QuestionQUESTION: i am new to car audio, i'm have a few things maybe you can tell me if they go well together. Two power acoustik stw 12 1000 peak 500 rms, one power acoustik pcx-5f (5 farad) capacitor, and i have one power acoustik ov2-1250 amp. i have an 05 jeep liberty, im thinking of making a horizontal platform at window level to place everything, and using the truck as the box. what do you recomend? do i need a second amp of the same, or will that one push the 2 twelves ok? is the 5 farad cap dangerous for my car, should i stick with something smaller? fyi, im sticking with the factory radio because i dont want to rewire all the doors."
ANSWER: Hi Rich,
My only serious concern about your system plan is your idea about using the vehicle's cargo area as an enclosure for the subs.
I think you'd be better advised to build or buy a properly sized box for the subs. The air trapped inside a subwoofer enclosure serves an important purpose: it helps damp the movement of the woofer cone, keeping it from moving too far in either direction. If the enclosure size is too large, or not sufficiently airtight, the effectiveness of the air "spring" is reduced. The result may be distortion or damage from over-excursion, when the woofer cone is forced past the mechanical limitations of the sub's suspension.
According to the manufacturer, the recommended sealed box size for your subwoofer is 1 cubic foot. You can give each sub its own chamber, or build a box with a volume of 2 cubic feet for both subs.
Incorporating your vehicle's cargo area into the enclosure construction might seem easier, but it's often more trouble than it's worth. The plastic side panels aren't usually rigid enough to work well as part of a subwoofer enclosure. They'll tend to flex and rattle from the air pressure. Also, it may prove difficult or impossible to effectively seal the enclosed volume.
As for your planned sub, amplifier and capacitor purchases, they should work together well enough. When you're matching subwoofer power with amplifier power, you should always look at the RMS ratings, and ignore the "peak" or "max" rating. Another thing to consider is that your subwoofers are a 4-ohm, dual voice coil design. When you wire the subs, you can make each sub 2 ohms or 8 ohms; if you combine the two subs into a single amplifier channel, the total impedance will be 1 ohm or 4 ohms. You need to know the load impedance before you can predict the power output of the amplifier.
In your case, you can either wire one sub (at 2 ohms) to each amplifier channel; or you can wire the two subs at 8 ohms apiece, and combine them to the amplifier in "bridged" mode. Either way, each sub will get 280 watts from the amp. This is enough to power them effectively, but well under their rated power capacity of 500 watts RMS. If you're trying to get the maximum possible output from your system, you can upgrade to a more powerful amp, such as the OV2-2200. This would be a better choice than adding a second OV2-1250. However, for ordinary listening purposes, I think a single OV2-1250 will give you all the bass you need (and then some).
You don't have to worry about the capacitor; it's probably bigger than you really need, but there's nothing particularly dangerous about it.
If you're happy with the features of your factory head unit, there's no reason to change it. However, if you did want to upgrade to an after-market head unit, it wouldn't be necessary to re-wire the doors (even if your Jeep is equipped with the factory Infinity sound system).
Hope this helps!
Brian
---------- FOLLOW-UP ----------
QUESTION: Thx, the only thing I am still not clear about is the ohms issue, I noticed the speakers are rated at 4 ohms. My amp is a 2 ohms rating, do I need 2 bridge the amp or the speakers, u confused me when u brought 8 ohms into the picture. If I bridge the speakers they will be 8 ohms each, is that what u meant? The info for the amp says somethin about it sending 4 ohms each channel or 2 ohms. How do I alter that option,therr's no button on it.
AnswerRich,
The key point about the subs is that they're dual voice coil subs. That means that each sub has two 4-ohm voice coils. Electrically, each one is similar to two 4-ohm speakers.
With a dual voice coil sub, you have two options. You can wire the coils in series, and double the impedance; or you can wire the coils in parallel, and halve the impedance. That's why each of your subs can be wired for 2 ohms or 8 ohms, but not 4 ohms.
Since you have two of the subs, the picture gets even more confusing.
-If you wire the subs so they're each 2 ohms, you can connect one sub to each channel of your 2-channel amp, and operate it in stereo mode for 280 watts per channel.
-If you wire the subs so they're each 8 ohms, you can bridge the amplifier and connect both subs in parallel. That means the total impedance at the amp will be 4 ohms, so the bridged amp will produce 560 watts. This is divided evenly between the subs, so each sub get 280.
-If you wire the subs so they're each 2 ohms, you can connect them in parallel so the total impedance is 1 ohm. In this case, you wouldn't be able to use them with the amp you've chosen; but you could purchase a 1-ohm stable mono amplifier.
The method you use for wiring the subwoofers will determine the impedance at the amp. With your particular amp, you can connect 2 ohms to each channel in stereo mode, but no lower than 4 ohms in bridged mode. There's no switch on the amp to change the impedance, because impedance is a characteristic of the subs.
JL Audio has some useful tutorials on their web site. This link will show you the various wiring methods for dual voice coil subs, including diagrams: http://mobile.jlaudio.com/support_pages.php?page_id=161
Brian
