PROPER stealth subwoofer upgrade - '01 Roady

[dkindig]

This post is to document my upgrade of my roadster's subwoofer system. When I got the car, the audio left much to be desired. The mids in the kick panels were trashed and when I went to check the sub, all I found in the compartment behind the seats was a snorkel!

My car is an '01 which should have had the single 6.5" sub, but obviously the transition from the earlier dual HK sub with snorkel to the single sub was haphazard at best. So, off to ebay for a new OEM 6.5" sub and enclosure. Plugged that up, and NO sound. The amp was shot as well.

I didn't want to spend a gazillion dollars on an 8" enclosure and sub, didn't want to hack up the interior, and I didn't want to fill up the trunk with amps so I decided that a high-quality stealth install was in order.

I did my homework on diymobileaudio.com looking for amps that would fit in the factory locations, and I found the Arc Audio Mini's. Their 2-channel amps fit the bill at 70Wx2@4ohms, 125Wx2@2ohms and 250Wx1@4ohms. The only thing I was having a tough time with was the $330 price tag.

I looked further and found the Elf Audio E2125X 2-channel amp and discovered it was manufactured by the same build house and used the same circuitboard as the Arc amp. The circuitboard was even silkscreened with the model number of the Arc amp! I found these on eBay for $150 shipped.

The OEM drivers are also a weak point, with the foam surrounds not holding up, and also being rated at only 70W, which I felt would not last too long with the upgraded amp.

I found on this forum that the Kicker 6.5" shallow-mount subs (CVT65) would fit in the enclosure and were designed for a 0.2-3.0 cubic foot enclosure (our enclosures are roughly 0.2 cubic feet) and rated at 150Wrms/300Wpeak. They are available in a 2-ohm and a 4-ohm version. I bought the 4-ohm version since the amp is not 2-ohm-stable in bridged mode.

First step: replacing the amp...

[dkindig]

I found the perfect replacement for the factory amp in terms of dimensions, power and features. The Elf amp has individually adjustable gain controls for each channel, selectable speaker-level or line-level inputs, can be set for low-pass, high-pass or full-range operation, has an adjustable crossover and has a 0-15dB bass-boost control centered at 45Hz.

The power ratings are rms, not peak like some other manufacturers show, and the output stage is a true class A/B so the sound quality is good. The amp gains it's efficiency by changing the rail voltages on the output transistors as needed (class G/H) so it doesn't have the issues that most class D amps have with sound quality.

The following pics show the dimensions of the Elf amp side-by-side with the factory amp, along with the locations I used for new holes to mount the Elf amp to the factory bracket after drilling and repainting the bracket.

[dkindig]

These pics show the amp in its mounted position.

I used "T" taps on the existing harness to tap into the remote turn-on wire and the speaker wires. The existing speaker wires were plenty large enough (between 14ga and 16ga) and they were twisted pair runs, so I didn't see a need to upgrade those.

I ran 8ga power wire to the positive battery terminal and 8ga ground wire to the grounding point just underneath the amp mounting bracket. I used twisted-pair interconnects from the head unit to the amp.

IMPORTANT NOTE: The HK guys did get one thing right. I noticed that from the factory amp to the subwoofer, the polarity was reversed to the driver itself. The OEM woofer used red/black for one voice coil +/-, and green/grey for the other voice coil +/-.

The brown wire and the blue/brown wire (brown is typically used for ground), which are the NEGATIVE speaker outs from the factory amp are connected to the red wire and the green wire on the voice coils (the positive terminals on the subwoofer). The yellow wire and the blue/red wire, which are the POSITIVE speaker outs from the factory amp are connected to the black wire and the grey wire on the voice coils (the negative terminals on the subwoofer).

Due to the subwoofer's position in relation to the front speakers, it sounds a lot better with the sub operating in reverse polarity. If you use "T" taps, or if your head unit can change the polarity of the sub output on the fly like mine, this is easy to experiment with.

These pics show the system wired up with the OEM subwoofer before I installed the Kicker sub, so you will see me using both channels out instead of the bridged outputs here...

[dkindig]

At this point I have a new amp installed with the OEM 6.5" subwoofer. I ran this setup because it took a few more days for the Kicker sub to come in.

I was marginally pleased. I definitely had more low-end fill and wasn't totally missing bass, but it lacked real impact. Since the OEM sub has dual 4-ohm voice coils, I was limited to 70W per channel from the amp.

