using 2 different impaedance taps simultaneously

[black_labb]

hi guys, this is a bit of an odd question, as its one of those that just pop into your head.

the idea is to plug in 2 separate cabs into an amp (holden wasp, 200w) where the cabs are different impedances. the taps on the amp are 16, 8 and 4 ohm. if i were to plug a 16ohm cab into the 8ohm tap, and then an 8 into the 4ohm tap. the rational i have are essentially to paralell 2 cabs, but being different impedances the taps on the ot can convert the impaedance, so that the primary of the ot is seeing what it should.

does this logic work? would the 4ohm tap, having a smaller resistance across it instead of the usual open circuit effect the workings across the 8ohm tap?


i must say that i dont plan on doing this. i have no need to, and dont even have a 8ohm cab, and will easily get a 16ohm impedance on the next cab i plan on making to match that of the 16ohm cab i currently have, its just a curious question i have due to my inquisitive mind.

[Steve Conner]

I've always wondered about that too! I've never tried it so I can't say for certain. But I'm pretty sure it would work.

You're using two taps at once, but you're loading each tap with twice the impedance it's meant for, so the maths all adds up.

This reminds me, I was once looking for a 16 ohm 15" bass driver but nobody seems to make them! There's plenty of 15s that are 16 ohms, but they're all meant for guitar. Maybe I'm missing the point, and the guitar ones would be fine for bass with a lower powered tube amp.

[black_labb]

well i've got 2 15" bass speakers, one ive just built a cab for, and the other waiting for the smaller of the cabs to be built.

heres the build thread
http://www.talkbass.com/forum/showth...ht=budget+1x15

i got the speakers from www.warehouseguitarspeakers.com which are the guys that were doing those excellent vintage speaker reproduction for great money. they had the 15" speakers on special before christmas for 50$ (8 ohm) and 30$ (16 ohm), so i jumped on the deal and picked up 2 16 ohms for 60$ when i was visiting family in canada and boston. the price for both impaedances is now 75$, which is still a great deal, but i got a better one.

id say the reason you dont find many 15" speakers for bass in 16 ohms, is most bass players run solidstate systems, where the most power comes out at 4 ohms or 2 ohms, which would mean you would need 4 of the 16ohm 15" speakers to get the 4ohm impedance, which may be a bit overkill for just about every sitiation.

[Steve Conner]

Awesome! So this

http://www.warehouseguitarspeakers.c...p?prod=15bass#

is the model you got? It looks pretty badass.

I know about the solid state thing, but it doesn't help me, I'm all tube, and my current bass rig only has a 16 ohm tap! I'm using it with a 8 ohm 2x10" and just living with the mismatch

[black_labb]

thats the one i got. id say that finding a bass cab to run 16 ohms shouldnt be too hard, as most 4ohm cabs should easily be reqired for 16, unless they are a single speaker.

if you were closer id sell you one of the speakers and get 2 10"'s, as i think 2 15" speakers would create more emphasis in the low end than i really need. id like some 10's to get some more mid presense, but im using a pick at the moment to keep that attack, so the 15" works great. having a 2x10 as well would also mean i could leave it at the drummers and just transport the head, or atleast have something thats easier to get into my 73 vw beetle (problem is the lack of doors other than the front door, and squeezing the thing in behind the front seats, once its in there there is plenty of room on the back seats.)

[Steve Conner]

Well, the cabinet I'm sitting on in my avatar was just that, a 4 ohm 2x15" that I rewired for 16 ohms.

It was the best sounding cab I've ever owned, and pretty light and compact for a 2x15". But even so it was a real pain in the arse to transport, and the band I play in isn't too loud, so it was just blowing everyone else off the bandstand even with a low-powered amp. The silver speaker trims looked gay too and I couldn't prise them off.

Then my car died and I had absolutely no way to move the thing at all, so I ended up selling it and getting an old green carpet Trace 2x10, which wasn't really that much easier to move! Ideally I'd like a 2x10 and a 1x15 and have them both be 16 ohms, and get a new OPT with an 8 ohm tap too. But the 2x10 is plenty loud enough by itself for now.

Don't know about a Beetle, but a VW bus to carry all this junk around in would be awesome!

[black_labb]

well if you get a 1x15 that is 8 ohms, you could make a box to wire them in series, and you wouldnt need a new ot, and you could keep the 2x10 you have, or make a new box for it if you dont like the one it is in now.

[Steve Conner]

I'm wary of wiring things in series like that. Ported cabinets have a bunch of peaks in their impedance vs. frequency chart. If you have two different cabinets, connecting them in parallel tends to average the peaks out. They damp each other's resonances and the result is a more even bass.

It seems to me like connecting them in series would have the opposite effect and make all of the cabinet resonances worse.

I think series connection is OK with multiple drivers of the same make/model inside one cabinet though. Or maybe two identical cabinets. I've used one of the big Ampeg coffin cabs before, that was split in two 8 ohm sections for biamping. I just made a cable to run the two sections in series. I can't remember if it was the 8x10 or the 4x10 + a 15 model, though.

Does anyone else know more about this?

[Liam]

It seems to me like connecting them in series would have the opposite effect and make all of the cabinet resonances worse.

I think series connection is OK with multiple drivers of the same make/model inside one cabinet though.
<snip>
Does anyone else know more about this?

As ever I don't know very much, but a bit of a non-sequitur (sp?) there. If all the resonant peaks building together in series cause a problem, it's got to be worse with identical drivers than with different ones, as the resonant peaks will happen at the same frequencies as each other. And even worse if they're all resonating within the same cab.

Personally I reckon you'd get the same damping effect in series as you do in parallel when using different ported cabs, but I'll have to think about it for a while!

[black_labb]

i dont really understand the issue with the multiple drivers in series vs parrallel. just imagine you are adding 2 different graphs. wether its series or parrallel, the average is going to be the average, with a multiple (either half for series or 2 for parrallel) giving you the impedance at the given frequency.

what liam said makes sense.

[stokes]

To go back to the original question about using the 2 output taps simultaneously,I think that since one tap is connected to the same winding,just earlier than the other,not much signal will get to the tap that comes later in the winding,no?

[black_labb]

i thing the arguement against that train of thought is that it is a transformer, and voltage is created with each winding, and you cant think of it as a simple wire with taps.

just thinking about it now, it makes sense that it would work. a output transformer is just a transformer that is made to achieve the correct output voltage from the input voltage (even if it is a signal, not just power). if you compare this to a power tranny, often the bias tap is on the same winding as the high voltage. seems to be the same situation as this case.

[stokes]

Yeah,I guess I was looking at it as if it were dc current,forgetting we are talking about an ac signal.I was looking at the fact that one end of the secondary is at ground and current would flow towards the other end and hit the earlier tap first.Give it a shot,and let us know.

[drewl]

So it wasn't a good idea for me to run my 18w clone's 8ohm speaker from the 8ohm tap and the 16ohm 4x12 from the 16ohm tap like I did last saturday?
It sure sounded good.

[black_labb]

that would have probably been similar in effect to connecting the 8 ohm to the 16 tap. a 2to1 impedance mismatch.

thats atleast what we think from our hypothesis.

if it sounded ok like this, then im sure using the placement we calculated should work fine.