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WATT theory?, So what does it all mean?
puntloos
post Jul 31 2006, 14:21
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I've recently come across (and bought biggrin.gif) a pair of Quad 989 speakers.

Now the speaker specifications are: "Power capacity: 100W, 10V RMS, 40V peak maximum signal input."

Yet a lot of people reccommend to buy MUCH more powerful amplifiers. (http://www.stereotimes.com/amp100702.shtml says a 2x250W amplifier is the 'ideal pairing').

Can someone explain to me what the deal is? When will 2x250W give speakers more breathing room (whatever that means), and when will 2x250W burninate my poor $9000 speakers?
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CSMR
post Jul 31 2006, 15:00
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That is nonsense. You need an amplifier that is rated for the maximum power you need. If you used 2*250W you can expect arson attacks from your neighbours. What you need depends on how good your hearing is, what music you listen to, the sensitivity of your speakers, and your personal preference.
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pepoluan
post Jul 31 2006, 15:33
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Not much bigger, no.

It's only that some amps, nearing its top power output, distorts.

That's what the fuss with the "breathing room". At 80% top power 99% of amps don't distort. Well, the quite good ones, that is (good <> expensive, mind you).

Of course if the amp is rated 2*250 W even 80% is big enough and, like CSMR said, will start a neighborhood riot biggrin.gif


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cabbagerat
post Jul 31 2006, 15:55
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One thing to notice is the rating:
100W, 10V RMS
What this means is that their real power rating is only 12W continuous (assuming 8ohm, if they are 4 ohm then it's 25W), so the spec is lying to you. The next thing is that their peak voltage is rated at 40V (200W into 8ohms. which is interesting) which is obviously specified for short transients.

Amp distortion near the top power rating is mostly due to the specification being a little out of sync with reality. For example, my amp can put 162W per channel of square wave into my speakers but only 82W of unclipped sine wave.

So, if your amp vendor is honest, then a 2x100W (or even 2x50W) amp with decent full power distortion figures will be plenty (in my opinion).


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Danny Kaey
post Jul 31 2006, 16:31
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QUOTE (puntloos @ Jul 31 2006, 06:21) *
I've recently come across (and bought biggrin.gif) a pair of Quad 989 speakers.

Now the speaker specifications are: "Power capacity: 100W, 10V RMS, 40V peak maximum signal input."

Yet a lot of people reccommend to buy MUCH more powerful amplifiers. (http://www.stereotimes.com/amp100702.shtml says a 2x250W amplifier is the 'ideal pairing').

Can someone explain to me what the deal is? When will 2x250W give speakers more breathing room (whatever that means), and when will 2x250W burninate my poor $9000 speakers?


what you have to take into consideration is "peak power", ie. a musical signal is never a constant level, it is more like valleys and peaks... the peaks are were for brief moments the amplifier has to generate multiples of its rated continous power to cover the dynamic range. By having a reasonably powerful amplifier you are buying yourself "headroom" in the sense that the amplifier will be capable of producing enough peak power as to not clip or distort the incoming signal. A clipping or distorting amplifier will damage your loudspeakers far quicker than having one that has enough peak power.

PS: this all assumes a reasonably loud listening level - you should be aware however, that your Quad's are not decibel monsters so don't expect to drive them to loud anyway...

This post has been edited by Danny Kaey: Jul 31 2006, 16:34


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DigitalMan
post Jul 31 2006, 17:07
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QUOTE (CSMR @ Jul 31 2006, 06:00) *
That is nonsense. You need an amplifier that is rated for the maximum power you need. If you used 2*250W you can expect arson attacks from your neighbours. What you need depends on how good your hearing is, what music you listen to, the sensitivity of your speakers, and your personal preference.


Not true - I've destroyed far more speakers with low power than high power. I destroyed two pairs of tweeters with a 25W receiver that was routinely driven into clipping (thus creating a lot of relatively high voltage/power ultrasonic harmonics that kill speakers). After switching to a pair of 500W mono power amplifiers (overkill for certain) I never blew a speaker again. And the speakers were "rated" at 250W.

Remember speaker ratings are just general ballpark figures based on typical music signals in a steady state situation, not high frequency squarewaves that come from clipping amplifiers. You can usually exceed the "maximum power rating" by quite a lot for transients if the signal is clean.

You can never have too much clean amplifier power as long as you are sensitive to not overdriving the speakers. Speaker distortion rises gradually to help you know when you're pushing it - amplifier clipping just happens without much warning. So it is better to have a higher powered amplifier.

Now the Quads are electrostatics IIRC, and can be fragile relative to arcing burning the transducer, so if you're rocking out you may not have the right speakers.

Be careful out there.


