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BMW E28 Lightweight System w/ 15" IB

26K views 88 replies 21 participants last post by  KrautNotRice 
#1 · (Edited)
Welcome to Kraut's lightweight, budget SQ build.
The goal of this stereo build is to have a great sounding system that is completely stock appearing and hardly adds any weight to the car.
Guidelines:
Maintain stock appearance
Front stage only (eventually active), no rear fill
Single subwoofer running infinite baffle to save weight
Only one amp for the entire system
Added weight must be:
1) kept to an absolute minimum
2) distributed towards the rear axle as much as possible
Sound deadener will be used sparsely
Don't break the bank *gosh*

I've been lurking here for a while and just recently signed up. In the last few months I've learned a ton from this forum alone, read countless inspiring build threads, reviews, how-tos and have been hunting for deals on equipment.
A year ago I had no idea what infinite baffle is, what it means to run active and I thought JL Audio were the greatest subwoofers...
My install experience from previous rides is limited to swapping head units, speakers and adding sub boxes in the trunk. Pretty basic stuff. I thought it was great at the time.

For this car I'm doing things a little different.
The reason for the stock appearance is not because I'm some kind of purist, I just don't want to attract thieves and I've always preferred the look of 'most' stock radios over the shiny, colorful aftermarket kind.
Luckily I stumbled across some OEM looking aftermarket decks:
VDO & Continental / Kienzle. The face plates are matte black not shiny, illumination is orange. The look is very similar to 80's & 90's OEM BMW & Audi. I love it.
I haven't bought the head unit yet, for now I'm running with the basic Kenwood deck that came in the car. Once all the other equipment I received so far is installed I'll probably order the Continental deck.
Eventually I also want to get a MiniDSP and go active.



The car is a '84 BMW 528: 6 cylinders, 5 speed, 4 doors & under 3000 lbs (and I intend to keep it that way). This is right after I washed it the weekend I bought it:



Part of this install is also relocating the starting battery from behind the headlight to under the rear seat for better weight distribution. The new battery is a Odyssey PC680 MJT (16 lbs). I don't plan on running the system ever with the motor not running. I'm also currently switching the stock rear bench for rear bucket seats from the 80's BMW E24 6 series coupe. The new rear seats don't leave any space for the 5 channel amp to fit below them, so I will most likely install the amp below the rear deck in the trunk. This way the weight of the amp is still between the wheels.

I scored this used amp here in the classifieds for $100 shipped: Next Audio Emotions Q.55 5 channel:







Found this pic online:



I'm hoping it will run the sub at 2 Ohms, even though the manual doesn't give any numbers for 2 Ohms. It says the stereo channels can run 4/2/1.5 Ohms but doesn't specify anything about the sub channel.

For the front stage I got some JBL P560C 2 way components new on eBay for $68 shipped. 2 Ohms, 75 watts RMS















The new sub arrived today: Image Dynamics ID15 v3 D4















Next to the 5.25" JBL and the 4x6" Polk plate:



Running the sub IB seems like a win win to me at the moment: Saves weight because there's no box and requires less power so I can get away with just a 5 channel amp. I guess I'll see if it's enough bass for me.
The nice man at the FedEx store where I received the sub let me weigh the raw driver on his precise scale:
20.4 lbs for that 15" sub! Not bad, pretty light.
I was originally gonna go with a single 12" Infinity 120.9w that only weighs 15 lbs, but errbody seems to prefer more cone area when going IB. Since it's my first go at IB I want to give it the best shot and trust the experts. See how easy I up sold myself on a larger sub? :)

I've torn into the car a little so far. Just removed the front & rear speakers, both 4x6". Since I'm not running rear speakers I'll close off the holes and build a new rear deck cover and upholster it. In the front there really isn't much space so I'm building custom baffles to space the 5.25" mids out a little. The cavity in the A pillar is too narrow for the JBLs to recess into:



These were installed by the previous owner in typical previous owner fashion: 3 out of 4 screws used, all 3 lose, grille rattling like crazy, speaker wire ran loosely under dash around other wires without even a single zip tie, bare speaker wire strands wrapped around speaker's terminals then electrical taped. The electrical tape had already fallen off. :) Classic.



