Overpowering Speakers

Am I in any danger sending 300+ WPC to a speaker rated for about a buck twenty? (120rms)

Or are their other factors like efficiency etc?
I don't know that I completely understand your question.
If you like to play your tunes very loud, it is possible to blow them up with any amount of power. You are more likely to blow up speakers with a 20 watt receiver than a 300 watt amp.
When you turn the volume up, your amplifier ask for more electricity to produce the current or volume to get louder. When you keep turning it up, there comes a time when your outputs are giving you all the volume that it can produce. When you turn it up past that point, your amplifier doesn't know what to do with the extra electricity that it has drawn to get louder, so it passes the raw electricity on to your speakers, this is what we call clipping. Clipping distortion is the number one cause in fried voicecoils on speakers. Adding bass draws much more current than just volume alone, often, you can just turn down the bass to maintain a safe volume level. If the volume of your music is not loud enough, you are typically much better off getting more power, than replacing your speakers. Raw electricity can burn any speaker, even those rated for very high power handling. If you like the sound of your speakers, you are typically better off getting more power to play louder. This is a guideline, not a fact. There are other things that come into play... Excursion limits of drivers, voice coil size, crossover points & slopes etc. I hope this answers your question, Tim
Tim - Not sure I've ever heard things explained quite like you did there, but if it makes sense to you and Audio381 I guess that'll work.

Audio8381 - If you have a 300w amp, you're not sending 300 watts to the speakers unless you turn the volume up to max (and even then, not really). As long as you don't play too loud you'll be fine. The speakers will tell you - When they start to sound like crap, it's too loud.
The best explaination that I've heard is that the speaker pulls power rather than the amplifier pushing power. When you turn up the volume the speaker pulls the required power from the amplifier and if you turn the volume past the physical limits of the speaker it can cause problems. Speaker, like people, are not smart enough to know their limits.

I've heard the Focal 706v speaker rated for 25-125 watts hooked to Krell amps rated for either 300 or 400 wpc and the volume was very loud. The salesman turned them up to see how well they sounded at high volume. There is no need to ever play music that loud and they handled it without any issues.

Bottom line, don't get stupid with the volume and I wouldn't expect any issues.
Sebrof is also correct that you're very rarely sending the full rated power of your amplifier to the speakers. An EE buddy of mine told me that a rule of thumb on a reciever that shows volume in -dB is that full power is at 0dB and, I believe, half power was something like -10dB. Someone can confirm my memory, but I believe it takes twice the power to get twice the volume and double the volume is 10dB. I have CDs that I can listen to at 0dB, but very few. The majority of them I listed to below -10dB.
You have to double your power to get a 3db gain. It takes 3db to get a noticable difference in volume. If you are listening to a speaker of 90db @ 1 watt, 2 watts give you 93db, 4 watts give you 96db, 8 watts give you 99db, 16 watts give you 102db, 32 watts give you 105db, 64 watts give you 108db, 128 watts give you 111db, 256 watts give you 114db.... 121db is our threshold of pain. This tells you how speaker sensitivity dramitically effects how much power is needed.
Just a quick add on to make the point of sensitivity and power. All other aspects being equal, a 93db sensitivity speaker will play a volume of 111db using 64 watts. A speaker with 84 db sensitivity will play a volume of 111db on 256 watts.
Your speaker choice makes all the difference in the world on how much power is required to hit the volume levels that you seek.
Timlub, I'm pretty sure you will need over 400 watts to drive an 84 db speaker to 111 db.

Here's a useful web page for things like this:


