Joe X

Its a high pass filter and the simplest implementation is a non polarized capacitor in series, will provide a 6dB per octave roll-off.

You do it with this free software: WinISD A little learning curve but it lets you calculate, sealed, ported and bandpass: 4th order and 6th order. Enclosures are built for your specific sub. Be warned build and align properly 4th order enclosures is hard, you have to do it perfectly.

You are not going to get any true bass from 6x9s, you get midbass at most, no matter how many you put, those speakers will not perform well on boxes, are designed to work in infinite baffle settings like your rear deck, will loose low end. 3 way will pickup earlier midrange frequencies which the big oval driver can't reproduce accurately. There are very good and inexpensive subs to choose from that will get you real bass (30-40Hz). Take a look: MB-Quart-FWA-304D

You would just discharge the battery after a while.

So what is wrong with the sa-12s?

pitbullninja, no audio hardware is for free..lol.. there was a thread next to yours asking about some cheap junk speakers which are rated 2500W plus free tweeters so they recommended them here in your thread for fun.

Yes, for free try them!

which 6.5"s and against what.

pitbullninja, it all comes down to how much you want to spend and how hard you want an installation to get, for $70 you can get well balanced full range sound and easy installation. There is no denying that you can improve over them, the best way to know is to go and hear a few 6x9s and 6.5" components to get some idea of their differences.

I have tried a few of them away from a car environment in big enclosures, many people use midbass drivers with comps help this.

My point is that 6.5" components lack midbass, the only components that really sound great are those with 7"-8" midbass drivers. 6x9s give great midbass, if you are not a SQ guy you not be bothered by their sound at all. Sanitarium you should try Focal 6x9s

6x9s have better midbass than any 6.5" components. And sound plenty well for the price. Now if you are a rich audiophile you can buy a nice $1000+ dynaudio 3 way component set for your doors, better than 6x9s for sure.

One decent option could be this: http://www.sonicelectronix.com/item_17734_JBL-GTO928-GTO-928.html

They have a long history of reliability issues, poor sound quality, malfunctioning peripherals and the xplod series has been stellar at that and you can dismiss specs, even if really had 120dB SNR, in a car environment that is good for nothing, it's too much to say that a particular model from them will be good or bad but there are so many alternatives that I wouldn't bother to take any chances.

$129.99 Here: http://www.sonicelectronix.com/item_23321_Sony-CDX-GT740UI.html You can always review it here after a while.

Here for $129.00, free shipping and installation accesories: cdx-gt740ui Buy it and then review it after a few months, Sony bashing must stop.

Ok, misread, how about the power acoustic eq having it's output gain low to the amp. You can even force a cheap HU to clip by having a low input gain on the amp. Probably bypassing the eq could be another test.

Disconnect the RCAs from the amp and if the noise stops then the problem is with the head unit.

baaudio, Sony aims at first time buyer, can't compare Pioneer SQ with Sony, I wouldn't mind the 2V (keep in mind the price). I can't say that I love JVC but they have a ton of features are inexpensive and reliable, what would make a good argument to buy Sony with so many alternatives.

Very cheap and good quality: http://www.sonicelectronix.com/item_32848_Pioneer-AVH-P2300DVD.html

You can get a Pioneer for less than $300 new.