The little Polk plates are actually pretty good. I'm gonna use them to build computer desktop speakers out of with a little mini amp from PartsExpress.com More on that later.



Positioning the tweeter: I'm thinking the stealthier the better and I don't like where the factory premium sound option (that my car didn't come with) places the tweeter on the sail panel pointed at the front seats. The mids in the kicks are so much further away from the listener than the tweeters, that's why I'd rather the tweeters not point directly at the listener. The goal is to have it sound as good as possible even before adding the MiniDSP down the road.
I will play with the positioning and decided what sounds best:
A) under the little vent on the actual dash firing up, reflecting off windshield
B) on the A pillar firing across dash
C) on the sail panel



For sound deadening I picked Second Skin Damplifier Pro based on good reviews here. I won an eBay bid from user 'nps' for an open box of 18 sheets (unused of course) for $160.95 shipped. That's around 30 sq.ft. and 18 lbs, didn't want to add any more weight than that for deadening. $160ish is what I was gonna spend on 40 sq.ft. of regular Damplifier new, so essentially I upgraded the quality at the expense of some quantity. I'm happy.



I'll update this thread as I move along. There's a ton of work left to do...
 
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#4 ·
Awesome, thanks. Hopefully I can get this build off the ground soon.

Love me a clean E28. I have memories of an M5 that belonged to a fellow spectator at Summit Point Raceway that I used to drool over. I was a teenager at the time. :D
I'd like an M5 :) My dad took me to Summit Point to watch amateur motorcycle racing when i was a teenager. Some good memories.
 
#3 ·
Love me a clean E28. I have memories of an M5 that belonged to a fellow spectator at Summit Point Raceway that I used to drool over. I was a teenager at the time. :D
 
#5 · (Edited)
Oops I did it again...

I'm a terrible person. First I hardly get anything done on my car in the last two weeks, then I buy another sub before ever even installing the first one:
Found this lightly used NVX VCW154 15" monster on eBay for a steal, just over half of the new price shipped and i couldn't resist. It was on my short list of 15" subs to own to try IB in my car.





Next to the brand new ID15







The VCW154 has 20mm xmax, Fs of 26hz. RMS is 850 to 1000 for ported and sealed, respectively.
Vas is 106L, sensitivity is 87db (1w/1m), Qts is .44



I know it's not at all lightweight. It weighs 10 lbs more than the ID15 (30.5 vs 20.4 lbs). I'll probably mostly run the ID and every once in a while switch just for fun. Which ever one is not in the car will be running in my home stereo system.
The modular trunk baffle system I'm building for the car will make it very easy to swap drivers. Each driver will have its own baffle that is attached to the main baffle that always stays in the car.

Some other subs on my list to own and try IB are the Alpine Type S 15", Dayton Ultimax 15", Dayton HF 15" (RSS385-4 HF), JBL W15GTi, ID MAX15, Sundown E-15 v3, RE Sex or Xxx 15" and Infinity 120.9w. The JBL GT5-15 WAS on the list but apparently got discontinued. Same for the JBL GTO 1514D.
On a side note -- I wonder if JBL is about to release a new 15" sub since they don't have a current 15.

Anyway, I'm still gonna try the ID15 first, let it break in and listen to it for a few weeks and then switch to the NVX to compare the two.
Next day off I'm working on relocating the battery so I can hook up the amp so I can hook up the speakers and sub so I can have tunes in my car again... Then there's also plenty of Damplifier Pro still to be installed.
 
