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Bi-amp questions

Discussion in 'Amps and Cabs [BG]' started by Eric Cioe, Aug 20, 2002.


  1. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    Ok, here's my situation. First off, I play 7 string bass, so I need a big frequency range.

    I have a Gallien-Krueger 400RB-III head, pushing an Avatar 2x10 cab and an SWR Workingman's 1x15 cab. It does an OK job of reproducing all the frequencies, except the lowest 4 or 5 notes. Below E, it breaks up a bit. By C#, C and B, it's farting.

    I am planning on getting a power amp and replacing the SWR with a Yamaha 1x18 PA sub (the kind JT uses).

    I have to signal chain options....

    1. Bass to head, speaker output on head to Avatar for 150 watts at 8 ohms. Line to power amp, putting 400-500 watts into the Yamaha at 8 ohms bridged. (Carvin DCM600)

    2. Bass to head, line to power amp, side 1 to Avatar, side 2 to Yamaha, pushing about 400-500 watts a side at 8 ohms. (Carvin DCM1500)

    3. Bass to head, line to power amp, bridged to both cabs, about 1000 watts at 4 ohms mono. (Carvin DCM1000)

    So far, I like option 2. It will cost more, and weigh more, and take up more room in my rack (assuming I get a Carvin)

    I _think_ I want to bi-amp, or at least try it for a while.

    How do I do this?
    What crossover do I need?
    Where do I put the crossover?
    What should I set the crossover at? (100hz is my idea)

    Sorry this is kind of scatterbrained. That's just how I work :D

    Thanks in advance.
     
  2. I bi-amp with a Rane MX22 active crossover. These are professional quality, fully adjustable, and plentiful/cheap on eBay. The crossover is mandatory for true bi-amping.

    The crossover provides a High and Low output to the power amp channels. Either a single stereo (two-channel) power amp such as the QSC or Carvin DCM, or two mono amps are required.

    The MX22 crossover range is 100 to 3200 Hz. Its big brother, the Rane AC22 or AC22B, ranges from 70 to 3600 Hz, but is more expensive. I run my MX22 around 325 Hz, because this is where my Lows roll off. YMMV. The loudness of each channel is separately controllable, and either crossover will provide greater than Unity gain. This is useful when your preamp does not put out enough voltage to drive the power amp to full output.

    To use an external crossover, you will have to see if your head will provide LINE OUT or EFFECTS OUT to the crossover, then accept either the Low or High from the crossover back into the head.

    A separate preamp is preferred over a head type amp, as the preamp provides signal to the crossover without wasting the power section of a head type amp. The preamp is also smaller and weighs less in your rack.

    The Yamaha SW118IV is pretty loud at 96 SPL, but is a back-breaking 10 cubic feet, external volume. Moving this big guy can get ugly. I played an entire evening with this sub as the bottom of my bi-amp rig. Don't expect it to go real low. It starts to roll off at 60 Hz, and is down -16dB at low F#.

    Your ears must be the criteria for choosing a sub. Many players here are 100% happy with cabs that do not produce a true, low fundamental. The harmonics give them everything they want from their basses. Only you can make this determination.

    If you are truly searching for low F# fundamentals, you will need LOTS of power, and LOTS of speaker cone area. True subs that can produce the F# fundamental are either enormous power hogs, or they require prohibitively large cabinet sizes. The laws of physics do not allow for Low + Small + Efficient in the same cabinet. One of these 3 items has to be sacrificed. Usually, this means efficiency is sacrificed in favor of a reasonable cabinet size that requires lots of power.
     
  3. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hey Bruce, I would add LOUD to that, maybe even in place of efficient. I'm thinking of headphones, which have small drivers and can do really low frequencies. But they don't have to do them loud. ;)
     
  4. Efficient and Loud are interchangeable.

    Headphones don't have the coupling problem that a non-horn loaded bass driver has. Anybody wanting to hear the true Low F# should do so through a good set of phones.

    My 15" subs are grossly inefficient (87 SPL) and require enormous amounts of power to drive them. Two 1x15 are a 4-ohm load on my PLX 3002 left channel, and the two JBL E-110 are on the right channel which is loafing. The sub channel constantly flirts with the clipping LED when I try to keep up with the guitar player and his 60 watt amp.

    My solution is finding a 2nd power amp for my bi-amp rig, so I can put the Highs into the second amp, and use both PLX channels for the subs. I have two more 1x15 under construction, so I can put two on each PLX channel.

    My only consolation is having the ability to knock glassware off the bar at the other end of the room.

    :D
     
  5. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    i rather like the yamaha sub. it may not reproduce fundamentals much, but it _sounds_ good to my ears.

    So here's what i'm getting from your posts.

    plus, i got a new idea.

    Bass into GK head, with the speaker out putting a full range signal into Avatar 2x10 on it's side, facing across the stage.

    effects loop out into crossover

    hi out into channel one of DCM2000, putting 425 watts at 8 ohms into Avatar 4x10 cab (high freq) (I would have to buy the Avatar, but it's worth it)

    low out into channel two of DCM2000, putting 425 watts into Yamaha 1x18 sub (low freq)

    that way, i would have a ton of flexablitily.
    for really small gigs, i would just bring the GK head into the avatar 2x10.

    for medium size gigs, i would bring the gk head into the crossover into the carvin into the 2x10 and 1x18, or just the poweramp and the 4x10.

    for big gigs, id bring the gk head into the crossover into the carvin into the 4x10 and 1x18.

    for gigs where i can fit everything, id bring gk head into avatar 2x10, effects loop into crossover into poweramp into 4x10 and 1x18.

    :D

    so, i can look to spend about...

    dcm2000 $540
    sw1x18 $380
    b 4x10 $250
    crossover ????
    1170
     
  6. $125 is the average selling price for a Rane MX22 crossover on eBay.
     
  7. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Ok then, if i have bi amp controls and output, or inputs, cant remember, never bi amped before, what else do i need?
     
  8. notduane

    notduane

    Nov 24, 2000
    Location
    You talkin' about that BT-350 P~B?

    I found an owner's manual! :) (it's in pdf format - takes forever
    to download :( ) -- http://www.stlouismusic.com/downloads/crate/owners_manuals/BT350.pdf .

    It looks like you have a "BIAMP OUTPUTS" section on the rear panel.
    There are "HIGH OUT" and "LOW OUT" jacks. Reading the manual,
    it looks like these two are line level outputs.

    They have recommended hook-ups for a couple configurations (ppg. 8 & 9).
    Bottom line is, you have to have ANOTHER amp to take advantage of the
    BT350's bi-amp capabilities. The BT-350 can function either as the
    low freq amp or the high freq amp, but not both.
     
  9. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    OH MY GOD! HOW THE HELL DID YOU FIND THAT THING?!?!?!?! IVE BEEN LOOKING FOR THAT FOREVER!!! HOLY CRAP! God, 2 years of looking, and can't find it, thanks Notduane! I still can't belive it..... I got the thing used, never had a manual to go buy. if i had this a long time ago some questions would not have been needed to be asked! I'm still tripping over this,, ...
     
  10. notduane

    notduane

    Nov 24, 2000
    Location
    pure   dumb   luck   :p

    (I FED "CRATE BT350 AMP" INTO GOOGLE)