Spkrboy

This weekend I had the opportunity, courtesy of Komoman, to get good measurements of the JL Stealthboxes intended for the C6 convertible. JL installs their 8W3v3 8-inch 8-ohm drivers.

We took the drivers out of the boxes, beat them up with a brutal 20-Hz continuous sine signal (nearly full excursion) for about 18 hours straight, then measured them in free air and in one my test boxes to get delta-compliance measurements. Then they were measured in the JL fiberglass enclosures so I could calculate how much space JL gave them. This is important in case someone would want to use a different driver in these enclosures.

Here are the measurements starting with JL's claimed specs, then our samples:

Spec____rating______#1______#2______AVG

Fs______35.4 Hz____35.7_____37.0____36.35
Qes_____0.49______0.54______0.52____0.53
Qms_____6.79______6.23_____5.90_____6.07
Qts_____0.46______0.50______0.47____0.48 5
Vas_____0.57ft_____0.48_____0.42_____0.4 5
SPL_____83.7dB____81.1_____81.3_____81.2 (this value is a 1W/1M calculation)

According to JL's specs, this driver should be in a sealed enclosure anywhere between 0.42 (Qcb=0.707) and 0.15 (Qcb=1.0) cubic feet. Using the above averages, I found the necessary volume to be between 0.40 (Qcb=0.707) and 0.14 (Qcb=1.0) cubic feet. Reversing a few calculations and testing the drivers in JL's encloseres shows the enclosures to be effectively 0.22 cubic feet (6.2 liters) including the JL-installed polyester batting. As installed in JL's enclosures, not including variable cabin gain, the expected F3 is 54.5 Hz.

As you can see, the test samples are very close to JL's ratings. The small observed differences are very typical of what I've come to expect from manufacturers who keep tight quality control variances. There are no unreasonable ratings.

I note only three drawbacks with these drivers:

1. They're much more expensive (~$160.00 street each) compared to similar performers from other manufacturers (call it a JL tax). I don't see any justification for this.

2. They have a low sensitivity (typical high-xmax driver in this regard).

3. They have a low power-handling spec (150 watts).

I did deliberately drive my Adcom GFA-555II to the verge of clipping using that same 20-Hz sine signal with these drivers in free air just to see if they could handle it. I'd estimate they were getting at least 250 continuous watts at that 20 Hz. I believe JL's power rating to be a bit conservative. While they still won't get very loud, I expect they could take somewhere in the neighborhood of 300-350 watts or more from a high-quality low-distortion amplifier.

These drivers, while expensive, would be a good choice for classic rock or jazz fans looking for a well-defined low end without unnecessary boominess or other attention-drawing behavior. Because of their designed location in right behind your head in a C6 convertible, a low crossover point is a good idea. I'd estimate 50-60Hz (12 db/oct). I'll let Komoman address the cosmetic integration as he sees it since he'll be the one living with them for a while.

TheKomoman

I'll check back in when I have some real time to spend with them but so far it's a mixed bag. We spent a crapload of our time moving the amp from the cubby to the trunk under where the top stores so I haven't had much chance to really look at them installed. I definitely need to make some adjustments on the waterfall position.

Quick impression is that it's a lousy match on the carpet. Neither the color nor the nap are all that close and for the retail on these (I bought used from Shangreer so my opinions are tempered by that) they should do a better job.

Performance-wise, I think they do a decent job for what they are. I'm currently using an Alpine that's putting 250 into the 4 Ohm load and they give a nice bottom end. It's the kind of performance you'd expect from a pair of 8's, kicking but not that "******** smashing oontz." Since that wasn't what I was after that's fine by me.

I've got some pictures from the weekend and I'll post after I have a chance to clean things up and take some true finished pics.

Fasthotrod

Thanks, guys!

While I am not currently considering a set of JL 8's, it's nice to see someone put forth an effort to test them and give an objective opinion about them.

The Corvette Forum is a great place... guys like you make it that much better. I appreciate it.

Mark

Spkrboy

Thanks, Mark.

A similar look at a sample of the eD 11kv in a day or two.

Shangreer

Good test guys. Sounds like you came away with the impression I had on the sound...good for rock, not so hot for Rap or anything where you want them to go really low. I like the fact that they use some otherwise wasted space, however.

Sorry about not mentioning the carpet match issue Komoman. I have the Tan interior so carpet match was never much of a concern...could not match any less than that.

Shan

Spkrboy

Just thought I'd give an example of the data this program provides:




The blank or "zero" data fields are user-entries that I didn't update and that have no effect on the other parameters.

Fasthotrod

So what hardware/software are you using for this?

That looks cool as hell...

