Trunk Space? IB Setup

[bmwman91]

If space is a concern, look into one of these.

http://www.madisoundspeakerstore.com/approx-10-subwoofers/sb-acoustics-sw26dac76-4-shallow-10-subwoofer-4-ohm/

Datasheet: http://www.madisound.com/store/manuals/SW26DAC76-4.pdf

The price seems to have almost doubled in the last year or so (bought mine for $200 new in mid-2010). I run it in the ski-pass hole, and it sounds just fine with the arm rest up. The trunk is so leaky that it doesn't seem to matter too much what you do with it if you aren't using a box. It is crossed over at ~130Hz, but I think I will make some adjustments to the active crossover to put it closer to 100Hz. At 130Hz you seem to get some directionality and I can tell that some low-mid sound is coming from behind. Theoretically, this sub has an F3 of 34Hz with the E30's trunk as the enclosure, although it is probably higher due to the trunk's leakiness.

Anyway, one of these subs, crossed between 100Hz & 120Hz and mounted to the rear bulkhead works pretty darn well. I would LOVE to see the results of putting one into a tuned box (Luke...!)...either sealed, or a conservatively designed ported box to keep group delay reasonable around the tuning frequency. It is a tad pricey though, but if you need trunk space, it is a great option.

If you want some idea of bass performance, find a sub with a proper datasheet (so probably not a car-brand) and plug the parameters into WinISD. Simulate it in a ~500L sealed box. The trunk is leaky and you will have some very real cabin resonances, but it is just how it is. That will give some idea of what you will get using the trunk as the enclosure ("infinite baffle" is sort of the wrong term for this setup, in a strict technical sense).

[Threehz]

First off, that is a beautiful woofer, fantastic specs, especially for a shallow mount. Then again for 300$, or even 200$ when you got it sounds about right.

Just to get this straight, you simply mounted this woofer TO the frame behind the armrest?

If I had the money I would probably get an RE sEX15, the sEX series has to be one of my favourite woofers.

Is the trunk of an E30 approximately 500L? That is the main reason I started this thread haha and that definitely helps me with my numbers. I used the outside dimensions of the car to make a VERY rough estimate of the trunk volume for winISD but of course it was mostly a guess.

[bmwman91]

I got 500L using a tape measure & some scratch paper. It isn't super precise, but it is somewhere between 400 & 600L. At that size, it doesn't matter too much if it is a bit off. The thing is so leaky that it REALLY doesn't matter, actually.

I mounted the sub to some plywood, which I mounted to the rear bulkhead. It's in my build thread.

http://www.r3vlimited.com/board/showthread.php?t=170725

[Threehz]

Fantastic build, I wish I had access to the tools and equipment you have! I love the way it's mounted, beats my original idea of leaving a little space in front of the woofer in the trunk. Your way it literally is trunk and cabin separated, perfect and I will probably do the exact same.

It's still a little hard to plan this all out as I do not even have the car yet, now I cannot wait though.

Do all E30's have a rear fold down arm-rest?

[bmwman91]

Fantastic build, I wish I had access to the tools and equipment you have! I love the way it's mounted, beats my original idea of leaving a little space in front of the woofer in the trunk. Your way it literally is trunk and cabin separated, perfect and I will probably do the exact same.

It's still a little hard to plan this all out as I do not even have the car yet, now I cannot wait though.

Do all E30's have a rear fold down arm-rest?

The arm rest was an option. My car didn't have it originally, but a guy on M42Club sold me the entire seat back + arm rest for $120 or something. Honestly, don't worry about it too much. I really can't tell a difference in bass with the arm rest up or down.

If you want to do this setup, you will probably need to knock out the metal panel that resides in the arm rest hole (the arm rest option was more for people that wanted to put skis in their car so that they could stick them through the bulkhead). Then again, depending on the subwoofer you use, you may not need to. If you flush-mount the sub in the plywood panel, the only thing you need to worry about clearances for is the foam/rubber surround of the cone. If you pull off the cardboard cover thing that sits back there, you will see two vertical sheet metal beams. I think that you have like 11.8" of space between them, so keep that in mind. The rubber surround on the SB Acoustics sub is pretty prominent, but it just fits between them.

[Threehz]

Yeah my sub is a good 15.4" I think and the surround is pretty dang thick, I guess I'll have to see and work it all out when I get the car. Actually I'm pretty sure the car doesn't have the armrest. What about porting through the back top "dash" behind the backseats?

[bmwman91]

To be honest, I wouldn't try any sort of porting arrangement unless it involves a tuned box. With the volume of the trunk and the pre-existing resonances in the cabin, no good can come of trying out clever ported-rear-shelf stuff. That huge volume combined with any port tuned for more than about 5Hz will lead to a gigantic, boomy resonance. Try playing with the woofer you want in WinISD with a 500L ported enclosure. You'll see what I mean.

Really, as along as the sub can hit 40-50Hz, you are good. As fun as it is to have a 20Hz setup, the vast majority of music has very little content that low. Some techno & rap does, but I don't listen to it. And in the end, road noise is going to dominate a lot of the experience. My bass sounds GREAT when I am parked, but it gets weak as engine & road noise, that happen to be in the low/mid range on the highway, drown it out. I don't want to go deaf either, so I don't usually crank the system up to mask it.

