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Is it better to overpower at the same ohms or different?

Discussion in 'Amps and Cabs [BG]' started by McGillicuddy 79, Oct 26, 2013.


  1. McGillicuddy 79

    McGillicuddy 79

    Jul 9, 2011
    Hey guys I've got a question here that I haven't seen an answer to so forgive me if it's been answered somewhere before. Hopefully in a month or so I will be buying a Hartke lh500 head and a Hydrive 112. The head is rated at 500 watts @ 4 ohms. The cab is rated @ 300 watts and is selectable for either 4 or8 ohms. My question is would it be better to run the cab at 8 ohms and get somewhere around 350 watts into it from the head or run the cab at 4 ohms for the full 500 watts and just watch my volume? I would assume that the former would be the better route to go but you know what they say about when you assume. :p Sorry for the long post and sorry if it seems like a ridiculous question. Thanks.
     
  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    It doesn't matter. Don't pay too much attention to power handling specs for cabs in any case. Instead, use common sense, and live by the rule: "If it sounds like it's going to explode, it will."
     
  3. McGillicuddy 79

    McGillicuddy 79

    Jul 9, 2011
    Well put sir and thank you for the swift supply.
     
  4. McGillicuddy 79

    McGillicuddy 79

    Jul 9, 2011
    Well the plan is to add another 112 a little later. The cab itself has a switch allowing you to select 4 or 8 ohms
     
  5. SactoBass

    SactoBass A retired civil engineer who likes all-tube amps! Supporting Member

    Got it. I deleted my post because I misunderstood. I though you could buy an 8 ohm version or 4 ohm version. But now I understand that the Hydrive 112 cab is switchable.

    I would first try it at the 4 ohm setting to see how well the cab handles the power. If the cab sounds like it's struggling, then go with the 8 ohm setting.
     
  6. McGillicuddy 79

    McGillicuddy 79

    Jul 9, 2011
    Thanks for the input Sacto. I didn't know how much of a difference it would make being with the head being 4 ohms but thought if I was gonna overpower it it's better to overpower by 50 (virtually nil) watts versus 200. The other side of the coin being the ohms not matching up. I've read in the stickies that with a solid state it doesn't matter much but just wondered which was the lesser of two evils.
     
  7. SactoBass

    SactoBass A retired civil engineer who likes all-tube amps! Supporting Member

    Yep. By the way, that 300 watt rating for the cab is the thermal rating (voice coil melt point). The mechanical rating (which manufacturers never publish because they don't like the lower number) is usually around half of the thermal rating. So even though your cab is rated to take 300 watts, don't fall for that. If you actually pumped 200 full watts at 100 hertz into that cab, you would blow the cone because you would exceed the speaker's mechanical limits. So going with the 8 ohm setting is probably your safest bet. And when it comes to solid state heads, there is absolutely no issue by doing that. In fact, the amp will run cooler with an 8 ohm load compared to a 4 ohm load.
     
  8. McGillicuddy 79

    McGillicuddy 79

    Jul 9, 2011
    Ah ok thanks for all the advice. I lurk here a lot and though I've been a member for the past 2 years I rarely post. Most questions I would ask have already been asked and answered by someone else. This is one I couldn't find an answer to. I've read up on how amps work and while I've gained a wealth of knowledge on the subject it's a lot to take in.
     
  9. dincz

    dincz

    Sep 25, 2010
    Czech Republic
    That figure of 4 ohms is the minimum load impedance you should connect to it - it's not the impedance of the head (which is typically only tenths of an ohm).

    Yes, if the speaker sounds like it's in trouble, then turn down.

    I'm surprised to see so many confident and definitive answers to this question without anyone asking how Hartke achieves the switchable impedance. If it was simply 2 equal impedance voice coils switched series or parallel, you'd expect to see options of 4/16 ohms, or 2/8 ohms.

    On the other hand, if the switch selects a 4 ohm coil or an 8 ohm coil, then I wonder if they have the same power rating.

    I looked online at the manual but it doesn't help - and it also contains some [DEL]dubious[/DEL] wrong info about "underpowering" and distortion burning voice coils.
     
  10. +1 sactobass. Heating up the voice coil not only damages it in the long run :help: ("I don't know why it blew today. I've run it like that for months!"), It also increases the resistance of the voice coil so its not 40hm any more - Thermal Compression.
    Also, don't be fooled by the 4ohm versus 8ohm argument. I know that 200watts sounds a lot but the difference is only 2db. Hardly noticeable. If volume is your goal You are better off looking for the most efficient cab. The difference between 96db and 98db is (you guessed it) 2db! i.e. the same as those 200watts.
    You could buy a barefaced 8ohm cab which is 99db.
    plus you don't stress the amp
    plus the power supply never has a problem keeping up with transients.
     
  11. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    i don't know why hartke bothers with the 4/8Ω thing on that little cab, that just leads to too much power getting dumped into it; they could just make them 8Ω like any normal cab and shave a few bucks off the price.

    the OP's plan to get two of them seems sound to me, that'll be a nice little stack.

    (by the same token, their 1000w 4x10 might actually benefit from 4/8Ω switching, since it more often will be used by itself; i suppose having four dual-voice coil speakers would push the price up too much, though.)

    if anything, i'd think combo amps are the one place where this idea has merit; there's always that design trade-off decision, to make it run all available amp power into its one 4Ω speaker or allow it to push an 8Ω extension cab.
     
  12. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal

    Marketing. Period.
     
  13. +1 I always thought the switching was a solution without a problem. You just know that a user somewhere will connect two cabinets to a 4Ω minimum amplifier with one or both switches in the 4Ω position.
     
  14. Interested in how they pull of this 4 / 8 ohm switch.
     
  15. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    Dual coil speaker.
     
  16. jamminology101

    jamminology101

    Aug 22, 2012
    Indianapolis In
    Endorsing Artist: Glockenklang
    They did it in response to customers bitchin that when they run the 15 on the bottom/4×10 full stack configuration, people complained that there was too much volume/db discrepancy between the two when running from one head. I dont know if it helped...but that was there "solution"...
     
  17. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    no, this only applies to the little 1x12 cab.
     
  18. jamminology101

    jamminology101

    Aug 22, 2012
    Indianapolis In
    Endorsing Artist: Glockenklang
    The little one...man that's crazy huh?
     
  19. Bassamatic

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

    I would run it at 8 ohms to be sure you don't blow the driver.

    There is almost no audible difference anyway. The SPL difference with twice the power is less than 1 dB. Twice the power does not make it twice as loud any more than twice the horsepower makes your car go twice as fast.

    You are in a good position to test this for yourself!
     
  20. sratas

    sratas

    Dec 15, 2007
    Parma, Italy
    thermal power ratings mean very little, in fact, it's the least parameter to look at when building a rig. Unfortunately, most manufacturers don't reveal other meaningful numbers like excursion ones and SPL output at various frequencies, for example.

    So, Jimmy is right, use whatever amp-cab combo you want and listen with your ears, if you notice hard straining of your speakers, turn down and/or lower the bass knob.
    This applies even with the 112 at 8 Ohms, many speakers reach their mechanical limits far before being thermal limited
     

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