Micro budget sub build - AVS Forum
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post #1 of 16 Old 08-27-2013, 09:19 PM - Thread Starter
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Over the past year I've been slowly stepping up from a cobbled together HTIB system to something a little more substantial. My upgraded components are:
Code:
AVR: Denon AVR-1612
L/R: Pioneer Andrew Jones speakers (2x SP-FS52) raised 11" off the floor
Cen: Pioneer Andrew Jones speakers (SP-C22)
Sur: Pioneer Andrew Jones speakers (2x SP-BS22-LR)

These components are a huge upgrade from what I had before but now it is painfully obvious how inadequate my sub is (8" ported Sony from a HTIB setup)

Luckily, I've gotten my hands on a 12" Alpine Type-R from a friend's old car stereo and I'd like to turn it into my home theater/music listening sub.

I have the tools, time, and skills to build a box for this thing but I'm not sure what else I'd need to do. I think my biggest hurdle is in picking a way to get power. Ideally I'd like to find the cheapest way to power this sub while maintaining passable sound quality. Is it feasible for me to meet my criteria for under $200 (for power)?

I'll keep updating this post as I work my way through this process from planning to completion.
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post #2 of 16 Old 08-27-2013, 09:34 PM
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hi and welcome!

a 500 watt plate amp from parts express goes for $200. it has some good eq and a protective high pass filter built in.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-752

sale ends this Saturday.

for the box, a medium-large ported enclosure tuned to around 22hz would work very well for you.

a slot port that is 12" wide x 3" tall x 35" long gives 22hz tuning in a 5 cubic foot box.

the final response would look something like this (with the eq in the bash 500 from parts express):



good luck with your project!

such a design has the driver well under its excursion limit (you could actually give it even more power than 500 watts) and also has air speed in the vent peaking at around 17 m/s, which is good and shouldn't chuff at all.
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post #3 of 16 Old 08-27-2013, 09:38 PM
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by the way, if anybody reading along has experience with a 180 degree turn slot port, i'd be interested to know if he could do that to keep the overall length down.

180 degree bends seems to work ok in horns and here the wavelength is that of 22hz, so long relative to the bend for sure, and actually long relative to the entire port length.

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post #4 of 16 Old 08-27-2013, 10:04 PM
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I've done a couple 180 bends with slot ports, both subs and speakers. The long pressure wave rounds the corner pretty well. I have not had issues from them, well actually you might want to make the port 10% shorter then modeled, mine seem to always come in tuned a few Hz lower then I planned.
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post #5 of 16 Old 08-27-2013, 10:23 PM
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thanks matt!

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post #6 of 16 Old 08-27-2013, 10:56 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

a 500 watt plate amp from parts express goes for $200. it has some good eq and a protective high pass filter built in
...
for the box, a medium-large ported enclosure tuned to around 22hz would work very well for you.

a slot port that is 12" wide x 3" tall x 35" long gives 22hz tuning in a 5 cubic foot box.
1. Thanks for giving me exactly what I was looking for as far as power goes.

2. 5 cubic feet seems like a pretty large box. I'm doing some measurements around my room to see where and how I could make something of that size work. Would I end up with something far inferior if I ended up with a smaller (~3 cu. ft) enclosure?
Quote:
Originally Posted by mtg90 View Post

I've done a couple 180 bends with slot ports, both subs and speakers. The long pressure wave rounds the corner pretty well. I have not had issues from them, well actually you might want to make the port 10% shorter then modeled, mine seem to always come in tuned a few Hz lower then I planned.

Thanks for the tip on slot ports. When I came into this project I had a sealed box in mind and actually had to google "slot ports" to see what you and LTD were talking about but now that I see them it doesn't seem too difficult to pull off. Basically a box that does something like the image below, right?


As you can both tell, I'm a pretty big newbie to DIY so this project should be pretty informative for people in my position in the future.

Sorry in advance to all readers for what will probably seem like very niave newbie questions.
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post #7 of 16 Old 08-30-2013, 11:07 AM
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as you start to get too small, the port has to become longer and longer to keep the same tuning and the result is that you can end up with a box that is half port.

the other option is to shrink the cross sectional area of the port and that will allow the use of a shorter port, but then you could end up with port noise.

you probably don't want to go much smaller than something like this:

http://www.svsound.com/subwoofers/ported-box/pb12-nsd#.UiDfOPfD-00

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post #8 of 16 Old 08-30-2013, 12:56 PM
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180 degree slot ports are the normal for the transmission line type enclosures. Not very common but rumored to sound similar to sealed. Should not be a problem as long as cross section is not too small.

