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Help! 2 Ohm or not 2 Ohm

Discussion in 'Amps and Cabs [BG]' started by Prouty, Aug 15, 2007.


  1. G'day all. I've been a member here for a while now but this is my first post. I just haven't had much worthwhile to say you know. That is until now...

    Need to ask your opinions on my current dilemma. I play in a pop rock band with a slightly darker edge. I play a Musicman Sterling through an Aphex Punch Factory and Boss Eq into a Mesa Big Block 750 and an Ampeg Svt610HLF. I have owned and been struggling with this setup (pedals excluded, they are a recent addition) for nearly 2 years and just can't get it to sound 'right'.

    My main issue, as i do 'like' the Mesa's tone, is lack of headroom. The Big Block marketing machine sucked me up and spat me out before I realised that the 750W power rating was into a 2ohm load.

    So...
    do I keep the head and reconfigure my cab setup? Options?
    can I wire the 610 to 2ohms?
    or do I sell the head and buy an orange ad200B (fell in love with this head on the first note I played)

    Cheers
    Luke
     
  2. sarcasticon

    sarcasticon

    Aug 14, 2007
    Belgium
    Apart from the obvious question what you're doing to run out of headroom in a pop/rock band with an estimated 450W going into the Ampeg ;) have you considered adding another 4 Ohm cab to your setup (so your Mesa would crank out its full potential)?
    Rewiring the 610 to 2 Ohm would be tricky, if at all feasible... Not sure if the Orange would give you that much more power compared to what you're currently getting out of the Mesa, so if you go for that option, better try to test it first.
     
  3. just buy another 4 ohm cab, then your amp will push out its full power.

    that is the easiest option, the other option being to re-wire your cab, but i'd suggest getting another cab as then you have even more speaker area pushing out.
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Your Ampeg will only take about 200 watts before farting out, so power is not the problem. Add another cabinet.
     


  5. Looking at the specs on that particular box, it'll take 600w. continuous.


    Bill, will you please explain your thoughts on "only take 200 watts before farting out"? Huh? :confused:
     
  6. fenderhutz

    fenderhutz Supporting Member

    Jan 28, 2007
    Harpers Ferry WV
    600w @ 4ohm

    You will running @ 2ohm.
     
  7. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    I'm surprised you run or work at a sound company and don't know the answer to this - excursion-limited cabs/drivers seem to be mentioned in so many topics around here on a near-daily basis. Arguably more drivers that end up getting damaged used for bass guitar applications die from being run past their mechanical travel limits than do from overreaching thermal limits. And those travel limitations almost always come into effect well before stated thermal limits when used with a broadband program.

    xmax, xmech, xlim are all something you should know about.
     
  8. I own a bb750 and a Sterling(and a Ric) and have no problem with headroom. I currently run a (4ohm)Scout 15 cab which is rated at 300w...what are your settings?(gain,bass,mid,active mid,treb)..generally I run my e.q.(bass,treb,active mid) at 12:00...for me,the magic happens in the gain control and the passive mid control...the gain has a very broad range..I like a fatter tubey like sound,so I run my gain a little high(around 12:00 w\ the Sterling and around 1-2:00 with the Ric) and dial in the passive mid til I like it,which is usally around 12:00...but,it sounds like your after a cleaner sound.Try a lower gain setting,go easy with the e.q.(it's very powerful)and turn up the master..I personally would not use the Boss e.q., too much e.q will actually rob you of headroom...in fact I would try not using any pedals and see what happens,maybe try the comp. in the f\x loop?..anyway,enough rambling,hope this helps.
     

  9. My apologies to the OP.

    Lets devide that up. 6 speakers in that box = 1 speaker for each 100 watts. Well, according to Ampeg all 6 are good for about 1200 peak. That makes it 200 w. peak per driver. Now, lets look at BFM's statement. 200/6 = about 30w to cause that 100 cont. / 200w. peak speaker to "fart"? Huh?

