# Impedance lesson

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#### Disco-Pete

Paid Member
Okay so how/why is a high impedance speaker an easy load for a ss amp? The higher the impedance the lower the output. Seems counter intuitive.

#### rayma

The higher the impedance, the lower the current. i = v/R
Most ss amps are designed as a voltage source, so the output voltage
is independent of the load. Not so for the current. Reactive loads are
even more difficult, since current peaks can be several times higher
than would otherwise be expected with resistive load.

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#### Galu

To put it simply, a 2 ohm load comes closer to being a direct short than an 8 ohm load.

Just imagine how much your amp would struggle if asked to push current through its shorted speaker terminals!

#### Disco-Pete

Paid Member
To put it simply, a 2 ohm load comes closer to being a direct short than an 8 ohm load.

Just imagine how much your amp would struggle if asked to push current through its shorted speaker terminals!
So how does the speaker impede the current?

#### BYRTT

So how does the speaker impede the current?

Most transducers impedance curve will be mounting situation dependant, current looks be the reverse of that executed impendance curve, in below free Xsim helped model curves.

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• 1060.png
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#### Galu

So how does the speaker impede the current?
I have to assume we are going back to basics here, so I hope the following may be of assistance.

A deeper explanation may be found here: Loudspeaker Impedance - Stetron

The opposition of a loudspeaker to alternating current is not simply due to resistance.

At certain frequencies a loudspeaker behaves like an inductor or a capacitor.

This introduces additional opposition, called reactance.

The total opposition to alternating current is called impedance and is measured in ohms.

Impedance (Z) is a complicated sum of resistance (R), inductive reactance (Xl) and capacitive reactance (Xc).

Although resistance does not vary with frequency reactance does, which results in the typical impedance versus frequency graph shown in the attachment.

#### Attachments

• Impedance Curve.png
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Okay so how/why is a high impedance speaker an easy load for a ss amp? The higher the impedance the lower the output. Seems counter intuitive.
You are right in the sense that the amp has to produce a higher output voltage to transfer power to a higher impedance speaker. Maybe we should be talking about speaker efficiency. The more efficient the less power the amp has to transfer for the same sound level. So a high efficiency speaker is literally an easier load for an amplifier for the same sound level.

Another aspect is the impact on the stability or other electrical behaviour of the amplifier circuit with different impedance loads. Using very low Z speakers, like less than 3 or 4 ohms, can cause problems with some designs even if the power transfer is low.

#### Disco-Pete

Paid Member
I have to assume we are going back to basics here, so I hope the following may be of assistance.

A deeper explanation may be found here: Loudspeaker Impedance - Stetron

The opposition of a loudspeaker to alternating current is not simply due to resistance.

At certain frequencies a loudspeaker behaves like an inductor or a capacitor.

This introduces additional opposition, called reactance.

The total opposition to alternating current is called impedance and is measured in ohms.

Impedance (Z) is a complicated sum of resistance (R), inductive reactance (Xl) and capacitive reactance (Xc).

Although resistance does not vary with frequency reactance does, which results in the typical impedance versus frequency graph shown in the attachment.
You are are definitely not making an *** of you and me here
Thanks for the explanation and link

#### Galu

Thanks for the explanation and link
Thanks for the feedback.

I wasn't sure where to pitch it - there's such a lot of physics involved!

#### N101N

The higher the impedance the lower the output.

???

The higher the impedance the lower the mass / charge / current / weight.
The higher the impedance of an object (speaker), the smaller is the current in that object (speaker).
It takes less force to move a lighter object.

#### N101N

Enchanting Controversial Sonnet

Currents do not flow.
Currents do not return.
Currents do not go anywhere.

Currents do not drive currents.
Currents do not drive voltages.
Currents do not drive anything.

Currents cannot be sensed.
Currents cannot be sourced.
Currents cannot be dumped.
Currents cannot be fed back.

Eternal loving Providence shines forth resplendent
Bringing deliverance to all.
Such a miraculous spectacle.

#### Disco-Pete

Paid Member
Enchanting Controversial Sonnet

Currents do not flow.
Currents do not return.
Currents do not go anywhere.

Currents do not drive currents.
Currents do not drive voltages.
Currents do not drive anything.

