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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: December 21, 2012 at 7:41 AM / IP Logged  
If you need a specific port dimension for an enclosure but can't get it with a single port (due to the size and shape of the enclosure), is it acceptable to have two ports at half the dimension? If so, is positioning of these ports critical?
Thanks
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: December 21, 2012 at 10:00 AM / IP Logged  
p40whk wrote:
If you need a specific port dimension for an enclosure but can't get it with a single port (due to the size and shape of the enclosure), is it acceptable to have two ports at half the dimension? If so, is positioning of these ports critical?
Thanks
Unfortunately it doesn't work like that. Using two of the same diameter ports requires each of them to be longer than if you only use one. Using a smaller diameter round port can shorten the length - with other tradeoffs, of course. Using a slot port is often a way to achieve larger port dimensions. What are you trying to do?
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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: December 21, 2012 at 10:15 AM / IP Logged  
Hi DYohn,
I decided to rebuild my enclosure this winter (from this post here: Boat Tower Speaker Post)
The original set up was just too heavy in one piece so I had planned to rebuild it as two separate units so I was reconsidering the shape of the enclosure and the porting I used. Since the pre-made plastic ports are easier I thought I could achieve the same thing with 2 rather than one large 4" port.
I can keep the slotted port as I have it so it's not a big deal but I've learned a few things with this setup that I'd like to improve upon in the next revision and while I was in the re-design stage, a lot of the shape depends on the ports I use.
Jeff
soundnsecurity 
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Joined: November 10, 2008
Location: Louisiana, United States
Posted: December 21, 2012 at 11:06 AM / IP Logged  
honestly, being that it is on a boat playing directly into the open air you should build the box sealed instead of ported. ported boxes work better by playing into a set volume of air to achieve the gains you expect of a ported box in a car. by having the ported box playing into an infinite volume of air you wouldnt get the major benefit of having a ported box.
im not 100% sure but this is what i think would happen after reading a bunch of documents on how ported boxes work but i could be misinterpreting what i have been reading.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: December 21, 2012 at 11:48 AM / IP Logged  
Nah, a ported enclosure doesn't care how large the area is it's being used in, and outdoors is just fine. The purpose of the port is to tune the frequency response of the enclosure, that's all. A sealed alignment will have less output in the lowest frequency band and sound more boomy with a peak in the frequency response. Stay ported with your drivers. You might consider just splitting the system up into two or four smaller enclosures instead of one large one, which might lower the overall weight.
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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: December 21, 2012 at 11:58 AM / IP Logged  
They sound outstanding as they are and I have had people with a lot more expensive systems ask me where I bought them.
I did build it kind of beefy to begin with, I used 3/4" MDF for the frame and laid up 2 layers of fiberglass matt on the inside of the felt. I think I can redesign the frame with a thinner material that's a bit lighter and still have the strength.
The whole unit weighs close to 40# which isn't too bad by itself but try to lift it over your head, support it with one hand while you attach and secure it to the wakeboard tower and you realize there's a mistake in the design.
Acoustically it's very efficient so I don't need to change anything there. I may change the shape a little keeping my 1.5cf dimensions for the set of drivers.
DYohn 
Moderator - Posts: 10,740
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: December 21, 2012 at 12:05 PM / IP Logged  
Glad to hear that they sound good (and i wish I could hear them!) If you rebuild you could think in terms of slicing the system in half and then you'd have two pieces to mount but they'd only be 20 pounds each... or get a boat babe in a skimpy bikini to help tighten your nuts for you... porting -- posted image.
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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: December 21, 2012 at 12:08 PM / IP Logged  
DYohn wrote:
Glad to hear that they sound good (and i wish I could hear them!) If you rebuild you could think in terms of slicing the system in half and then you'd have two pieces to mount but they'd only be 20 pounds each... or get a boat babe in a skimpy bikini to help tighten your nuts for you... porting -- posted image.
My thinking exactly... Although, my buddy helped me put the speakers up the first time and he has more hair on his back than a shag carpet! I like your boat babe suggestion much better!porting -- posted image.

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