Maximum port size?

[ramchip007]

I am Building two sono subs with 15's, 24 inch diameter 6 feet high, or about 18 cubes apiece tuned to about 17hz and feeding it with a ep2500, my question is what port size is too big. I got a piece of 8 inch tube but not sure if it's too large, speaker parameters
Re: 3.95 ohm
Qts: 0.578
Qes: 0.673
Qms: 4.095
Fs: 24.5hz
mms: 130g
cms: .300mm/N
BL: 11
Vas: 284L
Xmass 27mm
Exodus xj15

[SteveCallas]

You don't want to use a length of more than ~36", so with a tuning ~17hz, you'll need to use a 6" or 6.5" diameter port. An 8" diameter port would be too long for that tuning.

[ramchip007]

my effective volume is about 17.230. According to win ISd using an 8 inch port tuned to 17 Hz would make it 22.375 or did I miss something. I'm kind of new to this fancy software stuff. Very cool though. I just got my circles cut, but waiting to cut for the port. I used the cheap quarter-inch rotozip bits in from Harbor freight, cut 10 circles with one bit , got three bits for six dollars .

[SteveCallas]

So you aren't using a RL-p15? Why is this in the SS forum then?

[ramchip007]

Sorry my bad

[bobgpsr]

Thread moved to here. DIY Subwoofers

[WillyD]

Definitely go with the 8" port. With the large enclosure volume you're using (relatively), you can go with 8" diam because the port won't be too long. This is a good thing as port noise and port compression will be practically non-existent, even at the port air velocity peak.

I'd tune a bit lower than 17Hz though. At least 15Hz, if not 14Hz. Those should make for fine subwoofers.

[ramchip007]

Thank you for your response willy, just curious, what would be the advantage with a lower tune? To me it seemed the plot showed increased low-end performance with lower excursion. Please advise. Thanks

[WillyD]

Read Steve's writeup here: http://www.hometheatershack.com/foru...explained.html

You certainly don't have to go lower, but considering your subs and the amp, I think it makes sense.