There seem to be a variety of ways people bi-amp. I can only tell you what works for my system and ears.

In my dedicated listening room, I have a Power Amp driving the ribbon tweeters and carbon fibre/kevlar midrange drivers left and right speaker. And another Power Amp driving the 10' inch carbon fibre/polythrene bass drivers left and right.

The Power Amp driving the bass drivers isn't the same model as my amp driving the mid/tweeters, but is by the same manufacturer and power output.

I can't say I noticed any HUGE improvements when adding the extra amp, but there were definatley subtle improvements to the sound, not only at high volume levels, but also at lower levels as well.

I seemed to obtained a more detailed bass,there seemed to be far more detail in the sound of the bass and it was easier to distinguish the bass insturments from one another at low and higher volumes.

The midrange seemed to have improved as well, which was my biggest surprise at higher volume levels. Less stress on vocals when I turned up the volume and a 3d soundstage increased.

I also seemed to benefit slightly from more air and sparkle in the highs with the extra amp.

However, in my lounge system, I have a NAD C541 CDP, and a NAD C270 and NAD C370 and when I bi-amped these, I found little appreciable difference in sound quality....but when I Bridged ( and bi-wired speakers)the NAD Amps, I found a HUGE jump in sound quality.

I think you need to audition and bi-amp before you buy.

http://sound.westhost.com/bi-amp.htm

I have a set of Energy speakers which are wired with a jumper to two sets of binding posts. I asume I can use a separate amp for each set of posts but I have no idea how to wire such a thing.

Just remove the jumpers, and wire the Bass L/R speaker binding posts to one power amp speaker outputs and the midrange/tweeter L/R speaker binding posts to anther power amp outputs. (assuming you have a pre-amp with 2 power amps, or an integrated amp and power amp)

Or if you have an A/V receiver, check the hand book on how to bi-amp using it.

some integrated amps come with "pre-amp" out connections on the back of the unit. in my case, my speakers are very current hungry so the 65 watts of the integrated did not handle the bass very well. i was able to locate the companion power amp by the same company of the same wattage. in my case, i have the tweeter and mid on both speakers run from the speaker outputs of the integrated amp and the bass drivers run from the auxilary power amp for a total of 130 watts now. you need an interconnect to run from the integrated to the amp and either a biwire set of cables rewired for the two outputs or 2 separate sets of speaker cables. the system went from giving an impression of bass to real bass. with that said, i still believe a good stereo amp of appopriate wattage or a good set of monoblocks would sound better, but this was a good middle of the road upgrade that didn't cost too much. one thing, your speakers must be biwirable to do this.
good luck.

I have a follow-up question about bi-amping. I have thoroughly read the suggested bi-amping website several times, yet I am still unclear about certain aspects. The site makes it seem as if one MUST have external crossovers to use both terminals on the speakers. Couldn't I simply hook up two amps, one connected to the mids/highs and one to the lows? Also, if I did this would I need to have matching amps? I have an out on my integrated 25 watt tube amp that I could connect to a smaller 15 watt tube amp. Wouldn't this work just fine if I played around with the adjustments a bit?

Yes, you can bi-amp without removing the passive crossover and using an active one. The scenario about removing the speakers crossover any using an active crossover is the most drastic form of bi-amping. Almost no one ever goes that far.

> The site makes it seem as if one MUST have external crossovers to use both
> terminals on the speakers.

If you want the end result to be a modest improvement in accuracy then one needs to remove the passive crossover. The benefits derive from the direct and indirect consequences of doing this.

For loudspeakers that give significant weight to accuracy, using one amplifier per drive unit with an upstream active crossover has been pretty much universally adopted for many years. Audiophile loudspeakers are generally designed to meet the requirements of audiophiles and accuracy in a technical sense is usually not a particularly strongly weighted parameter. Your valve amplifiers are a good example of this.

> Couldn't I simply hook up two amps, one connected to the mids/highs and one to
> the lows?

If the passive crossover has been designed so that this can be done then yes. If you arrange things properly so that each amplifier puts out the same power when you adjust the volume control then it will perform essentially the same as before. Whether using two sets of cables and power amplifiers is better or not depends on you as an audiophile.

also, some integrateds come with a "pre-amp" out feature that permits you to attach interconnects to an amp and either use the integrated as a preamp only without attaching any speaker leads to it but only to the amp or as a bi-amp by using the speaker leads from the integrated to the tweeter/mid and the speaker leads from the amp to the woofer. i use an integrated amp with the companion power amp of the same family and power rating in my system. i have not felt the need to alter the internal speaker crossover at this point. you might run into problems if the amps you are trying to use are very different from each other. i would love to expiriment with a tube integrated for the highs and solid state for the lows.

