View Full Version : speaker impedance question

09-25-2011, 03:20 PM
I just got some infinity kappa 652.9i speakers for the front and rear of my all-trac and i have a hifonics Zeus zxi4410 amp powering the infinity kappa's in my doors and a alpine 10" in my trunk (rear). the rear speakers are being pushed by my 50x4 deck and can't hear them nowhere near as much as the fronts. My question is my amp is rated at 4 x 55 rms @ 4ohms and 4x 110rms @ 2ohms. My kappa's power handling is 75watts rms. On some web sites they say my kappa speakers are 4ohms and on the box it says they are 2ohms. Will i be ok running these kappa speakers on this amp or should i look for a lower rating amp? How can i check what ohms my kappa are?

09-25-2011, 09:22 PM
Most aftermarket radios put out between 12-20 watts RMS per channel, as opposed to what your amplifier is putting out. So the rear speakers are putting out half (or less) than your front speakers with your current setup. The Kappas should be a 2 ohm speaker.

While speakers are only rated for a certain amount of power, most speakers can handle a little abuse. Assuming your Kappas are 2 ohm speakers, hooking them up to an amplifier that will run them at 4x110 @ 2 ohms is okay. You can keep the gain on the amplifier between half and three quarters, and safely run the speakers within their rated range. If the Kappas are actually 4 ohm speakers (which these should not be, based on the model), then running them on the amplifier at 4x55 @ 4 ohms is under-powering them, even if the gain is set at the max. Either way, the speakers will work with the amplifier, but with less impedance, you will have more power/loudness at lower volumes.

I'm also guessing that you have another amplifier, or are looking into getting another one for the 10" in your hatch if you use the four channel to run all four Kappas?

To determine whether the speakers are 2 or 4 ohm, the wrong (easy) answer is to use a digital multimeter, set to the ohm function, to measure the resistance in the speakers, and round up to the nearest value. It is wrong because impedance (AC) and resistance (DC) are not the same thing. However, most aftermarket speakers are rated at 2, 4, 8 or 16 ohms, so you can generally use the resistance to guess the impedance. For example, a speaker may measure between 3-4 ohms in resistance (DC) on a multimeter, so you can assume that the speaker has a 4 ohm impedance. Another speaker may measure between 6-8 ohms of resistance on a multimeter, so you can assume that the speaker has an 8 ohm impedance. While this is not completely accurate, it is the easy way to guess if you are unsure or do not have the proper equipment. If you want to know the math behind properly calculating impedance, here (http://www.fixya.com/support/t174447-measure_speaker_impedance) is a write up that may help. The DIYMA site also has a lot of great write-ups, if you're interested in learning a little more.

09-25-2011, 09:44 PM
Infinity speaker impedence is two ohms in its Reference and Kappa lines -- they claim it's so that there's actually four ohms of impedence seen by the amplifier when tiny factory wiring and the speaker are combined.

09-25-2011, 10:41 PM
Thank you alltracNyx and Glacobar :)