#6 ·
So I messed around with the sub baffle a little.
Instead of using cardboard to make a template I used some 1/2" insulation foam we had around. It's actually ideal for making templates because it's light, very easy to trim and it holds its shape well unlike cardboard.
I forgot to snap a pic of the final foam baffle template, but it fit neatly to the sheet metal wall separating the cabin and trunk.
A shot of the trunk:



This wall is getting a big hole cut into it and it doesn't even know it yet...
Unfortunately there's a step on the bottom so my baffle has to start above that.
A 15" sub baffle JUST fits there:



Cabin side of ze wall:



There's some factory sound deadening on the trunk floor. Some people have referred to it as tar mat but I have no clue what it is:







It's damn heavy. My plan is to remove it entirely and put down Damplifier Pro not only in its place but everywhere in the trunk. Here's a close up of a chipped piece, it has foam backing. Is that just 80's OEM mlv?



Once I was happy with the shape of the foam baffle I transferred it onto 3/4" birch plywood:





I used a clamped on 2x4 stud as a guide to make the longer cut which worked well. For the shorter cut I just said f*** it and free-handed it. Mistake.

After test fitting the wood baffle in the vehicle I drew on the obligatory Union Jack. Then I used the NVX VCW154's rubber gasket as a guide to draw the cut out circle. I had previously confirmed that the diameter of that gasket was a good fit for both subs to be reverse mounted.





My dad helped me with his router. We made a circle jig out of a metal piece that came with the router and a long screw, using the plunge router base and a trimming bit:





It worked well shy of one little mishap at the end near the 12 o'clock mark. Luckily the woofer's 12 o'clock screw won't be affected.
Tried it on just for size even though this isn't the baffle the woofer gets reverse mounted to:









Fits well.
I then made a second baffle template out of some more 1/2" foam. This oval baffle will be what the woofer gets reverse mounted to. Each sub will have its own unique and custom fit oval baffle. These oval baffles will be easily swapped out to swap woofers. At this point I'm thinking of attaching the oval baffle to the main baffle using T-nuts & bolts, unless someone has a better solution. The reason I don't want to use wood screws is that I don't want the threads to wear out as I'm swapping baffles.

Here's the final oval template. I looked around the house for something large and oval to use for the shape and found a small side table with an oval top. Flipped the table upside down onto the foam and came up with the curve / arc. Turned out way better than anything I could've drawn free-hand:







I then transferred the foam oval onto 3/4" birch plywood twice; one oval for each sub I have so far. As I get more subs down the road I'll build more ovals. The reason why each sub needs its own oval baffle is because each sub has a unique reverse mount cut out (to clear the surround).





Once the first oval was cut out and lined up perfectly onto the main baffle I screwed it down with two screws so I can use the main baffle as a template to route out the cut out. In hindsight I should've used clamps DUH.





And a quick test fit: perfect.



Both baffles' outer edges then got routed with a 1/4" round-over bit to enhance appearance and make it easier to upholster. The camera doesn't really pick up the rounded-over edge well:



The next step will be to attach the main baffle to the car and cut the sheet metal *yikes* You gotta pay to play. I don't plan on ever selling the car again anyway.

That's all for this update. I hope this thread with its step by step pics will be useful to some peeps down the road on the quest to audio nirvana. I certainly have learned a ton from this forum through other peoples' builds.
 
#9 ·
Lookin good. Nice progress.
Thanks guys.
Yesterday I ordered some much needed parts for the battery relocation.

A junction block for the engine bay to run the + battery cable to from under the rear seat:



As well as a 150 amp breaker to protect the + battery cable from setting my car on fire in the case of a collision:



Both should arrive on Saturday so I can go to town this weekend.
The 1/0 gauge battery cable arrived weeks ago, as did the new Oddyssey PC680 MJT battery. I'll use some leftover 1/0 gauge to do the big 3 upgrade as well.
 
#12 ·
So I got some more stuff done, progress is slow because I'm doing other work on the car as well. I finalized the battery cable from under the hood to under the rear seat so the car can drive again.



