[serlvz]

It is recommended that I should bi-amp some speakers I'm looking into getting. They are older, large B&W's and though I believe my current SS amp could drive them well, I've been told that to get their best I might want to look into bi-amping them. The speakers call for 50-1000 watt.

Don't really want to get insane with $$, but could spend some. If I'm going to be driving the 15" woofers with their own amp what should I be looking at? 300+ watts/channel?

[opnly bafld]

What is your current amplifier?
I'm not a fan of passive bi-amping.

[Speedskater]

In general, I'm not a fan of passive bi-amping ether.

There any only a few situations when there might be an advantage.
a] tube amp for tweeters.
b] big Class D amp for woofers.
c] unusual speaker impedances.

[Tyson]

Passive bi-amping is a bad idea, IME.  With different amps it's really hard to match their different gain levels.  On the other hand, active bi-amping is a wonderful solution to getting the best out of 3 way speakers. 

[DannyBadorine]

Passive bi-amping is a bad idea, IME.  With different amps it's really hard to match their different gain levels.  On the other hand, active bi-amping is a wonderful solution to getting the best out of 3 way speakers.

I second this notion.  I don't think there is much of an advantage unless you are using an active crossover, but even then I would use the exact same amplifier on each channel in order to keep things consistent.  So, I think you're better off with one amplifier channel a side and that should allow for a higher quality amplifier.  IMO, this will get you the best results.

[planet10]

Passive bia-amping does not usually work that well, and as mentioned if you do best to use 2 amps the same.

Proper bi-amping requires a crossover before the amplifiers.

There can be huge benefits, but one still needs the XO to have the same transfer functions as the passive. Few off-the-shelf analog active XOs offer this kind of functionality (a counetr example is Nelson Pass’ LXmini XO). DSP XOs take versatility to the next level, but you now may have too many choices.

Multi-amping is allmost always seen when one adds subwoofers, and multi-amping can be more effective if you design the speakers with the specific XOs you are going to use.

I had really good results from passive biamping my acoustats, the speakers i am currently use were designed to be bi-amped using a simple PLLXO. Developemnt of the passisve XO was harder and the resulting passive cost more than teh PLLXO and the extra ampifier.

If you are adding an amplifier to just drive the bass, this is where a good Class D amplifier can provide very good performance for not much money. I have 2 that are 4 x 100w 4Ω, 1 cost about $100, the other has a buffered PLLXO and was $200.

In the OPs situation choosing an appropriate XO is the more important choice than the 2nd amplifier.

dave

[serlvz]

What is your current amplifier?
I'm not a fan of passive bi-amping.

I'm currently using a Van Alstine Vision SET 400, 225w/channel solid state. Speakers being considered are B&W 801 Nautilus.

It was suggested to me to perhaps look into a miniDSP for crossover duty. Wasn't sure how well these units do in terms of keeping the signal clean.

[planet10]

Get at least the miniDSPHD.

Still on the cheap end. Cheap enuff that i am going to get one just to use to quickly find a target for an active analog or a passive (rarely) XO.

dave

[WGH]

I'm currently using a Van Alstine Vision SET 400, 225w/channel solid state. Speakers being considered are B&W 801 Nautilus.

I use the AVA SET 400, terrific amp. Frank has written that output almost doubles into 4 ohms so the 801's will see at least 400w/channel. I would live with a single SET 400 and the B&W speakers for a while before deciding on bi-amping.

Wes Phillips writes in his Stereophile review:
"I also noticed that, while never short of air and detail, the speakers tended to present recordings as ever-so-slightly luscious. This probably indicates a mild reticence in the "presence" region (1-3kHz)..."

The AVA SET 400 is also ever so slightly luscious, the combination may be too much of a good thing. Consider trying out a pair of PS Audio Stellar M1200 Monoblock amps. Not exactly bi-amping but you get two amps without the DSP hassles, the M1200's are not reticent plus they have unlimited power (1200w into 4 ohms), probably just what the B&W speakers need.

I had a pair of M1200's in my house for a week and they were a big wow.
https://www.audiocircle.com/index.php?topic=176173.msg1856501#msg1856501

[Tyson]

I agree with WGH, what the B&W's really need is a bigger and ballsier amp.

