# Underpower Vs Overpower



## Kenwood

I need some advice about my car stereo before I have it installed. I need to know if an amp will be necessary with my head unit and speakers. I have a Kenwood KDC799 headunit and Alpine SPR68 speakers. Some people say I will need an amp and others say I dont need one. Would I need an amp? Would I damage my speakers if I dont get the amp? The headunit is 22 watts and the speakers are 100rms watts 300 peak power. Any advice??


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## FordEscape

Kenwood said:


> ... Would I damage my speakers if I dont get the amp? ....


Here's how you _could_ damage the speakers ....

IF, in the process of trying to get the loudness you want, you turn up the volume on the 'rated' 22 W / channel head unit to or beyond the point that the output is clipped (a form of distortion). The clipped/distorted output _can_ damage the speakers even at power levels below the 'rated' power-handling capability of the speaker.

This can happen when playing a track that has a volume peak that drives the output to clipping even without you touching the volume knob.

You'll likely know by ear when the signal is clipping/distorted. You can google for examples.

In general a higher power amp, properly set-up** with the head unit, would be capable of delivering more power (more volume) 'cleanly' (without clipping) all other things being equal.

If you exercise restraint with the volume knob and are happy with the volume you get from the head unit, all is good.

If you find yourself turning the volume so high that you hear distortion (or loud parts of tracks sound distorted), roll-back the volume ASAP and look at adding an amp.

Some would suggest it is much easier / more common to damage speakers by driving an under-powered system to clipping than by driving an 'over-powered' system to 'blow' the speakers. I don't have any statistics but would not argue that notion. IMHO most speakers are more tolerant of a clean (un-clipped/undistorted) high-power signal than they are of a clipped/distorted signal at any power level. So, in a sense, additional clean power properly matched** to the head unit could be viewed as 'speaker insurance', especially if you know you like to occasionally crank-up the volume. 

The 100W 'rating' for the speakers you mention gives a good indication of the clean power level they can tolerate on an ongoing basis; the 300W 'peak rating' gives a good indication of the occasional clean power excursions (e.g. peaks in a track of music) they can handle; but the key is having an amplifier that can deliver those levels cleanly if demanded based on where you have the volume knob.

**a reference to setting "gain" correctly, a different topic but related to preventing clipping in the chain of components.


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## Justin Zazzi

Kenwood said:


> Would I need an amp? Would I damage my speakers if I dont get the amp? The headunit is 22 watts and the speakers are 100rms watts 300 peak power. Any advice??


You don't need an amp unless you listen to music at loud volumes. "Loud" will vary from person to person. Have a listen to some demo systems at the place that will be installing your equipment and listen at a "normal" level for you. They should be able to guide you better than we can over the internet.

You will not damage those speakers if powering them from a 22 watt-per-channel head unit, so don't worry about it.


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## edzyy

Amp your speakers.


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## turbo5upra

You can run a car without an external amp?


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## Kenwood

Thanks Ford Escape....I guess Ill get an amp then. Any recommendations or brand?


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## Kenwood

Thanks Jazzi....Ill ask them tomorrow which way is the best way to go. I don't mind getting an amp, but I'd like to save on cost if I can. I have a Ford Taurus and the factory stereo is crap lol...Im so glad to be replacing it. I heard replacing it is a difficult task since everything is in the trunk.


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## Victor_inox

22W on paper is most likely 8 in real life. I`d get an amp.


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## Viggen

As stated this varies by person. Some are more then happy with the decks power... Heck look how many people use oem stereo systems. Then there are those of us who must have the extra power of a external amp. The sound will not just play louder, but it will be much cleaner!

If you are someone who likes to play music loud then to me a amp is a necessity. The 22w is of poor quality and over rated.... I would honestly consider adding a small sub when you are at it. You can simply add a 4 or 5 channel amp to power everything.


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## syc0path

The rule of thumb that is often told to car audio newbies is that "it's better to overpower than underpower." As FordEscape alluded to, that is basically a shorthand way to explain that cranking a head unit or small amp to put out more power than it can cleanly deliver causing clipping, and clipping in turn damages speakers. A clipped signal at 50W is far more likely to damage your speakers than a clean signal at 130W.

So there's nothing wrong w/ running these speakers w/ HU power, as long as u don't drive too much distortion. Hell, w/ that whole 8WRMS of HU power, u probably couldn't damage them no matter how much clipping there was.

My advice would be to hook them up to the HU, listen to it for a few days or weeks, and see how it sounds to u. Overall it will sound better than stock, but u may find that there is actually less bass (becuz the stock system uses psychoacoustic tricks to make u THINK there is more bass than there actually is). Then decide if u want an amp.

