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Old 4th April 2013, 04:05 PM   #1
CLS500 is offline CLS500  United States
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Default Port style info needed please.

I am in the process of trying to design a rather "thin" sub enclosure of a bout 3 cuft. for use in my garage. Max depth can be only about 12"; width can go to 36" and height to about 20". My calculations indicate that this will probably need a port that is at least 12" long if not longer (4" tube). Can I just use two 2" X6" rather than one 4"X12" with the same result ??? Pro and cons ?? Thanks..
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Old 4th April 2013, 10:42 PM   #2
Ron E is offline Ron E  United States
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Originally Posted by CLS500 View Post
Can I just use two 2" X6" rather than one 4"X12" with the same result ??? Pro and cons ?? Thanks..
A 2" port has 1/4 the area so it would be ~1/4 as long as a 4" diameter port, 2 of them will be half as long, as you indicated. How small you can go with the port depends on the driver size, the tuning frequency and how loud you want it to play without making nasty turbulent noises from air rushing in and out of the port. Making a slot port or putting a single elbow in the port can help fit it into the box.
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Old 4th April 2013, 11:28 PM   #3
CLS500 is offline CLS500  United States
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Thanks for answering. I am using this 12" sub Dayton Audio DCS305-4 12" Classic Subwoofer 4 Ohm 295-204. I will be using this in a three piece set up in a garage. It will be used at moderately loud levels but not ear shattering. Enclosure will be around 30" wide/18" tall/12" deep (approx. 3 cu ft??). A single port with elbow would be fine.
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Old 5th April 2013, 04:55 PM   #4
CLS500 is offline CLS500  United States
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OK , in a 3 cu ft box would it be better to use a 4"x14" or a 3"x7" port tube ??? (TFreq is 26 Hz.) and why?
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Old 5th April 2013, 09:18 PM   #5
OscarS is offline OscarS  United States
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the one that minimizes the internal surface area while simultaneously minimizing vent mach air speed wins.
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Old 5th April 2013, 10:33 PM   #6
Ron E is offline Ron E  United States
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Originally Posted by OscarS View Post
the one that minimizes the internal surface area while simultaneously minimizing vent mach air speed wins.
Those are opposites
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Old 5th April 2013, 10:37 PM   #7
OscarS is offline OscarS  United States
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I think you took that much too literally, for there is validityin my statement
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Old 5th April 2013, 10:44 PM   #8
Ron E is offline Ron E  United States
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Originally Posted by CLS500 View Post
OK , in a 3 cu ft box would it be better to use a 4"x14" or a 3"x7" port tube ??? (TFreq is 26 Hz.) and why?
Bigger diameter (area) is always better in ports. If you are worried about fitting the 14" port in it would probably be better to make a "diffuser port" as this is a bit better than making an elbow. Port downwards into a space walled on three sides. Start with the 14" tube but you will likely end up cutting a fair chunk off after testing....

[edit] You could also put a nice flare on the 3" port and it would probably work OK.
check out a paper called maximizing port performance mentioned in this thread:
Port area vs efficiency.
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Last edited by Ron E; 5th April 2013 at 10:59 PM.
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Old 6th April 2013, 04:10 AM   #9
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A 3" port is inadequate for a good 12" woofer. 4" port minimum, bigger if it's a long-excursion subwoofer.

Elbows...blecch. Think about it-how can air flow smoothly through that? Maybe a big radiused elbow, but you'd have to smooth the joints somehow.

It would be much better to run the port out the side or the top or the bottom-maybe a shelf port.
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Old 6th April 2013, 10:14 AM   #10
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go to your local hardware store and put a piece of pvc pipe in an elbow and see if it lines up smooth on the inside.
you might be surprised at how smooth it can be, because those pieces are modeled to work together afterall .. and any turbulence from a lack of smooth is going to help cause a clog.

it is easiest if you simply think about the air inside the tube as solid from one end to the other, no different than a solid speaker cone moving in and out.

if you really had a little bit of rough edges where the two pieces meet, and you really wanted to smooth them..
maybe this would work:
get a hot glue gun.. get a tube that wont burn or melt when touching the hot tip.. bend the tube at a 90 degree angle (or 45 if you want) and get yourself a tool that will smear the glue smooth like a putty knife.

as long as you can reach in there all the way and move, and as long as you can see what you are doing .. you should be able to smooth the joint.

but i think if you've got a smooth cut on the pipe and the pipe is shoved up all the way into the elbow, it should be smooth enough and i don't see why you are looking for such astonishing perfection .. but then again, computer modeling would be a whole lot more easier if the stupid tube was perfectly smooth right?..
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