Originally Posted by twinturbo11
On this topic of using an external amp with the SR7010, quick question to the group:
I have a 7.1.2 configuration all running from my SR7010 - so each channel is getting let's say "X watts" per channel. If I add a 2-channel external amp to power my L and R, would the remaining channels that are being driven by the SR7010 obtain a higher watt per channel? Say "2X watts per channel" ?
Post number 6
on the first page of this thread has some bench test numbers on the SR-7010 internal amp power capabilities courtesy of Sound and Vision, who had done the tests.
With all seven channels driven, one is looking just above 83W per channel. Compared to the 2-channels driven in "solid" stereo mode (128W/channel) the maths work out to be that when 7 channels are driven simultaneously the power output per channel drops to just under 65% of the the 2-channel mode. There is no all 9 channel driven test, but wouldn't be surprised if the per channel power output drops below 80W.
Not all channels are actively used during playback of a movie soundtrack. I.e. simultaneously used or all channels driven.
For instance the ceiling speakers are silent most of the time during an Atmos playback. A test can be carried out in a home setting by playing back an active Atmos movie (such as Transformers: Age of Extinction) and by disconnecting all the floor level speakers. Thus no sound can come from the floor level speakers and only the ceiling speakers. AVS member Keith Barnes did this test and was surprised that the ceiling speakers (Keith had all four installed in a 7.1.4 Atmos speaker configuration) were silent for majority of the movie. When the action on the screen did pick up, Keith was disappointed to find that the ceiling speakers made just ambient sound. One can easily replicate the test and verify this.
Having said the above, when the floor and ceiling speakers are combined and used during an Atmos movie playback, there an improvement in the overall sound field with a greater depth and immersion compared to say just the floor level speakers. So Atmos does work, but not as one expected it would after all the hard work of installing the ceiling speakers. There is some psycho acoustics involved in the object audio decoding and playback with the fixed position speakers.
So going back to your question of your 7.1.2 Atmos setup and powering the front L/R with an external amp. Would there be more available power to the remaining 7 speakers? The short answer is yes. You've got some extra headroom. How much headroom is a bit harder to answer as the available power is not evenly distributed to each speaker during playback. For instance the center speaker which carries the important dialogue (voice reproduction) in the movie, it is still demanding a lot more power than a pair of ceiling speakers. I.e. one channel is using much more power than two channels.
A lot depends on your speaker sensitivity, the physical distance between the speaker and Main Listening Position (MLP), where the speakers are positioned relative to the room boundaries, implementation of bass management (or not) and associated crossover frequency. The most important part is the desired listening volume level.
Recall that a +3dB increase in SPL means doubling the power requirement. For most people, a +3dB increase in SPL is just notable from the previous listening condition.
A +10dB increase in SPL means increasing the power demand by 10X! Because human hearing is log rhythmic, making something sound twice as loud as before means a +10dB increase in SPL. Problems generally occur at the amp section of the receiver when that last +10dB in volume level is reached. The amp section is quite happy supplying say 20W of clean/low distortion power to the speaker, when the Main Volume (MV) is turned up +10dB, it suddenly needs to provide 200W, which is going to exceed the amp current carrying capacity and cause the output to distort. Hence the general recommendation to place a volume limit within the receiver that will not exceed reference level of 105dB peak when the MV is set to 0dB. Most will find reference level to be uncomfortably loud and will listen well below 0dB.