take a look at the chart at the bottom of the page.
I appologize, I had just run the numbers off the top of my head, but the formula is fact, not opinion, so
84 @1 watt 105 @256
87 @2 watts 111 @512 watts @ 84db sensitivity
90 @4 111 @ 64 watts @ 93db sensitivity
93 @8 I missed one line in figuring.
96 @16 110 @ 16 watts @ 98db sensitivity speakers
99 @32
Thanks Atmasphere, your chart is correct, but I was quoting how much power it took to achieve a 3db gain, not how much voltage it takes to double your volume. My numbers are correct with all things being equal.
In any event-The question was about having an amp that exceeded specified wattage limits the speaker manufacturer stated. And if exceeding that predefined wattage limit would then cause harm?
The answer is yes, - an amplifier rated as having wattage exceeding your speaker's capacity at full output if played "continously" would damage your speakers.
BUT amplifiers typically deliver much much less wattage than full output during normal sane playback. As was already said the real problem is the sudden demand on an amp that doesn't have the "head room" to deliver the required wattage "cleanly" during short peaks or bursts in the music. If your amp is rated as a low output amp, it will be much more likely to deliver electricity (DC) to the speaker which is "clipping" as mentioned. It is this phenomena that suppsed burns up your speaker. I have also heard the limtation in the wave forms where they get cut off and demonstrate non linear highly distorted forms can also to a number on your speakers.
Given a choice, I will take the bigger amp any day. You run less risk of damaging the speaker! A smaller amp, if overdriven, is how most tweeters in the world get damaged. In fact, if the tweeter is damaged in a speaker, the repair technician should always tell the user that the amplifier is under-powered.
Although the conclusions and suggestions that have been expressed in this thread are generally correct, the explanations of why tweeters are commonly damaged by underpowered amps are not.

Tweeters are not damaged by DC (it would be blocked from reaching them by the crossover network, if it were somehow generated in the first place), and amplifiers that are called upon to supply more power than they are capable of supplying do not output "raw electricity."

What typically happens is that the amplifier will not have the ability to generate the output voltages that correspond to the peaks of high volume low frequency or mid-frequency signals. That will result in the output waveform abruptly transitioning from a gradually rising or falling sinusoidal waveshape to a flat level, until later in each cycle when the signal returns to an amplitude the amp can handle.

That abrupt transition contains high frequency spectral components (frequency components) which are not present in the original music waveform. Since they are at high frequencies, the crossover network in the speaker routes them to the tweeter, which is therefore called upon to handle a greater amount of high frequency energy than a normal music signal would require. That is what does the damage.

Best regards,
-- Al
Thanks Al,
I was trying to make very general terms understandable and as much as you are generally correct. Crossovers do see DC as High frequency and do route 1st to the tweeter. This DC is raw current. Crossovers do not block DC. In fact, Through the years, I have used circuit breakers to protect against current and have even put small light bulbs on 6x9's in cars. The kids used to think it was very cool to see them flash with the music. The sole purpose of these bulbs was to filter off DC. It worked very well.
This is from Club knowledge, an article about clipping distortion. I hope this makes sense. Tim

Glad you asked! The amp will try to meet the power demand placed upon it, but it cannot exceed its design capabilities. This in turn, produces the deadly "square wave" output to the speaker. The speaker sees this severely clipped signal as DC current. Speakers cannot deal well with DC inputs. The cone goes in or out and stays there. No motivation to cool the voilce coil and sooner or later, the speaker will fail.


Alright, we know what clipping is, how it affects amps and speakers. What do we do to keep this problem from destroying our expensive drivers? Easy deal:

1. Use amps that closely match or modestly exceed the power rating of the speaker. A 100 watt speaker will love getting 125 watts of "clean power" vs a 100 watt speaker getting 25 watts of badly clipped (distorted) power.

2. Know what distortion sounds like and prevent it by proper amp setup procedures. (HU/amp gain matching, limited bass boost usage)

3. If you are not sure your system is clipping, best thing to do is get out
of the vehicle, open the doors and step to the rear of the vehicle about 10 feet and listen...

a. Are the highs and mids clear and natural sounding or harsh, shrill and very poor SQ? You are clipping the amp if you hear the latter!

b. Does the bass sound full, tight, have a definite thump and smooth transitions from one note to another? If not, good chance the sub amp is clipping or your enclosure design is not optimal for the subs.

OK, that's about all I can do for now on this topic... Class dismissed and PLEASE... NO CLIPPING ALLOWED !!! 15 yard penalty and you will pay the piper eventually.
Sorry everyone if I have put you through all of this, I hope it has been beneficial, but I think that I'm going to leave this one alone, I didn't sign on to argue or prove anything, only to help, I'm a big stickler on seperating fact from opinion. I need to learn when to quit, I'm not trying to hurt feelings.
See you on the next thread,
Don't worry about your 300wpc amp powering your 100wpc speakers. You do not have to match the numbers. As stated above, it is much more likely to overdrive a low powered amp to clipping and damage a tweeter. You will hear the strain when over driving your speakers with clean power, so back off when they sound like they might explode!
By the way, an amp has to malfunction to "send DC" to your speaker. That is not what "clipping" is.
Tim, I sincerely appreciate your gentlemanly responses and your good intentions. However, I too feel a responsibility to separate fact from mis-information.

