Hi one and all. John, a newbie in Australia writing. Firts post actually, so don't be too cruel!
I have just upgraded my car stereo from the OEM cassette/radio to a nice new Kenwood system. The head unit is a 22W RMS/ 50W peak times 4 (front and rear, L+R) CD/AM/FM job with provision for aux. in via a 3.5mm socket, (handy to plug your Zoom H4 in after recording a gig or band practice) and additionally a USB socket, so a USB stick full of mp3's works well and sounds great. Speakers are 6 1/2" 3 way in the doors and a couple of 6 by 9's on the parcel shelf, all Kenwood and all 4 ohm.
I feel however (as a bass player) that the bottom end with this set up is a bit lacking, and no amount of bass emphasis using the standard EQ controls is really adequate. So I've bought a Polk Audio subwoofer, model db840DVC. This is an 8 inch unit 4 ohm unit with a claimed capacity of 180W RMS and 360W peak. It utilises dual 4 ohm voice coils and consistent with that has 2 pairs of speaker terminals, one each opposite the other on the speaker basket. Claimed freq. range is 30hz to 200Khz and sensitivity is a claimed 85db at 1 watt (and I assume I meter- that's approx 39 " to you guys). The plan is to mount the subwoofer within the boot, or "trunk" as you guys would say, on to a conveniently placed circular depression at the rear of the parcel shelf in my '98 Mitsubishi Diamente, sold here as a "Magna". Whether I cut a hole of the appropriate diameter in that circular depression in the parcel shelf stamping for the sub to fire through, or just drill it full of holes, I haven't yet decided. It doesn't look to be stress bearing.
Powering the subwoofer will be a stand alone amp, one I have had lying around for years from a previous car stereo installation. It is an Awia MA - 3000, a model dating from the early 90's when it was considered high powered. Specs are 35+35W RMS stereo/65+65W peak. It claims on the side of the unit, "Matching Impedance 4-8 Ohms". I'm assuming that the quoted wattage figures relate to a 4 ohm load rather than 8 ohm. It is bridgeable with an external switch from stereo to mono usage and mono is obviously how I plan to use it, so in theory I should have 70W RMS/130W peak available. It is old but in good nick. Usage wise, I don't listen to "doof doof" music, as car based rap is often characterized, but enjoy rock, jazz, pop and even orchestral. I'm not going for deafening volume, but headroom and a bit of bona fide thump. After all, I turn 53 this year!
The plan is to connect both of the amps output terminal pairs (ie. L+R) to the subs pair of speaker terminals. As the amp will be bridged it should deliver 35W RMS (max), across 4 ohm, to both coils. THe amp has an external sensitivity adjustment, and the head unit provides for independent subwoofer level adjustment
So much for the background. Now to the questions. (BTW, I've searched the Polk site to attempt to answer these Q.'s- no specific hard answers for this kind of issue forthcoming, so have posted on your forum).
Can anyone see problems with this proposition?
Is this insufficient power for the speaker?
How does this wiring plan look to you?
Glad of any help,