This project is my first time ever making my own cables, using TechFlex, heat shrink and soldering. When I placed my order for the TechFlex and heat shrink at wirecare.com (a while ago) I didn't know that 1/2" heat shrink wouldn't fit over the 1/0 gauge cable, that's why you see electrical tape in the pic. However, just after the above pic my dad gave me some 3/4" heat shrink he had so I actually peeled the electrical tape back off and did it right.

The new junction block under the hood is as far towards the rear of the car as possible, right above the fire wall, to keep the battery cable as short as possible (weight).
There were a few cables attached to the positive terminal under the hood and they needed to be rerouted and hooked up to the new junction block. The starter cable was long enough to be rerouted, just needed to be reterminated. The fuse box cable and one other relay cable, however, were too short so I ran some 4 gauge cable from the junction block to near the fuse box and connected them both. Glad I had ordered extra 4 gauge which will be the amp's power and ground btw.

Fuse box junction before final heat shrink:



Close up of junction: Each cable was terminated with the proper size ring terminal and individually heat shrinked, held together with a M6 bolt and self locking nut...



...then double heat shrinked over the junction to prevent it from shorting out against the inner fender:



How it looks with everything back in place: The junction is below all those relays on the side of the fuse box, the 4 gauge cable running to the junction block is ran along some other factory cables and uses their factory tie down points for a stealth look. The only give away that something is not stock is the shiny, new TechFlex:



On to the trunk.
I temporarily attached the baffles in place so I can pilot drill their mounting holes through the wood and the sheet metal at the same time. The calm before the storm:



Then I removed the wood and enlarged the sheet metal holes with a 1/4" bit because I'm using all M6 hardware:



Installed the threaded inserts into the wood baffles and test fit again:





Used the baffle as a template for cutting the hole. The point of no return:



I used the sawzall for the rough cut, then sheet metal sheers to trim most of the left over material, then a hand file to clean it up. It won't win any beauty contests but it works for now:



When installing the threaded inserts, I used 20 minute epoxy so they stay put:







 
#14 ·
Thanks!

I worked on it some more after this morning's update and finished the battery cables. I applied some Ensolite PnS to the floor underneath the battery, the wall it's pressed up against and the inside of the aluminum bracket to decouple the battery. For the ground cable I was able to go to a factory ground nearby (bottom left in the pic).

The brackets that hold the breaker also attach to the same mounting points (aluminum M6 rivnuts) as the battery bracket, the goal was to drill as few holes as possible and to avoid drilling into the floor / outside wall of the car. There's also some Ensolite on the tips of the brackets that rest on the floor.



 
#16 ·
Yeah that's a popular spot for a sub enclosure and I've considered it as well. However, the E24 rear bucket seats leave no space underneath for it, even to fit the battery I'm hacking into the seat pan a bunch.
I hope a 15" IB on low power hits as hard as any 10" sealed shallow sub I could've squeezed under the stock rear seat... We'll see.
I'm working on the trunk today, removing the factory sound deadening to replace it with Damplifier Pro, hopefully mounting the amp before the end of the day.
I was shocked just how much the factory 'tar mat' weighs while I was removing it one little piece at a time with a scraper. When it was all out I weighed it at 35.8 pounds!!!!! Incredible.
Btw I also weighed the 9'9" long main 1/0 ga battery cable before I installed it and fully dressed with TechFlex, terminals and heat shrink it weighs only 3.9 pounds. Much less than I expected.

Before:



After:

 
#18 ·
So I read in the MiniDSP thread that the MiniDSP doesn't take speaker level inputs. The head unit I was planning to use for OEM looks doesn't have any pre-outs:



...so I guess I'll "settle" for the Pioneer Deh-80prs.
I installed that unit in my brother's 4runner, played with it a bunch and really fell in love with it. My only gripe is its 'aftermarket' looks. Maybe I can spray the faceplate with a matte clear to get rid of its gloss and also black out the chrome trim on the dial.

