Guys,

You are all the absolute GODS of making things complicated. I didn't get involved in this but a lot of you have misconceptions about electronics.


Ernie:
Average power is definitely instantaneous. When you have DC voltage and current, which are both constant, your power draw will also be constant. Power consumptions varies with time, yes, but only if either voltage or current do as well. If you have an AC system, you have to integrate from time = 0 to time = infinity to get your average power. You can also plug in a specific time to see how much power is consumed at a specific time, t. When people say power, they almost always mean average power.


Since we are trying to be "correct", EMF is actually measured in volts per meter :).


There isn't a professional soul in electronics that wouldn't say a light bulb or speaker doesn't consume power. Of course it does. A speaker consumes power and converts it into an acoustic wave and heat. A light bulb consumes power and converts into light and heat. These are all transducers. They need to consume power to convert one form of energy into another.

I also saw another note someone made about AC resistance being different than impedance. This is not true. In DC, we have resistance. Inductance and capacitance do not exist. Inductors count as R = 0 and capacitors act as R = infinity.

in AC, a resistor has an impedance equal to its resistance since resistance isn't a function of frequency. It is the same for AC and DC.

In AC, capacitors have an impedance of 1/jwc and inductors have an impedance of jwl where w is equal to 2pi*freq.

I also noted that someone brought up skin effect. This is only true at high frequencies! You will NEVER have skin effect at the audible range of frequencies. As Ernie said, it literally has zero to do with this conversation and it was obvious that the entire paragraph was copy pasted from Wiki. Depending on what impedance you're working with, you'll need to be >= 500kHz to start seeing eddy currents.

This is honestly very basic stuff, guys. We learned about speakers in the VERY FIRST undergrad course electrical engineers take in circuit analysis. It is not complicated AT ALL.

A speaker is basically a resistor. Sure, it has some parasitic inductance and capacitance but for all intents and purposes its a resistor. As I said earlier, resistance is NOT a function of frequency. Yes, the parasitics will at some point come into play and make the speaker's response vary at different frequency's but this is NOT THE CASE FOR THE AUDIBLE FREQUENCY RANGE.

The speaker has a voltage applied across it by the amplifier. Based on this voltage it draws a specific amount of current since its impedance is fixed for the audible range. The voltage that is output by the amplifier will vary in amplitude based on volume and gain settings and of the actual amplitude of the signal it is amplifying. The signal it is amplifying is the input signal of the audio source connected to it.

When a speaker is specified at 60W it means that at a maximum it is capable of drawing or being fed 60W. A speaker cannot draw 60W if there is nothing to feed it 60W, thus the two go hand in hand. As an example, we have an 8 ohm 60W speaker and a 100W amplifier capable of driving an 8 ohm load. This equates to a maximum voltage output of 12.5V from the amplifier an a maximum accepted voltage of 7.5V at the speaker. While the speaker will only take a maximum of 7.5V, the amplifier can deliver all the way up to 12.5V if its gain is set higher than what is needed to drive an 8 ohm load at max volume.

Now lets please stop copy pasting from Wiki!

When have you seen a purely resistive speaker and how many speakers have fixed impedance over the audible range?

Also, when did E=P/R happen? 100W with an 8 Ohm load calculates to about 28.3V using a sine wave and a 60W speaker will take whatever it's given until it can no longer dissipate the extra heat, at which time it starts to go into thermal compression and then, mechanical and electrical failure. If the applied voltage is 12.5VAC, the speaker doesn't have much to worry about.

Speaker ratings often fall in the category of "Yeah, people say a lot of things" and while some speakers of that model may have lived through the number stated in the specs, only the ones that are specified as long-term and showing the conditions should be believed.

Alihashemi

To say that a speaker is basically a resistor is utter nonsenses! Just take look at any impedance plot of a typical speaker. More importantly take a look at a Smith Chart plot of a typical speaker! Your understanding of the electrical equivalent of a typical speaker is sorely lacking. I assure you the reactive effects of inductance and capacitance in a typical speaker are anything but parasitic! Try designing a power amp sometime, you will find out real quick.

A speakers impedance IS NOT fixed for the audible range. It goes from a resistive load a some frequencies to inductive then to capacitive! Again look at a Smith Chart plot of a speaker from 10Hz to 20kHz!

Average power is the sum of the instantaneous powers over whatever interval you choose, instantaneous power is one measurement, no interval to average!

YOU always have skin effect in an AC circuit! It may be very small but it is always present!

Ernie

The paragraphs were done AD HOC, sorry.

I have no idea what information this is meant to convey.

We've all definitely covered the basic questions of this thread and we've even gone far afield into subjects that have nothing to do with our actual need for knowledge. Much of the rest of this thread is a live test of us showing what we understand and how we choose to (or the limits of our capabilities to) express our thoughts.

