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Minumum Amp Load - 2 Ohms

Discussion in 'Amps and Cabs [BG]' started by hammer2748, Feb 26, 2002.


  1. hammer2748

    hammer2748

    Feb 22, 2002
    Hartford, CT
    I have read back and understand how impedence ratings are working relative to the load on the amplifier. Now my amp ( Peavey T-Max) is labeled at 550W at 2 Ohm Minimum Load. I currently have a 410TVX 4 ohm cabinet (about a month old) and a blown 4 ohm 1-15BW . I am about to replace the 15 inch BW. The question I have is this: If I run both cabs (which runs the amp at 2 ohm load), am I running in the "danger zone" so-to-speak being at minimum, or am I okay as long as I don't go below that?

    Follow-up: the speakers say they are 375watts rms, 700 watts program. What danger are/will they be in under the same circumstances described above?

    Appreciate your input. Thanks

    Hammer
     
  2. Aroneng

    Aroneng Supporting Member

    Sep 7, 2001
    Ft. Lauderdale, FL
    The higher the ohm rating of the speaker, the lower the load is on the amp. Therefore, the lower the ohm rating of the speaker, the higher the load is on the amp.

    Similar to your home stereo, you need to follow the rating of your amplifier. Some are capable of handling 8 ohm speakers, some 4 ohm.
     
  3. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Hammer,

    You said your amp is rated for a 2-ohm minimum load impedance, so you should be okay.

    Just be aware that running with a 2-ohm load gives you less margin of safe operation than at 4 ohms, and a lot less than at 8 ohms. In other words, it's easier to make the amp thermal or otherwise shut down if you push it really hard into such a low load impedance. However, you'll be getting more power out of it anyway, so you actually might not have to push it as hard as you otherwise would with only one cabinet.

    A generally safe approach to matching speakers to power amps is to get at least an approximate match between the speaker's "program" power rating and the amp's continuous power rating. You've got a lot more speaker than amp, but that shouldn't be a problem unless you can't get the sound levels you want without clipping the amp.

    P.S. Hartford, huh? Whalers forever! :)
     
  4. hammer2748

    hammer2748

    Feb 22, 2002
    Hartford, CT
    Hi Bob. Thanks for the advice. Sounds helpful and somewhat comforting. I've been nervous at getting that low. But the amp specs say it will run at 2 ohms. No problem getting the sound I want. I just want the capacity for some of our larger and outdoor venues if I needed it. Most of our indoor shows will not require any more that the single 410 I am already using. Thanks again.

    By the way, are you a CT native or just a Whalers fan? I've not let go of it either. Really miss having them here. Thanks for bringing some memories back to the forefront!

    Best regards,
    Hammer
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Hammer,

    If you put the two cabinets next to each other and facing the same direction, you can actually get a bit of acoustic gain, called "acoustic coupling." That's when the sound pressures from the two cabinets add coherently, so you get the equivalent of possibly up to a 6 dB boost, equivalent to quadrupling the power, at the expense of omnidirectionality (which might be a good trade-off anyway).

    I lived near Hartford from 1976 to 1997 and as a hockey fan, I used to go to a lot of Whalers games. I wear a Whaler jersey when I go out to a hockey game, and sometimes when I play a gig. It almost always gets positive responses from others, especially at hockey games.
     
  6. hammer2748

    hammer2748

    Feb 22, 2002
    Hartford, CT
    Coincidentally, my bandmates and I were discussing this last night as well. We're off this weekend, but will try next and see how it works out. Unfortunately (I think), my cab is rear-ported and don't know if I'll loose that benefit as a result of that. We'll see.

    I'll let you know how it works out.

    PS, I yank out my Whalers jersey every so often as well. Whalers forever!

    Cheers,
    Hammer
     
  7. Turlu

    Turlu Supporting Member

    Sep 11, 2000
    Ottawa, Ontario CANADA
    Hammer,

    I own a Peavey T-Max as well. I run with with a Peavey TXF 210 and a Black Widow 115 Cabinets. I had a gig last friday and I used both cabinets so at 2 ohms load.

    It went perfect!!! No problem going as low as 2 ohms with your T-Max head.
     
  8. jcadmus

    jcadmus

    Apr 2, 2000
    Me too, same set-up, no problems.

    Don't forget, the T-Max has an internal fan to help keep things cool (How could you forget? It's so darn noisy.)
     
