Vented cabinet 2xBP102 + 1xAlphalite 6A

Discussion in 'Amps [BG]' started by GustavFL, Dec 24, 2012.


  1. GustavFL

    GustavFL

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    Minas Gerais, Brazil
    Hi folks,

    I'm building a vented cabinet to be powered by a GK MB-500 which delivers 500 W at 4 ohms and 350W at 8 ohms. As I'm building just one cabinet I want it to have a load of 4 ohms to get maximum power of my amp.

    To be clear, I was actually building just a 2x10 cab but after some research I found that the BP102's wouldn't offer satisfatory mid/treble so the Alphalite 6A would be a great complement. Also it would put cab's power to 500 W.

    I already have the BP's and the amp head. I need assistance in the following topics:

    -How to wire (if it's possible) these 3 drivers to get 4 ohms?
    -If I was building the 2x10 cab I would wire in parallel directly to the speakon jack. Considering the third speaker should I use any crossover or filter (how necessary is it)?

    Some specs(ran on WinISD)of the cab you guys should consider:

    -Vb~5.3 cu.ft
    -Fb= 42 Hz
    -2 round shaped vents, Dv= 4 inches, Lv= 4.5 inches
    -One Speakon jack
    -SBB4 alignment

    Feel free to offer other shape/wiring/dimensioning options considering these 3 drivers in question.

    Thanks in advance guys!
  2. fdeck

    fdeck Supporting Member

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    In my view the design will need some sort of x-over to avoid damaging the 6"er. On the other hand, the impedance of the system doesn't need to be 4 Ohms at all frequencies, and in fact it won't be anyway, as the impedance of a cab varies with frequency. So you can let the 6"er operate at 8 Ohms while the 10's in parallel operate at 4.

    Now all's you have to do is figure out how to design a crossover for this arrangement, which I haven't studied how to do, but there might be Web based design tools for this. For instance here's one that lets you enter different impedances for the woofer and tweeter:

    http://www.diyaudioandvideo.com/Calculator/XOver/
  3. christw

    christw Get low!

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    On another note, the BP102 is only rated at 200w RMS power handling each and that's for thermal burnout. You'll probably end up with the cabinet's excursion limiting power handling to slightly over 200 watts RMS. If you want to make the most of your watts, use 2 2x10's. Running 350 vs 500w into a single BP102 loaded 210 will not have any real world benefit. Your amp will run hotter and you'll be more likely to blow your speakers though. ;)

    If I were you I'd cross over the BP102's around 1.5 kHz before the little peak around 2 kHz. Should you make an 8 ohm cab it would be easy to find an appropriate crossover. Since you're probably going to cross over well into a mid driver's range, I'd consider the Alpha 6 CBMRA and pad it back at least 3-4 dB. It's closed back so you don't need to build it a chamber, less than half the price of the Alphalite 6A, and closer in sensitivity (but still louder than) the pair of the BP102.

    Another catch, adding the Alphalite 6A will not increase the power handling of the cabinet. I'd suggest some reading into crossover design. I mean that in a friendly way as a guy who doesn't know too much himself. :D
  4. will33

    will33

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    Another one I'll throw out there is the regular Alpha 6 in a subchamber. It can hang with a pair of bp102's and can handle being crossed over lower into the midrange should you choose to.

    You'd basically end up with a 95-ish db cab that would run from very deep up to 5khz or so.

    The crossover calculations are the hardest part. Start with active biamping until you zero in in a frequency that works well for you in live gigging situations. Then begin working out a passive targeted for that particular frequency.
  5. gerryjazzman

    gerryjazzman Supporting Member

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  6. Growly Lytes

    Growly Lytes

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    BP102 will need help in the mid freq thats forsure.
    I had made two 410`s with them.Then i found another empty 410 cabinet & loaded that with Alpha 10`s.
    So the setup is 410 on top with Alphas & the bottom is a 410 with BP102`s.
    Watch out, you maybe able to hear me all the way over there in Brazil.
  7. fdeck

    fdeck Supporting Member

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    There's some good advice. Also, I just noticed that you're in Brazil. If you're ordering drivers from the States, neo drivers might end up being cheaper due to paying less for shipping.
  8. Growly Lytes

    Growly Lytes

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    BTW my cabinets with BP102`s dont have any filters or crossovers. I installed a Motorola Piezo Tweeter also without filter aswell. All that i added to the tweeter was a resistor to protect my amp from ultra sonic treble.
    Its been working for me.
  9. GustavFL

    GustavFL

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    Thanks for your answers guys.

    Well, I'm almost sure the cab will be 2xBP102 plus 2xAlpha-6CBMRA (or 2x8-MRA or 2x10-CBMRA) what do you think about the midrangers size/model?

    All of them are 8 ohms, so I'm gonna wire series-parallel to get 8 ohms output. As you said, Christw, it makes no sense using a cab limited to ~250 W at 4 ohms with a 500 W amp at 4ohms. Why the midrangers wouldn't increase power handling of the cab? I thought power would be 400W with the BP's plus 200W with the Alpha's, resulting in a ~400W real power cab.

    Wiring would be like this:

    [​IMG]

    Any ideas how to crossover them?

    With this 8 ohms cab I can still build and plug another 8 ohm cab in the GK MB 500 :D
  10. christw

    christw Get low!

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    You would want the crossover before the mid/high frequency drivers. The power rating is derived from the speakers that will take the brunt of the power, in this case, 2-4 x BP102. The higher frequency drivers will only see a fraction of that power when properly crossed over. For lack of a better explanation at the moment, a crossover will divide the power from the amp among the low, mid, and/or high frequency drivers with most of the juice going to reproducing the lower frequency content. A single 6 CBMRA with a proper crossover could keep up with four BP102's to give you a very deeply voiced full range cabinet. If you ignore the HF bit of this crossover (beyond the range of this particular midrange driver) this Emi would be a fair choice to mate 2-4 BP102's to a single 6 CBMRA and cover up the BP102's 500hz dip - http://www.parts-express.com/pe/showdetl.cfm?partnumber=290-654

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