[planet10]

I would live with a single SET 400 and the B&W speakers for a while before deciding on bi-amping.

That is the sensible approach

My only experience i have had with the 801s was at a buddies studio. He had a smaller amp with no issues driving them.

As old as they are some of the XO parts might need refreshing.

dave

[toocool4]

You are going by what you have heard someone else say, there is no substitute for your own experience.
I never go on someone else’s say so, I never part with my money on anything I have not tried myself and preferably in my home with the rest of my system. 
If you can try the speakers with your own amp in your system / room, that is the only way to know if it works for you or not. Anyone that blindly goes with someone else’s say so, better not be too bothered about losing their money as that is what they will get if it does not work out for them.

[Jazzman53]

If you can afford it; active bi-amping is always better than a passive setup.

I've bi-amp'd my hybrid ESLs for the past 15 years.  First with a DBX223 active analog crossover, then a Behringer DCX2496 DSP/crossover and now a DBX Driverack Venu 360 DSP/crossover.  The Driverack is wonderful. 

With the passive crossover components out to the loop, there is greater headroom, phasing errors disappear, and most sonically noticable is the quality of the bass.  Without a passive inductor between the amp and woofer; the amp has more authority over the woofer's motion, so the bass becomes tighter and cleaner.

Also, I recommend vertical rather than horizontal bi-amping.  By "vertical" I mean one amp on each speaker, with one channel driving the woofer and the other channel (of the same amp) driving the tweeter (or ESL in my case).  The logic being that a woofer typically draws more power and a tweeter less power-- so, if one amp is driving the woofers and a second amp is driving the tweeters, the woofer amp is being over-utilized and the tweeter amp under-utilized. 

In most amps both channels are powered from a common transformer, and the power is not being drawn by one channel is then available to the other channel (i.e. power not drawn by the tweeter is then available to help drive the woofer). 

[planet10]

active bi-amping is always better than a passive setup.

You cannot say that, there are way too many factors to have such a generalization.

With a hybrid ESL, different amps that suit each kind of driver element (ESL/Dyanic) makes a lot of sense, since each likely performa sbest with a different amplifier. And here, the significant skewing of an amplifier into a capacitive load will not be kind for delivery of power to the dynamic bass driver.

dave

[Jazzman53]

You cannot say that, there are way too many factors to have such a generalization.

With a hybrid ESL, different amps that suit each kind of driver element (ESL/Dyanic) makes a lot of sense, since each likely performa sbest with a different amplifier. And here, the significant skewing of an amplifier into a capacitive load will not be kind for delivery of power to the dynamic bass driver.

dave

Fair enough.  A qualifier is in order here:  "In my opinion" an active crossover is superior to a passive crossover. 

[kernelbob]

I'm not familiar with the design of your B&W speakers, so I'll relate my experience with biamping Von Schweikert VR100XS speakers.  These use custom magnesium/ceramic drivers on the bass & midrange and a ribbon tweeter.

Driving the midrange and treble, I'm running a pair of Lampizator True Balanced 211 Monoblock tube amps which are rated around 80 watts.  Each amp essentially consists of a pair of 211 amps, one per phase, with the two phases joined at the output transformer.  The amps use no local or global feedback, avoiding time smearing inherent with feedback loops.

The dynamic bass drivers, as is typical of the genre, benefit from a beefy amp with very low output impedance which is typical of amps with high feedback.  I use a pair of Spectron Musician III Mk2 amps which use a very fast feedback loop (500 kHz).  These provide vice-like control of the bass.  They have a rated output of ~1600 watts, so for a given input voltage they are louder than the 211 amps.

The speakers were designed to support biamping with separate inputs for the mid/tweeter and for the bass drivers.  No other external crossover is needed, nor recommended by VSA.  Each input has a dedicated crossover.  The mid/treble crossover presents a very high impedance at frequencies below the bandwidth of those drivers.  This prevents low frequency signals from reaching the midrange & tweeter.  The bass inputs connect to the bass crosssover which has very high impedance at frequencies above the operating range of the bass drivers.  Since the mid/treble crossover presents a high impedance to the amp, you will find that a tube amp will play louder since it doesn't send all those bass waveforms to the mid/treble drivers.

