effect somewhere back in high school physics.

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.)
Click to expand...
How long *are* their speaker wires?
 
Op 4/27/2011 3:08 PM, George Herold schreef:
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?
Click to expand...
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.
 
On Thu, 28 Apr 2011 06:20:28 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"



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.

** 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

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

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c2

Was there ever a time in audio when 'electronic'* impedance matching
was important?
Click to expand...
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
 
"John Larkin"

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.
Click to expand...

** 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
 
"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 fuckwit.
 
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"



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.

** 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
Click to expand...
Well here is where at least some of them get their information,

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c2

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.
 
On Apr 28, 9:46 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 28 Apr 2011 06:20:28 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"

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.

** 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

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

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c2

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

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- Hide quoted text -

- Show quoted text -
Click to expand...
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.
 
On Apr 28, 9:59 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"John Larkin"

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.

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

George H.
 
On Thu, 28 Apr 2011 07:27:42 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 28, 9:46 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 28 Apr 2011 06:20:28 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"

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.

** 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

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

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c2

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

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- Hide quoted text -

- Show quoted text -

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.
Click to expand...
---
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
loudspeaker as a load being driven at 10 watts, then the current in
the speaker would be:

P 10W
I = sqrt --- = sqrt ----- = 1.25 amperes, RMS
R 8R

Theoretically, the best efficiency you can get out of a class "A"
amplifier is 50%, so if the tube is dissipating 10 watts when it's
driving 10 watts into the load, then the plate resistance of the tube
must be:

VRMS˛
Rp = ------
P

Then, since:


(VPP/2) 125V
VRMS = --------- = ------ ~ 89.3V,
sqrt(2) 1.4


The plate resistance must be:

89.3V˛
Rp = ------- ~ 800 ohms
10W

We're now stuck with the problem of how to transfer 10 watts from an
800 ohm source into an 8 ohm load, and to solve it we'll do impedance
matching by using a transformer with an 800 ohm primary connected
between the tube's plate and its supply, and its 8 ohm secondary
connected across the loudspeaker.

--
JF
 
On Thu, 28 Apr 2011 06:20:28 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:


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

George H.
Click to expand...
---
Of course.

Take a look at almost any tubed radio or audio amplifier and you'll
find an "output transformer" designed to match the output tubes'
impedance to that of the loudspeaker load.

--
JF
 
On Thu, 28 Apr 2011 10:06:57 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 28, 10:35 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"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 fuckwit.

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.
Click to expand...
---
Why not?

After all, what the transformer is doing is making the tube think that
it's connected to, say, 1000 ohms and the loudspeaker to 16, so both
impedances are being matched.
---

(unless it's a one to onetransformer)
Click to expand...
---
How do you mean?
---

George H.
Click to expand...
--
JF
 
On Apr 28, 10:35 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"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 fuckwit.
Click to expand...
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.
 
"John Fields"
Was there ever a time in audio when 'electronic'* impedance matching
was important?


---
Of course.

Take a look at almost any tubed radio or audio amplifier and you'll
find an "output transformer" designed to match the output tubes'
impedance to that of the loudspeaker load.

--
Click to expand...
** Two errors:

1. The OPs question was about *equal value* impedance matching of sources
and loads.

2. The source impedance at the plate of a tube output stage is not the same
as the optimum load impedance.

In general - the *equal value matching theorem * has no application to
sources using active devices.



...... Phil
 
On Apr 28, 1:22 pm, John Fields <jfie...@austininstruments.com> wrote:
On Thu, 28 Apr 2011 07:27:42 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 28, 9:46 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 28 Apr 2011 06:20:28 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 27, 9:18 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"George Herold"

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.

** 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

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

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c2

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

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- Hide quoted text -

- Show quoted text -

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.

---
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
loudspeaker as a load being driven at 10 watts, then the current in
the speaker would be:

               P          10W
     I = sqrt --- = sqrt ----- = 1.25 amperes, RMS
               R          8R

Theoretically, the best efficiency you can get out of a class "A"
amplifier is 50%, so if the tube is dissipating 10 watts when it's
driving 10 watts into the load, then the plate resistance of the tube
must be:

           VRMS˛    
     Rp = ------
            P

Then, since:

             (VPP/2)     125V
     VRMS = --------- = ------ ~ 89.3V,
             sqrt(2)     1.4

The plate resistance must be:

          89.3V˛
    Rp = ------- ~ 800 ohms
           10W

We're now stuck with the problem of how to transfer 10 watts from an
800 ohm source into an 8 ohm load, and to solve it we'll do impedance
matching by using a transformer with an 800 ohm primary connected
between the tube's plate and its supply, and its 8 ohm secondary
connected across the loudspeaker.

--
JF- Hide quoted text -

- Show quoted text -
Click to expand...
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.
 
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