DrWho Posted April 20, 2005 Share Posted April 20, 2005 So I came across this subwoofer and amplifier from a friend who's friend gave it to him. The driver is a Rockford Fosgate PCH 128 (for those of you with winISD, it's already included in the list) and a Lear Jet XL-2000 amplifier. The bummer though is that I can't find any literature online anywhere about either of these two toys. Guess I'll have to trust winISD. Anyways, my question is about bridging this amplifier. It's 100 by 100 watts into 4 ohms, which means about 50 watts into 8 ohms. According to WinISD (and the back of my driver), I should be able to run 100 watts into the 8ohm driver with no problem. Ok no sweat, the amp has a switch to convert from stereo to bridged. But where do I plug in the speaker wires? On my Crown XLS 402 that I'm running in my home, you connect the speaker wires to the positive terminal for each channel. Is it the same for every SS amplifier? Is there any way I can open it up and determine where I should plug it in? There's a nice wiring diagram on the back, but they don't describe what to do for a bridged application. I know I could just plug it all in and try different methods until it works, but I'm afraid of breaking something. It's nice to have a free sub and all, but if I break the amp or blow the speaker, then I'll be forced to spend money because it would be such a waste to have a perfectly good speaker/amp laying around Thanks, -Mike Ok, I just have to make one more comment. Once I found out that WinISD had the driver in the list (which I found out after spending hours searching for info on the driver), I entered the 4th order bandpass design that this guy had built...even taking into account room gain, the speaker was like +10dB @ 50Hz (back into the +-3dB window at 35 and 65Hz). By removing one of the ports and sealing that up, and then removing the panel behind the woofer (thus converting it to a vented design), I get the same max SPL of 110dB at 45Hz, but I get it +-3dB from 17-100Hz (+-2dB from 21-80Hz). I'm not too sure why it was built that way (I don't know the original owner), but it's so depressing knowing that someone could have had way better bass and not known it. I think I'll have to try out both designs inside the car and see how the cabin gain effects things. Quote Link to comment Share on other sites More sharing options...
formica Posted April 20, 2005 Share Posted April 20, 2005 ---------------- On 4/20/2005 3:37:27 PM DrWho wrote: Ok no sweat, the amp has a switch to convert from stereo to bridged. But where do I plug in the speaker wires? On my Crown XLS 402 that I'm running in my home, you connect the speaker wires to the positive terminal for each channel. Is it the same for every SS amplifier? ---------------- Most pro amps (Crown, QSC, Peavey, etc..) work this way, but there is no official standard that I know of. The switch could easily be transfering the signal to one channel. What you can do is look at the literature from other LearJet amps and see how those are setup... or email the company if they are still around. They probably setup all their amps in a similar way for bridging. ---------------- I'm not too sure why it was built that way (I don't know the original owner)... ---------------- SPL... bandpass limits the drivers frequency response but therefore increase it's SPL in the region (I just call it peaky and boomy, Bo$e calls it revolutionary). It seems to have become the norm in car audio, where SPL reigns. Ironically there must be many users who would gladly trade SPL for the SQ but don't realise the purpose of the design they are using. BTW, wish I had friends who'd give me stuff too... Rob Quote Link to comment Share on other sites More sharing options...
DrWho Posted April 20, 2005 Author Share Posted April 20, 2005 So would it be safe to power on and try the "pro way" and try the channel 1 way? (I noticed that there are speaker wires still connected to +- on channel 1 that were just cut off for ease of removal). I'm just afraid of breaking something. Because channel 1 was already connected, I guess I can try that first, but I think it'd play no matter what because of the way bridging works (so basically I wouldn't get any benefit from bridging...i guess i could flip the switch and see if i hear anything). I've read that bandpass designs are popular for car audio because the roll off matches the cabin gain. For example, this same driver can do +-3dB from 13-100Hz after cabin gain (3 cubic foot 4th order cabinet). Granted, they're usually built to blast away at a single frequency, but they don't have to. The ironic thing about this design was I removed parts (decrease cost) and ended up with the same SPL, but now more frequencies doing that SPL. Free stuff is great. I asked his dad to help me build a subwoofer and when I show up, he's got it practically built for me (to my specs too). The driver I put in this cabinet I got free from work when we were moving the warehouse. Then his son comes over to visit (he's married and moved out), and invites me over to see his new house and said he's got a sub he'll give to me because he doesn't have room in his truck and it's just taking up space in the car. While I'm at it, I also pulled the Marantz 940s I have out of the trash and I've got two recievers that I got from members of the family. I have a feeling my luck will run out once I have money to spend though... Quote Link to comment Share on other sites More sharing options...
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