Box for 2 DC M3 8" subs

[bmwking]

Hey all!  Long time no post!  Hope you're all doing as well as possible, I've been lurking in my off time trying to keep up on the goings on around here.  I sold my Forester back in september after having my full build installed for only a few months (at least I got to enjoy it for a little bit), and bought a 2015 Mini Cooper S.  Such a night and day difference in level of quality and power, I might not have awd anymore but it's already faster than my hopped up Forester was!  Plus it's a 6 speed manual   Oh and the wife decided she wanted to move in October so we got the house ready for sale and started looking in the craziest housing market I've ever been a part of.  We finally moved into our new place on Dec 23rd after looking at (no shit) over 130 houses in person.  What a nightmare, but the new place is awesome and a huge step up.

 

Anyhoo, all that aside, life has finally settled down enough where I can think about doing a build in the Mini.  I won 2 DC M3 8s when I won SOTM way back when (actually with a build from our 1st Mini, mine officially makes our 4th).  And I was using one as my computer sub and one just stayed in it's packaging this whole time.  Well now It's time to use em!

 

So I have a Smart 3k, all the appropriate electrical to support it (180amp alt, 48ah headway lithium, 2/0 ofc, etc).  Obv I don't want to throw 3k rms at 2 800 watt subs, so I'm thinking with a conservative, clean tune I should be around 1500 rms to them.  

 

I've been doing some research and found that they love being in 0.95cu ft enclosures, tuned low so that's where I want to be.  

 

I've been farting around with torres and Triticums port calculator and think I have a decent design, but I'd like the resident box pros to weigh in and see if I'm on the right path or still a dumbass.

 

My max dimensions are 36" W x 15" D x 17" H

 

I've attached my 2nd draft with subs and port back, my first iteration had subs back port up, but I'm not sure how that'd sound in a hatchback.

 

So thanks in advance and glad to be back!

[Dafaseles]

7 hours ago, bmwking said:

Hey all!  Long time no post!  Hope you're all doing as well as possible, I've been lurking in my off time trying to keep up on the goings on around here.  I sold my Forester back in september after having my full build installed for only a few months (at least I got to enjoy it for a little bit), and bought a 2015 Mini Cooper S.  Such a night and day difference in level of quality and power, I might not have awd anymore but it's already faster than my hopped up Forester was!  Plus it's a 6 speed manual   Oh and the wife decided she wanted to move in October so we got the house ready for sale and started looking in the craziest housing market I've ever been a part of.  We finally moved into our new place on Dec 23rd after looking at (no shit) over 130 houses in person.  What a nightmare, but the new place is awesome and a huge step up.

 

Anyhoo, all that aside, life has finally settled down enough where I can think about doing a build in the Mini.  I won 2 DC M3 8s when I won SOTM way back when (actually with a build from our 1st Mini, mine officially makes our 4th).  And I was using one as my computer sub and one just stayed in it's packaging this whole time.  Well now It's time to use em!

 

So I have a Smart 3k, all the appropriate electrical to support it (180amp alt, 48ah headway lithium, 2/0 ofc, etc).  Obv I don't want to throw 3k rms at 2 800 watt subs, so I'm thinking with a conservative, clean tune I should be around 1500 rms to them.  

 

I've been doing some research and found that they love being in 0.95cu ft enclosures, tuned low so that's where I want to be.  

 

I've been farting around with torres and Triticums port calculator and think I have a decent design, but I'd like the resident box pros to weigh in and see if I'm on the right path or still a dumbass.

 

My max dimensions are 36" W x 15" D x 17" H

 

I've attached my 2nd draft with subs and port back, my first iteration had subs back port up, but I'm not sure how that'd sound in a hatchback.

 

So thanks in advance and glad to be back!

I'm not up in box building so I'm not even going to comment on it lol. 

But what I did want to say was my wife, before we had kids had a mini cooper S. That thing was pretty damn fun! When you get the box sorted out, please do a build log. My wife and I (probably me a lot more than her) would love to see it!

And congrats on the new house! 

[bmwking]

3 hours ago, Dafaseles said:

I'm not up in box building so I'm not even going to comment on it lol. 

But what I did want to say was my wife, before we had kids had a mini cooper S. That thing was pretty damn fun! When you get the box sorted out, please do a build log. My wife and I (probably me a lot more than her) would love to see it!

And congrats on the new house! 

