righto, i currently have an ashton 200w @ 8 ohm cab and im running a peavey mark 3 which is 150W @ 4 ohm, and im looking into buying a hartke 210, possibly even behringer, the hartke im not sure if im going to go tp or xl yet but the transporter is 150w @ 8 ohm and the xl is 200w @ 8 ohm, while the behringer is 600w @ 8 ohm....so what im curious about, i know that 2x 8ohm cabs will make 4 ohm and my head will run at the full 150w but will either hartke be suitable for this?

Either Hartke cab will handle 150w at 4ohms just fine. I've occasionally added a 2X10 XL cab to my 4X10 XL rig and run the Hartke 3500 head at the full 350 watts at 4ohms for larger venues.

So, if one puts two cabs together (eg, two 8 ohm cabs to get 4 ohms with the amp), what should the total watts of both cabs be? eg, if an amp is 300w at 4 ohms, should two 8ohm cabs be 150w or more each?

thats what i also wanna know, if a cab is rated at 150w @ 8 ohm, what will it be if i put it with another cab and it becomes 4 ohm?

If the speakers are both have the same nominal impedance (8 ohms each in this case), the head will split it's 150w evenly between the cabs. So each cab will get 75Watts. So if doesn't matter if it's a 150w cab or a 600w cab, it'll recieve 75w. At the moment, that head is producing about 105w wth just one 8 ohm cab connected. The bigger issue when mixing cabs is sensitivity / efficiency. Make sure you balance the cab sensitivities against the required frequency response. Otherwise, you could end up with one cab "burrying" the other.

so, will two 8ohm cabs at 150 watts a piece be louder than one 4 ohm cabinet at 300 watts? if not, then what is the reason for using multiple cabs (other than mixing speaker sizes) also, if you have an amp rated at 300w at 4ohms, and you attach a 4 ohm cab and a 8 ohm extension... does that mean you will really be running your amp at 450watts, thus possibly ruining it... or, if you run two 4 ohm cabs on a 300watt 4 ohm amp, does that mean you are running your amp at 2ohms then?

If the speaker area is the same, and the efficiency the same, then the volume will be the same. For example, all things being equal, two 8-ohm 2x10s, each receiving half of your amp's 300W of power, will be equally loud as a single 4-ohm 4x10 receiving it all. What it means is you will be running your amp with a 2.67 ohm load. The equation is R1xR2 / R1+R2, where R1 and R2 are the nominal impedances of the two cabs. So, here, 4x8 / 4+8 = 32/12 = 2.67 ohms. If your amp cannot handle such a load (some can, but some cannot), you can overheat and ruin it. How many watts it puts out in such a situation is irrelevant; don't do it. Yes. Using the same equation, 4X4 / 4+4 = 16/8 = 2 ohms.

Bigbeefdog's right, and I'd like to add - Most people use 2 cabs because it increases the efficiency and therefore delivers more volume per watt. It also brings the speakers closer to your ears so you can hear yourself much better than when the sound is being blown through your legs. As you mentioned, mixing driver sizes is another advantage. Or sometimes 2 smaller cabs is easier on your back than one large one.

no-ones answered my answer properly yet....i mean..i have a 15" cab which is rated at 25ow @ 8ohm....if i put it with another cab (dont even think of the details of the seccond) does my cab remain a handling power of 250w @ 4 ohm, or does it handle a higher wattage @ 4 ohm

Whatever cabinet you parallel with the 8 ohm, 200 watt (what you stated originally) one is irrelevant to the power handling of the first cab. It will remain just what it has always been, an 8 ohm cab with 200 watts power handling. The amp sees a different load, but the speaker doesn't know or care about that, as far as power handling, unless you clip the amp heavily. You were underpowering before, and will be underpowering even more now, since that cab now will see 75 watts, not 100 or so. Make sense? The question you might want to ask is: how much power will you need to properly drive that cab and another one? Assuming a second 8 ohm, 150 watt cab, 600 watts or so will do nicely, if both cabs are rated for RMS power to begin with. If the second cab is the 600 watter, you'd want to go with ~800 watts, being limited to 4X the lower rated cab's rating. This assumes equal impedances, it gets a bit messier if that's not so.

so if i was to get another 15" the same, so 2 cabs which are 200-250w @ 8ohm would my peavey mark 3 which is 150W @ 4 ohm have trouble powering them?...my other option is to get a 4x10 by the same manufacturer which is 400w @ 8 ohm

The spec you need to look at is sensitivity (often mistakenly called efficiency), not power handling, as long as you want to use that Peavey. You want two equally sensitive cabs, and the more sensitive they both are, the better. Say you get a 4 X 10, each driver is only going to get a bit less than 20 watts, which is pretty little. But, there's a MK III around here that's been gigging for many years, and I've only worked on it a couple of times in all those years. It's been thrashed, driving stupid-low impedance loads, etc., etc. A second cab will add a little more juice, if that's all you need.

so would another 15" cab be reccomended?....i prefer 15" cabs anyway...but the seccond cab i get will be the same as the one ive got but id probably put a horn in the seccond.... so therefore each cab will be recieving 75w each?, if i use the peavey head, im probably going to invest in a behringer head as well, so with the behringer head wach cabinet would recieve 150w?

Matching cabs has a certain appeal. At least it's predictable. I mix cabs a lot, but usually I power them separately. As far as getting another amp, now you're into totally different territory. If you stay with your current cab, it'll either see 100 watts from the Peavey, or whatever the Behringer can do into 8 ohms. You might consider a 4 ohm cab for one amp, and a second 8 ohm cab to go with your current one. I think I'd spend my money differently, but that's your call.

Reading through this thread, you seem to be connecting power handling and impedance. They are separate entities. You have a 15" cab which can handle 250 watts, period. That cab's nominal impedance is 8 ohms, and will always be. If you pair it with another 8-ohm cab which can also handle 250 watts, and connect the two in parallel to your amp, the total load that the amp sees is 8x8 / 8+8 = 64/16 = 4 ohms. So it will be able to deliver it's rated power at 4 ohms. But each of those individual cabs is still an 8 ohm cab. That will never change. And each can still handle 250 watts, no matter what. And since you now have two of them sharing the amp's power equally (they're both 8 ohm cabs; two paths of the same resistance), you can use an amp that puts out 500 watts @ 4 ohms (the total connected load from the calculation above). The cabs will share this equally, and each will receive 250 watts. It's likely that the cabs can handle somewhat more than they are rated for, as long as it's clean power, but that's another discussion. Any amp that you connect to this setup will be able to deliver it's rated output at 4 ohms, and yes, half the power will go to each cab. Your Peavey will not have any trouble "powering" them; the only question is if they will get as loud as you want/need them to.

i finds this all just a little too confusing...hell next amp i get is just going to be a combo a 210 combo with whatever reccomended 15" cab to go with it

But you won't know how to chose the 15 to go with it. Heath seriously man, learn this stuff. Take as long as you need to wrap your brain around it. You'll be glad you did. Start by Clicking Here . It's the TB amp FAQ. It's long, but it's very good. Print it and leave it in the toilet/car/bus/wherever you're likely to pick it up and read it occasionally.

I couldn't agree more. This is stuff every bassist needs to understand when setting up their rig. But if it continues to confound, you can usually protect yourself by following two rules: 1) Buy an amp that absolutely, positively can handle a 2-ohm connected load for extended periods at high volumes, and, 2) Never connect more than two cabs to the amp. Unless there are some 2-ohm nominal cabs floating around out there that I'm unaware of, this should, at least, keep you from tearing up expensive equipment.