  9. hammer2748

    hammer2748

    Feb 22, 2002
    Hartford, CT
    Hi Jcadmus, Turlu. Thanks for the reinforcement. I agree on the cooling fan, noisey as hell.

    I am curious about your T-Max rigs when you 1st got them. Did yours come in a combo set up with the 2X10 or 1-15BW? Mine came with the 1-15BW rear-ported. The T-Max really kicks a** with the 410TVX alone! Love the sound. My band-mates are really happy with it as well and in most circumstances would be awesome as is. Just wanted something with a little extra head-room in the larger and outdoor venues.

    Are your 15's rear-ported as well? I love my T-Max. Came across this thing as a new floor model in '91-92 and have only had to replace a tube. When I got it in the combo configuration the dinky 2 wire to 90-deg. 1/4 inch male connector they provided that plugged into the head went bad. Sounded like I had blown the coil in the 15BW speaker. Played around with it, found the problem in the wire, so I cut off the 1/4 male connector, bored a hole in the back and hard-mounted a 1/4" female connector. Back in business and ready to pair it up with my new 410TVX. Can't wait to hear 'em both together. Thanks again

    Hammer
     
  10. Turlu

    Turlu Supporting Member

    Sep 11, 2000
    Ottawa, Ontario CANADA
    Hammer,

    I have the T-Max head and I have two separate cabinets, one is a Peavey TVX 210 and the other one is Peavey 115 BX BW. The Black widow makes a huge difference in sound.

    Take care of the tube channel section. It can be fragile and break down if the head is placed directly on your cabinets and suffer from the "shaking" frequencies of the bass sound. The tube can get loose and break from the "shaking". I have never had any problem with that but I try to avoid placing my head directly on my cabinets anyway.
     
  11. bizzaro

    bizzaro

    Aug 21, 2000
    Vermont
    Does a rear porting effect acoustic coupling???
     
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    I asked one of our speaker engineers--a really sharp guy on speaker matters--about port location. His answer made sense; at the frequencies where the port comes into play, the wavelengths are so long that the cabinet is omnidirectional and the actual port location (front, back, top, bottom, et al) is irrelevent, as long as it's not blocked or otherwise impeded.
     
  13. bizzaro

    bizzaro

    Aug 21, 2000
    Vermont
    So naturally the follow up question would be: Is acoustic coupling effective at lower frequencies even though the sound travels in all directions?? :confused:
     
  14. jcadmus

    jcadmus

    Apr 2, 2000
    I got my T-Max and my 115BX BW about two years ago (just before they discontinued the T-Max head). Had bought the 210TXF cab about six months before.

    My amp is racked in an SKB four-space case with a Rackrider power conditioner -- one-space left to add a goody if I want to.

    Oh, and both my 1X15 and my 2X10 are front ported.
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Yes, anytime you're combining coherent acoustical signals. The closer together the two speakers are, the wider the range of frequencies at which they will be coherent (spaced within a 1/4 wavelength), and the broader the angles over which you'll get this phenomenon.

    If you were to space the cabinets apart, the angles where the sound from them is coherent would get narrower; where they'll always be coherent is along the line of points equidistant from them both. There's a phenomenon in live sound called "bass alley" where you get a lot of reinforcement of bass signals right up the middle due to the woofers on either side of the stage.
     
  16. hammer2748

    hammer2748

    Feb 22, 2002
    Hartford, CT
    jeezzz guys, all this talk about "acoustic coupling" has got me all worked up. Can't wait to try this out. I as almost everyone here came to these forums to learn and I have learned more (electronically) in the forums I've subscribed to in the last 3 months than I think I have in my entire career (25+ years). Thanks again guys. Appreciate the input. Will be sure to let you know how it works out.

    Just one more question (Bob). Being my 1-15 is rear-ported, in most clubs we play the cab will be somewhere near a wall. What distance would be sufficient not to choke of any positive effect I am looking for. I mean are we talking a foot or so away from any wall or more than that (in most cases any more than that in the clubs we play at this point would not usually be possible)?
     
  17. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    For the minimum distance from a wall, I guess a rule of thumb could be at least two or three times the diameter of the port.
     
  18. One diameter is sufficient. Effective port length is calculated as having 1/2 the diameter as additional "run" beyond the end of the port.
     
  19. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Thanks for the clarification, Bruce!
     
  20. But doesn't the distance between the rear port and the wall affect low-freq relections? The closer the port is to the wall the more chance of creating a bass trap, no?