Question about Bi-Amping

mlurie31

I've been told by multiple people that bi-amping using only an AVR doesn't work, and that you shouldn't do it, even if it says in the receivers manual that you can. I believe it, but I'm just trying to learn and understand why it doesn't help. For instance, according to Sound and Vision, the Denon X3400A has the following outputs for 5 and 7 channels:

Five channels driven continuously into 8-ohm loads:
0.1% distortion at 97.6 watts
1% distortion at 106.1 watts

Seven channels driven continuously into 8-ohm loads:
0.1% distortion at 72.7 watts
1% distortion at 80.8 watts

(Read more at https://www.soundandvision.com/content/denon-avr-x3400h-av-receiver-review-test-bench#WUK3myv8G3ZIsxeo.99)

That would tell me that if I didn't bi-amp, a 5 channel system would get 97.6 watts of power for each channel. However, if I did bi-amp, I could could get 72.7*2 = 145.4 watts for the front L/R speakers, while getting 72.7 watts for the rest. If the front L/R speakers are towers, and the rest are smaller bookshelves, isn't it better to get more power for those speakers?

Can someone explain to me what is wrong with the logic I just went through, I why bi-amping isn't ideal with an AVR? Like I said, I do believe you, I'm just trying to understand. Thanks!

F1nut

You cannot bi-amp with a single shared power supply as found in every AVR made.

As for your example above you are splitting the 145.4 watts between the top and bottom posts, so each half of the crossover has 72.7 watts to draw on. The tweeter draws say 5 watts, so 67.7 watts go unused while the mid/woofer can draw on 72.7. Now, if only 5 channels are driven the speaker can draw on 97.6 watts with the tweeter drawing 5, which leaves 92.6 for the mid/woofer. That's not exactly how it works, just a simplified example.

True bi-amping requires two separate amplifiers and the use of active crossovers.

mlurie31

Okay, I think I understand. So the problem is, the tweeter uses such little power that by bi-amping, the total power available to the speaker is greater, however the amount of power available to the mid/woofer is less, and that is the part that needs the power, not the tweeter.

Does that sound right?

F1nut

Other than the fact it isn't bi-amping to start with you've got it.

joecoulson

I have two NAD amps, 3240PE and a 2400THX
Both are stereo amps and the 3240 is 2x40 and the 2400 is 2x100. I have the bottom section of my LSi-705’s (which is all three bass drivers) running off the 2400 (stereo mode from amp into bottom taps) and the top section running off the 3240. Effectively sending more power to the bottom if I want (I have variable output gained down on the 2400)
I can tell you that is sound very clear and I have more power than the speakers can handle at peak but the Bi-amp benefits I have not been able to clearly define as a huge difference vs standard jumper hookup. I’ll try some tests this weekend.

delkal

Now I am really confused! So to get "true" bi-amping you need to buy a separate (and expensive) dedicated amp just to supply 5 watts to the tweeter?

F1nut

Not only do you need two separate amps, you need active crossovers as well.

joecoulson

So. Did some testing. Actually have better (might be because of the differ by power ratings) results with the one power amp on the stock (jumper in place) taps.
I guess if I had two 2400’s I could test the theory properly but it didn’t seem right to me that 1/2 of the power would feed the tweet and mid tweet and the other half power all three woofers. Thought the combo I had might help balance but I think it muddied the sound.
Keeping the 2400 feeding them pure magic.

delkal

F1nut wrote: »

Not only do you need two separate amps, you need active crossovers as well.

Sounds like I will keep biwiring then! Thanks for the info.