How Do You Calculate Watts Per Channel?

08-05-13: Hk_fan
If you are bi-amping with 2x200W (@8 Ohms) amps then yes you have 400WPC (@8 Ohms).

As Al said above, the instantaneous power is a function of the impedance of the speaker at a given frequency as well as the power supply of the amplifier.

However, note that I also said the following:

If the amps are rated at 200W into 8 ohms, and if the impedance of the speakers is close to 8 ohms at all frequencies (which is unlikely), 200W will be available at frequencies that are substantially below the crossover point, and another 200W will be available at frequencies that are substantially above the crossover point. But since music consists of many frequencies that are present at the same time, the answer will vary depending on the relation between the specific frequency content of the music at any instant of time and the frequency of the crossover point, as well as the slopes of the crossover.

Let me cite an extreme example to illustrate this point. Suppose that the crossover point is 5 kHz, and the slopes of the crossover filters are sharp. The high frequency amplifier will handle very little energy below 5 kHz, while the low frequency amplifier will handle very little energy above 5 kHz. On nearly all music at nearly all times the energy that is present above 5 kHz is vastly less than the energy that is present below 5 kHz. Therefore most of the power capability of the high frequency amp will almost never be utilized. Very conceivably no more than perhaps 20 watts of its capability will ever be used (20 watts being only 10 db less than 200 watts). Therefore it is incorrect to say that 400W is "available," which was the OP's question.

My understanding is that most music at most times tends to have a roughly equal amount of energy above and below a frequency of something like 350 Hz.

Regards,
-- Al

I was not trying to state what Wattage was being consumed by the speakers at any given time, merely the theoretical power available which is how I read the OP's question.

I think most people think of this question in terms of a perfect 8Ohm load and not the various impedance swings which we know is reality.

I stand by my assertion that there is 400W on tap... should it be required. :)

Hk_fan, in case it's not clear my last point has nothing to do with impedance swings, and holds true even if the speakers are a perfect 8 ohm load at all frequencies.

To further clarify my last point, consider the situation in which the speakers are single-amped, using either a pair of 400W monoblocks or a 400W per channel stereo amplifier. Let's say that the speaker efficiency and volume setting are such that during peak passages of some recordings the full 400W capability of that amplifier is called upon.

Then let's change the setup to a pair of biamped 200W monoblocks per channel. Will that setup be able to play those same recordings at the same volume levels, without clipping or otherwise running out of steam?

The answer is that it will not, unless the frequency content of those musical peaks happens to be such that their power requirements at frequencies above and below the frequency of the crossover point are equal, which is very unlikely. So it would not be correct to consider the 2 x 200W biamped configuration as having the same power capability as a single-amped 400W configuration.

Regards,
-- Al

.

So it would not be correct to consider the 2 x 200W biamped configuration as having the same power capability as a single-amped 400W configuration.

Al you precisely answered the question that I imprecisely asked. Thank you!
.

In your first scenario the full 400W are being SHARED among all the drivers.

For sake of simplicity lets say there are 2 drivers, and assume that they have exactly the same impedance and efficiency. Therefore the two drivers will perfectly split the 400W, 200W per driver.

This is no different than individual drivers connected to a single 200W amp each.