Conference napalm::guitar

    
    Bi-amping is similar to what's done with a PA system (bi-amped,
    tri-amped, quad-amped) whereas you can extend your range of frequencies
    by using a multi-amp system. Bi amp means two amps... one for
    the high freqs and one for the lows. Low frequencies can ony be
    reproduced efficiency by a 15" or an 18" speaker. These freqs also
    need more power to pump them out, thus a 200Wt - 600WT amp is needed.
    The higher frequencies don't need as much power to be reproduced,
    so you'd need an amp ranging from 100WT - 250WTs to drive 10" or
    12" speakers.  A Crossover determines where in the freq range you
    want to `split' your sound to either the low freq cab or the high
    freq cabinet.
    
    The pros are, say for a bassist, that he/she can get more power,
    better tonal response and a cleaner sound. The only disadvantage
    I can think of is cost and portability.
    
    It really is the only way for the serious audiophile.
    
    wjb

	But can't the same thing be accomplished by driving both the
	10"-12" and the 15"-18" with the same amp??

    Bi-amping is a method of dividing up your full range signal
    so that you can send just the frequencies you want to the
    component that is best suited for them (i.e., your highs -and
    only the highs-go to a horn or tweeter, and the bass/midrange
    -and only bass/midrange-go to your woofers). You've probably
    been told this a million times, but it's that simple. 
    The 'crossover' that does this magic is either passive (like
    in most home stereo speakers) or active, but they are a combination
    of "high pass" and "loss pass" filters. The technical heads will
    explain this in much more detail, I'm sure, but as I feel qualified
    to explain this 'cause I'm not very technical but have played with
    all the permutations of crossovers in my many years as a sound system
    'putter-together-er'.
    I expect you mean in the context of guitar/bass use when you ask
    'what are the advantages'. The biggest advantage is in the high
    end of the sound. Woofers can certainly handle the high frequencies
    (although they get muddled sounding due to the hugh excusions of
    the woofer), but you never really get acurate reproduction of said
    'highs'. So, if you have this frequency-dividing network (crossover)
    that filters the highs, you can send them to a component that more
    acurately reproduces them (tweeter, horn, small speakers, piezo's
    etc.). This will also clean up the bass because the large speaker
    has a much simpler job to do!
    It the context of guitar cabinets, I've felt this treatment makes
    for a harsh sound. We've gotten use to the natural 'cut off' of
    12" or 15" speakers (no real highs). But for bass guitar, I would
    highly recommend some bi-amping set up. I thinks somthing on the
    order of an 18" or two 15" speakers for the lows, and 10" for the
    "highs" (they aren't very high, obviously, so a small speaker can
    do the trick). A lot of newer bass heads come with a crossover
    network built in, which is great (some even have two amplifiers
    so you can power the two signals separately). You can also buy
    pre-amps to do this, or buy a crossover network (they come in
    2 way, 3 way mono, etc). You would probably need the so called
    'active' electronic crossover, which has a selectable cross-
    over frequency (for bass I'd guess in the 800 Hz to 1000 Hz
    range, a bass player will know for sure). Passive crossovers
    usually are fixed in what frequency they crossover at, and are
    usually limited in how much power they can handle (I recently
    went crazy looking for somthing that could handle 100 watts).
    This is a very simplified start of an explanation...You may want
    to go into detail on what you are thinking of using bi-amping
    for (obviously..it is a must for PA use if you want any efficiency
    at all!).
    
    Pat
    

There are more reasons for bi-amping, particularly in high-octane PA's.

Building a crossover robust enough to 'steer' several hundred watts
between woofers and tweeters is no mean feat.  Bi-amping allows the
crossover to deal with line level (~1 volt) signals.  Then, crossover
components don't have to handle the extra power (and use lots of it
to generate heat instead of noise).  High power wire-wound resistors
aren't cheap.

It's also more polite to speakers.  When amps are overdriven, they send
out high frequency spikes that can damage speakers.  Tweeters, with small
voice coils and teeny-tiny wires, are most easily fried.  Most of the
power DEMAND in PA's is on the bass.  If most of the clipping can be
confined to the bass amp/speaker, the tweeters can live longer.

