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Do speakers draw watts from an amp or get fed watts ?
This thread has 47 replies. Displaying posts 1 through 15.
Post 1 made on Saturday February 3, 2018 at 13:09
james_aa
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Do speakers draw watts from an amp or get fed watts ?

Eg. would a 60w speaker connected to a 100w amp draw 60w or get fed 100w ?
Post 2 made on Saturday February 3, 2018 at 14:27
buzz
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Neither.

Current causes heating and heating can cause fires.

Think about a home lighting circuit. Lighting circuits operate at a constant voltage (perhaps 120V). Let's say that it is a 1500 Watt circuit. This means that the circuit can supply a certain amount of current without overheating. Fuses are used to prevent over current situations that might result in a fire. This implies that one could safely connect up to (15) 100W lamps on that circuit -- each lamp drawing 100W from the circuit.

Speaker circuits are different because the signal level (voltage) varies from instant to instant. At the zero Volume setting or silent music, there is no current and one could connect a thousand speakers without hurting the amplifier.

Amplifier and speaker ratings are very slippery because there are no universal standards about how to specify the limits. An amplifier limit might be rated at 100W when driving an 8-Ohm load. This same amplifier would be rated differently if operated into a 4-Ohm load -- or the amplifier may not operate at all on 4-Ohm loads.

Speaker ratings are very complex because the same voltage presented to a speaker will result in more or less current -- depending on the frequency. Typically, the speaker will draw more current at lower frequencies and there will be a peak somewhere below 100 Hz. And, the maximum safe current varies by frequency. If you presented the speaker with a maximum level 20KHz tone for more than a few seconds, the speaker's tweeter will probably fail.

The speaker ratings quoted in the advertising literature are simply recommended maximum and/or minimum amplifier power for average use. If you think that this is a weaselly way to specify things, you are correct. However, in defense, the lay public could not deal with a series of graphs that properly lay out the speakers capabilities. Typically, the marketing department determines the maximum power number assigned to the product, not the engineering department. I tend to believe the number specified for low grade products (10W or so), I don't believe the 200-400W ratings for low grade braggart type products. If you give me a job "damage this speaker", I'll request a 50W amplifier, not a 200W gorilla. Certainly, I can ultimately damage the speaker using the gorilla or a wimp, but it will be a little more work for me.

I understand that the general public would like to purchase a 200W speaker, a 100W amplifier, and be confident that they could not hurt anything. I wish that it could work that way.

---

By the way, the above is how the amateur audio market deals with the physics of the situation. In professional sound contracting they talk about 70V systems, not 8-Ohm systems. It's the same physics, but the math is different (and, in my opinion, easier).
Post 3 made on Saturday February 3, 2018 at 16:13
Ernie Gilman
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buzz, I'm hardly the guy to say this, but this could have been answered more simply.

First, we don't know the guy's skill level, though the question is an indicator, but you don't need to scare him about a fire right at the outset.

Here's how I'd answer this:
The ratings tell us something about the capabilities of the components. The ratings are not enough information to tell us anything about the situation at the moment.

An amplifier rating shows how much power the amplifier can put out. A speaker rating shows the maximum power that the speaker can handle without damage. As mentioned, these ratings are slippery.

Also, you can connect a 60 watt speaker to a 2,000 watt amplifier and everything will be fine if you don't turn up the volume beyond the point where it's putting out 60 watts. A 2,000 watt amplifier with the volume turned down is still a 2,000 watt amplifier, even though, under this condition, it is not outputting anything at all.

In parallel fashion, a fire hydrant can output enough water to pierce the wall of a house, but a small faucet and hose can be attached to a hydrant and can gently water a lawn.

Amplifiers feed power to speakers. The impedance of the speaker (similar in effect to the diameter of a water hose) determines, in part, how much power goes to the speaker. With a hose, a larger diameter can let more water flow, but only if the faucet is opened up wide. With a speaker, a lower impedance can let more power flow, but only if the volume control is turned up more.

Eg. would a 60w speaker connected to a 100w amp draw 60w or get fed 100w ?

The answer to this is yes and no. The speaker's 60W designation tells you that you're going to blow it if you feed it more than 60 watts (well, within the slipperiness quotient, I'll call it, of the specifications). You'll feed it 100 watts because the amplifier can put out that much power if you turn the amp up loud enough.

That didn't turn out to be much shorter, did it?
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
OP | Post 4 made on Saturday February 3, 2018 at 16:32
james_aa
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Thanks, Ernie & Buzz

To pose the the starting point of what made me ask this question another way : how can you make sure that a speaker and amp pairing is correct and wont damage either ?
Post 5 made on Saturday February 3, 2018 at 16:55
buzz
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On February 3, 2018 at 16:13, Ernie Gilman said...
buzz, I'm hardly the guy to say this, but

Pot accuses kettle ...

