Current Questions

Take a typical amplifier with a set of 28V rails,

V = I R

So I =V/R

A speaker with an 8-ohm impedance would need a maximum of 3-1/2 Amps
A speaker with a 1 ohm impedance would need 28A 
4-ohm = 7A
2-Ohm  = 14A

Which is why those impedance plots are worth a look when considering speakers.

The impedance phase is important too, but beyond the scope of the question… But it gives you something to look forwards to. 😉

Yo Holmz, I appreciate the effort but you lost me in the first line. Rails? Volts? In the the equation V = I R, I assume that V is volts but what is the other stuff?
 

Still, there may be some gold in the stream. Is current measured in amps? And since low impedance speakers are harder to drIve, does that mean that they require more current, i.e., more amps. Am I right so far? Where does volts fit into the picture?

So when someone says that a particular speaker needs a lot of current, he could just as easily say that a speaker is low impedance and needs a lot of amps. Does that make sense?

But I’m left with a big question. If it’s true that current is measured in amps, what is being measured? Some kind of energy? What kind of work does this energy do in a stereo system?

You’re at a crossroads-

Simply enjoy the music or get TOO much information about what going on and learn how perfectly imperfect this hobby is.

I appreciate the effort but you lost me in the first line. Rails? Volts? In the the equation V = I R, I assume that V is volts but what is the other stuff?

google is a wonderful tool:

Ohm's Law is V = IR, where V = voltage, I = current, and R = resistance. Ohm's Law allows you to determine characteristics of a circuit, such as how much current is flowing through it, if you know the voltage of the battery in the circuit and how much resistance is in the circuit.

"Need lots of current" = "Hard to drive" = have low impedance and/or high phase angles (high capacitance or inductance). 

Amplifiers that are mismatched to a speaker will not be able to produce a flat frequency response, but this is typically true in the bass, where impedance tends to drop and bass gets mushy or weak.

So far this thread doesn't have electrical misinformation in it.  It will soon.  I like homes' explanation.  I is current.  R is resistance.  Someone will eventually point out that a speaker isn't a purely resistive load but his explanation is a good way to look at it.  if you halve the resistance (R) you will approximately double the current (I).  In my first physics class I asked why C wasn't used for Current and never got a good answer.  i have a physics degree from the University of Chicago.  So we will keep using I for current.

I'll add one more thing:  many good amps will provide double the power to a 4 ohm speaker as it is rated for an 8 ohm speaker.  but some can't.  That is generally a current (amps) limitation.

Jerry

True about power doubling, but the real issue is not many amps sound nearly as good driving a 4 ohm load as they do driving a 8 ohm load or higher. This isnt just true of tube amps.

more grist for the mill

Technically speaking no amp can really double it's power when resistance is halved, the manufacturer underrates the 8 ohm power output to come up with that figure. 

@carlsbad wrote 

In my first physics class I asked why C wasn't used for Current and never got a good answer.  i have a physics degree from the University of Chicago.  So we will keep using I for current

The conventional symbol for current is I, which originates from the French phrase intensité du courant, (current intensity). Current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of electric current is named, in formulating Ampère's force law

Technically speaking no amp can really double it's power when resistance is halved, the manufacturer underrates the 8 ohm power output to come up with that figure.

That's really not what happens.  Sometimes this is true, but usually manufacturers want the maximum possible 8 Ohm rating for spec and bragging rights, so they don't want to underrate it.   Take a look at any of the dozens of measurements avaialble at Stereophile for SS amps, and  you'll find only a ltitle bit of underrating at 8 Ohms, it at all.

 

Yo Holmz, I appreciate the effort but you lost me in the first line. Rails? Volts? In the the equation V = I R, I assume that V is volts but what is the other stuff?

V = Volts

I = Amps

R = Resistance

Still, there may be some gold in the stream. Is current measured in amps? And since low impedance speakers are harder to drIve, does that mean that they require more current, i.e., more amps. Am I right so far?

Yeah

Where does volts fit into the picture?

Speakers are voltage devices, and most amplifiers are.

So when someone says that a particular speaker needs a lot of current, he could just as easily say that a speaker is low impedance and needs a lot of amps. Does that make sense?

yeah mon. exact.

But I’m left with a big question. If it’s true that current is measured in amps, what is being measured? Some kind of energy? What kind of work does this energy do in a stereo system?

This is all what used to be high school physics.

The speaker need to push the air to make sound waves, so it needs force not energy. If that force need to move, and do it a lot, then that called power… Just like engine force in a car is called acceleration, and is from torque. And speed is from power. One is instantaneous and the other happens through time.

