Passive bi-amping - real benefit or waste of time and money? (1 Viewer)

[Wayne_T]

Also posted on AVS...

A couple of us were getting into this discussion in another thread and rather than take that thread hopelessly off topic, I thought I'd start a new one on this subject.

I've seen passive biamping refered to as "fool's biamping". My personal experience with passive biamping is that there was a benefit, but I do concede that it may not have been an apples to apples comparision as I had moved from my receiver's center amp to the its two main amps. The improvement could have been due to the receiver having better quality mains amplifiers than its other channels.

Here is what my Paradigm Reference speaker manuals say about passive biamping:

"Passive biamping provides a dramatic improvement in clarity, openness and detail with much better bass solidity and definition. The presentation of music is simply more intelligible and transparent.
With passive biamping the speaker's internal passive crossover remains connected. An external crossover is not required and cannot be used (there is no direct electrical access to individual drive units). This saves expense and set-up difficulties. Passive biamping fully optimizes your speaker" ... it goes on to explain the differences between horizontal and vertical biamping and the benefits of both.

Manufacturer's bull? Or is there perhaps a real benefit to biamping if the speaker has been designed for it?

 

[John Garcia]

I don't understand the question. Running two separate feeds from dedicated amps to each of the individual drivers should certainly make a difference. Each amp only has to handle it's respective frequency range and driver, allowing all of it's power to be used for that driver. IMO, they wouldn't design bi-ampable speakers if there was no benefit. This is not a gimmick.

 

[Frank_S]

Wayne_T,

Running two separate feeds from dedicated amps to each of the individual drivers should certainly make a difference. Each amp only has to handle it's respective frequency range and driver, allowing all of it's power to be used for that driver.

John, as was said by Wayne, the internal crossovers are NOT bypassed. This is why it is called "Passive Byamping". In an "Active Biamping setup, outboard crossovers are used rather than internal speaker X-Overs. IMO, this is the efficient way to go. I could go on to explain further but the archives have tons of info on this subject.

 

[John Garcia]

John, as was said by Wayne, the internal crossovers are NOT bypassed. This is why it is called "Passive Byamping". In an "Active Biamping setup, outboard crossovers are used rather than internal speaker X-Overs. IMO, this is the efficient way to go.

I am perfectly aware of this, however the amp is still only amplifying the frequencies passed by the passive x-over to it's respective driver. The use of the internal passive x-over gives the appropriate slopes and x-over frequency that were chosen for the design of the speaker.

What Wayne did is run two channels from the same amp section, though separate channels. This is not the same as two separate amps with individual power supplies, etc... because all the current is still coming from one power supply.

 

[Martin Rendall]

John,

Question: how does a crossover after the amplifier affect what the amplifier, er, amplifies? Is it a load thing? Is there any evidence to back this up, if it is your claim?

Martin.

 

[Marc H]

I attended a seminar on bi-amping by one of our suppliers and I asked the same question as Martin. The response was that the amplifier will only amplify the bandwidth the crossover allowed.
Sonically, the demonstration was most convincing too.

 

[Craig_Kg]

There is confusion here about the definition of passive biamping.

John, you and Marc H are assuming that the crossover is placed BEFORE the amplifier. Wayne_T is asking about amplifying the full signal and powering only 1 section of the biwirable speaker with each amplifier. That is why snobs call this configuration "fools biamping".

"fools biamping" is of benefit if you have an amplifier that doesn't have the power supply to handle a difficult load (low impedance speaker) - eg the ones in the receiver. In this case, you can either waste your amplifier and just use another one or use it in conjunction with another one so it isn't wasted. True, a passive crossover before the amplifier will increase the benefit but in the case of a receiver's amps, this is rarely possible.

I agree that what Wayne_T did was not indicative of either form of passive biamping unless he had his main amps powering his main speakers when they weren't powering his center speaker.

 

[ling_w]

When doing passive biamping, both amps are amplifying the voltage of the full freq spectrum, but each respective amp has to only deliver the current that the crossover allows it to pass. So there is some benefit, but not all the benefit of active biamping.

 

[John Garcia]

When doing passive biamping, both amps are amplifying the voltage of the full freq spectrum, but each respective amp has to only deliver the current that the crossover allows it to pass.

I think I will have to do more research on this, because that statement doesn't seem to hold true. For a given channel, full range singal is sent, but the driver only draws the current to reproduce the frequencies that it is allowed to by the passive x-over, in which case, only that amount of power is needed for that channel. I don't really see how this is dramatically different from active, with the exception that there is no PHYSICAL device inline with the driver which will affect the sound slightly in different ways depending on the exact components used in the construction of the crossover as well as slight changes to resistance.

 

[ling_w]

I don't really see how this is dramatically different from active, with the exception that there is no PHYSICAL device inline with the driver which will affect the sound slightly in different ways depending on the exact components used in the construction of the crossover as well as slight changes to resistance.

In a passive biamp system, the voltage for the full spectrum still has to be amplified. But in an active biamp, it doesn't have to voltage amplify the signal that the speaker will not draw. Keeping the amp from having to amplify unecessarily signals. Its like forcing your amp to amplify in addition to the original signal, also a whole bunch of hf hash in the 50-100khz range. Even if you put a 8th order low pass on the tweeter at 25khz, the amp is still at work amplifying that 500-100kzh hash. IM distortion from those hf signals could easily appear in the audible region. Plus, those signals could clip, causing other problems.

