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amplifier power


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14 replies to this topic

#1 of 15 Phil P

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Posted November 26 2002 - 05:07 PM

Is it "bad" or can you have too powerful an amplifier? For example, a speaker that recommends a maximum of 300 watts and you have a 450watt rated amplifier. Bad for the speakers? I've heard it is better to have too much power than too little power for speakers. However, can too much power be detrimental to your speakers?

#2 of 15 Khoa Tran

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Posted November 26 2002 - 06:04 PM

I doubt having too much power will damage your speakers unless you play them at insane levels....

#3 of 15 Lyden

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Posted November 26 2002 - 08:50 PM

hmm curious would a 100watt amp damage speaakers that say 5-200watt recomended amplifire? and really who makes low end 200watt per chanel recivers?
"Remember the first rule of survival is to think about oneself."

#4 of 15 Bob McElfresh

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Posted November 27 2002 - 02:43 AM

This section of the HTF Primer and FAQ may answer your question.

In truth, for movies your receiver is only putting out about 5 watts per channel for normial dialog & low background music.

#5 of 15 AaronBatiuk

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Posted November 27 2002 - 03:35 AM

Quote:
hmm curious would a 100watt amp damage speaakers that say 5-200watt recomended amplifier?


Not necessarily, but I maintain that any amplifier can damage any speaker.

The single most common source of speaker damage is clipping; that is, trying to get more power out of an amp than it can put out. When you do this, the peaks of the signal get chopped off. This introduces very large amounts of harmonic distortion, which is mostly in the high frequencies. Because your speakers direct high frequencies to your tweeters, they receive this high level signal (the distortion). Tweeters are very small and delicate; they cannot withstand much power, and they don't normally need to. When you push your amp into clipping, your tweeters receive 10 to 1000 times as much power as in normal operation. They are quickly damaged from either bottoming out or their little voice coils heat up and melt themselves. Even the lowest powered receiver on the market can blow the tweeters out of most speaker systems. In fact, you are much more likely to cause this type of damage with a low powered amp, because it clips sooner.

Another source of speaker damage is bottoming out the woofers. This is usually caused by cranking up the bass on little speakers. Big speakers usually do not suffer this type of damage, because you will usually be satified with the amount bass before the point that you would be bottoming out the woofer. This type of damage does require lots of power to push the woofer beyond it's limits.


So basically, you can damage a speaker with too little power or too much. You should be able to hear the amp clipping or the woofers bottoming out. When you do, turn it down. You are probably damaging your ears by this point anyway, so that's good advice from more than one point of view.

#6 of 15 Chu Gai

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Posted November 27 2002 - 04:06 AM

I found this story on Usenet and some may find it amusing. I think you'll know which way to go after reading it Posted Image

Quote:
A letter from one of you out there set my mind a-thinkin, and I recalled the following incident. The letter, from a Mr. Peter Christy, went something like:


"Don't know where you spent your youth but remember
some Boston stories. During my college days there got
together with Danny Boynton who owned Audio Lab. He was
wonderful -- he didn't get confused about the issues,
but rather shamelessly sold on the psychological
issues. ... His only redeeming grace was that he sold
top of the line, quality material, and ... sold it to
me at cost so I got a Mac amp and preamp early on."

Well, I was quite familiar with Mr. Boynton and some of his shenanegans, one of which is most amusing.

Audio Lab was quite fanatic about MacIntosh equipment. Any criticism of it (and I was more than willing to supply a lot of criticism!) was treated simply as heresy. The equipment was kept in a showroom noted more for its reverential hush than its suitable listening environment.

As expected, less than rational means were used to promote the equipment. One example that impressed many uninformed buyers was the EPI 100 loudspeaker kept in the MAC room. The grill cloth was burned out completely, the speaker cone was mere ash and portions of the front of the cabinet were charred. This speaker, according to the Audio Lab legend, was set upon by none other than the almighty MacIntosh 2105 power amp. "So much power," it was told, "that the speaker literally caught fire!"

This seemed most suspicious to me. I inspected the speaker casually, and noted with great interest that in spite of all the apparent damage, the voice coil, the spider and the linen wrap on the speaker frame were in perfect condition!. It was, at this point, very apparent that the speaker had been burned, not by the almighty MacIntosh, but by the lowly Burnz-O-Matic propane torch.

I decided to play a little trick of my own. I challenged Audio Lab to a bet. I said that I could do the same thing to a MacIntosh speaker with a mere Japanese receiver. They accepted willingly. I purposely selected the lowest power receiver around that also proved to be the most unstable into reactive loads (I think I finally ended up with a 25 watt Pioneer of some sort. We hooked it up to the Mac speakers, and I was given the helm.

My game plane was well established. I ran the volume to full level, selected (purposely) an album of Beethoven String Quartets, to make the situation even more ludicrous, and, with the cuing lever down, dropped the stylus onto the middle of the record at about a 45 degree angle, at a very impolite speed. The stylus bounced once, and then obligingly scooted across the record to land on the label.

