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Passive Biamping: How much improvement?


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#21 of 66 OFFLINE   PaulT

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Posted June 19 2003 - 08:29 AM

Here is an article you may find interesting:



http://www.sound.wes....com/bi-amp.htm
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#22 of 66 OFFLINE   Brett DiMichele

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Posted June 19 2003 - 08:34 AM

Chung, So wrong you are.. But hey that's fine... I will stick with my "Fools" Bi Amplification rather than some jerry rigged setup with an active crossover that does not even take into account baffle step, time alignment or numerous other "specific" crossover issues that go into designing a proper network, passive or otherwise. As a side note... Even IF the amp is sending a full range signal to the crossover and then to the specific driver. The amp is NOT under the same loads. As soon as you remove those shorting straps on a properly designed crossover network you are now driving "seperately" the tweeter and midranges and the woofers. A woofer always will present a lower impedance than a tweeter and will require more work from the amplifier than the tweeter will. So it's not accurate at all to say that "even though" the XO is now seperated that the amps are still working just as hard because it has to send a full range signal to the crossover. *Shakes head* Keep reading... But perhaps you should "try" it.. It's NOTHING at all like Bi Wiring, not even close.
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#23 of 66 OFFLINE   Jigesh Patel

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Posted June 19 2003 - 09:25 AM

Thanks, Paul, for the web-link.
Quote:
Originally posted by Brett... A woofer always will present a lower impedance than a tweeter and will require more work from the amplifier than the tweeter will. So it's not accurate at all to say that "even though" the XO is now seperated that the amps are still working just as hard because it has to send a full range signal to the crossover.
Interesting..and kind of convincing....Thanks. Jigesh

#24 of 66 OFFLINE   Chu Gai

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Posted June 19 2003 - 10:08 AM

Well I certainly wouldn't rip out the crossovers and try an active approach especially if the speakers were designed by competent engineers. I think Paradigm is competent Posted Image



However, in this case, I'm assuming the poster wants to remove the strap and basically run two amps into the upper and lower binding posts. This, I assume, will be done without the amps having been preceded by any sort of active crossover (filter). If so, then both amps will certainly be presented with the same full range frequencies and they will do what amplifiers do: amplify the full range of frequencies. Hence any increase in the amp headroom would be very speculative. Were it that they were preceded by filters, then yes, I could see there being this headroom increase. The amp just doesn't know how the frequencies that it's sending out are being used. So I must politely disagree with you Brett.



Often what occurs, is a situation where the gains of the two amp are not critically matched. In this case you've changed the frequency response of the system. Run a little more juice up top and I'll just bet things might be called sparkling and greater delineation of cymbals and such. If you like it, who am I to argue with it? Since you own the equipment already, it's not going to hurt matters for you to play around.



However, if you carefully match, you may find that the primary benefit was to the person who sold you the amps.



On a side note, keep in mind that most of your acoustic power is down below. Only about 10% or so exists above ~ 3.5 kHz.

#25 of 66 OFFLINE   chung_sotheby

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Posted June 19 2003 - 10:23 AM

