Thinking of building Sub box - Home Theater Forum and Systems -

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post #1 of 6 Old 06-05-07, 07:04 PM Thread Starter
Join Date: Jun 2007
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Thinking of building Sub box

Ive been thinking about building a sub box for a couple of weeks now. I have build some sealed boxes for my truck with impressive results, and I just feel I can get more quality for a lower price this way. I have since been readin this forum for the last couple of days and Im almost ready to buy stuff.

1. my box size cannot exceed 25x15x18 I plan on making it around this size.
2. I was thinking this speaker Dayton RSS315HF-4 12 PE: 295-464
3. I was thinking this amplifier Bash 500S PE: 300-752
4. Im mostly sure I am using a vented box, at it will give the flattest response.

I plugged the numbers in WinISD, and I got a pretty flat curve. The Yellow one is with 4.3 some ft^3 and my box dimmensions is abotu 3^ft If i add a 2db boost at 20hz this is my curve (Green) Basically yellow=target, green=actual

Im trying to keep this <300 so I got 250 tied up in amp and sub, and 50 bucks for everything else. I allready have a BFD that was actually used for its intended purpose, but I am now looking foward to using this in my configuration. I fully plan to use the SPL analyzer hooked up to my notebook for fine tuning.

I guess what I am asking, is it ok to sacrafice box design and make up for it with technological means?
Any other recommendations?
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post #2 of 6 Old 06-06-07, 10:04 AM
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Re: Thinking of building Sub box

For that small of a box I'd go sealed and use a higher wattage amp. I'm not much of a subwoofer designer but I've built my share. If you are going ported with only 500 watts I'd think the enclosure would need to be quite a bit bigger. Sealed with a BFD and > 1000 watts should get you a small box with the curve you are looking for.

I'd stay away from any boost near 20Hz... 2 db boost will bring your amp dangeroulsy close to clipping on dynamic scenes. The rules for BFD are no boost, only cut.

You got that curve with that small of a ported enclosure?
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post #3 of 6 Old 06-06-07, 11:06 AM Thread Starter
Join Date: Jun 2007
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Re: Thinking of building Sub box

Yep I got that curve with ported encosure. I tried lots of different speakers until I found one that seems to fit what I need pretty well.

Here are my numbers without fiddling with EQ's .

Grey=Default Ported box 4.3999 cuft
Red= Ported with 3 cuft
yellow=sealed 3cuft Most sealed boxes seem to have large dropoff after 50hz
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post #4 of 6 Old 06-17-07, 02:37 PM
Join Date: May 2007
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Re: Thinking of building Sub box

Closed cabinets start rolling off very soon. This is inherent in their design. Ported enclosures usually are louder and start rolling off very quickly below the tuning frequency due to an acoustic "short curcuit". Nevertheless they reach the lowest frequencies. They do have some other downsides though, like being a bit less precise due to their higher group delay, which is why a closed sub is usually used for music whereas a ported sub is the choice for home theater use, where the real low frequencies are needed for special effects etc. Precision and impulse behaviour is not much of a problem there. But this is only a rough generalisation and I digress... You should go for the ported version, if possible use the 4,3ft^3 version and tune to somewhere around 22Hz. I very much doubt, that you won't be satifsfied with it You won't have to boost anywhere (rather the opposite!), firstly there is the room gain to consider, secondly my experience has shown that you need very good performance at around 30Hz, anything more is not that interesting. Off the shelf subs ususally employ so-called subsonic filters will kick in at around 25Hz, to ease off on the cone excursion so you don't kill it with frequencies the average human doesn't really hear anymore and which usually aren't common in either movies or music. Of course this is a generalisation and there are exceptions, but I digress again.

The result which you will undoubtedly accomplish will surely be great! If you go ahead with your project (which you should!!) don't forget to build the vent big enough! Judging from the simulation the driver can move quite a bit of air and we don't want to hear him breathe, do we? Also the TSP data I found on the web are all a bit different. The simulation changes a bit due to this (esp. the tuning frequency shifts a bit).

Keep on posting your progress!

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post #5 of 6 Old 06-17-07, 04:15 PM
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Re: Thinking of building Sub box

wouldnt a 500W amp be a bit overkill for this box size and a 12? If it were me I think i would lean toward a 300W bash and the Dayton RSS390HO-4 15" sub.
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post #6 of 6 Old 06-18-07, 11:32 AM Thread Starter
Join Date: Jun 2007
Posts: 9
Re: Thinking of building Sub box

I ordered my 500w amp, and put in some old 12inch mtx thunder 6000 speaker I had from an old car sub installation.

I made the box, which is 25x15x18 Volume of 3.02^3 ft. added accousta stuff box filler, and a 500w bash plate amp. I went with the higher power amp, because it was only $50 more, and who knows what ill decide to build a year from now, I just have the amp at 50% volume, and that seems balanced to me.

Built this weekend, and I am so far really happy with the results. Played U571, and it made the couches shake, so I think there is enough power. I ran through REW and then my old BFD, and have a pretty good house curve at +6 at 30 0 at 80, with a roll off at 27. I think I need better front speakers now. I guess Ill have to wait a couple of months for that. I think room gain helped favorably in this case.
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