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post #1 of 6 Old 07-24-2015, 12:11 PM - Thread Starter
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Help with enclosure design Sundown SD-2 8"

I'm tired of having weak bass response in my BMW so I'm wanting to build a box for a Sundown SD-2 8" D4 that I have lying around. Sundown says this particular driver was designed for a sealed enclosure, but I was curious about a 4th order bandpass and have the ported side vent into the cabin via the 9.5"x13" ski hole opening behind the arm rest in the rear passenger seat. Initially I was thinking of a 0.6 cu ft to 1 cu ft (ish) sealed enclosure, but 4th order bandpass seems very tempting (because I'd like to build one one day!). Not sure if it will work well for this driver? I haven't built a 4th order bandpass before, and I hear they are very finicky? Thoughts?

Driver parameters:

Fs: 45.2 Hz
Re: 6.03 ohms
Qms: 7.31
Qes: 0.63
Qts: 0.58
Cms: 138 uM/N
Mms: 89g
BL: 15.55 NA
Vas: 7.74 L
Sens: 82.29 dB 1w/1m
Le: 6.26 mH
RMS: 300 watts (under rated from what I understand?)

Thanks!

Last edited by mlah384; 07-27-2015 at 03:10 PM.
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post #2 of 6 Old 07-24-2015, 02:01 PM
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You get a high amount of cabin gain in a car and that gain will flatten out a sealed sub pretty well. It would likely do the same for a bandpass box but why go to the extra trouble? All the bandpass will do will in return for the extra complexity is give you some roll off on the high end - which isn't worth much.

BTW I have a 2010 BMW 535i with a 12" Earthquake low profile sub playing through the ski hole. Its a sealed box just over 1 cu.ft. with a slant front that matches the slope of the seat back. The driver is recessed to leave room for the surround at full extension. It does quite well. The most obvious benefit is eliminating the boom from the stock premium audio setup that you hear even when the program isn't bass heavy but on bass heavy material it makes itself felt.

If I were doing this over again I think I would go .with a IB type sub playing through the ski hole. 12" AE IB12AU would be ideal. The high Q of your Sundown driver suggests it might work well IB also. Just some how seal a baffle/mainfold against the ski hole and use the trunk for the enclosure.
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post #3 of 6 Old 07-25-2015, 06:22 AM - Thread Starter
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Yeah, the cabin gain in the car can get ridiculous (too bad I don't have that issue in my house!)

I initially was just going to throw it in a sealed box and call it a day, but then I started thinking about all the "tricks" in a car that allow you to kinda "horn load" the sub. Like in a hatch back you can fire the sub upwards or even backwards and the hatch back tends to horn load the sub greatly magnifying the output. Same with a trunk, you can fire the sub backwards into the trunk and kinda create a 4th order bandpass type of effect with the trunk being a chamber of sorts. My car has a trunk but, the BMW trunk is totally sealed, so I figured my only option was to fire the driver straight into the cabin. Then I started thinking about a 4th order bandpass design venting directly into the cabin. I haven't thought of IB... I've never had much success with IB in the past...
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post #4 of 6 Old 07-25-2015, 09:05 AM
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given the relatively high inductance of that driver, getting an accurate model in winisd (or any program) is going to be a challenge. recalculating qes/qts using a bl that is reduced by about 30-40% probably gets close. the bandpass offers the potential for higher spl in a limited region at the expense of wider frequency response. it also has a built in low pass feature which can be nice, but that can also work against you depending on the application. here are the three, roughly, before cabin gain, which will typically be pretty large. so considering all that, unless you are looking to really crush things in the 30-40hz region, I'd probably just go sealed. if you really want to shoot for a bandpass, then at least keep the slot port large, so as to minimize chuff.
1.5 c.f. front chamber, 1.5 c.f. rear chamber, 4"x10"x18" slot port.
response with 1w:



cabin gain for a variety of vehicles:


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post #5 of 6 Old 07-25-2015, 09:32 AM
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one concept for bandpass enclosure. not sure how much space there is under the deck, but something like this, roughly, might work.


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post #6 of 6 Old 07-27-2015, 10:00 AM - Thread Starter
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