Vertical Bi-Amping

[mep]

I agree w/ you Don. To me active Biamping should be done if you really want to get the benefit of using 2 stereo amp or 4 monoblocks in driving a pair of speakers. There should be an active electronic crossover network.

I think you are dead-wrong and aren't thinking this through clearly. First of all, we are not talking about using an AVR reciver. We are talking about using identical 220 watt stereo amps. Since you are using both channels of a stereo amplifier to drive one speaker, you are putting double the power into that speaker and now have isolated power amps for each speaker just like you would if you had a pair of monoblocks.

Since the speakers are set up for bi-wiring and they already have their own 14" subwoofer powered by an internal 1800 watt amp, you are essentially asking one channel of the stereo amp to drive the tweeters and the other channel of the stereo amp to drive the bass/mid woofers. Pretty simple load for each channel.

I think that by putting an electronic crossover in front of each amp would cause more problems than benefits in this case. I really don't want another crossover in front of the crossovers in the speakers causing wacky phase issues and adding the sound of the electronic crossover plus another pair of interconnects. The method I'm using is pure and simple and I only see positives and no negatives. I see a whole bunch of negatives if I decided to use an electronic crossover in front of these amps. There is no reason to make something more complicated than it needs to be and hope it will somehow sound better than the elegant solution being used.

 

[docvale]

Mep,

I'm not 100% convinced you are right... According to what you say, I guess your speakers have two pairs of binding posts each plus an input for the amp that powers the subs. Am I correct? If so, the subwoofer amp should be preceded by an active crossover, in order to let all the 1800W to work on the subs. Differently, the binding posts (to which you're connecting your amps) come before the passive crossover: accordingly, your amps work on all the frequencies till the posts, after which only the signal that is allowed by the internal passive crossover remains. Based on this, you're not truly doubling the power that you put into your speakers; instead, if your amps came after an active crossover, each channel would work only on the frequencies of the corresponding driver, allowing you to have more and more power.

This doesn't mean that the active crossover approach is necessary better. I agree with you that issues could raise and, intuitively, the role of the internal crossover would become superfluous. I'd say that I would prefer to use an active crossover between the pre and the power amps only for those speakers that are conceived for multiamping (e.g., B&W Nautilus and many professional designs).

 

[DonH50]

Hmmm... If you had a 200 W amp driving full-range, then use two, 200 W amps for the top and bottom, isn't the net power the same as if you had a single 200 W amp? You have twice the power available, but each amp is only covering half (or whatever) the frequency range, so I am not sure I see a significant benefit...

You do "unload" the "other" frequency band at the amps' outputs, but a full-range signal still has to go through the amp. The current draw may be lower, but voltage headroom (dynamic range) is still lost, along with higher distortion etc. For example, a big bass signal still taxes the amp's voltage headroom even if it is only driving the tweeter.

The best bi-amping systems, and the ones I have virtually always implemented, bypass the speaker's crossovers (if they were even their to begin with, not a given in the pro world) so you are replacing a passive network with an active network. This generally allows much finer control of the crossover (frequency, slope, and phase) than practical with a purely passive in-the-box approach. Whether that is better is, as always, a matter of some debate.

Finally, just to throw a curve into things, the last time I bi-amped my speakers I actually used a passive line-level crossover network between (inside, actually) my preamp and the power amps, and eliminated the passive outboard speaker crossover box. Perhaps that's about as simple as it gets for "active"...

IMO - Don

edit: I was typing whilst Valerio was posting, so my referent is mep's post one up.

 

[mep]

Mep,

I'm not 100% convinced you are right... According to what you say, I guess your speakers have two pairs of binding posts each plus an input for the amp that powers the subs. Am I correct?).

Why, yes they do. How else are you going to bi-amp a pair of speakers if they don't have separate inputs for the bass/midrange drivers and the tweeters?

If so, the subwoofer amp should be preceded by an active crossover, in order to let all the 1800W to work on the subs.).

What makes you think that the 1800 watt subwoofer amp is doing anything besides driving the subwoofer?? That's all it is doing.

Differently, the binding posts (to which you're connecting your amps) come before the passive crossover: accordingly, your amps work on all the frequencies till the posts, after which only the signal that is allowed by the internal passive crossover remains. Based on this, you're not truly doubling the power that you put into your speakers; instead, if your amps came after an active crossover, each channel would work only on the frequencies of the corresponding driver, allowing you to have more and more power.)

What I am doing (or was until the one amp crapped out) was having a single channel of a 220 watt stereo amp drive both the bass/midrange drivers and the tweeters. Now there is a dedicated single 220 watt channel feeding each one separately. You can't tell me that it doesn't translate into more total effective power being delivered to the speaker. It only makes sense that 2 channels of 220 watt power driving one speaker will have more power than 1 220 watt channel driving one speaker.

