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Discussion Starter · #1 ·
As the title says, I'm going to build a home theater sub using an Alpine Type R 15" sub. I bought this speaker before I started reading the forums and learned about the whole DIY world that existed for home theater. I already own the beast though, and it is one, so I would really like to use it, even if it is not perfect. It is a DVC sub and I am using a pro amp to power it. It is an American DJ amp. Don't laugh too much, it was free. It is rated for 1050W into 4ohms mono.

I have gone through and downloaded WinISD and designed a box. I just would like some experienced input to make sure that I am on the right track. Here are the T/S parameters. (Sorry they are not in order for WinISD, I am going off of the manual.)


Alpine Type R SWR-1541D

Impedance 4 ohms per coil (will probably be wired series for the amps sake)

Power Handling 500W RMS/ 1500W Peak

Frequency Response 24-1,000 Hz.

Sensitivity 89db

Re 4 ohms per coil

Le 6.2mH/1.86mH

Fs 24Hz

Vas 98L

Qms 9.68

Qes .5

Qts .48

X max 14.5mm

X peak 29mm

Mechanical Excursion (P-P) 68mm

Hag 15mm

Hvc 44mm

Sd 754.77cm2

Magnet weight 129.6oz

Voice Coil Diameter 65mm


Those are all of the parameters that I have. I am looking at a 6 cu. foot internal volume max. I might could fudge a little to the larger size, but would like to keep around 6. I was looking at a 18hz tune since it seems to plot nicely, but I'm not sure how much I should be worried about that. If I go for a 15hz tune, I see a -6db down point of 14hz. Which I have read is pretty good. Then there is the whole port noise issue to worry about. Truth be told, I'm just over analyzing this, I think.



Thank you guys in advance for sharing your knowledge with me.
 

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I guess if that were me I would go ahead with the 6 cu ft enclosure for that with a 6" port. I like tuning freq at 25 Hz rather than the lower numbers with this driver, though. It keeps the port response closer to the driver's output and will make the sound more unified, and will be easier to adjust output to the rest of the sound system. You'll still have plenty of output at the lower freqs for HT use. The port thus maintains a reasonable length of 16".


You will need to use a 20 Hz HP filter on this sub no matter what Fb you decide to use. Add the filter using the EQ/Filter tab, choosing 2nd order Butterworth in the program. See the cone excursion graph for results.


Note that you will not achieve sub-20 Hz output with this subwoofer. But it will turn out better than the vast majority of HT subs that are commercially available.
 

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Discussion Starter · #3 ·
Thank you for your thoughts. Like I said, I didn't realize there was as big of a DIY world for home theater as there is. Other than BFD, SMS-1, R-DES and similar products, are there any ways of adding the 20hz high pass filter? I'm trying to keep this as cheap as possible.
 

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Your amplifier may not even output below 20 Hz anyway...I have no idea. You can certainly build it and try it out without the HP filter. Test with sub-20 test tones and watch the excursion. If it starts to flap wildly, you'll need the filter. Passives in that low range are not worth the trade-offs involved, so active filtering is the best way to go.


You might want to keep an eye out for an amp that provides this feature.
 

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Quote:
You will need to use a 20 Hz HP filter on this sub no matter what Fb you decide to use. Add the filter using the EQ/Filter tab, choosing 2nd order Butterworth in the program. See the cone excursion graph for results.

There's probably no need for a high pass filter, or at least not that high. You only need 200 watts in a 6 ft^3 enclosure tuned to 16hz to make it play at up to 110db, and there it will not hit max cone excursion until you're around 13.5hz. If you did need a high pass filter you would only need one at around 15-17Hz at the highest.


I would probably just keep the low tune and not worry about the cone excursion since it will have to play at really high volumes to hit that, and it would have to be at around 13-14 Hz for it to happen.
 

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My mistake was inputting the Xmax as the 14.5 mm given instead of the peak value of 29 mm. It looks like there is some room to play with port length between 16 and 20 Hz Fb, and still you wouldn't have to worry about the HP filter.
 

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Discussion Starter · #7 ·
Thank you guys for the info. I was kinda getting a little down hearted that this was not going to be as powerful of a sub down low as I was hoping I could have. I'm really new to designing something like this. I've built an enclosure or two before, but they were sealed and not designed very well. I was also still in high school which was over 10 years ago.

I figured that I would either need a high pass filter or would really need to be careful about the over excursion. I guess that I will have to watch my levels for now. I haven't checked with a meter, but I don't think I will be playing this to those kind of levels anyway.

Again, thank you for your help.
 

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Discussion Starter · #8 ·
Let me bring this thread back up here. Again I would like to say thank you for the help.


I would like to know, which would be better, one 4", two 4", or one 6" port. I've been looking at the graph in WinISD for rear port air velocity and none of them look to be great according to the help info for WinISD. I have read someone stating that the sound output would probably mask any noise from the port, but I don't want to find out the hard way that this is a problem.


I was also looking at the SPL on WinISD, and I was wondering, it shows a -3db down point of 19Hz and a -6db of 15.6Hz when using an 18Hz tuning in a 6 cu. ft. box. For a 16 Hz tuning in a 6 cu. ft. box, the -3db is 27Hz and a -6 of 14.8Hz. It looks to me like I would be fine with an 18Hz tuning, which would make the ports a little easier or should I still go with a 16Hz tune or even lower. I'm still learning how to interpret these graphs.


I guess really I'm just trying to split hairs. I probably will not even know the difference between 16 and 18 without serious testing, will I. If this thing will be solid just to 20Hz, then it is way better than my old Velodyne that I'm currently using. It starts to rolloff pretty sharply around 28 or 25Hz.
 

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Discussion Starter · #9 ·
Here are some pics of the used sub that I bought with a Nokia phone for size reference. Like I said, this thing is pretty much a beast. I know the JLW7 is a little more impressive, but I can actually afford this one.


 
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