Here and there throughout the Saloon people have discussed whether to run the normal single pathway all the way from pre/pro to loudspeaker or split the signal at some point with either bi-wiring, common signal bi-amplification, active crossover bi/tri-amplification and/or variants of each. The decision for most with financial limitations is a balance of benefit vs. cost. Rather than having the discussion of potential benefits only in pieces here and there, I thought it might be a good idea to have a topic where all of this can come together with fresh discussion, with links to other pertinent posts, and eventually links from other topics to this topic as questions about this arise in other threads.

With regard to power and clarity, very simplistically:

Let’s say that a certain amplifier has a maximum output of 20 volts before clipping sets in and provides a gain of 20. Let’s also say that the input to the amplifier is receiving an input signal of two sine waves mixed together, 0.7 volt of 200Hz and 0.3 volt of 3200Hz, and this feeds a two-way loudspeaker that has a passive crossover at 800Hz. With a gain of 20, the amplifier will provide 14 volts of 200Hz and 6 volts of 3200Hz on the same output, adding to 20 volts at some points of the resulting waveform, which will be split between the woofer and tweeter respectively.

With passive bi-amplification, the same scenario exists except that two channels are outputting the 200/3200Hz mix. One output goes to a crossover which blocks the 3200Hz and lets the 14 volts of 200Hz pass – this output channel has almost no load at 3200Hz but still must use 6 of the available 20 volts reproducing the 3200Hz. The other amplifier output goes to a crossover which blocks the 200Hz and lets the 6 volts of 3200Hz pass – this output channel has almost no load at 200Hz but still must use 14 of the available 20 volts reproducing the 200Hz. So each amplifier channel will have a reduced load, but does not provide more voltage at each individual frequency. This load splitting may be helpful in some ways, or hurtful in others, but no significant increase in power is gained for either frequency, and passive crossover elements are still between the amplifier and the drivers.

With an active crossover, the channel handling the 200Hz signal does not have to handle the 3200Hz signal. The 200Hz channel can now receive a 1-volt 200Hz signal and output 20 volts at 200Hz. Increasing the 200Hz voltage output from 14 to 20 volts doubles the power available at 200Hz. For the 3200Hz signal, increasing the voltage by the same ratio, an input of 0.43 volts instead of 0.3 results in an output 8.6 volts instead of 6 volts.

If the wattage delivered in a passive crossover scenario, with either single or bi-amplification, were 33 watts to the woofer and 6 watts to the tweeter, with an active crossover and increased amplifier input voltages, the power delivered can now be 66 watts and 12 watts respectively.

In the real world, one would not have two clean sine waves mixed together. There would be a mashing of many, many frequencies with narrow transient spikes all over the place. In the two passive crossover examples above, if high frequency transients were added to the mix, either they would be lost because the amplifier has no headroom left, or the overall input level would have to be reduced so that the peak voltage output required, transients included, would never exceed 20 volts. In the active crossover example above, the low frequency channel wouldn’t have to deal with the spikes at all, and the high frequency channel still has 11.4 volts of headroom for transient spikes even when the low frequency channel has reached its output limits.

Without a lot of further details, one could conclude that as far as maintaining clarity while raising power output is concerned, in very rough terms, two 50-watt channels fed by an active crossover are as just as useful as 150/200-watt channel(s) using single or bi-amplification into passive crossovers. By extension, two 200-watt channels fed by an active crossover are just as useful as 600/800-watt channel(s) feeding passive crossover networks.

Why wouldn’t a single amplifier output of 100 watts through a passive crossover be just as good as two 50-watt channels with an active crossover ahead of the amplifier?

Using the example in the previous post, if I actively bi-amp through two 50-watt channels, I have 20 volts available to the woofer for low frequencies and 20 volts available to the tweeter for high frequencies including transient spikes’ headroom.

In order to make 20 volts available for the woofer and 20 volts available for the tweeter through an ideal passive crossover (no losses due to the crossover), my amplifier would have to output 40 volts cleanly. Doubling the available amplitude means quadrupling the available power, so my amplifier now has to be rated for 200 watts per channel to accomplish what 2 channels rated at 50 watts each can accomplish - true for a signal consisting of a myriad of upper and lower frequencies mixed together, not true if all frequencies present are within the range of only one of the drivers. While it would take an amplifier rated at 200 WPC in order to deliver the 100 WPC in this mixed-frequency scenario, 200 watts is not delivered – the amplitude of 200 WPC is needed, but not the full current that would mean 200 WPC was being delivered.

Note that, almost without fail, professional systems for large scale sound reinforcement use active crossovers ahead of amplification. This provides for, among other things, better overall power efficiency and better ‘control’ of drivers with direct-to-amp connections where lots of power transfer and excursion will occur.