Mark

Spkrboy

SoundEasy v14. Link:
http://www.interdomain.net.au/~bodzio/

I was using IMP, then Liberty Audiosuite (Both DOS-based). The system Liberty was installed in died on me a few months back and SoundEasy became the favored new method for me after some evaluation. I still use Praxis from time to time, but it's not a modeling program, only data acquisition. EasyLab in SoundEasy does much of what Praxis does, but not as easily. SoundEasy's also a rather complex program, so the data I can offer the group will be limited for a while until I learn the program.

I you're interested, it's about a $500 investment not including the computer to run it.

5W0P3

I've been considering this sub for my frc, but i listen to a mixture of music including rap,hip hop, country, rock, classic rock and jazz, i dont want the boominess you referred to though. Would this sub still be a good candidate?

Spkrboy

It's a good driver for what it is, but as I originally posted, it has low sensitivity and is expensive compared to similar performers from other companies. If you want to fork over extra cash for no particular reason, they're a decent choice. They will not do particularly well for rap/hip-hop, but then again, accurate drivers rarely do.

More importantly, you need to determine if their space requirements are tolerable in your car.

TheKomoman

As I promised a while back... some pics & impressions of the C6 vert Stealthboxes now that I've had time to finish off the install.

My biggest concern regarding fit was the waterfall, but I hadn't had a chance to fit the hardware that connects it to the cabin/trunk partition. Because of the install of the Stealthboxes it can no long directly attach to the partition, so JL provides an approx 1.5" long nut threaded at both ends. The nut attaches to the partition and the waterfall and acts as a spacer. Once that was installed then everything went together nicely. Still wish the carpet was a better match, but I'm much happier with the fit now. The install itself is really very simple.

I had to send the Xtant out for repairs as it was overheating, so I'm back to using the PDX for now. I bridged it on the rear channels to feed 300W to the pair of 8's. The really are power hungry, though. I don't care what JL recommends, I'm pretty sure those drivers would be plenty safe to run with 500 instead of 300. Gonna take some time to play around to get the crossover right but I think the pair of 8's will be just fine for me. At the moment they're a bit on/off When I'm cruising with the top down I tend to listen to up-tempo rock. The 8's do a nice job kicking me with the bass drums and adding that extra oomph that you just aren't going to get with a 6.5" midbass, no matter how good the driver. I think they're gonna stay, though I really wish they looked better. At least you can barely see them!

I have the power top, so that gets me the trunk partition that trips the safety switch(the protect me-from-myself switch, which for me is a good thing). I took the male connector that holds the back of it in place and attached it to the back of the trunk/cabin partition. I ran out of time before I could do the passenger side so I can't really evaluate it, but I think it will work and act as a cover for the amp, etc to boot.

Here's a few pics to illustrate what I've discussed:

The boxes installed




A closeup


The partition attached to the cabin partition


And for comedic value, the little PDX lost in the big amp sled.

Shangreer

Looks sharp. Glad the subs worked out for you.

Shan

cmb13

Two 8's were used b/c there was no good spot for a larger sub. The problems with the 10" in the rear were both the sound travelling through the top when down and the fit. The curve of the convertible trunk prevents the coupe's unit from going the storage unit.

JL knew that these 8's were meant for rock / blues / jazz, and tested them extensively with all kinds of music. They were well aware that the lows of rap were not optimal, but put them out as they still sound great, and were the best custom alternative possible without filling up the entire trunk.

Overall, I'm very pleased with the fit and finish, and I think they sound awesome. Admitedly, I'm not a rap kind of guy.

Tarheels1

I have heard the JL will come out with an "ultra small" Amp like the PDX. Have you heard about it? I have 07 vert will little space to put a couple of amps. When we travel my wife is slightly high maintance. There is not room in the trunk for anything, not even a regular size amp. Where have you guys been installing the amps?

TheKomoman

I haven't heard about the JL, but it wouldn't surprise me because there's certainly a market for it. The Alpine PDX does fit in the passenger cubby of the C6, I just chose to move to a different amp and since I'm divorced I don't have to worry about the high maintenance wife.

scofolo

I've heard it could be as soon as the first quarter of '08 but I'm not holding my breath. They are coming in two models. 600/4 (150x4) and 600/1. (600x1)

Ozona

I installed a pair of these today, I got them from Crutchfield.

I spent a fair amount of time monkeying around to get it all to fit, they are definitely packed in there. JL did a good job of making sure they soaked up every bit of space they could. The fit with the waterfall is tight. I found that by leaving everything loose you could move it around a bit before snugging it all down.

One thing that made it a ton easier is getting 3/8" bolts that are 1/2" longer. It made getting them started much, much easier.

The carpet match in my '08 is pretty close. The "partition" or flimsy thing that held the stock speakers doesn't match the carpet in the car exactly either...oddly enough.

This is a great write up that these guys did, was helpful.