I have an Epifani 210 8ohm 500 watt cab with SPL rating of 102db. I would like to add an Epi 112 4 ohm 350 watt cab with SPL rating of 100db. If I'm not mistaken this will give me a total impedance of 2 ohms? which my Eden WT550 can handle. Can anyone tell me if this will create a NOTICEABLE difference in the output level between the two cabs? I tried using the search function for this queston but only found a thread that had so many math equations in it my head started to hurt. Me not like numbers (grunt).

For starters, a 4 ohm and 8 ohm cabinet combined in parallel will total 2.66 ohms. The 4 ohm cab will take 2/3 of the power and the 8 ohm cab will get the other 1/3 or, if I have the amp specs right, around 400W for the 112 and 200W for the 210. Not sure about the actual db expectations but I can tell you this - I have an Epi 210 8 ohm and a 115 8 ohm that I drive with a QSC PLX1602. If I run the amp in stereo, I get 300W per cab. If I run bridged into the cabs in parallel, I get 800w per cab. The sonic and volume differences are significant (lots more punch with more power). These cabs like power. Running you Eden into the 210 alone should be getting you about 300W. You'll lose some of that power to the 112 if you run them together (the 112 will get ample juice but the 210 will be underpowered at 200W). You'll likely get some coupling effect that will result in more low end but I don't think you'll get appreciably more volume and the cabs probably won't get the juice they want to REALLY perform. Then again, I don't know that amp. The only way to know is to try it...

My math shows 2.67 ohms. I'd bet the 4 ohm cab will be noticeably louder. As always, I could be incorrect.

The 1x12 would get approximately twice as much power as the 2x10, BUT because the 2x10 is 2db more efficient and sonically a bit punchier, there should not be a significant difference in the output (if both cabs were identical except one 4ohm and one 8ohm, the 4ohm would be approx. 3db louder; in your case, difference should be approx. 1db -- just barely enough to notice if their sonic character were the same).

Thanks for the advice. I was afraid it would not be a very efficient combination and it sounds like that's the case. I guess I really need to go with two 4 ohm cabs.

You know, Humabass, I don't think your conclusion is really right. First, I hate to throw cold water on the impedence calculations above, which would be perfectly correct if the cabinets were resistors, but the combined impedence of these two cabinets is much much more complex an issue. At any given frequency, the impedence of the combination is probably more than the 2 2/3 ohms cited, and unless the minimum impedence for both cabs is at the same frequency, the combined impedence shouldn't be anywhere near 2 ohms. Secondly, your choice of whether this combination of cabs is right depends on what you are after. Are you looking for more in the bottom octave, or just more volume overall, or what? The two cabinets will without much doubt move more air than the 210 alone, and probably provide more low end in most rooms. The combination also might be more balanced across the whole frequency spectrum than either alone. As far as "efficient" goes, the cabs are so closely matched in efficiency that the difference should be minimal at most frequencies. Finally, I just don't think your idea of "going with two 4 ohm cabs" is the answer at all. The issue is not ohms, but what sound the cabs make at each frequency involved. Combining a cab that excells at the low end with one that excells at midrange frequencies might be the nirvana you are after--or not. Forget the ohms. The only way you will know will be to test-drive the combination and see if it floats your boat.

I don't think I made myself clear enough. I was talking about the difference between the output of one cab compared to the other cab while using both cabs at the same time. There would be a very significant difference between just using one cab and using both cabs; you'll have more cone area moving more air and more power from your amp.

What prompted my inquiry was that I wanted to add a smaller cab that I could use for smaller gigs or rehearsals and that would be 4 ohm to maximize the power from my amp but that I could also add to my 210 for bigger gigs. I actually used to use an Epifani 310 with a Berg 112 on top and got good results. I am looking for a little more low end from a 12 to add to the punch and definition of the 210 but was concerned that I would be underpowering the 210 and emphasizing one cab over the other.

So, you have tried something very much like this, and it worked. I don't see where the 210+112 should be much different, even given the difference in nominal impedence. When you say you want cabs "that would be 4 ohm to maximize the power from my amp", there you go real wrong. It takes twice the current from the amp to drive 2 ohms to the same relative dB level as an equivalent 4 ohms. In other words, it takes twice the watts to do the same work. So, instead of "maximizing the power" you might more accurately say "demands twice the power". You move the same air, it just takes more current to do it into a lower impedence. Watts are not decibels. That's what I meant when I said forget the ohms and listen to the combination.

As long as the efficiency of the two cabs used are the same (for instance, between either an 8ohm total impedence or a 4ohm total impedence), then twice the watts pumped through the cabs will mean approximately a 3db increase in output volume. Definitely noticable.

Well, this is true as far as it goes, but it depends on two cabs having the same "efficiency" rating measured at 1Watt at 1 Meter, not 2.83v/1M, which is more accurate as a comparable spec, and that you are comparing the output at one frequency more or less under constant lab conditions. You did not take part in the drawn-out mess of a couple of weeks ago on this topic, but you might be interested in wading through http://www.talkbass.com/forum/showthread.php?t=124766 The basic fallacy, though, is that 4 ohm cabs offer a 4 ohm resistance at all frequencies, which they do not, and that they have the same "efficiency" at all frequencies, which they also do not. And, the same with cabinets whose specs are nominally 8 ohms. In the real world, there is not nearly that much difference between 4 and 8 ohm cabinets, except in their minimum impedence, and the idea of "maximizing the power of the amp" by using lower-impedence cabinets is, IMO, hogwash, based on a misunderstanding of simplified "efficiency" specs and nominal impedence ratings which mask a much more complex situation.

Your ears can tell you more in 5 seconds that you can get from hours of discussion and mathematical calculations. Get in the car, drive yourself to a store that has the facilities for you to try it out.