OHM Loads on Amps

[texplorer1994]

Okay, I need a little clarification on this. I was taught that to calculate the ohm load there are two equations. One for series and one for parallel. For a series it is the total ohm load and for parallel it is the inverse of 1 over each ohm load added.
Series
4 ohms + 4 ohms = 8 ohms
Parallel
1/{(1/4)+(1/4)}= 2 ohms

Various people have confused me. A friend of the family has a high end stereo and he was told that the amplifier had to have the ohm load set to take advantage of a different resistance. Another guy at a circuit city told me that an amplifier was set to a 4 ohm load while pushing 3 10 inch 4 ohm subs. Maybe my math sucks, but I don't see any possible way a resistance of 4 ohms could be achieved. Am I confused or do the speakers actually provide the resistance? Is there any way to set the ohm load on the amp? I am incredibly bothered by this.

 

[Jefe]

Your math is perfect. Sounds like you were talking to some less knowledgable people

Yes, amplifiers are designed with a certain ohm load in mind. When the correct load is aplied it will operate at its best.

And no. . there is no way to make 3 4 ohm subs equal 4 ohms. (I believe that when they use 3 subs, they are 8 ohms each, wired in parallel to give ~2.5 ohms but I'm no expert in that field)

 

[leenjen]

a lot of systems with three subs have dual 6 ohm voice coils and they are either wired @ 1 ohm mono or 4 ohms mono.

 

[texplorer1994]

I just wanted to make sure that I had not missed anything. Thanks for the help. There are few amps running around out there that are 1 ohm stable, but is that there best range? I would imagine that they would be much more comfotable at a higher ohm. Also, the guy I spoke with at Circuit City told me that there were SVC. I asked specifically when he told me that it was receiving a 4 ohm load. He told me...yep...three 4 ohm subs, SVC delivering an overall 4 ohm load. You gotta laugh.

 

[exploderdriva]

it would be a 1.333 ohm load or a 12 ohm load. there is an easier way to figure out the load when subs are in parallel. take the impence of one of the subs and divide it by the total number of subs.
As for what amps like better... if they are designed to run at 1 ohm run it at 1 ohm. if they are designed for a 4 ohm load then give it a 4 ohm load.

 

[texplorer1994]

Rockford Amps

Are most amps designed for four ohms? I have seen many amps that will take various loads and even try to brag that they are 1 ohm or even a half ohm stable. Where can you find what the amp is specifically designed for? Running the amp at a dirrent load then its designed for will cause extra heat and could shortent the amp life, right?

This brings me to another point...I had a Fosgate amp that I bridged two of the four channels. I ran everything at 4 ohms. I got rid of one of the subs and I ran the amp bridged at 4 ohms for a while until I got a sub amp. The amp gave out and burned up. I had it rebuilt and never found out specifically what went wrong. After the rebuild it went out again (probably after a year or so.) I still have the amp, but I was wondering if anyone else had this problem or had heard of this. After the rebuild I never ran it at anything but 4 ohms.

 

[leenjen]

maybe the amp was just defective.
all four channel rockford amps can be bridged @ 4 ohms mono X 2