When Bi-amping is there change in sensitivity

>03-18-12: Gago1101
>Another question I had was if the transients in the mid-high frequencies require as much headroom as the transients in the bass region.

Yes provided that you are passive bi-amping (although I'd argue active bi-wiringis a more useful description of what's going on). Both amplifiers see the same input signal and (assuming you don't change the tap on an ampliier with transformer coupled outputs) will clip almost exactly where they would have when running the entire speaker full-range.

Active (real) bi-amplification lacks this drawback but takes a line level cross-over which in hi-fi applications must be designed for the drivers and enclosures in question and means it isn't a viable DIY proposition for most people.

>Would a 80wpc amp be able to give enough power to provide clean high volume sound (mid-high only) with a moderately affecient speaker, say 89db sensitivity?

Probably.

>03-19-12: Frogman
>Also, while I understand that each amp would see a full range signal at it's input, I don't understand why the amp would not still benefit from not having to DRIVE a full range signal. What am I missing?

There's "a benefit" but it's not significant.

It's like what happens to your car when you neglect to eat breakfast. Assuming the two of you together weigh 3700 pounds the half pound you don't eat before work reduces the weight reduces rolling resistance and kinetic energy at a given speed by 0.01%. With most of your power going into overcoming aerodynamic drag your gas mileage increases will be even less substantial.

You'll get a little less power supply sag but aren't going to net a full dB of headroom. If you weren't clipping before you'll still be fine, and if you were clipping you'll probably still be and assuming you keep the same passive speakers and cross-overs need amplifiers with at least 2-4X the power rating to avoid that.

>03-20-12: Manitunc
>I dont quite understand how the crossover circuit prevents the low frequency currents from being supplied by the mid/hi frequency amplifier since the amp is being fed the full range and only after it reaches the speaker does it get split off by the coil used in the crossover. How does that coil draw off the low frequencies if they never get there in the first place? That is why I dont believe that biamping with the same amplifiers changes the sound other than perhaps some additional headroom for the mid/hi amp.

You're confusing voltage (potential, like the 80 PSI or whatever that your pipes are at, or the voltage across the amplifier output terminals) and current (what's flowing - crack the faucet so there's high resistance to flow and only a trickle comes out. Open it all the way creating a low impedance and you get wet. Little energy flows into a high impedance load and lots goes into a low impedance).

Reactive components have inductive (coils) and capacitive (capacitors) impedance that varies with frequency.

A capacitor's impedance magnitude is 1 / 2 pi f C with f in Hz and capacitance C in farads.

As f approaches 0 impedance becomes infinite. With current flow voltage divided by impedance current and therefore power (V * I) approach 0 as you get down to DC.

An inductor's impedance magnitude is 2 pi f L with f in Hz and inductance L in Henries.

Impedance is proportional to frequency; so as frequency goes up, less current flows, and less power is delivered.

The voltage dropped across impedances in series is proportional to them. IOW, put 3 volts into 1 and 2 Ohms in series and you'll have 1A flowing with 1V dropped across the first resistor and 2V across the second resistor.

The simplest possible cross-over circuit (first order electrical) puts a capacitor in series with the tweeter and inductor in series with the woofer.

At the highest frequencies the capacitive impedance becomes negligible, current flow is as high as it can get due to driver impedance, and all the voltage goes into the tweeter. The inductive impedance is large, essentially no current flows, and the voltage drop is almost entirely across the inductor in the low frequency circuit.

At the lowest frequencies the inductive impedance becomes negligible, current flow is as high as it can get due to driver impedance, and all the voltage goes into the woofer. The capacitive impedance is large, essentially no current flows, and the voltage drop is almost entirely across the capacitor in the high frequency circuit.

Assuming a purely resistive text book driver load (which only exists where the capacitance of the moving mass equals the inductance from the suspension compliance and voice coil) with resistance R at the cross-over frequency of 1 / 2 pi R C about 29% of the voltage is being dropped across inductor and capacitor and the two drivers are each seeing about 71% of the total.