[JohnnyWash1]

I have two Dayton HO 12" subs, each in a 2.0ft^3 box. They sound good, but lately I have really been missing the lower octave. I modeled these in winisd pro and found an F3 of 60hz, which is completely unacceptable for a HT setup. After some quick modeling, I found I can add a 4" port that is 23" long and get basically a flat response (-1dB) to 30hz, which is fine for me. My question is, how long is too long? Has anybody run a port of this length? at 30hz my port velocity is 28m/s, which is a touch high but not offensive--plus the ports I purchased are flared to over 5", so that should help. Is 23" ridiculous? Will it affect sound?

 

[Jay1]

No it's not to long. Ideally you want to tie the port into your cabinet somewhere near the end to reduce the possibility of audible vibrations. Dont forget to account for the volume the port is going to take up and recheck your sim

http://www.hometheatershack.com/forums/enclosure-volume-calculator/

 

[JohnnyWash1]

Thank you! I am fairly sure it will fit, I was just unsure of the impact of having a ridiculous 2 feet of tubing curled inside. I guess I will test and find out!

 

[Jay1]

Don't forget to leave at least a few inches from the end of the port to the cabinet wall

 

[LTD02]

the port can go on the outside of the cab and work just as well.

 

[JohnnyWash1]

Another question, should I keep the stuffing in the box? The box is currently full of stuffing fabric, which seems like it would interfere with the port.

 

[garciab]

Johnny, have you considered using a passive radiator instead of a port? I remember reading that a rule of thumb for port length is to avoid it being longer than 4x its diameter. I try to stay within that rule, but I'll confess to never trying a port that breaks it just to test the results. PR's cost more, but it's worth considering.


Also, I believe the recommendation for vented boxes is 'lining of the walls', and not 'stuffing of the enclosure'.

 

[JohnnyWash1]

Thanks for the reply. I have not considered a PR, mainly due to cost and engineering. I just wanted a quick fix for this box and really just to test the idea. As for the stuffing, I suppose I'll take the majority out?

 

[BillCinLR]

You need to keep in mind that your internal volume will be reduced with the addition of a port (assuming it is INSIDE the enclosure.).


Bill C

 

[JohnnyWash1]

Well, I completed a port today. It went much smoother than I expected. I ended up with using two 4" 90* elbows for each port (one per sub) and a total length of 23". What I hadn't counted on was how long the 90* bends are--they are 8.5"! Here I was thinking I needed approx. 23" of PVC for my ports, which meant I had to buy the 10' pipe. I ended up using 5" per port (flared end was 4"). Anyway, lesson learned. I now have plenty of 4" PVC...


As for sound, holy cow. I was very skeptical, mostly of my shoddy workmanship (the port isn't even glued in at the moment, just a dry fit and I may leave it that way). Let me tell you, back to back against my sealed Dayton HO is no comparison. There just isn't any depth with the sealed version; the ported sub DIGS DEEP, filling the room with very low tones. LOVE it. There does seem to be some overhang on some of the lower notes, or that may just be my ear. It seems a bit sloppier (not as "tight"), but PERFECT for HT. I can't wait to port the other!