Port length question

[Quinn88]

I am building a box with round tube port the person that helped me with the design suggested 6" diameter by 14" long port due to that size only being available in sections that cost $50 I have to use 4" diameter tube when I did the port calculator it says the port only needs to be 5" long and I used two different calculators with same result and when I imput the suggested 6" diameter it gives me the 14" long this seems very odd to me Does any one know if this calculation is accurate if not a good port calculator also the box is 3.7^3ft

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[Snapper_Slapper 10+ year member]

Calc is right. Bigger diameter will be longer for the same tune. A single 4" or even 2 of them will not do at all. Not enough port area. Even a 6" port is a little small for 3.7cu/ft net. If that 3.7 is gross before displacements you'll be ok though. When you use the calc(Torres I assume) try to keep your round port area per foot in the 8-9 in^2 range.

 

[Quinn88]

After port displacement with the 8 inch diameter port the volume would be 3^3ft with the 6" diameter port it would be 3.5^3ft would it be better to go with over kill than to small also I can get sonotube for cheap at 8" diameter so that could work budget wise what do you think @Snapper_Slapper

 

[bgowdy 5,000+ posts]

[quote name='Quinn88']After port displacement with the 8 inch diameter port the volume would be 3^3ft with the 6" diameter port it would be 3.5^3ft would it be better to go with over kill than to small also I can get sonotube for cheap at 8" diameter so that could work budget wise what do you think @Snapper_Slapper[/QUOTE]

thats what i did on my build, i used just sonotube only for a port as a temp until i can buy another and make one and fiberglass it and make it nice.

my port right is pretty much carboard(nothing but the sonotube lol) and worked out pretty well. Metered on Termlab pretty good also, did 145.8 with about 800-1k watts

 

[Quinn88]

So do u think the 8" diameter sonotube would be legit at 3^3ft

 

[will3 10+ year member]

Round port without out flares will be the same as a square port without flares, with proper flares on each end will allow you to use a little less port area (because of the lower velocity #'s) , unless you are trying to shove 3 x10's in 3ft3 enclosure a single 8"port should be plenty of port area

 

[Quinn88]

Awesome thanks for the reply

 

[Snapper_Slapper 10+ year member]

So do u think the 8" diameter sonotube would be legit at 3^3ft

No. With 3.7 gross volume and 8" port your port would have to be 40 inches long to get to 35.97hz and leave you around 2.25 net after displacements. The only option I see is the 6" port. Did you also factor in woofer and bracing displacement? If not then the 3.7 box would be around 3.25 net which is near optimal for the 6" port. This is all just guesstimation because I don't know specifics but 3.7 gross - .26(6" port x 15") - .17(assuming 1 15' woofer) - .1 (bracing) = 3.27 cu/ft tuned to 34.65hz and 8.64 sq/in of port area. You can also add more bracing or blocks to bring your port area per foot up. Use the Torres calc. Play around.

 

[Quinn88]

The 3.7 does account for sub displacement and it is a single 15. I found some 6" pvc for cheap thankfully so I can do that size port after displacement the final volume will be 3.45^3ft that's the 6" x 15" added an inch because I'm going to make a flare on one end will this be a good size port for volume since I'm adding a flare and thanks for all the Replies this has proved much more confusing than I thought would be possible