Plus active filters are easier to implement since speaker level crossovers has to contend with the various impedence issues of the drivers.

 

[Craig_Kg]

Plus active filters are easier to implement since speaker level crossovers has to contend with the various impedence issues of the drivers.

Except that with better speakers, the crossovers are also adjusted to the drivers' properties to control the impedances, resonance points and phase shifts.

 

[Wayne_T]

There is some confusion about how I had implemented passive biamping on my system. Let me clear that up.

I have a Yamaha RX-V3000 and I'm on a path towards separates. My first step was to get a Bryston 4B-ST power amp for my mains. BIG improvement. Then I wanted a better sounding center and it occurred to me that the mains of the RX-V3000 were sitting idle. I fed the center pre-out to the mains-in jacks of the RX-V3000, and biamped the center speaker with the Yamaha's mains amps. The improvement was very noticeable, particularly the clarity of dialog (movies) and vocals (music DVD's). BTW, the center is a Paradigm Studio CC.

I attributed the improvement to (a) the passive biamping and (b) to the doubling of power to the center. Both of these assumptions have been challenged by people that seem to be knowledgeable in how amps and speakers work. They suggested that if I heard a difference, the explanation would be that the Yamaha's mains amps are superior to its other channel amps. I started this thread to try and learn the "truth" about biamping, as there was such a contradiction between what the speaker manual and the critics were saying.

For me its kind of a moot point now, as I have since picked up another amp (Anthem MCA-3) and I'm running the center off it without biamping. When I heard for myself the dramatic improvement that external amplification made, I just had to have it all around. The Anthem is not of the same quality as the Bryston, but its a good interim solution. That being said, I'm still interested in the topic, as I may want to go that way in future.

 

[Craig_Kg]

Why not try biamping with the receiver's amps and the outboards?

What you did shouldn't have affected things much (assuming symmetic amps) since the amps were amplifying the full signal and shared a common power supply. The benefit of "fools biamping" is in having more power supplies. As you intimated in the OP, maybe the amps aren't all the same.

 

[Wayne_T]

Why not try biamping with the receiver's amps and the outboards?

Because the outboards are conservatively 200WPC (Anthem) and 313WPC (Bryston), whereas the Yamaha is optimistically 100WPC.

Thanks,
Wayne

 

[Amir]

I tried this on Sunday. I have Parasound HCA-2205 amp Paradigm Studio 60's front with Studio CC center and 20's for back with Paradigm PS-1000 powered sub. Currently I am using my Denon 2800 receiver for pre pro for the front three channels and sub ( it does not have pre out for surrounds) I was using only three channels of the Parasound for the front three channels. The Parasound is rated at 220x5. I hooked up the other two channels for the front L & R as biamped. The difference, well, it was hard to say but it seemed that the bass got a bit stronger and maybe, maybe a little clearer. But with out being able to switch back and forth between the to the best I can say is a big maybe. It could be that my pre-amp is not as revealing and can mask any improvement. I couldn't tell.

Amir

 

[Craig_Kg]

Because the outboards are conservatively 200WPC (Anthem) and 313WPC (Bryston), whereas the Yamaha is optimistically 100WPC.

Well it might help (just) if you use the Yamaha to power the upper driver(s) since they don't draw as much current but with those outboards, it would be a marginal thing

 

[Charles Gurganus]

Passive biamping has been a real improvement for me. I've passive biamped NHT VT1.2's and currently biamp NHT VT2's with 2 channels each from the Sherbourn 5/1500. Of course you get more of a benefit biamping hard to drive speakers like NHT. It is hard to go back to single amp once you biamp, IMHO.

 

[Mike Veroukis]

I'd have to agree with Chris_Kg on this. Why would you want to bi-amp at all when you have over 300Wpc?!? That's more then enough for the paradigms. Unless you've placed these speakers in a concert hall and wish to play above reference levels, you got enough power to keep you (and your naighbours) happy. What you should be more interested in at this point is the quality of the amps themselves, not how many watts they can add up to. I like Yammies (I own one), but if I had an Anthem and a Bryston I'd leave the Yamaha's amps out of the loop entirely.
However if you are serious about bi-amping for the sake of improved sound quality then I'd recommend active bi-amping with the cross-over between the pre/pro and amps and using the same brand of amp all around. Instead of passive bi-amping you'd probably be better off investing in a higher quality main amp and just bi-wire.
That's my view on the matter, feel free to disagree.
- Mike

 

[Wayne_T]

Mike,

Why would you want to bi-amp at all when you have over 300Wpc?!? That's more then enough for the paradigms.

I couldn't agree with you more. I have no further intention of bi-amping the Paradigms as I now have ample power and performance, which is why I said it was a moot point now.
Wayne

 

[KeithH]

I have a passive biamp configuration in my main stereo system. Here is the set-up:
Speakers: Totem Arro (4-ohm load, 85 dB sensitivity)
Amp for tweeters: NAD C 370 stereo integrated amp
Amp for drivers: NAD C 270 stereo power amp
The C 370 and C 270 share the same amp section, so they are gain-matched. I realize that this is not considered as good as active biamping, but many active crossover components are costly. Also, I was not about to disable the crossover in my speakers. Despite this, I could immediately hear a benefit upon adding the power amp. The soundstage is deeper and wider. Also, the highs are smoother.
Passive biamping has been discussed here quite a bit as well as on the General board on www.audioasylum.com . Search both sites for more information.