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boojum
post Jul 31 2006, 17:11
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I have a pair of SoundLab Pristines I drive with two 1,200 watt amps. In the '38-'39 US Worlds Fair in NYC Westinghouse found that 80 watts were needed to reproduce solo piano with the then high efficiency speakers.

If you match your speakers and amps watt for watt you will be over-driving your amps at musical peaks. This often results in clipping which translates to square waves which translates to broken speakers. My electrostatics play bass pretty well, way better than most electrostatics, and sound better than the Martin-Logans which are "mushy" to my taste. The ESL's are sweet, but could handle no power/volume in the past. They seem to have gotten past that. My speakers are rated at 200 - 500 watts, I think. The high wattage amps I have allow the amps to act as a damping agent, too, as I understand it. I do not over drive them, but they handle power well.

Anyway, the point is that more speakers are destroyed by underpowered amps than overpowered. Old ESL's would arc when driven too hard! Yeah, the old 63's. I just preached on this in another post: check JBL's pro web site for info on speakers blown from too little power. Having huge amps does not mean you will be playing the speakers that loud. You control the volume with that little round knob. I think the rule of physics is to double the volume you need square the power, so do not worry. cool.gif

QUOTE (puntloos @ Jul 31 2006, 06:21) *
I've recently come across (and bought biggrin.gif) a pair of Quad 989 speakers.

Can someone explain to me what the deal is? When will 2x250W give speakers more breathing room (whatever that means), and when will 2x250W burninate my poor $9000 speakers?



They will work just fine out of the box. If you feel better about it, give them a week. Most hi-end audio lore is BS. cool.gif


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MedO
post Jul 31 2006, 17:29
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Maybe I missed something, but isn't 200 Watts quite a lot for home use? A friend once showed me the volume of a pair of speakers running with 1 Watt (measured at the speaker cable), and it was already too loud for normal listening imo. I know that double power is not double volume, but still, it seems a bit much for me. My speakers are rated for 15 Watts each, and I never used them anywhere near the point where they would start to distort (in fact, when I tried to find this point it was very uncomfortably loud). I do get them to distort at lower perceived volume when I turn up the bass all the way, but that's not how I would normally listen.

Maybe I should add that the most expensive piece of audio equipment I own are my Sennheiser PX100s, so I have no experience with good speakers, amps etc.
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cabbagerat
post Jul 31 2006, 17:42
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QUOTE (MedO @ Jul 31 2006, 08:29) *
Maybe I missed something, but isn't 200 Watts quite a lot for home use? A friend once showed me the volume of a pair of speakers running with 1 Watt (measured at the speaker cable), and it was already too loud for normal listening imo.
The efficiency of the speakers comes into play quite heavily here. This can range over about 100x (20dB), so judging one set by another is not really that educational.

I have linked to Rod Elliot's article on why small amps kill tweeters many times. It's really worth a read for those of you who haven't read it yet.

Boojum: What is the real power of those 1200W amps? If they can really put 1200W of sin wave into an 8ohm load then I am seriously impressed. I have a 6kW test load that I use as a footrest at work (don't use it much) which could do with some warming smile.gif


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bhoar
post Jul 31 2006, 17:56
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QUOTE (MedO @ Jul 31 2006, 12:29) *
Maybe I missed something, but isn't 200 Watts quite a lot for home use? A friend once showed me the volume of a pair of speakers running with 1 Watt (measured at the speaker cable), and it was already too loud for normal listening imo. I know that double power is not double volume, but still, it seems a bit much for me.


Note also that twice the power is only +3db an increase in volume, assuming the speaker has a relatively linear sound output increase vs. the electrical input increase. 1dB is considered the smallest perceivable change in volume that an average human can notice in tests (this may be the definition of the dB).

I've read that increasing +6db to +10db is the range people generally count as "twice as loud". If we work with the upper end (perhaps a good idea since the speakers might be losing efficiency as the power increases), 1W to 100W is generally going to be a change in perception of "four times as loud".

Essentially, you're not supposed to be buying the 200W vs. 100W amp for volume purposes. You're buying it for greater rail-to-rail headroom before the amp starts to clip and sends a frequency distribution that the speaker drivers are not designed to handle.

-brendan

This post has been edited by bhoar: Jul 31 2006, 17:57


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arpeggio
post Jul 31 2006, 18:46
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QUOTE (bhoar @ Jul 31 2006, 18:56) *
....
Essentially, you're not supposed to be buying the 200W vs. 100W amp for volume purposes. You're buying it for greater rail-to-rail headroom before the amp starts to clip and sends a frequency distribution that the speaker drivers are not designed to handle.

I second that! Volume is not a purpose in itself. What is most important is that your amp should have more than enough power to handle all the dynamics in the audio signal before it will even start producing audible harmonic distortion. And it should absolutely be capable of handling these dynamics without clipping.