Quote:
an active crossover that does not even take into account baffle step, time alignment or numerous other "specific" crossover issues that go into designing a proper network, passive or otherwise.
Brett, I know that an active crossover does none of these things, but at which point did I say that active biamping would take all these factors into account? Many times, especially with well designed speakers (Paradigm, B&W, Revel, Dynaudio) the internal crossover is far more favorable than an external crossover, as it has had months (maybe even years) or R&D put into its design and its implementation with the specific drivers that it is paired up with.
Quote:
Even IF the amp is sending a full range signal to the crossover and then to the specific driver. The amp is NOT under the same loads. As soon as you remove those shorting straps on a properly designed crossover network you are now driving "seperately" the tweeter and midranges and the woofers. A woofer always will present a lower impedance than a tweeter and will require more work from the amplifier than the tweeter will. So it's not accurate at all to say that "even though" the XO is now seperated that the amps are still working just as hard because it has to send a full range signal to the crossover.
Again, when did I say that the amp is under the same loads? I hate it when people put words into my mouth. I said repeatedly that the loads on each amp channel in a "fool's biamped" situation will be more than an amp on a passive or active biamp setup. I NEVER said that the loads of a "fool's biamped" system would be the same as when the amp was powering both drivers. However, the amp channels are working harder in the "fool's" setup than the active or passive setup because they are always going to be pushing a full range signal which will have to be sifted through at some point(the internal crossover), instead of just pushing a constant signal along the path. Now when you say that the drivers are "separated" from each other when you remove the shorting strap from the crossover, you do know that the drivers themselves are still connected to some sort of crossover, right? So while you are driving the tweeter, midrange and woofer "seperately," they are still connected to some sort of crossover inside the speaker. The path is not a clear path from amp to speaker wire to binding posts to driver, like in passive and active biamping. As for Brett, I think that you have posted rebuttals to statements that I NEVER made, statements that you guessed I would have said but nonetheless I NEVER wrote (or even thought, for that matter). This is a very bad habit in the HTF and in life, so it might be best to only post replies to statements and phrases instead of conjecture and assumption. Now, on a personal note, I have tried active, passive, and fool's biamping as well as biwiring on a myriad of speakers (B&W, AAD, Revel, KEF, Paradigm) using a myriad of amps (McIntosh, Krell, Adcom, Rotel, B&K, Anthem, Odyssey), and for the most part have found that with enough power, and a good set of speaker wire and jumpers, just using a single two-channel amp provided the best sound for my tastes. More often than not, I found that in the fool's biamp setup, the most noticeable improvment in sound was more to do with the amount of total power as opposed to the removal of the shorting strap or jumper and the use of another amp. As always, I will try to urge anyone to try it first, but it helps to exactly why one would try something new. The whole idea of Biamping is to help the amps as much as possible so that they can pass along the best possible signal to the speaker. However, simply passing along the signal doesnt take into account baffle alignment, driver deising, crossover points, phase shifts, or any other speaker-related issues any more than it takes into acount room treatment, listening position, or frequency holes. I believe that it just helps to know specifically WHY something should be done before actually doing it for experiment's sake.

#26 of 66 OFFLINE   Michael R Price

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Posted June 19 2003 - 12:24 PM

Passive bi-amping improves sound mainly by reducing the current demands on the high frequency amplifier. However, active bi-amping will improve sound even more because the amplifier only amplifies the intended signal and nothing else (that would be filtered by a passive crossover), so the intermodulation distortion and any voltage swing related compression will be reduced. But it's important that the active crossover keep the same frequency response as the passive one... which can be difficult.

#27 of 66 OFFLINE   Chu Gai

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Posted June 19 2003 - 01:08 PM

difficult? perhaps next to impossible considering the monumental task of 1st matching what the engineers made then 2nd improving upon it. IMHO, it you want to actively biamp, buy it that way. so Jigesh, whatcha gonna do?

#28 of 66 OFFLINE   Jonathan M

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Posted June 19 2003 - 03:26 PM

There seems to be quite a bit of mis-information here, so I'll try and help clear some things up. In a passive bi-amp setup, where one is using the internal (passive) crossovers on a speaker with the various sections separated (ie any plates removed) then one has one amp powering the lowpass xover inputs, and one powering the highpass xover inputs. The LOAD on each of these amps is LESS than the load present if one of the amps was driving both xover inputs in parallel (As is the case in a normal single amp situation.) WHY? Because the impedance of the tweeter+highpass network is high at low frequencys - there is a capacitor in series (and perhaps an inductor in parallel) with basically a resistive device (The driver) in the below 1kHz range. This presents a very high impedance which is very easy to drive - the current involved is minimal. Thus the amp is under less stress. It has higher current reserves for the highs (Which it doesn't need much for anyway as Chu indicates above). What about the lows? The impedance of the woofer plus any series inductors and parallelled caps rises at frequencies above the xover point. Thus, the load the amp must supply current to is reduced. Note that it is not reduced all that much as the power content of high frequencies is very low. Thus, one does not see the same advantages as for the tweeter amp. What's the benefit of active biamping (possibly using a passive xover before the amps)? This has the further effect in that the amp is no longer amplifying any signals outside of the small(ish) passband that the particular driver it is supplying is operating over. Thus one achieves all the benefits of the above PLUS the added benefit that there is no xover network between the amp and the speaker. This means that ALL the power that the amp is producing is used to drive the speaker. None get's wasted away through heat via the inductors and resistors etc. in the xover network. One sees benefits here for the amp supplying the lows as there is no series inductance which has an inevitable loss of efficiency due to the DCR of the inductor. Efficiency is also increased in the amp supplying the highs as there is no series resistance involved (Usually used in passive xovers to decrease the level of the tweeter to that of the woofer). As has been indicated above by other posters, any active setup has to be well designed from the beginning. I strongly suggest you learn something about speaker design before attempting anything of this nature. There's no point throwing money at something in hopes of improving it if you don't understand how things work - this is a waste of time and money and is why so many charlatans exist in this industry. So what's the answer? YES, it IS possible to increase the quality of sound in this fashion. Any improvements will come in the highs mainly - note that you can use a lower powered amp on the highs in this case. Will you HEAR any difference? Try it and see. (Yes, I wussed out).
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#29 of 66 OFFLINE   Greg_R