I use a passive LDR based balanced controller.  This controls the volume of the output.  It has two sets of output, one set connecting to the 211 tube amps and one set connecting to another LDR attenuator which is connected to the bass amps.  I typically have that secondary attenuator set to -8.4 dB relative to the output of the main controller.  Once the optimum balance of the mid/treble and the bass amp is determined (just use your ears), that setting rarely benefits from adjustment (exceptions are when a recording's bass level is inadequate, e.g. very old recordings, or a few labels with chronically weak bass such as Naxos).

So, it's not necessary to use the same brand of amp on the top and bottom when biamping.  Actually, biamping lets you us different types amps with different strengths to suit your speakers needs.  There is one caveat.  If the throughput time of the two sets of amps are very different, then the output of the top and the bottom amps may not properly integrate.  I've never seen this occur when I've helped friends set up their biamped systems.  As a example, the architecture of my two sets of amps could not be more different, but the combined result integrates perfectly (excellent imaging, coherence, etc.).

Hope this helps.

[FullRangeMan]

It is recommended that I should bi-amp some speakers I'm looking into getting. They are older, large B&W's and though I believe my current SS amp could drive them well, I've been told that to get their best I might want to look into bi-amping them. The speakers call for 50-1000 watt.

Don't really want to get insane with $$, but could spend some. If I'm going to be driving the 15" woofers with their own amp what should I be looking at? 300+ watts/channel?

To avoid disappointment you must be aware more amps, more connections, more output Transistors, more Watts etc are not the hi-fi road, just more expensive and maybe more sound.  With bi-amp you will note the sound will be different but not better due many equipments in the system.

[kernelbob]

To avoid disappointment you must be aware more amps, more connections, more output Transistors, more Watts etc are not the hi-fi road, just more expensive and maybe more sound.  With bi-amp you will note the sound will be different but not better due many equipments in the system.

My experience in running a single amp full range has been that very frustrating.  No single amp was best at everything.  For example, finding an amp that provided the needed control of the bass (via high damping factor) and the mid/treble realism that my tube amps provide (no local or global feedback, a single output tube per phase).  Yes, the additional amps are an expense.  Yes, the additional interconnects and power cords are an expense (I'm using MasterBuilt Ultra interconnects and power cords, so yes more expensive).  Was the additional cost and complexity worth it?  Is the realism of the result better?  Is the opportunity to fine tune the level of the top and bottom amps worthwhile?  In my experience, absolutely yes.

[Speedskater]

Active bi-amping is a different ball game.  You are throwing away the speaker designer's voicing of the loudspeaker and instead using a DIY voicing.
No, you can't just look at the speaker's specs or schematic and use those numbers. Part of a passive crossover never makes it to paper.

* * * * * * * * * *
David Rich wrote:

Crossovers

“In the old days, there was a lot of trial and error in designing a crossover. So, adding more than a few components was futile, since it wasn’t practically possible to optimize them. Simplicity yielded better optimizations”.
“The individual crossover components usually don’t have functions in a way that can be isolated. A crossover is a filter network that implements a transfer function as a result of all of its parts. Sometimes it is possible to generalize and say, Oh, this resistor adds damping. Or, This network compensates for a resonance. But, really, the better a crossover design is, the more the parts work together, symbiotically”.

Dave Rich

[DannyBadorine]

My experience in running a single amp full range has been that very frustrating.  No single amp was best at everything.  For example, finding an amp that provided the needed control of the bass (via high damping factor) and the mid/treble realism that my tube amps provide (no local or global feedback, a single output tube per phase).  Yes, the additional amps are an expense.  Yes, the additional interconnects and power cords are an expense (I'm using MasterBuilt Ultra interconnects and power cords, so yes more expensive).  Was the additional cost and complexity worth it?  Is the realism of the result better?  Is the opportunity to fine tune the level of the top and bottom amps worthwhile?  In my experience, absolutely yes.

I think there are some good times and places to bi-amp a passive crossover, but if you're not careful, you can definitely make things worse.  I like your approach to it as you understand that different speaker loads and drivers require different characteristics from amplifiers and therefore you can get more out of the speakers if you know how to match this correctly.  I still side on using properly designed speakers with crossovers that are easy for amplifiers to drive and then you only need one amplifier.  But there is no doubt that there are situations where both methods can be advantageous.  So much of this is just subjective anyway.