500 mono vs 350+350 biamped

Discussion in 'Amps and Cabs [BG]' started by awaker85, Jul 16, 2008.

  1. awaker85


    Jul 15, 2008
    My basic question is which head will be louder/more powerful. I don't really understand how biamping works, and I don't really know a whole lot about ohms other than the lower the better, that every cabnit you add after one splits the ohms in half, and that you generally don't want to get below four ohm's. So that being said, what would be a better said up, as far as power goes with a Hartke 2x15xl and a Hartke 4.5xl? Either the HA5500 (500 watts mono at 4 ohms) or the Hartke HA7000 which is 700 biamped? The HA7000 also has an adjustable crossover which would be nice. Thanks!
  2. awaker85


    Jul 15, 2008
    Also, the 2x15 cab is 4ohms and the 4x10 cab is 8 ohms. Does that matter at all when you are using them together?
  3. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    You'll want to read the ohms FAQ, as actually your understanding so far is mostly wrong. I don't mean any offense by that at all, just letting you know.

    A four ohm cab plus an 8 ohm cab gets you a total load of 2.66 ohms. If your amp head says it is rated for a 4 ohm minimum, then you risk damaging it badly by running it at 2.66 ohms. There are certain amps which expert users who know exactly what they're doing can use below their rated minimum, but you should not even consider it at this point.

    Loudness and power are not just a question of wattage, but how the wattage is used. Different speaker cabs have different efficiency; EQ can affect the usage of watts; adding more speakers can often get "more loudness" out of a certain amount of wattage, but only if you have carefully considered the total ohm load, and also taking into account the effectiveness of each cab in relation to the other. Also each cab may handle power differently, resulting in different perceived loudness; and if they are not the same ohm rating they will each be sent a different amount of power, causing problems in figuring out the overall loudness you're liable to expect.

    IOW don't use those two cabs together unless (a) you get an amp head which is safe to run as low as 2 ohms, and (b) you understand and are OK with each cab getting a very different amount of power.
  4. awaker85


    Jul 15, 2008
    Thanks for your help.

    Here's a quote I got from Hartke's owners manual. "When two speakers are wired in Parallel the total impedence is cut in half and when two speakers are wired in Series the total impedence is the sum of the speakers individual impedance."

    Does that mean if I ran it in Parallel it would be below 4ohms but if i ran it in series it would be like 12 ohms. And if that is true would that be alright to use with a head that can do 4ohm minimum? Also, what is biamping, and what affect does that have on ohms?
  5. Jaco who?

    Jaco who?

    May 20, 2008
    If the Hartke owners manual really does say that, the person responsible for writing it should be forced to read this section of the ohms FAQ above:

    Total impedance = 1/(1/a + 1/b + 1/c ... + 1/n).

    When all the cabinets or speakers are the same impedance, all you have to do is add up the # of speakers and divide the resultant number into the # of ohms of each speaker. For example, three 16 ohm speakers wired in parallel in a cabinet = 3/16, or 5.333333.… ohms. That’s how they get those 5.3 ohm 3x10s btw! (The 2x10 cabinet with 4 ohm speakers mentioned above wired in parallel would have a net impedance of 2 ohms). When the impedance of the different cabinets or speakers is different, you have to use the full formula. With a 4 ohm cabinet and an 8 ohm cabinet run in parallel the formula is 1/(¼+1/8). You can’t add ¼ to 1/8 without having the same denominator (I told you this was gonna sound like school), so you have to reduce ¼ to 2/8 so they match. Then adding 2/8 to 1/8 gives you 3/8, dividing 8 by 3 gives you 2.67. So, hooking up an 8 ohm cabinet and a 4 ohm cabinet in parallel to your amp gives the amp a load of 2.67 ohms to power.

    You can think of bi-amping in the HA7000 head as having two heads inside of one that can also be run in mono mode together, also known as bridged mode, but generally only at 8 or 4 ohms minimum load.
  6. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    FYI the bit above only applies when both speakers have the same impedance rating. When they have different ratings, like a 4 and an 8 together, the math gets more complex.