Last edited by buzz on February 3, 2018 17:14.
Post 6 made on Saturday February 3, 2018 at 17:01
kgossen
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On February 3, 2018 at 16:32, james_aa said...
Thanks, Ernie & Buzz

To pose the the starting point of what made me ask this question another way : how can you make sure that a speaker and amp pairing is correct and wont damage either ?

Don't worry about ratings. You can blow a 50 watt speaker with 10 watts and play 100 clean watts through it. Look at efficiency, the more efficient a speaker, the less power required to get it going.

Power ratings on speakers and most amplifiers are a complete joke anyway.
"Quality isn't expensive, it's Priceless!"
Post 7 made on Saturday February 3, 2018 at 17:13
buzz
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james_aa,

In some respects you are asking for us to help you specify a car that is "totaly safe". The reality is that the operator is responsible for safe operation.

If the sound is clean, you will probably not damage the speaker. (I'm assuming that this is a decent quality product, and they are not hard to purchase from many, many manufacturers). An interesting counter intuitive rule of thumb is that: if the tweeter is damaged, the amplifier is too small. If the woofer is damaged, the amplifier is too large.
Post 8 made on Saturday February 3, 2018 at 17:24
Ernie Gilman
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On February 3, 2018 at 17:13, buzz said...
james_aa,

In some respects you are asking for us to help you specify a car that is "totaly safe". The reality is that the operator is responsible for safe operation.

If the sound is clean, you will probably not damage the speaker.

kgossen said as much, and it's true.

It's possible to have a line level signal that is large enough that an amplifier, turned all the way up, can distort. The simplest type of distortion caused this way is that a sine wave turns into something resembling a square wave.

A sine wave is a sound of only one frequency. A square wave has the same basic tone, but a horrendous amount of high frequency overtones are added by the way the signal is distorted. This will be WAY MORE such high frequency power than music ever contains.

Thus, while a speaker may play okay with 60 clean watts of power, 10 watts of horribly distorted power may blow it. And you'd expect the woofer to blow, because that's where most of the power usually goes... but remember that this kind of distortion has a lot of high frequency energy, so tweeters will blow!

There's a lot to it. Learn to recognize distortion, and avoid it. That's a really good rule for pretty much all of audio.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 9 made on Saturday February 3, 2018 at 19:15
Mac Burks (39)
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On February 3, 2018 at 13:09, james_aa said...
Do speakers draw watts from an amp or get fed watts ?

Eg. would a 60w speaker connected to a 100w amp draw 60w or get fed 100w ?

I am going to save you from reading all that craziness in the responses. Here is the actual answer to the question you asked.

On February 3, 2018 at 16:13, Ernie Gilman said...

The answer to this is yes and no. The speaker's 60W designation tells you that you're going to blow it if you feed it more than 60 watts (well, within the slipperiness quotient, I'll call it, of the specifications). You'll feed it 100 watts because the amplifier can put out that much power if you turn the amp up loud enough.

Also...

"Slipperiness quotient" is Ernie for the reality that watt ratings are usually a joke. Don't expect your 100W amp to "feed" 100W exactly. And don't think that you can turn your 50W amp all the way up with a 60W speaker and not blow it.
Avid Stamp Collector - I really love 39 Cent Stamps
Post 10 made on Saturday February 3, 2018 at 23:58
highfigh
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On February 3, 2018 at 16:32, james_aa said...
Thanks, Ernie & Buzz

To pose the the starting point of what made me ask this question another way : how can you make sure that a speaker and amp pairing is correct and wont damage either ?

By making sure the input level to the amplifier is enough to allow it to provide sufficient undistorted power to achieve the desired SPL and by making sure the signal to the speakers isn’t more than they can handle, for whatever time is needed.

You need to determine the SPL needed, coverage and duration before anything else, based on the program material (live or recorded music, speech, etc). The speaker sensitivity & efficiency, distance from speakers to the listeners, size of the room and other factors will determine amplifier power.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 11 made on Sunday February 4, 2018 at 02:33
ErikU
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I think the OP was asking a question about the correct use of terminology. I cringe when I hear electrical terms misused, so I suspect that was the point of the question..?

Amps are a measurement of current. (I)
Watts are a measurement of power. (P)
Volts are a measurement of potential, voltage, or electromotive force (E)
Ohms are a measurement of resistance (R)

A pet peeve of mine is hearing things like "how many amps is that", instead of "how much current does that draw". It sounds as awkward as asking someone "how many pounds are you" instead of asking "how much do you weigh".

Unless you are referring to a specific measurement (ie. that circuit is rated for 5 amps, or I weigh 200 lbs), you should refer to what it is you are trying to measure.

I think to the original question I would say that speakers are a consumer of watts, just like a light bulb. Unlike a light bulb though, that consumption is not static.

