Bi-Amping for Frequency Response Tailoring

[Ampexed]

I respect all views but some things cannot be measured and have conclusions
observation is key on many aspects of audio.

But drilling down through enough with measurements will eventually reveal something which is responsible for the subjective observations. That's how designers, like myself, are able to create components with a desired 'voice'. Otherwise, the design process would be uncontrolled chaos with no ability to repeat, much less control, the outcome.

 

[Ron Resnick]

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.

Hi Jack!

So nice to hear from you!

Thank you for weighing in on this!

I respect and appreciate these warnings and concerns. But I am not hearing any problems, and I am loving the result!

The different gain structures of different amplifiers (different input sensitivity, different internal gain, different input/output (balanced versus single-ended) topology) doesn't matter, because however it all comes out in the wash, I can attenuate whichever is the higher gain structure amplifier with an fairly purist Electronic Visionary Systems discrete resistor attenuator.

 

[Ron Resnick]

I would suggest there is little advantage of bi-amping if the passive XO remains.

If the goal is frequency response tailoring one advantage is that no active crossover is necessary. (I have no problem with active crossovers. The CS Port ACN400 is a wonderful device.)

 

[Ampexed]

If the goal is frequency response tailoring one advantage is that no active crossover is necessary. (I have no problem with active crossovers. The CS Port ACN400 is a wonderful device.)

On the contrary, with active crossovers, there is far more potential for tonal shaping because at line level, you can voice any way you wish, to any extreme you wish. With the passive crossovers built into speakers, the limit is either the excess sensitivity of (usually) the high frequency driver, or how much overall sensitivity you wish to throw away. Either way, that is limited to only a few dB at most.

While changing power amps does change tonality, especially swapping a solid state amp for something like an SET, doing so pales in flexibility compared to going the fully active route, where using a low power SET to power the tweeters in a relatively insensitive speaker is feasible.

 

[Ron Resnick]

On the contrary, with active crossovers, there is far more potential for tonal shaping because at line level, you can voice any way you wish, to any extreme you wish.

Nothing contrary between our posts. You're saying active is more flexible. I'm saying active is not necessary. Both of these statements are true.

 

[Ampexed]

Nothing contrary between our posts. You're saying active is more flexible. I'm saying active is not necessary. Both of these statements are true.

Well, not necessary maybe to you. I'm not about to say that active is the only way to go, because that would be insane. However it can remove a lot of barriers to achieving the best sound quality. In the end, isn't that important on a forum called "What's Best"? I'm merely putting out there what is generally acknowledged as the best way possible. Some very high end speakers do just this.

It isn't generally more popular because it involves more effort and expense. But since when has the very high end been allergic to expense?

 

[andromedaaudio]

If expenses

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

Audiophile reasoning not based on anything .
It doesnt pass the science test thats for sure.
At least i tried and actually measured and listened
I stopped reading audio magz .long long time ago .

 

[Jazzman53]

I've been tri-amping my 6-channel stereo setup using a DSP crossover feeding three identical stereo amps for many years now. Two amps are vertically bi-amping the ESLs and the third amp driving a pair of RiPol subs.

The DSP/crossover (a DBX Driverack Venu 360 with mic) provides almost infinite tuning capability. In fact; it's spoiled me to the point where nothing else will do-- It's my dream system for life.

Aside from cost, there's really no downside for active bi-amping with a DSP crossover.

 

[knotscott]

My system features a hybrid bi-amping approach that includes both vertical and horizontal configurations, plus both passive and active crossovers.

There are two identical modified Dynaco/VTA tube monoblocks on the mids/tweeter with passive crossovers, and a solid state amp with a low pass active crossover to the woofers at about 80z. Overall volume is controlled by a tube preamp that acts as a master volume.

Prior to that configuration the Dyna/VTA monoblocks were driving all three drivers with passive crossovers. Based on personal observation, and comments from others, including Ken Stevens, bass output from the woofers sounded a bit lean relative to the mid/tweeter output in my current room. Placement changes, nor the addition of subwoofers, did not satisfactorily compensate in the lower vocal range that seemed to be lacking weight.

The addition of the SS amp and active crossovers provided independent control of the woofer output relative to the mid/tweeters, and offered superior bass impact and control...all of which were anticipated as the desired result. The result that was not expected was the improvement in overall clarity from the tube amps driving an easy 8 ohm load vs 4 ohm.

The results of any bi-amping experimentation will be unique to the given setup and situation. In this case, it was easy and affordable to try, could be done using the existing woofers, and the results exceeded expectations.

 

[Robh3606]

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.

Yes but in practice once you are dialed in to your "house curve" it's more set and forget. You typically have more than enough gain adjustment built into an active crossover where different amp gains are simply not needed. I use 4 essentially identical amps in my 4 way active set-up.

It's also fun to use a base woofer cabinet and use different tops. This gives you the ability to switch from HEIL to horn to all direct radiator with minor adjustments to the bandpass as the upper cabinets arte using passive networks on the upper drivers.

Rob

 

[JackD201]

Well, not necessary maybe to you. I'm not about to say that active is the only way to go, because that would be insane. However it can remove a lot of barriers to achieving the best sound quality. In the end, isn't that important on a forum called "What's Best"? I'm merely putting out there what is generally acknowledged as the best way possible. Some very high end speakers do just this.