    But yes, running an 8 and a 4 in series will get you 12 ohms, and 12 ohms is safe. Unfortunately at 12 ohms your amp will only put out a small fraction of its potential power, IOW you'll get a lot less watts from it if you do that.

    Biamping is where the signal gets split (usually at the preamp stage) into two frequency ranges on two separate channels (lows and highs) and sent into two separate power amp sections. Typically the highs will go to a smaller (less watts) amp section. Each of those power amp sections will drive a separate speaker cab.

    In the case of some systems that are designed for biamping, you can buy a "single cabinet" that is actually two separate systems in one big box. So with a head that is designed for biamping, the "highs" output on the amp would go to the highs input on the cab, and same for the "lows" output and inputs.

    Or you could use separate cabs, like one big one for the low channel and one small one for the highs. You cannot biamp into just one input of one speaker cab.

    I'm not sure about how the Hartke head handles those ohm loads coming out of two separate power amp sections; it may be that it will treat each cab as a completely separate load, i.e. not parallel or series, in which case maybe the 4 and the 8 can work together. You'll seriously have to read the amp's manual carefully, and maybe even call Hartke, to answer that one for sure. The more I think about it, the more that would make sense; IF I'm right, the, the biamped system (with two cabs) would definitely be louder than the mono system with only one cab.
  7. BlacksHole


    Mar 22, 2000
    Rockville, MD
    The Hartke 700 is two separate amps, each capable of driving a minimum of 4 ohms. IOW, you can run a 4 ohm cabinet on one side and an 8 ohm on the other and adjust the balance to your liking. The 4 ohm cabinet will get more wattage, but perhaps for the sound you want and the efficiency of the speaker systems this will work to your advantage. Not all biamp heads will work this way but most will. Since to be a true biamp head, the frequency split comes before the power amplification, hence, each amp drives it's own load. On my polytone biamp, I actually also have separate preamps and tone controls for each amp. BTW, I also have a Hartke 5000 and even running two 8 ohm cabinets, it can get quite loud, so the 7000 should be extremely loud and be able to drive the speakers you want with little problem (other than the poor solder joints that tend to surface on these older Hartkes).
  8. Supertanker

    Supertanker Watch the dog! He is trained to bite!

    Jun 23, 2005
  9. Rick Auricchio

    Rick Auricchio Registered Bass Offender Supporting Member

    RE: Bi-amping:

    The two cabs are designed to reproduce the full range of bass frequencies. So splitting the spectrum via bi-amping won't be good. You can't just send the highs to one cab and the lows to the other easily. You would need cabs designed to cover each chunk of the spectrum. For example, a subwoofer and a mid-high cabinet. Standard bass cabs won't fly.

    If, instead, you are talking about a two-channel power amp without splitting the spectrum, then that should never be called bi-amping. In that case, you have two full-range channels that you can balance nicely.
  10. The Hartke 7000 does NOT have bridging capability. Dual mono or bi-amp. Each side (amp) will provide 350 watts @ 4 ohms, or 240 watts @ 8 ohms. Very easy to use different impedance loads on the ouputs, using the Balance control. It's a very capable amp, power-wise, mainly when considering use of two cabs.
  11. Supertanker

    Supertanker Watch the dog! He is trained to bite!

    Jun 23, 2005
    I regularly biamp 2 full range bass cabs.
    They sound dramatically better than when they aren't biamped.

    If a bass cabinet is designed to cover let's say 40hz to 15000hz,
    biamping (with a crossover) two such cabs will only improve the sound
    because you will eliminate the comb filtering between the two cabs (YMMV)...
  12. NKUSigEp


    Jun 6, 2006
    Bright, IN

    As for:
    This isn't necessarily wrong but it's not necessarily right either. It all depends on the application. If you're looking for high fidelity then what Rick said is totally correct. The majority of bassists in pop, rock, country, and many other genres don't use that kind of tone though so regular bass cabs will do.

    I don't know if I agree with this statement though...might want to get Bill FM to comment here.
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