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Posted June 19 2003 - 03:41 PM

Quote:
So while you are driving the tweeter, midrange and woofer "separately," they are still connected to some sort of crossover inside the speaker.
Are you claiming that the HPF and LPF sections of the crossover share the same input, even after the external straps have been removed? In my experience this has not been the case. However, I feel that biamping with passive crossovers is not beneficial when compared to a single large amp, assuming the same amps for biamping!. Hooking up two completely different amps will obviously result in a different sound (gain stages are probably mismatched, etc.). I agree with Chu that hooking up two of the same amps in a passive bi-amp config will result in the same sound as using each amp in a monoblock conifg (i.e. using a more powerful amp). IMO, Active crossovers are only beneficial if the speaker was designed with that in mind (and includes the active crossover). For example, Paradigm's Active 40s (custom amps and active crossovers) was a clear step above their studio line...

#30 of 66 OFFLINE   Michael R Price

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Posted June 19 2003 - 05:07 PM

Thanks for clarifying Jonathan, you seem to really know what you're talking about. I think that because of the intermodulation distortion in the amplifiers (Chu rolls his eyes Posted Image), bi-amping can help (cleaned up highs for me, except I didn't have a good enough bass amp so I had to go back). Also, it can give more headroom to bi-amp than to simply use an amplifier of twice the power rating... the sum of the wave amplitudes with momentary peaks can be double what it was before, that's in theory up to 3db more headroom than a double-power amp with 40% higher voltage rails.



And yes, mirroring a passive network's response is really hard. I'll be trying, soon, to get it "close enough" actively with my speakers. Steep filters and nice linear/accurate drivers help, except mine are iffy.

#31 of 66 OFFLINE   Craig_Kg

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Posted June 19 2003 - 07:02 PM

Quote:
Posted by TylerR Baucause, unless I'm misreading, you are suggesting that all multiple channel amps without mulitple seperate ps's will not make more power with 4 channels driven as opposed to 2 channels. This simply isn't the case...
If you feed the same source signal into the 4 channels as you do for the 2 channels and "fool's biamp" them across a pair of stereo speakers, then where is the advantage in power coming from? Each amp section receives the same rail voltage (as the power supply is common) so output will be identical whether 2 or 4 channels are used. If the power supply saturates, then the rail voltage will sag and power will drop in either case - there is no increase in headroom.
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#32 of 66 OFFLINE   RichardHOS

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Posted June 19 2003 - 07:03 PM

In some cases, others have already done the work involved with modeling the factory passive crossover network as an active network.



And, with a little understanding, you can recognize compromises made in the factory crossover due simply to the values of components available for a reasonable price. It's not always difficult to improve on what the factory did. But, even if sticking with the factory slopes/points, going from passive to active crossovers doesn't have to be a three year government funded research project! Posted Image



It would help to have access to knowledgeable people on forums like this though. Posted Image

#33 of 66 OFFLINE   Chu Gai

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Posted June 19 2003 - 08:29 PM

that'd be one hell of a challenge let alone expense to even match a good crossover using active components don't you think?