Now how many watts is 'enough' ?
The amplifier volume you need depends on the sound pressure level (SPL) you want to achieve in YOUR listening environment with your preferred kind of music.

To determine the SPL you want there's a very nice article on this subject here.

Especially for puntloos being a Dutchman here is a Dutch site that gives some info too.

Cheers!

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CSMR
post Jul 31 2006, 19:55
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QUOTE (DigitalMan @ Jul 31 2006, 08:07) *
QUOTE (CSMR @ Jul 31 2006, 06:00) *

That is nonsense. You need an amplifier that is rated for the maximum power you need. If you used 2*250W you can expect arson attacks from your neighbours. What you need depends on how good your hearing is, what music you listen to, the sensitivity of your speakers, and your personal preference.

Not true - I've destroyed far more speakers with low power than high power. I destroyed two pairs of tweeters with a 25W receiver that was routinely driven into clipping (thus creating a lot of relatively high voltage/power ultrasonic harmonics that kill speakers). After switching to a pair of 500W mono power amplifiers (overkill for certain) I never blew a speaker again. And the speakers were "rated" at 250W.

You can never have too much clean amplifier power as long as you are sensitive to not overdriving the speakers. Speaker distortion rises gradually to help you know when you're pushing it - amplifier clipping just happens without much warning. So it is better to have a higher powered amplifier.

Obviously you were using an amplifier which is not adequate for your power need, hence the clipping. Nothing wrong with an amplifier being higher power, it just is not useful if you don't need the power, so you restrict your choices and likely pay more than necessary.
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cabbagerat
post Jul 31 2006, 20:15
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Another one of Rod Elliot's articles is somewhat relevent to this discussion. It was something I found very interesting the first time I read it - Power Amplifier Clipping. It's really worth a read if you are interested in amplifier clipping.


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Gecko
post Jul 31 2006, 20:15
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I don't really buy into this "your amp needs to be much more powerfull than your speakers". Just as speakers can take transients with much more power than their RMS rating, an amplifier can deliver transients much stronger than its rated RMS power without much distortion. There's nothing wrong with some headroom to steer clear of clipping but you don't have to overdo it.
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cabbagerat
post Jul 31 2006, 22:01
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QUOTE (Gecko @ Jul 31 2006, 11:15) *
Just as speakers can take transients with much more power than their RMS rating, an amplifier can deliver transients much stronger than its rated RMS power without much distortion.
This depends on the limits of the amplifier - if it's power is limited by clipping (most designs behave this way) then they can't deliver transients above rated power without distortion. For example, an amp with 35V rails can only deliver 153W into 8ohms. Granted, such an amp could only deliver about 80W of unclipped sine, but that extra 73W only gives you 3dB of headroom. If the amp is power limited by dissapation in the output devices (heat) then you will likely have more headroom - but results do vary.

Another thing is that some amps (badly designed ones, granted, but this is not uncommon) behave nastily for a little while after they clip. Bad behaviour can include oscillation, sticking to rails, spurious low frequency signals and other ugliness. Speakers, on the other hand, generally behave decently for sharp transients (within reason). The original poster's set, for example, can only handle 10V RMS but 40V transients.


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puntloos
post Aug 1 2006, 00:52
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Let me recap all this a little bit.

- Amplifiers that start to clip can easily damage speakers with the dirty output
- (attempting) playback at higher volume than the speaker can do is Bad™ in any case.

So the key here is:
- Buying an amplifier that can give clean output up until the levels that will cause the speaker to clip
- And try to never reach that speaker-clipping point.
- if you do try to find the absolute max, reach it carefully, and once determined never reach it again with ample safety margin.

Therefore buying an overdimensioned amplifier depends a little bit on your assessment on how badly the amplifier manifacturer lies about its amps capability to deliver clean output. If they say it can do 400watt, does that mean 300watt clean and 100 watt dirty?

All in all would you guys agree that (also given that double wattage only increases volume (i.e. wave amplitude) 3db, if a speaker would be linear) an amplifier of 2-2.5x the rated speaker power is ample, and not too much, if you act sensibly with your volume control?

With that theory the evo 4 would (@360Watt rated) would be a decent pairing for my 100-140Watt rated speakers, a bit on the hefty side, but not insanely so..
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boojum
post Aug 1 2006, 04:21
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QUOTE
Boojum: What is the real power of those 1200W amps? If they can really put 1200W of sin wave into an 8ohm load then I am seriously impressed. I have a 6kW test load that I use as a footrest at work (don't use it much) which could do with some warming smile.gif



These are mono-bridged halfer 500 watt amps. They were measured floating from 1,100 to 1,300 watts each into 8 ohms steady output. My dynamic speakers are KEF 104/2's which are 4 ohm, yielding roughly twice the power. Yet the KEF's will cause the amps to overheat and shutdown to a cool-down mode as they can absorb ~4,500 watts each! Yes, check the specs. Funkytown, Saint-Saens' 3rd (Organ Symphony) pedal notes and jets taking off will rock you.