This doesn't mean that the active crossover approach is necessary better. I agree with you that issues could raise and, intuitively, the role of the internal crossover would become superfluous. I'd say that I would prefer to use an active crossover between the pre and the power amps only for those speakers that are conceived for multiamping (e.g., B&W Nautilus and many professional designs).

How are they conceived for multi-amping? Do the contain no passive crossovers and require an outboard crossover?

 

[microstrip]

(...) The best bi-amping systems, and the ones I have virtually always implemented, bypass the speaker's crossovers (if they were even their to begin with, not a given in the pro world) so you are replacing a passive network with an active network.

Dion,
My experience building active systems is very limited - a simple system using an active crossover designed by Ben Duncan and published in Hifi News and Record Review in 1981. But there is one aspect we can not forget - most of the time the exact transfer function of a passive crossover is very complex and can not be reproduced using the common active filters used in these active modules. What you get when you replace the passive crossover with an active system is not anymore the speaker that the original designer wanted you to listen - it is a new speaker with a different response.

One of the classical arguments against active designs was that the proper design of passive components could compensate some aspects such as the variance of coil resistance with current due the temperature transients, and the active systems do not allow it to do it. Some designers even prefer a mixed mode - active with passive driver "matching". Surely, not everyone thinks the same on these matters.

 

[mep]

Don/Micro-I agree with Micro's statements that once you change from a passive crossover to an electronic crossover, the speaker will not sound the same. Even if you knew the exact crossover frequencies and slopes, there would be a difference in sound. Def Tech got the crossovers right in the BP7000SC speakers. They are seemless and the driver integration is beyond fault in my book. I don't want to muck with that. It would never make sense to me to drive a passive crossover network with an electronic crossover.

And Don, while the effective power each driver sees is 220 watts, it just seems that each speaker cabinet having two 220 watt amps driving it will sound different than one 220 amp driving both the bass/midrange drivers and tweeters. You are putting double the power into each speaker cabinet. That has to make a difference me thinks.

 

[DonH50]

This is one of those "religious" arguments not really worth having, IMO, so I'll be brief:

microstrip: I agree in general, but it goes both ways. The actual crossover networks in the vast majority of speakers are pretty simple; it's the interaction with the driver that gets complicated. Using an active driver you can the speaker directly, and that has benefits as well. Including negating some of those effects. I agree the design can be tricky. As for it not sounding the same, isn't that sort of the point? Yes, yes, yes, the "new" sound can be better or worse...

mep: A badly designed active crossover is a sin, of course, but properly designed an active approach can make many systems sound better, at least IME/IMO. While it can be fun to tweak and play around, in general I would say it is not a design for the hobbyist (unless it's an EE with the proper tools and skill to do the job right, natch ). As for the difference, most of the time (I hesitate to use the word "majority" but suspect it would be true) the difference is going to be far less than you might expect. BUT, it is very dependent upon the amp and speakers and how they interact. And, again, passive or active bi-amping, "different" ain't always "better" -- but it ain't always "bad", either.

Enough blather from me - Don

 

[docvale]

Why, yes they do. How else are you going to bi-amp a pair of speakers if they don't have separate inputs for the bass/midrange drivers and the tweeters?

My point was to specify that your speakers have a low frequency input that is placed before an active crossover.

What makes you think that the 1800 watt subwoofer amp is doing anything besides driving the subwoofer?? That's all it is doing.

It works like that because the 1800W amp comes after the active crossover. If the amp were placed before, it would work on full frequency and than only the frequency accepted by the sub would be used (so, lots of power would be wasted)

What I am doing (or was until the one amp crapped out) was having a single channel of a 220 watt stereo amp drive both the bass/midrange drivers and the tweeters. Now there is a dedicated single 220 watt channel feeding each one separately. You can't tell me that it doesn't translate into more total effective power being delivered to the speaker. It only makes sense that 2 channels of 220 watt power driving one speaker will have more power than 1 220 watt channel driving one speaker.

Ok. If you have a 220W/channel stereo amp and you drive speakers that accept biwiring (like yours), you inject in each speakers 220W that amplify all the frequencies. The energy that will arrive to each driver will be dictated by the passive filter inside the speaker. Accordingly, your vertical amplification project is not converting the couple of stereo amps in a couple of 440W monoblocks: the energy that goes to each driver when the speaker is driven in normal amplification and in passive biamping is (more or less) the same. IMHO the passive biamping is (very) interesting only when the design of the speaker wants very different kind of amps (e.g., horn-loaded tweeters and large cone woofers).

How are they conceived for multi-amping? Do the contain no passive crossovers and require an outboard crossover?

