posted
Just wondering what a good indication of an unrealistic port dimension would be. I've just finished designing a box for a 15w3d2 and come up with a 7.5 x 10 x 3.79 inches long port. The airspeed in the port seems reasonable according to the program but I cant picture the real world results in my head being spectacular. I can increase the volume of the port mouth to increase the port length but when does the port become a hole rather than a port. Any information would be helpful.
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Posts: 4 | From: victoria | Registered: Feb 2001
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posted
If your port is that short you will want to make it bigger (have more surface area). Increase the surface area until the length becomes impractical while maintaining the same tuning frequency. What size box is it? That seems like a very shallow port for that surface area. What is your tuning frequency?
------------------ rybaudio@freeze.com
The goal: Accurate musical reproduction in the mobile environment
Posts: 3957 | From: State College, PA | Registered: Sep 2000
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posted
I believe the limit on the short end is the depth of the woofer. If the port is shorter than the depth of the woofer, you could run into problmes.
------------------ Jeff Sony CDX-7850 Sony XDP766-EQ 3 Sony 752-EQX 2 Sony ES 6.5 Seperates 2 Crossfire CFA-1000D DD-9515
posted
Don't get too caught up what the port looks like, I've built many boxes with port lengths under 6 inches, trust the design program. Increasing the port area to facilitate increased length also increases the overall box volume, ports of this short a length can become real assets when you consider the cosmetic possibilities, working with plastics or laminates can really enhance the visual effect without inducing extreme amounts of cost and time to complete a killer looking project.
------------------ Mabeita@audioexpressusa
Posts: 1706 | From: Phoenix, AZ USA | Registered: Feb 2001
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posted
I'm with Mabeita. As long as you have sufficient area the depth doesn't matter.
I once ported a 36cuft net box with a pair of 14.75" holes. Port depth was the thickness of the wood: 3/4" Virtually no port velocity made for effortless sound. It really hammered.
I think at 75sqin you should be fine.
------------------ Blow your mind - PORT your box!
posted
Damn dukk, that's the first post I've seen by you in a Looooooooong time. I wuz begining to wonder if you still were here or not.
? - Is there a limit to the overall length other than what the box size limits? I guess what I'm getting at is: At what point does the port get too long and create a transmission line enclosure? How might this affect tuning?
Reason I'm asking is cuz of my current ported enclosure for an 8". The port is 2"x9"x33.5" The box enclosure w/o port, sub, bracing is .65 cubes. (box dimensions are 13"x10"x19") Is this bordering on a TL enclosure? Thanks, Steve
posted
In a TL the port is larger, typically the port volume exceeds the enclosure volume. In the accoustic wave design the port volume is typically smaller in relation to the enclosure but can be very long while still small in diameter, unlike the TL where both diameter and length can be quite large.
------------------ Mabeita@audioexpressusa
Posts: 1706 | From: Phoenix, AZ USA | Registered: Feb 2001
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posted
The point where a ported enclosure doesn't function as one anymore would probably have more to do with the surface area of the port than the length. I can see where the extreme length could be a problem due to too much resistance in the port. I'm guessing it would differ from application to application.
------------------ rybaudio@freeze.com
The goal: Accurate musical reproduction in the mobile environment
Posts: 3957 | From: State College, PA | Registered: Sep 2000
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posted
In THE LOUSPEAKER DESIGN COOKBOOK Vance Dickason advocated the use of ports up to the driver Sd I beleive ( or maybe 1/2, Im tired now and too sleepy to look it up). Anyway the port surface area is better larger, the problem can run into super long lengths that will gain a resonance of their own of a higher harmonic I believe to degrade the sound quality .
------------------ TEAM THUNDER TEAM NOISY TOYS Mobile Image Autosound
[This message has been edited by The Buzz (edited 02-12-2001).]
[This message has been edited by The Buzz (edited 02-12-2001).]
posted
I generally try to keep ports under 20" or so. I have no idea where I picked that up but I heard/read it somewhere. Anyways - if you need a port longer your box is probably too small, the port too large, or the tuning too low.
------------------ Blow your mind - PORT your box!
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