Vertical Bi-Amping (Why does it work?)

Freo-1 · « **on:** 10 Oct 2010, 04:50 pm »

Decided to check out bi-amping with a pair of Legacy Signature III's. They cross over VERY low, so bi-amping with these is a good thing to do. I checked the Legacy website, and they seem to prefer vertical bi-amping to horiz. bi-amping.

I tried both vertical and horiz. bi-amping with a pair of Nakamichi PA-7,s. The speakers worked better with Naks in the vertical bi-amp configuration.

Next, tried both vertical and horiz. bi-amping with a Yamaha M-80 and M-85. Again, the vertical bi-amping was the better performer.

So, re-evaluated the vertical bi-amp option with both the Nak ans the Yamaha. The end result was that the Legacy's sounded the best with the Nakamichi PA-7's in vertical, followed by the Yamaha's in vertical.

I'm a bit puzzled by the end results. I had been running with a single Yamaha M-85 connected to the Signature III's, and that DOES sound better than the Nakamichi PA-7 connected to the Signature III's as a single amp.

There is obviously some speaker/amp interaction differences going on with the Signature III's crossover network once the jumper is removed for bi-amping. The tech from Legacy had told me when I got these that the impedance curve is better overall when bi-amping (it goes up to a nominal 6 ohms bi-amped.)

The PA-7 can indeed be a fine sounding amplifier with the right speakers. As for the M-80 and M-85, I'll use the M-80 for the rear channel in the HT setup, and use the M-85 with the 2 channel setup, connected to Source Technologies 277 SE speakers (which sounds great with the M-85).

Was wondering what other's experience with bi-amping has been? There does not seem to be a lot of agreement on this. Some people swear by it, while others seem to swear at it

At least for the Signature III's, they do indeed sound better when vertical bi-amped. The question is: Why?

"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)

*Scotty* · « **Reply #1 on:** 10 Oct 2010, 05:49 pm »

When an amplifier is asked to deliver the full spectrum of the signal given to it to the loudspeaker it produces a certain amount of intermodulation distortion. When you divide the spectrum in half that each amplifier has to deliver into the load the IM distortion is reduced. Also the amplifiers don't have to look at the entire speakers impedance curve just part of it and this can also reduce distortion.
Scotty

koyaan · « **Reply #2 on:** 10 Oct 2010, 06:02 pm »

Please forgive the dumb questions, but what is the difference between vertical and horizontal bi-amping ? Also, what is the effect of the speaker's internal crossover when you bi-amp?

opnly bafld · « **Reply #3 on:** 10 Oct 2010, 06:28 pm »

Vertical is 1 stereo amp per speaker, horizontal is 1 stereo amp for bass and 1 stereo amp for mids and highs.

Lin

geezer · « **Reply #4 on:** 10 Oct 2010, 07:52 pm »

Quote from: opnly bafld on 10 Oct 2010, 06:28 pm

Vertical is 1 stereo amp per speaker, horizontal is 1 stereo amp for bass and 1 stereo amp for mids and highs.

Lin

I see I've gotten tangled up in the language. I have one amp doing both L and R bass, and another doing the L and R mid/high. I've always thought this to be vertical bi-amping because it's in the vertical direction that I have two amps.

Does everyone agree my definition is wrong?

sts9fan · « **Reply #5 on:** 10 Oct 2010, 07:58 pm »

He amp is still delivering the whole signal. Correct? The only real difference is how large a crossover the signal goes through.

Jazzman53 · « **Reply #6 on:** 10 Oct 2010, 08:34 pm »

Typically it takes more amp power to drive the bass than it does to drive the mids/treble. And, in most amps, both channels draw their power from a common supply so at any given time, whatever power is not being used by one channel is available to power the other channel. With vertical bi-amping, one channel pushes bass and the other channel pushes mids/treble-- so the excess power on the mids/treble channel is then available to the other channel to drive the bass.

With horizontal bi-amping, the bass amp is over-taxed and the mids/treble amp is under-taxed. But if you have two matching power amps, you then have the option to vertically bi-amp and utilize all the power on both channels of both amps.

