View Full Version : overpowering and underpowering speakers

steve s
11-20-2002, 02:49 AM
what happens when u overpower a speaker with an amp? i know (i think) if u underpower a speaker u might get distortion or something...some websites said it's better to overpower than to underpower...but they never say what happens when u overpower....

say, amp rms power is 50W and the speaker rms power range is 2-35W?

what about if the amp peak power is 200W and the speaker peak power handling is 160W?

Hank Scorpio
11-20-2002, 02:55 AM
Well, you'll know it pretty quick when you really over power a speaker, it goes kuput.

Under power does cause distortion, though differently, the sound just always seems muffled. Overpower won't have a problem unless you really push the piss out of them, though that depends on how over powered.

Want a fun scientific test? Go find a intact cheap (I mean CHEAP) little car speaker. Hook it up to your home entertianment system and blow it up, atleast this will let you know what they sound like when your pushing them to hard. Oh ya, that and its fun!


I guess I could go into depth, but I think you'll be ok.

Oh, I don't think your amp is 50rms, seems to me that OE amps are probably 20-30rms.

steve s
11-20-2002, 09:24 PM
no ur right, 25x4...thanx :)

have u tried adding an amp? there seems to be a space in the rear next the spare tire on the driver's side where the cd changer's supposed to be...think it'll fit an amp?

Hank Scorpio
11-21-2002, 01:32 AM
Sure it will, though I have yet to dive that far into a 850. Arandall850 did some neat mods w/ something similar.

on my buds stereo-monster 850, he added amps to the stock stereo using line-level inputs from the rear speakers, and that didn't sound that great imo. Best bet, if your going to add amps, it's time for a good deck unit now.

steve s
11-21-2002, 02:18 AM
arr...so many issues :eek:

thanx for so many of ur replies :)

11-24-2002, 05:34 AM
If you want a cleaner signal without buying a new deck use my little RCA adapter dealy. See the thread "how to get RCA preouts from a factory deck"

11-24-2002, 07:36 PM
Money money, mo money. The strentgh of the system is always determained by the cheapest part. You need my wife's ears, can't tell the difference between a Realistic and Alpine system, can you say close and play?

steve s
11-25-2002, 01:51 AM
Originally posted by steve s
have u tried adding an amp? there seems to be a space in the rear next the spare tire on the driver's side where the cd changer's supposed to be...think it'll fit an amp?

i meant under the carpet...i remember there's some space under the panel to the left (driver's side) covering the spare tire as well as the side panel. this is not what i mean musterdbom's installation (http://www.volvospeed.com/vs_forum/index.php?act=ST&f=13&t=4872&st=0&#entry29864), i mean under or behind the panel that musterdbom put his amp...

08-13-2004, 09:59 AM
The truth to this, if you underpower speakers you get distortion, the distortion will overtime rip the cone on the speaker since it doesn't have enough power to get the entire signal out. Overpowering is much better for a speaker if it's a short term thing. When I say short term that means if you have a 200 watt max speaker don't run 250 watts RMS to it, but you can have 250 watt peaks going to it, and it should be fine. For instance you know a good sub, my Bose 502 subwoofer for instance, it has a 900 watt peak to it and I push 2000 watts peak to it for 7-8 hours straight almost everynight and i've never had any problems with it. And that's more than double the power! So the moral of this story is, it's always better to overpower on a short term basis than to underpower a speaker at all, just if you do start to overpower speakers just know how good of a speaker you are doing it to.

Volv-a-Ratti Man
08-13-2004, 11:16 AM
Well, I hope you have some $$'s to eventually replace that expensive Bose sub & amp.
Overpowering the speaker is a no-no, and explained in simple physics and knowelege of an electrical circuit , power = v x a; and for a audio amplifier, the output is alternating current governed by the frequency of sound that the music contains.
Low frequencies contain the most peak current, so over driving the sub will cause didtortion in the voice coil of the cone or driver.
High frequencies on the other hand, require little amounts of current by comparison but have very high peak voltage and will usually cause excessive high frequency distortion before any speaker damage is done. It is the smaller diameters of the cone that produce the high's and larger diameters produce bass, driven by the excursion distance of the voice coil resonating the cone.
If the peak frequencies that are amplified exceed the spec's of the cone, the circuit, both amp and speaker will be subjected to damage casued by heating of the coil or mechanical limits of the cone material - RIP!!! Or more common in a sub, the coil seizes due to long periods of overpowering. Since heat is the cause of this, the coil requires more current which over taxes the amplifier, and will blow the amp if not protected.
Extended periods of overpowering can slowly degrade the cone material. Have you ever taken a piece of paper and folded it repeatedly? Eventually it tears apart easilly. This is what you're doing to your speaker by overpowering it.

