Bi-amping Revel Salon2 makes an ABX audible difference

[RichB]

In terms of level matching/quick switching between such?

The session uses a single speaker. The left channel is split with a Y Adapter and both amp channels are used for the same source.
A short patch cable is used and out of view, the switch is made between the bi-amp with the duplicate cable, and the patch cable (single-amp). The channels are duplicated so there is no need to level match. The levels were also checked with a volt-meter playing sinewaves to confirm.

- Rich

 

[Chrispy]

The session uses a single speaker. The left channel is split with a Y Adapter and both amp channels are used for the same source.
A short patch cable is used and out of view, the switch is made between the bi-amp with the duplicate cable, and the patch cable (single-amp). The channels are duplicated so there is no need to level match. The levels were also checked with a volt-meter playing sinewaves to confirm.

- Rich

So there's no electrical difference when passive bi-amping? I'd thought there was, albeit very minor.

 

[DonH56]

So there's no electrical difference when passive bi-amping? I'd thought there was, albeit very minor.

The electrical difference is that different amps (or amp channels) are driving woofer and tweeter sections instead of the same amp output. No difference on the speaker side, same crossovers inside the box, and they are still in the signal path.

The only cognizant technical argument I have seen for this is that, since the woofer amplifier need not supply tweeter current (and thus power, only voltage is the same) and the tweeter amplifier does not provide woofer current/power (but again the voltage at the terminals is the same), there is less distortion due to the lighter load on each amplifier channel and reduced "mixing" of distortion products due to charge kick-back ("back-EMF") from the speakers. That assumes a single amplifier channel distorts enough to be audible due to the heavier load vs. using two amplifier channels.

Restated:

• An amp drives the woofer, and the woofer "kicks back", causing the amplifier's output to change a little since the amplifier does not have perfect 0-ohm (ideal) output impedance. That change can cause the signal to the tweeter to change as well, and perhaps induce distortion in the tweeter. The same situation is true for the tweeter "kicking back" into the amp and causing the woofer's signal to change.
• Using two different amplifier channels, any woofer kickback is not seen by the tweeter amp and vice-versa. So even though the voltage from each amplifier channel is the same, since the current delivered is different, any modulation of the signal by the "other" driver is isolated.

How much that matters is the subject of endless debate. Most of the little data I have seen indicates this could only be audible with high amplifier output impedance (e.g. tubes) working into speakers with impedance that varies greatly over frequency (not all that uncommon) and probably driven very hard. I don't have any links to data; it has been years since I looked into this. Most of the marketing literature I have seen shows big changes but on plots enlarged so much as to obfuscate the magnitude (i.e. they make it look way worse than it is in practice) and/or using unrealistic conditions.

I tried this once, I think, when I first set up my media room and was trying to understand the benefit since it was not at all obvious to me why you would do this. I heard no difference, and measurements at the speaker outputs were unchanged, but I did not measure the amplifier outputs. Just has not been worth the effort to me and I do not have extra amp channels for it anyway.

This might be an interesting test for @amirm, @pma, or one of the other test experts on ASR in their spare time...

 

[Lsc]

While there may be technical reasons why bi-amping does or does not benefit, it’s up to the end user’s preference. If I choose bi-amping because I think it sounds better but others in this forum and others say I’m hearing things…my response is “ok, thanks for your feedback and your wanting to help me.” Still, since I’m the only one listening to my system (rest of family have other systems), I’ll connect based on my own personal preference. If bi-amping is harmful then I’ll switch but if it nets zero or a fraction better, then there is no harm.

I did bi-amp then revert back because I don’t have matching amps - one ATI4000 and one ATI6000. The ATI4000 now powers my surrounds.

 

[ROOSKIE]

Does bi-amping make a difference? My Revel Salon2 speakers come with two pairs of binding posts, and the manual says:

Revel does not endorse one particular connection method over another.... The design of this loudspeaker is such that optimal performance can be attained using the standard connection method.

By connection method, do they mean bi-wiring, or is bi-amping included? When I switched to vertical bi-amping (one stereo amp per speaker), I sensed a subtle but definite improvement in clarity of high frequencies.

To start, let's compare frequency responses. In the vertical bi-amp configuration, each Salon2 is powered by one Benchmark AHB2 in its low gain mode, with the high and low frequency binding post each driven by one of the amp's two channels. In the normal configuration, the manufacturer supplied shorting bridge is used and the speaker is powered via one pair of binding posts. Note that in the normal configuration, each Salon2 is still powered by a separate AHB2, i.e. monoblocking using a single AHB2 channel per amp. This means any differences would be attributable solely to separation of high and low frequency amplification, and not to elimination of stereo crosstalk between the amp's two channels.


