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Cab/speaker matching question

Discussion in 'Amps and Cabs [BG]' started by davelowell, Apr 17, 2004.


  1. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    I have a Mesa RR 1x15. I want a 4 ohm box. EVM-15L is OEM.

    Anyway, I am having a hard time finding a 4 ohm version of this speaker, so I pose this question to the pros.

    What is a good 4 ohm replacement for this box?

    Any and all considered, but I would like a 400 watt speaker.

    What do you think?

    Thanks, Dave
     
  2. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Bass cabs are designed for a particular speaker. This makes recommending a replacement very error prone. If you really want a 4 ohm cab, you are better off selling the current one and buying a new one. If you like the current cab, why not keep it?
     
  3. NeedMoreBass

    NeedMoreBass unregistered

    Feb 14, 2003
    May I ask why you want a 4 ohm speaker?
     
  4. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    >>>>>May I ask why you want a 4 ohm speaker?

    Because I play an SVT and I can use my Mesa RR 2x15, which is 4 ohms, OR the 1x15 Mesa RR by itself, which I want to be 4 ohms, OR I can use both at larger shows.

    Thanks for those links Poseur!

    So, has anyone actually replaced one of these drivers with a non OEM speaker? What were your results?

    Thanks, Dave
     
  5. NeedMoreBass

    NeedMoreBass unregistered

    Feb 14, 2003
    I've tried several different speakers in the RR and none sounded as good as the EV. There's an easy fix for your situation though. Add a 8 ohm dummy load, that will give you a 4 ohm cab. This also makes more sense if you plan to use both cabs together.
     
  6. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    I don't know a thing about a "dummy load". Can you explain?

    Dave
     
  7. NeedMoreBass

    NeedMoreBass unregistered

    Feb 14, 2003
    The techie guys can explain it more in detail, but it's a 8 ohm power resistor that's wired in parallel with your speaker. Therefore, your speaker(which is 8 ohms) plus the dummy load(also 8 ohms) makes your amp think you have a 4 ohm cab. Very cheap and easy and to do.
     
  8. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    Any of you techie guys care to explain how to make one of these? and will it work for what I want to do?

    Thanks, Dave
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Don't do it.

    The 8 ohm resistor in parallel with an 8 ohm speaker will split the power between them equally. In other words, the resistor will steal half your power and the speaker will get less watts than it would have if you ran it at 8 ohms.

    Mathematically:- I'll assume your amp puts out 400w at 4 ohms, just for simplicity.

    With an 8 ohm resistor in tow, the speaker recievs 200w and the other 200w is wasted on the resistor.

    Run the cab at 8 ohms, and the amp loses some power (typically 30%), so the speaker gets 280W.
     
  10. davelowell,

    I think it's hardly worth the trouble or money; your volume gain from a 4 ohms cab over an 8 ohms one will be 1.5 decibels at best. 1 decibel is a "just noticable" rise in sound pressure level.

    And a dummy load is a very, very bad idea, like Petebass explained. It makes things worse.
     
  11. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    Thanks.

    So no dummy, can anyone suggest a 4 ohm replacement?

    Dave
     
  12. NeedMoreBass

    NeedMoreBass unregistered

    Feb 14, 2003
    Here's my reasoning for suggesting a dummy load, and before I get into explaining my rationale I must say I am no electronics expert and anyone who can explain me wrong is welcome.

    The elements of the original question along with his response to my question to why he wants a 4 ohm cab tells that he is running a SVT and wants to be able to run both his 2-15" 4 ohm cab and his 1-15" cab together.

    I've never owned an SVT but I do recall a switch on the back to run it at either 4 ohms or 2 ohms. I don't know for sure, but I assume this amp likes to be run at whatever load setting this switch is set to. So maybe even if half of the power is going to the dummy load, the amp may be running more efficiently as opposed to running it a 8 ohms. I don't know what the SVT is rated at @ 8 ohms so I may be wrong on this point.

    My next point refers to running both cabs. If the 15" cab were 4 ohms w/o the dummy load and the 2 15" cab were 4 ohms, wouldn't the power be split between each cab? Hence say 300 watts would be split sending 75 watts to each of the speakers in the 2-15" and 150 watts going into the single 15". Seems to me this would make the 15" cab uneven in output with the 2-15" cab. Having a dummy load will make 75 watts to each load given a more balance output from the combined cabs. This may also be a good argument to leaving the cab @8 ohms so the power would be split evenly between 3-8 ohm loads assuming the amp likes to run at 2.66 ohms.

    I do know that I have tried several different speakers in the RR and none sounded as good as the EV. That cab was designed around that speaker. So unless someone knows of a 4 ohm EVM, I would suggest anything that would leave that speaker in that cab.


    Believe me, I normally would not recommend a dummy load, but looking at the elements involved it seemed to make sense in this situation.
     
  13. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    We can try. What are the dimensions of the cabinet?
     
  14. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    If you can find a woofer with similar specs as these, you're in business: Fs = 43, Vas = .24496, qts = .238.


    This was posted earlier in the thread. I haven't got the box yet, so I can't measure. Do these numbers mean anything to you? Do you need more measurements?

    Thanks, Pete!

    Dave
     
  15. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I'd still prefer the cab measurements when they're available. That's just how I'm used to doing it. Plus theres a good chance that a completely different combination od QTS and VAS may also work in that cab.
     
  16. This is meaningless.

    Vas is a measurement of volume. It will be cubic feet or liters, and certainly won't be a tiny fraction. I suppose somebody could try and interpret Vas as cubic meters, hence a fraction. This is unlikely.

    Recheck your sources.
     
  17. davelowell

    davelowell

    Jan 18, 2001
    stl, mo
    Bruce, I just copied what Poseur had written a few posts up. I have no real knowledge of these types of numbers, hence the call for help.

    Dave