Review and Measurements of Benchmark AHB2 Amp

[waynel]

Even with fourth order crossovers some of this distortion will still find its way to the next driver.[

This doesn’t make sense to me as the distortion that we are talking about is created and propagated by the driver in question. Therefore biamping can not help with driver created distortion.

Btw , I agree that salon 2s are fine speakers but they can be improved by adding a couple of good subs (which is what I and many others do)

 

[bigguyca]

(1)This doesn’t make sense to me as the distortion that we are talking about is created and propagated by the driver in question. Therefore biamping can not help with driver created distortion.

Btw , I agree that salon 2s are fine speakers but they can be improved by (2) adding a couple of good subs (which is what I and many others do)

(1) The drivers create what is call back EMF. Essentially a voltage that opposes movement. This voltage is expressed on the connections to the driver and back the crossover where a small part of it, including distortion, will be transferred to the upper bass driver. This is a real effect whether if makes sense to you or not; think Maxwell's equations. The size of the effect and its importance are certainly open for debate. The effect is worse for speakers with 1st or 2nd order crossovers.

Denon/Marantz describe the effect of EMF this way, although the tech. writer has a bit of an odd description, perhaps translated from Japanese.

"This connection enables back EMF (power returned without being output) from the woofer to flow into the tweeter without affecting the sound quality, producing a higher sound quality."

(2) At least four subs are preferred and a separate treated room, however that is another subject.

 

[Coach_Kaarlo]

Thanks for the welcome and for concurring with my listening impressions.

I do like the additional power that AHB2s provide in mono mode and intend to continue using it in mono mode. However, I am looking for all ways and means to improve the lower frequencies, if I can.

Two that I have found till now:
1. Keep the speaker cable short or move the amplifiers closer to the speakers (not my preferred option - so will try it last if nothing else works)
2. Use vertical passive bi-amping - will appreciate if someone can share their experiences

3. Any advice on other techniques?

My experience has been similar - trying to find that elusive setup which replicates previous testing, and trying to fact check what I am hearing against what could be causing the issue.

1. This was also my least preferred option, but after doing the numbers it was the option I ended up with. See below.

1. Assuming your speaker cables are adequate and currently normal domestic lengths, then shortening them is very, very unlikely to make an actual audible difference.

2. Bi-amping will restore the damping factor in the bass to what it was during stereo use, so if (and it's a big if) damping factor was the cause of your dissatisfaction, then that's obviously the solution. However, you'll be wasting most of the extra power you've bought, because most demand is in the bass, where you'll be back to one channel + one channel, like you had before. The other two channels will be basically idling, in the face of HF demand, which is modest.

3. Moving your speakers by trial and error - back and forth, in and out, even a few inches here and there - will produce definite audible changes, way more than anything else, and you might find a position that works better. This is your obvious first move.

Audibility is always up for debate IMHO - blind testing, hearing loss, room conditions, level matching etc etc.


Damping factor however follows some universal rules. @Neel I would humbly suggest putting your numbers into the spreadsheet (links below or find it on Benchmark website) and seeing the difference for yourself. Mono halves the available damping factor, and running longer cables actually further reduces the available damping factor - particularly if your cables have above average impedance. When you consider the entire system, amps, cables, cable distance, speaker impedance/ phase - it seems very easy based on the numbers for things to significantly compound and at some point become audible (and measurable although I am still working on that one myself).

https://cdn.shopify.com/s/files/1/0321/7609/files/DampingFactorCalculator.xlsx?v=1591278482

https://cdn.shopify.com/s/files/1/0...actor_isn_t_Much_of_a_Factor.pdf?v=1591622781

 

[waynel]

(1) The drivers create what is call back EMF. Essentially a voltage that opposes movement. This voltage is expressed on the connections to the driver and back the crossover where a small part of it, including distortion, will be transferred to the upper bass driver. This is a real effect whether if makes sense to you or not; think Maxwell's equations. The size of the effect and its importance are certainly open for debate. The effect is worse for speakers with 1st or 2nd order crossovers.

Denon/Marantz describe the effect of EMF this way, although the tech. writer has a bit of an odd description, perhaps translated from Japanese.

"This connection enables back EMF (power returned without being output) from the woofer to flow into the tweeter without affecting the sound quality, producing a higher sound quality."

(2) At least four subs are preferred and a separate treated room, however that is another subject.

