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Ohm Question

Discussion in 'Amps and Cabs [BG]' started by low down shame, Dec 10, 2013.

  1. low down shame

    low down shame

    Jan 23, 2011
    Hey Talk Bass People ,
    I own an SVT 6 Pro that Ampeg claims is 1100 w @ 4 ohms. I've got a Guy who builds Custom Cabs so I called Ampeg to ask a few questions. My question is this, if I'm having a 2x12 built what watt Speakers should I use. I'm looking at Faital Pros and a Ciare Tweeter. Since the Amp is 1100 watts at 4 ohms pegged wide open ( Gain and Volume) I'm assuming I need 2 300 watt @ 8 ohms Speakers rms. If I understand wattage and ohms correctly that would give Me a 600 watt Cabinet @ 4 ohms with a 1200 watt peak. Am I correct and will that work?
  2. wmheilma


    Jan 5, 2010
    It would work, but there are a lot of drivers to choose from. If you describe the sound you are after you will get some good direction from the folks on TB.
  3. tbz


    Jun 28, 2013
    That's 1100 RMS at 4 ohms. You'll want considerably more than 600 watts for the cab.
  4. That amount of power isn't intended for 2x12. More like 8x12 would be appropriate.

    To make best use of those watts without spending a stupid amount on drivers you want to look at 3way cabs with big subs.
  5. tbz


    Jun 28, 2013
    I'd have to concur that there are very few 2-4 speaker cabs that can handle 1100 watts RMS. Eden 410XSTs run at 1000, and that's towards the top end.

    IIRC even the fEARful 151566 series will generally only do up to 1500 watts.
  6. chienmort


    Aug 15, 2012
    You may find them hard to come by but the Precision Devices PDN.12SB40 models well and has a 600W power handling and 2400 peak power handling.
  7. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    The limiting factor is usually where the woofers exceed their linear excursion limits and "fart out'. That's not a simple number to come up with, it depends on many things, but it usually happens well before the woofer is close to its rated power handling.

    For instance, the Faital 12PR300 is rated at 300 watts, but depending on the specifics of the cab and port tuning (asuming it's a ported cab), and depending on your EQ settings and how aggressively you dig it, it may well run out of excursion and fartout at about 1/3 to 1/2 its rated power.

    When choosing woofers, compare them on the basis of how much air they move, rather than how many watts they're rated for. So take the cone area of the 12PR300 (489 square centimeters) and multiply it by the linear excursion (4.92 millimeters, or .492 centimeters), and you get 240.6 cubic centimeters.

    If you want to approximate the SPL of a 8x10, make an educated guess about the speakers in it and go from there. The Eminence Beta 10 is probably a reasonable approximation of the average low-cost 10" bass guitar speaker, and it will move 103.5 cc of air, so eight of them will move about 828 cc. So to equal or exceed the displacement of an entry-level 810, you'd probably want to use four 12P300 woofers (or their approximate equivalent).

    Note that the Eminence Kappalite 3012LF will move 496 cc, so one 3012LF will fartout at about the same SPL as two Faital 12PR300s, and two of them can rival an 810. But the 3012LF doesn't go up as high. Tradeoffs, always tradeoffs.

    Hopefully I'm just going over this for your benefit; hopefully your guy who builds custom cabs is taking displacement into account, and not just looking at watts.
  8. Yes, the tone/sound is what matters. Ratings of amps and speakers are more like guidelines.

    I can use a 300w speaker @4ohm with your amp and be ok as long as I know my limits. Usually your ears can tell you when a speaker has a hard time. The master volume knob is key in this situation.

    If you want to utilize your power rating because this was your intention for clean loud power, then make sure you purchase something that can withstand this 1100w amp. I would recommend a cab that has a rating of at least an extra 1/3 the power rating which is like 1500w.

    If your looking for that SVT sound by pushing the gain section and amp section, get a cab set @ 8ohms rated for over 1000w.

    Hopefully you understand that you don't have to match perfectly with ratings. Your tone should be more important and not compromised.
  9. low down shame

    low down shame

    Jan 23, 2011
    I was actually looking at the Faital 500 and the Kappa Lite LF 12''s. The Kappa's have a higher X-max but Faitals are waterproof. I also hear Bergantino is using them in His Cabinets. Both come in at the 450 to 500 watt range.
  10. low down shame

    low down shame

    Jan 23, 2011
    If that's the case then I should probably go with the Kappa Lite LF's. 2 of those would bring the Cab in at 900W @ 4ohms with an 1800watt peak.
  11. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

    Build the cab for 8 Ohms, to bring the amp power into a safer level. Then you can always add a second 8 Ohm cab later. You won't hear the power difference and won't accidentally blow a driver.
  12. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    If the guy who builds "custom cabinets" is any good he should be able to tell you what drivers he designed the cabinet for.
  13. chienmort


    Aug 15, 2012
    DukeLeJeune (how cool is that name) is right as usual. For example I have an old Fane 10" that is rated at 200W but farts at about 70-75. I should also mention that if I try to tune it lower than it wants to go, fart out comes sooner.

    Many other drivers are similar, with fart out occurring at well below the power rating. I have not tried one yet but I believe that the Kappalite 3012LF does not fart out easily and that is probably why they are so popular.
  14. father of fires

    father of fires Commercial User

    Nov 29, 2006
    Chief of Medicine at Damnation Audio
    My thoughts exactly.
  15. Not many players are happy with 3012lf tone by itself with no mid driver. It's a subwoofer.
  16. low down shame

    low down shame

    Jan 23, 2011
    Then the Faital Pro 500's might be the way to go but it would be a 4 ohm 1000 watt Cabinet or get the Faital Pro 300's in 16 ohms. The Cab would be an 8 ohm at 600 watts and the Head would see a 750 watt 8 ohm load. The X-max is less on the Faitals.
  17. If you're anywhere near NYC you should buy the pair of 12/6/1 LDS cabs in the classifieds.