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If you want the end result to be a modest improvement in accuracy then one needs to remove the passive crossover.

I'll go farther and say that leaving a passive crossover in place pretty much negates any advantage from bi-amping. There are a few advantages to bi-amping, but the main one for me is to avoid distortion from the passive crossover inductor (and possibly capacitor). Take those out of the circuit and distortion can only be lower.

--Ethan

I am currently a full-time college student and do not have unlimited funds to play with. I scrape money together by doing odd jobs and am learning about this world as I go. I am not trying to gain extreme accuracy just yet, my only hopes are to be able to drive my speakers with two amps in order to run both at lower power while maintaining the same volume. Does it not work like this? If I were to use the more powerful amp for the lows and the less powerful amp for the highs, or vice versa, wouldn't this -in essence- provide more power to the speakers? Like I said, I do not have the money to go all out with crossovers and what not. If I had the extra money to buy crossovers I would rather buy a single, more powerful amp. I just have this extra tube poweramp lying around that seems to put out 15w (so I was told by an audio engineer at my school who checked it out). I could always play around with the ohms and wiring to figure out what is best, but what I am afraid of is buying a pair of B&W CDM9 nt speakers (used from a guy who is in bankruptcy currently) and messing them up because of my inexperience. Would amps with different power outputs damage the speakers? I want to leave the passive crossovers in place for now, until I have money to invest in better amps.

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but what I am afraid of is buying a pair of B&W CDM9 nt speakers (used from a guy who is in bankruptcy currently) and messing them up because of my inexperience.

That would be an excellent rationalization for not doing anything that could mess them up.

With the passive crossovers in place, you won't be using any less power with two amplifiers than you would with one. The amplifier must produce a certain amount of wattage to get the speaker to a certain level.

Each driver has a specific electrical sensitivity to input voltage, they play at "X" level when "Z" voltage is applied. Should one driver's sensitivity be higher than another (tweeter higher than woofer), it is typical for a designer to level match the pair by using the crossover components. If the amp still must work through the crossover to drive the system, you cannot overcome the total system sensitivity of the speaker. In other words, if the speaker as a whole is capapable of playing at 89dB with the equivalent of 1 watt input, then it will remain at the same relative sensitivity even if you drive each portion of the system independently with two amps, 89dB remains 89dB.

Any likely change in relative level would be due to different input gain within each amplifier and would only serve to alter the intended sound of the speakers unless you had inpedendent control over each amplifier's input level.

The overall load on each amplifier might be lower but not typically to the degree where it would be worth the effort as long as you are still driving a passive crossover before you send the signal to the drivers. Both amps will still be dealing with the full frequency spectrum of the music if you do not use a crossover in front of the amplifiers, this negates many of the gains to be found in bi-amping. To do the task properly would require more cables which would up the ante for the entire system. If you scrimp on cables here, you'll loose any slight advantage you might have found otherwise.

If you wish to invest in a high quality active crossover and the cables to go with the device - and you bypass the internal passive crossover, then you would very ikely hear some degree of improvement from the system if both amplifiers are of similarly high quality. Mixing a low quality amp with a higher quality amp isn't the way to satisfaction. Bi-amping works best when both amps are of similar design and sound quality. Otherwise, you are wandering into some very strange stuff that isn't really for those just with idle curiosity. I suspect most of us here would say you would be better served by selling both amps and using the money for one much better amp rather than the scheme you've devised here.

B&W is a high quality speaker manufacturer and they don't put lousy parts in the speakers. Replacing what B&W has designed with questionable parts of unknown quality is not in any way a good idea. Why mess with a proven design only to head off in an unknown direction without a map?

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I have an out on my integrated 25 watt tube amp that I could connect to a smaller 15 watt tube amp. Wouldn't this work just fine if I played around with the adjustments a bit?

Once someone uses the term "play around a bit", they do not have a good map in their hands and likely don't know where or how to find a good map. We've all played around a bit with connections and oddball setups. Most of us either learned how to make the correct connections and set ups or eventually relented to the fact what we were doing was just playing around and we should get back to letting someone who knows what they are doing do the job right in the first place. Sorry to quench your curiousity but you really should let the B&W's exist as they were designed while you save up for a better amplifier.

