Need help from smart people - biamping


Hi, I know some of you are electrical engineers or just knowledgeable - looking for your input. I'm looking at the option of bi-amping my speakers. One amp on the mid-tweet connection and an identical amp on the bass connection. Speakers are B&W N804s. Question is, if you do this do the two amps react to the loads as one amp would, or is it possible that if the two connections (drivers) have different impedences, the bass might be louder relative to the mid-tweet, or quieter? In other words, if the upper end has impedence of 8 Ohms and the amp puts out 100 w/ch at 8 ohms, and the lower end is at 4 ohms, and the amp 200 w/ch at 4 ohms, will this result in a problem in the resulting aural output than would have been experience with a single amp? Thank you.
jimmy2615
You will be passive bi-amping, which means the signal will still use the speakers internal crossover. No issues with impedance or loudness.

Unless you need the extra power, I doubt you will hear much of difference sound wise, but give it a shot, you never know.
Do not try to biamp unless you know what you are doing.
For the average not into the scene it is way better to just buy one bigger better amp.
Biamping seems easy, but is really hard.
It is a common question among non experienced folks.

On the other hand plenty of people swear by biamping.
My heartfelt recommendation is do NOT do it.
It is a waste of money and time spent for an iffy result.
(at least for the average beginner)
I concur with Meiwan's doubt. Tried it with three times with three different amps and never thought there was any real improvement. Different speakers were used also.
If the upper end has impedence of 8 Ohms and the amp puts out 100 w/ch at 8 ohms, and the lower end is at 4 ohms, and the amp 200 w/ch at 4 ohms, will this result in a problem in the resulting aural output than would have been experience with a single amp?
No, that won't result in a problem. The proportion between the amount of current and power drawn by the speaker at high and low frequencies in response to a given amplifier output signal voltage will be the same regardless of whether the current and power required at each of those frequencies are provided by the same amplifier or similar separate amplifiers. This assumes, of course, that identical signals are provided to the inputs of both amplifiers, and that the amplifiers are either identical or their gains are matched in some way.

If you do end up biamping, since you would be using two identical amplifiers you may want to also try a "vertical" configuration, in which the two channels of one amplifier drive the high frequency and low frequency sections of a single speaker, respectively, and the two channels of the other amplifier drive the high frequency and low frequency sections of the other speaker, respectively. Compared to the "horizontal" biamp configuration you are proposing, the vertical approach would have the advantage of having the same signal going through both channels of a given amplifier, potentially reducing interchannel crosstalk.

In general, though, I agree with the others that simpler is usually better, and that a single higher-powered amp will often be a better solution.

Regards,
-- Al
I was going to say something but not sure if I qualify.
here's some more info for you re. biamping
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1274907651&openflup&4&4#4

i like Eldartford's phrase that this should be called "dual amping" because biamping means something different (where you gut the speaker's internal x-overs & use an external x-over to split the frequency spectrum & pass on only that portion of the freq spectrum that the driver is capable of handling).

And, back in Jan 2012, we discussed this bi-amping thread, which you should read (skip over the bickering, please):
http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1326877788
What is known as passive biamping (I also like the description "dual amping") is certainly not difficult when using two identical amps. Anyone can do so; it simply takes more time and care to ensure that the connections are set up properly. You also need enough power receptacles, something which is often overlooked. It may be necessary to obtain a longer power cord for a component if you do not wish to use power bars or other power conditioning equipment.

It is unnecessary to scare people away from trying it with suggestions that it is very difficult. Diagrams for how to hook up two stereo amps are numerous (note that you can also use a multichannel amp with four channels, and if our speaker has three sets of inputs you can use a six channel amp). Going the other direction you can use four or six monos.

Al is right to suggest vertical dual amping. I have tried horizontal dual amping with all sorts of amps over the years and in every instance have preferred vertical. It has been so consistent that I would not even suggest trying horizontal. If you simply keep the amp's channels dedicated to a particular speaker, one channel to M/T and the other to Bass, you'll do fine. Make sure that you are using the proper settings on the amp; some, like the Cambridge Audio Azur 840W, allow for several combinations and have multiple switches for those settings for inputs and outputs.

As to sweeping conclusions regarding the usefulness of dual amping those who have never done so really don't have much to contribute. The fact is that there will be a noticeably different presentation whenever passive dual amping is tried as opposed to using amps in Mono mode.

I just finished a review of an approx. $15k speaker, one of the systems for which was dual amped integrateds, a most unusual approach. Dual amping brings its own particular "flavor" to the sound, and for some they may prefer it. It is generally true that a larger, more powerful and likely more refined amp does often sound better, and yes, often putting two stereo amps in Mono mode is superior. However, imo you will not get the full advantage of one stereo or two Mono amps unless you biwire the speakers. Note well: Switching to an entirely different brand of larger stereo amp is NO assurance that it will outperform the two more diminutive amps in dual amping mode. One simply has to conduct the comparison; a simple comparison of aggregate Watts is wholly insufficient to settle the matter of which is perceptually better.

Speaking to biwiring, after working with literally dozens of single wired (one pair of L/R inputs) speakers I strongly urge owners to try doubling up their speaker cables. No, I am not joking. You will get easily noticed superior results by doubling speaker cables, simply joining the proper leads as you would a single set. You must be absolutely sure you are not crossing wires; double and triple check. If you cannot hear the difference, then you will not really benefit much from chasing different brands of cables - just get something you like and be done. But if you love your speaker cables go get another set and slap them on, as you have not heard what a speaker can do when you have only single wired it. (And no, I have no intrest in arguing this.)