#34 of 66 OFFLINE   Brett DiMichele

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Posted June 19 2003 - 08:58 PM

I just personaly feel that this term "Fools BiAmping" should be applied to Active Bi Ampification. Because only a Fool would take a prebuilt speaker and throw an active crossover in the mix. Unless your name is Likwitz I doubt you have the skills to do it correctly (I am not pointing at anyone in particular, just a general rambling). And I stick by what I said Chu, sure the amp is being feed a full range signal and yes it is amplifying said signal but if the ampifier is only feeding say one midrange and one tweeter it has a much easier load than if it was feeding a woofer a midrange and a tweeter. Bi Amplification (call it passive or active or whatever) has worked wonders for my system not only due to more head room available but the ability to run Tubes on the Mids and Highs and Solid State on the lows.. Absolutely wonderful!
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#35 of 66 OFFLINE   Brett DiMichele

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Posted June 20 2003 - 01:53 AM

Quote:
Brett, I know that an active crossover does none of these things, but at which point did I say that active biamping would take all these factors into account? Many times, especially with well designed speakers (Paradigm, B&W, Revel, Dynaudio) the internal crossover is far more favorable than an external crossover, as it has had months (maybe even years) or R&D put into its design and its implementation with the specific drivers that it is paired up with.
The point is that you gave information about Active Crossover implementation but chose not to point out the issues that Active Crossovers do not take into account. A crossover isn't guesswork and doesn't take "years" to develop. With the right equipment and software which any speaker company surely has, designing a passive crossover is relatively simple. It's all based in measurements and electrical theory so anyone with the knowledge and the equipment can do this. I guess the bigger issue is the materials used, most speaker companies skimp on the components used. I would love to see the Crossover Boards from a Dynaudio or Revel. I doubt they use better materials than any other prebuilt speaker. Some would say that you can't hear a difference between capacitors and that may or may not be true but if you are shelling out thousands for a pair of speakers they should at least use the very esoteric components to put one's mind at ease.
Quote:
Again, when did I say that the amp is under the same loads? I hate it when people put words into my mouth. I said repeatedly that the loads on each amp channel in a "fool's biamped" situation will be more than an amp on a passive or active biamp setup. I NEVER said that the loads of a "fool's biamped" system would be the same as when the amp was powering both drivers. However, the amp channels are working harder in the "fool's" setup than the active or passive setup because they are always going to be pushing a full range signal which will have to be sifted through at some point(the internal crossover), instead of just pushing a constant signal along the path.
I disagree that the amp is working "harder". I believe that even though the amp is still working with a full range signal it has less impedance per section of the crossover to deal with and the load is much easier for any amo to drive.
Quote:
Now when you say that the drivers are "separated" from each other when you remove the shorting strap from the crossover, you do know that the drivers themselves are still connected to some sort of crossover, right? So while you are driving the tweeter, midrange and woofer "seperately," they are still connected to some sort of crossover inside the speaker. The path is not a clear path from amp to speaker wire to binding posts to driver, like in passive and active biamping.
I am fully aware of how a crossover works, how it is implemented in a Bi Amp design and how Active approaches work. What I said was that in a true Bi Amp Passive XO network you have 2 completely seperated networks. For example my Bi Amp Crossovers have 4 Seperate Inputs at the Network. Two of those inputs feed my LF Section wich routes through an iron core inductor and capacitors then into the 10" Sub Woofer (Highpass = 100Hz). The other Two inputs feed through a Zobel and appropriate Inductors, caps and resistors and then go to the Tweeter and dual Midrange. (Mid Highpass is 3.5Khz) In my setup when I run one amp into all 4 posts I am driving one hell of a load.. You have 2 8Ohm Subs that dip as low as 2 Ohm on thier own impedance curves, add to that a pair of Mids that also have broad impedance curves and you have a hard to drive load. Remove the shorting staps and you can now run an amp to the subs and another to just drive the Midrange and Tweeters. This is a far easier load for most amps to run and you will have more headroom also. My setup is also semi Active in that the amp I drive the subs with also has it's own Highpass variable filter so that my sub amp is only generating 15Hz to 120Hz (max) signal. The Mid/High amps are running full range since I am running from a 2Ch Pre. But if you were running them off a Reciever's Pre Outs you could easily kick in the Recievers Crossover and this too would be "active" since the Pre would only send out information from say 80Hz up to 20Khz or where ever you set the Lowpass. I am sorry you took my posts so personal and in return said that I put words in your mouth. I merly provided the information that you didn't provide. We want others to make educated decisions from all of the facts not just some of the facts. And I honestly wish you would drop the "Fools BiAmp" terminology. Because IMHO only a fool would remove a passive XO network and replace it with Active's not fully understanding the Advantages/Disadvantages of both. As always: YMMV IMHO AFAIK and all of that stuff!
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#36 of 66 OFFLINE   Jigesh Patel

