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Head/cab setup Q [technical]

Discussion in 'Amps and Cabs [BG]' started by jumpingbob, Sep 20, 2004.


  1. jumpingbob

    jumpingbob

    Jan 10, 2004
    Louisville, KY
    So I bought a BX3000 head which Im very pleased with however I dont have the money this month to buy a nice cab. So I decided to use some old car/home audio 2x10 box. They are nice speakers, its ported and works well, its a bare wire connection with tweeters. However the impedance on each speaker is 4 ohms, so if I use the 1x4ohm output of the head Ill have to either wire in series giving me an 8 total ohm load or in parrellel giving me a 2 total ohm load.

    Id like a 4ohm total load to get my full 300rms watts. So is there any way to wire it or set it up to get that? Would it be possible to wire a 2ohm resistor in so itd be wired in parrellel to both speakers then in series from the resistor to the speaker system? That'd give a 4 total ohm load but im not sure if thats possible...

    Any input would be appreciated!!!

    Thank, Ben
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    nope
    any setup incorporating a resistor (like a power brake) will take 1/2 of your signal if you try to get a 4 ohm net rating

    besides that, the cabinet you have chosen is unsuitable for bass at best.
    those cabinets are designed fro recieving compressed and mastered program material, not the "raw" signal from a bass amplifier. Not to mention that the speaker in question is probably quite inefficient compared to a bass guitar speaker.
    Those type of speakers also typically have a narrow bandwidth that they operate in and are typically tuned to a sort of "gimmicky" frequency response. I doubt you'd be happy with the result on any level.
     
  3. jumpingbob

    jumpingbob

    Jan 10, 2004
    Louisville, KY
    Ah, well thats no good. Looks like im staying in parrellel for the time being then. And its not a question of whether or not im happy with it, its all I have right now, and it really doesnt sound *that* bad. Thanks for the help!

    -Ben
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Ivan Mike brought out a very good point: your speakers are totally wrong for the job. You're worried about getting the most power out of your amp, but that has little to do with how loud you can actually play. Home/autosound woofers on average have a sensitivity of 87dB/watt; pro-sound woofers on average have a sensitivity of 97dB/watt. That 10dB differential means that 100 watts into your speakers are the equivalent of 10 watts into a real bass cab. While the rig may sound OK in your livingroom you'll fry something for sure on a gig, probably the amp, as with a 2 ohm load it won't hold up under full power. The only way you'd get your speakers as loud as a real bass cab is with 3,000 watts, which is obviously out of the question.

    Before you fry the amp or speakers or both you need to fix this problem. Either get pro-sound drivers to mount in the box you have or take your existing drivers and mount them in horn-loaded cabinets that can raise their sensitivity by 10-12dB. Examples of those can be seen on my site.
     
  5. jumpingbob

    jumpingbob

    Jan 10, 2004
    Louisville, KY
    Right now I have it wired at 8ohms so I dont think it should hurt anything, and the box has 2 horns. Im not so sure that 100watts to 10 is correct... Ive played many amps with 10-50 watts and this system should be at around 160watts or so...and its much much louder. I know the sound quality isnt near what it could be but I cant just up and spend another few hundred that I dont have!
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I'm quite sure. It's one of those things they make you learn to obtain a degree in Audio Engineering. A ten decibel change in level requires a tenfold increase in power. An 87dB/watt speaker requires ten times the power input as a 97dB/watt speaker for equal output. An 87dB/watt speaker requires one hundred times the power of a 107dB/watt speaker for equal output. Keep this in mind when you are able to upgrade.
     
  7. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    Word.