They are also excellent for playing at room levels objectionable to no one. Plenty of reserve or "headroom." I always wanted a stereo which could play louder than I could stand it, and I got it. Now I just play music with it. Good for quartets and trios, too. cool.gif

This post has been edited by boojum: Aug 1 2006, 04:24


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cabbagerat
post Aug 1 2006, 06:36
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Considering that this topic keeps coming up - maybe this thread (or one like it) should be linked to in the FAQ. There is some good information here that people might find helpful.


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hel96
post Aug 1 2006, 12:36
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According to this link:

http://www.tnt-audio.com/casse/quad-esl989-2_e.html

it's an electrostatic transducer designed for a tube amplifier, so most of the power handling considerations usually regarding dynamic speakers may not be helpful. The first goal has to be stability, as resisitive load is
only a small part of the impedance.
I suppose it has a transformer with an 8 or 16 Ohms input which in combination with the capacitive load
has the mentioned voltage limitation that must not be exceeded. Some audio freaks put a resistor in
series to avoid stability problems with transistor amplifiers. Additionally, some put a bipolar capacitor of
~600 F in series to avoid saturation effects with low frequency burst signals in that transformer.
Anyway, I would cautiously try to test it for stabiliy first slowly increasing level without entering the
saturation region.

Good luck!
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CSMR
post Aug 1 2006, 18:06
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QUOTE (puntloos @ Jul 31 2006, 15:52) *
All in all would you guys agree that (also given that double wattage only increases volume (i.e. wave amplitude) 3db, if a speaker would be linear)

yes
QUOTE
an amplifier of 2-2.5x the rated speaker power is ample, and not too much, if you act sensibly with your volume control?

It may be ample. An amplifier of 1/100 the rated power may be ample also. And it may not be ample if it doesn't give enough volume for you, but then you would have to change your speakers as well as your amp.
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greynol
post Aug 1 2006, 18:15
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QUOTE (CSMR @ Aug 1 2006, 10:06) *
QUOTE (puntloos @ Jul 31 2006, 15:52) *
All in all would you guys agree that (also given that double wattage only increases volume (i.e. wave amplitude) 3db, if a speaker would be linear)

yes
No, the correct answer is 6dB.

QUOTE (CSMR @ Aug 1 2006, 10:06) *
QUOTE
an amplifier of 2-2.5x the rated speaker power is ample, and not too much, if you act sensibly with your volume control?

It may be ample. An amplifier of 1/100 the rated power may be ample also. And it may not be ample if it doesn't give enough volume for you, but then you would have to change your speakers as well as your amp.

Exactly. You want your amp to be ample wink.gif


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CSMR
post Aug 1 2006, 18:57
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Twice the power is 3db I believe. Twice the wave amplitude is 6db. Twice the amplitude is four times the power.

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Zealot
post Aug 1 2006, 20:19
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Yes, twice the power is 3 dB gain in volume.
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greynol
post Aug 1 2006, 20:51
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QUOTE (Zealot @ Aug 1 2006, 12:19) *
Yes, twice the power is 3 dB gain in volume.

This is correct, I didn't read carefully enough earlier. blush.gif


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DigitalMan
post Aug 2 2006, 03:11
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QUOTE (Gecko @ Jul 31 2006, 11:15) *
I don't really buy into this "your amp needs to be much more powerfull than your speakers". Just as speakers can take transients with much more power than their RMS rating, an amplifier can deliver transients much stronger than its rated RMS power without much distortion. There's nothing wrong with some headroom to steer clear of clipping but you don't have to overdo it.


The problem here is that amplifier ratings are relatively (!) accurate vs. speaker power ratings. Speaker power ratings are a general guideline - many tweeters can only take 25W, but because the majority of the music spectrum is below about 3kHz, in a multi-way system (midrange, woofer, etc.) you could likely get away with 100W no problem on typical music. Unless you send a 100W sine wave at 20kHz which will pass through the crossover a toast the tweeter pretty quickly.

Speaker power rating is a very ambiguous, general guideline whereas an amplifier output can be unambiguously measured and verified. Speaker power handling will depend on the spectrum of the signal, duration of the high amplitudes , crossover design and potentially how heated the electromagnetics are.

I would never fear hooking a 1,200 watt amplifier to any speaker because I could easily tell when the speaker was being overdriven. My 25W receiver example (from the poor school days) would make me leary of underpowering.


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