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I believe good information will get lost soon, so I formally request that a mod sticky this and potentially lock it, as this is fact and not up for debate.
Often times people get lost on a spec sheet. We have all been guilty of it from time to time. How much do we really need to power a speaker?
The following is credited to AV-OCD for taking the time to explain this:
Keep in mind that not all Watts are created equal. This rule would apply to solid state amps, as tubes follow their own rules. Other factors include, but not limited to: Design, Engineering and Implementation, which all very from brand to brand and model to model.
Often times people get lost on a spec sheet. We have all been guilty of it from time to time. How much do we really need to power a speaker?
The following is credited to AV-OCD for taking the time to explain this:
The wattage needed for a given application depends on three things. The sensitivity of the speakers, the volume of playback you want to achieve, and the distance from you to the speakers. Nothing more, nothing less. Doesn't matter if you speakers have one bass driver or twelve, the above dictates the power requirements. There is one other factor and that is the impedance of your speakers and the current output capability of the amp, but all Classe amps provide enough current for even 4 Ohm nominal speakers.
Let's use your pair of 803D's for example:
• The 803D’s have a sensitivity rating of 90dB for 1 speaker for 1 watt at 1 meter.
• With a pair, you gain 3dB. So now you have 93dB with just 1 watt of power.
• You also have room gain, which varies by room from 3 to 6dB. Lets use 3db to be conservative, bringing the total to 96dB for 1 watt at 1 meter.
• You have to subtract 6dB for every doubling of distance from the 1 meter point. So if you sit 12 feet away from your speakers, we are now down to 84dB of output for 1 watt at 4 meters away. This is our starting point.
• With an amp you get a 3dB increase in output for every doubling of power.
• At 1 watt, you will get 84dB from the pair of 803D’s at the 4 meter listening position.
• To get 87dB you need 2 watts, for 90dB you need 4 watts, for 93dB you need 8 watts and so on.
• Continue up the scale to 100 watts and you get a total gain of roughly 20dB.
• Add this 20dB of amp gain to the 84dB from above and you have the ability to listen at a constant volume of 104dB. Plus, any of the Classe amps are going to have reserve power for peaks above this (not enough for the dynamic swings of Classical, but probably enough for Rock / Pop).
• However, we probably don’t want to push the amp to it’s limits, so lets leave 10dB of headroom at set the max volume to 94dB.
Have you ever listened to 94dB? It is very loud. Most people like to listen between 75 and 85dB. If you refer to the above calculations, 85dB is going to require under 2 watts of power!
So lets say you splurge and go for the CA5200. Since a doubling of power only gets you an increase of 3dB at the top of the amp’s range, you can now blast your ears with 107dB of sound over the 104dB provided by the CA5100. I’ll never use it and frankly not many will. Those that do won’t need to for long, as their hearing will be permanently damaged if they listen that loud on a continual basis.
Let's use your pair of 803D's for example:
• The 803D’s have a sensitivity rating of 90dB for 1 speaker for 1 watt at 1 meter.
• With a pair, you gain 3dB. So now you have 93dB with just 1 watt of power.
• You also have room gain, which varies by room from 3 to 6dB. Lets use 3db to be conservative, bringing the total to 96dB for 1 watt at 1 meter.
• You have to subtract 6dB for every doubling of distance from the 1 meter point. So if you sit 12 feet away from your speakers, we are now down to 84dB of output for 1 watt at 4 meters away. This is our starting point.
• With an amp you get a 3dB increase in output for every doubling of power.
• At 1 watt, you will get 84dB from the pair of 803D’s at the 4 meter listening position.
• To get 87dB you need 2 watts, for 90dB you need 4 watts, for 93dB you need 8 watts and so on.
• Continue up the scale to 100 watts and you get a total gain of roughly 20dB.
• Add this 20dB of amp gain to the 84dB from above and you have the ability to listen at a constant volume of 104dB. Plus, any of the Classe amps are going to have reserve power for peaks above this (not enough for the dynamic swings of Classical, but probably enough for Rock / Pop).
• However, we probably don’t want to push the amp to it’s limits, so lets leave 10dB of headroom at set the max volume to 94dB.
Have you ever listened to 94dB? It is very loud. Most people like to listen between 75 and 85dB. If you refer to the above calculations, 85dB is going to require under 2 watts of power!
So lets say you splurge and go for the CA5200. Since a doubling of power only gets you an increase of 3dB at the top of the amp’s range, you can now blast your ears with 107dB of sound over the 104dB provided by the CA5100. I’ll never use it and frankly not many will. Those that do won’t need to for long, as their hearing will be permanently damaged if they listen that loud on a continual basis.
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