Hello everyone,

I have been wondering about the reason why speakers are rated using watts rather than amps ?

Why is it that voltage is necessary when speaking about speakers for example? Why can't we just use current to rate a speaker ?

I mean, if current is what generates the magnetic field that moves the speakers, why does voltage even matter here?

I am confused about this! Speakers are just one example. Light bulbs are also rated using watts rather than current.

Could anyone please shed some light on the reasons behind this?

In the case of speakers, how is the energy converted into magnetic fields, and then further how is it transferred into air waves ?

Thanks a lot, I know this is a very good question

 

Watts = Voltage * Current.
60 W lightbulb = 120 Vrms * 0.5 Amps
If 250 W speaker had 0 volts, there could be no watts..

and yes, someone will say that in certain conditions voltage can be nil and still have current,

 

Watts = Voltage * Current.
60 W lightbulb = 120 Vrms * 0.5 Amps
If 250 W speaker had 0 volts, there could be no watts..

and yes, someone will say that in certain conditions voltage can be nil and still have current,

I understand that power is voltage * current.............. please re-read the question

 

You can have 200 watts with 1 V, but you will need 200 Amps to have same effect. 200 amps, will require a thick wire to transfer that much current, or it will melt instantly. Or you could have 200 volts and 1 amp, and the wire size would be much smaller.. The thickness of the wire determines how much current it can handle. If you look at some tesla coils, they operate at tens to hundred thousands of volts, and yet they have thin wire on their coils, that's because the current is in mili-amps or lower.

 

You can have 200 watts with 1 V, but you will need 200 Amps to have same effect. 200 amps, will require a thick wire to transfer that much current, or it will melt instantly. Or you could have 200 volts and 1 amp, and the wire size would be much smaller.. The thickness of the wire determines how much current it can handle. If you look at some tesla coils, they operate at tens to hundred thousands of volts, and yet they have thin wire on their coils, that's because the current is in mili-amps or lower.

Very good thank you........ I think what confuses me is how the power is converted into sound waves in a speaker for example. Suppose you have a high voltage of 200 volts and 1 amp of current, then you have 200W into the speakers. How are these watts converted into sound waves, and what would be different if instead you had 1 volt and 200 amps ?

 

thickness of the wire connecting to the speaker, thickness of the traces on circuit board..

would you like a 1" diameter wire going to your speakers of would a smaller wire suit better?

 

thickness of the wire connecting to the speaker, thickness of the traces on circuit board..

would you like a 1" diameter wire going to your speakers of would a smaller wire suit better?

I understand about the thickness. I want to know how the energy is converted from electrical potential energy to air waves in the speaker, Boss

 

http://www.explainthatstuff.com/loudspeakers.html

 

http://www.explainthatstuff.com/loudspeakers.html

That article does not explain it. I apologize. Please find me a better article ?

 

The speaker converts the electrical energy to sound by Electromagnetism, by the coil around the permanent magnet, connected to the diaphragm moving in and out.

 

I understand about the thickness. I want to know how the energy is converted from electrical potential energy to air waves in the speaker, Boss

Very basic:
http://www.physics.org/article-questions.asp?id=54

More Detail:
http://web.mit.edu/2.972/www/reports/speaker/speaker.html

 

The speaker converts the electrical energy to sound by Electromagnetism, by the coil around the permanent magnet, connected to the diaphragm moving in and out.

That I knew. Please explain to me how it actually does it and why you need power rather than just amps. Voltage is Joules per Coulomb. But seriously, voltage doesnt sound like it can do anything. How is voltage made into actual energy ?

Its more natural to say the amps do it because they actually flow and make the diafram move. I dont get this shit man. You need to help me here for my homework.


i always think of voltage as a static thing, so how can voltage drive speakers man this doesnt sound right.

say u got 1 volt, and then your source can drive at most 1mA of current. you get a total of 1mW. this 1mW goes to your speakers and then what ? then you change your voltage from 1V to 2V. now you got 2mW of power.

hows the physics taking place here buddy

 

That I knew. Please explain to me how it actually does it and why you need power rather than just amps. Voltage is Joules per Coulomb. But seriously, voltage doesnt sound like it can do anything. How is voltage made into actual energy ?
...
hows the physics taking place here buddy

Derp...

 

Imagine voltage as size of hose, and current is the amount of water flowing thru it.

If you want to fill out a bucket of water, you could take .5" hose at high pressure and fill it out in x amount of time, or take 5" hose at lower pressure and fill it out at same amount of time..

It's the combination of volts and current that drive the speaker, not just one one item.
as for the workings of the speaker it self, there are plenty of websites that can explain it for you.. if one doesn't explain to your satisfaction, find another site...eventually you will find what you are looking for.

 

Think of it as the power to move a mass of air. Power (P) is work done. Work is the integral of P dt from 0 to t.

In reality, you want to know how much horsepower, your horse/automobile/speaker is capable of delivering either intermittently or continuously,

You might have tweeters rated at 35 W and woofers rated at 100 W in the same enclosure. The speakers can't deliver 100 W of high frequency content, but can at the low frequencies.

Power heats and that's the enemy of the voice coil.

Another parameter that comes into play is efficiency. This might be stated at the SPL (Sound Pressure Level) at 1W.

 

Okay, buddy.
Voltage is the force that drives the current and, as has been noted, power is voltage times current.
If either one is zero, you have no power.

i always think of voltage as a static thing, so how can voltage drive speakers

No, to drive a speaker the voltage is definitely not static, it is an AC voltage which is proportional to the sound in frequency and amplitude.
The sequence for a speaker (ignoring the coil resistance):

• This varying voltage generates a speaker current which generates a varying magnetic field in the speaker coil.
• This magnetic field interacts with the speaker magnet, causing the speaker cone to move in response, which in turn moves the air to generate the sound we hear.
• The movement of the cone coil in the magnetic field generates a back voltage which appears as a voltage across the speaker terminals.
• The more applied voltage, the more current and the greater the cone movement, until the generated back voltage equals the applied voltage.

So it's this voltage times the current that is the power to the speaker to physically move the cone.
Thus electrical energy is magnetically converted to mechanical energy which moves the cone.

Make sense?

 

Just as a side note while we love Power = Voltage * Current there is also Power = Voltage ^2 / Resistance and also we have Power = Resistance * Current ^2. When looking at speaker or amplifier power ratings it is also important that the power be specified, for example RMS Power, Peak Power or Peak to Peak power.

Ron

 

The speakers are rated in Watts, as is the amplifier, so you can match them properly.

You know you can't hook up a 200 mW speaker system to a 100 W stereo amplifier, well, you can, but you can't crank it up without causing damage to the speakers.

How would you rate the amplifiers and speakers?

 

The speakers are rated in Watts, as is the amplifier, so you can match them properly.

I think "matching" is a bad word to use here. "Selecting" might be better.

A speaker is plain weird anyway. Look at the impedance vs frequency curves here: https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers Now you can try really hard to rate you speaker for max current.

 

Selecting is a better word.