And if we really want to go in deep, I wouldn't say that just current could start a fire. High potential can arc. Combine those two into high power and you really have something dangerous!
Post 12 made on Sunday February 4, 2018 at 09:53
highfigh
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On February 4, 2018 at 02:33, ErikU said...
I think the OP was asking a question about the correct use of terminology. I cringe when I hear electrical terms misused, so I suspect that was the point of the question..?

Amps are a measurement of current. (I)
Watts are a measurement of power. (P)
Volts are a measurement of potential, voltage, or electromotive force (E)
Ohms are a measurement of resistance (R)

A pet peeve of mine is hearing things like "how many amps is that", instead of "how much current does that draw". It sounds as awkward as asking someone "how many pounds are you" instead of asking "how much do you weigh".

Unless you are referring to a specific measurement (ie. that circuit is rated for 5 amps, or I weigh 200 lbs), you should refer to what it is you are trying to measure.

I think to the original question I would say that speakers are a consumer of watts, just like a light bulb. Unlike a light bulb though, that consumption is not static.

And if we really want to go in deep, I wouldn't say that just current could start a fire. High potential can arc. Combine those two into high power and you really have something dangerous!

How a question is worded can be due to their native language, too- many Eastern European languages consider one hair to be 'a hair', but more is considered 'hairs', which is the reason many older German-speaking people would say "I got my hairs cut".

They don't actually consume Watts- the Laws of Conservation of Energy states that Energy can neither be created, nor destroyed- it can only be converted to other forms of energy. It's also the reason speakers and amplifiers die- heat that can't leave the object before its destruction occurs.

Lots of people came into the stereo store where I worked and would ask questions about this, without understanding what they were dealing with, mainly because the stereo rags would make comments and list specs without explanation. "How many Watts does this have?", "How many Amps does this have?" and "What's the slew rate?" were common.

Might be more correct to say that "excessive current in a conductor can start a fire" and high voltage isn't needed if the available current is sufficient- who hasn't made lots of sparks and melted spots on a wrench when it contacted a car battery and something that was grounded to that battery?

Last edited by highfigh on February 4, 2018 10:00.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 13 made on Sunday February 4, 2018 at 10:14
highfigh
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On February 3, 2018 at 13:09, james_aa said...
Do speakers draw watts from an amp or get fed watts ?

Eg. would a 60w speaker connected to a 100w amp draw 60w or get fed 100w ?

To answer the question without going off of the rails more than I/we have, Watts is a calculated value, based on the speakers impedance and the voltage/current from whatever it's connected to, whether it's an amplifier, a battery, an outlet, lightning bolt, etc.

A speaker doesn't draw Watts, nor is it 'fed' Watts- the amplifier's output voltage can be present without a load, but no current is 'flowing' until a circuit is completed, with or without anything more than a wire. Current is the quantity of electricity carried in one second by a current of one Amperes- (one Ampere being defined as 1 Coulomb per second), Coulomb being the units for a specific quantity of electrons.

If you want to think about this in terms of water, Voltage is like water pressure, Current is like water flow and resistance is just that- resistance to current, which can be constant (bend a hose to cause a specific rate or bend it and vary the effect). If the water pressure is excessive, something will burst, or it will cause the flow to reach a maximum, due to the inability to pass more water.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 14 made on Sunday February 4, 2018 at 13:44
ErikU
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Yes, good explanations.

In the light bulb example most of the power (measured in watts) is converted to heat, and a little bit of that is in the visible spectrum.
Post 15 made on Sunday February 4, 2018 at 22:42
Dean Roddey
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From the speaker's point of view, as others mentioned, it's the light bulb. If you take the two side of the wire that connect to a light bulb and you touch them together, bad things will happen, because there's no resistance at all and the current flows way too much. Hopefully there's a fuse in the circuit designed to blow when that happens. When light bulb is in the circuit it resists the flow, so that it doesn't flow too fast, and it also just happens to make a nice light in the process.

The speaker acts as the same sort of resistance to the amp trying to push electrons through it. If you connected the two sides of the speaker cable together, you'd probably blow up the amp or trip a fuse in it, because there would be no resistance to the electron flow.

But, like the light bulb, it can only provide so much resistance. If the pressure being applied is too high, something in the path will fry, just like a light bulb filament will burn out if you apply too much juice to it. That's why speakers have power limits set for them.

That's also why amps have limits on how low the ohms (resistance) on the speakers can be. If it's too low, there's not enough resistance to the electron pressure and it's like a slightly less bad version of touching the wires together with nothing in between. The speaker won't be bothered, AFAIK, but the amp will not see enough resistance and start pumping electrons at a greater rate than it is designed to handle.

Anyway, probably no clearer than anyone else, but I can never resist the challenge to be less understood than my fellow man.
Dean Roddey
Chairman/CTO, Charmed Quark Systems
www.charmedquark.com
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