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Acoustics experts, chime in: 1-4ohm or 2-8ohm?

Discussion in 'Amps and Cabs [BG]' started by eli, Aug 6, 2001.


  1. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    This should start a GREAT argument, but I really do need the answer.

    THE QUESTION:

    All other things being equal, do you get more apparent volume (read: LOUDER SOUND) out of one 4-ohm speaker or two 8-ohm speakers wired in parallel?

    THE SETUP:

    Assume that we are talking about the same power amp driving either one enclosure with a single 4-ohm speaker in it, or two identical cabinets each with a single 8-ohm speaker. All cabinets and speakers are the same model -- the only difference is the resistance. Since few mfr's offer both, let's use Carvin as an example. They offer a 1x15 500-watt enclosure in either 8-ohm or 4-ohm versions. That's the kind of thing I'm driving at. Please ignore the capability of placing two speakers far apart -- that's a separate question altogether. Assume they are right by each other. If I need an explanation of the difference between apparent volume, SPL, and "just plain HOW LOUD IS IT" (if there is a difference), please feel free to provide it.

    THE BACKGROUND:

    If I run an amp rated at 250 watts@4ohms into a single 4-ohm cabinet, I will get 250 watts into and out of that speaker. Now, if I run the same amp into two 8-ohm cabinets connected in parallel, the amp will still put out 250 watts, but each speaker will only get 125 watts. (Feel free to stop me as soon as I make a mistake, but I'm pretty sure I haven't yet.) So really what I have is two speakers outputting 125 watts standing side by side.

    THE REASON I'M ASKING:

    I have heard that, if you have a given amp/speaker combination, adding another identical system will not increase the apparent volume very much. Applying this theory to my above example, a 125-watt amp powering a single speaker doensn't gain much by adding another identical 125-watt amp powering another identical speaker.

    So *I'VE* always felt that the single 4-ohm speaker would be the way to get the most volume out of the amp. (From a logistics standpoint, this is also the more portable AND less expensive solution. But that's not the question...)

    I own a stereo amp head that runs 250w/side into 4 ohms. I'm considering going biamp and adding speaker(s) for the low end. So, will I get MORE BASS out of one 4-ohm spk or two 8-ohm spks?

    OK? Fire away... and please, reply only from the standpoint of direct experience or acoustics training. Answers beginning with "Well, it would seem to me..." won't really help, because I already HAVE that. Plus, those seem to start fights and then the original question gets lost...

    eli@readyforthefireworks.org
     
  2. EString

    EString

    Nov 20, 2000
    Los Altos, CA
    Two 8 ohm speakers will be louder. The effect of doubling the amount of speaker area you have is much more noticeable than doubling your power. Also, both the setups you described are putting out the same wattage, but one has more speakers, so naturally the two speaker configuration would be louder.
     
  3. MikeyD

    MikeyD

    Sep 9, 2000
    Agreed - especially in the case where the cabinets/speakers in question are identical except for coil impedance. There have been recent threads on similar subjects, some of which contain good posts. If you don't mind lugging around more equipment, more cabinets can give you more volume, generally. Those who don't like hauling a lot of cabinets sometimes upgrade their power instead. But getting a second speaker is akin to a *least* doubling the amp's output.
    - Mike
     
  4. Monkey

    Monkey Supporting Member

    Mar 8, 2000
    Dayton, Ohio, USA
    Eli, I had the same dilemma. I play reggae, and need really deep bass, but don't want to haul around tons of equipment. I decided to go with the Carvin 4-ohm 1x15 powered by the 1000-watt Carvin head bridged. I rarely have to turn it up past 2, and I get deep bass. I realize that the Carvin cabs aren't the most efficient, but it works fine for me. I'm not as young as I used to be, and I got tired of hauling two cabs.
     
  5. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    Monkey --

    I'm surprised you didn't get the 118 for reggae. It's rated up to 2kHz -- do you use anything higher than that? And even if you do, it's available, just not as loud as the 45 Hz stuff...

    But you may have helped answer my question anyway. I have a Carvin 15 8-ohm in a Sonic Micromini cabinet, good for 500 watts. The head is an old Carvin PB-500 that bridges mono to 500 watts into 8 ohms -- and I play primarily for a soft jazz group. Even when I play with the good-time rock-n-rollers, I only use one side (175 watts into 8 ohms) and I never have to turn it past 4 or so. Of course, they do use an acoustic guitarist and a harmonica, so they never really crank.

    So maybe I really did get *my* ultimate bass system back in '95.

    But -- that old GAS thing is getting to me. On occasion it can be kind of annoying to have gear that does everything you want. (But what about biamping...?)
     
  6. First off, I must say that the way in which Eli posed his question was done in the most ordered and succinct fashion I've yet seen at Talkbass. Eli, if you're ever in NYC, I'll buy you an egg cream!

    Secondly, you mean to tell me everyone's in agreement in an amplifier thread? This has got to be a first! Way to go guys.

    Mike J.
     
  7. Certain persons, whose names will not be mentioned, have yet to discover this thread. :D
     
  8. Monkey

    Monkey Supporting Member

    Mar 8, 2000
    Dayton, Ohio, USA
     
  9. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    Oh, now, don't you start...:eek:


    But hey, I gotta consider the :all in agreement" thing...