It allows a mix 'n match approach to designing the PA system.  Less
efficient, mondo bass cabinets can be paired with extremely efficient,
horns for the mids and treble.  Bi-amping allows the use of level
matching BEFORE the amp rather than power-soaks AFTER.

Finally, it's sexy.  "...we're so hot we need FOUR amps just to get
STEREO..."

Enjoy,
Dave

	More questions from the uninitiated.  What do you mean by
	"clipping"?  

	Also, when bi-amping.  If I have a set-up with a primary
	amp (with crossover) whose low-end is connected to a 15"
	speaker, and whose high-end is connected to a second amp
	with 2 8" speakers, does the impedance of the 15" affect 
	the second amp (and/or does the impedance of the 8"s affect
	the primary amp or are they mutually exclusive)?  In other
	words, if the primary amp requires a 4 ohm impedance,
	would the 15" speaker be 4 ohms (or would it be something
	other than 4 because it's in series or parallel with the
	2 8"s.)?

    
    Clipping is distortion. Ie - when a sine wave turns into a square
    wave, etc etc.         
    

Unless I misundertake your question, you shouldn't have impedance
problems with INTERACTION between the two amps.

Crossover low out goes to the bass amp.
The bass amp outs go to the bass speaker.

Crossover high out goes to the high amp.
The high amp outs go the the midrange/tweeter.

The bass amp outs and high amp outs don't ever join back-up do they?
It may be interesting, even fun, but it wouldn't be wise.

Enjoy,
Dave

    Re-.4 Passive cross-overs consist of coils and capacitors. Resistors
    are incorporated if a pad (attenuator), or impedance matching is
    needed, but decreases efficiency. Also, if an amp is driven to square
    waves, the DC component can only pass through the coil of a passive
    cross-over, which is in series with the low frequency spkr. The
    capacitor will effectively block the DC to the tweeters or horns
    and save them. 
    	When a passive crossover system, (15" spkr + horn), is really cranking,
    the power needed by the 15" sucks up most of the power and the horns
    tend to crap out a bit. High power cross-overs can help minimize
    this, but can be just as expensive as bi-amping.
    
    Neal
    
    
    	 

    

	Thanks for the info.  It's been informative and very helpful.

		Tom

    
    	I use a bi-amped setup for bass.  It takes a lot of tweaking
    to get a great sound.  One nit I have is that, unless the high-end
    cabinet is sidefilling the stage, the rest of the band tends to
    hear only the rumble of the low end.  Even as the sound is killer
    from where I'm standing, the drummer complains that he can't hear
    the 'definition'.   
    
	Sorta the same problem you have with those Marshall 4-12" cabs where
    standing 3-4 feet to the side makes them almost completely dissapear
    in a stage mix.
    

    Your problem is caused by the inherent directionality of higher
    frequencies.If you've noticed,you can here the low end almost anywhere
    --even behind the cabinet (assuming your rig is on par with the
    rest of the band's equipment).The simplest and probably most practical
    fix for the problem is using 2 hi-end cabinets and aiming one for
    yourself and another angled across the studio or stage for the other
    band members.If cash flow is a problem, you can probably get by
    moving your setup more towards the rear of the room--maybe 1-2'
    behind the drummer's seat (but not behind his head unless you're
    into s+m!).This will allow you to make maximum use of the hi-end
    cabinet's dispersion pattern--almost like sawing off shotgun's 
    barrel.I'm not only too stingy to shell out for another 2-10'
    cabinet;I'm also a concientious objector to any unnecessary
    physical labor (for example-lugging another cabinet) so that
    this method is the one I've been using. Anyhoo--please give 
    me an ack or a nack if you try either suggestion, if for no 
    other reason; I'll at least get the satisfaction of knowing
    that typing this reply was of some use to somebody!
    (even ^p or or abbreviated commands are my private HELL!!!!!)
     
            good luck and may your strings never break,
                                                 Bill
    

    Stevie K has left the company, so you may not get an answer
    
    /rick

    thanx Rick, i was really just wondering if anyone reads these older
    topics !!!!!!!