Currents cannot be sensed.
Currents cannot be sourced.
Currents cannot be dumped.
Currents cannot be fed back.

Eternal loving Providence shines forth resplendent
Bringing deliverance to all.
Such a miraculous spectacle.
But they do undulate

#### nigelwright7557

I have to assume we are going back to basics here, so I hope the following may be of assistance.
The total opposition to alternating current is called impedance and is measured in ohms.

Impedance (Z) is a complicated sum of resistance (R), inductive reactance (Xl) and capacitive reactance (Xc).

Square root of (R squared+(XL squared - XC squared))

.

#### JMFahey

Impedance lesson
Okay so how/why is a high impedance speaker an easy load for a ss amp? The higher the impedance the lower the output. Seems counter intuitive.

Quite the contrary.

1) ss amps in general are quite good (near to perfect) voltage sources
So much so that they will put out almost same voltage from rated impedance load to no load (infinite impedance) , go figure.

2) power out is V^2/impedance or V^2/Z

3) amp dissipation is a fraction of output power

so when, say, Z is doubled:

4) power is halved

5) dissipation is halved.

Which by definition is easier on the amplifier.

as a side note, components have maximum current limits, but no minimum current ones, so:

6) doubling Z halves current, putting devices used further away from a maximum limit.

What of the above you find counter-intuitive?
Please feel free to express yourself.

#### PRR

Paid Member
We do NOT need to get into the wacky impedance of real speakers to address Discopete's basic question.

We do need a tight grip on Ohm's Law.

I have a power line to my house. Rated 240V, 100A max.

Say I know the "ohms" of all my appliances. (And say all my appliances are 240V.)

A 60W light-bulb is 240V 0.25A. (240V*0.25A is 60 Watts.) Its resistance is 960 Ohms. (Hot; nevermind the part-instant while it is cold.)

The toaster is say 240V 5A, 1,200 Watts, 48 Ohms.

The dryer is 240V 20A, 4,800 Watts, 12 Ohms.

The water-heater of my dreams is 240V 60A, 14,400 Watts, 4 Ohms. (mine is really 1/3rd this power.)

Which is the "easy" load for my power line? (And my power Bill!)

The light-bulb is easy, the power line has "no" heat", I can afford to leave the lamp on all month. (7 bucks.)

If I ran the monster water heater and two dryers, I'd hit 100 Amps. The wire is literally rated 95 Amps (in warmer states) and would run warm at that load. The electric bill for a month-straight of that would be \$2,700 (gasp!).

So the 960 Ohm lamp is "easy", the 4 Ohm heater is "hard" (and heater+2dryers, 2.4 Ohms, is ridiculous).

The flip-side is that the 60 Watt 960 Ohm lamp will not warm the house enough to notice. Not getting a lot of work done. Whereas running 4 or 2.4 ohms of loads will cook the house very quickly! (It's twice the power of my whole-house gas burner.)

#### N101N

Panta rhei. A profound thought of a profound mind.

It is a not commonly known that Heraclitus made an exception for electric current (?!?)

#### PRR

Paid Member
> Heraclitus made an exception for electric current (?!?)

Citation needed.

However I met a passage in fiction which weaves electricity through Christian dogma.

"Is it not said, In the beginning was the Word and the Word was God? Did not all being begin with a bolt of lightning? It struck the sea and the sea conceived. All is charged. The words that tell of charge are themselves charged. The ampere is produced by one watt acting through one ohm and it is equal to one coulomb per second and its sign is I. And I-ampere is by interpretation God the Father, and watt is What the Ineffable, and coulomb is by interpretation Dove, which is to say the Holy Ghost, and ohm has the sound of homme, which is Man. In short, I saw that God is Electricity. And I said weeping, 'Why me, O Lord, why me?' But His will I will not resist."

Seven Day's Wonder, by Edward Wellen
The Magazine of Fantasy and Science Fiction, March 1963

#### N101N

Well, that assertion of mine can only be refuted, I`m afraid. "Electric current" was introduced some two thousand three hundred years later, just like "electricity". It was Ampere who coined the phrase "(I)ntensité de courant" in the eighteen hundred twenties, and currents have, after all, a propensity to flow as a phenomenon.

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