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Cab impedance advice needed.

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Hi there I'm currently running a head into a 1x15" 8 ohm cab. I own a 2x12 cab loaded with only one 8 ohm speaker...I plan to buy another identical 12. The amp I am using has an impedance selector which can be set to 4, 8 or 16ohms. It also has a jack for an additional series cab and one for a parallel cab to be used in conjunction with the main (which I am running the 8ohm 15 through). If I wired my 2x12 in parallel for a 4ohm cab  and connected to the parallel input I would be looking at a load below 3 ohms  which I don't want to do, so connecting the 4 ohm cab in series at around 12 ohms seems to be the thing to do and then set the impedance selector to 8 ohms. OR do I wire the 2x12 in series for a 16 ohm cab and then connect to the parallel input for a load around 5.3 ohms and set the selector to 4 ohms?   To clarify, the amp I am using is an old Fender 100watt 6l6 guitar combo made into a head and I'm only just able to get away with it live with the help of the 15"  kappalite cab I have, so adding the  kappalite 2x12's is something I'm eager to do. My question is would the amp respond differently operating at 12 as opposed to 5 ohms ?

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I can't see the need for more than a Kappalite 3015 with only 100 watts pushing it. If you're not getting the volume you need you should be looking at a better amp, not more speakers.

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You're right Bill, was a daft question considering I'm only pushing 100 watts. I'm happy volume -wise with the one 15. I have the Kappalite in an Ashdown ABM cab which I measured inside after taking out the stock Blueline speaker and came up with about 4.5 cubic feet, it's vented and has no dampening material at all inside. I'm not at all savy about cabinet tuning etc. but the 3015 enabled me to get similar volume with the amp volume dialed back which was the goal, and tonewise it blows the Ashdown driver out of the water.

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I'd line that with polyester batting, it will clean up the mids considerably. I'd investigate the tuning as well, you may not be taking full advantage of the 3015 capabilities. I doubt that the cab is braced either.

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If you did want to get the 2x12" up and running for use with that head, there may not be much benefit in choosing the Kappalites over certain cheaper 12"s, given that they'd only have to handle 50 watts per driver.  A pair of something like Eminence Betas or some of the Celestion bass drivers would cost less than one Kappalite and can be got in 4 or 16 ohms to make an 8 ohm cab.  Of course, mixing it with your 1x15 could still be hit-and-miss though. 

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3 hours ago, Beer of the Bass said:

If you did want to get the 2x12" up and running for use with that head, there may not be much benefit in choosing the Kappalites over certain cheaper 12"s, given that they'd only have to handle 50 watts per driver. 

It's not the voice coil thermal rating that counts, it's the driver displacement. Back when my 50 watt '65 Bassman was new the Fender 212 couldn't handle it, nor could two. I eventually wound up with a pair of 412s before hitting the books and learning how to design my own cabs. In retrospect I owe Leo Fender a debt of gratitude, as he set me on the path to making my living as a speaker designer. I do agree though that 3012s would be overkill, a pair of 2012s would suffice for a lot less money. Betas aren't bad either.

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Thanks for the advice guys, I'm going to use the 1x15. I will get some polyester batting for it. I can't find a proper spec for the cab, as Ashdown has updated it, making it smaller and have no idea about cab tuning. It is not a braced cab and my guess at the dimensions are from measuring internally, and subtracting the estimated space the handle sides and the speaker take up, which would be very roughly just over 4 cubic feet. Thanks again.

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