Bi-Amping for Frequency Response Tailoring

[Ron Resnick]

We typically think of bi-amping to power loudspeaker drivers directly and/or to power one driver of the loudspeaker with one type of amplifier and another driver of the loudspeaker with another type of amplifier (such as solid-state on the woofer and tube on the midrange/tweeter*).

Bi-amping also can be used conscientiously to change the relative output of one driver versus another driver. This gives the user great flexibility and control over the overall tonal balance of the loudspeaker.

If you feel your upper bass to lower midrange is a little thin and lacking in weight or impact, configure your system so the higher gain structure amplifier is on the woofer, and just raise to your subjective frequency response preference the attenuator that is in-line with the woofer amplifier.

*There is a school of thought that this is a terrible idea because the difference in amplifier topology will be heard as incoherency between the loudspeaker drivers, or as phase or timing anomalies. While I respect this view, I personally have never heard this incoherency or any anomaly.

 

[Another Johnson]

My minimal experience with this idea suggests that success relies on serendipity.

 

[Audiohertz2]

We typically think of bi-amping to power loudspeaker drivers directly and/or to power one driver of the loudspeaker with one type of amplifier and another driver of the loudspeaker with another type of amplifier (such as solid-state on the woofer and tube on the midrange/tweeter*).

Bi-amping also can be used conscientiously to change the relative output of one driver versus another driver. This gives the user great flexibility and control over the overall tonal balance of the loudspeaker.

If you feel your upper bass to lower midrange is a little thin and lacking in weight or impact, configure your system so the higher gain structure amplifier is on the woofer, and just raise to your subjective frequency response preference the attenuator that is in-line with the woofer amplifier.

*There is a school of thought that this is a terrible idea because the difference in amplifier topology will be heard as incoherency between the loudspeaker drivers, or as phase or timing anomalies. While I respect this view, I personally have never heard this incoherency or any anomaly.

Altering FR of a speaker as you suggest will lead to higher coloration , subjectively good on some , subjectively bad , chesty and or wooly on full recordings, good on recordings sounding thin normally , not to mention a oneness in making most recordings sound similar ....

 

[Iving]

Hi Ron,
You refer to Horizontal bi-amping.
As someone who has futzed about quite a bit with bi-amping, I have two remarks which I hope you don't regard as too off-topic:
1. If you use two different amps in your scenario (Horizontal), one will always be better than the other - and you will notice the overall SQ detriment vs. using two instances of the better amp. This will be especially true the more you are familiar with the amps. In fact, a Subjective prejudice is likely to be in play.
2. I vertically bi-amp my Snell Type A III (as recommended by Snell when they were manufactured). The benefit is such - to my ears - that I can barely imagine not vertically bi-amping - even if I were to spend big bucks replacing the Snells. I'd be looking for two sets of binding posts as a purchasing factor.
Not to dissuade anyone, of course, from experimenting as you suggest - for "frequency response tailoring".

 

[Ron Resnick]

Altering FR of a speaker as you suggest will lead to higher coloration

This assumes that the native frequency response of the speaker is in some (objective?) sense correct or "accurate" to start with.

 

[Ampexed]

True active bi-amping generally assumes no passive crossovers in the speakers, and that the speaker drivers are directly coupled to the outputs of those amplifiers. In this case the crossover duties are done at line level before the power amplifier. Importantly, it also assumes that the voicing of the system which would normally be done by the manufacturer with the passive crossover in the speakers is now being done at line level as part of the active crossover. Crossover and voicing duties in systems such as this can also be done purely passive at line level rather than speaker level, the benefit being no noise, no distortion, and no signal degredation from active electronic stages.

This type of arrangement is superior to passive horizontal bi-amping where the speaker's passive crossovers are left in-circuit. This type of bi-amping has benefits, but not of the magnitude of the type of active bi-amping described above. The upside is that the voicing done by the manufacturer remains intact, for better or worse.

 

[DonH50]

You do not have to use different types of amplifiers; in the pro sound reinforcement world (part of my youth) it is common to use a bank of SS amplifiers of different power ratings to reduce overall system size, weight, and power (heat). For example, you might put a 1 kW amp on the bass, 300 W amp on the midrange, and 100 W on the treble drivers. That was common when I was working with such systems. OTOH, for my home system, I chose to run a tube mid/treble amp and hybrid (tube front end, MOSFET output stages) bass amp on my Maggies.