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post #9 of 16 Old 08-30-2013, 01:20 PM
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A ported enclosure can be done in a 20x20x20" box with 500w.

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post #10 of 16 Old 09-03-2013, 04:41 AM - Thread Starter
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Again, Thanks for all of the guidance in this thread. I have a few questions and a proposed box design using LTD02's ~5cu ft. box size and scaling down port length per mtg90's recommendation 12x3x31.5

Questions:
  1. When you say ~5cu. ft. box with 12x3x31 port do I first make a box with 5cu. ft. internal volume then build the port OR should the internal box volume be 5 cu. ft. + volume of the port? I ask because if port volume does not add towards the 5 cu. ft. box then I need to make my design slightly larger.
  2. Is there any benefit to putting two pieces of MDF together to make the front baffle extra thick? I see some people do this and I'm not sure how much of an affect (if any) it has on final sound quality.
  3. Do I need to add dowels to brace the box or is that overkill for a 12" driver? If not, would 3/4" hardwood dowels get the job done? How many points/ways should I brace?
  4. Is there some inherent benefit to making a sub box a cube? I ask because I'm planning to build a rectangular prism and don't know how much of a role shape has on sound.

Now, onto the fun part. Here are two views of the current design that I'm planning to build. I'm going for something narrow and shallow but tall. The first image is a sideview that shows how I plan to implement the 12x3x31.5" port(green) into the box. I also have a proposed area to mount the sub(red) and where I'm planning to put the Bash 500W Plate amp (neon blue). What do you think about my simple plan of attaching the 27.5" tall front and back pieces to the 18" long top/bottom?
.

The second image is the front view of the same box. I'm just trying to give you an idea of how I'm thinking of building this thing so people can tell me where I'm screwing up before I actually start cutting MDF. As you can tell, I plan to place the port at the horizontal center of the box so the two pieces I'll need to make that aren't pictured are the pieces that will seal the left/right of the port from the rest of the box.


So, how am I doing? Any and all help is appreciated. My plate amp arrives on Wednesday and I'd like to get to the wood working of this project so I can enjoy some nice bass sooner than later
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post #11 of 16 Old 09-03-2013, 08:14 AM
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If you are making the box 19.5" wide you can make a 18" wide port 2.25" high and 31" long to achieve the 22hz tune. That way it goes from one side to the other of the 3/4" meterial.

Port volume does not add to box volume.

Adding dowels or broom handle to brace opposing panels is very a good idea. A double baffle is often used to recess the driver so that it is smooth with the baffle. It is mostly aesthetic, although it does add some rigidity to the baffle. If you do a double baffle you can then run a brace across the rear panel of the box and not have to mess with front to back dowel bracing.
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post #12 of 16 Old 09-03-2013, 07:33 PM - Thread Starter
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Quote:
Originally Posted by nograveconcern View Post

Port volume does not add to box volume.

Just to be clear, is the following correct if I want to get close to a 5 cu ft box?
Code:
Internal box volume (18x28x20) = 5.83 cu ft
port volume: (18x2.25x31) = 0.73 cu ft
MDF for port walls = 0.22 cu ft

So my final box volume = 5.83-0.73-0.22 = 4.88

Based on the recommendation of changing the port to cross the entire front of the enclosure I've updated my design. The box is also taller (+2") and deeper (+2") to add to the internal volume because I'm now using the above calculation to figure out the box volume. Before I was simply calculating internal volume and not considering the space the port takes up.
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post #13 of 16 Old 09-04-2013, 04:57 AM
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Yes, but don't forget driver displacement and bracing.
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post #14 of 16 Old 09-04-2013, 10:48 AM - Thread Starter
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Quote:
Originally Posted by nograveconcern View Post

Yes, but don't forget driver displacement and bracing.

haha, the box grows again! +1" depth
Code:
Final Internal Box Dimensions
H: 28"
L: 18"
D: 21"

(Box Volume)-(Port)-(Displacement)-(Dowels) = 5.07 cu. ft.

Tonight I measure twice.

Tomorrow, I cut.
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post #15 of 16 Old 09-04-2013, 11:09 AM
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I think you've got it. smile.gif
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post #16 of 16 Old 09-04-2013, 07:10 PM
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http://www.hometheatershack.com/forums/enclosure-volume-calculator/

 

or you can build a sketchup model and calculate the volume yourself by measuring the inside of the enclosure.

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