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More Power Equals Less Volume?

Discussion in 'Amps and Cabs [BG]' started by LeonD, Jun 8, 2001.


  1. LeonD

    LeonD Supporting Member

    I purchased my current bass rig years ago. The amp is an SWR Bassic 350. Because at the time I had a small car, a 4 x 10 cab would not fit. I decided to go with a Goliath II Jr. 2 x 10 that is rated at 4 ohms.

    This rig had a good sound and I was happy with it. But I noticed the amp could be used with a 2 ohm load and produce more power. I figured, "why not get a second 2 x 10 and get more of a good sound?" So I did.

    And that's the rig I used (Bassic 350 and 2 2 x 10 cabs) until playing out one time, in the middle of an aggressive passage, my rig farted! Clear as day. I kept playing and it kept farting. When I backed off, it stopped.

    A call to SWR explained the problem. It seems like while the amp will work with 2 ohms, the amount of headroom is minimal. So even though I had more power and more speakers, it was very easy to distort the power amp. Too easy!

    I cut back to one cabinet and the farting left. I almost think I was getting more volume with less watts and one cabinet than with more watts and two cabinets. It's hard to tell for sure as I was on the stage with the rig and I don't know how the sound was different out in the crowd.

    Does this make sense? Has this happened to anyone else?

    LeonD
     
  2. MikeyD

    MikeyD

    Sep 9, 2000
    There is some technical justification for what happened - and SWR's response. While the amp's output stages may be designed to drive a 2-ohm load, its power supply may be in a borderline condition wherein the higher current demanded would draw the supply voltage down more readily than if feeding only a 4-ohm load. So perhaps the amp goes into hard clipping more quickly at the lower impedance and therefore sounds worse when it clips. A power supply with a higher current rating and better voltage regulation would probably improve this condition.

    As far as what sounds louder, it seems doubtful that using one 2x10 at 4 ohms would be louder than two of them at 2 ohms. You'd have to do a comparison in a controlled experiment if you have any doubts. Human hearing can be tricked sometimes.

    - Mike
     
  3. As far as what sounds louder, it seems doubtful that using one 2x10 at 4 ohms would be louder than two of them at 2 ohms. You'd have to do a comparison in a controlled experiment if you have any doubts. Human hearing can be tricked sometimes.

    - Mike [/B][/QUOTE]

    MikeyD, could this "volume deception" LeonD was experiencing be that, when he used just one cabinet, the amp was putting out a good amount of power into a cabinet that could handle it, thus causing what I refer to as speaker scream, but, when he added the second cabinet, two possible things happened: 1) With the second cab added, and *two more mouths to feed* the power amp having less headroom can't produce as clean a signal as with just one cab, and: 2) With each cab receiving less of a clean signal, the speakers aren't
    driven as close to their limit as the power available
    must now be shared amongst 4 rather than 2. In my mind, I view this like watering the lawn; if you have 10 gallons of water per minute passing through a hose with a diameter of one inch it will shoot out with more force than if the same amount of water is exiting through a hose with a two inch diameter, although it's the same amount of gallons per minute. Just a layman's theory, what do ya think?

    Mike J.
     
  4. LeonD

    LeonD Supporting Member

    Mike J.: Sounds good to me! I think also what happened is that with the 2 ohm load, I turned down enough to prevent clipping. That point may have been less than where I was at with the 4 ohm load.

    Is this common with all amps that can run at 2 ohms? That the headroom is less as the resistance is less.

    LeonD
     
  5. MikeyD

    MikeyD

    Sep 9, 2000
    Mike J, generally you are correct in that each cabinet in the parallel pair will get slightly less power than the single cabinet alone. This means that the single cabinet is likely to generate higher THD (distortion) at the higher power levels, because the cones will have greater excursion. The distortion byproducts will be audible - probably more than the fundamental because of the nature of human hearing (Fletcher-Munson curves). However, I seriously doubt this effect is greater than: (a) the increase in power going to a pair of cabinets, (b) the ability of the pair of cabinets to move more air, and (c) the pair, if stacked, slightly increasing their directivity and forward sensitivity.

    When one turns *down* the volume to avoid clipping, the psychological effect may be to think that the net volume has gone down. I'm skeptical at this point, unless the amplifier is rather sick and in need of surgery.

    - Mike
     
  6. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    This is why I always say it's not such a grand idea to run any amp at 2 ohms, even if it's rated for it. You give up a lot of headroom. Some high-end power amps may be able to do it successfully, but I'd just buy more power rather than squeeze the amp.

    OK, guys, go ahead and have your way with me ... again.
     
  7. if you want to use two 2x10's, why not buy two 8ohm 2x10? you could get a Eden D-2x10xlt 8ohms, and then have highly efficent cabs. More speakers = more sound. Only thing what happend with you, like explained was that you lost head room wiht your head cause it went down to 2ohms. I also remeber reading that SWR also says dont go down to two ohms, cause the amp tends to over heat, therefor the amp burns out.

    what i want to know is why swr tells people their amp can go down to 2ohms. why not just leave it out, if they're saying its bad to do it. bad marketing choice. Lure is customers with the ability to run at 2ohms, and squeezing out an extra 100w. Down side? you get crappy tone. VERY crappy tone, and risk burning out your amp. FUN.
     
  8. I'll try blaming my amp next time I cut loose!!
     
  9. When one turns *down* the volume to avoid clipping, the psychological effect may be to think that the net volume has gone down. I'm skeptical at this point, unless the amplifier is rather sick and in need of surgery.

    - Mike [/B][/QUOTE]

    Good point, MikeyD. Also, as we all know more volume is not necessarily better. I bought a pair of Bose speakers for my home stereo a few years back, and after a few weeks I realized just how good a well designed speaker can sound. They're not the most efficient speakers out there, but the quality of sound is amazing. One of the selling points they use is that their speakers don't give the user "listener fatigue," something a lesser speaker can do. Something we can all ask ourselves when considering a more powerful amp or second cab is; do we REALLY need it?

    Comparison:(I love doing these)
    One girlfriend = Good
    Two girlfriends = Better, 'till they both come over unexpectedly at the same time, and bust your *HEAD* and kick your *BOTTOM* then you just lay on the ground and go *OOOHM!*

    Good Night!
    Mike J.