The current it what is making the force in a piston speaker with a voiced coil.
But some of the big flat panel speakers are doing the pushing using voltage to make the force. And other big panels use current.

I think maybe the education system is not what it i once was, but a community college 101 course or a private tutor for an hour would pay off.

Best might be to just ignore the physics and enjoy the music.

@testpilot Thanks for the history of physics lesson.  I guess I never asked that question again after the internet was invented.  Now people pick up a lot more of those kind of facts.  

See?

The Force be with you....all beyond that is all the fiddly bits to Nirvana, although I prefer Enigma...*G*

It's easier to think about it in terms of energy storage than volts and current. The more energy an amplifier stores, the more current can be drawn from it. It is similar in concept to an electrical outlet for a speaker to "plug into".

An electrical outlet will give as much current as the load demands. If you took a piece of wire and shorted a wall outlet, the wire will burn (as well as the wires in the wall) if there was no circuit breaker. If you use the same wire to short a 9-volt battery, nothing happens. Ohm's law can explain the wall outlet, but not the battery. If the wire has a resistance of a tenth of an ohm, the current drawn from the wall outlet is 120 volts divided by a tenth ohm, or 1200 amps, which is lots of current. However, Ohms law says that same wire will draw 90 amps from the 9-volt battery (9 divided by a tenth). No way that will ever happen, a 9-volt battery will max out to half an amp. That limitation is because the battery does not store a lot of energy. The energy storage for the wall outlet is the transformer on the utility pole, which has tens of thousands times more energy than the battery and therefore can easily supply very high short circuit current. 

An amplifier is an energy storage device due to the power supply transformer and filter capacitors. The amplifier power rating at different impedances is a direct measure of the energy storage capability -- the higher the power rating, the more energy is stored, and the more the ability to deliver current to the speakers when the speaker impedance drop demands it .

The correlation I have is from car audio, where you must somehow grab as much current as possible from a 12v system. The alternator in your vehicle may provide a bit more voltage like 13v. A capacitor or ‘cap’ can placed in the current supply to suck up as much current as possible, so it can discharge it to the amplifier on demand. When you see the terms ‘high current amplifier’, the power supply of these amps is like a big capacitor for the energy needed to drive the speakers in momentary high demand situations. When I look at a toroidal power supply I see a big thing that holds a lot of juice. 

When I look at a toroidal power supply I see a big thing that holds a lot of juice. 

What you should see is a transformer that keeps the magnetic filed inside.

It holds no juices.

GS5 etc.,

your answer begins to explain why high current amplifiers tend to cost more and are less commonly found in mid-fi…they require larger transformers and more storage capacity.  I believe Krell was first to go for broke in this area. How does this all apply in the world of class D?  Maybe it was Bob Carver whose cube amp broke this open by generating high current capacity without big storage?  

I believe Krell was first to go for broke in this area. How does this all apply in the world of class D?  Maybe it was Bob Carver whose cube amp broke this open by generating high current capacity without big storage?  

In the chicken versus egg sense, it was the hard to drive speakers, which then became a problem to solve with amps that had the current to drive super difficult s loads.

I’ll quote myself 😎 from post #2:

Which is why those impedance plots are worth a look when considering speakers.

I remember looking t the curlicue plots of phase angle in Audio...couldn't interpret what they meant worth a da**!  Ditto Stereophile's phase angle overlays on their impedance curves.  Anyway, those Krell amps sure had some bass.  Since many Class D amps quote the same output power into 4 and 8 Ohms, I'm wondering how that relates.  Many comparisons say Class D has rock solid bass as a general characteristic.  The NAD M33 certainly got great acceptance from the usual suspects.

let's keep this simple. Voltage is the "force" pushing electricity through the speaker.  Current is the amount of electricity that moves.  They are related by the resistance of the speaker (or whatever) to the flow.  If it has little resistance, lots of electricity will flow.  This varies by many factors in speakers, and dynamically changes with frequency etc.  Some speakers are "easy" to drive (lots of resistance, don't need to push much current)others the reverse.

Note that instantaneous current it typically more useful than continuous.  Music is nto continuous and has a peak-to-average ratio of 7-15X.

G

I'm going to shoot for a non-technical explanation which is what I think you are looking for.

We'll take two examples. #1 is a speaker that has a nice flat impedance of 8 ohms across its entire frequency band. Devore speakers, for example, are designed with this goal in mind. This type of speaker is easy for an amp to drive. Any good quality amp that is rated for enough watts to make the speaker go loud will allow the speakers to operate with a reasonably flat frequency response.

