BIAMPING

Half an answer - Using your 125W example, assume a 5 ohm nominal speaker impedance for convenience. If the amp can supply the 125W to the 5 ohm load, it is supplying 5 amps. P=I*2 x R > 125 = I*2 x 5 > 25 = I*2 > I=5. To do this, the output must swing 25 volts. I = E/R > 5 = E/5 > E = 25. Now, bridging essentially puts the two amp outputs in series. Therefore there is a possible swing of 50 volts. E/R = I > 50/5 = 10 amps. P = I*2 x R > P = 10*2 x 5 > P= 100 x 5 > P = 500 watts. Apparently, though, the amps can't quite supply the 10 amps because of component limitations (transformer, transistors, etc), but can only supply about 9 amps, so 9*2 x 5 = 400 watts limit in that configuration. PS - a single one of those amps could also supply 9 amps, but that would be about a half ohm load, which it not where it's rated! :)

It looks to me like you have the following options:

1) Run each amp bridged mono, wired in to each speaker.
2) Run each amp stereo, one for highs, one for lows
3) Run each amp stereo, high and low of one speakers in one amp and v.v.

I went through this scenario fairly recently, and there are things to be set for each of the three setups. I preferred using scenario 2, using one amp for left and right mids, the other for left and right bass. It just seemed to create an energy and bass clarity that the other combinations did not.

(I did this with a set of NHT 2.9 speakers I own, and two ML331's I had on loan.)

Hmmm...perhaps an important point to make here... If the speaker just has dual connectors without some sort of shorting bar you can remove, the speakers could be BI-WIRABLE but NOT BI-AMPABLE. I don't know if there are any speakers to which this would apply, but if you have no shorting bars you can remove, be extremely careful! Tying the outputs of two amps together is almost certain cause of serious amp damage...

More answer - in the example, if you can't play your system loud enough (at least on peaks) then perhaps you are output voltage limited and need the higher voltage swing to drive your speakers (and ears) to their potential. Voltage limitation like current limitation current limitation can result in clipping and distortion or damage. That is the argument for bridging as long as the amps can supply the additional current. You must also know that the speakers can accomodate the extra current/power; that is, they were meant to play louder. If your system plays loud enough, even on peaks, you would just be running the level control lower with the bridged amps and not accomplishing much. Now comes the counter responses, I guess. :)

Hi Sfrounds; You may be interested; there is passive vertical biamping and passive horizontal biamping. To do vertical biamping you need a pair of identical stereo or dual mono amps (ideally). In vertical biamping, one channel drives the bass of the left speaker, and the other channel drives the mid/tweeter of the left speaker. To do this, the speakers must be bi-wireable, and an important advantage is that the amps can sit right next to the speakers and very short speaker cables can be used.

Horizontal biamping differs in that one amp drives the bass of both speakers, and another amp drives the mid/tweeters of both speakers. Some use this with a tube amp for the upper frequencies and a solid state for bass. In horizontal biamping the shortest speaker cables can be achieved by placing both amps right between the speakers.

About bridging and power; I've recently been on the 'phone with Steve McCormack discussing this very thing as I'm going to vertical biamp my speakers with McCormack amps. According to SMc when the DNA.5 (100 wpc, 8 Ohms) is bridged, it will put out 400 wpc, but when the DNA-1 (175 wpc, 8 Ohms) is bridged it will only put out about 370 wpc. Further, when the DNA-2 (300 wpc, 8 Ohms) is bridged it will put out an incredible 1200 wpc. So, the bridged power level depends on the original configuration of the amps power supply. I have a pair of DNA2s, but decided not to have the channels bridged as I don't need that kind of power. SMc is going to upgrade the amps and match them for me for biamping. Good Luck. Craig.