Lee Jackson Cabs anyone?

[micha]

band-buddy is looking for a new cab.
he uses an Attax 100 Head as a poweramp, and he's got an 8 Ohm Attax cab he wants to pair the new cab with.

now he's found a second hand lee jackson cab loaded with V30s at a decent price, but we're afraid it's a 16Ohm cab (two 16 Ohm speakers wired in series and the whole thing twice in parallel mode).
now the Attax head is designed with two parallel outputs with at least 4 Ohms 120Watts (H&K sugests to run it with two 8Ohm cabs).
we've been discussing wether this cab would suit his amp-configuration or not.

now running an 8 Ohm cab and a 16 Ohm cab parallel would sum up to ~5,3Ohm which would do the "at least 4 Ohm" justice, but the 8 Ohm cab would get far more power out of the amp this way, wouldn't it?

further I thought about modifying the lee jackson cab to 8 Ohms, but I didn't get to a solution so far without having to use resistors.
I thought about running all four 16 Ohm speakers parallel and adding another 4 Ohm resistor in series.
would this be an option that delivers satisfying results?


further I read in one review at harmony central that the Lee Jackson cab would have an Ohm selector slide switch (4/8/16 Ohms), but the other reviews did not mention anything like that.
so, does anybody have any further information on these cabs?

I'd be glad for any kind of help!

[Spivonious]

As long as the switch matches the cab impedance, you won't get any more or any less power out of the amp. If there is no switch, then you'll get the most power by using 16 ohm cabs. (P = i^2 x R)

In the new 4x12, if the speakers are 8 ohms, just wire pairs in series and then each pair in parallel and you'll get 8 ohms.

(1/(8+8) + 1/(8+8) = 2/16 = 1/8)

If they're 16 ohm speakers, you're out of luck. You could either go pairs to get 16 ohms, all parallel to get 4 ohms, or 3 in series parallel to the 4th to get 12 ohms (if my math is correct... 1/(16+16+16) + 1/16 = 4/48 = 1/12

I've never heard of adding a resistor to a speaker chain, or a cab that has an impedance switch. I guess it might work, but remember that speaker impedance is not constant across frequencies.

[micha]

hey Spi!
thanks for your reply!

yes, that's just what I've thought. I'm afraid the cab is loaded with the 16Ohm speakers.
and as I wrote, I'm not sure about the switch, that's my main reason why I asked.
one review mentions a switch, but the others don't. well, a switch isn't that common on cabs AFAIK and it's a great feature, so I think if every reviewed cab had one, it would be part in the features list.

if there really is something like a cab with impedance switch I wonder how it's done. :think:

I think you got me wrong with more or less power. I was afraid that one cab would get more power than the other if I mix two cabs with different impedances?

[Spivonious]

hey Spi!

Spi...that's a new one

I think you got me wrong with more or less power. I was afraid that one cab would get more power than the other if I mix two cabs with different impedances?

No, the amp outputs are parallel, so you'd get equal power going to each cabinet. Now the speakers inside might be more or less efficient than the other cab, so you would see volume differences then. The Vintage 30 has a sensitivity of 100dB. This measurement is how loud it will be with 1W of power at 1 meter distance. If the old cab has a lower sensitivity, it will be quieter. I wouldnt' worry about it though. Humans can't pick up volume differences of under 3dB, so if your old cab is 97dB or 103dB, it won't make a difference.

[micha]

Spi...that's a new one

yea, I like my forum-members-names short.

No, the amp outputs are parallel, so you'd get equal power going to each cabinet. Now the speakers inside might be more or less efficient than the other cab, so you would see volume differences then. The Vintage 30 has a sensitivity of 100dB. This measurement is how loud it will be with 1W of power at 1 meter distance. If the old cab has a lower sensitivity, it will be quieter. I wouldnt' worry about it though. Humans can't pick up volume differences of under 3dB, so if your old cab is 97dB or 103dB, it won't make a difference.

mmhh... so anything above 4 Ohms would be on the save side?
wouldn't it be best to switch speakers?
let's say put two of the V30s in the old cab and vice versa?
unfortunately I don't know much about the AX412s speakers.
these are rockdriver juniors AFAIK (50watts and 8Ohms I guess) and they're not on the celestion homepage...

well, I sent Lee Jackson an email a couple of hours ago, maybe he knows more about his cab than the seller does (Lee was really nice the last time I asked some stupid questions... ).
I'll let you know if there really is something like this mysterious impedance-selector-switch.


but you've been really helpful aswell!
at least I know I don't have to be afraid to blow anything up!

[Spivonious]

Switching speakers shouldn't make any difference unless they are wildly different sensitivities.

I checked out the manual for the amp. It says 4 ohm minimum for one cab, 8 ohm minimum for two cabs.

So 8 ohm and 16 ohm parallel isn't going to work. You'd be driving the amp really hard and risk blowing it up. Is it possible to rewire the other cab to be 16? Then you'd be right at 8. Or rewire the new cab to be all series at 64 ohms and get a total of 7.11. That's close enough to 8 where you should be okay.

[micha]

oh, I thought 8 ohm cabs (when driving two cabs) would be a suggestion due to the matching cab beeing 8 Ohms (surprise, surprise), but now you said it, a minimum of 4 Ohm should equal two 8 Ohm cabs driven parallel...
thanks a lot for that hint.
I would have overlooked that.

well, maybe I should tell band-buddy to just pass on this one (unless it does have the mistery-switch! ), there's always great cabs to be bought on the second hand market.

sooner or later he will get a new amp, he's been lurking the ENGLs for months now, and you wouldn't like to have a 64Ohms cab then anyway...

again, thank you very much!

[micha]

wait a minute, guess, I've been talking BS here.
the speakers are connected parallel to the amp, so the 8 Ohms are meant for each cap, not for both...

wow, this shit is wearying.
I've been typing some stupid lectures for university all day, I guess calculating with reciprocals is just too much at the moment.

[micha]

to bring this to an end;
we decided to pass on this one yesterday.

but I got an email from lee jackson concerning this selector-switch;
it seems to allow to switch between 16 and 4 Ohm, so I think no resistors are used for this and it just switches between parallel and partial seriel arrangement of the speaker.
so it's not the magic-switch I was hoping for...