Example #2 is a speaker that has a variable impedance, say 8 ohms, at some points in the frequency spectrum and a lower impedance of say, 4 ohms, at other points. When the impedance drops the speaker will draw more power from the amp if it is available. If it is drawing 20 watts at 8 ohms it will potentially draw 40 watts at 4 ohms.

So what happens in example #2 if the amp is rated for 100 watts at 8 ohms and 100 watts at 4 ohms? The speaker will not produce a flat frequency response. The amp doesn't have enough current to double its power into 4 ohms and the result will be reflected in lower output in the frequency range where the impedance is 4 ohms. In other words, using a low-current amp on a demanding speaker acts like an unwanted tone control.

So why don't all amp manufacturers make their gear so that it doubles the output with each halving of the impedance? The simple answer is cost and practicality. I'm running a pair of Thiel CS6 speakers which dip below 3 ohms in part of the spectrum and I'm powering them with a Krell KSA 300S which puts out 300 watts at 8 ohms, 600 watts at 4 ohms, and 1200 watts at 2 ohms. This amplifier was quite expensive in its day (mid 90's), weighs 185 lbs, and runs very hot. Most people would not consider it practical to own.

So why don't all speaker manufacturers make their speakers with a flat impedance curve? There are hundreds of tradeoffs in speaker design and several high end speakers have difficult impedance curves which require monster amps. Wilson and Thiel are notorious examples. In order to meet their specific goals for sound, these speaker designers are willing to require their customers to buy a very limited selection of amps that can supply high current (a lot of watts into low impedances). At audio shows you will often see large Wilson speakers powered by D'Agostino amps which are heavy, expensive, and double their output with each halving of impedance. The large Pass amps also have this capability.

A clarification: Impedance is different than sensitivity. There are speakers that have low sensitivity (say 86 db) that also have a nice flat impedance curve that stays around 8 ohms. In this case you can get away with an amp that puts out reasonably high wattage (say 200 watts) but doesn't increase its output at lower impedances. Even with the high wattage an amp of this type can be reasonably small and light weight or be powered by tubes. The most brutal load that an amp has to deal with is a low sensitivity speaker that also has a difficult impedance curve. This is what people mean when they say that certain speakers "need a lot of current."

Because there is such a range of sensitivity and impedance between speaker models it is imperative that a buyer analyze how much power the speaker needs before buying. If someone bought my CS6s and hooked them up to a high quality expensive tube amp they would sound terrible. There would be a nasty suckout in the upper bass region and the sound would be anemic. On the other hand, you wouldn't want to hook up my big Krell to a pair of Avantgarde horn speakers that only require a few watts to play loud.

So the point of all this is "current" has become sort of a general way to warn potential buyers that certain speakers need a beefy amp. The specification dealing with output at various ohms is critical to note. Matching a speaker to an appropriate amp is a big factor in achieving good sound.

Here is a good video from John Devore that explains this stuff in basic terms.

@gs5556 + 1

I can't believe no one has answered the OP's original question. What is current? To do so we need to go back to electricity 101. Forget Ohm's law for now. Think of electricity as the flow of water in a pipe. Current is like the flow of water. It is actually the flow of electrons. Voltage is the pressure that is causing that flow. Resistance is anything that restricts the flow in any way such as a restriction in the pipe or water flowing over rocks etc. If you think of an electrical circuit in terms of plumbing, it's a very good analogy.

To determine if an amp is "high current" - ask the salesman to take off the cover. Look for:

- one or two metal boxes or toroids (transformers) - bigger is better;

- several cans (capacitors) - again, bigger is better;

- a dozen or so 1" squares with 3 whiskers or ovals (power transistors) mounted on the inside of an exterior surface - yet again, more is better.

All of these are required to make a "high current" transistor amplifier. Or you could just ask for a brand that’s famous for it, like Bryston.

Just as well the electron flow doesn't spill out of any unused wall sockets.

And yes, it is important. Otherwise amp could go "poof" when a few undersized power transistors are asked to handle too much power. First the amp would just sound nasty - that's a warning. Power is defined by current x voltage, that is, IV.

falconquest,

 After skimming through these many posts about a simple question, your answer has the best potential to answer the basic question asked by someone admits right up front that this isn't exactly his line of expertise. Thanks for that. The fact that some of the posts accurately describe current with the inclusion of OHMS law, or other related truth, does not help the person who is asking in the first place. 

 When working with customers, one goal is to connect with them on the level that they are at and not just spew out your vast knowledge, using terms, definitions, laws, ad infinitum about the product or subject. What seems easy to understand with a background for reference in physics or electronics, is not where most people are at.