Personally, I would go w/ Viggen's advice and add a sub. But I would get a 4ch amp -- 2 channels for the front speakers, and then bridge the other 2 channels for the sub. I wouldn't bother amping the rear speakers. It's a little more expensive, but this setup will give u the best bang for the buck.


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## pbasil1

If you have a small budget for an amp, look around on here. There are tons of great deals on used components. I for one have a used Eclipse 4CH amp, pm me if you need.

syc0path summed it up well.


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## Alextaastrup

Danger of demaging a speaker by clipping is a question of cooling efficiency and heat energy dessipation. Some speakers are better than others.

SMD device can help to find the volume level when clipping starts. You could even use 315Hz sine tone and to listen when it changes sound. That's it.


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## gijoe

There is a lot of missleading or downright false information in this thread.

First, you cannot damage a speaker by underpowering it. If you clip the signal heavily you are no longer underpowering the speakers. Underpowering a speaker cannot and will not damage a speaker. Having said that, even a heavily clipped signal from a very low powered amp won't cause damage. Clipping causes excess power, and reduced cooling, if it damages a speaker its from overpowering, never underpowering. 


Secondly, the HU might be rated for 22 watts per channel, but in likelyhood, that's max wattage, measured at a very easy frequency, with only one channel driven at a time. Real world, you're looking at less than half that power. This might be ok, depending on your listening habits, but it won't get particularly loud, and as others have mentioned, you'll probably start to clip the amp and get loads of distortion before you reach a satisfactory SPL. I don't see a real big risk of damaging a speaker though, even if you clip it heavily it will sound so bad that you'll turn it down. 


A budget friendly amp is going to be your best bet. You don't need a ton of power, if you can find a true 50 watt RMS, that would be significantly better than the HU power.


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## Jepalan

gijoe said:


> There is a lot of missleading or downright false information in this thread.
> 
> First, you cannot damage a speaker by underpowering it. If you clip the signal heavily you are no longer underpowering the speakers. Underpowering a speaker cannot and will not damage a speaker. Having said that, even a heavily clipped signal from a very low powered amp won't cause damage. Clipping causes excess power, and reduced cooling, if it damages a speaker its from overpowering, never underpowering.
> 
> 
> Secondly, the HU might be rated for 22 watts per channel, but in likelyhood, that's max wattage, measured at a very easy frequency, with only one channel driven at a time. Real world, you're looking at less than half that power. This might be ok, depending on your listening habits, but it won't get particularly loud, and as others have mentioned, you'll probably start to clip the amp and get loads of distortion before you reach a satisfactory SPL. I don't see a real big risk of damaging a speaker though, even if you clip it heavily it will sound so bad that you'll turn it down.
> 
> 
> A budget friendly amp is going to be your best bet. You don't need a ton of power, if you can find a true 50 watt RMS, that would be significantly better than the HU power.


^^^ Spot on. This man speaks the truth.
Thanks for saving me the typing @gijoe


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## Viggen

gijoe said:


> There is a lot of missleading or downright false information in this thread.
> 
> First, you cannot damage a speaker by underpowering it. If you clip the signal heavily you are no longer underpowering the speakers. Underpowering a speaker cannot and will not damage a speaker. Having said that, even a heavily clipped signal from a very low powered amp won't cause damage. Clipping causes excess power, and reduced cooling, if it damages a speaker its from overpowering, never underpowering.
> 
> 
> Secondly, the HU might be rated for 22 watts per channel, but in likelyhood, that's max wattage, measured at a very easy frequency, with only one channel driven at a time. Real world, you're looking at less than half that power. This might be ok, depending on your listening habits, but it won't get particularly loud, and as others have mentioned, you'll probably start to clip the amp and get loads of distortion before you reach a satisfactory SPL. I don't see a real big risk of damaging a speaker though, even if you clip it heavily it will sound so bad that you'll turn it down.
> 
> 
> A budget friendly amp is going to be your best bet. You don't need a ton of power, if you can find a true 50 watt RMS, that would be significantly better than the HU power.


Underpowered we are referring to a amp rated at less power then what the speaker is rated at, it's a general term. Obviously a clipped signal changes things... Our point is typically people reach the clipped signal before their ears say that's loud enough. Thus the smaller underpowered amp can blow the speakers due to pushing the amp. Technically you are correct but it's just a general statement

I would bet I could blow a tweeter rated at 100w with well less then 50w of power.... Simply giving it a 20hz test tone should fry it pretty quick thus it IS possible to blow a speaker with less power then it's rated at. Extreme example but it could be done with any speaker.

Stating you can't blow or damage a speaker when running less then rms power is like stating you can run more power and never damage a speaker. If I have a amp rated at 100w rms and the speaker is rated at 99w I highly doubt manufacturers rate their rms rating at its true max..... Has to be some fudge factor/safety margin in their number. Obviously the more power that's pushed through a speaker the more important the frequency the speaker sees becomes more critical


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## Alextaastrup

Agree with Viggen uppon definitions under/over...