Accurate speaker and amp rating are done in RMS watts, not peak watts, so disrgard any manufacturer's rating based on peak handling performance, because this is solely dependant on the music or alternating current distribution from the amp and music you choose to play.
RMS, or root mean square is the description of a balanced power distribution for a time weighted average across all frequencies the speaker is intended to reporduce, meaning this speaker or amp can handle X amount of power at X to XX frequecies over a given timed average interval.
Underpowering cannot produce distortion in itself. The audible difference in sound is apparent, as Doug mentions above, but it is due to the fact that different frequiencies take different power levels to achieve a uniform balanced decible lever out ot the speaker. So when the power is too low, the low and mid frequencies are not getting the correct excursion of the speaker cone to accurately produce those frequencies. The minimum RMS value is the lowest power that is recommended to produce a balanced flat frequency response from the speaker.

In general, the speaker should be able to handle far more power than the amp can put out. This way, speaker distortion never enters the picture, nor does overheating of the voice coil. This also ensures tha the amp doen't get overdriven, mostly because you would hear the amplifier disortion and turn it down before any amp damage is done. Also, turning up an amp and driving a speaker with noticable distortion can cause the speaker to be damaged because the alternating current for any given frequency gets out of phase with respect to another frequency. Think of it like one's pushing the cone while the other's pulling.

I would choose an amp with an RMS rating that is 60% of the speaker RMS rating.

08-13-2004, 12:44 PM
What he said.... ^

Take it from me, er.....him. If you know anything about electrical engineering or acoustics engineering, he's right on the ball in terms of a quick, fairly general answer.

Thanks for posting a well thought out post Peter, you saved me from having to type a looong post. :)

08-13-2004, 01:56 PM
I'm a professional sound engineer, I design large sound reinforcement loudspeaker systems for clubs, schools, etc. And my Bose has been doing this for years, with the same amp. Trust me, for 2 grand this sub better do something. It's a 12 inch woofer with a 4 inch voice coil. I've never had any trouble, when I push it, and the amp goes into hard clipping where the clip light doesn't turn off, the amp goes through a thermal shutdown (from poor ventalation) before the sub starts distorting. But I only push the amp like that if i'm outside, but i've worked on the ventalation :) cause it's a 1000 dollar amp and I don't want to fry it lol. So it's a 1000 dollar amp and a 2000 dollar sub, so you better believe for all that money that it better be a decent system. And i'm not worried about it, if they get trashed, i'll just go out and buy another one :) but that wont happen anytime soon, since I just inspected my sub last week and no signs of tears or stress marks on anything, so it's still going to last me for a long long time. If it does deside to die on me someday no big deal, i'll just buy another one. It's the joy of owning your own company.

08-13-2004, 01:59 PM
one more quick thing, i'm talking about top of the line speakers. Anything like car audio subs, you can still overpower but they won't last long, you have to use true pro line speakers to really get away with overpowering. And if you really want to see what speaker i'm talking about it's the Bose 502 BP. So take a look if you want to

Volv-a-Ratti Man
08-13-2004, 04:00 PM
Your luck may last only because the Bose is either very conservatively rated for RMS power handling, or the amp isn't really pumping out the RMS values it is advertised to have (which is a highly likely situation, since only the best amp manufacturers give an accurate RMS rating at a low distortion). Good speaker manufacturers under rate their speakers to prevent people from overpowering their produict and run into frequent warranty claims. They, justifyably rate them at the point of exceeding the distortion spec, not the break point.
It can only be 'power out cannot exceed power in', because of loss due to the coil impecence and heat generated further reduces output power. If the speaker was rated lower than the amp and you've pushed the amp to clipping, then you cannot have exceeded the speakers capability, regardless of what the rating is. Something is not correct in you assesment.
Described by V = I/R*t, where t = temp, r = the speakers coil resistance. All things considerd, the voltage drops as a function of increased temp and the current consumption also goes up with increased temp, always reaching an equlibrium for the A/C circuit.

