Extension cab with different number of speakers?

StuartV · #1 05-18-2010, 12:42 PM

I'm wondering about using an extension cab with a different number of speakers than the base combo. E.g.:

A 1x10 combo with a 2x10 ext cab, or,

A 2x10 combo with a 4x10 ext cab.

Is there any problem with either of these scenarios? I'm not an electrical engineer. I've read some threads here where people are talking about scenarios like this and saying that half the power would go to the ext cab and half to the internal speaker(s), implying that there might be some kind of problems that would result. I.e. saying that the internal speaker(s) would receive twice as much power as each of the speakers in the ext cab.

Specifics:

1) If I have a Promethean 1x10 combo and an 8 ohm 2x10 extension cab, would I better off to run them all together (for a total of 3 - 10s and a total of 500W of power), or should I disconnect the head from the 1x10 and just connect it to the 2x10 (for a total of 2 - 10s and 250W of power)?

2) If I have a Peavey BAM210 combo and a 4 ohm 4x10 cab, is there a problem hooking them together, for a total of 6 - 10s and 500W? (The Peavey BAM is 350W at 4 ohms and 500W at 2 ohms)

In the cases where I have the internal speaker(s) and the ext cab all running, if I listen very carefully (or separate them), would I notice one being louder than the other?

StuartV · #2 05-18-2010, 12:45 PM

Oh, and if you're responding that there is somehow something wrong with running all the speakers, can you then tell me if you think it would be okay to use, for example, an extension cab with 1x15 instead of the extension cab with 10's? And if you think running 1x15 is okay, but 10s is not, then why?

StuartV · #3 05-19-2010, 12:07 PM

Well, I guess nobody has any thoughts on this. But I did have one thought on it.

Just as an example, if I'm using a 1x10 combo (8 ohms internal) and a 2x10 ext cab (8 ohms), then I suppose I would have to assume they're each consuming half of the output power. This, in turn, would suggest that the speakers in the 2x10 are each getting half the power of the speaker in the 1x10.

But, the speaker in the 1x10 is 8 ohms and, presumably, the 2 speakers in the ext cab are each 16 ohms. Or, I guess they could each be 4 ohms, wired in series.

So, is it possible that the different impedance of the individual speakers involved would result in an overall output that would have the same actual volume coming out of all 3 speakers?

JimmyM · #4 05-19-2010, 12:20 PM

depending on the time of day, sometimes questions drop off fast and we don't always see them. sorry.

anyway, no, the overall output won't be the same no matter how it's wired. each speaker in the 210 will get half the wattage that the 110 gets, so there's no way to make it work without a volume imbalance. the amp sees each cab as separate units within themselves, not as separate speakers.

StuartV · #5 05-19-2010, 12:26 PM

Thanks, Jimmy. That's how the math was coming out in my head.

So, that suggests (I may be making a bad leap here) that having a 1x10 and a 2x10 ext, or a 2x10 with a 4x10 ext doesn't make the best sense.

But what about, for example, a 2x10 with a 1x15 extension? That would also mean that the 1 15 would be getting twice as much power as the 2 10s, right? Does that really make any more sense than having a 2x10 with a 4x10?

I'm starting to think that if I want the flexibility of having a 2x10, but also want to have a bigger rig, I would be better off to get a second 2x10 than a 1x15.

OTOH, it seems like I see a fair number of people with a 2x10 and a 1x12 or 1x15 that seem to be pretty happy with the sound they're getting. Or one friend of mine that has a 4x10 and a 2x12 that he runs together.

JimmyM · #6 05-19-2010, 12:30 PM

most 115's have approx the same output as most 210's so they will match a little better. but as for me, i'd never do either. i'd do two 115's or two 210's, never both. i think matching cabs sound better.

mulchor · #7 05-19-2010, 12:40 PM

The impedence ("Ohms") matters more than the number of speakers or power-handling.

E.g., if you have a 4 ohm and an 8 ohm, the combined impedance would be 2.67 Ohms. In that scenario, twice* as much current goes to the 4 ohm speaker. If you don't push to the limit, nothing will break (your amp, speakers, etc), but it'll sound a bit wonky.

It sounds like your amp can go down to 2 ohms.

