Originally Posted by Gumbygreeneye
Enjoying continuing to read this forum. I am hugely enjoying the TX NR5008 (my second one) but have seen a few guys using Emotiva additionally.
I understand the logic of "more power" (ow ow ow) and greater headroom but would this still be beneficial with listening at lower volumes? Most of my listening would be at night when the girls are asleep.
My next step seeing as Buttkicker aren't likely to come to New Zealand any time soon is to get another PV1 for my MT30 + 4 in-ceiling B&W set-up. I understand the second subwoofer is a good next step to improve the sound. Another question is, are people matching subwoofers or can Audyssey work to integrate two different subs effectively such that perhaps a deeper sub might be used? I am considering the B&W DB1. Wife acceptance is a big deal as she is very tolerant about hifi stuff taking up the room but I can't take the p***.
The intent is not to hijack the thread but really get an opinion from some one who already has the 5008 with additional external amplification.
I am using a 5007 with an Emotiva XPA-3 on the front R, L and C channels. The AVR itself drives the height and surround channels.
You will only benefit, IMO, from an external amp if you can tick these boxes:
You have very inefficient speakers
You have 4 ohm speakers which are difficult to drive
You listen at high SPLs and/or have an enormous room
If you can tick two out of the three, then you will benefit from an external amp. The 5008 is already a very powerful amplifier putting out about 145 watts (claimed) into 8 ohms and over 200 watts into 4 ohms.
However, those figures are for two channels driven. When all channels are driven the power drops considerably (in any amp). A recent test somewhere showed that the power dropped to about 76 wpc when all channels were driven. (Personally I think that test used the 4ohm setting which reduces the power output but regardless, the unit will produce a lot less power when all channels are driven than when two are driven).
However, again, the chances in real world listening of all channels calling for peak power all at the same time are zero.
What you will gain from an external amp is a much higher true power output. My XPA-3 for example gives a genuine 200 wpc into 8 ohms and 300 wpc into 4 ohms when all three channels are driven at the same time. This is bound to give you more headroom (see below). Also, one of the limitations of an AVR is its power supply. Effectively you have one power supply supplying 7 or 9 channels in the 5007/8. This is one of the reasons that the output into 7 or 9 channels is lower than into 2 channels - they all use just one power supply. When you add an external amp, you are adding at least one additional power supply. This also has the side benefit of relieving the load on your AVR's power supply if, like me, you use it to power some of your channels. The heavy lifting on the main frint R, L & C is being done by my Emo, easing the burden on the 5007 for the other 4 channels in my system. This, theoretically, should enable my 5007 to deliver better sound quality in those channels by not being driven so hard, avoiding clipping and so on.
You also need to factor in the efficiency of your speakers. They will be rated as xxdB for 1 watt at 1 metre. Typically, they could be, say 88dB/1 watt/1m.
This means that just one watt will deliver 88 dB from 1 metre away from the speaker. Every additional 3dB requires a doubling of amplifier power. So 91 dB will require 2 watts, 94 dB 4 watts, 97dB 8 watts, 100 dB 16 watts and 103dB (very loud!) will need just 32 watts. Of course you don't sit 1 metre from your speakers (I hope) so you need more power than 32 watts to reach 103dB at you normal listening position.
Most of the time, even if you like to listen "loud" your system is ambling along delivering perhaps 85dB. It's only on peaks - explosions, loud music, action scenes etc - where your amp has to work really hard. In order to meet this 'headroom' requirement, you need an amp that can deliver big gobs of power when it's called for, without strain and without running into clipping (when an amp is asked to deliver more than its rated power capability). Clipping can wreck your speakers and also sounds very bad to your ears.
HST, from how you describe your listening, at moderate SPLs, unless you have an enormous room and/or very inefficient speakers, it seems unlikely to me that you are going to stretch your 5008 very much. So I would suggest that your money would be better spent elsewhere rather than on an external amp.
Re two subs. I also use two. Two will enable you to more easily smooth out room-induced humps in your frequency response to give you a better quality of bass. By moving the two around you have a good chance of counteracting room modes and so on. You don't have to have two identical subs if you are inending to place them in different parts of the room. The 5008 will let you set up two subs independently, getting the best out of each.