# What does the rating on speaker mean?

#### yaantey

Joined Oct 7, 2011
48
I have a speaker which has 8ohms and 0.5W written at the back. What does that mean? From this can I calculate the max or min voltage or current the speaker can take?

#### sabazeshan

Joined Feb 4, 2012
1
Hi
the speaker that you are using is 0.5 Watt and load resistance is 8 ohms so you can calculate the current using P=I^2R, formula and also voltage i hope i am right.

#### bountyhunter

Joined Sep 7, 2009
2,512
Wattage ratings on speakers means absolutely nothing. The impedance tells you important information.

#### bloguetronica

Joined Apr 27, 2007
1,423
Wattage ratings on speakers means absolutely nothing. The impedance tells you important information.
No, it is completely wrong. Both impedance and wattage rating are important. Impedance tells you the average "resistance" of the speaker when powered by the amplifier. Wattage rating tells you the maximum RMS power that the speaker can accept without getting blown. For sure you don't want to hook up a 10W speaker to a 100W amplifier. It will burn at high volume, and worse, you can short out the output of the amplifier in the process, rendering it unusable (though most amplifiers have short circuit protection).

#### holnis

Joined Nov 25, 2011
49
A speaker's power rating (in general) tells you how much A.C. power can be dissipated in the speaker's voice coil without damaging the

speaker.

Giving the rating as continuous RMS watts is the most honest way to rate a speaker (ex: 150 watts continuous rms power). You may

hear speakers advertised as "150 watt 6 x 9s" or "100 watt 6 x 9s" and you may instantly think that the "150 watt 6 x 9s" are better and

will play louder than the speakers rated at 100 watts. The first thing you should realize is that speaker ratings are often exaggerated.

Then you should ask if the rating is in RMS or peak watts and are the speaker ratings for instantaneous or continuous power.

#### PaulEE

Joined Dec 23, 2011
423
I have a speaker which has 8ohms and 0.5W written at the back. What does that mean? From this can I calculate the max or min voltage or current the speaker can take?
The power rating on a speaker expresses the power through the coil upon which full deflection of the speaker cone occurs in one direction or the other. This is directly related to the strength of the magnet inside the speaker that the coil surrounds, as well as the coil inductance/resistance/capacitance (impedance). If too much power is inputed, the coil may overheat or the cone may fracture/rip.

The impedance on a speaker tells the designer of the amplifier circuit the number of rms volts that can be applied that tells him/her the number of amps that will flow. This allows the designer to decide the amplifier specifications such that the power rating is not exceeded.

#### Audioguru

Joined Dec 20, 2007
11,249
If the power rating does not say RMS and CONTINUOUS then it might just be a peak instantaneous useless rating. Frequently speakers are rated in Music Power ratings that is the peak power (double the RMS power rating) for a brief moment.

A cheap tiny speaker with a power rating of only 0.5W is a joke anyway. No bass, no highs and no loudness.

#### bountyhunter

Joined Sep 7, 2009
2,512
No, it is completely wrong. Both impedance and wattage rating are important.
If you think speaker's printed watt ratings are anything besides pure BS, I have a bridge I'll sell you.

#### MrChips

Joined Oct 2, 2009
22,107
If you think speaker's printed watt ratings are anything besides pure BS, I have a bridge I'll sell you.
OK, let's not go there. You have to have something to go by. I would not install a 1W speaker if I'm looking to pump out 100W. I play bass and my speaker is rated at 400W and I believe it!

At 400W, I don't care if this is average music, RMS or peak power.

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#### mcgyvr

Joined Oct 15, 2009
5,394
If you think speaker's printed watt ratings are anything besides pure BS, I have a bridge I'll sell you.
How much? I'm in the market for a bridge.
So in your opinion is the wattage rating for a resistor BS/useless too?

#### Audioguru

Joined Dec 20, 2007
11,249
Cheap speakers have fake power ratings. High quality speakers have detailed and true power ratings.

Look at the datasheet for resistors. They are made to get extremely hot at their rated power when they are not enclosed but have open air all around for convection airflow.
Even a short length of a resistor's lead is spec'd as part of the power rating so it can transfer some of its heat to the copper on the pcb.

You should not operate a resistor at its rated power where it can char a circuit board, melt a nearby plastic capacitor or burn you badly. Use half its power rating when it is in free air and use much less than its power rating when it is enclosed.

#### holnis

Joined Nov 25, 2011
49
BTW, Most car audio speakers (with the exception of some subwoofers) are rated in peak power (peak power = 2*RMS power) or music power. Only a few speakers (generally the higher quality speakers) are rated in RMS watts. While peak power is a legitimate way to rate speakers (as long as the manufacturer tells you that the power rating is in peak watts), it can be deceptive.