So, don't stress too much over the details if you want a decent sounding system while driving. You can put the best parts in the world in there with 0.001% distortion, but still effectively get 25%-50% undesired noise reaching your ears thanks to the fact that it is a moving car! If anything, cars are nice because you don't really NEED super low distortion stuff since it is kind of a waste in a way. As long as you tune your crossovers well to get reasonably flat frequency response and have sufficient amplification to avoid clipping at desired volumes, you will be happy.

[Threehz]

Very good point. Modeling my sub in a 500l closed enclosure in WinISD gave me the cleanest flattest curve I have ever seen from this sub. Only time will tell how it actually turns out but it's definitely nice to see.

Here's the graph:


Surprisingly perfect is it not?

How well did your setup perform compared to how it was modeled? (I mean sounds like it turned out great, would you say it turned out pretty consistent with WinISD's model of it though)

[bmwman91]

I haven't measured the frequency response (need a deck with an aux input so I can get my measurement mic & software going). It sounds good to me.

The ACTUAL response in the car, versus WinISD, will be quite different. There are cabin resonances since the thing is a tin can with flexible walls, and lots of leakiness between the trunk & cabin, and cabin and outside. For the most part, don't worry about it though. A little too much bass is better in these cars than the total lack of it you get without a sub.

[drtwofish]

I hate to bring a dead thread back, but I was wondering if one of you guys could point me in the right direction to learn more about the "open air" sub setups. I have a 12" Infinity in a sealed box from my previous car (318ti with a hatch), but from what I read I'll never be able to hear it in the cabin. I do have a ski pass-through, but due to a baby seat I can't fold down the center arm rest. Also due to baby and other car priorities I can't dump a ton of money into a stereo setup, but I would like to add a little bass to the system. Ideas are welcome. Thanks!

[Threehz]

Wow, well seeing as this popped back up...

I've finished my setup, just been way too busy with school and work to update it. I'm going to try and get some audio samples this weekend so I can do an spectrum analysis and see how my response is.

Anyhow I went through with the original IB setup idea. This picture is right after finishing up the entire install (components up front, coaxials in rear, woofer, both amps, new deck and my custom made amp rack). Anyhow this gives you a pretty good idea of how the IB looks.



There is a board that is 36" wide, and 20" tall, it is two layers of .75" thick MDF glued together so it totals 1.5" thick. Around the circumference of the board is about 3" of memory foam. Then I wrapped the entire thing in some automotive carpet as you can see in the picture.

The 15" Lanzar MAXP154D subwoofer is mounted right in the center and fires into the back of the rear seat.

I mounted it with the bottom of the board snug into the most inner bottom corner of the trunk. It is angled back so it fits (trunk height is about 16").

Now there are speakers in the rear deck slots which otherwise would be a straight passage from where the woofer fires to the cabin. I also do not have a ski-pass rear seat (there is the ski-pass hole in the metal behind seat). What I did was cut a bunch of holes in the back of the rear seat's foam where the ski-pass hole would be, you can't feel a difference in the seat, but I'm sure it lets sound through better.

Anyhow I was quite scared it was going to sound like total shit. It isn't even totally sealed off, around the top right and left corners of the board there are pretty substantial holes and the trunk liner leaves more gaps behind it. I might plug up the holes in the future but for now,

It sounds great. Turned out much better then I expected. Some people said that it might sound good at low volumes but higher up would sound awful, not at all. I have the woofer's amp's gain set really low because that is all it needs. But I've played around with it a lot, I've turned the gain up again half way and played everything from folk to rap with deep bass, sounded great, I mean my ears were about to bleed and I thought my little E30 was about to fall to pieces but the sound wasn't noisy or muddy at all.

Personally I did this setup because I had this MDF left over, I already had two of these woofers and the amp and it made perfect sense. Honestly I couldn't build a better sounding setup any other way with what I had, MAYBE if I built a box that took up the entire trunk and I still doubt it would compete with this setup.

In the future I plan to convert my trunk to wood lining, and build a hardwood ported box with an RE Audio sEX12 in it, switch to a powerhouse 5 channel. That's just my dream setup.

Anyhowz back at your question drtwofish, I don't see why you wouldn't be able to hear it? Obviously you probably won't get bass that people will hear down the block but if you just want bass that will probably work. Why not try it out how it is and if it's not what you want go from there? It's not like setting up the amp and everything else is going out of your way, so if you change your mind you already have everything set up.

[drtwofish]

Hey man, thanks for the update - that setup looks amazing. You're right, of course - I should just try it out, especially since the wiring will be the same for whatever setup I end up with. I'd seen a few folks on the boards saying that a box in a sealed trunk will just give you a case of the trunk rattles with nothing actually making it into the cabin, but that may be what I get for surfing forums instead of actually giving it a shot.

Back in the day I put bazookas tubes behind the driver and passenger seats in my old 325is - sounded pretty decent with minimal work! Now I'm old and desire footspace for passengers though. Thanks again.

[Threehz]

Yeah definitely man, and you know, if you're not too adverse to messing with stuff, you can use winISD to figure things out and turn your sealed box into a ported one, that will give it some extra power and beef it up a little. Hope it works out for ya!