 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
64.109.157.130
In Reply to: You don't know what you're talking about posted by mbnx01 on February 21, 2007 at 07:12:23:
so it's called "passive bi-amping". I still don't see any compelling reason for doing it this way. In your set-up, each channel (mono amplifier/speaker driver) sees the full signal, so the advantage of splitting the signal with an electronic crossover (thus limiting the bandwidth that the amp must handle) is lost. Also, since a y-connector is used, the imput impedance seen by the preamp feeding the amps is effectively halved, also not desirable.A further disadvantage is that the amps must still work through the passive crossover network in the speaker, with its large-value inductors and capacitors that are often responsible for phase shifts and roller-coaster impedance curves. Needless to say, with an electronic crossover, these problems are side-stepped.
I see no advantages to "passive bi-amping", other than the cost savings of not having to buy an electronic crossover. Why not go "all the way" and do it right, especially since the extra stereo amp has already been purchased? Is there some objection to using an electronic crossover? Please enlighten someone who "doesn't know what he's talking about".
Follow Ups:
Although I agree that for the full benefit there is need to use electronic crossover thus directly coupling amps to the driver(s), there IS benefit to the biamping.First I believe my ears, and they say that there is noticeable improvement, in respect to the biamping, usually in a better bass definition & depth, smoother top end and midrange, and easier presentation overall.
We can speculate why but IMHO benefit is to great extend due to the significant reduction of the woofer coil movement induced negative affect on the "tweeter" amp, and possibly reduction of the tweeter impedance related issued on the "bass" amp.
Also, any decent preamp should have no problems driving two amps, unless both amps have unusually low input impedance in combination with preamp's high output impedance. (but that comes in to "system matching" category.)
And finally, IMHO, active biamping with cheap active crossover may actually sound worse than passive biamping.
Considering cost of good active crosover, pasive biamping is viable option and definitively great intermediate step for those who go all the way.
At one stage I was passively biamping my Maggie IIIas. This was better than when I single-amped them but not as good as when I went 3-way active! :-))I wonder how good cheap digital (generally pro) XOs like Rane, Behringer really are in terms of sound? Yes they have a lot of flexibility in terms of twiddling knobs to change slopes and corner frequencies (which my analogue XO doesn't have! :-(( ) but do they sound as good as a top-flight analogue XO??
Not many people have made a direct comparison!
Regards,
Andy
Hey ANdy,I know it is not the cheap pro crossovers, but there is a poster who has compared a digital crossover (PC based) directly with his passives and his Marchand crossover. And he prefered the pc based crossover.
www.thuneau.com is where the crossover can be downloaded.
Here is the post
- http://db.audioasylum.com/cgi/m.mpl?forum=pcaudio&n=16422&highlight=marchand&r=&session= (Open in New Window)
as it contains sub-standard DACs that color the sound. Unless, of course, you attempt some major mods, as a few people have done and documented (Thorsten Loesch, for example).
Thanks for this advice. I will continue to look into active crossover options on the market (this afternoon I found one for $85, which I would think would land it in the potentially harmful "cheap" category, and one for $2,400 (Bryston), which I know lands it in the "absolutely out of the friggin' question" category). I have a feeling, given your advice, that I will remain passivly crossed over(?).
the premium version--in kit form, under $400 (see link).
I fully agree with C.B.
Why not adding this further step ? Add an electronic crossover to your setup, christopher, and you will get the maximum.Besides, active bi-amping could be easily implemented with just a single smart component without compromise solutions (www.firenzeaudio.com/rosso460B.htm)
Well, two arguments against the electronic crossover: (not saying it wouldn't be worth doing, but...)1. If the argument is against the signal going through one or two passive components, what do you think is inside an electronic crossover? I'm holding one in my hand right now, with the cover off it. Let's see: 37 resistors, 4 trim pots, 6 potentiometers, 14 film caps, 6 electrolytics, 6 opamps, well 12 really, they're dual opamps (ok, those are active), 9 non-rectifying signal diodes (also active), and yet another complete power supply to make sure is good enough to not interefere with the signal. Oh yes, and 6 more sets of connectors.
2. Unless you know your speaker's crossover REALLY well, are you sure the active crossover you choose can duplicate the crossover points, slopes, notch filters, polarity shifts, zobels, etc. built into the carefully designed passive crossover inside the speaker? (this is of course assuming we are talking about decent speakers) For instance: Most people know that a Thiel speaker uses first-order crossovers. How many of you guys have seen a Thiel crossover? It may be first order, but I can promise you there are many more components on that board than can account for a first-order network on each driver. That crossover has been carefully gone through and tweaked and notch-filtered and zobeled, etc. to make sure those drivers work together exactly as intended. Now, it very well may be possible to do that with a really nice active crossover, but I'll bet it even has more "stuff" inside it than the one I was looking at a second ago. I'm no fool when it comes to electronics and acoustics, BUT, by the time i reverse engineered something as complex as a Thiel, or Clements (also first-order), or a vintage KEF crossover, and figured out how to exactly duplicate that setup with an electronic crossover, I could've spent a LOT more time listening to music through crossovers built by people that know a LOT more about crossover building than I do.
