I just bought a subwoofer from a thrift store for 60 bucks....its a MTX audio thunder 6000 with a q-logic box....the only thing wrong is I dunno if its 4ohm or 8ohm....how can you tell?....I went to their site to find out but the same model comes with both so is there a way to tell? Also what would be the best amp to get with a low budget?

 

Usally if you take it out of the box it will say on the back.

 

I have no experience whatsoever with audio, but can you just hook up a multimeter and measure the resistance accross the sub?

 

No, you can't.

Impediance cannot be measured with a DC source like a multimeter.

Easiest way (like posted above) is to open up the thing and hopefully it's listed on the driver magnet.

BTW, 4 or more ohm impediance will work on all (4 ohm) car stereo equipment. 8 ohm just won't sound as loud.

 

4 ohm > 8 ohm.
There is a way to get 4 out of an 8 speaker. I don't know how to do it, but I've read that it is in the way it is hooked up with the rest of your speaker. I think you have to split the signal with another sub.

 

Actually, you can measure it using a multimeter. Impediance is resistance varying with frequency... therefore, the resistance is never the same, but it will be pretty close to the actual number. For example, if you get a reading of 3.7 ohms, then you have a 4 ohm speaker.
And I wouldn't go as far to say that 4 ohm will work on all stereo equipment. 8 ohm speakers are sometimes extremely useful and much more beneficial than 4 ohm speakers. Many times you can wire 8 ohm speakers to sound just as loud as 4 ohm speakers.

 

4 is not always > than 8, see my previous post

You can wire speakers different ways to present a different load on the amplifier, for example, if you have two 8 ohm speakers, you can present either a 4 or 16 ohm load on a mono amplifier. If you have two 4 ohm speakers, you can give either a 2 or 8 ohm load on a mono amplifier.

 

Ok I get it. I think
As far as 4>8, that's still my opinion, but I see what you're sayin too.
My next question would be how common are mono amps? Is there a liklihood that todays high tech amps made with mono outputs as an option?

 

Mono amps are still around, alot of the class d's that you see are 1 channel, cost saver to produce a class d over say class ab or 'true' a. Many people on a higher listening level tend to veer away from class d because it has a reputation for having "dirty" power. I don't really see any benefit to using a mono over two channel if they are both class a/b, and if we flip it around a two channel amplfiier is much more flexible than a mono, so I don't see too many high end companies producing mono amplifiers.

Of course this is assuming the two channel is bridgeable.

 

A lot of companies produce class d mono amps. The main advantage to them is efficiency. Ab amps are typically only 60% efficient while class d's can be much higher. This makes class d's good for high power sub amps were you want like 1000 watts but dont want to kill your alternator. If you are thinking about maybe in the future using it for mids or highs then you should probably get a 2 channel ab amp. Class d's are typically used only for subs. As for being dirty its been debated but on a sub im not sure most people would even notice.

The only full range class d i know of is from xtant:
http://www.cardomain.com/item/XTAXTANT11