I have a question. How do you wire a 3-speaker cab to acheive a 4ohm resistance? (Like the epifani ul-310) You can do it by alternating the speaker ohm, but what if you want keep the same speaker ohm? Say, if i want to wire a cab using 3 - 8ohm speakers, how would you go about doing this? I already ordered the cab construction book, but im gonna jump the gun and ask you guys first.

Note: for a long time Epifani listed the resistance of their 310s as 5.3 ohms. I can think of four ways you might accomplish this: 1) Use a dummy load instead of the fourth driver 2) "Fudge" the actual rating (a la Bergantino) 3) Use drivers with nonstandard ohm ratings 4) Put a tweeter (or ideally a couple tweeters) in the cab

I thought so too. When i checked the website recently it said 4 ohms. I was wondering if they had wiring diagrams, but apparently they dont

My mistake, I should have been more specific. I was actually referring to the NV610. It says on the cab that it's 4 ohms, and upon examination of one of the drivers it says that they're 32 ohms. Assuming there's not some crazy chicken crucifiction ritual associated with building it (though mine sounds so good that there almost has to be), running all those in parallel gives 5.33 ohms. I mentioned this in another thread and someone else claimed to have tested his and gotten that particular rating. I haven't done the test myself since my meter has been in a box in the attic since college. So I had just assumed you were fudging. I apologize if I was incorrect on that, though I'd love to hear what's actually going on instead if I am. Oh, and thank you for building such wonderful cabs. I own two of them.

Why would you do that? The resistor would just steal watts away from the speakers. Plus you'd probably heat the resistor to the point there it starts smoking. It doesn't work that way. You'd have to put the tweets behind a crossover to keep away those low frequencies that will blow it up. Doing so mean the tweet never sees frequencies that generate the low impedance readings. So the tweet's nominal impedance doesn't figure at all in the cab's overall nominal impedance rating. The only interest in the tweet's nominal impedance is for calculating the crossover component values. In practice you may as well treat 5.3 ohms as though it's 4 ohms. I'm not suggesting it's the same thing, but it's closer to 4 ohms than 8, and too close to be considering it as anything else. Yes you lose watts by not running the full 4 ohms, but it's not a lot in the overall scheme of things. Full credit to Jim for not Fudging the figures. 3 x 12 ohm drivers was a good idea and a nice touch!

thanks for the suggestions. 12 ohm speakers are pretty hard to find. Pretty uncommon as far as I've seen. Anyone feel free to give me some tips on finding some I could use it as a 4 ohm cab but my poweramp doesnt go 4 ohm mono-bridged. I could get 910 watts at 8 ohms monobridged. So 4 ohms would be pushing it.

You won't find them in an over-the-counter variety. Jim's are custom made. If your poweramp bridges to 8 ohms, you'd be better off using 4 speakers, each one 8 ohms. Wire them in a combination series/parallel to get a final nominal impedance of 8 ohms.

You would do that to get it to 4 ohms, which was his goal. Hey, he asked. I wouldn't use a tiny resistor personally, but whatever. Agreed! Thanks for the clarification, Jim!

I have a Epi UL310......and it is rated 5.3 Ohms, as before. I know the website says different, but they say you should "think" of it as 4 Ohms!(presumably when combining with other cabs etc) A bit misleading, I think Cheers Oz

You forgot to mention that inductors exhibit some capacitance and resistance, resistors exhibit some inductance and capac........ I'll stop there. All we're doing is unnecessarily complicating things. True impedance changes with frequency. The whole purpose of quoting "Nominal" impedance is to give an idea of the representative load an amplifier will see when fed a harmonically rich signal (ie a musical signal). OK so a 4 ohm cab doesn't always present a 4 ohm load to the amp - actually it probably never ever shows an exact 4 ohms. Have a look at a typical impedance graph for a vented enclosure. (I'll hunt one down and attach it when I get a chance). You'll see two impedance peaks, one below the tuning frequency of the porting, and another just above. The null in the middle represents the tuning frequency and the impedance reading should be very close to the speakers DC resistance. The impedance at the peaks skyrockets into double digits. So how do we show all this as a summary? Industry standard is to take an average, which usually works out to be a little bit higher than the speakers DC resistance. There's really no other way to do it.