amp rating vs. speaker rating

[67 455 Bird ragtop]

I hope some one can clear up a possible mis conception I've had for a while. I was always under the impression that your speakers should always be rated higher than your amp. But I was discussing this with a co-worker and he suggested it's just the opposite. And here was his reasoning. It sounds logical. But is it correct.

Let's say you have a speaker rated at 50 watts RMS. You should run an amp rated at between 80 and 100 watts. The raeasoning is you wil get better clear sounds at the lower output from your amp but still not over drive your speakers. Kind of makes sense. if you only run your volume/amp output at say 40% you're only sending 40 watts to your speakers but since it's down in the amps power band the distortion will be much less than running a 50 watt amp at 80% volume putting out the same 40 watts.

Opinions ???

[LSx_88_Ciera]

Don't agree.
With a properly set quality amp you will not be creating very much distortion so it is a non factor. Where people run into trouble is when they overdrive the amp and it starts to clip. In case you are unaware of what clipping is, it is the point that the wave becomes to big and instead of a proper sine wave the + & - peaks turn into a square wave otherwise known as DC offset. This DC offset causes the voice coils to heat up near the limits of it's excursion and can burn the VC. One thing to remember is that to gain 3db of output from a speaker you have to double the power so once you reach the 50% point there is only 3db left in the speaker. This is where the distortion comes from not the amp provided you are using a quality piece.
I will say that most reputable speakers will hold more power than they are rated at especially when it comes to subs provided they are in a proper size enclosure. The size of the enclosure has a drastic effect on power handling.

[mc84_zz4]

The RMS rating of the amp is the constant power output the amp provides, the Max watts is the high output it can reach during a musical peak.
For Subwoofers the matching is suggested to fall within the top 40% of the speaker capability in RMS, so a 200 watt amp would work well with a speaker rated in the 200-250watts RMS range.
If your amp is on the lower side of the musical capacity, there is not enough power to make them sound good.
As mentioned before, you can overpower some speakers a little, as long as the Max watts handling is not exceeded.
HTH

There are also some great tutorials on www.crutchfield.com for doing research, and they also can help you match your system components too.

[MonzaRacer]

OK after 20 plus years of building stereo systems Ill weigh in here.
Most solid, common sense rule of thumb I always go by is look at your RMS wattage, forget the peaks.
First of all reason to ignore peaks as this is old school marketing lets tell them its a 3000watt amp, yet that is only at 20,000khz, something the human ear cannot hear, its not a lie, just a big snow job as some of those amps would only be rated at 100watts RMS.
Now RMS ratings are set in stone as for the testing.
Now another way to see this is like looking at CB radios, they use dead key then peak wattage, but dead key gets it done, peak wattage or swing make it heard.
worry about the dead key and get a clean smooth peak swing that doesnt slam the limit wall ofthe driver chip. or you get clipping of the wave form. and its all muddled up.
So now that your confused the issue your wrong friend has given is that your amp, at even modest volume levels will cause speaker over excursion of the speaker cone/voice coil, ie it blows stuff up or the voice coil will over heat and burn out.
Think of it this way, a starter pulls 125 to 150 amps and uses a minimum of 4 gauge cable, now rewire it with 12 gauge wire and see what happens, the cable will burn and dang fast.
Now rule of thumb, low end amps have higher total harmonic distortion (%THD)are less efficient and ie less quality.
Lower is better.
Now if you figure the THD is high then its ability to actually maintain a true, say 80 watts RMS, is suspect and the closer your amps RMS output is to speaker your probably still ok.
BUT on high end amps these are usually very accurate if not able to make better performance than advertised so watch your ratings.
OK that being said and hopefully your not too confused here is my professional opinion:
Speaker RMS input at 4 ohms 100watts= use a n amp in the 80 watt RMS range at 4 ohms, if you use caps on high end and mid range speakers to limit the bottom end frequencies from the speaker you can get away with 90W RMS amp.
On subs use inductor coils to limit the high end frequencies going into the speaker and you can use same limits, oh and just for rule of thumb 6.4-7.0 mH inductor coil on a 4 ohm system will limit the signal to 100hzand below, right where most subs are designed to run.
Now the caps and coils idea is called first order frequency control and for just about everybody its going to do 90 percent of the jobs out there. The use of those huge ,expensive 32 band EQs, well if you got the cash fine but I have taken many a places with systems I built for people and only use caps and coils and against EQ systems.
Now trick is if you stay in the 90 percent or less you should have long speaker life, have a system that makes good sound and is plenty loud. Oh and unless your going for the chrome remover system 100-150 watts RMS amp out put is plenty for most drivers.
Can you use more with better subs, yep. Is it needed, only if you measure your worth by the excess watts you bought.
One of the neatest setups I had was a Marantz BP750 with amp blocks, would run up to 5 blocks per power supply and was 1 ohm stable, and was rated at 90W RMS@ 4 ohms. Ran 2 / 10 in Blaupunct (sp) Pro Components subs (100W RMS @ 4 ohms) and Optimus 6x9 ways from Radio Shack rated at 100W RMS.
I never broke a sub but did wear out a couple of 6x9s.
That system was fed from the RCAs of a Kenwood KDC 4003, still got it but it doesnt like to spit out CDs so it got repalced. I split the rca cables with Y s and ran 2 out to 4 amp blocks and that system would return an RTA rating of 39 out of 40.
And with a system rating only 360W always got tagged in with the 501W-749W crowd but still I would lose t oguys with more and bigger subs, but my system way always ran to listen to music for most everyone as my system would play anything nearly with only a change to the base settings.

