Ah, I was just being a bit silly. These are always good discussions, and your thread is a good one in communicating to players that the topic is not so simple, and not just about volume (although sometimes it is about volume...that extra little headroom at the end of the night when things start to really push.
I always tell players when discussing this issue to ignore those who say it doesn't matter, and also ignore those who say it always matters. It really does depend.
Buying a 4ohm 210 from a big box store when you have a DB750, not so much. Choosing a 4ohm 212 over the 8ohm version (again, assuming you are a player like me that would never schlep two large cabs) when you have a GKMB200 or Aguilar TH350..... that could be a life changing decision on the gig
And, per other posts above, if you use aggressive techniques like slap that pump huge peaks into your rig, it is surprising what a bit more power and headroom can do (again, assuming a relatively moderate 8ohm power output and a cab that can use the extra power). It is like taking a compressor set too sensitive out of your signal chain!
At the extremes like unable to hear by far at 100hz, then doubling it can still be unable to hear. But right at the point you can hear, a 3db change is a lot. At higher levels, it isn't. First thing in the morning a low DB could possibly sound loud, at the end of the day after exposure to sounds all day a low DB could possibly be undetectable.
I agree with the point of this thread, trying to squeeze out every watt is not a big benefit. Given a Solid State amp of modern design, the frequency response is going to be fairly flat in the human hearing range.
IMHO consumers need to demand frequency response charts that show the cabinet can do with the power it is fed. You can use these kind of charts, with the equal loudness, and you're own experience with other measured cabinets to know how the whole system, amp and cabinet will behave for you.
A Bill Fitzmaurice 12" T39 versus an 8x10"
Here, you can see that at 150hz and below the Black 12" line is above the Blue 8x10. The amount it is above is on the vertical grid line. You can count the DB difference at any given frequency and see that in most of this range you'd need to feed the 8x10 many factors of power to have it match the 12". For example at 50hz the 8x10 is a little over 90db, the 12" is around 97 db. That right there is 7db of power you'd have to add to the 8x10 to reach the same level. And that's if the cab could handle the power and not compress it more.
If you could superimpose these two graphs, the cabinet measurements start at 80DB, that's halfway up the equal loudness chart. At 50hz your own hearing is way down at 50hz compared to 3000hz. You need a lot more bass power compared to power at mids. Mids can easily be adjusted with EQ. In the natural worlds, it more important survival trait to hear midrange over bass.
Frequency charts are critical on understanding the value of your set up, mostly for cabs. Can you use your ears? Sure, but they are not good test instruments, and you can't compare your hearing to that of others and the conditions they were listening under.
Get the charts. Compare that to what you hear as a starting point. Listen to other cabs and compare the charts. It all correlates, it's an eye opener. IMHO
My opinions are the result of years of rational, objective analysis. I analyze all factors before making a choice. I update my opinions to include new facts. Fallacies? No?
You can count the DB difference at any given frequency and see that in most of this range you'd need to feed the 8x10 many factors of power to have it match the 12". For example at 50hz the 8x10 is a little over 90db, the 12" is around 97 db. That right there is 7db of power you'd have to add to the 8x10 to reach the same level. And that's if the cab could handle the power and not compress it more.
To get 3dB from power alone the cab must be able to handle 2x the power, no matter the amp.
It gets sticky doubling cabinets with a tube amp which delivers same power to various loads. The same amount of power split between two cabinets is only 3dB extra but this disregards the power compression of the single cabinet and the fuller expression of headroom that comes from doubling the cabs.
Doubling up cabs on a SS amp gives more power, more power handling, and if the single cab was working hard you could be going from say 6dB to 12dB of headroom. Lean on a note and get your "I am bass" on.
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Want to put out the same sound as the original source material = take the mix off the CD and put it out in a live venue?
That aint a small wish.
Here's 60 Hz at 0 dB versus 1k Hz at -20 dB - a power reduction of 1/100th.
If your band puts 10 watts into 1K Hz [typically vox and guitar in a modern band] then the sub 100 Hz bass frequency components [typically bass and drum elements] gotta bring upwards of 1,000 watts for equal loudness.
It means that if your 5-string bass rig gets in the ball park of its share of the 100:1 ratio of power required in order that the sub 100 Hz component of the total mix keep up with the 1k Hz component of your band's output - that only gets you "equal" loudness. It is quite common, especially with modern music, that accurate reproduction requires more loudness in the lows - sometimes a lot more. A 1/f distribution [-3 dB per octave as you go up the scale] means that across the 4 octaves from 60 Hz to 1k Hz, the low end needs to be about 12 dB louder than the high end.
+1 Many amps hover around about a 1.5X power increase from 8 to 4 ohms, which is only about a 2 dB increase in actual volume.
Just to be pedantic, Ohm's law dictates that the amp will double power into the 4 ohm load. SO if you're playing painfully loud in your living room at say 100 watts, using a watt or two, when you change to a 4 ohm speaker you'll get the two or four watts that yield a 3 dB increase. What the amp almost certainly cannot do is output twice the power at clipping. So it matters if you are driving your amp to its limits. And 1.5 is a pretty reasonable expectation for max power increase in the real world.