Technical Question - How Much Amplifying Does a Pre-Amp Actually Do?

[lindsayt]

Benedict, I don't know about passive bi-amping. I've never done it.

However I am listening to an actively bi-amped system now.

I don't know about your speakers. But all of my speakers have more efficient drivers for the upper frequencies than they do for the lower frequencies. IE in all of my speakers the tweeters need less power than the midrange units to achieve the same measured sound volume. The midrange units require less power than the bass units to achieve the same volumes.

With my speakers a relatively flat frequency response is maintaned when used in passive mode by a combination of the lower frequency units having a lower nominal impedance (and therefore sucking more power from the amps) combined with the upper frequency drivers being padded down (resistors used as a simple volume attenuator).

As well as the efficiency there's also damping factor requirements. At higher volumes bass cones will move in and out. In extreme cases this movement is visible. Midrange units and tweeters never move in and out to anywhere near the same extent. This means that bass cones generally benefit by being powered by amps with a high damping factor. In general, on average, the amps with the highest damping factors tend to be the most powerful ones.

Also, check out a few frequency spectrum charts. You'll see that pop and rock music has significantly more content below 1 khz than above.

All of which adds up to me always using my most powerful amps for the bass and my least powerful for the midrange / treble.

 

[davedotco]

If you go to a disco or a rock concert, don't they turn down the treble at high volumes to stop everything sounding too shrill (Rush fans please take note :-0 )?

And that matters why? What have either got to do with hi-fi.?

You have wittered on about impedance and how it alters the power delivered by the amplifier, what do you think a crossover (or separate hi and low pass filters in a bi-wire setup) actually does?

How does it actually stop an amplifier, being driven full range remember, delivering all that juicy bass power into your tweeter and blowing them up?

Come on, the answer is right there, work it out...!

 

[Vladimir]

I'll say that again, the maximum power of a passively bi-amped system is the maximum power of the smaller amplifier.

But where do the rest of the watts go????!!!!

Down the pughole, counter clockwise in the southern hemisphere.

Think about it.

Clue. What impedance does the amplifier 'see' when driving out of band frequencies into a passive crossover?

What crossover? If the HF and LF are no longer connected...

Yes, my argument abou the Mundane-Oh and the Ferarri falls flat if the two are tied together by a tow rope, but if they're independent of each other....

But you'll end up plowing the room with bass and no mids and highs that way. Only way to balance everything to listenable is to lower the LF amp. No?

Which goes back to my position that you should use the LOWER paower amp for the bass...

Brilliant!

Check this thread on AVS where they measure PA amplifiers how well they hold up to manufacturers declared specs. Notice how on every amp as load impedance drops, amplifier consistently delivers less power both in extreme low and high frequencies. Sometimes more in the highs! Clicky