Exactly! The B&W Nautilus come with an external active crossover and no passive filter: they can be driven only by quadriamplification. I think that Ocean Way speakers (which are demoing with Viola amps) and the big Wisdom Audio also are designed this way.

 

[mep]

I don’t know what is going on here, but I have the second Phase Linear 400 Series 2 running again and I’m back to the vertical bi-amp mode. When I bought the second amp on Ebay from the original owner, I had a feeling it wasn’t working based on the famous “it was working when I put it away” comment. He was the original owner, had the original box and manuals, and it was in good physical shape. It arrived with one blown fuse which is an AGX-8. The closest I could come on my first trip to 3 stores was an AGX-7. I thought the only difference was one amp less of current capability, but I was wrong. When I initially installed the AGX-7 fuse the amp worked perfect for a night and the next day was dead again. And when I say dead, I mean that both channels were distorted.

So, I went to my local electronics store and bought their last box of AGX-8 fuses. Last night I installed 2 new fuses and the amp worked perfectly. I noticed that the AGX-7 fuse was about an 1/8” shorter than the AGX-8 fuse. I came home today and pretty much expected it wouldn’t be working correctly again, but it is still working fine. I’m going to cross my fingers and hope it continues working.

There is no doubt in my expectation bias mind that vertical bi-amping sounds more powerful than a single stereo amp playing both channels. I switched back to my Yamaha C2a preamp so that there would be no impedance mismatch. When I tried the vertical bi-amp the first time, I was using my Counterpoint SA-5.1 and I noticed that the impedance change caused me to have to increase the volume control to get the same level I had previously with one amp. Not so now.

It makes sense to me that if you have 2 channels of over 200 watts driving each speaker that it will sound different than having one channel of over 200 watts driving each speaker. The benefit you have when you use monoblocks with a separate power supply for each channel is also in play here.

I will post further thoughts when I determine if this is a good change or just a different change as Steve likes to say.

 

[MylesBAstor]

There is no doubt in my expectation bias mind

Mark, you are a trip dude! LOL X3

Tom

Well I'm not going to say what I would choose if I had no expectations.

 

[mep]

Well I'm not going to say what I would choose if I had no expectations.

Another amp?

 

[Mark (Basspig) Weiss]

I'm running my bridged Haflers into 8 ohm loads, at frequencies above 90Hz, so for my situation, the bridging is ideal. On a purely resistive load, I'm getting a swing of 342 volts peak to peak for 350 mS, which sags to about 75% of that value for the settling long-term power level. I have 90,000uF of capacitance in each Hafler 500, which greatly increased the duration of peak power output. It's ideal for a midrange frequency situation, due to the low crest factor. Delivering over 1800W of music power to each of three front speakers is pushing the envelope, even on industrial professional drivers like I'm using. With bridging, it makes an ideal headroom situation.

 

[mep]

Ok, so here is the latest change. I switched from vertical biamping to using one channel from each amp to power each speaker. I inserted a shorting plug into the input of one channel of each amp, turned the sensitivity control to the off position, and hooked up a dummy load resistor to the speaker terminals in order to protect the amplifier. So now we have the entire power only having to respond to the power demands of one channel. Also, I was able to remove the kludge of cables I was using for the vertical biamping as well as the splitter for the IC from the preamp. I’m back to using my MIT Shotgun S-3 bi-wire cables.

How does it sound? Damn good and I may prefer this setup over the vertical biamp mode. The only setup I haven’t tried is the horizontal biamp mode, but I just see no point in that. It’s good to have choices.

 

[ack]

You don't appear to have bridged each amp, so how do you get the entire power of an amp available to its speaker? Or did I misinterpret your description?

 

[DonH50]

I believe he meant this:

"So now we have the entire power supply only having to respond to the power demands of one channel."

 

[mep]

I believe he meant this:

"So now we have the entire power supply only having to respond to the power demands of one channel."

That's exactly what I meant and thought I clearly said that. Apparently not so. I left out the word "supply" out after the word "power."

 

[ack]

Does the transformer have one or two secondary windings? I would expect that you'd be able to utilize the full power (if the transistors are up to it) only if it has a single secondary winding...

 

[mep]

Does the transformer have one or two secondary windings? I would expect that you'd be able to utilize the full power (if the transistors are up to it) only if it has a single secondary winding...

I have no idea. If the power transformer/power supply is only being taxed by one channel, it stands to reason that you will have more headroom available to the active channel.

 

[ack]

I have no idea. If the power transformer/power supply is only being taxed by one channel, it stands to reason that you will have more headroom available to the active channel.

The reason I asked is because a larger secondary winding will result in more available power; if you have two, indeed driving one channel will probably get more power, but not the full possible from the xformer... No?

 

[DonH50]

Depends upon how the transformer is wound. Should gain more power to a single channel before transformer saturation vs. it having to service two channels.