*Scotty* · « **Reply #7 on:** 10 Oct 2010, 10:06 pm »

sts9fan,Yes his amps are still delivering the whole signal to both high and low frequency networks but because the load is bandwidth limited for both amplifiers the IM distortion produced by each amplifier is reduced,the result of lower IM distortion is better imaging.
Inter-channel power supply cross-modulation can be largely eliminated by going dual mono after the transformer by using separate diode bridges and storage caps for each channel. In fact it is better to have single 1Kva transformer feeding both power supplies, than a pair of 0.5Kva transformers one for each channel. With dual transformers you are limited to what ever size they are for your maximum current capability, the upper limit being 0.5Kva..
With a single 1Kva transformer you have lowered the dynamic power supply impedance to half what a 0.5Kva Xformer has, and any current demands not made simultaneously by both channels leave a surplus current capability for which ever channel might need it.
This might be equivalent to a 0.75Kva transformer on an instantaneous basis for either channel. Plus you can usually get one honking big transformer in the box but not two of them.
Interestingly enough the scenario outlined by Jazzman53 where the amplifier is not designed as a dual mono after the transformer and power supply cross-modulation is allowed to take place make this cheaper and more conventionally designed amplifier theoretically superior for the vertical bi-amp application.
Scotty

Freo-1 · « **Reply #8 on:** 10 Oct 2010, 10:50 pm »

Good stuff. Thanks for the feedback.

There is another thead about bi-amping on anther site. Some folks seem to say that passive bi-amping does not achieve much it it's after the amp. I respectfully disagreed, and the feedback here helped fleshed out what I thought was happening.

The engineers at Legacy told me they recommended vertical bi-amping for the Signature IIIs. I can state wholeheartly that I agree with them!

Speedskater · « **Reply #9 on:** 11 Oct 2010, 01:24 pm »

I would chose Vertical if we had two identical stereo amplifiers.
But Horizontal if we wanted to use a high power (maybe solid-state or Class "D") amplifier for the Woofers and a smaller more detailed (maybe tubed) amplifier for the Tweeters.

geezer · « **Reply #10 on:** 11 Oct 2010, 02:28 pm »

How is vertical bi-amping different from using a single stereo amp with the corresponding watts per channel? I understand that in the latter case both channels share the same power supply, but if it's properly designed that shouldn't matter. (And don't some amps have separate power supplies for the two channels?)

koyaan · « **Reply #11 on:** 12 Oct 2010, 04:41 pm »

Thanks for the info, guys!
Whe bi-amping, is it necessary to use an external crossover, or does the internal crossover in the speakers still function?

DustyC · « **Reply #12 on:** 12 Oct 2010, 05:19 pm »

Freo-1,
What are you using for an active crossover?

opnly bafld · « **Reply #13 on:** 12 Oct 2010, 09:06 pm »

Quote from: DustyC on 12 Oct 2010, 05:19 pm

Freo-1,
What are you using for an active crossover?

He is passively biamping with 1 channel powering 3 10" drivers from 120 hz down and the other channel powering (from 120 hz up) 2 7" drivers , a 1.25" dome tweeter, and a ribbon super tweeter.

Lin

HIFIhoarder · « **Reply #14 on:** 12 Oct 2010, 09:55 pm »

Good Stuff. Now see if anyone can answer this. I have a pair of Plinius SA100's that can be used as stereo 100w/ch or mono at 400w/ch. I am using the mono switch wich produces more power and each mono is running a B&W 802D. However, the way Plinius works in mono mode, the user can only use the positive outputs. So i am not even sure if you could biwire if all you have are the positive posts.

