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Old 3rd August 2004, 10:09 PM   #1
beady is offline beady  United States
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Join Date: Aug 2004
Location: Portsmouth, Virginia, USA
Default Help on Dual Chamber Reflex box & car audio response Q's please (LONG)

Hi all, new to the forum but this place seems to have TONS of great info and knowledgeable members. Iíve already spent days reading old posts and doing searches, but Iím still not up to a level of knowledge to make educated decisions, lol. Iím not an audio newbie, having had several systems in the past and currently. Have also designed and built 4th order and sealed sub enclosures before.

What I want is to design a new subwoofer enclosure for my car. Iíve got a late model 300ZX, and it has an aftermarket exhaust. So, right off Iíd like to point out that the car was never ďquietĒ and is hardly that now. So, I do not need ďaudiophileĒ quality sound, as I will not be able to hear the differences most likely. To let you know that I have a somewhat decent starting point(I think, lol), my system consists of a Rockford Fosgate RFX-8120 CD headunit, a Kenwood 3-way active crossover network, Boston Acoustics RC61 6.5Ē components in front and some Audioart 5.25 coaxs in the rear(they were in the car when I bought it). I have two amps, an Alpine MRV-T505 and a Rockford Fosgate Punch 150(old school from the early 90ís). The alpine is currently running the 6.5ís and 5.25ís and the Punch150 runs sub duty. System is installed well with power wires down door sills, RCAís down one side of center console and speaker wires down the other and it sounds clean. I built this system about 4 or 5 years ago, so it is hardly cutting edge, but does what I need it to well.

My music tastes are rock/pop/electronica-techno. In a previous vehicle (280ZX) I had a 6+ ft^3 4th order enclosure running two Kicker Competition C12-8ís in parallel bridged mono on the Punch150. Back in 1990-1991 this made more bass than most anything I had heard. However, Iíve grown a little past that now, and want a cleaner sound with fast transients. I have one Kicker C12-8 still, and two JL Audio 10W3-D4ís to play with. I can swap the amps up and run the Alpine for subs and Punch for mids if need be; like I said, it doesnít have to be super clean, and I donít do audio contests. The Alpine has a parametric equalizer on it, which might be useful for dialing in the sub response to the car. I have run one JL10W3 on its own in the Z as well as one JL10 and the Kicker 12 together. The single 10 just doesnít cut it, and the 10+12 sounds pretty good, but Iíd like more/better. The single 10 and 12 are in separate sealed enclosures of the appropriate size. The car is not large, with 75 ft^3 interior volume and is a hatchback style. Enclosure volume will play a part in my decision, as the install has to remain somewhat ďstealthĒ. I can build a false floor in the hatch, but I do NOT want a large, visible box that is an open invitation to thieves.

I am not particularly happy with the bass(or lack thereof) produced by the RC61ís. They just donít put out much impact, even when driven with close to their rated continuous power. So, Iíd like my ďsubĒ to be able to play up high enough for me to fill in the midbass(if thatís the correct term) which I feel is missing. Also, I want it clean, and to have as much low bass extension as possible with the power I have available.
I was thinking of building a dual chamber reflex (also known as double chamber ported I think) enclosure of the Weems type with the 2:1 volume, 3 ports setup. From my reading, this seems to offer good cone control to lessen distortion, while being efficient like a ported enclosure down low and also able to play up high since the speaker faces out and has two tuned frequencies. Iíve modeled the box in WinISD, but I do not know what type of group delay, phase and gain plots I should be looking for to create a ďcleanĒ sub that will have fast transient response. Also, I do not want to overboost areas of the lower frequencies due to cabin gain, but I donít know what shape of the curves I should be aiming for to avoid this. ANY help in these areas would be much appreciated.

I wouldnít mind using all three speakers (one 12 and two 10ís) in an interconnected design if I could figure out the tuning and make it come out within the volume specs I have to work with. Or, I would not mind running the 10ís in tri-mode off my mids amp tuned higher for midbass and the 12 on the other amp in an enclosure tuned for lower frequencies. That way I could have a sub or subs in a ďboomyĒ more sloppy enclosure for down low and the other sub(s) in a cleaner, tighter enclosure for higher up.

Please feel free to offer any suggestions, or ask any questions of info I may have left our (Iím sure I have).

10W3 specs: http://www.jlaudio.com/subwoofers/pdfs/8_10W3_MAN.pdf

C12-8 specs: please see WinISD or other, canít find specs on the web

Alpine MVR-T505 specs: http://www.lava-electronics.no/Alp_b...90664W91-B.pdf

Punch150 specs: http://www.rockfordfosgate.com/scrip...ted=1088630787

Thanks for any responses,

Mike
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