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      09-12-2018, 01:57 PM   #1
shiftdnb
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Custom Subwoofer Box for F31

Last weekend I installed a custom subwoofer enclosure for under the cargo floor of my F31. When I bought the car I upgraded the stock speakers and amp through Musicar Northwest, with morel components, jehnert subs and a helix dsp. For me it sounded great but the limitations of the sub enclosures under the seat left me wanting for more low-end. My solution was an 8" Sub in a box that fit in the cubbyhole under the cargo area of the wagon. I went back and forth on the design as I wanted a ported box. I really stretched the limits of box design and tuning and was a little worried because of the port dumping out into the side, as I might have issues with chuffing. I would have liked to have fit a bend inside the box on the port but that was impossible for the size as I had to keep the sub below the actual floor height. So I reduced the size lengthwise and kept the box the same distance away from the side as the port is big so it will not ruin the sound. I ended up wiring the subs dual voice coils in series, cutting the power in half as I didn't need all 500 watts and wanted to keep the amp running cooler. The sound in this thing is impressive, I ended up dropping down the frequencies between 32-50 in the dsp just because it was too much. I didn't want to rattle everything in the car, I wanted sound quality with being able to feel the lows while driving. I can still rattle everything if I want but I finally am happy with the sound in my wagon.

Next step is wrapping the wood and a false floor for when my dogs go in the car. I'm also planning on installing a switch that will switch the modes of the dsp to either use the sub or not. So one will be my old setup and one will be the new one with the sub.







Here's a link to more steps.
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      09-12-2018, 03:46 PM   #2
BEM-S4
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Honestly curious what's the advantage of that setup versus this one I have in my F31 with a 10" Focal? I thought under the floor was bad sonically but the guys who helped you (and it sounds like you too) know what the hell they are doing. Do you leave it exposed all the time?
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      09-12-2018, 05:36 PM   #3
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Do you have comfort access by any chance? The module for mine takes up like half the space of that area so I couldn't get as much space in the back. It's also where I keep my tire compressor. And the big thing is I really have no experience with fiberglass and didn't really want to deal with the smell in the car, if I did decide to fabricate my own. I got a couple quotes to have one built but they were very expensive.

Musicar quoted one in the side but I would have had to remove the comfort access and since they would have had to build one from scratch it was going to be expensive for the labor alone.

I also went with it under the floor because I have a large dog that needs as much space as possible. I'm working on the floor design right now so that I can quickly cover it and uncover it. I'm waiting on a custom cargo cover to come in that I ordered that will be the template and the covering for the false floor. It'll probably be one of those expectations vs reality buys but we'll see. It was cheap enough for me not to worry about cutting into it.

Last edited by shiftdnb; 09-12-2018 at 05:43 PM.
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      09-12-2018, 06:51 PM   #4
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I do have comfort access and I don't mess w fiberglass either - I sourced the enclosure from a shop in Poland it arrived in a week I was surprised. I don't know much about this stuff I just made sure it was the right volume for the speaker I wanted to run and ordered it up. My JL amp is in the same area basically as yours but I just did put some Velcro on the back and stuck it to the floor. Will maybe have a pro do something more permanent at some point.

I'd have to look but I think the website is something like basset.pl and the cost was $200-ish.

Your install looks very slick I only asked to see if it was worth doing the same and upgrading my current deal.
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      09-12-2018, 07:52 PM   #5
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lol, that website is a polish basset hound site. I think you meant this site http://basser.pl/en/. Your box is sealed too right? That's another reason why I went with that spot under the floor because I wanted to go ported, so needed more room.
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      09-12-2018, 08:25 PM   #6
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Quote:
Originally Posted by shiftdnb View Post
lol, that website is a polish basset hound site. I think you meant this site http://basser.pl/en/. Your box is sealed too right? That's another reason why I went with that spot under the floor because I wanted to go ported, so needed more room.
Yes - that's it. Autocorrect fail. Yes it's sealed it's in dad's car he was complaining about too much base which I took to mean bass was too forward and mids / tweeters were not up to the task so add a 10" w/ 600 watt amp in the trunk to solve the problem. Seemed like a good idea.

To answer your question yes sealed, which made sense considering. I've got sealed 8" in my vert since it's all I could fit and it did a surprisingly good job, so kind of stuck to what I know with this one.
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      09-12-2018, 09:33 PM   #7
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Most of the time sealed subs work better than ported in a car anyway. The extra sensitivity in the low end that's provided by porting in a home stereo or home theater sub isn't necessary in a car, where that sensitivity is provided by cabin gain.
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      09-13-2018, 08:45 AM   #8
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I think it depends on what type of music you listen to. Pretty much all my music is heavy on rumbling low end. You're right in that the cabin does give you a boost in the lower end frequencies but right now I can hook up the RTA and see I'm getting everything loud enough where I can get down to 25hz and level it of with 40hz without having to push the gains of those frequencies. Do I need 25hz? Probably not but to finally be able to hear and feel those notes below 40hz is nice because they're usually subtle but add so much to a song.
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      09-13-2018, 09:18 AM   #9
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Quote:
Originally Posted by shiftdnb View Post
I think it depends on what type of music you listen to. Pretty much all my music is heavy on rumbling low end. You're right in that the cabin does give you a boost in the lower end frequencies but right now I can hook up the RTA and see I'm getting everything loud enough where I can get down to 25hz and level it of with 40hz without having to push the gains of those frequencies. Do I need 25hz? Probably not but to finally be able to hear and feel those notes below 40hz is nice because they're usually subtle but add so much to a song.
And we've officially shifted the conversation over my head
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      09-13-2018, 09:43 AM   #10
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The chart on the first page here shows a JBL 8" in a sealed box outside the car and inside the car:
https://www.manualslib.com/manual/79...-8.html#manual