Think of it this way, if you pump water into a pipe with a large diameter pipe that tapers down to a small diameter (Bernulli's principle), the pressure goes up until the smaller pipe's conductance is exceed and the pipe bursts. It's still the same amopunt of water, cannot get more through the pipe than the inlet flow provides. Although this is fluid dynamics, the illustration is relavent.
Conservation of energy. It works the same way with acoustic wave theory.

11-18-2004, 11:40 AM
If you're going to have a mismatch, it's always better to have the amp rated higher than the speaker.

Amp power > speaker power:
As you know, the amp doesn't pump out the maximum power all the time. The power output is proportional to the volume level. As you increase the volume beyond the speaker's capacity, you'll first just rattle the speaker cone as it begins to exceed its mechanical limits. In this region, you're just making noise, but not really damaging the speaker. If you turn it up further, you will eventually get to the point of exceeding the electrical limits, and you might overheat the coil or burn it out altogether.

Amp power < speaker power:
Starting at a low volume level, the amp is probably able to drive the speakers without distorting the signal. That means the amp is producing the sinuous sound waveforms correctly at the output. As you increase the volume, the peaks of the waveforms begin to approach the electrical limits of the amp's transistors. Eventually, you reach the transistors' limit: The waveform peak voltage is somewhere above what the transistor can put out. So, the transistor simply stops when it reaches this ceiling.

Instead of smooth, sinuous peaks, the waveform now plateaus. This is called "clipping". On paper, it would look like someone cut the waveform off with scissors.

This is where the real damage is done. Your speaker has a filter that passes only high frequency energy to the tweeter. (Someone mentioned earlier how tweeters use less energy than woofers, and would be damaged if they were connected directly and forced to take the woofer signal.) When the waveform clips, instead of a smooth curve, you get a sharp 90-degree angle. Electrically (and mathematically), a 90-degree angle is a composition of ALL frequencies. So in that one instant, taking the sum of all frequencies, you have a HUGE burst of energy. Most of this energy is above the cutoff of the tweeter's filter, so most of it goes right through the filter - straight to the tweeter. Too many clips like this, and it doesn't take long before the tweeter's coil burns out.

The woofer sees this energy, too, but it's coil has too high of an inductance for the higher frequencies. It simply reflects the higher frequencies back.

Summary -
In short, too much power just rattles woofers (up to a point). Too little power destroys tweeters.


Volv-a-Ratti Man
11-18-2004, 12:02 PM
I appreciate your analysis, although I have my own personal opinion that the speaker if designed properly should never have components (except a fuse!) that can be exceed by the amps capability to deliver any sound form, including a square wave input signal. (my rule of thumb is amp peak output=1/3 of speaker capability)
I agree that the square wave that is transmitted during clipping will do the most damage to the tweeter, but a well designed crossover that has volatge limiting circuit that bleeds high frequencies to the tweeter in parallel to the woofer inductive coils will reflect back the excess power to the woofer and/or simply take out a capacitor long before the tweeter sees the destructive power. It is important that the fuse is placed in the crossover network at the high-pass location, along with an amp speaker line fuse to prevent low impedance mismatch due to load current that takes place when the speakers heat up and the impedance drops especially when the bulk of the music content is low frequencies.

11-18-2004, 12:15 PM
That makes perfect engineering sense, and that is what I would do if I designed a system.

It's unfortunate, though, that most of us don't have well-engineered crossovers. Most of us have "two-way" or "three-way" speakers that often have nothing more than an electrolytic cap in series with the tweeters.

Funny - I always go for an amp rated at least as high as the speaker, and double if I can afford it. I ran a monstrous Rockford Fosgate 200W amp to power a (relatively) cheap set of two-way Pioneer 6x9's in my 260 for many years.