 
#20 ·
Wow MiniDisc takes me back like Mountain Dew Throwback!! I actually love MiniDisc, used to have all kinds of Sony portables in the 90's. While that is a sweet headunit, no doubt, it's expensive and I would still need a miniDSP with it to run active.
My choice of decks is between:
A)something cheap for OEM looks + miniDSP
B)something expensive that does it all (deh-80prs)
 
#22 ·
This is what the trunk floor looked like after removing the factory 'tar mat' sound deadener:



Once I scraped off the brown glue residue I wiped it down with alcohol and started applying the Damplifier Pro:





Here you can see the non-op factory power antenna that is getting yanked soon. I'm putting a stubby in its place:



I added some deadener to the flat panel between the taillights:



Some scrap 2x10 wood works well as a cutting board for the deadener:



The trunk's no yet done, still gotta do the spare tire well and the rest of the floor and cover with Ensolite.
My question is how much Ensolite should be applied? Since the deadener coverage doesn't need to be 100%, is it best to cover 100% with Ensolite?
 
#23 ·
IB wall setup looks great.

If you're trying to block outside noise entering through the trunk, you'd want to use MLV over ensolite.

Ensolite is really only good as a decoupler. So anywhere two hard surfaces touch or loose wires that might cause a rattle. Doors, rear deck, roof... are good places for that.
 
#25 ·
Made some much needed progress this past week.
First of all the Deh-80prs arrived a few days ago and I got to terminating its harness:



As you can see I just heat shrank all the speaker leads together because I won't be using the deck's built in amp, only the rca outs.
I know it's nothing special but it was the first time I ever tried to make a harness look clean. In all my previous installs I've never cared about neat wiring, but since I stumbled across this forum I've gotten inspired by some seriously top notch installs and also some neat wiring threads. So in an effort of stepping up my wiring game I ordered lots of different colors and sizes of heat shrink, TechFlex, connectors, some new tools like a heat gun, side cutters and a soldering iron etc.
Just having fun with it all.

I also made a harness for the rca leads and sub level remote Cat5 cable to go from the deck to the amp, TechFlex'd it and ran it along the transmission tunnel. However, I had to use some old rca cables, even extending one of them and they don't match so I was too EMBARRASSED to snap a pic of it.
I was just going to place a Sonic order for the NVX 6 channel rca lead and a Scosche rca level remote for the sub channel when I stumbled across a classified ad on here of a used NVX JAD900.5 5 channel amp and I had to have it. I've installed that amp into my brothers car a few months ago and really fell in love with it.
I'll have to order the 6 channel rca lead in a few weeks.
So the oldschool NEXT amp you saw in previous pics has become my spare 5 channel and the NVX is going into the beemer.
The NVX is a much better fit for this install because it's lighter, smaller, Class D meaning it puts less of a draw on the weak factory alternator AND it puts out more power.
I weighed the NEXT amp at 10.8 lbs and the NVX at 6.5 lbs. What can I say :)
An added bonus is that because the NVX is so much more compact I can now fit it under the rear seat instead of mounting it in the trunk which saves me lots of time & effort.

Just finished the mounting brackets out of 1/8" aluminum bar stock for the amp. They look a little weird but secure the amp nicely without having to drill into the floor of the car or using wood. One bracket attaches to a M6 rivnut I set into an unused factory hole in an interior sheet metal wall, the other bracket just velcros to the floor and side wall. The industrial strength 3M velcro is as strong as Chef's salty chocolate balls.
I'll post a pic tomorrow after it's installed and it will make more sense.
Underside of amp:



Got some M4 socket head bolts, washers and nylon self-locking nuts so nothing comes loose:



All the wiring is in place now and tomorrow the deck and amp is getting installed and the tuning can begin so stay tuned for more pics!
Thanks for watching!