I know what back EMF is , I’m an electrical engineer. I don’t believe that back EMF harmonics are significant compared to the mechanical harmonic distortion of the drivers . That’s why I don’t believe that bi amping helps with driver distortion. You are welcome to prove me wrong.

 

[restorer-john]

That’s why I don’t believe that bi amping helps with driver distortion. You are welcome to prove me wrong.

@amirm could actually do this a bi-wirable speaker when doing a Klippel run. Instead of using just one channel of the power amp for the speaker under test, he could use both channels driven with a splitter. On channel drives the LF and the other drives the HF section.

It would be interesting to then compare the distortion plots with a single "normal" connection. I've never been able to demonstrate a difference, but if there is, the Klippel rig would find it.

 

[waynel]

@amirm could actually do this a bi-wirable speaker when doing a Klippel run. Instead of using just one channel of the power amp for the speaker under test, he could use both channels driven with a splitter. On channel drives the LF and the other drives the HF section.

It would be interesting to then compare the distortion plots with a single "normal" connection. I've never been able to demonstrate a difference, but if there is, the Klippel rig would find it.

That would be interesting but I don’t see why there would be a measurable difference. I’m predicting a null result.

 

[restorer-john]

That would be interesting but I don’t see why there would be a measurable difference. I’m predicting a null result.

It would be nice to put to bed the "bi-wiring is better" argument for good.

Useful for people who want to experiment with different "voiced" amplifiers for LF and HF. Or using the amplifiers to lift/tame LF or HF by having slightly different gains. I've never found a good use for bi-wiring apart from easily being able to test each driver and x/over combo individually without having to unscrew the drivers and go inside.

 

[Coach_Kaarlo]

I know what back EMF is , I’m an electrical engineer. I don’t believe that back EMF harmonics are significant compared to the mechanical harmonic distortion of the drivers . That’s why I don’t believe that bi amping helps with driver distortion. You are welcome to prove me wrong.

@amirm could actually do this a bi-wirable speaker when doing a Klippel run. Instead of using just one channel of the power amp for the speaker under test, he could use both channels driven with a splitter. On channel drives the LF and the other drives the HF section.

It would be interesting to then compare the distortion plots with a single "normal" connection. I've never been able to demonstrate a difference, but if there is, the Klippel rig would find it.

That would be interesting but I don’t see why there would be a measurable difference. I’m predicting a null result.

It would be nice to put to bed the "bi-wiring is better" argument for good.

Useful for people who want to experiment with different "voiced" amplifiers for LF and HF. Or using the amplifiers to lift/tame LF or HF by having slightly different gains. I've never found a good use for bi-wiring apart from easily being able to test each driver and x/over combo individually without having to unscrew the drivers and go inside.

So is it BI-WIRING or BI-AMPING we are discussing? First references were to bi-amping, vertically. Buy-wiring has been explored a little, occasionally......seems the jury ruled on that one......thank you ASR!

 

[restorer-john]

So is it BI-WIRING or BI-AMPING we are arguing about (discussing)?

No arguments as far as I am concerned.

Bi-wiring allows either two runs of wire from one amp (rather pointless if you ask me) or it allows bi-amping, where two (or more) amplifiers are implemented for each part of the X/over.

I must admit, I like the extra set of terminals and shorting bars, but after experimentation finding no audible benefits whatsoever, they are not used. Just an excuse for audiophiles to play with and buy more gear/cable.

 

[mafelba]

I've been reading a lot of posts here at ASR and quite often this debate comes up: coloration vs transparency. I am still not persuaded either way and I will tell why. Regarding transparency: transparency would be king IF the source was a decent VERSION of sound as our ears hear it.

The capture and playback of sound may need a new paradigm. We capture sound by placing a microphone near live sound and use pressure waves to move a stationary diaphragm which moves a magnetic coil to create electric signals. Then we take those electric signals and run them through magnetic coils which move a diaphragm back and forth. Does this way of apprehending/playing back sound seem a bit limiting, intuitively, or maybe even woefully inadequate to fulfill its goal of representing live sound that sounds natural to us? I'm not sure that this 150 year-old technology is capable of producing the presence and naturalness that we hear when someone is playing an acoustic guitar 3 feet away from us or the sound of a conga slap on a real conga drum. We either need more microphones/speakers or perhaps moving microphones/speakers (transparency) or we need some coloration along the lines of DSPs that will artificially supply another dimension of sorts. Our current state of recording/playback is missing something. From within our current process for recording and playing back sound springs the debate about transparency and coloration.

