Ported enclosure design question

[noonej21 10+ year member]

I am in the process of designing my first ported enclosure for my Eclipse 8122. Based on the suggestions from many members of the board I think I am going to shoot for a design around 1.75 ft^3 @32 (if this sounds bad for this speaker please let me know, I will be giving it around 600 watts). I was going to use one of the Moe Lester designs but I am working with a smallish trunk so I did not want to have a very deep box and I also wanted to do it myself to learn the design proces.

Now on to my question, what is the process for starting the design? Based on my design I know the net volume of the enclosure and the tuning frequency. Would the next step be to determine the port area so then I can back out the port length, and then lastly figure out the external dimensions for the box?

I have already taken one cut at it where I designed up a box as if it were going to be sealed and then I tried to play with the various dimensions, as well as port areas and legths to get what I was shooting for.

thanks for any insight you may be able to provide

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[Trixter 10+ year member]

the length of the port depends on the port area. the mfg usually has a recommendation for this. i'm not familiar with eclipse subs so i don't want to give out any numbers. but once you find the area you need, then figure out it's length. if your doing a slot port that shares a common wall with the box you need to add 1/2 of the ports width to it's length, this is called port correction factor. once you add the correction to the previous calculated length, you get you total length. now you need to figure out the port displacement. remember to include all material that makes the port. (example: if the port is 2"w x 14"t x 28"l then the displacement numbers would be, assuming your using 3/4" material, 2.75" x 14 x 27.25". the .75 added to the 2 is for one wall of the port, if the other is shared with the box. the 14 stays 14 and the 28 becomes 27.25 because you don't count the front face of the box...you alreay did by taking the internal measurements of the box before.) now that you have the port displacment add this volume to the box net volume and build from there. just remember that this volume is internal. so, if using 3/4 material, add 1.5" to each dimension and that will be your build size.

hope this helps.

 

[noonej21 10+ year member]

Thanks for the help, I had taken one cut at the design and came very close to what I wanted the end result to be. I designed this with an "L shaped" slot port so for total length I measured from the front of the port opening (port opening is on front of enclusure with sub) to a point that was half the port width away from rear wall(so if port was 2" wide I measure to 1" from rear wall) and then from that point to the end of the port wall. I basically meaured the length along the centerline of the entire port. Hopefully this is what you are referring to by the port correction factor.

Thanks again for the help!

 

[Trixter 10+ year member]

umm...not exactly. you did measure your port correctly, by going down the center the way you did. but the correction factor is adding 1/2 the width to that length...in your case another 1". but in all honestly, it will only effect your tuning by less than 1Hz. if your port was like 4-5" wide you can see where it becomes crutical.