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Bi-Amping in High Power Environments

Discussion in 'Amps and Cabs [BG]' started by bgavin, May 8, 2001.


  1. Anybody out there bi-amping with a high powered environment?

    I'm curious what the *correct* setup is concerning preamp, electronic crossover and a pair of power heads.

    My reason for asking is that passive crossover networks capable of dealing with 1000w and higher will be difficult and/or expensive to come by. The capacitors alone are $31 each, and I need more than half a dozen for each of two cabinets.

    It seems to be cheaper and more flexible to bi-amp the bass drivers and mid-ranges separately, and do the frequency division in the low power preamp stage.
     
  2. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, again. I'm not sure if I understand your question, but here goes... If you split the signals after the power stage (via a passive crossover to the speaker drivers), you need a high-power-rated crossover, as you said. To get higher-order filters involves considerable expense, particularly at low crossover frequencies. This is why, IMO, professional sound reinforcement people use bi-amping and tri-amping. They split the signal ahead of the power amplification, because it can be done much more effectively.

    The bi-amping built into my Carvin heads is done at the line/preamp signal level (after the initial instrument buffering stage) - probably about the level of the effects send/return loop. So I agree with your conclusion about doing it at that stage.

    Given your technical knowledge, I will now give you something else to consider: IMO, bi-amping for bass applications leaves a lot to be desired. I would rather see amplifiers set up such that the "low" channel is simply a variable low-pass, and the "high" channel is a variable high-pass. So, in each case, if the crossover freq. could be varied between 50 Hz. -1 kHz, then one could choose to run the amps with some overlapping frequencies (desirable for many speaker configurations). In my case, I'd feed my 2x15 + tweeter with full range (or at least have it low-pass up to 1 kHz.) and my 2x10 + tweeter with 100-150 Hz. on up. The overlap ensures both amps are providing juice in the most important (common) frequency range.

    - Mike
     
  3. My experiencing with bi-amping is zilch, which is why I posted this question.

    A 5-string bass (or more) is a full blown bitch to reproduce with any accuracy. The fundamentals start at 31 Hz or 23 Hz (low F#!!) and the harmonics extend to 5 KHz or higher. The bass amp speakers should produce close to the same volume in the lows as it does in the highs, or it will sound anemic. A speaker that produces sufficient volume with 0.031" cone movement at upper B has to move a whopping 0.500" to produce the same SPL two octaves down at low B.

    These requirements left me with the choice using a Bag End ELF subwoofer, or rolling my own. I rolled my own, and got everything I wanted in bass response: flat response all the way down, very long cone excursion, and fabulous crushing lows. But damn... these things are HUNGRY. One cab takes everything my SWR 750 will give it without farting at all.

    Absolutely correct. My bass drivers are all done at 200 Hz, so I will cross over here with a 24 dB slope, which means a minimum of (4) caps and (4) inductors, separate from any impedance matching circuitry. At $31 each, these components get pricey in a hurry.

    I need to find a good pre-amp, then a good pre-amp stage cross over and direct the two signals to a pair of amps. What I'm not sure about yet, is if I can do Pre-Out from the SWR into the crossover, and route the highs back into the SWR power section, and route the lows to a separate power head such as a QCS.

    This would let me keep the SWR tone that I like, use 750w for the highs, and a big-boy QCS for the lows. The pre-stage crossover will be about the same cost as building my own 1,000w passive crossovers.
     
  4. leftybassdog

    leftybassdog Senior Supporting Member

    Wow talk about power! I use our sound system for the big lows, SWR 750 is mono and will work with the crossover, I would not use it like that , too much stuff to move. the SWR grand prix pre-amp would be your best bet with a good power amp. you will get the SWR sound and the power to boot in a rack that will be easy to move.also the crossover in the pre-amp will be less cables and jumpers,
     
  5. Amen to that. I stopped playing in the middle 70's cuz I was carting around a full sized Hammond C3, Leslie, and PA. Got sick of carrying the junk, so I played 5-string bluegrass banjo until this year, and doing bass now because it needs to be done.

    I was thinking I could hold onto the SWR 750 and use it as the preamp + power amp for the Highs, and add a 2nd amp for the Lows. Right now, the SWR runs in an SKB 6-space rack, and I have room for a rack crossover, etc.
     