View attachment 199194

As we can see, frequency response is unchanged. Variations below 50hz are within usual variation on each measurement, so I wouldn't put any credence on differences there. Still, I was not convinced that the difference I was hearing was all placebo. It's impractical for me to do a blind test, given the time and effort required to change from bi-amp configuration to normal. An ABX with enough repetitions to prove audibility would take dozens of changes, each of which takes longer than ideal for our short audio memories.

Recently in my previous experiment, it was shown that recorded speaker outputs can be used in an ABX test to demonstrate an audible difference for a change of speaker feet, so I wanted to see if this ABX method would also work here. I recorded the output of my Revel Salon2 speakers playing music in stereo using a pair of high quality cardioid microphones (Shure SM81), each mic 2' in front of the tweeter's logo.

I've attached sample clips of the recordings. The original is available free on 2L.co. I think you'll agree upon listening that these recordings are a good enough representation of the original to plausibly reveal differences. I did the ABX test using a piece I'm more familiar with, another recording of a classical string quartet.

The difference was minute, and ABX is hard. There's the time, effort, and mental fatigue. The default of 16 trials requires at least 32 intense listenings of the same passage, likely more. It takes training to tease out perceived differences that are real and can be repeatedly ascertained, versus those that turn out to be due to memory blur or too weak to be detected repeatedly with sufficient accuracy. Repeated listening causes a kind of burn in of the senses and memory. Eat a bite sized piece of single-origin chocolate and you can taste the nuances down to the trees that were planted next to the cocoa. Now imagine eating 32 pieces in a row and then asked to distinguish the nuances between the last two pieces.

I only take a test when I'm able to get good accuracy in training mode, and still my first two tests were only 10/16 and 9/16 correct, which led me to devise techniques to limit fatigue and its effects. It helped to identify an extremely short passage of 2 seconds and to limit listenings by reducing trials from 16 to 10, which is a tradeoff that requires a higher accuracy for statistical significance. I did the third test after training and improved to 9/10 trials correct (p = 0.0107).

View attachment 198976

It's no wonder to me now that ABX tests have come up null for all manners of changes. If I were a random subject brought in off the street, with no practice and no incentive to get the right answer, I would have performed even worse than my initial trials and we would have concluded there was no difference.

I do think the real difference is greater than is captured by the recordings, but that cannot be shown by this ABX setup.


TLDR

Vertical bi-amping of Revel Salon2 using 2x Benchmark AHB2 has the same frequency response but makes an audible difference.

I sure seems telling with all that it appears is required to maybe tease out differences, the most minute differences, between two variations of a system using some of the best gear on the planet.
Even when sighted and in full knowledge.

I imagine Harman has blind tested biamping and biwiring because they could so easily. To bad nothing has has been overtly published.

 

[blueone]

I imagine Harman has blind tested biamping and biwiring because they could so easily. Too bad nothing has been overtly published.

Most likely they say nothing about bi-wiring and bi-amping on the Salon2 because they know that the second pair of binding posts are there only for marketing reasons.

 

[RichB]

I sure seems telling with all that it appears is required to maybe tease out differences, the most minute differences, between two variations of a system using some of the best gear on the planet.
Even when sighted and in full knowledge.

I imagine Harman has blind tested biamping and biwiring because they could so easily. To bad nothing has has been overtly published.

Actually no, Harman stays away from the speaker wire recommendations except for gauge.
High-end speakers allow bi-amp and one could argue for marketing reasons.
The Revel Ultima brochure includes the following:

https://www.revelspeakers.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dw12377a82/pdfs/Revel_Ultima2_Loudspeaker_Series_Brochure.pdf

Crossover networks
Each Ultima2 loudspeaker employs separate filter boards for each frequency range. Ultima2 fourth-order crossovers provide greater power handling and less distortion than simpler networks and achieve superb integration, transparency and musicality.

Separating boards was implemented to reduce the crosstalk. If that is indeed the case, then electrically separating the crossovers may have benefit.
That's basically the potential for benefit. So, for those interested, it is a fairly simple experiment to SBT at home. All you need is a friend or patient significant other and interest.