 

[RichB]

No arguments as far as I am concerned.

Bi-wiring allows either two runs of wire from one amp (rather pointless if you ask me) or it allows bi-amping, where two (or more) amplifiers are implemented for each part of the X/over.

I must admit, I like the extra set of terminals and shorting bars, but after experimentation finding no audible benefits whatsoever, they are not used. Just an excuse for audiophiles to play with and buy more gear/cable.

The poster asked about bi-amping (two AHB2s channels) for the Salon2s. I did this exact thing. So the best answer is try is SBT mono (one speaker) and draw your own conclusion.

- Rich

 

[DonH56]

IIRC (have not read through all of this) the back-EMF argument depends upon crossover+cables+amp output impedance being such that intermodulation happens. Superconducting wires and ideal voltage source (0-ohm) outputs would not exhibit any change; real cables and amps will but "it depends" if it is audible. Assuming the shorting strap on the speaker is the lowest-impedance path, and not the cables back to the amp, then there will be intermodulation among drivers through the crossover elements. I have always thought that, since most cabinets do not internally isolate the drivers, this effect would be swamped by the acoustical interaction (e.g. woofer's air movement in the cabinet modulating the midrange and tweeter cones), but I do not know.

As @RichB said bi-amping does not provide more power, or not much, particularly if it is the "passive" scheme of most AVRs so the same signal is passed to both amplifiers. The load is different for the two amp outputs, but the output voltage is the same, so no voltage headroom and no power increase. (There wil be a little due to differences in current demands but that is usually very slight.) Bi-amping with two 100 W amplifiers still means no driver can ever draw more than 100 W -- it is not the same as using a 200 W amplifier. If you do active bi-amping, splitting the signal before the amplifiers, then you do gain some headroom since the lows and highs are split so a single amp is not handling both.

FWIWFM - Don

 

[waynel]

IIRC (have not read through all of this) the back-EMF argument depends upon crossover+cables+amp output impedance being such that intermodulation happens. Superconducting wires and ideal voltage source (0-ohm) outputs would not exhibit any change; real cables and amps will but "it depends" if it is audible. Assuming the shorting strap on the speaker is the lowest-impedance path, and not the cables back to the amp, then there will be intermodulation among drivers through the crossover elements. I have always thought that, since most cabinets do not internally isolate the drivers, this effect would be swamped by the acoustical interaction (e.g. woofer's air movement in the cabinet modulating the midrange and tweeter cones), but I do not know.

As @RichB said bi-amping does not provide more power, or not much, particularly if it is the "passive" scheme of most AVRs so the same signal is passed to both amplifiers. The load is different for the two amp outputs, but the output voltage is the same, so no voltage headroom and no power increase. (There wil be a little due to differences in current demands but that is usually very slight.) Bi-amping with two 100 W amplifiers still means no driver can ever draw more than 100 W -- it is not the same as using a 200 W amplifier. If you do active bi-amping, splitting the signal before the amplifiers, then you do gain some headroom since the lows and highs are split so a single amp is not handling both.

FWIWFM - Don

Here is a summary from my perspective:

Bi-wiring : With competent amplifier design will make no difference
Passive Bi-amping: With competent amplifier design will make very little difference (there are some current limited corner cases where this will give a bit more headroom)
Active bi-amping : a great idea (but need to bypass the internal crossover and use a lone level or preferable digital crossover)
Bridging AHB2: a great idea if you want more headroom with no sonic degradation (damping factor is still plenty high)

With a pair of AHB2s and a pair of Revel Salon 2s bridging will give a measurable improvement in headroom with no audible degradation and is preferable to bi-amping (unless you are removing the speaker level crossovers). But bi-amping should do no harm so feel free (it's your money, I'd rather spend mine on subs).

Wayne

 

[DonH56]

Here is a summary from my perspective:

Bi-wiring : With competent amplifier design will make no difference
Passive Bi-amping: With competent amplifier design will make very little difference (there are some current limited corner cases where this will give a bit more headroom)
Active bi-amping : a great idea (but need to bypass the internal crossover and use a lone level or preferable digital crossover)
Bridging AHB2: a great idea if you want more headroom with no sonic degradation (damping factor is still plenty high)

With a pair of AHB2s and a pair of Revel Salon 2s bridging will give a measurable improvement in headroom with no audible degradation and is preferable to bi-amping (unless you are removing the speaker level crossovers). But bi-amping should do no harm so feel free (it's your money, I'd rather spend mine on subs).

