Speaker wattage[rms] versus amp wattage[rms] - diyAudio
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Old 8th November 2002, 09:25 PM   #1
Bull is offline Bull  United Kingdom
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Default Speaker wattage[rms] versus amp wattage[rms]

I've been told different things about amp and speaker wattage,and which one is the truth,as i know the owners of this site are professionals in audio,unlike some people who i've spoke to who are just ordinary repairmen/disco hiring shop.
I've been told 4 different things
1. The power amp and the speaker has to be the same equal rms as each other to sound clean.Eg 150w rms speaker 8 0hm with 150w rms 8 ohm amp.
2. The amp has to be twice the power of the speaker,to sound clean and undistorted,but would this overheat the speaker voicecoil.Eg 150w rms 8 ohm speaker driven by 300w rms into 8 ohm amp.
3.The amp has to be three -four times more powerful than the speaker to allow for 'Headroom'.Could someone please explain 'Headroom'.But 3 to 4 times more power than the speaker can handle will definatly blow it.
4. The speaker has to be twice than power of the amp,it allow for excessive EQing common in a Disco enviroment

Also; I know AES,RMS and IES are the same but progamme is twice the rms,and peak is 4 times the rms.
But i'm confused about,maximum input power,p.m.p.o,m.p.o, short term power,long term power,normal,max power,and max transit power.

Also many people have told me good quality manufactors can easily handle twice the given rms wattage for a continus time,eg 8 hours.
Makes such as: Bumper,Audax,Peavey,Fane,Celestion,Eminence,RCF,JB L,EV[Electrovoice]Precision Devices,Gauss,Altai,OHM,Mc Kenzie,
Mc Cauley,ZEUZ,Vifa,Peerless,SEAS,QTX,U.S Blaster,Skytronic,Selenium,Pioneer,Skytec
Are all these 25 drivers good or are some rubbish.
I have my doubts against QTX,ZEUZ,U.S BLASTER,SKYTEC,SKYTRONIC,PIONEER,BUMPER, because these are cheap.
If you could please help me with the Amp-Speaker dilemma,and which of the above drivers are any good,and also say why some of them are rubbish,i'd like to hear another persons opinion rather than just mine and my mate called Rudi who works in a disco repair shop.
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Old 8th November 2002, 10:00 PM   #2
halojoy is offline halojoy  Sweden
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Default The speaker must be able to handle

the wattage from the amp.
Or it will be destroyed.
That means that:
Loudspeaker must be specified for the maximum
power that your Amp will deliver.
That is if you ever puts out max power with your amp.
Max is when volume is in full position.

So to be safe Loudspeaker should have the highest watt.
But this is only true if the "type" of watt
is calculated in same way, for both of the devices.
For instance contunious Watt-Rms.
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Old 8th November 2002, 10:10 PM   #3
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Well, as with most things there is no single truth to this one.
Of course, a too powerful amplifier can blow the speakers, but
one that has too little power can also do that. How? If your
amp starts to clip it will produce a lot of overtones that might
give the spectrum too much of a tilt towards the high frequencies
causing the tweeter to burn.

I don't know why anybody in his right mind would let the
amp clip, but considering what comes out of most peoples
speakers nowadays makes me think most people are not
in their right minds.
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Old 8th November 2002, 10:17 PM   #4
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Hi Bull

Hmm, where to start...

To give a specific answer, I would need to know your application, home, disco, PA etc. but as this is a hifi site I will base my answers on that topic.

The easiest way to sum up the multitude of points you have raised is by giving an example. Most listening at home with reasonable levels, and with average efficiency , (88db ish sensitivity) speakers requires less than 20w RMS. This will require an amp to occasionally provide transients of about twice as much, i.e. 40w. To be honest, most of the other ways of measuring power are marketing fudges, used to make a speaker or system seem more impressive, and to be honest , I have never paid much attention to how they are calculated.

Yes, most real drivers are conservatively rated in their power handling, and will take more power than stated, and to provide the headroom needed above, I would suggest that twice the speaker RMS is a good thing to have in an amp. This is because when an amp is overloaded, it clips the sound waveform, producing high frequency transients, and this can easily take out tweeters, due to them having to dissipate more power than is evident in the signal.

However, long term listening at high volumes can also overheat any voice coil in a speaker, resulting in the driver being damaged irreparably.

However in a disco or PA situation things are very different,, and mostly depend on the amount of supervision over the way a system is run.

So , if you can give us a more specific idea of what you need then we can be more exact, but without knowing your application, it is difficult to be definate.
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Old 8th November 2002, 11:12 PM   #5
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Hi Bull,

Just a few thoughts for you...

A driver's Pd is a Thermally Limitted rating and the driver will be capable of taking more power for short periods; how much more is determined by the Excursion Limit of the driver.

RMS Power is not a valid term in this respect. RMS Voltage x RMS Current = Average Power.

As already noted, one of the most important considerations is that the amplifier is delivering clean undistorted power. Clipping will blow drivers (especially tweeters) quicker than most other things.

Many amplifiers can not produce their rated power output into a real load and so many 'small' pure class A amplifiers will play louder than many 'large' Class AB amplifiers.

The distribution of power through out the musical spectrum will depend on the type of music you like to play and so will effect your choices with regard to individual drivers and also total amplifier output power.

Regards,
Daniel Flynn
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Old 9th November 2002, 05:55 AM   #6
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AudioFreak & PinkMouse cover things off fairly well.

Consider that the whole speaker wattage rating thing in hifi (it has more relavance in PA work), because of the wildly varying ways of measuring power and the real power that amps put out into a real load, actually becomes almost meaningless.

Some examples of why:

A SS amp going into clipping produces a lot of ugly stuff, and is very prone to taking out tweeters (Advent actually distributed a single page brochure on this) so it is best to have a SS amp with more power than less power. But i have had real world situations where a 200 W amp (Carver cube), did not put out as much power before clipping than a 20 W amp (NAD3020), so we have an example that shows that power amp ratings are often not very real world so you can't use them to judge.

Now consider a tube amp. They tend to compress instead of clip so their behaviour with overload is more benign, so you can get away with less power.

And then you have to consider how much power you actually use on a regular basis. With medium efficient speakers, in an average room, at reasonable listening levels the average requirements from the amp are milliwatts, with maybe 10-20 dB headroom for peaks.

I hope that is confusing. Because it is. Power ratings and power handling should only be used as a very rough guidline because they are often totally meaningless.

What you should do is learn to listen for your amp clipping. If it starts to clip turn it down. Then you are usually safe. A little harder is to learn to hear your speakers compressing -- that is a clue that the voice coils are getting hot -- turn it down.

My speakers are rated at 3 W. Two in parallel means i have 6 W rated power handling. I use amps between 4 W and 100 W on them.

The last time i can remember actually blowing a speaker (excepting PA work when i lost an occasional tweeter) was in 1978. Big room. Big amp (Bryston 4B). Listening to Tangent RS-4s with the head Tangent guy visiting from England. Turn it up he says. I don't think we should. Go ahead he says. Everything is sounding great and then nothing from one side, quickly followed by a cloud of room filling white smoke from the square ports. It was quite a sight (and smell). In the interest of keeping costs down the Rs were a little underrated, they got very warm, and the plastic damping had "caught on fire" just enuff to generate the cloud of smoke. We quickly swapped in a fresh Audax 8" and continued the listening seession.

dave
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