It isn't generally more popular because it involves more effort and expense. But since when has the very high end been allergic to expense?

Fully active is something I would not recommend to somebody without the inclination to learn how to use this new tool set. Point, gain and Q are simple enough on paper but they do require a deft and thoughtful touch.

I also wouldn't recommend it to the paranoid knob twiddler set to whom nothing is ever "set and forget". I suppose there is a spectrum to this so perhaps the ability to go at least two whole listening sessions without tweaking anything would be my most arbitrary exception LOL

Other than those people.....Go for it!

 

[Holmz]

Well, not necessary maybe to you. I'm not about to say that active is the only way to go, because that would be insane. However it can remove a lot of barriers to achieving the best sound quality. In the end, isn't that important on a forum called "What's Best"? I'm merely putting out there what is generally acknowledged as the best way possible. Some very high end speakers do just this.

It isn't generally more popular because it involves more effort and expense. But since when has the very high end been allergic to expense?

If you could expand on ^that^ it would be appreciated.

I just picked up a couple of amps that can be run bridged, or vertically biamped.
And the speakers have two sets of binding posts

I am leaning towards bridged because the voltage excursion will be dominated with the bass notes, unless I run some DSP or active analogue filtering beforehand, then all I get is less current on the higher frequency band side.

If I was to do some active XO, then it makes more sense run the high and low bands through the different pairs of amps.
However it seems like in that case, I should remove the passive XO in the speaker.
(My thinking is that that would give the amp a much firmer grip on the driver as the damping factor is not diminished with the passive XO in place.)

The speakers are 1st order XOs, so that also factors in heavily I believe.

 

[Robh3606]

The speakers are 1st order XOs, so that also factors in heavily I believe.

You need the schematic to see what the crossover is doing and run it in a simulator to see the voltage drives to the drivers. Just because it's a first order crossover don't assume it's just a cap and coil. There are likely some form of impedance correction like a zobel on each driver.

Rob

 

[Holmz]

You need the schematic to see what the crossover is doing and run it in a simulator to see the voltage drives to the drivers. Just because it's a first order crossover don't assume it's just a cap and coil. There are likely some form of impedance correction like a zobel on each driver.

Rob

How would ^that^ change the approach?

I was under the impression that I might just select the slopes, frequencies, and polarisation, and then have a digital stage for each band.
Those could be tested individually for each driver using pink noise, and then with all the driving together.

How does knowing the XO schematic help @Robh3606 ?

 

[Robh3606]

How would ^that^ change the approach?

I was under the impression that I might just select the slopes, frequencies, and polarisation, and then have a digital stage for each band.
Those could be tested individually for each driver using pink noise, and then with all the driving together.

How does knowing the XO schematic help @Robh3606 ?

Hello

You could go that way. How are you measuring the responses? You going to be using an RTA with pink noise? It can work.

Advantages of having the schematic in a simulator are:

You can actually see what the crossover slopes and voltage drives are before hand as opposed to looking at an RTA. Easier to see in the sim better resolution.

You can see any impedance correction or notch filters used to tame the raw driver response. If there is a hidden notch filter you are going to get an unexpected result that may set you chasing ghosts. If you have the raw driver response measurements it gives you a heads up WRT the likely hood of one being used.

You can remove components and see what changes occur to the voltage drive. So no surprises if you take out a pole and need changes elsewhere.

Here is an example of a voltage drive for a compression driver and waveguide as an example. The two curves are differences between using actual driver measurements vs dummy 8 ohm load.

Rob

 

[Holmz]

Hello

You could go that way. How are you measuring the responses? You going to be using an RTA with pink noise? It can work.

I figured gated measurements with a mic.

Advantages of having the schematic in a simulator are:

You can actually see what the crossover slopes and voltage drives are before hand as opposed to looking at an RTA. Easier to see in the sim better resolution.

You can see any impedance correction or notch filters used to tame the raw driver response. If there is a hidden notch filter you are going to get an unexpected result that may set you chasing ghosts. If you have the raw driver response measurements it gives you a heads up WRT the likely hood of one being used.

You can remove components and see what changes occur to the voltage drive. So no surprises if you take out a pole and need changes elsewhere.

I am not much of a EE though.

Here is an example of a voltage drive for a compression driver and waveguide as an example. The two curves are differences between using actual driver measurements vs dummy 8 ohm load.

Rob

Those 2 curve look largely the same to me…

 

[Robh3606]

I figured gated measurements with a mic.

I am not much of a EE though.

Those 2 curve look largely the same to me…

Hello

Much better than an RTA. Just remember you loose LF resolution when you gate so when doing the LF measurements keep that in mind. You want repeatability. Without that the measurements are useless. You can also use your measurements system to get raw driver measurements and as you remove or add components.

You don't have to be an EE just do some reading on crossover basics to get started and go from there. An example:

https://www.audioholics.com/loudspeaker-design/crossover There is quite a bit available.

The two curves are just a comparison between a measured driver response vs a dummy 8 ohm load. They show that a dummy load simulation can be a good starting point in determining the actual voltage drive the driver "sees".

If your measurement system allows for voltage vs frequency you can measure your crossover with the appropriate dummy load just use a dB scale. This will give you the voltage drive and it's a good starting point for working out the filters in your DSP.

Rob