Wayne

I'd say on bi-wiring "Competent amplifier design and suitable speaker cables..."

I'm jealous of your pair of AHB2's. Someday I may upgrade my cheapie amps but the way life and work is going lately I'm not using them enough to matter.

 

[RayDunzl]

IIRC (have not read through all of this) the back-EMF argument depends upon crossover+cables+amp output impedance being such that intermodulation happens. Superconducting wires and ideal voltage source (0-ohm) outputs would not exhibit any change; real cables and amps will but "it depends" if it is audible.

Back EMF:

Recently, I planned to measure my amp output at low levels (around 5W).

With the amplifier off, the speaker was seen to act as a microphone. It was picking up the sound from the TV. There was also 60Hz and harmoonics.

With the amplifier on (no signal), the speaker's voltage ceased to be seen at the output terminals of the amplifier. The 60hz and harmonics were reduced.


https://www.audiosciencereview.com/forum/index.php?threads/krell-fpb-350-mcx.9870/#post-266190

 

[DonH56]

The model for a mic and a speaker is basically the same, just different parameter values. Remember all those "walkie-talkies" that used a little speaker as a mic?

When the amp is off, its output impedance is usually undefined and much higher than when it is on. How high depends on the topology.

At least you know how you can surreptitiously monitor sounds in the room when the amp's off...

 

[RichB]

IIRC (have not read through all of this) the back-EMF argument depends upon crossover+cables+amp output impedance being such that intermodulation happens. Superconducting wires and ideal voltage source (0-ohm) outputs would not exhibit any change; real cables and amps will but "it depends" if it is audible. Assuming the shorting strap on the speaker is the lowest-impedance path, and not the cables back to the amp, then there will be intermodulation among drivers through the crossover elements. I have always thought that, since most cabinets do not internally isolate the drivers, this effect would be swamped by the acoustical interaction (e.g. woofer's air movement in the cabinet modulating the midrange and tweeter cones), but I do not know.

As @RichB said bi-amping does not provide more power, or not much, particularly if it is the "passive" scheme of most AVRs so the same signal is passed to both amplifiers. The load is different for the two amp outputs, but the output voltage is the same, so no voltage headroom and no power increase. (There wil be a little due to differences in current demands but that is usually very slight.) Bi-amping with two 100 W amplifiers still means no driver can ever draw more than 100 W -- it is not the same as using a 200 W amplifier. If you do active bi-amping, splitting the signal before the amplifiers, then you do gain some headroom since the lows and highs are split so a single amp is not handling both.

FWIWFM - Don

I got a about 1 dB of additional headroom bi-amping, at 4 ohms roughly 60 watts. Not a lot given the power levels involved.

Revel makes a point to separate the crossovers on separate boards to reduce or eliminate electromagnetic interference.

The use of separate filter boards for each of the crossover's four frequency ranges is said to prevent distortion-causing magnetic interference.

If that is a problem, could not electronically connected crossovers have some interference as well?

- Rich

 

[waynel]

I'd say on bi-wiring "Competent amplifier design and suitable speaker cables..."

I'm jealous of your pair of AHB2's. Someday I may upgrade my cheapie amps but the way life and work is going lately I'm not using them enough to matter.

Honestly one AHB2 is enough for the volumes at which I listen. But I figured why not two?

 

[RichB]

Honestly one AHB2 is enough for the volumes at which I listen. But I figured why not two?

I like the way you think. Why not 5?

- Rich

 

[JimB]

I'd say on bi-wiring "Competent amplifier design and suitable speaker cables..."

I'm jealous of your pair of AHB2's. Someday I may upgrade my cheapie amps but the way life and work is going lately I'm not using them enough to matter.

! With so little time to listen, that means you want those few precious minutes to be the highest quality experience possible, no? AND, if you'll buy them 'someday', why not now and enjoy them longer? It's the same amount of money spent. Just trying to help.

By the way, I have a pair of AHB2s with active crossovers driving my tweeters and mids. My woofers have mono Hypex NC400s. Very nice.