Haha definitely will!  and thanks for the kind words   We've had a 2003 S, 2010 S, 2014 Countryman JCW ALL4 S, 2017 Clubman ALL4 S (still have, this is the wife's), and now the 2015 S.   You could say we're gluttons for punishment lol

[Dafaseles]

2 hours ago, bmwking said:

Haha definitely will!  and thanks for the kind words   We've had a 2003 S, 2010 S, 2014 Countryman JCW ALL4 S, 2017 Clubman ALL4 S (still have, this is the wife's), and now the 2015 S.   You could say we're gluttons for punishment lol

I wish I still had it, but I used to have a picture of me, my wife, my first born (about 6 months old in the picture) our chihuahua, and our mastiff all in the mini 😳 that's when we decided we needed to upgrade lol. Though she wants to get another one once the explorer is paid off. She misses the manual. I kind of do too....shhhhh 🤫

[bmwking]

bump just to draw attention

[Arthur79]

20 hours ago, bmwking said:

bump just to draw attention

Hey bmwking,

 

I modeled your box up in WinISD and have a couple of thoughts.  I set the box volume to 1.91 ft^3 with a tuning frequency of 31Hz and an input wattage of 1200w (80% of your 1500w tuning target).  All of these model statistics are for the enclosure sitting on a bench, inside your Mini will of course measure a lot different (and hard to say how).  That said:

 

The box is REALLY peaky/loud between around ~29Hz and ~45Hz with the highest peak between 32-33Hz reaching +5db.  I normally try to stay at or under +3db for my highest peak.  That doesn't mean you have to, but at +5 the box is more in the max SPL style than SQ/daily driver and it might sound funny for daily driver listening.  Again, in the car it will have a totally different dynamic and it's possible that peak is a lot more mellow across a wider frequency band.  The f3 for the box is almost 25Hz exactly:

 

 

 

Taking a look at cone excursion, you start to run into the danger zone between 27-28Hz so you would want to set your infrasonic/subsonic filter above that (probably just set it at 30Hz assuming a 24db/octave crossover slope):

 

 

 

I didn't see the port width in your diagram above, but playing around it looks like 3" width was close to your calculations.  At 9.5" high and 3" wide with a 31Hz tuning frequency it clocks in at just over 37 1/4" long.  The biggest "problem" I see with this box design is that the port air velocity peaks at almost 32 meters/second (at around 30Hz).  The "best practice" is to try and keep it under 16-18 meters/second.  Much over that and the port will be very noisy, causing "port chuffing".  Chuffing isn't as big a concern when the box is in a trunk, but in your Mini it could easily be audible.  You can get around that to an extent with a flared port, but that would mean kerfing the port wall(s) for a slotted port or switching over to a flared round port that would then need elbows to get the full length:

 

 

 

 

Hopefully this helps some.  If you want, I can try to play around with the modeling to get the port air velocity down and/or lower/even out the frequency output peaks.

 

 

[bmwking]

On 6/4/2021 at 3:03 PM, Arthur79 said:

Hey bmwking,

 

I modeled your box up in WinISD and have a couple of thoughts.  I set the box volume to 1.91 ft^3 with a tuning frequency of 31Hz and an input wattage of 1200w (80% of your 1500w tuning target).  All of these model statistics are for the enclosure sitting on a bench, inside your Mini will of course measure a lot different (and hard to say how).  That said:

 

The box is REALLY peaky/loud between around ~29Hz and ~45Hz with the highest peak between 32-33Hz reaching +5db.  I normally try to stay at or under +3db for my highest peak.  That doesn't mean you have to, but at +5 the box is more in the max SPL style than SQ/daily driver and it might sound funny for daily driver listening.  Again, in the car it will have a totally different dynamic and it's possible that peak is a lot more mellow across a wider frequency band.  The f3 for the box is almost 25Hz exactly:

 

 

 

 

Taking a look at cone excursion, you start to run into the danger zone between 27-28Hz so you would want to set your infrasonic/subsonic filter above that (probably just set it at 30Hz assuming a 24db/octave crossover slope):

 

 

 

 

I didn't see the port width in your diagram above, but playing around it looks like 3" width was close to your calculations.  At 9.5" high and 3" wide with a 31Hz tuning frequency it clocks in at just over 37 1/4" long.  The biggest "problem" I see with this box design is that the port air velocity peaks at almost 32 meters/second (at around 30Hz).  The "best practice" is to try and keep it under 16-18 meters/second.  Much over that and the port will be very noisy, causing "port chuffing".  Chuffing isn't as big a concern when the box is in a trunk, but in your Mini it could easily be audible.  You can get around that to an extent with a flared port, but that would mean kerfing the port wall(s) for a slotted port or switching over to a flared round port that would then need elbows to get the full length:

 

 

 

 

 

Hopefully this helps some.  If you want, I can try to play around with the modeling to get the port air velocity down and/or lower/even out the frequency output peaks.

 

 

hey man i really appreciate the modelling!  so this is what I was basing my enclosure off of, being that he modelled the sub in winisd and then set about finding the best size enclosure and tuning.   youll see the info i went for in post #3 https://www.the12volt.com/installbay/forum_posts.asp?tid=137330

 

It was kind of my base map ykno?  does his info make sense to you?

 

 

[Arthur79]

On 6/5/2021 at 7:41 PM, bmwking said:

hey man i really appreciate the modelling!  so this is what I was basing my enclosure off of, being that he modelled the sub in winisd and then set about finding the best size enclosure and tuning.   youll see the info i went for in post #3 https://www.the12volt.com/installbay/forum_posts.asp?tid=137330

 

It was kind of my base map ykno?  does his info make sense to you?

 

 

Sure thing!  Sorry for not getting back to the thread sooner, it's been a crazy weekend.  I'll take a look at that post and see if I missed something and try to give an update tomorrow if possible!