SS vs. tube amps might require phase compensation across the crossover region but for audio circuits the delay through the amps is usually low enough to be neglected. A big counter example is any amp that includes DSP or an internal filter circuit used with a more basic amplifier that just amplifies the signal -- there could be significant delay (phase) differences that should be compensated. And of course there is always the fun experience of hooking up a couple of amps after the crossover and sitting back to enjoy the results, only to realize one amp inverts the signal and the other does not... That can be embarrassing (don't ask how I know this).

With an active crossover all you need do is adjust the level controls of the individual filter sections. For myself, no real problems with it, but it's a pretty broad brush and provides a shelving response whereas most of us may want more precise adjustments of specific frequencies and/or a rising/falling curve (slope) rather than a flat shelf above and below the crossover. IME, rather limited, the subwoofer amp is the one I have seen turned up the most, since it covers a fairly narrow band compared to the mains and in a region we are less sensitive to frequency response irregularities.

FWIWFM - Don

 

[dcc]

Using different power amps in passive bi-amping requires either power amps with the same gain or that the output gains on the preamp are separately adjustable which is not a feature that this commonly available on most preamps.

I have been bi-amping for almost 3 decades (active and passive since the last 15 years) but now that I have relatively high efficient loudspeakers (95 dB), I am really reconsidering going back by adopting less powerful but likely more musical power amps.

 

[mtemur]

Bi-amping can sound superior to using a single amplifier—if done correctly.

With few exceptions, like Kharma, most speaker crossovers are designed to connect drivers in parallel. When you bi-amp a speaker, you effectively double the impedance for each amplifier. Considering most speakers are rated at 4 ohms, this doesn’t seem bad but for 8 ohms doubling impedance can place significant strain on some solid-state amplifiers. More importantly doubling impedance halves the power output of SS amps. Additionally speaker crossovers are typically designed to account for the overall impedance curve, not the individual drivers. Impedance change can be very challenging for many amplifiers.

Another issue is power distribution. Power requirements are not equal between bass and mid-high drivers. When a single amplifier drives all the drivers, the bass driver can draw as much power as needed—up to 90% during certain passages. For instance, with a 30-watt amplifier, the bass driver might use 20–25 watts when required. However, with bi-amping, using two 30-watt amplifiers doesn’t double the output for the bass; instead, the bass is limited to 30 watts, which is far from double.

Using different amplifiers introduces additional challenges, such as inconsistent tonal characteristics and, more critically, phase irregularities—especially when mixing solid-state and tube amplifiers. Using amplifiers from the same brand but with different power outputs may be the most logical choice. For example, Mark Levinson designed the input sensitivity of its amplifiers to match their power output. This allows a 100-watt amplifier to be paired with a 300-watt amplifier, so when the preamp sends 1V, both amplifiers deliver the same power output—e.g., 80 watts—ensuring consistent performance.

 

[Ron Resnick]

Using different power amps in passive bi-amping requires either power amps with the same gain or that the output gains on the preamp are separately adjustable which is not a feature that this commonly available on most preamps.

Hello,

Actually, there is a third way: in-line attenuators on the amplifiers with the higher gain structure.

 

[JackD201]

Hi Ron

If we are talking high end gear, I really don't recommend it. The main issue for me is the input sensitivities of domestic power amplifiers. As you noted some amplifiers do have attenuators that can damp the input sensitivity, I personally have not come accross any with really fine adjustability like professional amplifiers do. Without identical input sensitivities it would be like having half a broken clock, in that it will likely tell the time correctly once and not even twice in a day. MAJOR coherence issues as amplitude varies.

That said, if you happen to be one of those super loyal customers, some companies will fit you with a fine input attenuator. If they do accept your request, you will typically have to wait until your unit can be slotted into the production line. So typically these are only done for the very low volume halo products whose case work is usually made to order.

I think all tube heads have fantasized this. I sure have. Who wouldn't want 2a3 highs, 45 or 46 mids and kt150 bass? Dreaming isn't a crime.

If I were to do a multi-amped set up it would be at least a 4 way and I most certainly would do the crossover work at line level. This is definitely repeatable work. I used to use pro mosfet amps for midrange drivers because they were warmer.

The only really practical and predictable way is in a sub-sat system where one amplifier will be doing the heavy lifting from 20+khz to at least 100 to 70Hz. As another member posted, beyond that serendipity will be playing the major part.

