Passive Bi-Amping (Bi-Wiring) vs Single wiring

[BitPerfect_]

Hi,
Let’s suppose we have an amplifier with Speaker A and Speaker B outputs, rated for A+B operation at 8–16 ohms. We are using the Speaker A output to feed the LF section and the Speaker B output to feed the HF section of a pair of L/R speakers (8 ohms each), which constitutes Passive Bi-Amping.

• Using two different cables (e.g., 3 meters L/R of 2.5 mm² silver-plated for HF and 3 meters of 4 mm² OFC copper for LF), could this still bring measurable or audible improvements compared to standard single wiring using only the Speaker A output with the bridges mounted on the speakers?

• In Passive Bi-Amping, with the speaker bridges removed and the xover network fed separately for HF and LF, is the amplifier susceptible to impedance mismatch due to the speaker components (HF: 3 ohms, MF: 4.4 ohms, LF: 10.8 ohms) not having the same impedance? Or do we consider the nominal impedance, which is 8 ohms?

I am already aware that Bi-Wiring, in general, is purely marketing driven by cable companies, and Passive Bi-Amping is essentially the same as Bi-Wiring, as I discovered while watching the educational videos. However, I am still interested in understanding these aspects because I’ve come to this realization after years of using my speakers in Passive Bi-Amping A+B mode, I have purchased these different cables. Thanks,

 

[antcollinet]

Using two different cables (e.g., 3 meters L/R of 2.5 mm² silver-plated for HF and 3 meters of 4 mm² OFC copper for LF), could this still bring measurable or audible improvements compared to standard single wiring using only the Speaker A output with the bridges mounted on the speakers?

No, and in most cases here you are only bi-wiring. The amps typically drive both speakers outputs with a single amplifier. Which is why the impedance rating increases to 8ohm minimum when driving both. But even with bi-amping, if you are still using the internal speaker crossovers, there is no benefit to be had.

In Passive Bi-Amping, with the speaker bridges removed and the xover network fed separately for HF and LF, is the amplifier susceptible to impedance mismatch due to the speaker components (HF: 3 ohms, MF: 4.4 ohms, LF: 10.8 ohms) not having the same impedance? Or do we consider the nominal impedance, which is 8 ohms?

It doesn't matter. The amp outputs a voltage and the speaker responds to that voltage. As long as it can deliver enough current to drive the impedance at the frequency of concern there will be no issue.

 

[JeremyFife]

What @antcollinet said!

Additionally: don't fuss about with different cables, there's no benefit or point. Use thick enough copper and move on.

 

[SIY]

Using two different cables (e.g., 3 meters L/R of 2.5 mm² silver-plated for HF and 3 meters of 4 mm² OFC copper for LF), could this still bring measurable or audible improvements compared to standard single wiring using only the Speaker A output with the bridges mounted on the speakers?

Yes. The measurable difference will be the reduction in your checking account and the corresponding increase in that of the cable peddler who sold you on this notion.

 

[Keith_W]

About the only improvement bi-amping brings is that clipping or distortion in one channel (usually the low frequencies) will not affect the other channel.

 

[Randyman...]

About the only improvement bi-amping brings is that clipping or distortion in one channel (usually the low frequencies) will not affect the other channel.

But that version generally suggests no active bi-amp filtering is involved and all amp channels are identical - so all amp channels are seeing full-range (granted - driven through a passive Xover to likely increase impedance outside the passband to reduce current-limited based clipping / while voltage-limited based clipping can still occur at higher Z's)...

 

[SPL15]

About the only improvement bi-amping brings is that clipping or distortion in one channel (usually the low frequencies) will not affect the other channel.

There’s also an often undiscussed / unknown reduction in harmonic distortion due to reduction of high current flow on the channels used for the top end (assuming it’s a common 3 stage Lin topology class B amp using a BJT output, which is often stupidly called “Class AB”). It’s measurable, albeit debatable whether it’d actually be audible to most folks & even those w/ magical “golden ears” without listening to sine wave test tones.

