medway creek

iTrader: (1)

Noobie theoretical question here:

Say I have a 2-way passive component set and an amp with 150wrms per side, all numbers @ 4ohms. Does each of the 4 drivers see 150w or 75w or some variation I'm not taking into account?

Your patience is appreciated.

Tom.F.1

iTrader: (1)

A crossover splits frequency, not power.

If you put 150 w @ 100 hz into your component set, most of it will go to the woofer. There are normal, expected, losses in the passive crossover.
If you put 150 w @ 10,000 Hz into to your component set, most of it will go to the Tweeter. And you'll kill the tweeter.
Music contains much higher power levels at low frequency than at high frequency. i.e. it takes a lot more power to make that 100 Hz seem as loud to your ears as the 10,000 Hz.

This is why we need bigger amps for subs.

medway creek

iTrader: (1)

I think that answers my question - without looking at losses in the system or fq response or anything like that, just the electrical side of it, all the drivers have the potential to see the full 150rms? it's not halved or doubled or anything like that?
What I'm trying to figure out basically is if there would be a major difference in power delivery potential (active/passive issues ignored) between say a 150rmsx2 vs (50rmsx2 + 100rmsx2).

zoomer

iTrader: (3)

yes you would remember watts = V^2/R Vsquared divided by R
Let me explain:

lets say you have 10volts rms at 100Hz and 5 volt rms at 5KHz
that would be 25 watts at 100hz and 6.25watts at 5Khz for a total of 31.25 watts needed to be delivered to the speakers. However, if the 2 voltages add up, your amp will have to put out a voltage of 15 V rms and would be like asking the amp to deliver voltage equivalent of a 56.25 watt amp. So you will need a 56.5 watt amp to deliver a clean 31.5 watts to the speakers.


If you stay passive but biamp your speakers, in other words an amp for each driver with the crossovers split into a low freq and high freq section (not all crossovers let you do that, only the high end ones) each amp will still be asked to amplify the total signal of 15 volts and the result would be very similar to using a single amp. The only difference is that the HF amp will not have to deliver the LF current and thus will distort a bit less and will run cooler. Why? becuse the HF amp sees open circuit at low frequencies and thus delivers no power at low freqs and vice verse.

However if you go active, then each amp only sees its own frequencies..
The LF amp will only need to be a 25 watt amp to deliver 25 watts and the HF amp only needs to be 6.25watts in order to deliver 6.25 watts.

There is a very good explanation at
http://sound.westhost.com/bi-amp.htm#elect_xovers

in that article he uses the term bi-amplification for both active and passive systems, but does a good job at explaining the advantage of active vs passive in a bi amped system