 

[Alrainbow]

Has anyone tried bi amping same amp outputs but using different speaker cables
a heavy gauge on woofers and smaller gauge on mid tweets.
this I’ve read has effects on tonal balances

 

[JackD201]

Has anyone tried bi amping same amp outputs but using different speaker cables
a heavy gauge on woofers and smaller gauge on mid tweets.
this I’ve read has effects on tonal balances

It does. Differences in gauge, material, dielectrics, connectors, they all can affect tonal balance. Even length which is logic defying in many ways, makes a slight difference in volume.

 

[andromedaaudio]

Has anyone tried bi amping same amp outputs but using different speaker cables
a heavy gauge on woofers and smaller gauge on mid tweets.
this I’ve read has effects on tonal balances

BS afaik
I ve tried many different size wires on woofers mids tw .and did lots of measuring .
Off course there is a electrical minimum diameter you need to respect .
But going extra large and change the FR is BS imo.

 

[andromedaaudio]

Regarding Biamping if the speakers allow it why not give it a try .
I personally rather design a perfect flat measuring LS and high impedance X over and use a single stereo or mono amp.
Less variables , less mistakes usually

 

[Hear Here]

I would suggest there is little advantage of bi-amping if the passive XO remains. Get the XO done electronically before amplification, and here's another potential advantage - if you are an advocate of "room correction DSP" - cross over first, then send the 2 digitals signal to 2 amps that include a DAC. Only in the bass amp should include a DSP, so that the top end reaches its drivers unmolested by the DSP filter.

I wonder if others agree with this arrangement? I have had 4 different "room correction DSPs" (surely a very poor description as they never correct the room) and all have caused a small loss of top-end sparkle with the music. I can only put this down to the unavoidable signal processing that the top end endures (even if not adjusted) if the DSP is built into a single full-range amplifier.

 

[sbo6]

We typically think of bi-amping to power loudspeaker drivers directly and/or to power one driver of the loudspeaker with one type of amplifier and another driver of the loudspeaker with another type of amplifier (such as solid-state on the woofer and tube on the midrange/tweeter*).

Bi-amping also can be used conscientiously to change the relative output of one driver versus another driver. This gives the user great flexibility and control over the overall tonal balance of the loudspeaker.

If you feel your upper bass to lower midrange is a little thin and lacking in weight or impact, configure your system so the higher gain structure amplifier is on the woofer, and just raise to your subjective frequency response preference the attenuator that is in-line with the woofer amplifier.

*There is a school of thought that this is a terrible idea because the difference in amplifier topology will be heard as incoherency between the loudspeaker drivers, or as phase or timing anomalies. While I respect this view, I personally have never heard this incoherency or any anomaly.

*I've rarely heard amplifiers of different gain, type, topology employed on one loudspeaker sound coherent. It's commonly a flavored mess IME.

 

[Another Johnson]

Hello,

Actually, there is a third way: in-line attenuators on the amplifiers with the higher gain structure.

If a listener can’t hear the affect of attenuators in cables or interconnects beyond the volume change they introduce, then either the system has other serious weak spots OR the listener’s ears could be better.

Seriously, the idea of adding attenuators to fix this amp matching issue is out of the same playbook as the original suggestion. Anything good to come of either is serendipitous.

My mileage varies.

 

[Ampexed]

I would suggest there is little advantage of bi-amping if the passive XO remains. Get the XO done electronically before amplification, and here's another potential advantage - if you are an advocate of "room correction DSP" - cross over first, then send the 2 digitals signal to 2 amps that include a DAC. Only in the bass amp should include a DSP, so that the top end reaches its drivers unmolested by the DSP filter.

I wonder if others agree with this arrangement? I have had 4 different "room correction DSPs" (surely a very poor description as they never correct the room) and all have caused a small loss of top-end sparkle with the music. I can only put this down to the unavoidable signal processing that the top end endures (even if not adjusted) if the DSP is built into a single full-range amplifier.

The only potential problem with DSP is the unavoidable latency through the DSP box. If the speakers were time aligned before using DSP, it will be impossible to regain that with the approximately 11mS delay for the processing verses the unprocessed drivers.

I'm a firm advocate for active crossovers, and go a step farther with the crossover being completely passive at line level using small-value precision components. The voicing filters which follow the basic crossover are also completely passive using small-value components.

 

[Alrainbow]

BS afaik
I ve tried many different size wires on woofers mids tw .and did lots of measuring .
Off course there is a electrical minimum diameter you need to respect .
But going extra large and change the FR is BS imo.

I respect all views but some things cannot be measured and know the effects it may have while listening.