The in-car response is very good, essentially flat from 20-50Hz. On the second page there are examples of ported and bandpass in a car versus out. The sealed response is better, with the additional advantage of the sealed cab being half the size of the ported and bandpass.
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      09-13-2018, 01:17 PM   #11
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Quote:
Originally Posted by Billfitz View Post
The chart on the first page here shows a JBL 8" in a sealed box outside the car and inside the car:
https://www.manualslib.com/manual/79...-8.html#manual

The in-car response is very good, essentially flat from 20-50Hz. On the second page there are examples of ported and bandpass in a car versus out. The sealed response is better, with the additional advantage of the sealed cab being half the size of the ported and bandpass.
It really comes down to the type of music you listen to. Does your music have punchy crisp bass, Rock and Roll, R&B? Sealed enclosure will be fine. Do you listen to Drum and Bass, Trap, Electro and Chop and Screw with long low frequency bass notes? Ported is going to be better for that. What you can also do with a ported box is tune for a specific frequency based on the size of the box and the length and size of the port. I was shooting for 32hz in this design. If you're not looking for that and you were to build the box in the same space, I would definitely put two speakers in the box and use the whole space. You could probably even fit 10s in there.
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      09-13-2018, 01:25 PM   #12
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Quote:
Originally Posted by BEM-S4 View Post
Quote:
Originally Posted by shiftdnb View Post
I think it depends on what type of music you listen to. Pretty much all my music is heavy on rumbling low end. You're right in that the cabin does give you a boost in the lower end frequencies but right now I can hook up the RTA and see I'm getting everything loud enough where I can get down to 25hz and level it of with 40hz without having to push the gains of those frequencies. Do I need 25hz? Probably not but to finally be able to hear and feel those notes below 40hz is nice because they're usually subtle but add so much to a song.
And we've officially shifted the conversation over my head
Quote:
Originally Posted by BEM-S4 View Post
Quote:
Originally Posted by shiftdnb View Post
I think it depends on what type of music you listen to. Pretty much all my music is heavy on rumbling low end. You're right in that the cabin does give you a boost in the lower end frequencies but right now I can hook up the RTA and see I'm getting everything loud enough where I can get down to 25hz and level it of with 40hz without having to push the gains of those frequencies. Do I need 25hz? Probably not but to finally be able to hear and feel those notes below 40hz is nice because they're usually subtle but add so much to a song.
And we've officially shifted the conversation over my head

Those are just frequencies, the lower the number the lower the note. When you are tuning your system it is better to take away than add gain so you want to do a proper gain structure from the radio to dsp to amp as your setting it up.

Here is a good diagram as to what instruments play in what ranges.
[img]https://www.audio-issues.com/wp-cont...main_chart.jpg[/img]
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      09-13-2018, 01:29 PM   #13
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That helps, thanks. I never got into the really technical side of things - I know what sounds good but don't really understand the science, I didn't invest the time to learn about it.

I have a friend who built listening rooms for people like Billy Joel and Mariah Carey so when I'm shopping I literally just tell him "your budget is $X go find me..."

I'm like the audio equivalent of a wine snob who knows nothing about grapes.
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      09-13-2018, 08:34 PM   #14
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That's basically what I did for the retrofit of the stock system. I didn't really want to fuck up the head unit to dsp connections, which were really confusing coming from the old analog days. They sent me all the stuff ready to go and I just installed it. I work with digital sound boards for live production so the DSPs were such a welcome tool to have. It was my struggle to get anything below 40 hz to stand out that put me on to this project. The underseat subs are good but the enclosure is it's downfall and I was tired of hearing my side sill's rattle. I feel my sound is complete now. I can drive at highway speeds with the windows down and hear my music that's how crisp and clear the morels are and now that I can fully feel the bass, I'm finally happy with it. The sub and amp I got were super cheap because this was such a shot in the dark I didn't want to waste a bunch of money. In the future I might upgrade them to Morels because I'm so impressed with the ones I have in the doors.
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      09-16-2018, 05:02 AM   #15
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Thanks for the post! I am also planning a sub install to my F31 in the same trunk floor space. I have a Gladen D2 80.6 DSP at the moment and I would add one more amp with the sub.
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