What is Bi-Amping, really?

Discussion in 'Amps and Cabs [BG]' started by Guiseppe, Nov 27, 2003.

  1. Guiseppe


    Oct 26, 2003
    Vancouver, WA
    OK...I've played for a long time, had a few axes and amps, but I never really have understood what bi-amping is, how a amp is set up to utilize it, and what it does. Can someone explain it for me?
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Biamping involves splitting the signal into two frequency bands BEFORE the power amplifiers. This is done with an electronic crossover. Some amps (like GK) have these internally.

    One way to use biamping is to send the very lows to a dedicated subwoofer type speaker and the low-mids on up to a regular bass cabinet. Another school of thought (like many Gallien-Krueger amps) is to split off the highs and have a dedicated power amp section in the amp for the tweeter only.

    Does that help?
  3. kirbywrx

    kirbywrx formerly James Hetfield

    Jul 27, 2000
    Melbourne, Australia.
    good explination :)

    Basically, you get take 2 frequencies (mabye even more) and send them to certain cabs. perhaps everything below 2KHZ goes to your 15 inch, and everything above goes to your 10's or tweeters :)
  4. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Bi-amping has one big practical advantage, which is that it protects your dinky 10" speakers. The idea is to send all the lows down to a big sub or something that sits on the ground. That's the one that needs a lot of power, 'cause it has to get the bass frequencies way out into the audience (and most of 'em travel through the ground). Then your small speakers go on top, those are the ones that get all the midrange and high end, and they basically push air out to the audience in the usual way, but if they're bi-amped they won't have to handle the extreme low frequencies at high power that makes those 10" speakers want to jump out of their sockets. Plus it frees the subs to do what they excel at, which is reproducing the very low frequencies (and maybe not the mids and highs). Bi-amps are cool, they add some tonal flexibility and they're also helpful when you have to play in places with a resonance, you can easily tune down the low frequencies and still get a balanced sound.
  5. pyrohr


    Aug 28, 2001
    Pakistani compound
    I seen it mentioned here that GK has the bi-amp operation. GK does not use a crossover to do this like some of the others, they use two different amplifiers, one is the main amp for the speakers in the cab and the other is a 50 watt amp that is dedicated to the horn. By doing it this way there is no way to distort the horn when you turn up the main volume. That means pushing the woofer to the max and the tweeter remaining clean and free from clipping distortion.
  6. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    They still (have to) use a crossover.
  7. pyrohr


    Aug 28, 2001
    Pakistani compound
    The woofer amp has a stand alone x-over while the tweeter amp has a hi-cut. The GK does not seperate the bass and the tweets via x-over. Meaning woofer amp does not affect the tweets and the tweet amp does not affect the woofers.
  8. Uh, what you're describing is a crossover. The frequency ranges going to each amp have to be split somehow. The only way it can be done is with the use of high cut and low cut filters. This is what a crossover does by definition.
  9. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    AFAIK that's still a crossover. Although most crossover are a combination of low- and hi-pass filters (maybe even a band-pass for the mids), just one of them already makes it a crossover.
  10. Technically, a crossover is a pair of filters: a high-pass, and a low-pass. The filter components are chosen to attenuate at a common (crossover) frequency. The design of the filter determines the rate of attenuation.

    Woofers use the low-pass filter to gradually roll off (attenuate) the signal as the frequency increases. Tweeters use the high-pass filter to block low frequencies and prevent damage.

    You can run the filter combinations as Low, High, or Low+High (crossover). Often, the woofer will receive full range and the tweeter has a high-pass capacitor protecting it. I believe this is how the Avatar design works, having never seen it.

    When you bi-amp, you are using an active (powered) electronic device as the crossover, but it acts on the input signal at LINE level, and not on the output signal which is SPEAKER level. Active crossovers have variable crossover points at the twist of a dial and each channel is gain controlled. I use the Rane MX22 as my active crossover.

    The true advantage to bi-amping or tri-amping, is each driver is restricted to producing only the range of frequencies for which it is designed. This is much more power effecient, as it does not waste high frequency power into woofers that cannot produce those frequencies. The restriction also lowers distortion by reducing the range of frequencies the driver must produce.
  11. Bi-amping sounds like a great idea. But are there any drawbacks? I'm thinking that amps that are bi-ampable are more expensive than regular amps because of the additional electronics. Do you need special speakers for biamping? I have heard the term "full-range" speakers - are there other categories of speakers and would they apply to this situation? And when would you not want to biamp - in a recording or playing situation?
  12. The drawback to biamping is that at the point of crossover(the frequency itself)may sound funny. All you really need to biamp or triamp is 2 amps or an amp that can run in stereo which is basically 2 amps. You can buy a basic crossover for less than 100$. Most bassists who biamp use a 210 with a tweeter(which is considered a full range cabinet since it has the ability to cover most of the bass guitar frequencies) and a 15 or 18.

    As far as full range speakers. Most of todays bass cabinets are considered full range because they have the addition of a tweeter or a horn, but the lows are almost always a problem or if it's a 15 and a horn you loose alot of the 10 or 12 punch.
  13. This is a problem inherent in all multi-way systems, whether bi-amped or not.

