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Is a 4ohm cab louder than an 8ohm cab w/same amp?

Discussion in 'Amps and Cabs [BG]' started by Flux Jetson, Aug 7, 2012.


  1. Forgive the naive nature of the question, but I want to get myself straightened out on something.

    Here's a set of specs for the sake of this conversation:

    AMP:
    400 watts @ 4 ohms and 200 watts @ 8 ohms.

    Two cabs:
    1.) A 2x10 @4ohms rated at 500 watts.
    2.) A 2x10 @8ohms rated at 250 watts.

    When used one at a time, will 4 ohm cab be louder than the 8 ohm cab?

    I realize that one cab is drawing more power from the amplifier (4 ohms) but is it actually pushing any more air?

    Let's assume same brand, and same cab design, you just have two to chose from, one is a 4 ohm 2x10 the other is an 8 ohm 2x10.

    Some companies offer choices like this (such as Carvin) presumedly to allow you to set up your rig with more than one cab if need be, so I'm just trying to gain an understanding of something here. Many times when I think I "get" something I come to learn I had it all wrong.

    Thank you.
     
  2. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Two cabs that are identical save for impedance will put out and handle equal amounts of volume and wattage respectively. And if you find a 210 that will truly handle 500w without sounding like crap long before you get to that mark, buy it, because I've never once seen it in my life. If you can get 250w into a 210, you should consider yourself lucky. Power handling ratings are by and large completely bogus and based on when your voice coil fries, not when your cab starts to sound farty.
     
  3. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    It probably wont be any louder, 250w can push a 210 cab it its limits just as easily as 500w can. It could possibly have more clean head room, but being that its a 210 thats doubtful. I always go 8ohm regardless, because it allows for expansion.
     
  4. Show me the 4 ohm 2x10 that has the same senstivity as the 8 ohm one and carries 500W.

    They can say it carries 500W but actually it won't. It will fart out with the same amount of power as the 8 ohm one, rendering all the maths theory worthless. Those same 8 ohm tens would be making a 1kW 4x10, the greatest speaker never made.

    Always, more speakers to get louder. Physics is a beatch. She tells you one thing without the other thing and then kicks you in the goollies.

    Yes the amp can put more power through a 4 ohm loading. No, the speakers in your example can't handle it. This is true of all 8ohm vs 4ohm versions when the amp is powerful enough to drive the 8 ohm one to its max output.
     
  5. I picked those numbers out of the air, they are just there for the sake of this conversation (exactly as I stated in my opening post.)

    But thanks for the answer! :)
     
  6. Thanks for the help.

    And .. again .. fake numbers used for comparison only.
     
  7. Mehve

    Mehve

    Jun 2, 2012
    Kitchener, ON
    Technically speaking, power is power, regardless of what impedence it's developed across. And the impedence has no relation to how much air is moved with a certain amount of power. So all else equal, more power will equal more volume (although 2x power doesn't mean twice the loudness).

    To use your example, picture two 210's, both rated 500W, but 4 and 8 ohm impedences. Now imagine you're pairing each one up with a typical mid-size head that can output 500W into 4 ohms, but only 300W into 8 ohms. In this case, the 4ohm version would have the potential to be louder. Not because of the impedence itself, but because of the head's different limits at different impedences.
     
  8. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Oh sure, you say that now...

    :D
     
  9. Ok folks .. thanks for the verification.

    And again .. don't got too worked up over the specs, I just grabbed two sets of specs out of the sky ... as I explained in the first post ... for the sake of this conversation. I had to have two sets of numbers to explain my meaning. The point here wasn't whether or not the specs are to be taken seriously - because they are not - the point was are 4 ohm cabs any louder than 8 ohm cabs .. all other things being as equal as practical (same cab, same design, etc .. you know what I'm getting at here. :))

    Thanks again for hte explanation, I figured it was that way, I just needed to have it verified.

    Best wishes. :)
     
  10. Heheh ... :)
     
  11. monti2889

    monti2889

    Jul 19, 2012
    Ohms measure resistance
    watts measure power
    volts measure electromotive force (pressure)
    Amps measure current
    decibels measure sound
    feet...measure.....(well, it was bound to come up sooner or later):bag:

    anyway to answer your question...cabs being similar, with only a different wattage and ohm rating will most likely have a similar volume due to the voice coils having the same decibel output, with the 4ohm 500w cab, you would just be matching your cabinet to the specs of your head, making it run a little more efficient, and having a little extra headroom to cover signal spikes that occur while playing a percussive instrument, so you have less of a chance to blow your speakers.
    8ohm 250W also matches the output of your head, but would also allow you to add a second cabinet (say a 15 or another 2x10, now the added surface area would allow you to create more decibels as you would have a 4ohm 4x10 load or a 4ohm 2x10+1x15 or whatever...LOL) anyway, I know it gets a little more complicated than that, but that's the short story/book...it's late and I'm tired.
     
  12. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    Assuming impedance were the only difference between two otherwise identical cabs, a 4-Ohm cab would theoretically have the potential for a 3dB (barely perceptible) increase in SPL, if the cab weren't already being pushed to maximum loudness.

    Before I bought my Wizzy 12M, I tried 4-Ohm and 8-Ohm versions and the differences were unremarkable.
     
  13. JHAz

    JHAz

    Jun 29, 2011
    Assumed, I assume, in the above responses is equal or at least closely comparable sensitivity for the 2 imaginary cabs. An 8 ohm cab with 400 watts thermal rating and sensitivity of 100 dB at 1 watt at 1 meter will be louder another 8 ohm cab with a 600 watts thermal rating and 96 dB sensitivity. To make up the 4 dB difference in sensitivity requires over 2 times the power.

