Expert: Cleggsan - 6/5/2010

Question
Hi there ,Im in need of a diagram to wire my system correct i have (2) 15" kicker L7's that are 2ohm dvc's and i have a mmats D300hc amp can you please help me out so i know i have the ohms correct on the speakers so the amp will play them correctly.Im not currently running a HO alternator should i purchase one make sure i have enough current powering my system??Thank you Fred

Answer
http://www.carsound.com/reviews/amps/d300hc.html

The MMATS is a class D switching amp that, typically, as given above, will handle a 2 ohm load. But, in my personal opinion that is pushing the design technology and you are better off having a little higher load on it if you can arrange it.

Follow the suggestions in the above carsound site especially about keeping the speaker wires independent.  No accidental connections or touches to ground or you will have a very bad hair day.

Since the L7s are 2 ohm dvc you have a number of choices for wiring them up.  But, look at it as 4 each 2 ohm coils.  If they were all in parallel you would have a 1 ohm load - which is too low.  If they were all in series you would have 8 ohms - too high.  If you put each speaker's two coils in parallel for 2 ohms, then in series with each other you would have 4 ohms - which is okey but higher than the amp can handle.  So, you are left with putting each speakers two coils in series, then in parallel with each other giving you an impedance of 2 ohms - just right, theoretically.

Crutchfield has a good summary of hookups:

http://www.crutchfield.com/S-lAUzS4Mkc6c/learn/learningcenter/car/subwoofers_wir...

This one is maybe the one you should try:

http://a248.e.akamai.net/pix.crutchfield.com/ca/learningcenter/car/subwoofer_wir...

If the amp goes into protection or cut-off mode often then switch over to this one:

http://a248.e.akamai.net/pix.crutchfield.com/ca/learningcenter/car/subwoofer_wir...

Hoping this did not overload your thinking.... but pretty simple once you have the images in your mind.  Cheers; best wishes.

PS:: The question of adding a high output alternator is a function of how hard you are hitting the amp/speakers.  The amp can draw as much as 150 amps when everything is perfectly matched, but with music power and if you go with the 4 ohm loading your average power consumption would be much, much less than that. In music conditions we find that the average music power over a period time is maybe 1/10 full, maximum capability of the amp/speakers.  In this case the current draw on average might be only 15 amps or less  - or more if you plan on pumping the bass system pretty hard.  Those kicker speakers are pretty sensitive being almost 90db which will put out a pretty hefty rumble if they are mounted in adequate boxes.......  and so on.....

PPS: The reason we have to watch amp/speaker matching closely is due to the manufacturer impedance ratings.  When they say it is a 2 ohm or 4 ohm impedance that is a nominal rating and the impedance vs frequency curve might dip well below the rating at its resonant frequency - a very common speaker problem, especially with Infiniti units.  In the case of the L7s  I don't have their curve so I can't tell you what it does in the bass registers but you can measure the dc resistance with and ohmmeter and that will give you the lowest impedance at the main resonance point of the curve.  If the dc resistance, for example, comes out 1.5 ohms that could be dangerous for the amp......