Also, to get it to reach lower, I adjusted the bass-boost on the amp to about 12dB at 45Hz. I knew that this would be taxing the sub AND the amp in this configuration.

I also knew that the OEM sub was at best a temporary solution as it was only a matter of time before the foam surround gave up or I blew the speaker with the new amp.

So, on to the Kicker upgrade...

[Z3Vulron]

Looking foward to the Subwoofer mounting.

[dkindig]

Unfortunately, the Kicker sub is not a drop-in upgrade. The hole in the enclosure is large enough, but the mounting ring of the driver itself won't fit between the two sections of the enclosure that protrude forward.

I used a bench grinder and trimmed away the left and right edges of the mounting ring. There is also a rubber bumper that goes around the magnet assembly that needs to be pried off the magnet to make room for the driver in the enclosure.

These pics show the modified Kicker sub and the OEM sub side-by-side...

Notice that the Kicker surround is a heavy-duty rubber surround that has reinforcement ridges molded into it, and is actually SEWN to the cone!

[dkindig]

Now that the Kicker sub has been modified to fit between the ears of the enclosure, a couple more things need to be done to allow it to seat all the way into the enclosure and to optimize the response.

I used a dremel with a small circular saw blade to remove the raised reinforcing ridges from the back side of the enclosure. The Kicker sub's voice coil is vented from the sides instead of the back like conventionally-designed voice coils, so it can sit all the way against the back of the enclosure.

Since this is a single-coil sub, I put heat-shrink over the unused terminals on the harness. The Kicker uses spring terminals so I stripped and tinned the other two terminals (red and black in this case).

One thing that was really poorly done was the stuffing, or fill, in the enclosure. They used a really dense material that looked like a piece of carpet pad. You can see this in the starting picture. In a decent speaker design, this kind of pad is used more for absorbing standing waves (internal reflections) and only works for much higher frequencies.

Stuffing a subwoofer enclosure, when done properly, actually makes an enclosure appear larger acoustically than it really is physically. Optimal fill will make it sound like it is about 35% larger. The right stuffing is called polyfill. I used fiberglas insulation because 1. it works very well, and 2. I had it laying around. The important thing is not to pack it in, but to loosely fill the enclosure so that the fibers can vibrate.

[dkindig]

Okay. The enclosure is ready to go. Only a couple more small details and it will be ready to drop into the car.

Even after removing the ridges from the inside of the enclosure, the sub sits about 1/16" off the face of the enclosure. With a sealed enclosure, it is critical that there are no air leaks for it to perform the best.

I took 1/8" thick, 1/2" wide self-adhesive closed-cell foam weatherstripping and placed it around the back side of the sub's mounting ring to provide a seal between it and the box.

The sub's mounting holes didn't line up with the existing screw holes from the OEM driver, but that worked perfectly since they are sealed from behind anyway because of the way the box is molded. I used self-drilling pan-head sheet metal screws and ran them in with a drill in about five minutes.

Done!

[dkindig]

Wow!!!!!

The first thing I noticed was that when I was tuning the amp, I only had to dial in about 5dB at 45Hz on the bass-boost control instead of 12dB like I had with the OEM sub to get the low-end extension where it sounded nice and full.

The bass-boost has been a really nice feature. It is not uncommon in subwoofer design to use equalization to compensate for less than ideal enclosure sizes (a linkwitz transform). Note that I said it compensates for enclosure size, not driver size. Physics can only be bent so far. The bass-boost is centered at 45Hz, so it does a decent job of artificially extending the low-frequency response. What it costs is power, but with 250Wrms available, that's not a problem.

I have been running this for about 3 days now, and the bass keeps getting stronger and stronger as the sub breaks in. I can already hear that I am either going to have to reduce the gain controls or dial back the bass boost. I haven't figured out which yet.

I crossed the sub over at 100Hz and my mids at 125Hz and as the sub is breaking in it is becoming harder and harder to localize the low frequencies. It sounds like everything is coming from the front soundstage. I am getting great thump from kick drums and a lot better low end than I ever thought I would get from a 6 1/2" speaker.

I'm very happy with the outcome, and I think it's going to get even better over the next week or two. If anyone local wants to hear it, let me know.

[daaaveee]

Enjoyed reading, thanks for posting.