 In my case, don't even start with the basics of a tax form. Screw it, I give you the papers and pay you money for that. Explanation will often lead to even more confusion. 

Thank you everyone for trying to drag me into the light. 
 

Unfortunately it seems that the light isn’t so bright. The implication of Terry9’s post—take off the cover and look for this and that—is that there isn’t a spec I can look at and get quick understanding of a given amplifier’s current capabilities. No equivalent of watts as it relates to power. Is that right? Nothing that will give me even a rough idea? Something for fools like me who didn’t write a dissertation on Ohm’s law?
 

I could easily be wrong but it seems that, back in the 1980s and ‘90s, most every amp doubled in power as it moved from eight ohms to four. Like a manufacturer would be embarrassed if it didn’t. I think even my Harmon Karden 330c went from 20 watts to 40 as the impedance changed. (Dropped? Rose?) Is that just a warm, fuzzy feeling I’m getting from the past?

4krowme, we went to the same school of income tax preparation. I’d probably be better off if I stayed there for electronics. But I hate to be completely ignorant when talking to a salesman or reading glowing marketing materials. Knowledge is power and I don’t like being defenseless. 

When a speaker is determined to need a lot of current it means it is not efficient at converting amplifier power to sound level.  Therefore you will need greater power than a more efficient speaker would take. This involves both sensitivity and impedance. A speaker having a true 8 ohm impedance and is 90dB sensitive at 8 ohms requires far less current than one that  has 4 ohms impedance and is less sensitive. 

Best i can do at the moment.

falconquest,

 After skimming through these many posts about a simple question, your answer has the best potential to answer the basic question asked by someone admits right up front that this isn't exactly his line of expertise. Thanks for that. The fact that some of the posts accurately describe current with the inclusion of OHMS law, or other related truth, does not help the person who is asking in the first place. 

If only thing should be understood here, it is that the speaker’s impedance is what determines whether a particular amp is gong to work or not work.

The equation (V=IR) itself, defines a relationship between resistance and current.

So we need to understand either the I, the current, (which relates to the amplifier) or we need to understand the R (which relates to the speaker).

Which means that:

we either start with amp, and determine what speakers are not going to work, and look at the rest that will.

or

we start with the speaker, and determine which amplifiers will work and which will not, and then go from there.

We can talk about current in isolation, but it seems easier if we started with an example of what speakers you wanted to consider running.

Before I continue, let me say that holmz gets it, i.e. in reference to my post. No BS, no put down or what is too commonly seen on this site, so thanks for that. Better that we can explain our writings to each such as is being done here. 

 Now I do agree with the idea that this involves more than a single component. The basic question however, now addressed, was about current and it's definition for the common man. We tend to automatically answer in a way we know, but not everyone knows the meaning behind V=IR, or E=mc2 for that matter. So from the beginning there little chance by this definition that the OP will 'get' the meaning.

 Man, I do remember all the talk back in the day about current/amperage output of power amps, X WPC, TIM and anything 'new' to sell.  In some cases it was relevant for the consumer, but then not so much in other cases.

 Once the idea of current is basically understood, then it is time to move to the next logical step of current need. Sorry, couldn't resist.

To my knowledge, current capacity is rarely discussed. Twenty years ago someone used to talk about the number of joules (energy) stored in the capacitors of their amps, but I haven't seen that for a while.

Speaking of twenty, that's Bryston's guarantee. They build their stuff to last, and last it does. Not a shill, just a satisfied customer - I've owned one or more of their amps for years and years, now running the subs in my HT.

Before I continue, let me say that holmz gets it, i.e. in reference to my post. No BS, no put down or what is too commonly seen on this site, so thanks for that.

I’ll work on being more “common” and lace in put downs and humiliations 😁

(On a serious note, thanks man.)

It is easy to assume that others have the equivilent of a H.S. Electronics shop class or HS physics, but it is apparent that this is not a universal truth.

On the sales side, there is push for saving parts costs and manufacturing costs. And hiding factual performance in specs that make it hard to get to what exactly a piece of gear provides.
That makes it very hard to not be sold garbage or gear that is marginally appropriate.

On the subjective side:

Speaking of twenty, that's Bryston's guarantee. They build their stuff to last, and last it does. Not a shill, just a satisfied customer

^This^ person, and others I have know, speak very highly about the Bryson gear. I do not know much about their gear, except that a lot of people that I respect (and who are use similar speakers) use Bryson.

So if one is disinclined towards understanding the inner workings, then finding what others are using successfully with similar speakers (in terms of amplifiers) is a good strategy… assuming that success often repeats itself. 

