Hey all, Ive been cruising through the archives on this site trying to figure out what route to go in setting up an audio system in my 03 f250 xcab. Ive got 4 infinity kappa 6x8 and i am shopping for an amp to use with them. The speakers are advertised as having a 2 ohm impedence, and I see some amps advertise 100w x 4 at 2 ohms, and some say 100w x 4 at 4 ohms. If these speakers are set up for 2 ohms, can i not use an amp rated at 4 ohms? I was thinking of getting a 400w amp as the speakers i have are rated at 2-100w rms and 300w max. Would a 400w amp be the right size to go with? Thanks for any help you guys can give, Im in the dark on the audio stuff. Thanks

 

An average amp that doesn't have some special kind of power supply and is rated@100x4 into 4ohms will produce 2x that into 2 ohms. Look at the rated RMS power into 2 ohms. Not total watts. 400 watts may be meaningless, depending on the quality of the amp. That could be an amp rated@25 watts x 4 RMS and the manufacturer wants to "lure" someone unknowledgeable with the big numbers. A quality amp may produce its rated power at a distortion figure of less that 1%, while one of "fleamarket" quality will produce its rated power(MAYBE) at 10%, which will be an audible degradation of the sound. What brands of amps have you been looking at?

Welcome to the forums!!

 

Thanks linear power, I have been looking at rockford amps as they have been recommended to me by a few people. They advertise a 400w amp as 50x4 at 4ohms and 100x4 at 2ohms. What exactly is the difference in running 2 or 4 ohms? I also looked at a phoenix gold amp that advertised 100x4 at 4ohms. Which of these woulod be better. Thanks alot for the help.

 

One thing about Rockford amps is they will produce their rated power at a decent distortion figure. They are not the ultimate amps that they were in the '80s and '90s, but they are above the average, I would say. They do have different lines, with some being better than others, so be aware of what you are getting. The 50x4 amp will be perfect because it produces the 100 watts you need for the 2 ohm Infinitys. The Phoenix Gold will produce in the area of 200x4 into 2 ohms. If you were sensible with the volume ****, you would be fine with the PG, also. I know of a competitor who had speakers rated to handle 100 watts RMS driven with amps CAPABLE of over 1000 watts RMS. Just because an amp is capable of a certain level does NOT mean it is running at that level. Depends on set-up. Knowledge is a wonderful thing.

Ohms is a measure of resistance to the flow of current. Less resistance, in this case 2 ohms, allows more current to flow, causing the amplifier to produce more power into the speaker, IF THE AMP HAS THE CAPABILITY. This extra current flowing through the amp increases the heat in the output devices. That is why the ohm set-up presented to the amp by the speakers is crucial. Too little resistance and the amp will still try to flow the current that the speakers want, but without the capabilties to keep up, it will overheat and will eventually shut down in protection mode or suffer damage to some degree. A higher resistance like 4 ohms, or even 8 ohms, is much easier on the amp. And the difference in a system like you suggest being powered with 50 watts RMS vs. 100 watts RMS is not astounding. Even if you drove both set-ups to their rated RMS power, the 100 watt system would only be 3dB louder.

 

Thanks alot man, its starting to make some sense now. Basically 50x4 at 4ohms is equal to 100x4 at 2 ohms?