[cngizbleevng]

When I replaced my woofer, there wasn't any of that fill material in the OEM box.

[Vigilante]

Damn good write up. Do the RCA's go to the back of the stock deck as they should?

[sdmike1]

Great stuff! Thanks for the write-up. I'm going to replace my new Pyramid with a Kicker in the coming weeks, so your information was very helpful.

[dkindig]

Damn good write up. Do the RCA's go to the back of the stock deck as they should?

RCA's route through the grommet behind the driver's seat, over through the area where the sub sits, and along the console back to the sub out's on the head unit.

Right now I have an Alpine CDA-9833 with the internal V-Drive amp running 28W per channel direct-wired to each driver (midrange and tweeter are driven separately in active-crossover mode using the front and rear outputs).

When the Elf 4-channel amps come out in February, I am going to mount the 4-channel amp on the other side of the trunk in the factory location and run 4 more RCA's to the trunk and 4 speaker wires back up to the front to drive those speakers at 70W each instead of using the head unit amp.

Stay tuned!

[felonious monk]

Excellent info. Thank you. My only concern is the amps may get too hot on the warmer days.

[sdmike1]

Question - Does that amp control all the speakers, or is it just for the sub?

[billyr3d]

I didn't want to spend a gazillion dollars on an 8" enclosure and sub, didn't want to hack up the interior, and I didn't want to fill up the trunk with amps so I decided that a high-quality stealth install was in order.

.

I have to say, the 8" roadstersound is hardly "hacking" the interior. The fit is factory like - infact Ive had people question if it was a bmw option. Yes, I will agree that the price is a bit steep, however, the sound is great and absolutely no cabin space is lost. As far as amps go to power the 8" there are plenty of cost and size efficient amps that have more then enough to power it up and can tuck behind the panels. I on the other hand went with the overkill option . Your project sounds interesting and when i can view the pics I will. Hope its going great for you. If anyone would like pics of my set up i'd be glad to provide.

ps.. the one negative with the roadstersound sub is that the sun will damage the sub if exposed to long.

[Jamesons Viggen]

Good info.

I just bought the 6.5" box to replace mine. I am now prepared to do some modifying.

What is the BEST sub that is 6.5" that should work in such a small enclosure? I see the Kicker CVT65 is about $50 on ebay, I am willing to spend more. Does JL offer a better option?

If the Kicker is the BEST sub that fits, cool $50.

Pioneer makes a shallow mount 8"
Recommended Enclosure : 0.15 ~ 0.5 cu.ft.
Dimensions : 8-7/8" dia. x 3"
Mounting Depth : 2-1/2"
Cutout Hole : 7-3/8" dia.


I am thinking that's not going to happen

[kostverloren]

Excellent info. Thank you. My only concern is the amps may get too hot on the warmer days.

Make sure you vent them or their life will be shortened.

[sdmike1]

I know JL makes a sub in this size range, but it's a fair bit more money.

[Jamesons Viggen]

I know JL makes a sub in this size range, but it's a fair bit more money.

Price I am fine with(upto say $175-250). I have always used JL products for sub, my last was an 8W7 which I was very happy with.

I just need to know what fits. What is the max mounting depth that fits the stock box, 2.75"?. What about the max that opening can be trimmed to fit?

Pioneer AND Kenwood make some 8" shallow depth subs, but the hole needs to be 7" and change.

[sdmike1]

I think 2.75 is about the max. I just installed a 2.79 and it took a small spacer, but I probably could have gotten away with just using some weather stripping/seal. You're not really going to get the hole any bigger. There's only about 1/4 inch on the sides, and you really need that to seal the sub.

[Jamesons Viggen]

I think 2.75 is about the max. I just installed a 2.79 and it took a small spacer, but I probably could have gotten away with just using some weather stripping/seal. You're not really going to get the hole any bigger. There's only about 1/4 inch on the sides, and you really need that to seal the sub.

That's about what I figured. Would like to know the measurment of the hole.

[sdmike1]

That's about what I figured. Would like to know the measurment of the hole.

If nobody posts it before, I'll be taking mine out in the next few days and will give you the diameter.

[Jamesons Viggen]

If nobody posts it before, I'll be taking mine out in the next few days and will give you the diameter.

Thanks.

If I get my hands on one first I will post it up and save you the trouble.