Hey guys, I know I haven't posted in this forum in a couple of years, but I'm back with a small problem I'm trying to solve. I know you guys love a challenge, so here goes. (Forgive the long post....)

When I got my S2000 about 4 1/2 years ago, I self installed a Clarion MP3/CD head unit, PPI PCX-480 amplifier, a set of Boston Pro Series components, and my own DIY audio control mod. I've been very happy with over the years, but recently I started thinking of ways to add a little bass.

I had an old subwoofer setup from my previous car - two JL 10W0 subs - that have been sitting in a closet for years. I had some leftover 3/4" MDF in the garage, so why not build myself a new box for one of them? I went with the trapezoidal profile design from the FAQ, and was very pleased with how well it came out (I enjoy a good woodworking project every now and then). A great fit in the trunk well, and I even found a carpet/felt that's a good match.

So now I have this great sub box in the car, right? I wire it up, and on the first try, I get nothing. The PPI amp uses a proprietary connector plug at the amp, so it's easy to get something miswired. I swore I had it right, but no sound came up. I confirmed that I had a signal on the RCAs feeding the back channels. I finally switched the speaker terminals to the exact oppposite of what the manual illustrates, and then I get sound (go figure). Convinced that the manual is in error, I go ahead and set the input switches, crossover, gain, etc., and we're in business.

First thing I notice is that I'm not getting anywhere near the volume I would expect out of this 10" sub. The PPI is 4x80 @ 4Ohm, 4x160@2Ohm, and bridges to 320W @ 4Ohm. I'm bridging the 2 rear channels for the sub. Then I remember that the sub is actually 8 Ohm - I ran the pair in parallel previously to get a 4 Ohm load. I guess I'll have to remedy that soon with a new speaker. Still, I have at least some low end punch, so it's an improvement over what I had before, right?

So, I drive around with the weak-powered sub for a couple of weeks, even dialing back the gain on the component speakers to balance out the levels (at 3Ohms, the amp delivers ~120W to each channel). A few times I thought that the bass was lacking, other times it wasn't so bad. I couldn't tell if it was just my perception, tire/road noise, bad vehicle acoustics, etc. Then, today it seemed like there was no bass at all. My first thought was that a wire must have somehow worked its way loose. I popped the trunk to check, and when I stuck my head in, I find that the sub is still playing, but barely audible. This is with the amplifier gain set pretty high, and the head unit at around 25% volume.

So, what's going on here? Bad speaker? Bad amp channel(s)? Dying output from the head unit? Maybe the amp doesn't like the bridged 8 Ohm load? Suddenly I'm second guessing the wiring for the bridged channels of the amp. Maybe it's gone into protection mode, or it blew a fuse on that side of the amp? I'm going to start by checking the amp's fuses, fiddle with the gains, see if there's any change. I still have the 2nd speaker, so I could try that one to see if it's a problem with the speaker itself. Beyond that, I'm not sure what else to do...

Assuming I can prove that the amplifier is still good, I would like to replace the sub with a single 12". Historically, I've been very happy with JL, possibly leaning towards a 12W3v2-D2. I'd love to hear other suggestions for decent subs designed for small sealed enclosures that don't break the bank. I prefer to spend somewhere in the ballpark of $150 (not opposed to used stuff on Ebay either), but if there's something really compelling I could go higher.

Any other ideas?

-Jeff

 

I'd try wiring the rear channels of the amp as stereo (unbridged),
and then confirm that you have output signal on each channel.
If not, recheck the RCA input signals, and if they're good, sounds
like an amp problem. If you do have output signal, try comparing
the two subs.

 

OK, this is almost funny. Almost...

After I posted above, I went out to the car and starting messing around with it. The head unit has a separate line out for the sub, and they let you boost/attenuate that signal. I set it to +6 and listened, not much. I set it to -6, and it was about the same. Weird, eh? So, I set the fader towards the rear to quiet the front speakers, and when I went to the trunk, the sub was also quiet. Hmmm, that's interesting...

So, I grabbed the manual and started checking all of the audio routing switches/options. Sure enough, a toggle switch was pushed in that was routing the audio from the front channels over to the rear channels driving the sub. The signal AFTER the front crossover. So, the audio was going through a -12dB/octave high-pass filter, stripping away almost everything below ~120Hz, then it went through the sub channel's -12dB/octave low-pass. Kinda makes sense that the sub performance was lacking with 12dB attenuation across the band.

When I de-activated the switch, the sub easily quadrupled in volume.

 

Oh, and I'd still like to hear recommendations for a 4Ohm 12" sub that's good in small sealed enclosures.

 

Alphasonik 600 or 800 series

 

Wow, I plugged the T-S parameters for the PSW812J into a box calculator, and they're the best I've seen for small volumes. Much better low freq rolloff than some of the others I've been looking at.