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Posted June 20 2003 - 05:47 AM

Thanks a lot, everybody...! Too much knowledge to digest over the coming weekend! This was my first post on this forum and as you could already see, I am a novice in the HT area. I appreciate everybody's time and painstaking care for the details in replies; and a very healthy debate.



It occurs to me that since I am already using a 200w per channel (multi-mono design) amplifier (Sherbourn 5/5210) to drive my speakers, I might get more improvement by replacing the receiver with a prepro than by adding two channels to biamp passively as I suggested earlier.



Anyway, in case I still happen to experiment with passive biamping, I will be happy to post my results here. Have a nice weekend everybody!



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#37 of 66 OFFLINE   RichardHOS

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Posted June 20 2003 - 06:39 AM

Chu:

Quote:






that'd be one hell of a challenge let alone expense to even match a good crossover using active components don't you think?






One example: http://home.attbi.co.../Magnepan36.htm



Total cost of active version of this crossover for two channels is probably less than $50, even using high quality components.





Brette - the best passive crossovers have unavoidable issues with level matching (burning off power in resistive padding), higher amplifier loading (due to increased impedance seen by output section), temperature induced drift, component tolerance, available component values at reasonable prices (for example, high quality and high value capacitors that might be "ideal"), degradation over time, etc.



Any passive network can be emulated by an active network (AFAIK), with relatively large gains in effective power output (100W total per channel in active biamping is equivalent to 200W total per channel in single amplifier setup), reduced intermodulation distortion, increased dynamic headroom, closer tolerance from channel to channel, no temperature drift, easier level matching, etc.



Of course, nirvana (for me) will be when all sources are using a standardized digital connection (unlike DVD-A and SACD now), such as 1394, allowing all crossovers to be done in the digital realm. Then, emulating the transfer fuction of a passive network is a trivial task.

#38 of 66 OFFLINE   Brett DiMichele

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Posted June 20 2003 - 08:41 AM

Richard, Ok how to you rework an active solution that can take into account Baffle Step, Lobing, Comb Filtering and numerous other specific issues that the OEM Passives ARE engineered to combat? There is absolutely NO question that Passive networks are horrible by design.. Active is most definaty an "Ideal" setup. But I don't see how you can just rip the passive out and stick an Active in it's place without fudging the way the speakers work.. Show me a way to do it with my mains, I have the amps.. I will buy the active components tomorrow...
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#39 of 66 OFFLINE   Michael R Price

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Posted June 20 2003 - 09:53 AM

Well, let's see, to replace the 4th order passive 2-way crossover in my Kit281s, I'll put a notch filter on the woofer to take out the breakup peak, put a passive zobel on the tweeter. The active section will use 4th order filters, and apply a shelving filter of 3-6db for baffle step. The response won't be the same, but it will probably be close since my speakers don't have much significant EQ going on... and I can always add filters to change the response to my liking. I may have to experiment with baffle modification to get the treble response flatter without the impedance interactions of the passive crossover. Either way it's cheap, fun to try, and I can always go back to the passive filters. Now, if only I could get these doggone amplifiers working again...

#40 of 66 OFFLINE   Brett DiMichele

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Posted June 20 2003 - 10:00 AM

Mike,



That's all well and good for experiments sake.. But it

seems like any time "I" even mention crossover mods I get

smacked upside the head "What are you, Crazy?" Posted Image



Good luck.
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