  6. MikeyD

    MikeyD

    Sep 9, 2000
    I would bet your self-designed cabs sound great, and besides, they're *your baby*, but... you might want to think a bit about efficiency. Seems like you are about to go down the path of getting huge amps, and as I suggested in another thread, there's only so much you can really deliver, given that the ubiquitous 120v wall outlet can only do 1800 watts RMS continuous (15-amp circuit, and also assuming nothing else is on it!). Now, that's *input* power. Amps aren't 100% efficient, so depending on what you get, you might only be able to get half that level of continuous output to your speakers. Transient or short-term power response would be better, of course.

    That's what made me re-think speaker efficiency in my own rig. Anyway - if you do opt for more power, you will have to purchase another amplifier (and as you are indicating here) a crossover system. With that kind of money, you might be able to make good headway on a new speaker design that - if it were even 3 dB more efficient, would save you from having to double your amplifier output. Something to ponder. (Please also check out my other posts regarding "sensitivity" vs. "efficiency".)

    Hey, aren't you looking for another excuse to get designing speakers again?? :D With all the cool discussion going on in the other threads, maybe you could now design a cabinet with a slightly different approach, but get a bit more efficiency this time...?

    The other thing is, just because low B's fundamental is around 31 Hz. does not mean everyone needs to hear (more like feel) that frequency with flat response. The harmonics of it are more likely what people hear from most 10"-loaded cabinets when they say their cabinets are cranking out low B. I mean - I can "hear" low B clearly out of my Carvin 2x10, yet its frequency response starts dying at about 100 Hz.! Nevertheless, I'm with you on being true to the fundamental, within reason: I like "hi-fi", too, with deep bass extension. But the price of those low notes gets steep rather quickly, as you know. The guys who want the low F# (23 Hz. fundamental) must have a lot of money! And perhaps strong backs! I have found that my Eden 215 supplies plenty enough fundamental down to low B and sounds really good (I do boost the lowest band on my EQ a bit to get a flat overall response down there). It is rated at 103 dB @ 1w 1m, with basically flat response to 40 Hz., according to Eden. Claimed to handle 400 WRMS, one would expect around 129 dB at 1 m under full power. It is persuasive! And the cabinet is not that big/heavy. So... maybe you can design something along that line, but maybe flat to 30-35 Hz., but maybe just a bit less efficient than the Eden.

    - Mike
     
  7. MikeyD

    MikeyD

    Sep 9, 2000
    I also note that you are California. Why not help out your neighbors and make better use of the limited electrons available there? ;)
    - Mike
     
  8. I'm sorry, it's late and I'm dead tired.. that should be "half as loud" and not half power. Doh!
     
  9. Brad Johnson

    Brad Johnson Commercial User

    Mar 8, 2000
    Gaithersburg, Md
    Boom Bass Cabinets, DR strings
    Originally posted by bgavin
    ...Absolutely correct. My bass drivers are all done at 200 Hz, so I will cross over here with a 24 dB slope, which means a minimum of (4) caps and (4) inductors, separate from any impedance matching circuitry. At $31 each, these components get pricey in a hurry.


    Is there a perceived advantage to going with a passive crossover?

    I need to find a good pre-amp, then a good pre-amp stage cross over and direct the two signals to a pair of amps. What I'm not sure about yet, is if I can do Pre-Out from the SWR into the crossover, and route the highs back into the SWR power section, and route the lows to a separate power head such as a QCS.

    Absolutely. It's probably the simplest way to do what you're talking about...if you "must" bi-amp. I used to tri-amp...I don't anymore.

    I seem to annoy some people with this question but I'll ask anyway:

    Is there no PA support?

    I'm not trying to discourage you from dragging around tons of s--- or getting lots of gear but I've yet to hear a rig used in a non-roadie situation that rivaled me playing through my 400w head into one D210XLT and sending that through a decent house system with subs and monitors. I've always been able to get waaaay too much bottom.

