Mr Wolf
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First I cranked up the volume to an uncomfortable level (a level at which it compromised my enjoyment). At the this level the system still played cleanly and the amp volume setting was typically between -5db and -15db, depending on the source. I guess this practical test is the ultimate test but...that wasn't enough for me. I remained envious of other amps' THX reference status badging and I needed to know that I could achieve the coveted "reference level" of 85db continuous and 105db peaks. I therefore tried to calculate my own system's SPL capabilities.
I read up on the subject and sought to estimate the SPL at my listening position of a single 90db sensitive speaker as my L/R mains have that rating. I learned that SPL rises 3db as input wattage doubles and falls 6db as distance from the speaker doubles - please correct me somebody if I'm wrong! Anyway, with this know-how I created this chart on a spreadsheet.
View attachment 1008708
My Yamaha RX-V3900 amp (rated at 140W - [email protected]%THD) was bench tested by www.soundandvision.com years ago at 190.4 and 62.9 watts per channel for 2 and 7 channels driven respectively ([email protected]%THD). As my listening position is almost exactly 4 metres from the speakers the two highlighted figures of 96db and 99db are the most useful ones for me.
Remember, the chart is for one speaker only. I learned that as the number of speakers doubles, you add 6db so with both the L/R main channels driven, 128 watts should give 105db (99+6).
So what about the 7 channels driven rating? Well, 7 channels plus subwoofer makes 8 speakers (and I'm sure my sub can hold its own against one amp channel) so I used the 64 watts line to calculate 114db (96+6+6+6). An over-simplification I know due to different distances, speaker sensitivities room gain etc. but this is just an estimate afterall.
Both these estimates are based continous power ratings, not peaks, and still exceed the 85db continuous reference level by some margin. In fact, the two L/R channels can hit 105db on their own. Continuously!
The bottom line?
I think that, provided you don't have woefully inefficient speakers and/or sit miles away from them, most quality AVRs out there have plenty enough power for home cinema applications. I think we're all influenced by how manufacturers always throw in a bit more power for the next model up in the range. This is just the marketing men trying to convince you to spend up to your maximum budget...yes, yes...a little bit more power...just to be sure.
Of course, all other things being equal, more power is always better than less but if you don't actually need it then it has little or no value to you in practice. Certainly, an extra 10 or 20 watts isn't going to make an appreciable difference to your system.
Just hoping this might help some people out there achieve peace of mind and maybe save you a few quid on your next amp.
Any thoughts, comments welcome...and please, please, please tell me if any of this theory is wrong.
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