BB4TB, congratulations on starting this topic. My Magneplanar 1.6QRs aren't biampable without a crossoverectomy, but I'm still interested. If I understand you correctly, one could use a 7075 for a high quality 5-channel system, with four channels used for biamping front speakers, and get about the same practical power delivery as using 5 200w channels plus better sound - assuming a good enough active crossover that wouldn't raise the overall cost above that of the 200w-per-channel system. Too bad Outlaw doesn't make one. Any suggestions?

BB4TB, I agree completely with your explanation above. Another benefit of active bi-amping would be a reduction of IM distortion as separate amplification is being used for low and high freqs. A long time ago I scratch built an active crossover (when cd's first came out) and I was very impressed with how much cleaner everything sounded.

I think it would be fantastic if Outlaw would put some if its independent spirit into an active crossover option for at least their own loudspeakers. Hopefully the overall cost would not change that much. Some purchasers would not be spending money on the passive crossover design and components, instead putting those resources into the active crossover. For those willing to give this a try, Outlaw may be selling a greater mix of 7075’s/7125’s and fewer 200/300 WPC amps (unless you’ve got some serious watt lust), but still it would be a good start. True bi-/tri-amplification needs an everyman audio enthusiast champion company that lets people who are not comfortable with DIY move into this arena without spending really big bucks.

Speaking of DIY and big bucks, even if only for education:

Some interesting reading on bi-amp/tri-amp can be found at Elliot Sound Products – Articles , Benefits of Bi-Amplification, parts 1 and 2. Links are in there for related projects.

Some of the best loudspeakers in the world are direct-to-driver from the amplifier stages, like the B&W flagship Nautilus . What can they achieve partly due to active crossovers and four amplifier channels per speaker? Within the bandwidth of 25Hz to 20kHz, a response flat to within +/- 0.5 dB! The odd cabinet design puts the rear-side driver radiations into what amounts to one section of an anechoic chamber sized for the individual frequency ranges as needed.

For the less wealthy, do some exploring at LinkwitzLab . Even if you never buy his products, there’s a lot to learn there.

For those not familiar with this stuff, take it slow and read some of the above information in bite-size doses. Happy learning!

Active crossovers allow much more precise and potentially adjustable crossover circuits, all other advantages aside.

A more detailed discussion is found in applicable portions of the article at this web address:

http://sound.westhost.com/bi-amp.htm

For even more: http://sound.westhost.com/bi-amp2.htm

If that discussion is too much, and my examples seem either too much or not clear, a simple way of explaining:

1) Feeding two different amplifier channels the same full-range input means each channel is reproducing a full-range output.

2) The output feeding the high-pass crossover filter will have low-frequency current greatly impeded. The output feeding the low-pass crossover filter will have high-frequency current greatly impeded.

3) Since power is delivered only when a voltage is present AND current flows, while each output channel makes all frequencies available, each individual channel delivers power to either the ‘hi’ portion of the loudspeaker or the ‘lo’, but not both at once.

Result 1: This reduces the power ‘burden’ on each output channel, but since each channel is still reproducing the full range, there is no substantial unused headroom in either output channel to allow much increase in power to either the ‘hi’ or ‘lo’ portions of the loudspeaker. As such, there is no substantial power increase available if the same full-range signal is fed to multiple amplifier channels.

Result 2: Depending on the type of amplifier channels being used, sharing the same overall power delivery between two channels that was previously delivered by one channel, and removing the interaction between two portions of a crossover network, might offer some increase in fidelity. In other cases there will be no improvement or maybe even a detriment.

Conclusion: If an overall increase in power is the priority goal, doubling the number of full-range range outputs and feeding them to split two-way crossovers will not provide what is wanted. If you wish for a possible increase in fidelity, you might carefully experiment, see which way sounds better to you.

When I started reading this thread, I was going to suggest the Elliot articles, but I see that's been done. Active crossovers are definitely the better way, as passive crossovers introduce compromises as the Elliot articles reveal. For one thing, they dissipate a substantial amount of power, which is one reason you gain more output with active. One point I'll add to this discussion is that audio power distribution is not linear, and more power is needed at lower frequencies than at high frequencies.The 50% power distribution point occurs at about 325 Hz (from a graph I obtained from a National Semiconductor databook some years ago). What this means is that to equal a single 100 watt amp driving a lossless passive crossover (which doesn't exist), two 50 watt amplifiers would need to be crossed over at 325 Hz. For a more typical midwoofer to tweeter crossover of 2 KHz, the lower frequencies would require approximately 85 watts and the higher frequencies only 15 watts to equal a single 100 watt amp. From a practical standpoint, this is a good thing, because most reasonably priced tweeters will not handle a lot of power while woofers and midwoofers will. Beyond the power distribution, eliminating the passive crossover also eliminates the power loss it causes. It's not uncommon to have a passive crossover dissipate half the power delivered to it. So, it might take 200 watts delivered across a passive crossover to equal the sound output of a total 100 watts in an active crossover arrangement. Amps with suitable wattage for the lower frequencies are readily available. Low wattage amps for the upper frequencies are not, although would not be difficult for DIY. Using even a 7075 for the upper frequency split would be overkill for a typical system.