- Rich

 

[ROOSKIE]

Actually no, Harman stays away from the speaker wire recommendations except for gauge.
High-end speakers allow bi-amp and one could argue for marketing reasons.
The Revel Ultima brochure includes the following:

https://www.revelspeakers.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dw12377a82/pdfs/Revel_Ultima2_Loudspeaker_Series_Brochure.pdf

Separating boards was implemented to reduce the crosstalk. If that is indeed the case, then electrically separating the crossovers may have benefit.
That's basically the potential for benefit. So, for those interested, it is a fairly simple experiment to SBT at home. All you need is a friend or patient significant other and interest.

- Rich

Howdy, appreciate what you are saying however I think @blueone covered what I was implying.

 

[HansHolland]

If biamping or even biwiring works, then it is due to reduced intermodulation distortion.

But, the mid range frequencies are still influencing the bass and the other way around. So, a 3-way speaker with 3-amping is needed.

And how about the lower midrange influencing the higher midrange, etc. Ehm, what do you think about for every note a separate amp plus speaker driver? That is 12 amps and drivers for each octave. And then only listen to western tuned music. Ehm, impractical and expensive.

Ok, this example was over the top. But I like the coherence of single driver loudspekers. Yes, I have 2-way loudspeakers because I think a 1-way loudspeaker is too limited. But an amp and loudspeaker cable do not have these limitations.

So I prefer single wiring and single amping.

 

[Deleted member 49736]

I actively seek out speakers with bi-amp binding posts for multiple reasons. Reasons 1 and 2 are really only made possibly by DSPs.

1. It’s very easy to take a 2-way passive speaker with bi-amp binding posts, rip out the passive crossover, add new wiring and turn it into an active speaker.

I’ve done this with affordable monitors like RP-600M and electrostat towers like ML ESL-X. The results are both objectively and subjectivity significant in all cases. The tuning flexibility is unrivaled. In most situations, you’ll have 10-band PEQ and individual delay per each driver. That makes a huge difference.

2. It’s equally easy to take a 3-way passive speaker with bi-amp binding posts and bypass the passive crossover for woofer(s).

I have done this with a B&W 603S2 and eliminated my desire to add a subwoofer.

3. More relevant to most everyone else: IRL, audio signals are not sine sweeps, and they causing unpredictable impedance changes outside of what’s possible to measure. Dividing the load between more amplifier channels is going to yield more stable loads. In most cases, even though there’s no active crossover and all of the amp channels still receive a full 20-20k signal, they aren’t all experiencing the same impedance shifts because they are connected to loads that reproduce different frequency ranges. I believe this is the most overlooked benefit of conventional, old-school bi-amping.

 

[DonH56]

I actively seek out speakers with bi-amp binding posts for multiple reasons. Reasons 1 and 2 are really only made possibly by DSPs.

1. It’s very easy to take a 2-way passive speaker with bi-amp binding posts, rip out the passive crossover, add new wiring and turn it into an active speaker.

I’ve done this with affordable monitors like RP-600M and electrostat towers like ML ESL-X. The results are both objectively and subjectivity significant in all cases. The tuning flexibility is unrivaled. In most situations, you’ll have 10-band PEQ and individual delay per each driver. That makes a huge difference.

You can rip out the passive speaker crossovers and replace them with "old-school" analog crossovers before the power amps. DSP may make it easier (if you know how to use one) but is not a requirement.

2. It’s equally easy to take a 3-way passive speaker with bi-amp binding posts and bypass the passive crossover for woofer(s).

I have done this with a B&W 603S2 and eliminated my desire to add a subwoofer.

As above. Adding a subwoofer provides many benefits, some of which you cannot realize by bi-amping the main speakers. Improvements in low-frequency distortion and reduction of the impact of room modes among them. But you said "desire" so those may not be benefits you need or want.

3. More relevant to most everyone else: IRL, audio signals are not sine sweeps, and they causing unpredictable impedance changes outside of what’s possible to measure. Dividing the load between more amplifier channels is going to yield more stable loads. In most cases, even though there’s no active crossover and all of the amp channels still receive a full 20-20k signal, they aren’t all experiencing the same impedance shifts because they are connected to loads that reproduce different frequency ranges. I believe this is the most overlooked benefit of conventional, old-school bi-amping.

Audio signals are in general comprised of a multiplicity of sine waves, and the impedance of speaker is both predictable and measurable using sweeps. It's not like music includes frequencies the sine sweeps do not. I wish that myth would die...

Dividing the load among amplifier channels will not change the load itself, making the load more or less "stable", though it might help the amplifier (though it would be rare to find an amplifier today that does not handle most any speaker load). Conventional "old-school" bi-amping using line-level crossovers before the amplifiers better controls back-EMF and so forth from the drivers to reduce distortion, reduces wideband intermodulation products, allows more precise crossover control, and allows the amps to be "right-sized" for the driver. I think handling "impedance shifts" is someplace among those benefits, and they are well understood.

