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Discussion Starter · #1 ·
I had a stereo shop install an old Rockford Fosgate 800a2 Power amp and two 12" Fosgate HE2s in a sealed box (that my friend used to have in his BMW) in my 300C(sound group II w/ Nav). The setup sounded pretty good in his BMW but it isn't up to par in my C. They used a converter off the rear deck speakers. The speakers barely moved. Apparently the signal wasn't strong enough so they installed an Audio Control Overdrive line driver to boost the signal. With the gain on that all the way up, I am getting somewhere between 2 and 5 volts. The 2V light flashes, but not the 5v. With the gain nearly all the way up on the driver and the amp gain set a bit more than halfway, the bass would be "OK" but then the amp would eventually overheat. I backed off the gain on the amp just slightly and solved the overheating, but the bass level dropped far below what I thought was normal. I have 4 ideas as to what my problem is.....and would appreciate any suggestions you pros might have.

1. The RCA converter needs to be installed between the head unit and the factory amp. I believe the factory amp may be processing the signal and cutting off some of the low frequencies needed to get to the sub. The subs hit well at some frequencies, but some low frequencies just aren't there.



2. I checked the subs with my multimeter and they are only putting an 8 ohm load on the amp. The amp is 4 ohm stable bridged. Maybe replacing the speakers with better ones with bigger magnets that have dual 4ohm voice coils wired in series-parallel to place a 4ohm load overall would help so I could get max power out of the amp.

3. The speakers need to be in a vented box or bandpass to extend the lower frequencies. (If this is the case, I have considered just getting a better sub and running one 12" to save some space.

4. Maybe I am just used to my truck which has four 12" Rockford DVCs in the rear cab.


Any suggestions?? :confused:
 

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2. I checked the subs with my multimeter and they are only putting an 8 ohm load on the amp. The amp is 4 ohm stable bridged. Maybe replacing the speakers with better ones with bigger magnets that have dual 4ohm voice coils wired in series-parallel to place a 4ohm load overall would help so I could get max power out of the amp.


yea thats one of your problems..8ohm load gives you nothing..amps now and days are rated at 2ohm stable..so if your sub-amp is 800 watts mono at 4ohm's you would have double if you get the speakers to a 2ohm load at the amp..1600watts..now your talking "BOOOOM"..good luck..herbs
 

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I am running one Infinity 12DVQ at 2 ohms and I tapped the signal source off the factory 7" in the back and have it crossed over at 60hz... I am not looking for huge thumps, but it is more than enough for me and too much for people in the back seat with it turned up.

Running the subs at a 8 ohm load is going to give up some power handling, but as you said, if you get 2 dual voice coil subs, you'll get more power out of the amp.. But I would worry about the amp overheating, if it's getting hot and cutting out under an 8 ohm load, a 4 ohm is just going to create more heat... Have you tried moving the subs around in the trunk and facing them different directions? Also how big are the boxes and is it one open box or two sealed boxes held together?

And going from 4 DVCs in the same cab with nothing between you and them vs 2 SVCs seperated by seats that are designed to cut road noise from the trunk out will be noticeable. :)
 

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ohm's and such

it sounds to me like you have two issues, one the freqencies are not all coming through since the head unit must be sending mid bass to the 6x9's. try the sub for the source. second, change the config of the speakers in your sub box. if you have (2) 4 ohm woofers that are displaying an 8ohm load to the amp, you could run it stereo or at 2 ohm mono.

let me know how it turns out. im really wanting more bass and less rattle in my C

Michael
 

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Discussion Starter · #5 ·
I had a friend take my car around the block and it sounds pretty nice, you can definetely hear it coming. I think I may just be used to my truck with four 12"s right behind my seat. That being said....here is my plan.

I have a friend with a Kicker L7 12" in a sealed box. He has it in his 350z running off of some swap meet amplifier. I am going to borrow his sub for a day and hook it up to my amp in bridged mode. The sub is at 4 ohms. From there I should figure out if it's the sub configuration, or the signal conversion. I am also going to see if I can find anybody with some subs in a vented box. To see if that might be more along the lines of what i'd like to hear.

I think that I'm just not used to having the seats there to block the noise from coming through. Nor am I used to the subs firing rearward.

I am hoping that I may just get the sound I want if I turn the box so the subs fire forward, dynamat the trunk, and upgrade the subs. Also, I would like to cut a port to allow some air to move freely to the cab. I was looking at the piece that is behind the rear cupholders when they are folded down. Feels like it's just plastic underneath the upholstry. Anyone know for sure?Should I just get out my jig saw and cut it out and reupholster the perimeter? any help is appreciated.


Also, Hatax....isn't the sub channel just two wires? how do you tap into that source instead (since my amp requires two RCAs)? just tap all 4 wires for the converter into that channel?
 

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If using a stereo line level converter, just hook both leads up to each side of the sub

Left + & Right + ----> + on factory sub
Left - & Right - ----> - on factory sub

You could also just split the one RCA to both inputs on the amp. The source doesn't need to be stereo as the sub channel in the car gets audio from both sources.. I would not advise running two subs in stereo mode, they tend to get out of phase due to the stereo seperation on two channels... Just my experiance.....

You could even pull the factory sub out and open that hole up from the bottom to allow more bass into the cabin and that is a little less intrusive than cutting the seat back.
 

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Discussion Starter · #7 ·
so here is where I am at right now.

I tried putting that L7 in my car. That was a waste of time....it sounded like shit. The box looked way too small for that sub.

Anyways, I decided to drop the seats down and drive around for a bit. Huge difference!! I guess I was just used to my truck. The seats block a whole lot of the sound. So here is where I am going from here....

Going to turn the box around so the subs fire forward, dynamat the trunk, then see how that sounds. If more is needed, then I will remove the stock sub to allow more sound to travel to the cab. While I am at it I will try running the convertor off of the sub channel.

If I still need more, I guess it'll be time for some better subs, or I'll have to drive around with one of the seats down.

BTW, I looked into the panel behind the cupholders. It is just plastic, but there is also a metal brace that supports the cupholder hinge brackets. Hard to describe, but you can check it out for yourself. There is a zipper at the bottom of the seat that you can unzip to expose that panel. Anywho, I don't even feel like messing with that just for a small port.

I will keep you guys posted. Thanks for all your help so far.
 
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