Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

????????

Discussion in 'Amps and Cabs [BG]' started by fenderbluesdude, Jul 14, 2004.


  1. i have the avatar 2x12 and i am planning on getting the avatar 2x10, to power these i have a behringer bx3000t ( im planning on getting a better head maybe ampeg but this works fine for now). as soon as i get the 2x10 i think i am going to need somekind of power spliter or something that alows me to split the lows and highs to each cab beacuse if i dont use this i will have to push the 2x10 through some hard times i dont think it could handle what the 2x12 can handle so what i would do is assign all the lows to the 2x12 and assign all the high-mids to the 2x10. this way i wouldnt ruin the 2x10 by giving it more lows than it can handle. what is this device called if they make it?
     
  2. It's called a crossover, but I don't think you really need one.
     
  3. well i dont thinkl the 2x10 could handle waht the 2x12 could handle. i dont want any distortion
     
  4. the avatar B210 is rated at 700 watts RMS....if you need more power handling than that then you're playing sold out arenas without a PA system :D
     
  5. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Yes, a passive crossover will work for this purpose. Carvin sells one that mounts right into a cab, if you're willing to drill a hole into one or the other of your cabs that might be a way to go. If you get a passive crossover, make sure it will handle the full power of your amp.

    But, you can do something much simpler than that. Just connect a large non-polar capacitor in series between the 2x10 and whatever it's connected to. That will keep the lows out of your 2x10. It'll have to be a fairly large capacitor, and it'll probably have to handle a decent amount of voltage, depending on your amp's power output.

    To calculate the (approximate) value of capacitor that you'll need, use the following series of formulas. These are "DC approximations", but they're close enough for all practical purposes.

    First, you'll need to know the impedance of your 2x10 cab. I'm guessing it's 4 ohms. Then, use the formula t=RC to determine the value of the capacitor you'll need. The 't' is "time", which is the inverse of frequency, so if you do all the math you'll end up with C= 1/(f*R), where f is the frequency at which you want to start limiting the lows, and R is the speaker impedance.

    Here's a f'r instance: Let's say you have a 4 ohm cab, and you want to set it up so that nothing below 200 Hz gets into it. C=1/fR, so 1/(4*200) = .00125, and this will be the capacitance in "farads", which equates to 1250 microFarads. This is a fairly large value. It'll probably be impossible to find a non-polar cap that big. So, what you do is, put two 2500 uF electrolytic capacitors in series, back-to-back (in other words, the two negative terminals are tied together), and that will give you what you need.

    To figure out the voltage that will be required, use the formula P=(E*E)/R (or "E squared over R"), where E is the voltage. Doing the math again, E=sqrt(P*R). Use the "peak-to-peak" power to calculate the required voltage (usually this will be about triple the amp's rated RMS power). Again, here's a f'r instance: if your amp is rated at 100 watts RMS, and you're using a 4 ohm speaker, the RMS voltage will be sqrt(100*4), or about 20 volts. The peak-to-peak voltage will be about triple that, or about 60 volts. To be perfectly safe, try to get a 100 volt capacitor. That will give you plenty of headroom.

    Note that this method will not keep the highs out of the 12" cab, but will keep the lows out of the 2x10. It sounds like this will accomplish the desired result.

    In practice, and in the above example, the cutoff at 200 Hz isn't "instantaneous", instead there will be a "smooth rolloff" that starts slightly higher in frequency, and the rolloff will get more significant as the frequency decreases. So for instance, at 200 Hz you'll allready be at about 1/3 of your signal strength. At 50 Hz you'll be down to around a few percent. At 20 Hz you'll be down so far that you won't hear a thing. This will protect your 2x10 speakers. If you wish, you can experiment with the value of the capacitors to get the rolloff characteristics that sounds best to your ear.
     
  6. i know the 2x10 is rated 700watts i just dont think it can handle some serius lows before it starts to fart out.
     
  7. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Yep, that's pretty typical for 10" speakers. For the most part, they don't handle the extreme low frequencies very well. IMO your concept of limiting the lows through your 2x10 is a very good one, and it should work fine when you're using another cab (with bigger speakers) to handle the bottom.
     
  8. What's the frequency response of the 2x10?

    Cool idea about the capacitor, I was reading about that last night actually.
     
  9. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Let's make this guys life a little easier........

    Click here for an On-Line Crossover Calculator.....
     
  10. ....C1 (µfd) = 1,000,000 / (6.283 x Impedance x Crossover Frequency) Capacitor - C1 Microfarads (µfd) ....


    ...yes much easier... :D
     
  11. does anybody know of any good rackamount crossovers? and what would be a good head for the 2x12 and the 2x10?
     
  12. do i even need as head???


    could i just use one of those powerful poweramps like those QSC ones and then just use that crossover, and then use one of those preamps or thing that equalizes your sound.
     
  13. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Er...um.....I think what you mean is put two 1250uf caps in parallel to get a 2500uf value......this also combines the voltage capacity of both caps, so you can get better power handling capability - i.e., two 250V caps in parallel gets you a 500V capacity........

    Coils get hooked up in series....
     
  14. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Well, yes and no......plenty of good rackmount crossovers, but they won't do what you want. You're talking about processing an amplified signal; rackmount crossovers only split line level (i.e. before amplification) signals.

    You have to use a passive crossover to do what you're planning; rackmount x-overs are active.
     
  15. so this is all i need to make sound!!! just a

    power amp (QSC)
    preamp (sansamp RBI)
    and if i want that crossover
     
  16. they dont make passive rackamounts.

    so tell me what i could do with a setup like what heads or power amps and preamps or not ect.
     
  17. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    If you use a preamp/power amp setup, you can use an active crossover. This is Biamping.

    Like this.....

    Preamp -> Crossover;

    Crossover High Out -> Power Amp Channel 1
    Crossover Low Out -> Power Amp Channel 2

    Power Amp Channel 1 -> 2x10
    Power Amp Channel 2 -> 2x12

    This also gives you independent control over the volume of each cab.

    edit**Obviously you have to use a stereo power amp, and most power amps are stereo; your Behringer head may have a power amp input, but it's just a single channel amp, so you cannot biamp with it alone.
     
  18. i think i will just give up on the crossover thinger. does anybody own a 2x12 and 2x10 setup and dosnt use any kind of crossover just a head? how does it sound?
     
  19. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    I wouldn't bother with trying to do a passive crossover, honestly.

    Bass guitar cbainets are NOT subwoofers, they are designed to deliver flat signal to about 80 Hz then start rolling off for the next octave and that's true pretty much regardless of the speakers in the box.

    Any signal you feed to the 2-10 that might damage it is probably also going to damage the 2-12.