 

[Deleted member 49736]

You can rip out the passive speaker crossovers and replace them with "old-school" analog crossovers before the power amps. DSP may make it easier (if you know how to use one) but is not a requirement.

Good luck getting that dialed in and sounding right.

As above. Adding a subwoofer provides many benefits, some of which you cannot realize by bi-amping the main speakers. Improvements in low-frequency distortion and reduction of the impact of room modes among them. But you said "desire" so those may not be benefits you need or want.

I don’t agree and that’s not the point. Indeed I said desire.

Audio signals are in general comprised of a multiplicity of sine waves, and the impedance of speaker is both predictable and measurable using sweeps. It's not like music includes frequencies the sine sweeps do not. I wish that myth would die...

Music is not a sine sweep. Music is dynamic.

 

[fpitas]

Music is not a sine sweep. Music is dynamic.

It is. But it is still composed of sine waves, added together. That math goes back hundreds of years.

Fourier transform - Wikipedia

en.wikipedia.org

History​

Main articles: Fourier analysis § History, and Fourier series § History
In 1822, Fourier claimed (see Joseph Fourier § The Analytic Theory of Heat) that any function, whether continuous or discontinuous, can be expanded into a series of sines.[10] That important work was corrected and expanded upon by others to provide the foundation for the various forms of the Fourier transform used since.

 

[Sokel]

Music is not a sine sweep. Music is dynamic.

So?

 

[DonH56]

Good luck getting that dialed in and sounding right.

Done it many times over the years. Lots of good-sounding systems before DSP came along, and plenty even now without DSP. DSP is a really cool tool but there are other means to the goal.

I don’t agree and that’s not the point. Indeed I said desire.

Not sure how you do not agree with placement countering modes and such but your choice. The point is that you are disagreeing with basic physics. Again, your choice.

Music is not a sine sweep. Music is dynamic.

Sine waves are dynamic. Music is made of sine waves. What is your technical background? There seems to be some fundamental misunderstanding of basic electrical theory.

 

[Deleted member 49736]

Done it many times over the years. Lots of good-sounding systems before DSP came along, and plenty even now without DSP. DSP is a really cool tool but there are other means to the goal.

A model A Ford will still roll down the road, but a 2017 Ford GT will go down the road a lot better in every conceivable way.

Not sure how you do not agree with placement countering modes and such but your choice. The point is that you are disagreeing with basic physics. Again, your choice.

I don’t agree with the blanket statement that subwoofers are necessary to have deep, articulate, distortion free, even sounding bass. Plenty of tower speakers are full range. Room size plays the largest role in this argument.

Sine waves are dynamic. Music is made of sine waves. What is your technical background? There seems to be some fundamental misunderstanding of basic electrical theory.

I professionally mind my own business. How often do you ask that question? I would bet pretty often.

We’re not talking about electrical theory here. There is no dispute how sound waves move through the atmosphere. Also, that’s physics, not electrical theory. If there was a specific, scientific, mathematical answer to this question, we would not be on a forum offering theories in the first place. The fact is bi-amping does change the electrical behavior of a stereo system.

 

[Deleted member 49736]

So?

So a perfectly tidy sine sweep is not a perfectly accurate representation of the electrical load created when speakers reproduce music. Music is not a perfectly tidy sine sweep, it’s many sine waves compounded together simultaneously.

 

[fpitas]

I professionally mind my own business. How often do you ask that question? I would bet pretty often.

We’re not talking about electrical theory here. There is no dispute how sound waves move through the atmosphere. Also, that’s physics, not electrical theory. If there was a specific, scientific, mathematical answer to this question, we would not be on a forum offering theories in the first place. The fact is bi-amping does change the electrical behavior of a stereo system.

This begins to sound like trolling. You've been presented with mathematical proof that any waveform can be decomposed into sine waves. I'm afraid the argument, such as it is, ends there.

 

[Deleted member 49736]

This begins to sound like trolling. You've been presented with mathematical proof that any waveform can be decomposed into sine waves. I'm afraid the argument, such as it is, ends there.

Apparently, you have an intimate understanding of electrical theory, but you can’t read or you have a reading comprehension impairment.

 

[fpitas]

Apparently, you have an intimate understanding of electrical theory, but you can’t read.

Uhhhh...yeah. But I think I understand you better than you think.