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Cab theory question

Discussion in 'Amps and Cabs [BG]' started by 6stringvince, Jul 20, 2012.


  1. I recently bought a Markbass Momark 500W amp, with it I bought a Eminence Kappa 15A (450 watts at 8 ohms). My intent was to build a 8 ohm cab with the 15, and down the road another 2x10 cab (both cabs at 8 ohms, eventually giving me the full potential of 500w, 4 ohms from my amp). Just for the hell of it, to see what would happen I installed the 15 in to my Traynor Dynabass 100 combo, and wired in a separate input jack allowing me to use it as a cab, eliminating the amp, or switching it as the original 100 w combo, to my surprise it sounds great. According to spec, the cab is too small, and the two vents are way too small, but as I said, to my non audiophile ears it sounds great. Now the question, any danger of blowing up the speaker? From what I've read less venting = added speaker cone resistance to movement, and therefore less chance of the speaker overextending itself, and blowing up. Is this correct? What other possible downsides to this? Am I potentially loosing out some frequencies?
    Thanks for any help
    Vince
     
  2. Hi Vince, I don,t know the volume of the Dynabass combo and how close it is to the min spec of the Kappa 15A, the only caution I would say is if a cab is way to small there is a lot more resistance which means more power to get the same volume, there is a danger of overheating the voice coil. There is normaly a bigger roll of of the very low frequencies in a smaller cab. Hope this helps.
     
  3. You are just limiting what the speaker can do. Low end is restricted, and chuffing from the ports will be heard at high volumes.
    To the other part of your post: you are far better off using two identical cabs, rather that a mix of driver sizes.
     
  4. I always thought the low end of the 15, and the "punch" of the 10's would give you the perfect mix?...
    As an alternative, what about one cab with the 15 and a 6 (like the fearful 15/6)? With my 8 ohm 15, would I add an 8 ohm 6 to get my 4 ohms?
    Thanks
     
  5. wcriley

    wcriley

    Apr 5, 2010
    Western PA
    You'd need a crossover between the 15 and the 6.
    End result = 8 Ohm cab.
     
  6. When you say I'm restricting the low end, does it still matter that I'm only putting in 250w to the speakers capacity of 450?
    Excuse my ignorance, I'm new to this, but eager to learn.
    Thanks again
     
  7. Can I get it to 4ohms?
     
  8. jsa0100

    jsa0100

    Apr 6, 2005
    Norway
    There is no problem using a smaller cabinet on speaker, but you should avoid using a to large cabinet. The rule her is that a cabinet should not be tuned under the speakers resonanse frequency. The Kappa has a fs 33 hz and VAS on 321 liters so you need a large cabinet before that happens.

    Using a to small cabinet will of course make the speaker system less efficient on lower frequencys. So let's say that the speakers have a efficiency on only 87 db at 41hz. Then you need 10 times a much power to give your low E string the same level as if the cabined was tuned to 41hz (-3db)

    Using software to caluclate, the perfect cabinet size is 150 liters. tuned to 41hz.

    Now a to small cabinet in itself doesn't always sound to bad, you can compensate with some use of eq.

    A couple of years ago i built a cabinet with two 12" and tuned the enclosure to -3db at 41 hz. I felt that the cabinet sounded a little to deep and was a little to large so i sold it. It did a mistake because i never testet it a band situation. Later on i heard the speaker beeing used together with a 2x10" speaker it gave the band a very nice firm deep bass.
     
  9. According to Eminence specs the Kappa 15 needs a 1.6 - 4 gal cab, that's a broad range, I think the cab I have falls within that range, but I think it falls short in the venting ( I know when I crank it it feels like I'm standing in front of a fan). I ran the specs in to WinISD (without really knowing what I'm doing) and the venting specs were way shy.
    Having said all of that, the tone I get is very usable, one I would try to achieve (I need to test it in a jam though). I think the low end I'm missing is probably what I would avoid anyways, it's not at all boomy, but deep enough.
     
  10. jsa0100

    jsa0100

    Apr 6, 2005
    Norway
    Another huge factor is Room-Q. A large 15" enclouser might sound to deep and boomy in a small room, but excellent in a large stadium.

    To opposit would be true for systems that don't have enough volume in the lower end. And where you only hear the higher frequencies of the bass.

    If the bass port is to small you will get high friction in the port, you might lower the SPL a little. Hovewer the biggest problem is that you might get a whistling sound at high SPL.

    If you want to connect a 6" speaker to help you with the higher frequencies, you moust use a filter. Not only will the 6" sound better, the 6" can not handle the low frequencies and might get destoryed.

    If you but the 6" in a seald enclousere you only need a codencer in series, a seald enclousere wil give you around -12 db roll off by itself.
     
  11. I want the full potential of the amp at 4 ohms, it doesn't sound like I can do that by adding a 6 to my current 15, 8 ohms driver.
    So do I build another enclosure with another 15 (8ohms), or a 15/6 (8ohms), or a 2x10 (8ohms)? Do I tune the second enclosure to match the first, or do I try to make up for the lost lower freequencies on the second enclosure? Or do I scrap the Traynor box Idea and start fresh with two new matching enclosures?
    Of course cost is always a consideration...
     
  12. will33

    will33

    May 22, 2006
    austin,tx
    You're not going to gain anything by going to 4 ohms on a single 15. Aside from a few LF specific models in the right box, there are very few 15's that can really make full use of the 300 watts you have now. Save the 4ohm thing for adding another cab when you need to. That's how you get a real jump in output.

    +1 to not enough port area chuffing at higher levels.
     
  13. jsa0100

    jsa0100

    Apr 6, 2005
    Norway
    I think it's a bad idea to make another speaker with a 15" to compensate for another 15" who dosen't cover the bottom end. Because the advantage with a 15" like the eminence is that it gives a deep low end in a larger cabinet. I think the best would be to put it in a cabinet tuned to -3db at 45hz.

    Usually having different speaker cabinets covering at least parts of the same frequency is a disadvantage. There is a huge advantage when the LF comes from a single point (try googling "single subwoofer advatage")

    If your fixed on having a 4ohm system, have the cash for a second speaker, and dont want a to huge cabinet, then you can make a push-pull system

    Take a look at this.


    However having each elment in a separat large cabinet will give you an increase in SPL compared to a smaller push-pull system.
     
  14. BogeyBass

    BogeyBass

    Sep 14, 2010
    Kappa 15A is a PA midbass.

    it will do 300 watts all day on a highpass filter as a midbass
    like it was designed to do.

    fullrange bass guitar. wont do more than 15 to 30 watts below 100hz. Smaller box is the only thing saving it, wont have any bass response.

    "push pull" otherwise known as Isobaric is a waste of time.
    more bass in smaller box is the benefit. Sensitivity is cut in half not increased.
     
  15. jsa0100

    jsa0100

    Apr 6, 2005
    Norway
    According to Eminence itself :

    Recommended for professional audio in a vented mid.bass or bass enclosure, Also suitable for bass guitar.

    I get good results when calculating various enclusures, in fact the ideal and most linear configuration for this speaker is -3d at 41 hz. (The low E is 41 hz). Perfect for bass.




    As i said, with 4rth order isobaric, if he want's 4 ohm and a small cabinet it might be somthing he could consider.
     

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