    FWIW, if two otherwise identicalish cabs, one at 4 oand one at 8 ohms, are auditioned against each other without touching the volume knob on the amp, the 4 ohm should be louder because the amp is delivering more power to it. But it's not that difficult to turn up the volume control.

    Also FWIW, the gone but not forgotten BFM used to say you could expect speakers to start compressing and or farting out around one half of their thermal ratings. That is they sound bad before they burn up.
     
  14. KJung

    KJung Supporting Member

    This is a complex question. The answer is 'it depends'.

    With a relatively low powered head, and a cab that has moderate to low efficiency, the impact of almost doubling the power can be huge. Remember, that 3db increase that some poster said is 'barely noticable', is basically the amount of increased volume you would get by adding a second cab using a tube head.... huge.

    I would highly recommend that you ignore those who post 'it doesn't matter' as much as those who post 'it does matter' in all situations.

    It all depends (assuming you are using a solid state head) on the absolute power output of the amp, the mechanical capability of the drivers in the cab, and the size of the cab.

    For example, most 112's are pushed to their limits with the typical 250 or 300 watts of the typical micro running at 8ohms. So, there would be little to gain getting a 4ohm version of a single twelve.... UNLESS, that 12 is a very high quality and somewhat low efficiency driver. Cabs like the new Thunderchild cabs (which only come in 4ohms) and especially the Acme 112's really open up with those 200 or 300 more watts from the typical micro in their 4ohm versions. Of course, if the 8ohm output of the head is huge already (i.e., if you are using a 900 watt monster), then cab impedance, even with large cabs or low efficiency cabs matters much less.

    With a large cab like a 212 or 410, if you know you are only going to use a single cab, 4ohms (again, assuming a moderately powered solid state amp) can make a HUGE difference when you are pushing it a bit. A bit more absolute volume, a more open low end, and the amp less likely to hit its limiting circuit (again, assuming a moderately powered ss head).

    I wish there was a correct sticky on this in the site. Lots of bad information (in this thread and other threads on this topic). You need to think a bit about all the interacting components in a rig, and take into account a number of variables when making the decision on cab impedance. It can be a VERY impactful decision.

    I would think some of the posters in this thread who have participated in other threads on this topic would start to understand this. I don't get this 'it doesn't matter' thing, etc. Incorrect as often as it is correct. It depends.
     
    Mpike and wolffire99 like this.
  15. KJung

    KJung Supporting Member

    This is a good example of where it would not matter... a very midrange voiced, very small, high efficiency cab witha driver that cannot use much power (and does not need much power). If you would have done the same test with, for example, the Acme112, it would have been a totally different story:) It depends!
     
  16. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal
    Ken, I hear you, but with the sample specs the OP gave, it would not matter :)
     
  17. punkjazzben

    punkjazzben

    Jun 26, 2008
    Australia
    So... I have a Warwick head that does 300w@4ohms. I'm running it through an 8ohm cabinet. My understanding is that an 8ohm cab will not draw the full 300 watts. I suppose what the OP is getting at is whether there is a perceptible difference in decibel output between an 8 and 4 ohm cab... i.e. 200w with an 8 ohm cab, and the full 300 with a 4 ohm cab. Assume that the cabs are the same model.
     
  18. KJung

    KJung Supporting Member

    Not necessarily. Power ratings of cabs are not really correlated with efficiency at all, and amps rarely put out their maximum rated power. A good example is the Acme 210's, which have low absolute power ratings, but are very low efficiency. The higher power is all about not hitting the limiting circuitry of lower powered ss amps on peaks, etc.

    It is typically fine to put a bit more power into a cab than the thermal rating of the cab. Most cabs can easily handle higher powered, short term peaks (within reason).

    Also, even the mechanical specs of drivers are greatly impacted by the tonal preference and also the power/frequency curve of amp output (hi passing, voicing, etc.). A very bassy tone preference, or an amp with limited hi passing that pumps out a lot of sub bass can behave VERY differently regarding the match-up of amplifier output to speaker capability (thermal and wattage).

    It depends.... every situation is different. Hi passing, preamp voicing, cabinet tuning, bass control setting, technique (i.e., digging in and slapping give the mechanical spec's of drivers a much more extreme 'test' than a soft 'finger touch' style player.

    It depends!
     
  19. JTE

    JTE Supporting Member

    Mar 12, 2008
    Central Illinois, USA
    Cabinets don't "draw" watts. They only what's given them


    Comparing two otherwise identical cabinets, one rated at 4 ohms nominal impedance and the other at 8 ohms using the same amp, generally the difference in what you hear is negligible going from say 300 WRMS @ 8 ohms to 400 WRMS @ 4 ohms.

    John
     
  20. KJung

    KJung Supporting Member

    Again, disagree, and most solid state amps more closely double power (i.e., typically 300 to 500 watts) versus your example (the oversimplified view of getting about 2db to 3db more absolute volume when increasing power by between 80% to 100%).

    The mistake here is just thinking about pure volume, and thinking that you will hear a difference in your living room with the same amp and the same knob setting. The difference (when there is one) will only become noticeable when you reach the amp's and the cab's limits when pushed to the max. That difference (again, it again depends) can be quite noticeable, with the amp/cab not compressing as much down low, and sounding 'good' at a bit higher volume.


    Again, it depends:) I agree, often it won't matter a bit, but many times, it matters quite a bit, especially with relatively low powered solid state amps, and especially with higher end cabs that have mechanical specs that can keep up more with that 'thermal rating' of the cab versus 'back in the day'.
     

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