Obviously you can swap different brands of cables, but if you have found one you enjoy then double it. You have not begun to hear the capabilities of your speakers if you have not tried this. Sure, you can get a biwire pair of speaker cables, but many times the sum of conductors is split, versus having double the conductors when using two sets of speaker cables - a huge difference in total gauge, and sound.

I do concur that proper active (x-over) biamping is much more involved, but is well worth trying if you have the money and time, and are not afraid of more complex systems. With any given amp I have used in a passive mode versus active the active system has conferred upon the amp the ability to sound more powerful and with far more control over contouring the desired sound of the system.

Though I do not recommend mixing brands of speaker cabling, this also allows for some tuning of the rig's sound. If you do have different sets you will need to try all hookup options to know which will yield the best sound. Again, if you cannot easily hear any distinctions in sound when trying such things then it is less likely that you will be able to perceive distinctions betwen the two methods of amping.

Once you factor in the variable of cabling the audiophile has a lot of options for setting up even dual amping. :)
I didn't read all the posts, so I don't know if anyone brought this up already. Have you considered verticle biamping? You will hear a difference using this method. Take your identical amplifiers and use one for each speaker. Biamp each speakers using the left and right channels.
Wow, thanks for all of the responses ! Most helpful. I was only considering horizontal biamping; the vertical approach as described did not even occur to me.
I was contemplating exact same configuration. With vertical passive bi amping, would the SPL increase at same volume level at preamp? If not, how about potential SPL increase capability with biamping at comparable before and after biamping?
Hi Nil,

In a passive biamp arrangement employing identical amplifiers, whether vertically or horizontally, any given frequency component of the input signal to the amplifiers will be subject to essentially the same gain as if only one of those amplifiers was being used full-range. Therefore there will be essentially no difference in the volume control settings that are used in the biamp and single-amp configurations. (I say "essentially" because there are some subtle effects that might result in extremely small differences, such as the very slight volume loss that can result from splitting the preamp's output signals, depending on the impedances that are involved).

MAXIMUM volume capability, before clipping occurs, may increase SLIGHTLY in the passive biamp configuration, to the extent that the output voltage swing capability of the amplifiers increases as a result of the fact that each amp would no longer have to supply current and power across the full frequency range. Or (less commonly) if the maximum volume capability of the particular combination of amp and speaker is limited by the current capability of the amp, rather than by voltage swing.

The main benefit, if any, would be with respect to sound quality.

Best regards,
-- Al
Hi Al,

Thanks that is exactly my thinking was. My preamp does have 'designed in' two sets of outputs (a balanced set and single ended set- I currently use only set of balanced at present). Not sure what that means to volume loss since both will pre-amplify the full signal still. Hopefully not much volume loss.

I was thinking that max volume capability increase, before clipping occurs, now would be close to 3db. Aren't we 'doubling' (than what it was) the power essentially to both m/t and l freq drivers? No? That is my primary goal. I am happy with the sound quality and overall tonal balance right now with one mono block pair.

In any case I would audition before buying an extra pair of amps but still there is shipping, extra pairs of same quality cabling, same tubes etc involved.

You do give enough technical info and reasoning for me to think about. Thanks!
I was thinking that max volume capability increase, before clipping occurs, now would be close to 3db. Aren't we 'doubling' (than what it was) the power essentially to both m/t and l freq drivers? No? That is my primary goal. I am happy with the sound quality and overall tonal balance right now with one mono block pair.
Not necessarily. Since in a passive biamp configuration the amplifier channels driving the low frequency and the mid/hi frequency sections of the speaker will BOTH have to output a voltage range corresponding to the full frequency range of the signal, there may be very little increase in the total power capability. As I indicated earlier, in the single-amp situation if power capability is limited by the voltage range that can be output, passive biamping will only result in a power increase to the extent that the voltage range capability increases as a result of the reduction in the amount of current that each amp channel has to supply (the low frequency amp will not be supplying current at high frequencies, and vice versa). How much that voltage range increase will be depends on the particular amplifier, and may be correlated to some degree with the dynamic headroom of the particular design.
My preamp does have 'designed in' two sets of outputs (a balanced set and single ended set- I currently use only set of balanced at present). Not sure what that means to volume loss since both will pre-amplify the full signal still. Hopefully not much volume loss.
It would probably be best to use a balanced y-adapter to split the signals. Using the balanced output for one amp channel and the single-ended output for the other would probably introduce a gain mismatch. Also, some designs may not intend for both outputs to be used simultaneously, and the single-ended output might be the same signal as one of the two signals in the balanced pair (probably the non-inverted signal on XLR pin 2). In that situation using both sets of outputs would, to at least a small degree, unbalance the balanced signal pair, and nullify some of the advantages of a balanced interface.

Some inexpensive XLR y-adapters can be found here.

The volume loss resulting from splitting the signal will be negligible (less than 1 db) as long as the parallel combination of the two amplifier input impedances remains at least a factor of 10 higher than the output impedance of the preamp, at the frequency for which preamp output impedance is highest. Which is a necessity anyway, to avoid compromising sound quality.

Best regards,
-- Al
Thanks Al.

I do now understand the vol increase potential, which is to say slightly not to extent (3db) I was thinking. Dynamic headroom will most likely increase (==>better sound quality)

I meant to say that my preamp has 'designed in' TWO pairs of balanced and TWO pairs of single ended outputs for specifically this reason (biamping) So I suspect the output signal is already Y-split internally for each pair 'sets'. BTW, I just got A response back from my amplifier designer/rep (Zanden) and they also sort of said expected results in line with what you said.
Overall sound quality= better, SPL increase potential = slight.

I really appreciate your insight.