(first) subwoofer project

[jumpus]

I'm trying to design a box for a project that I'm working on. This is my first subwoofer project, so I'm not really sure of what I'm doing. I've pretty much decided on an Eminence Lab 12 Gen II 12" for the driver. I found this <link> and I think I want to follow the "Med Vented Subwoofer Cabinet" (3rd one listed in the pdf) for the design of my enclosure. My question is regarding the vented aspect of the cabinet. How does this work? These parameters are listed for the vent: Dv = 3.5 in, Lv = 12.44 in. I assume this is diameter and length. I searched through Parts Express, and found some stuff about Precison Ports, and these intrigued me. Their website <link> has a calculator for the port. I put in the parameters for the box, and came up with some results.
Basically, I could use some instruction. What's the best course of action here? Do I even need the tube style port rig, or could I make a maze of sorts inside the box using MDF which terminates in a slot?

Sorry if this has already been covered, but I'm new here and terrible at searching through old threads.

Thanks!

 

[jumpus]

Hmm...reading that again, my question doesn't seem clear. Basically I want to know: Are the port dimensions dependent on volume of the port (the area separated from the main chamber of the enclosure)? For instance, could I create a slot in, say, the front face, and create a "tunnel" out of MDF that separates the slot from the main chamber until the port volume has been enclosed?

I really appreciate any advice. Thanks!

 

[Marsh]

I don't know if this will help you but I used

http://www.linearteam.dk/default.aspx?download=winisdpro

To work out my port size and length, the prog also covers slot ports.

Good luck, show us what you make!

Rich.

 

[jumpus]

Thanks! That's exactly the kind of program I could use. Another question: what's a good frequency to tune the port to? I've designed the box (at this point) to be tuned around 25 Hz. Should the port be tuned above or below the frequency of the box, and by how much?

Thanks

 

[Marsh]

Sorry, I don't know about box response Vs Port response but surely porting the box will completely change its character anyway??????????
I just used the prog to give me as near as damn it a flat response down to 20Hz, hopefully eliminating the need for electronic equalization later on.
I tuned my sub to 20Hz which seems to work pretty well for me but I use large Mission floor standers anyway so my sub only has to work from 40Hz (ish) and below.
Once I get below 25Hz though port noise becomes quite audible (only on test tones or with main speakers turned off though) with my 8cm X 40cm port so I would go bigger next time and flare the ends.

Rich.

 

[jumpus]

Well, I came up with a graph that looks good, so I guess I'll just trust the program. Have you had good luck just trusting it?

Also, how did you figure out the volume that the speaker would occupy inside the enclosure? I don't have the driver yet, and I'm not too keen on dunking it in water once I get it (I saw that suggested as a method somewhere else). Do those specs get listed anywhere? I've written to Eminence to see if they'll tell me, but I'm real anxious to get the final dimensions and start building.

 

[Marsh]

a guesstimate!

I was concerned at first but found that changing the internal volume by a couple of litres either way didn't make that much difference to the graph. You need to allow for displacement for internal bracing and the port itself too.