I'm still going to make one more comment, though....

Speaking practically, YES, there is skin effect at audio frequencies. But you're being smart but dumb if you don't figure out if it matters. A chart at a Belden article on skin effect says that the "skin" is thicker than the entire wire at 20 kHz with 24 ga and 22 ga wire. 12 ga wire's skin effect reduces its conductive area to 75% at 20 kHz -- still giving us the equivalent cross sectional area equivalent to that of a wire between 13 ga and 14 ga in size.

FURTHERMORE, an effect at 20 kHz won't be heard, because the way it might manifest would be via distortion. The first overtone, where a distortion product might appear, would be at 40 kHz. So, speaking practically, it makes no sense to even look at 20 kHZ as a frequency of interest. This means skin effect would have even less effect than shown above.

SO WHILE THERE IS SKIN EFFECT AT AUDIO FREQUENCIES, IN OUR WORLD THE ACTUAL EFFECT OF SKIN EFFECT IS NEGLIGIBLE. SO PLEASE STOP BRINGING IT UP!

Mention that on some audio fora and they'll want your head on a pike.

Highfigh:

First, E is not used to denote a voltage, V is. P = V^2/R and I made a math mistake.

A load draws current based on its need. A power amplifier is a voltage source, not a current source. It doesn’t drive the speaker with current.

G007:

Do you know what a smith chart is used for? This is typically used in the RF range for matching. For a speaker in the audible range, it is only an estimate. I’m pretty sure you won’t find a smith chart on any data sheet for a speaker. Please show me the smith chart you are mentioning.

I said that Instantaneous power is NOT OVER AN INTERVAL, but at a specific time. You do realize the sum of the instantenous power is the same integrating the power function over time = 0 to time = infinity?

I am not an expert in audio, I will always admit. It is not my area of work or study. But there is more to than just the impedance of the speaker varying over frequencies. I agree, you are right and I was wrong, but regardless, the maximum power drawn from a speaker will still be the relevant to the DCR as the the lowest impedance a speaker exhibits is its DCR.

I never denied that skin effect exists. It always does in AC circuits, but like Ernie said, you have to figure out when it matters to you. Just because it schists doesn’t mean it’ll actually effect your operation. It still has absolutely zero to do with the OP.


EDIT: for math purposes :)

V is used to denote a voltage. E is used to denote electromotive force, which is, of course, a force expressed in units called volts. This leads many people to think that E and V are the same. Because they are.


A load does not draw current based on its need. It draws current based in its impedance at the moment. I say "at the moment" only to be picky-correct. Since loudspeakers, our putative loads here, do not present the same load at all frequencies, the load at any moment depends on the particular frequencies being played.

In school, my professors told us to ignore skin effect below 10MHz. But, at the same time they showed how power companies could improve their bottom line by paying attention to it at 60Hz. After the audiophiles jumped on the skin effect train, I made a few crude calculations. Yes, there is an effect at 20KHz, but when expressed in dB, the loss is not very significant. In terms of speaker current, speaker impedance typically rises significantly at 20KHz, reducing the current and any associated speaker wire voltage drops. That last 0.0x Ohm increase in the wire's impedance at 20Khz is not a very significant fraction of the total circuit impedance.

In many calculations, E IS used to denote Voltage and it has been for a very long time. I have seen it used this way since my Physics class in 1974. Any subsequent training in electronics used either E or V, depending on whose books were used. E is used because it stands for Electromotive Force, which is measured in Volts, as you know.

You seem to be looking at current via the calculation but the rate of electron flow depends on voltage and resistance- ‘current draw’ is commonly used, but i think ‘flow’ is a better word- if the resistance is high enough, it’s definitely not being ‘drawn, especially since Voltage is equated to pressure. Electrons move through a conductor or circuit at a rate determined by its resistance and the voltage

Yes, I know an amplifier is a voltage source and if you read my first comments about the original question, I made that clear.

Alihashemi

The use of the Smith Chart in audio is not that well known but it is very revealing. The use of the Impedance Chart is what most people are use to, Magnitude versus frequency. What this plot fails to show is the movement from inductive to capacitive to pure resistive.

Google speaker impedance Chart and the Smith Chart will also show up.

When we discuss things on this forum, I am more interested in function rather than form, introducing elements that pertain but not strictly to the point. Athe point is to broaden our knowledge base.

Most driver measurements show the phase plot along with the impedance curve, so the phase angles can be seen.

Highlight

Yes, but I am talking about the total speaker system, not just the driver.

Now my skin itches. Thanks.

The system needs to be measured, too- it's an easy way to see if that product will cause amplifiers to puke, or not. Some crossover designers are more concerned with this and some just don't seem to care, with their roller-coaster impedance/phase plots. A few designers try to present a load that's close to purely resistive, too.