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I am currently a full-time college student and do not have unlimited funds to play with. I scrape money together by doing odd jobs and am learning about this world as I go. I am not trying to gain extreme accuracy just yet, my only hopes are to be able to drive my speakers with two amps in order to run both at lower power while maintaining the same volume. Does it not work like this? If I were to use the more powerful amp for the lows and the less powerful amp for the highs, or vice versa, wouldn't this -in essence- provide more power to the speakers? Like I said, I do not have the money to go all out with crossovers and what not. If I had the extra money to buy crossovers I would rather buy a single, more powerful amp. I just have this extra tube poweramp lying around that seems to put out 15w (so I was told by an audio engineer at my school who checked it out). I could always play around with the ohms and wiring to figure out what is best, but what I am afraid of is buying a pair of B&W CDM9 nt speakers (used from a guy who is in bankruptcy currently) and messing them up because of my inexperience. Would amps with different power outputs damage the speakers? I want to leave the passive crossovers in place for now, until I have money to invest in better amps.

First, power is power. Power in equals power out, minus losses. No magic, no increase in power from magnets, oxygen free copper, biamping, switching power supplies, etc. Just three variables. Power in, losses and power out.
I hope that your idea of using two amplifiers does not mean paralleling their outputs and connecting them to the speaker. Just want to be sure. Very bad.

While I am quite familiar with bi-amping, what is bi-wiring?

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... what is bi-wiring?

http://search.yahoo.com/search?ei=UTF-8&...&fr2=sp-top

If you are unaware of the relationship between power in and SPL out, here is where you will find yet another problem with your proposed system connection.

To achieve a +3dB increase in overall volume level from a particular loudspeaker, you must put in approximately twice the power. In other words, if you are playing the system at 90db peaks and that requires 5 watts to achieve, you will need 10 watts to go up +3dB to 93dB peaks. Since the music is not a constant level but fluctuates from loud to soft constantly a +3dB level change is actually difficult to hear. It is just about where you notice an increase in volume when comparing one to another side by side. Taken without a direct comparison most people wouldn't say +3dB was even all that noticeable. When someone says they want their music "louder" they usually mean twice as loud. To achieve that jump in level you will have to increase the available power by approximately ten times, or, in your case, a jump from 25 to 250 watts available.

Each time you double the wattage into the same speaker you will only get out an approximate +3dB increase in volume. If you're playing at 50 watts, going to 100 watts into the speaker will still only gain you an average of +3dB from where you started. As I said, not very noticeable when playing music.

Obviously the inverse is also true. If you are playing at 90dB peaks and you now lower the power output to play at 87dB peaks, you're using half the power when you lower the volume -3dB. If that 90dB peak required 5 watts beforehand, the 87dB peaks will require 2.5 watts.

If you consider just how inefficient power is when dealing with output level from a speaker that is only about 1-2% efficient in converting electrical watts into acoustic watts, you should see it would require a substantial jump in overall efficiency of the speaker system to make even a relatively small gain in the amount of power you woud require. As long as you stay with the same drivers and the amplifier must also drive the signal through the same passive crossover components, the amount of change provided to the amplifiers when bi-amping is, in the best of cases, negligible. If - a big if - you managed to play at 90dB with five watts using a normal connection and you dropped down to 4.9 watts to achieve the same volume level, what have you really gained for all your efforts?

If what you are trying to accomplish is higher volume levels, you should be looking toward more efficient speakers. The electrical sensivity of the speaker system is where you begin judging just how loudly a speaker will play. Buying a speaker with a higher sensitivity spec will in most cases provide that same 3dB change in overall level. Using your 25 watt amplifier with an 87dB sensitive speaker will be the same as using a 50 watt amplifier with an 84dB sensitive speaker. Or, you could consider using a 90dB sensitive speaker with your amplifier. This would be the equivalent of going to a 50 watt amplifier had you been using an 87dB sensitive speaker.