    While your frequency points are probably correct IME you can achieve massive low frequency response using a PA. As has been mentioned you don't need to be flat down to 31hz to hear a B string. An Elf system for a five is, IME, overkill but hey, maybe that's what you're going for:D

    This would let me keep the SWR tone that I like, use 750w for the highs, and a big-boy QCS for the lows. The pre-stage crossover will be about the same cost as building my own 1,000w passive crossovers. [/QUOTE]

    Chances are you aren't going to make a variable passive crossover. With a two band xover after the preamp stage, preferable with seperate xover points for each section you'll probably get the most flexible bi-amp results. As was mentioned already, you could run your low cabinet full range and run you high cabinet with a low frequency rolloff.

    Have fun. For me, full range works best;)
     
  10. Two points. First, I have tried biamping on a couple of occasions, but always go back to full range. I just find the fullrange sound to be more satisfying. I'm not sure why, it just seems fatter.
    Second, surely you dont want all those nasty fundamentals floating around the stage and muddying up the band's sound?
     
  11. Exactly the point why I am asking about bi-amping: I'm sure others have been down this road before me. As for muddying up the band's sound, I wonder if the mud is not from the fundamentals, but from poorly reproduced fundamentals amplified to crushing volume. For years, every band I've seen plays too damn loud and they sound like mushy crap. It is worse in the small venues I frequent.

    I play bars and the PA sux. They are overdriven into mush and the voice is lost in the roar. The argument "use the PA" is an often repeated mantra. Short of very large venues, I have yet to see a PA that can reproduce a bass cleanly, plus handle all the other chores forced on it. A 12" woofer and a horn just doesn't cut it.

    Yes, the harmonics of the B can be heard even if most of the fundamental is missing. One can also hear music over AM radio, or hear it on the telephone. Both methods provide restricted-range music, but both can still be heard.

    I'm curious as to your experiences about the downside of bi-amping. Agreed, ever-increasing amounts of gear are a pain to carry. I'm just kicking the tires right now for my own education.
     
  12. Brad Johnson

    Brad Johnson Commercial User

    Mar 8, 2000
    Gaithersburg, Md
    Boom Bass Cabinets, DR strings
    A speaker system with 12's isn't much of a PA. The smallest venues I play (think coffee house) doesn't require much in the way of amplification, period. When we get up to 100 and more people we hire a soundman who brings whatever's needed to comfortably give us the best sound. That may be 15" subs, double 15's, 18's, etc. Here in Maryland you'd be amazed at what some soundpeople are willing to bring out for $100-$200.

    Or I play with groups who have their own rig. Either way, for a good, full house and stage mix, a killer bass rig is not the way to go IMO.

    At the height of my big rig days I carried around a rack with:

    3 power amps
    3 way crossover
    bass preamp
    the other rack stuff that goes with the rack thing

    Then I had two 4' tall JBL4530 scoop cabinets for the bottom. Could I throw low end?...oh yeah, and it's not all it's cracked up to be.

    Then I had two custom 2-12 cabs for the mids.

    Used a couple of PA horns for the highs.

    What I realized was, while I could throw sound all over the place, that wasn't really what was important to me. Tone was and this rig didn't excite me as much as playing through a B-15. So, I sold my rig, as a PA, to a band;). It still cracks me up that I was willing to drag that stuff around, setting it up and breaking it down. I'd even use half of it in small bars.

    Having an amp that sounds great, for me, onstage and then rolling up the level on the PA to compliment it is what's worked best for me. My rig is so small and simple it really annoys drummers (one trip setups/breakdowns). I never really have to push it really hard which probably helps extend the life of my gear.

    Even most people I know who use seperate pre-amps and power amps don't bi-amp. With the popularity of high performance low to mid frequency drivers and the proliferation of horns and tweeters I get the sound I want, full range.

    Hey, I tried bi-amping and tri-amping, lost some money, learned a few things. If you're really curious, give it a shot. For the people who do it and love it, it's the perfect setup.

    I would have killed for the resources available nowadays on the web;)
     
  13. I got a note back from SWR tech support, and they say I can use the SWR 750 for bi-amping.

    The technique is to run the Pre Out into the crossover. Feed the crossover HIGHS back into the SWR 750 using the Effect Return. The crossover LOWS will go to a separate higher powered amplifier.

    Last night I scored a Rane MX22 crossover from eBay. It provides for individual control of the low and high output levels, and should make bi-amping a simple chore.