Well, the first bounce absolutely destroyed the midrange, the skipping then promptly fried the tweeter with a most satisfying flash that was visible through the grill cloth! Now, as I had hoped, this poor little amplifier, clipping up the wazoo, was staring at a most awful reactive load, as the destruction of the drivers had now rendered the crossover something else entirely.
The amplifier promptly latched up to the positive supply, dumping about 30 volts DC into the voice coil of the woofer. The speaker gave a couple of final squacks, and then was silent. The whole affair took, maybe, 4 seconds. Then, there was the unmistakeable odor of burning resins, and but the slightest hint of a curl of smoke coming through the grill of the speaker.

The staff was absolutely dumfounded. The scene must have been like that in biblical times, with the mauraders staring in horror as Goliath lay dead, bleeding by the temples, on the battlefield, slain by a mere boy. My only comment was, "When in Rome, don't f*** with the Gladiators."

You see, it was all quite simple. A small receiver, driven into clipping, can be most unstable, oscillating at high frequencies, suffering from power supply recovery problems, and so forth. I had a much better chance of killing the speaker with something small than with something big.

Needless to say, I was quickly made Audio Lab's official
Persona-non-Grata for Life. And till their dying day, I made sure that everytime I was in Harvard Square, I was sure to pass by and wave. By the way, the poor little receiver that couldn't but did survived unscathed, and ended up in a friend's apartment where, as far as I know, it remains playing music to this day.


#7 of 15 Phil P

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Posted November 27 2002 - 09:17 AM

Optimally then, should you get an amp whose power rating is higher than the maximal recommended power handling of your speakers? If so, then how much higher? Optimally, how powerful an amp should you get for a 4 ohm speaker whose minimum recommended power is 100 watts and maximum recommended power handling is 300 watts?

#8 of 15 Chu Gai

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Posted November 27 2002 - 11:59 AM

you need to come back with a bit more information...speaker efficiencies, room size, listening tendencies such as are you constantly listening at ear splitting levels or are your needs more modest...got a subwoofer...stuff like that Posted Image

#9 of 15 Phil P

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Posted November 27 2002 - 12:18 PM

how about speaker sensitivity of 90, 4ohm impedence, 22x15x7.5 foot room with acoustical paneling, reference level loud and sometimes louder, and have a sub?

#10 of 15 Chu Gai

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Posted November 27 2002 - 06:47 PM

more power's not going to kill you and having it provides things like peace of mind, the ability to handle wide program material, future speaker choices, if there are any, tend to be non-issues as your amp can handle lower sensitivities with ease. As you're probably aware, the actual effective efficiency of a speaker is about 2 or so dB higher when played in a room. To continue, each doubling of power means your speaker will play 3 db louder. 2 watts gives you about 95, 4 watts gives 98, 8 watts gives 101...etc. I'd say if you had an amp or receiver that did around 200 watts, you'd probably be in good shape given the size of your room.

#11 of 15 Phil P

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Posted November 28 2002 - 01:57 AM

What if I changed the speakers to 8 ohm, 50 to 500 watt handling, with 91dB efficiency and left everything else the same? Also, should you have less powerful amplifiers for your surrounds as the surround speaker max handlings are generally less, or match the same amplifier power rating across the board?

#12 of 15 Chu Gai

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Posted November 28 2002 - 05:12 AM

i don't see where my earlier 'ballpark' answer would change signficicantly based upon your parameters. More likely than not, when you go to separate amps, they'll handle 8 or 4 ohms easily. 2 ohms can be problematical for some. Regarding your rear channels, you're correct that they require less power so if you went with say something like 200 wpc up front (including center channel), than the rears would be adequately handled by say 100 or so. If you're looking for a hard and fast # for wpc then I'm afraid there isn't any. to give you a little perspective on relating to dB from a practical perspective,

180 dB: Rocket at take-off
140 dB: Jet engine at take-off
120 dB: Rock band
110 dB: Loud thunder
90 dB: City traffic
80 dB: Loud radio
60 dB: Ordinary conversation
30 dB: Very soft whisper

You won't go wrong more power but generally speaking you'll have to be prepared to pay for that headroom. Good luck.

#13 of 15 Phil P

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Posted November 28 2002 - 06:10 AM

Thanks for all the input.

#14 of 15 David Berry

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Posted November 28 2002 - 06:58 AM

Chu,

Good input with respect to the story. Kept me smiling throughout the read.

Phil,

As people have said, having a higher rated amp than what the speaker manufacturer calls for is not going to fry your speakers upon turning it on. The limiting factor for most people is that the cost gets high fast when purchasing good high output amps.

#15 of 15 Chu Gai

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Posted November 28 2002 - 07:17 AM

wouldn't you just love to pull that off at some snot-nose audio 'emporium'?? i sure would Posted Image





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