On a classic 3 stage linear amplifier that uses BJT output devices, the voltage gain stage (trans impedance amp) is loaded by the base current draw of the output stage. The higher the current draw of the output stage, the higher its base current requirements are which loads the voltage gain stage in direct proportion. This current loading of the trans impedance amp causes increased odd order harmonic distortion in typical designs that don’t have a complementary trans impedance amp design, which causes non symmetrical positive & negative excursion voltage gain as current demand increases.

May sound like fabricated BS to most folks who proclaim to be knowledgeable about audio electronics design; however, it’s a well established distortion mechanism described in Douglas Self’s audio amplifier design reference books. Distortion mechanisms 3A & 4 are directly related to high output current induced distortion & is reduced in proportion to output current reduction. Having separate full range channels for the top end won’t give benefits regarding voltage excursion clipping; however, it will provide some degree of measurable reduction in harmonic distortion due to reduction of higher current output demands of lower frequencies.

 

[antcollinet]

There’s also an often undiscussed / unknown reduction in harmonic distortion due to reduction of high current flow on the channels used for the top end (assuming it’s a common 3 stage Lin topology class B amp using a BJT output, which is often stupidly called “Class AB”). It’s measurable, albeit debatable whether it’d actually be audible to most folks & even those w/ magical “golden ears” without listening to sine wave test tones.

On a classic 3 stage linear amplifier that uses BJT output devices, the voltage gain stage (trans impedance amp) is loaded by the base current draw of the output stage. The higher the current draw of the output stage, the higher its base current requirements are which loads the voltage gain stage in direct proportion. This current loading of the trans impedance amp causes increased odd order harmonic distortion in typical designs that don’t have a complementary trans impedance amp design, which causes non symmetrical positive & negative excursion voltage gain as current demand increases.

May sound like fabricated BS to most folks who proclaim to be knowledgeable about audio electronics design; however, it’s a well established distortion mechanism described in Douglas Self’s audio amplifier design reference books. Distortion mechanisms 3A & 4 are directly related to high output current induced distortion & is reduced in proportion to output current reduction. Having separate full range channels for the top end won’t give benefits regarding voltage excursion clipping; however, it will provide some degree of measurable reduction in harmonic distortion due to reduction of higher current output demands of lower frequencies.

That does sound though, like a very specific distortion mechanism for a very specific design implementation. It may not exist, or may exist at very differnet levels in different implementations. For example, I'd expect that distortion to be dramatically reduced in any design implementing an appropriate level of feedback.

it won't (of course) exist at all in any class D amplifier.

PS the difference between amplifier class B and class AB is not down to the specific type of output device chosen, but is about how those devices are biased.

 

[Chrispy]

Don't see how it's passive bi-amping in the A/B scenario with only two channels of amplification available. Seems more a waste of wire than anything.

 

[HaveMeterWillTravel]

There is another factor which generally seems to be missed, thou of limited applicability. In many speakers, the tweeter or midrange have higher efficiency/sensitivity than the woofers. Reducing their output is typically done by adding inline resistors (*). In addition to the often quoted reason of the reduced higher frequency spectral content in most music allowing the use of a smaller amplifier, bypassing the inline resistance can reduce that as well (assuming the impedance is still high enough for the amplifier).

However, recollections may differ on the wisdom of such mods.

(*) as an aside, this adds to the hilarity of one overly concerned with 'damping factor' at higher frequencies.

 

[Speedskater]

The Tweeter and resistor form a series circuit, voltage divider. If the Tweeter's impedance changes with frequency, it's input voltage without the resistor will be different at some frequencies.

 

[HaveMeterWillTravel]

The Tweeter and resistor form a series circuit, voltage divider. If the Tweeter's impedance changes with frequency, it's input voltage without the resistor will be different at some frequencies.

I omitted the need to adjust channel gain and possibly active filtering.
I myself wouldn't do it simply out of concern of being more likely to damage the tweeter.