Originally Posted by m. zillch
Don, yes there are many perks to active bi-amping, which I myself have done as well, but the selling point that naïve consumers fall for is that passive bi-amping will net them a +3db gain since they've, um, "doubled the power". Oy. ....
You are pointing out the biggest misunderstanding in Passive Bi-Amping. If you apply 50w to the woofer, and 50w to the Tweeter then the total is 50w not 100w.
If you use a single 50w amp and apply it to a complete speakers, then both the woofer and the tweeter have 50w of potential
applied to them. If you break the Woofer/Tweeter apart and apply a 50w amp to each of them, then the woofer still have 50w of potential applied to it, and the Tweeter still have 50w of amp potential applied to it. The originally had 50w each and they still have 50w each, it is just that in the second case, they have a separate and different 50w amp applied but it is still 50w.
Using math, the rail or peak voltage of a 50w amp is P = SqRt(P x R). We will assume that the power was rated at 8 ohms, and so use an 8 ohm load.
P = SqRt(50 x 8) = SqRt(400) = 20 VOLTS
Now we do the same for 100w amp -
P = SqRt (100 x 8) = SqRt(800) = 28.28 VOLTS.
If you have a 50w amp on the Woofer, and a 50w amp on the Tweeter, the maximum voltage potential is limited to 20v. It doesn't go up because there are now two amps.
But, there could be some advantage in having independent control of the Woofer and Tweeter, that is, assuming the Amp used allow some degree of independent control. For example, if the tweeter is overly bright, you can turn that amp down just a small amount to smooth the response relative to your personal taste, and of course, you can always turn the bass up a bit too.
The above has an advantage over the tone controls as the tone controls tend to work on a slope. That is the change is not uniform across the effected frequency. But by turning the Amp up or down, it is uniform across the range that the drivers the amp is connected too.
As in my example, on the other thread, by random change I use two amp that were very suited to the task they were assigned. The Onkyo Amp was very well suited to clear Mid/High, and the Yamaha was very well suited to bass. Between the two I have never heard my speakers sound better.
Did I level match? Yes, I connected only the Mid/High section and played Pink noise, The Right speakers was standard single amp wiring, the Left speaker was Bi-Amp using the amps described. I measure the Right standard speaker, and adjusted the Mid/High to the same measured level. But at the same measured level, there was still too much Mid/High, I dialed it back a bit to suit my personal taste, and this work fantastic. Like I said, never heard those speaker sound better.
But this happened by random change. Those just happened to be the two amps I had. For someone starting cold with different amps and trying to determine which amps will sound best together is a very difficult, long, arduous, and expensive task. Unless you want to make a hobby of it.
I suspect for someone with a lot of first hand knowledge and experience with a wide variety of amps, you might be able to guess which combination would work best, but short of that, you are shooting in the dark.
Now, let's take the alternate example. Let's say you have an AV Receier and you Bi-Amp the Front speakers using previously unused Amp Channels. How is it going to sound. Well given that you are using identical amps, you can only expect it to sound identical. There could still be some very slight advantage, but while there, you are unlikely to hear it.
So, let's take another alternative. Let's say you have a Rotel Integrated Amp, and you add to it a Rotel Power Amp, and use this combination to Bi-Amp the speakers. How is it going to sound, well given that you are essentially using identical amps, logically it is going to sound identical. Though again, there would be some suble underlying advantage that is not easily heard. In this case, each amp on a given speakers is driven from a separate Power Supply so that could be an advantage if you play loud demanding music or watch movies with very high dynamic range. Likely, while it could be helping you, only in the most subtle and non-obvious way would it be helping you.
So, yes, there are circumstances where there can be some gains, but for the most part, to the average listening ear, expect it to sound pretty much the same.
For someone on a tight and limited budget, you might be able to get some sense of an upgrade using two amps. You have a amp of very modest power, and you bi-amp to that a amp of considerably more power. But, if you have an amp of considerably more power, why not just use that amp?
It is always worth doing for the experience, but experience is about the only tangible gain from the process.
And, unless you have the Technical Knowledge to effectively implement Active Bi-Amping, you would never go down this road when buying a new system. Rather they buying two new amps, simply pool that money into one better more powerful amp. This is something a poor person can do out of desperation, but it is never something a person who can afford quality new equipment does. It simply makes no economic sense.
In my case, I just had amps laying around, so I gave it a try. I liked what I heard, but from a pratical sense, I just couldn't make it work on a day to day basis. So, I went back to the original configuration. I don't regret trying it, but practically, it wasn't worth keeping it that way.
But to the original point, the power is not additive. Each driver gets the power potential of the amp you attach to it. They do not add together. TWO 50w Stereo amps is still just 50w per driver or driver section.
Within the limited context I've laid out here, there could be circumstances where Bi-Amping might work for the individual. But, it makes more sense to simply buy a new more powerful amp.