#### Audioguru

Joined Dec 20, 2007
11,249
Peak Power is also called Maximum Power which is deceptive.
But cheap amplifier ratings are also deceptive or worse so that nothing blows up.

#### PaulEE

Joined Dec 23, 2011
423
I actually do have a bridge that I legitimately could sell someone. It is in northwestern Pennsylvania, built by PennDOT in 1993. It is on property that a friend just bought and he wants it gone.

As far as the power ratings, what I said is what it is. Whether the company that makes the speaker is lying is another story.

I over-spec every critical component in a circuit by 10 to 20% to alleviate issues with liars. There are a lot of them.

#### bountyhunter

Joined Sep 7, 2009
2,512
The biggest lie about speaker power ratings is that the speaker can be blown to bits at power levels probably 1/20 of the rating, even if the rating is "honest". The ratings typically used (for "true RMS" rated speakers) are the RMS power rating where the voice coil burns out.

FIRST: the speaker has to be installed in a proper enclosure to get anywhere near rated power.... or the cone will be blown right out of the frame. Hence my point above.

SECOND: most speakers can easily be destroyed by "bottoming" using low bass notes, so the speaker can easily be blown up at a fairly low power level.

THIRD: many speaker manufacturers are not honest about the power ratings or test methods used to get it, or the info is simply omitted

Hence my point that the rating stamped on the speaker is essentially meaningless. It certainly is not something that one can read as a "real spec" which can be used to address a design margin derating.

The speaker power handling ratings that you often see advertised are among the most misunderstood and often exaggerated specs you will find in the consumer electronics world.

//

So, how important are power handling ratings for speakers anyway? Not very important at all, as it turns out. There are a few ways that speakers are commonly damaged. When driven by too much power, a woofer can reach the mechanical limits of the travel of the cone, or more specifically, the voice coil. The voice coil is suspended in a magnetic field and moves piston-like to move the cone. If it travels too far, it will bottom out on the magnet, which can cause permanent damage. Physical damage to the voice coil can then blow your amplifier.

///

Back in the early days of hi-fi, the way manufacturers came up with performance specifications varied widely, making it difficult if not impossible to compare products. The industry then came up with standard test methods and criteria for publishing specifications. Participation from manufacturers is voluntary//

Speakers, however, can be an exception. Test methods and standards are not as cut and dried. One manufacturer might rate the power handling across the full spectrum of frequencies that the speaker reproduces, while another may look only at one particular frequency. Now try to define the maximum that the speaker can handle. Does it handle that much power when driven continuously, or just for a fraction of a second? Is the maximum the point just before the speaker is physically damaged? How many speakers do you blow in order to determine that point? There are just too many variables.

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#### mcgyvr

Joined Oct 15, 2009
5,394
agree to disagree
Sure there are many aspects to properly designing anything.. But just because something bad can happen even when 1 specific spec is still being met doesn't mean that spec is pointless though..
That's like saying the drain current rating (Id) on a mosfet is useless just because it can cook well before that single rating is met. Just means you need to look at the total picture.

#### Audioguru

Joined Dec 20, 2007
11,249
Many speakers have their power rated when they are fed continuously with pink noise that randomly produces all frequencies.

Here is part of the datasheet for a ScanSpeak 8" woofer. It is very high quality and it is not cheap. They recommend the size of its enclosure and size of its vent.
Its power rating is with 100 hours of pink noise:

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#### mcgyvr

Joined Oct 15, 2009
5,394
Cheap speakers have fake power ratings. High quality speakers have detailed and true power ratings.
Its all already said right there.. Just like anything that's knocked off/copied,etc.. The ratings printed on the "fakes" are typically just as "fake" as the product itself.. But if you purchase the "real thing" you can usually count on there being some "sound" (no pun intended) reasoning behind the printed/stated ratings.
Just don't claim all power ratings are BS when they aren't

#### c0de3

Joined May 1, 2009
50
I have a speaker which has 8ohms and 0.5W written at the back. What does that mean? From this can I calculate the max or min voltage or current the speaker can take?
As people have said these numbers have limited use. I think on the surface it is supposed to be *claiming* that this speaker has 8 Ohms of Impedance. And can *handle* 1/2 watt of power. As everyone is pointing out, that is probably debatable.

Do you have another question? Perhaps some detail about what you are trying to accomplish that perhaps someone can help with?

As far as calculations, I'm not a EE so take with a grain of salt, the formulas you'd need to consider are:
Power = Current * Volts
Ohms = Volts / Current