Think of it in terms of plumbing.
Water pressure is equivalent to voltage. Resistance/impedance is analogous to a valve which controls the flow. The water flow is the current. The more the water flow, the better your shower. The more current into your speaker, the better your sound.

Back in the late 70’s I read a review on a power amp made by (I forget) stating that the amp was capable of 35 amps of power per channel. This sort of talk lasted for a bit longer and constant current, power envelope, and other sorts of talk too.

It is pointed out in a previous post to sell the high points of a product within the confines of its capabilities. So, if there is a scratch on the hood, make sure and open it quickly and talk about the engine.

we start with the speaker, and determine which amplifiers will work and which will not, and then go from there.

We can talk about current in isolation, but it seems easier if we started with an example of what speakers you wanted to consider running.

Not to get too technical but in terms of current, since the speaker is a "load" can we not say that the speaker will have a certain current "draw" in order to reproduce the signal being sent? If the amp does not have the capability of providing that draw, is that what leads to the amp clipping? In other words, the question isn't so much amp output current but, as some have been saying, the amount of current draw by the speaker. One must understand that and choose an amp that will meet that requirement. I have never seen specs. for either but I have experienced it.
 

Not to get too technical but in terms of current, since the speaker is a "load" can we not say that the speaker will have a certain current "draw" in order to reproduce the signal being sent?

At a specific voltage and frequency, then yes. The draw is linear with voltage in the equation V=IR or I=V/R.

If the amp does not have the capability of providing that draw, is that what leads to the amp clipping?

There is clipping as in trying to reach a voltage that is too high to achieve as it is beyond the rails.

And there is inability to provide the current. When the current cannot be provided, then the desired voltage will not be achieved. This would be more of a distortion than clipping. (Almost like compression).

In other words, the question isn't so much amp output current but, as some have been saying, the amount of current draw by the speaker. One must understand that and choose an amp that will meet that requirement.

If the speakers draw less, or equal, to what the amp can provide, then all is well.

I have never seen specs. for either but I have experienced it.

The specs for impedance is common for most decent speakers, and maybe half of the speakers show it.

Just reading through this thread and came across this statement

Current is like the flow of water. It is actually the flow of electrons.

I have encoutered this depiction many time in various threads - I might have been guilty of using it myself way back when - oops🙄

Here is a very good explanation...

Drift velocity, the average speed at which electrons travel in a conductor when subjected to an electric field, is about 1mm per second. It’s the electromagnetic wave rippling through the electrons that propagates at close to the speed of light. The dimensions of the wire and electrical properties like its inductance affect the exact propagation speed, but usually it will be around 90 per cent of the speed of light – about 270,000 km/s.

This clip is from the following link if you would like to read more.

• https://www.sciencefocus.com/science/how-fast-does-electricity-flow/

With an audio (AC) signal, the electrons shuffle between electrons in the wire randomly

Regards - Steve

High current amps are heavy.  That's a rule of thumb.  Transformers and heat syncs.  Current creates heat.

I understand the "I" for current and its origin.  Why do all or most electrical items use the letter "A"  example:  1.2A

I understand the "I" for current and its origin.  Why do all or most electrical items use the letter "A"  example:  1.2A

It is same as referring to resistance as a thing, and the quantity of the resistance in ohms.

Similarly “speed” can be given in Mach number, MPH or KPH, or percentage of the speed of light… etc.

@daledeee1 "Why do all or most electrical items use the letter "A" example: 1.2A"

A for amps. Amp for Ampere.

A for amps. Amp for Ampere

you need to watch "the story of electricity" done by, i believe channel 5 in the UK with a physics professor from U sussex. Superb and answers many fundamental questions.

And as both an engineer, and also one who's stupid enough to have spent a lot of time designing high end stuff commercially (its a terrible way to make money) -my advice is absolutely learn some basic engineering, but really dont worry about it.  In the end all this suff is a trade off of cost/size/heat.  What is important is that inefficient or lower impedance speakers, which demand lots of those current things (amps, or getting really techie, movement in electrical charge) need beefy amps.

Beware a little knowledge.  Continuosu current emands serious beef, weight, size etc. But most music is not continuous - it has a peak:average ratio of about 10X. So what one really needs is the ability to seamlessly burst. The burst is actualyl voltage, but (because I=V/R remember) if it doesnt have the current ot back up its "ask",the burst will be truncated into some pathetic shadow of its self.  Flabby at best, loss of dynamics, etc.  Distortion of one kind or another.

So given how inter-related these thigns are either learn it really really well, or dont assume you can make major inferences.

Sorry: complex.