Just something to think about guys,
BT
The component count in a piece of gear is a completely bogus argument--your preamp, power amp, CD player and tuner contain far more components than any electronic crossover. Does that mean you should eliminate them?Obviously not. The point here is that the RC circuits of a quality electronic xover contain much smaller value capacitors (note that there are typically NO inductors), as compared to the much larger value components in a typical passive xover network. The gain stages of a typical electronic xover (IC op-amp or tube-based) do a much better job of driving their associated small-value xover networks than the typical power amp does driving its large-value passive xover. Better transient response, fewer unpredictable phase shifts and response anomalies, etc. In a nutshell, better sound.
Yes, this is all predicated on driving the individual speaker drivers directly, something I neglected to mention before (in the interest of brevity), but which should be obvious. Yes, bypassing the passive xover in a multi-driver dynamic speaker such as the brands you mention is a risky proposition, for the reasons you mention, and I probably wouldn't attempt it myself. Active bi-amping with an electric xover is much more successful with planar speakers that don't need response tailoring, such as Newform Research (which I own) or Magnapan, as somebody has already pointed out.
I think you must pay attention to the inductances of a passive xover. You can find easily ohmic values of tens of ohm. If you have, for example, a 4 ohm speaker with a 0.1 ohm resistor placed in series, you will get a DF worse of 4/0.1=40 whenever amp you use, so with a passive crossover let's forget the DF=4000 of Nuforce...
Ops...I meant few tens of mohm (milli-ohm) not tens of ohm...
Hi C.B.I don't think the component count point is bogus at all. In a way, you kind of make my point for me. If using all those 'passive' components is such a bad thing, my point is that even an active crossover adds many passive components to the signal path, smaller part values or no. Also, getting rid of the tuner, CD player, preamp, poweramp is a moot point, you must at least have a source, and something to apply enough gain to that source to drive some sort of transducer.
My way of thinking is this, the simpler something can be, the better. I personally don't do this, but a lot of people DO eliminate their preamp, simply to get as many things as possible out of the signal path, and simply use a selector switch, and some kind of attenuator as a "preamp" (I'm sure you know this, but not everyone reading might).
And, actually, my preamp (my design) only has 1 opamp (well, 2, it's a dual), 10 capacitors (would be less if some weren't bypassed), 5 resistors - and that's counting the volume pot, and 1 selector switch. I didn't include power supply parts in the active XO count, so I leave those out of this count. They are about the same anyway.
Why so few resistors? To me, resistor noise is MUCH easier to hear than when compared to just about any other component. So, back to our active crossover, which added SIX more potentiometers to the mix, and by the looks of each pot's function, at least 4 of those, probably 5, are directly in the signal path. That worries me more than an inductor. In my entire system, front to back, there's only one potentiometer, period. Also, that one pot is definitely of the "not suck" variety, I just hope my wife doesn't find out how much it cost! :)
I've taken similar steps to make sure there are as few items in the signal path as can safely be done away with in other parts of my system as well, but I need to learn more about power amp design to really be able to effectively un-clutter things.
Now back to our active crossover - who's to say the designer of said active crossover wasn't paying attention, and part of their circuit inverts its part of the signal? I'm not talking about phase shift, I'm talking totally inverted polarity. It evidently is a fairly easy mistake to make, as it's my understanding that most CD players actually invert polarity. I recently found out mine does, when I aquired a preamp that has a polarity switch (It's a big enough difference I'm going back and adding a polarity invert switch to my normal preamp). The CD player isn't some thrown-together piece of junk either. It's older, yes, but in it's day it was very highly regarded, and it still holds its own compared to a lot of modern offerings.
Also, if you need the gain of an active XO to get the transient response you need, I would suggest there's something REALLY wrong upstream.
Then again, you have made me curious enough to at least look into it. Now I wish I still had that pair of Magnepan MG IIIa's. They would've been a lot easier to experiment with.
Now, the active XO design I would want to try, does one exist that:
1. has unity gain.
2. crossover point, slope, and relative volume level to the other drivers is set by individual fixed resistors and caps in the circuit that can be adjusted by plugging in, such as can be done with a lot of phono preamps to tailor the response of the cartridge to the preamp.
3. that the circuit designer not only closely paid attention to phase (time alignment), but making sure no part of the signal has its polarity inverted.
4. has all of the above.
5. has all of the above with the most efficient number of components as possible.Hmmm, now you've got what's left of my brain churning...
...lemme go find my stack of opamp data sheets, if someone already builds something like the above, let me know, otherwise, I just might build one...
...anyone in the Atlanta area got a spare pair of Maggies I can play with?
BT
It's all very interesting, if a bit over my head! I'll definitely look into the electronic crossover option. Thanks for the info, everyone!
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