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## gijoe

Viggen said:


> Underpowered we are referring to a amp rated at less power then what the speaker is rated at, it's a general term. Obviously a clipped signal changes things... Our point is typically people reach the clipped signal before their ears say that's loud enough. Thus the smaller underpowered amp can blow the speakers due to pushing the amp. Technically you are correct but it's just a general statement
> 
> I would bet I could blow a tweeter rated at 100w with well less then 50w of power.... Simply giving it a 20hz test tone should fry it pretty quick thus it IS possible to blow a speaker with less power then it's rated at. Extreme example but it could be done with any speaker.
> 
> Stating you can't blow or damage a speaker when running less then rms power is like stating you can run more power and never damage a speaker. If I have a amp rated at 100w rms and the speaker is rated at 99w I highly doubt manufacturers rate their rms rating at its true max..... Has to be some fudge factor/safety margin in their number. Obviously the more power that's pushed through a speaker the more important the frequency the speaker sees becomes more critical


"Underpowering" may be a general term, but it's mostly used incorrectly, and it gives people a very wrong impression of what's happening. It may be most commonly used to describe an amplifier that is rated too low and pushed too hard, causing clipping, but that's not underpowering. I've been in the hobby long enough to see just how many people actually believe that underpowering a speaker will cause damage, and it simply won't. 

With regard to sending a 20hz tone to a tweeter, of course this can cause damage. The second way to damage a speaker is over excursion, making a tweeter play a 20hz tone to an audible level will destroy it from over excursion, but not necessarily from thermal issues (overpowering). 

You can damage a speaker with too much heat, or you can damage a speaker with too much excursion. Too much heat comes from too much power, whether it's simply too much clean power, or a clipped signal is really unimportant, it's still more power than the speaker can handle, and not enough cooling taking place. Playing a speaker below it's usable bandwidth can easily cause over excursion. You need to move a lot of air to play low frequencies, small speakers don't move a lot of air, so you damage them with over excursion trying to get them to displace enough air. 

I'm not here to argue semantics, I'm simply trying to clarify that sending a speaker less than rated power isn't going to hurt it. You can send a subwoofer a single watt all the way to it's rated power without fear of any damage. If you use a small, amp and try to get loud, and push it into clipping, you aren't underpowering anything, you are overpowering. Sure, the overpowering came from an underpowered amp, but you've used that amp outside of it's design specs and overpowered your speaker.


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## annoyingrob

Viggen said:


> Stating you can't blow or damage a speaker when running less then rms power is like stating you can run more power and never damage a speaker. If I have a amp rated at 100w rms and the speaker is rated at 99w I highly doubt manufacturers rate their rms rating at its true max..... Has to be some fudge factor/safety margin in their number.


There is, but what's important to understand is that the rating is "Average power over time". A speaker designed to handle 100w of power means that it will handle 100w continuously for an indefinite period of time without damage. As you start pushing power levels above that, you are adding more themal energy into the speaker than it can dissipate in a given period of time, the speaker will begin to heat up beyond the levels its designed and can fail. It's not going to happen immediately though.

If you were giving that speaker 200w of power in small bursts such that the power averaged out to 100w or less, the speaker *generally * would be able to handle it no problem. For example, giving a speaker 200w of power for one second, and then 0w of power for another second will have an average of 100w of power over the 2 seconds. Something that the speaker should be able to dissipate thermally assuming something else catastrophic didn't happen.

Music is dynamic. Most music has a crest factor of at least 6db, which means that the average power is 1/4 or less of the peak power. If you had your 100w speaker on a 200w amp, the speaker is still only receiving an average of about 50w. This is a highly debated topic even on these forums but most people agree that doubling (or more) the rated power is not an issue. The one exception to this would be subwoofers on bass heavy music where the crest factor can be much much less.

As far as "underpowering", it's been discussed well here already, but maybe this makes it a little clearer.

a 100w amplifier can produce 100w of clean un-distorted sound. If you were to drive it DEEP into clipping, the amplifier will produce 200w of garbage (assuming the power supply in the amplifier is up to the task). P = Vavg^2 / R, and Vavg = 1/sqrt(2) * Vmax for a sinewave => P = 1/2 VMax^2 / R

As you drive the amplifier into clipping, the average power approaches Vmax. Worst case, the average IS Vmax. Pclip = VMax^2 / R

Pclip = 2 * P (absolute worst case scenario).


So your "underpowered" amplifier is suddenly an overpowered amplifier. Better yet, if you're NOT using any sort of passive filtering on your speakers (like you have an active setup), that clipped signal is now full of energy all over the spectrum, causing your speakers to play lots of frequencies they weren't designed for. This means the very real potential to reach the mechanical limits of your smaller drivers.