If you understand all that, also understand the numbers are not specific and not all 90dB sensitive speakers will play at the same perceived output level with any particular amplifier. To begin with, not all manufacturers are totally honest about their specs and some are just more hopeful than others. More importantly, how your specific amplifier deals with the demands of a specific speaker will be highly important to how loudly your system will play. In this regard the B&W's you are considering are not known to be particularly easy speakers to drive and will typically require a rather ballsy amplifier to sound good and play with any amount of "oomph". If I were considering such a purchase and my amplifier was a 25 watt unit, I would certainly make the effort to hear these speakers playing on my 25 watt amplifier before I gave anyone cash for what might not be an increase in performance from a mismatched speaker/amplifier combination. Given the right combination of speakers and amplifier, things can get pretty loud with 25 watts available. However, if you choose poorly, you'll need far more than 25 watts to get things jumping.

The bass has more energy than the treble, so a lower power amp will work for the mids and highs. That's sort of why some subwoofers have a high-power built-in amp (for short-term peaks) and a much lower continuous-power rating overall.

Quote:
If you are unaware of the relationship between power in and SPL out, here is where you will find yet another problem with your proposed system connection.

To achieve a +3dB increase in overall volume level from a particular loudspeaker, you must put in approximately twice the power. In other words, if you are playing the system at 90db peaks and that requires 5 watts to achieve, you will need 10 watts to go up +3dB to 93dB peaks. Since the music is not a constant level but fluctuates from loud to soft constantly a +3dB level change is actually difficult to hear. It is just about where you notice an increase in volume when comparing one to another side by side. Taken without a direct comparison most people wouldn't say +3dB was even all that noticeable. When someone says they want their music "louder" they usually mean twice as loud. To achieve that jump in level you will have to increase the available power by approximately ten times, or, in your case, a jump from 25 to 250 watts available.

Each time you double the wattage into the same speaker you will only get out an approximate +3dB increase in volume. If you're playing at 50 watts, going to 100 watts into the speaker will still only gain you an average of +3dB from where you started. As I said, not very noticeable when playing music.

Obviously the inverse is also true. If you are playing at 90dB peaks and you now lower the power output to play at 87dB peaks, you're using half the power when you lower the volume -3dB. If that 90dB peak required 5 watts beforehand, the 87dB peaks will require 2.5 watts.

If you consider just how inefficient power is when dealing with output level from a speaker that is only about 1-2% efficient in converting electrical watts into acoustic watts, you should see it would require a substantial jump in overall efficiency of the speaker system to make even a relatively small gain in the amount of power you woud require. As long as you stay with the same drivers and the amplifier must also drive the signal through the same passive crossover components, the amount of change provided to the amplifiers when bi-amping is, in the best of cases, negligible. If - a big if - you managed to play at 90dB with five watts using a normal connection and you dropped down to 4.9 watts to achieve the same volume level, what have you really gained for all your efforts?

If what you are trying to accomplish is higher volume levels, you should be looking toward more efficient speakers. The electrical sensivity of the speaker system is where you begin judging just how loudly a speaker will play. Buying a speaker with a higher sensitivity spec will in most cases provide that same 3dB change in overall level. Using your 25 watt amplifier with an 87dB sensitive speaker will be the same as using a 50 watt amplifier with an 84dB sensitive speaker. Or, you could consider using a 90dB sensitive speaker with your amplifier. This would be the equivalent of going to a 50 watt amplifier had you been using an 87dB sensitive speaker.

If you understand all that, also understand the numbers are not specific and not all 90dB sensitive speakers will play at the same perceived output level with any particular amplifier. To begin with, not all manufacturers are totally honest about their specs and some are just more hopeful than others. More importantly, how your specific amplifier deals with the demands of a specific speaker will be highly important to how loudly your system will play. In this regard the B&W's you are considering are not known to be particularly easy speakers to drive and will typically require a rather ballsy amplifier to sound good and play with any amount of "oomph". If I were considering such a purchase and my amplifier was a 25 watt unit, I would certainly make the effort to hear these speakers playing on my 25 watt amplifier before I gave anyone cash for what might not be an increase in performance from a mismatched speaker/amplifier combination. Given the right combination of speakers and amplifier, things can get pretty loud with 25 watts available. However, if you choose poorly, you'll need far more than 25 watts to get things jumping.

You are correct that a 3db increase in power level will require approxamatly a two times increase in power. In fact it will require exactly a 2X increase. But you're claim that a 3db increase in power will create an increase in volume of 2X is incorrect. Power is one thing, but volume is another. Due to the nonlinearity of the human ear, power and volume are not equal.