As someone with multiple electrical engineering degrees, and multiple decades of experience in electronics design, I can tell you that DC is not "seen as high frequency"; that a clipped audio waveform is not DC and is not seen as DC (as Blkadr correctly indicated, and contrary to what is stated in the article you quoted); and that the portion of a crossover network that is between the speaker terminals and the tweeter (which is designed to pass high frequencies and to block low frequencies, and may be simply a capacitor in series, or something that is similar at a simplified conceptual level but more elaborate) will block DC. DC is actually the LOWEST possible frequency, zero Hertz. Capacitors block DC, and impede low frequencies.

If DC is ABRUPTLY applied to a circuit, high frequency components may be briefly present, corresponding to the abruptness of the change in voltage. Those are referred to as transients. Similarly, the abrupt waveform changes I referred to in my earlier post, that occur when a LOW frequency waveform is clipped, contain HIGH frequency spectral components.

Which leads me to simply reiterate that my earlier post correctly explains why tweeters are commonly damaged by the clipped waveforms that can be generated by underpowered amps.

Best regards,
-- Al
The OP question of (my interpretation) "can I use a 300 watt amp with speakers rated for only 100 watts safely" has not really been addressed.
Yes you can use the 300 watt amp with 100 watt rated speakers if you abide by some rules.
First, the amp is just like the wall outlet in terms of raw power. The wall can allow up to 15 amps.. but a small light bulb only needs 25 watts. The wall just lights up the lightbulb, using 25 watts. So the rating of the wall socket of 15 amperes does not matter, unless you stuck a couple of screwdrivers into the wall and crossed them. Then your 15 amps would give you a big spark and a tripped breaker.
The VOLUME control is more like the limiter in the case of stereo. So you can use the big power amp with smaller rated speakers IF YOU KEEP THE VOLUME DOWN to non-earsplitting levels.
When you are listening at very low sound volumes, the wattage is like one watt or less actually being used to power the speakers. So even though the amp is rated at up to 300 watts, it is actually using just a watt or so to drive the speakers. When you play music loud enough to allow a person in the next room to hear, you are probably around 50 watts or so, and when your neighbor down the block can hear your music clearly, your speakers will burn out, because then you WOULD be exceeding the speakers rated 100 watts average.
So take it easy on the volume control and do not play louder than you can generally put up with if you were a foot from the speakers, and you will never have a problem.
Watch out for drunken guests, and small children though, as they may turn UP the volume to fatal (for your speakers) level.
Say if you turn it on and accidentally had the volume all the way up and the blast hit your ears and you immediately turn it down... You will probably not damage the speakers (because the speaker coils did not have enough time to overheat and melt... this is with 300 watts.. if you had 1,000 watts.. I think your speakers would be toast with a 100 watt rating, even if it was only for a second.)
So the answer is yes you can safely use a 300 watt amp with 100 watt rated speakers IF you keep the volume control from overdriving the speakers: IE too loud to stand listening. And you are good.
This means NO body massaging bass attempts. no 'can I break my lease" levels.
Hope this helps.
Elizabeth is right on the money. Before in my 2 channel set up in my basement I had a Phase Linear 700B powering a pair of Tannoy bookshelf speakers that were rated up to 120 watts at 8 ohms. I was careful with the raising of the volume and listening level and had no issues. The music sounded fine and the speakers were not damaged. People thought I was crazy to use a Flame Linear or Fuzz Linear to power bookshelf speakers for a time but I just had to be careful.
Thanks for your kind response Almarg, Pulled my old Speaker
Craft notes out, here is what I had word for word. I'm just old.
The bulb wires in series with the tweeter, under normal average music conditions it is just a low value resistance as the power sent to the tweeter increases the current through the bulb increases. since the bulb filament has a positive temperature coefficient as it heats up it's resistance goes up and takes a larger share of the power that the tweeter would get without the bulb in series. this does cause compression but saves many tweeters in a cheap easy way. Ideally the bulb should go before the tweeter crossover circuitry so it does not affect the crossover frequency.