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## gijoe

annoyingrob said:


> There is, but what's important to understand is that the rating is "Average power over time". A speaker designed to handle 100w of power means that it will handle 100w continuously for an indefinite period of time without damage. As you start pushing power levels above that, you are adding more themal energy into the speaker than it can dissipate in a given period of time, the speaker will begin to heat up beyond the levels its designed and can fail. It's not going to happen immediately though.
> 
> If you were giving that speaker 200w of power in small bursts such that the power averaged out to 100w or less, the speaker *generally * would be able to handle it no problem. For example, giving a speaker 200w of power for one second, and then 0w of power for another second will have an average of 100w of power over the 2 seconds. Something that the speaker should be able to dissipate thermally assuming something else catastrophic didn't happen.
> 
> Music is dynamic. Most music has a crest factor of at least 6db, which means that the average power is 1/4 or less of the peak power. If you had your 100w speaker on a 200w amp, the speaker is still only receiving an average of about 50w. This is a highly debated topic even on these forums but most people agree that doubling (or more) the rated power is not an issue. The one exception to this would be subwoofers on bass heavy music where the crest factor can be much much less.
> 
> As far as "underpowering", it's been discussed well here already, but maybe this makes it a little clearer.
> 
> a 100w amplifier can produce 100w of clean un-distorted sound. If you were to drive it DEEP into clipping, the amplifier will produce 200w of garbage (assuming the power supply in the amplifier is up to the task). P = Vavg^2 / R, and Vavg = 1/sqrt(2) * Vmax for a sinewave => P = 1/2 VMax^2 / R
> 
> As you drive the amplifier into clipping, the average power approaches Vmax. Worst case, the average IS Vmax. Pclip = VMax^2 / R
> 
> Pclip = 2 * P (absolute worst case scenario).
> 
> 
> So your "underpowered" amplifier is suddenly an overpowered amplifier. Better yet, if you're NOT using any sort of passive filtering on your speakers (like you have an active setup), that clipped signal is now full of energy all over the spectrum, causing your speakers to play lots of frequencies they weren't designed for. This means the very real potential to reach the mechanical limits of your smaller drivers.


In addition to the speaker now being overpowered, the shape of a clipped signal keeps the speaker in a it's peak position longer, lowering it's ability to cool itself. So, not only do you have more power, but you have less cooling capabilities, not a good combo.


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## ppia600

If you aren't going to get a quality amplifier, don't waste your time... just run deck power. An amplifier will improve sound quality if it is a quality amplifier and your speakers are capable. I usually use an amplifier that makes more clean rms power than the speakers can handle, so the speakers will do the absolute best they can without the amp breaking a sweat. It is pointless to have a speaker that will handle 75wrms of clean power and run a 50wrms amp, take advantage of all of what the speaker is capable of or don't waste your time.


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## syc0path

ppia600 said:


> It is pointless to have a speaker that will handle 75wrms of clean power and run a 50wrms amp, take advantage of all of what the speaker is capable of or don't waste your time.


That's hardly pointless. Sure, a 50WRMS amp won't squeeze every dB out of a 75WRMS-capable speaker, but it would probably use 90% of the speaker's potential. And that amp will get a hell of a lot more out of that speaker than HU power! As long as u don't push that 50WRMS amp into heavy clipping and damage the speaker, this setup would yield some decent results. Not as good as a 75-100WRMS amp, but still decent.


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## DDfusion

Every time you double power it's a 3db gain. So if you have the normal 10w HU and go to a 50w you can potentially gain 6db. That's a very nice increase.


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## gijoe

syc0path said:


> That's hardly pointless. Sure, a 50WRMS amp won't squeeze every dB out of a 75WRMS-capable speaker, but it would probably use 90% of the speaker's potential. And that amp will get a hell of a lot more out of that speaker than HU power! As long as u don't push that 50WRMS amp into heavy clipping and damage the speaker, this setup would yield some decent results. Not as good as a 75-100WRMS amp, but still decent.


Agreed. Some people get way too caught up on having gobs of power. Sure, it's nice to get as much power as you can afford, but even a relatively inexpensive 50 x 4 is a significant upgrade from head unit power. Even with 200 watts to my midbasses, I would suspect that I rarely send them more than 50 watts. You can drastically improve a system with a well built amp, even a low powered, well built amp.


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## gstokes

Kenwood said:


> .. I have a Kenwood KDC799 headunit and Alpine SPR68 speakers. The headunit is 22 watts and the speakers are 100rms watts 300 peak power. Any advice??


In order to listen to those speakers play as Alpine intended you will need an amplifier, a 2-channel amplifier with 75 - 125 Wrms / channel would serve you well..


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