* speakers are dynamic so the impedance is a result of resistance and inductance and varies with freq & the box, so "twice" is approx. Power=VI=I^2 R, so double the current on half the impedance gets you double power. Everything else being equal, double the power gets you 3 dB louder.

megadan · #8 05-19-2010, 12:50 PM

Generally TB experts frown on mis-matching speaker sizes, so you're on the right track with same size speakers in the extension cabs. Ultimatly it's up to you and your ears to figure out what's best, but be aware that a scenario like, for example, a 1x10 combo with a 4x10 extension probably isn't going to be optimal - the 4x10 is just going to drown out the 1x10, and you could blow the single 10 if the power is split evenly - just the right amount for the 4x10 could be way too much for the single 10.

StuartV · #9 05-19-2010, 01:03 PM

Thanks for all the input. I may yet try a 2x10 matched up with a 1x15. But, I will definitely avoid pairing up my 1x10 with a 2x10. If the 1x10 is not enough, I will just disconnect the Promethean head from the combo enclosure and just hook it to the 2x10 only.

And I guess I should also avoid using my BAM210 combo with my Peavey 4x10 ext cab. I tried it out hooked up like that, but I haven't really *used* it. And here I thought the Peavey Pro410 cab was the "perfect" extension cab for the BAM210... bummer.

JimmyM · #10 05-19-2010, 01:20 PM

yeah, well you wouldn't be the first to buy gear with the "engineering by looks" criteria, so don't feel bad.

StuartV · #11 05-19-2010, 01:26 PM

Ha ha! I *might* buy something without hearing it first. Maybe. If it's a good deal and I can flip it for no worse than a small loss.

But I won't be keeping anything that doesn't sound good (to me). And as long as it sounds good and isn't going to blow up or blow up my amp, I don't care what the "engineering by engineering" analysis is.

mulchor · #12 05-19-2010, 01:28 PM

Quote:

Originally Posted by StuartV

And I guess I should also avoid using my BAM210 combo with my Peavey 4x10 ext cab. I tried it out hooked up like that, but I haven't really *used* it. And here I thought the Peavey Pro410 cab was the "perfect" extension cab for the BAM210... bummer.

It very well may be perfect.

Can you determine the impedance of the 210 in the BAM?

StuartV · #13 05-19-2010, 01:32 PM

I'm pretty sure the 210 in the BAM is 4 ohms. The specs for the combo say 350W at 4ohms and 500W at 2 ohms. The Peavey Pro410 cab is 4 ohms. The specs don't specifically say that the internal 2x10 is 4 ohms, but the specs for the amp imply it.

JimmyM · #14 05-19-2010, 05:15 PM

Quote:

Originally Posted by StuartV

Ha ha! I *might* buy something without hearing it first. Maybe. If it's a good deal and I can flip it for no worse than a small loss.

But I won't be keeping anything that doesn't sound good (to me). And as long as it sounds good and isn't going to blow up or blow up my amp, I don't care what the "engineering by engineering" analysis is.

i suppose that's a legit attitude. but denying yourself knowledge is never good, imho. doesn't hurt to learn a little about how audio works, especially being a bass player where there's so much that can totally screw us out there unlike any other instrument.

Jaco who? · #15 05-19-2010, 05:37 PM

Straight from the Peavey pdf" : "Two professional ten inch cast frame 8-ohm speakers wired in parallel for a total impedance of 4 ohms."

From strictly a power distribution point of view, an 8 ohm 1x15 would take the same amount of wattage from the Bam's power as each of the 10"s would. If you were to use a 2x10 extension cab, a 4 ohm would get equal power to all the drivers.

elavate7 · #16 05-19-2010, 05:48 PM

i think the 210+115 would sound balanced and even.

StuartV · #17 05-19-2010, 09:06 PM

Quote:

Originally Posted by JimmyM

i suppose that's a legit attitude. but denying yourself knowledge is never good, imho. doesn't hurt to learn a little about how audio works, especially being a bass player where there's so much that can totally screw us out there unlike any other instrument.

I wouldn't deny myself knowledge. That's why I'm here asking the question! I'm just saying that I wouldn't let the knowledge of the engineering stop me from using something that sounds good (to me), as long as I know it won't cause anything to blow up.