Originally Posted by jes182
I am ready to build my first 2 channel system for music only. I'm pretty well set on getting B&W CM9s. As good as the low end performance is on these speakers, I'm a bass nut and won't just be playing jazz and classical on these suckers. Anyway there are a million threads on how to integrate a subwoofer into a 2 channel music system and I'm stuck. I was originally going to get a Marantz PM8004 and feed the sub with the pre-out terminals. This is okay except I would not get the benefit of reducing the bass requirements of the speakers since they would still receive full range. I now know digital processing is required for this. My solution is the use a standard AV receiver (going to dust off my Denon 2807) and use the pre-outs to an external amp like an Emotiva XPA-2. Thoughts?
I'll spend a little time schooling you. I think it might help. The efficiency rating of 89db means that the speakers will produce a sound pressure level of 89db with one watt of power at a listening distance of 1 meter. 89 db, by the way, is quite loud - louder than I ever listen. Each 3 db of additional SPL requires a doubling of the power - 92db would need 2 watts, 95 db would need 4 watts etc. Let's say we're going to blast the room with a humongous 2 watts of power for purposes of analysis. We normally want twice the average volume available to handle peaks. That requires 10 times the amplifier power. So basically, your speakers will be able to play loud quite happily with a 20 watt amplifier. The receiver has 100 watts or so. Do you really think the receiver can't handle the speakers?
Don't get too hung up on the nominal impedance number. Firstly, the impedance is not constant. It varies all over the board based on frequency. Secondly, most manufacturers lie about it anyway because people are afraid of low impedance. The issue is heat. The lower the impedance, the more current the speakers draw and the more heat the amplifier generates delivering that current (they aren't 100% efficient.) If a receiver is rated for, say, 6 ohms that means it will overheat if full power is applied at a lower impedance for enough time to heat the output stage. But we aren't using anywhere near full rated power, are we? And B&W is actually pretty honest about their nominal impedance rating. If they say it is 8 ohms, that means it is safe to use it with an amplifier that is rated for full rated power at 8 ohms or more. Remember, we aren't getting to the low points in the impedance curve for long periods of time and we certainly aren't doing it at full rated power. In other words, people are afraid of low impedance, but for the most part, they shouldn't be. Check around to see how many people have cooked an amplifier by using a low impedance load. You won't find many.
Bottom line. The receiver is more than capable and competent to drive your speakers loud enough to drive you out of the room with no damage done anywhere. Feel better now?