[67 455 Bird ragtop]

Thanks for all the feedback. Was VERY helpful. Will probably use the 80-90% "rule of thumb" as my guidelines for this. Since my car is a sort of prostreet vert I plan to have speakers in the kicks, doors, and something where the back seat used to be as fill in. Maybe some 6x9s and/or a sub. Still a few months away from really worrying about my stereo. Just wanted to get some good info up front.

[John Wright]

to gain 3db of output from a speaker you have to double the power

speaking of dBs....I thought you doubled every 6dBs.<thinking back to my old ultrasonics classes many moons ago>

6dB = 2:1 ratio
12dB = 4:1 ratio
18dB = 8:1 ratio
etc......

[nekkidhillbilly]

i try to match rms to rms

[MonzaRacer]

The reason for NOT matching rms to rms is would you build a 500 hp engine the run it at 500 hp or build a 1000hp engine make 500-600 and add a 250 shot. See the reason for the 80-90% rule is to give your self some lee way,,,reason is that your amp may be rated at 80 watts at 13.5 volts, yet your car runs 14.2 volts then you may get more out of it.
Its like running an engine with a redline of 6000 at 6000 all the time.
Now actually for every 1db increase you have to double the power in audio terms.
Matching audio items and doing it successfully is an art and it took me 10 years of steady reading, learning and doing to get where I am and I DONT do it everyday as it is a time consuming job.
Properly installed quality components will sound awesome, average quality components properly installed will sound very good and most people will never know difference.
Even super cheap quality stereo parts can be made to sound much better IF the installer knows what they are doing.
I have pieced together some really awesome sounding systems and made the barely passable parts work together.
Also I do not get totally into major electronic gadget to make stereos operate, last set up that I fixed had several add on pieces including a 32 channel eq,,,pulled almost all of it , did simple caps a nd coils on the speakers, reset the amps as the previous installer cranked the gain all the way up.
Oh and had several speakers wired backwards!
That car really rocked after the redo.
KISS=Keep It Simple, Stupid

[GM Muscle]

90%

[MonzaRacer]

again if you keep it closer to 80% your good and honestly even a 60% system will blow you away.

[hifi875]

95% of the time lack of power blows speakers not power. its better to have too much power than not enough. most listening is not done at a amps rms output. the key is to buy a reputable speaker/amp from a reputable company that has a reputation for making a good product. you get what you pay for. a high power cd player is way more dangerous to a pair of speakers than the same deck w/a separate amp. stay away from 1k power ratings, they are useless. that is a single frequency. we do not listen to a single frequency. you need a 20-20k power rating(the effective range of the human ear) with a thd spec in the .04-.10 range.

[Joker69Camaro]

I run my midranges, tweeters and subwoofer at double their RMS in my competition car (This is a sound quality vehicle, not one of those things rattleing your windows at a stoplight). With safe crossover points and clean signal (no clipping) your fine. As long as you dont play the speaker/driver to the point of it distorting you shouldn't have a problem. Of course there are exceptions to the rule, but they are allmost allways very high end speakers/drivers that don't like being overpowered for long period of times. These speakers usually are very sensative >100db sensativity and are VERY expensive. Nothing most of us would ever use in a car unless thats what the car was built to do solely.

PS: My competition car is my daily driver and this stereo gets beat on daily. Had the same speakers in it since 2007 when it was built, allmost 100k miles ago!

My $.02
Jeff K

[castine917]

i try to run my rms close to 80% but look at variance of manufactures. specs from some are lies while others are accurate and yet others are under rated. check for independent testers is what i'm saying.

[nekkidhillbilly]

i usually go a little higher like if its 60 rms speaker ill go 75 rms to it

[MonzaRacer]

95% of the time lack of power blows speakers not power. its better to have too much power than not enough. most listening is not done at a amps rms output. the key is to buy a reputable speaker/amp from a reputable company that has a reputation for making a good product. you get what you pay for. a high power cd player is way more dangerous to a pair of speakers than the same deck w/a separate amp. stay away from 1k power ratings, they are useless. that is a single frequency. we do not listen to a single frequency. you need a 20-20k power rating(the effective range of the human ear) with a thd spec in the .04-.10 range.