    An active system can be adjusted to sound better than a passive system at the crossover region. The first problem is relative loudness between the two drivers at the crossover point. By design, each driver is rolled off -3dB at the crossover point, so the sum of both takes the combined response back to 0dB. No dip in the response at the crossover point. Active crossovers allow for control of the gain on each channel, so the outputs can be exactly balanced.

    The second problem is more subtle, and that is time delay induced by different positions of the two drivers. In a time-aligned system, the center of both voice coils are aligned in the vertical axis. When misaligned, the output tends to "lobe" erratically and point downwards. It has been demonstrated that specific frequencies will generate an almost total suck-out of the sound. The more expensive active crossovers such as the Rane AC2x series, have precision delay circuits available to the user to correct this problem. The ideal solution is physically aligning the voice coil centers, but this is often not possible due to cabinet constraints.

    As pointed out above, the real drawback to bi-amping is cost. And size/weight of the required rack equipment.
  14. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    Bi-amping is nice. It was pretty popular when huge rigs were in vogue. But with today's PAs, it seems a little overkill to me.

    If you play smaller clubs and stay out of the house most of the time, you might have reason to put together a back breaker rig like that.

    If you depend on the house for most of your sound, there is no point.
  15. Guiseppe


    Oct 26, 2003
    Vancouver, WA
    I just wanted to take a minute to say "thanks" for the great explanations you all have put up...it does a lot to clarify what biamping does. I'm working with some guys who are all actually fairly accomplished "hobby" musicians and we're all getting to the point where we're starting to realize what we have is a lot better than what is around our area (Salem, OR) and we're starting to want to really focus our sound.
    For what it's worth for those who aren't familiar with attenuation, it's essentially "thinning" the particular frequency before it's passed to the particular speaker (hence low freq's are cut prior to being sent to the horns, and highs cut from the 15's/swoofers)...I think I have it now! Thanks for the enlightenment!

    Right now my rig is a 74' Fender Bassman 100 head through a 215 BW Peavey cabinet (I know, some of you are groaning, but I'm in post-divorce recovery mode lol)...I'm thinking I like the 15's bottom end and want to look at a 4/10 cabinet and am thinking bi-amping sounds like the way to go to get both sides of the spectrum. Thanks again everybody!
  16. I played 2.5 years continuously at my bar gig, and a second weekly one during the summer months. Yes indeed, hauling it around gets old. My bi-amp rig lived in the back of my truck for all this time, because it was a waste of my back moving it into the garage for a few days, then loading it again.

    A friend moved away and gave me his Peavey TKO115 combo that I've been playing for the last few months. It has no bottom, as expected from a cab just large enough to hold a single 15" Black Widow. It is loud enough for bar gigs (never any PA support), and easy to move around. At quitting time, this is a blessing.

    That said, I'm building a micro bi-amp setup with a single 1x10 sub and 1x10 B102 for the highs. The cabs are only 0.6 cubic feet each, and very easy to move. For intimate gigs, this will get me all the way down to the bottom without hauling giant cabs.
  17. Personally, I don't think biamping provides any advantages over full range for my particular situation. I like the sound of an SVT through a sealed 810, even though the frequency response isn't 'ideal.'
    But, if you're looking for a truly full range, truly hifi sound, it's your best bet. A properly set up biamped rig with a true sub is something else! I'd love to hear your big rig, Bruce...

    I've been dealing with large multi-way concert systems for years and getting everything properly time aligned is a huge part of that racket. There are some incredibly powerful DSP-based speaker processors out there and some amazing measurement tools as well (Meyer SIM, for example)but when it comes down to it, I still do final tweaks by ear....
  18. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Attenuation is turning it down.
  19. I play in bars with crappy acoustics, so the big bottom is a hindrance to clarity. I play a Peavey TKO115 in these venues and it works fine, and is much easier to haul around.

    The place where it really shines is outside. We play a lot of outdoor gigs and street fairs during the warm season. The big bass lends an intimacy and presence that cannot be had from a small cab with a few 10" installed.

    Links below are photos from last Summer's Chili Cookoff street party in Locke, CA. We had two drummers, congas, sax/flute, two guitar players, and two bassists. My friend Rick was down from Portland for the party, and when he wanted to play bass, I played Hammond keys. PA support was multiple 15" Carvin mains with horns, half a dozen floor monitors. I had two 1x15 subs and two 1x10 highs, and I was completely out of gas. Will have to bring four and four next year.

    Crowd View

    Playing the P-Bass

    Mikey the Monster Drummer
  20. redneck2wild


    Nov 27, 2002
    Memphis, TN
    If you already have a 2x15 cab for the lows, you may not need much for the highs if you go with a biamp rig.
    A 1x10 with a horn or a 2x10 would most likely be plenty for mids/highs.

    How deep is the 2x15 cab you have right now? Some of the Peavey cabs are not very deep and produce more low mids than deep lows. You may find a 4x10 actually puts out better lows if you have a shallow model 2x15.

    Is your current head only 100 watts?
    You may be able to get more volume using your current cab by just adding more power. If you have BW speakers, they should be able to handle a good bit of power. On the other hand, if you do go with a biamp rig and only send the lows to the BW speakers, then you maybe able to push them even more.