Do you still think Vertical bi amp is better when you lose the 400w but you can biwire to the speakers? Thanks

charles28722 · « **Reply #15 on:** 12 Oct 2010, 10:09 pm »

Hifihoarder:

I vertically bi-amp with two identical stereo amps. I ran them for a while bridged mono and then later switched to vertical. The latter was better. Be careful with the load you are placing on your amps. The 802d's are a nominal 8 ohm load. If I am correct, when you bridge your amps to mono they are going to read your loudspeakers as a 4 ohm load, dipping down below 2 ohms. Just be sure they can handle it.

opnly bafld · « **Reply #16 on:** 12 Oct 2010, 11:06 pm »

Quote from: HIFIhoarder on 12 Oct 2010, 09:55 pm

Good Stuff. Now see if anyone can answer this. I have a pair of Plinius SA100's that can be used as stereo 100w/ch or mono at 400w/ch. I am using the mono switch wich produces more power and each mono is running a B&W 802D. However, the way Plinius works in mono mode, the user can only use the positive outputs. So i am not even sure if you could biwire if all you have are the positive posts.

Do you still think Vertical bi amp is better when you lose the 400w but you can biwire to the speakers? Thanks

From a Stereophile test: The B&W's impedance plot reveals the speaker to be moderately difficult to drive, with a magnitude that drops to 3 ohms throughout the upper bass and an awkward combination of 4 ohms and –50° electrical phase angle at 60Hz.

From a Stereophile test:Table 1 Plinius SA-100 Mk.II Discrete Clipping Levels
(1% THD+noise at 1kHz), class-A setting

    Both Channels Driven   One Channel Driven
Load   W (dBW)     W (dBW)
ohms   (L)     (R)     (L)
8   133.6 (21.26)     133.6 (21.26)   135.9 (21.33)
    115V     115V     115V
4   210.6 (20.23)     207.3 (20.17)   216.6 (20.37)
    115V     114V     115V
2             288 (18.6)
              115V

Using the amps bridged into the 802s they see between 1.5 and 2 ohms in the mid and upper bass, IMO it is best not to run amps this hard, and using each stereo amp per speaker is not giving up much power.

The best answer I can give is: listen to the amps both ways over several weeks and let your ears decide.
If you hear no difference IMO using each amp in stereo would be the way to go because they should run cooler and last longer.

Lin

doug s. · « **Reply #17 on:** 13 Oct 2010, 06:18 pm »

Quote from: geezer on 11 Oct 2010, 02:28 pm

How is vertical bi-amping different from using a single stereo amp with the corresponding watts per channel? I understand that in the latter case both channels share the same power supply, but if it's properly designed that shouldn't matter. (And don't some amps have separate power supplies for the two channels?)

see jazzman's post above. the only difference would be if you had true dual-mon amps - ie separate power supplies/transformers for each channel. in this case, there would theoretically be no difference between wertical or horizontal bi-amping. and, even w/a dual mono amp, bi-amping would offer better results than using a single stereo amp , as, per jazzman's post, the strain of driving the woofer would not affect the midrange/tweeter.

one theoretical adwantage to wertical bi-amping over horizontal bi-amping, even w/dual mono amps, is you can use shorter speaker cables, w/the amps situated much closer to the speaker. i feel shorter speaker cable/longer ic's are the way to go, tho others disagree about this, as well...

doug s.

celo · « **Reply #18 on:** 4 Jan 2019, 09:14 pm »

Can passive vertical bi-amping be done with an multi channel AV receiver? Say 5.1 receiver. Fronts for one speaker, rears for the other.

srb · « **Reply #19 on:** 4 Jan 2019, 09:54 pm »

Quote from: celo on 4 Jan 2019, 09:14 pm

Can passive vertical bi-amping be done with an multi channel AV receiver? Say 5.1 receiver. Fronts for one speaker, rears for the other.

Only if a "5 Channel Stereo" mode is available and used, where the Front L + R speakers receive the same equal level stereo signal as the Surround L + R speakers.

But not "Fronts for one speaker, rears for the other". The Front L and Surround L would provide amplification for the left speaker and the Front R and Surround R would provide amplification for the right speaker.

In 7 and 9 channel receivers, many models offer a menu option to use the Back L + R speaker outputs to bi-amplify the front speakers.