Thats crap, I have seen more speakers with burnt voice coils and over excursion more than anything else and that was with big amps on weaker speakers.
Now if the person is trying to run a 500 watt rms sub on 5 watts yeah maybe but then signal breakdown might be doing odd things to voice coil.
you push 20 volts in to a 12.6 volt system and your gonna blow something.
I have built systems for decades, and most of the bigger systems are still functional,,,and I still go by the 80%to 90% rule,and I really like to use regulated line voltage, used to buy Jacobs Electronics adjustable regulators, these and good caps always made my systems thump,,,and not blow chunks.
But just professional opinion, and from experience. I have repaired WAAYYY too many systems that go overkill. Again I have seen so many good sounding systems and the ratings came in the 60%to70% range.
Ill take lower wattage and better sound specs any day, quality over quantity.
Kind of like the guy with the big slobbery over cammed POS over the guy with a well built well tuned car that runs and drives and is controllable will pretty much out run the first.
run 500 watts into a 300 watt speaker and you can watch the cone get out of control.
ok if you want to run 200 watts rms into a 5 watt rms speaker, but after seeing systems fall aprt all with good stuff just way over powered. If you get away with hooking up 4 times too large amps to speakers go for it, but I took my old 70 Monte with 2 10" Blaupunkt subs and 2 Optimus 6x9s and they were mounted in a board inplace of my package tray, the car pulled 39 out of a 40 max in RTA real time analyzer and I was running 360 watts and took a 3rd behind a 5 yr champ who got 2nd but trashed 3 speakers and number one who killed an amp and a battery. and those guy just couldnt get over my system.
But then I learned stereo back when there were no amps, heck I can remember breaking open amp/boosters and putting in circuits to clean them up. then amps started becoming mainstream, heck I can remember buying home audio subs cause there were no automotive subs yet.
Do what you want, Ill stick with what I learned and rules that actually make sense over "well i do this and its still together" . Kind of like building an engine to have some lee way. If your reasoning stands why build the 350 for 500 hp, just slap that 300 shot on a stocker and go to the races. see how long it lives, oh and ever watch small speakers actually burn? Been there and seen that Alpine V12 ran to A pillar tweets and mids. guys car never had any distortion, but he actually melted speakers.

[hifi875]

No its not crap. You double power and get 3db not 1db increase in spl(theoretically). Most all amps today are rated at 14.4v (cea 2006 spec). Reality is in a car the amp will never see 14.4v due to voltage drop from battery to amp. Normally they will see 13.8 or lower. And then when you start leaning on it the current will usually drop more. And as the current goes down amperage consumption goes up, things get hotter, distortions rises. Thats when you blow up stuff w/ underpowered equipment.
The use of coils and capacators is virtually nonexistant except in the case of tweeters and up to 4inch speakers in which a capacator is used. coils on subwoofers stopped in the 80's w/the advent of electronic xovers. most aftermarket decks even have electronic xovers in them now. Electronic xovers are alot more efficient than coils and allow for alot more tuneability. and just because you say you scored a 39 on rta doesn't mean it sounds good. If you limit the signal that the speakers gets to its effective operating range, then there really isn't any harm in running more power than the rms rating of the speaker. duh common sense.

[Draginutz]

Straight from Crutchfield.

Choose an amplifier whose power output is rated at least 70% to 125% of the power handling of the speakers you'll be amplifying. Make sure you're comparing the RMS power ratings of both the amp and speakers. And remember — it's better to overpower your speakers a little than to send them too little power.

[dipren443]

Straight from Crutchfield.

Choose an amplifier whose power output is rated at least 70% to 125% of the power handling of the speakers you'll be amplifying. Make sure you're comparing the RMS power ratings of both the amp and speakers. And remember — it's better to overpower your speakers a little than to send them too little power.

Yup, and you can always adjust the gain back a little on the amp if need be.

[nekkidhillbilly]

you can clip them and burn up voice coils by being underpowered by some. you would have to be decently underpowered not like 10 watts under.

[dcozzi]

Yup, and you can always adjust the gain back a little on the amp if need be.

I run quite a bit more powerful mono amp than the RMS rating on the woofer and a little bit more powerful on the mid/tweets 4 channel amp. Basically using the "headroom" principal. I set the gains lower and use a cap/coil based crossover for the mid/highs. The deck crosses over the signals 2-way before going back to the amps.
The system is a single 12" woofer, 4 X 6.5" mid, 4 X 1" silk dome tweets. Also, 2 X 1" silk dome (attenuated) pillar tweets to bring up the soundstage a bit.
I had an Epicenter, high end processor, 32 band EQ/Crossover and it sounded like a $200 stereo. Took all that crap out and, now, it sounds perfect.
Strictly SQ.

I agree with the point that the size of the box dictates the amount of power to feed the sub. A smaller box needs more power for the woofer to reach maximum excursion. Bigger takes less power, sometimes plays a little lower, but takes up space most interiors do not have. The only way I have seen a woofer blown is by distortion at high volume and over-excursion. Damn kids!!