R.I.P Chef

 
#26 ·
So lots of progress happened over the last week or so.
The deck got installed, I ran into a little bit of a depth problem but was able to overcome it. Then I installed the NVX amp (Class D), all the wiring was already in place since I did that first.
I hooked up only the front components for the first few days to let them break in and start tuning. All was well up to that point.
I listened to the front stage for about 3 days on its own, enjoying them breaking in and messing with the levels and eq. The JBL mids started to really loosen up after about 4 hours or so and then kept getting more and more midbass. At this point I've got about 10 hours of listening in with them, I'm pretty happy how they sound.
The tweeters are just stuck on top of the dash with double sided tape for now reflecting off the windshield.
Then I hooked up the sub for the first time, the brand new ID15. I had the gain at minimum and the volume on medium. It sounded really good already, very deep bass.
As I begin to turn up the gain, all of a sudden I get this really violent ground loop / feedback loop that sends static at full power on all channels. This only happens when the sub is hooked up, not at all with the front stage only. Luckily the tweeters didn't blow from it, but I bet they were close. I could hear them just frying from the noise, it was terrible.
So I at first assume the amp's sub stage might be bad and switch it out for the NEXT Q.55 amp (Class AB). It does something similar, but instead of a full mental static that doesn't stop 'til the ignition is turned off, it just clips really bad on all channels when the bass hits, only at medium volume and up.
Since the headunit is grounded to the chassis (I ran a dedicated ground cable from the deck's harness to a factory ground nearby) and the amp is grounded to the battery I've arrived at the conclusion that there's a ground loop present.
I unplugged all input rcas from the amp and plugged my ipod directly into the amp as a source and the problem went away, even though it was very noisy and not at all ideal, but it confirmed the issue.
So I've got to run a new ground for the amp to the chassis and see if that fixes my problem. If that doesn't cut it I may have to extend the headunit's ground cable all the way to the amp's ground location, but hopefully it won't get to that.
I haven't started deadening the cabin yet, there's lots of little holes around the mids that need plugged. The rear deck is also very perforated and has a TON of flex. Hopefully Damplifier Pro alone is enough for the rear deck, otherwise it might need its own baffle for added stiffness.
I'll snap lots of pics of the progress. Thanks for following along and have a great weekend!
 
#29 ·
Regarding the ground loop issue I'm having: I changed the amp's ground from battery to chassis (the factory ground that the battery is grounded to) and it actually made it so bad that I couldn't even play any music. As soon as the system powered up without any music playing yet there was so much static noise coming out of the sub and then the front stage started popping and I just shut it off. Scary ****.
So my next move is to run the headunit's ground to the same ground as the amp.
THEN we see whats happens.
 
#30 ·
Figured it out: The sub's mounting bolts going through sheet metal was the culprit of my feedback issues. That's why I didn't have any problems playing just the front stage without sub and that's why the ipod as source directly into the amp was fine even with the sub playing.
Here's a picture of how the sub's mounting bolts go through sheet metal:



I know there's rust already even though I just cut the metal like a month ago. Gotta go back and seal it properly...
I guess I have to redesign my baffle or cut the hole in the metal even larger to clear the sub's bolts.
Suggestions?
 
#32 ·
Yeah I might have to redesign my baffle setup, I'd rather not cut any more sheet metal. But before anything I will try these and see what happens:



They're a fiberglass (Isoplast) bolt allegedly with nearly the tensile strength of steel, much stronger than Nylon bolts. I found them at
www.non-ferrousfastener.com
Lets see how 8 of them hold up a 15" sub with 500 watts flowing through it. That will be quite impressive...
If anybody has any experience with these or something similar (non-conductive hardware) please do share. Thx
 
#33 ·
Good thing you are in SC. If your car was back in Germany, it would be deemed unfit for road use since you cut the metal wall behind the back seat. See, in Germany cutting of any structural metal is strictly prohibited. And their inspections are 10 times as tough to pass than here in the US. (Watch this Top Gear Series 15, Episode 2 clip where their old German cars get inspected: https://youtu.be/BGla79jWB9k?t=38m18s ) I guess if your doing 150 mph+ on the Autobahn you better have all the structural rigidity intact that the government mandates. However, in the US, cut away!!
 
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