Which impedence output should I use if I don't know the impedance of my cabinet?

[lifeless gamer]

Hey, I have a 15 inch speaker cabinet from a company called soundtech that I kind of inherited from my uncle, and I've never seen this brand before. Anyway, I looked on the back of it and the sticker with all the specifications is left completely blank so I don't know what the impedance is. Would it be safer to use the 2 ohm or the 4 ohm output on my amp head for it? I don't really know how this stuff works.

[mulchor]

Odds are you should use the 4 ohm output.

If you happen to know someone with a multimeter, it's a 15 second task to measure the resistance.

[Selta]

Since you're profile isn't filled out, I'm just going to have to take a stab in the dark here, and assume you're using an all-tube head like an SVT-CL or something...
If the above is true, I would figure out what the impedance of that cab is. If you have a multimeter you can just measure it and the measurement will be in the ballpark of the cab's impedance.
If you're instead using a solid state or hybrid, I would safely assume you'll be OK as it's very unlikely the cab is 2 ohms, and your head should be OK with a 4 ohm load.

[PSPookie]

What type of head will you be using?

If it's a tube head with a maximum impedance rating of 4 ohms then I might steer clear of using that cab by itself until you figure out it's impedance. If the head has a SS power section you're in the clear.

Not knowing anything else, I would use the 4 ohm tap though it's likely that the single 15 is an 8 ohm cab. You could run a multimeter across it and use the passive resistance as a sort of baseline.

[lifeless gamer]

Sorry my profile isn't filled out, I haven't done much on this site yet. I kind of have a weird setup right now. As of right now, I'm using a fender rumble 15 as a preamp into a Fender 100roc pro guitar head which I got really cheap at a flea market. I understand that it's odd and doesn't sound too great for a bass, but it sounds better when I use the rumble 15 as a preamp. I have a Marshall MD450H hybrid bass amp head coming in the mail right now and I'm planning on using this speaker I have until a few weeks from now when I have the money to buy a bigger, higher quality cabinet.

[BassmanPaul]

Typically most single speaker cabinets will be 8Ω. You can check this by using a digital multimeter set to Ohms. The DC resistance will be somewhat lower than the AC impedance. Around 6Ω will be an 8Ω speaker, less than 4Ω will be a 4Ω driver.

Paul