    Now according to you 30w. and the driver is going to reach its Xmax? :rollno:

    Maybe I'm missing something.
     
  10. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    It's possible but the threshold may be higher because of the distribution of energy within the overtone-laden content. If much of the energy is above the danger zone, no problem. But if suffiicient energy at the area within the cab/driver combination's weak bandwidth for cone excursion - including frequencies that unload a ported box but not limited to them by any means - it will do drivers in. Bass boosting or instruments that can really make a lot of energy below 125 Hz or so are more likely to put drivers/cabs running full range at risk.

    And in fact for bassists it's probably best to be aware of that, rather than worrying about RMS/thermal cab or driver figures.

    PA mains run on the high side of an active crossover (also driving subs on the low side) generally are not at risk despite their often small or moderate xmax because they are not seeing energy at the frequencies that are most likely to overexcurd them, but run them full-range with a decent amount of kick drum and bass and at best you will listen to the cabs complain and quite common especially with club floor monitors, be damaged. At the worst it's more blown drivers with clueless operators spreading myths about underpowering or overpowering or DC coming off of perfectly fine power amps.
     
  11. JonathanD

    JonathanD

    Dec 13, 2006
    Atlanta, GA
    To the OP, addng more speakers is more affecive than adding more watts IME. Also try a search for EQ setting adn power ratings and see what you find.

    As for the side discussion... please elaborate for me.
    Jonathan
     
  12. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    That's a very bold statement..... and is not true in general.....

    Do you mind stating any particular reasons you might have for making the statement?

    And, any particular conditions under which YOU consider it to be true......?

    Any speaker has a low frequency below which it won't handle much power, of course. I assume you are not relying on that.
    The HLF series uses a longer excursion driver than the "classic" type.
     
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Displacement limited power is explained above by Greenboy.
     
  14. BillMason

    BillMason Supporting Member

    Mar 6, 2007
    How are you EQ'ing your head and bass?
     
  15. Actually, you're missing a whole lot.

    Very few bass drivers can operate at full rated power over their working range. The reason is displacement limitation. This is when the driver exceeds Xmax, which you know is the range of linear cone movement. This is frequency dependent, and also dependent upon the tuning frequency of a vented box, or the resonant frequency of a sealed box. Typically, this is around 30w or less for the average driver. The Ampeg uses something close to an Alpha 10, so the tendency to fart out below 50 Hz is more keen.

    Many drivers in vented boxes exceed Xmax at frequencies within the bass power band, circa 60 Hz. This typically occurs at the upper resonance point, Foh, which is about a half octave up from the tuning frequency. Plot any driver in a vented enclosure, and note the rise in cone excursion above the tuning frequency. Cone movement at the tuning frequency is almost nil.

    Longer excursion drivers have a longer Xmax, and a corresponding lower sensitivity. This is why you find subwoofer drivers with 25mm Xmax, and 1000w capabilities. And an 85 SPL rating.

    The manufacturer's peak power rating is meaningless. At best, it means the voice coils will accept X (peak) watts before melting the coils. No manufacturer publishes displacement limited wattage, and that includes Ampeg.

    All of the above is basic Speaker Design 101, and should be well understood by everybody running a Sound engineering business. If you are a retailer or rental service, it does not apply to you.

    To the OP, a 2-ohm load is the most stress on your electronics. It generates the most heat, and heat is the killer of electronics. Do not assume your 4 ohm rated cab is a true 4 ohms. At the tuning frequency of vented boxes, the impedance drops to almost that of the DC coil resistance. This could be down around 3.25 ohms. The only way to know for sure, is by taking an impedance sweep measurement.

    I don't know how the 610 cab gets 4 ohms, but I sure as heck would not wire it down to 2 ohms. I've played this cab a number of times, and it does indeed fart out when driven hard. As noted above, add another cab. You can only drive a cab so hard before it hits its limits. The problem with heads and 4-ohm cabs is you hit the impedance limit very quickly when you add another cab.
     

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