can somebody tell me how to figure out net cubes and port info on already built box

[blkvenm97]

I have an enclosure that was designed by a local audio shop for two 12 inch p3 rockfords and I asked to be tuned to 33 hertz...I don't know any other specs but I want to figure them out and also is there a way to calculate for sure that it is indeed tuned to 33 hertz? Port is 3 inches wide, 14.5 inches tall and 17.5 inches deep the way from the outside to the back of the enclosure on the inside of the port. External demensions are 37x16x18 and all wood is 3/4 inch thick mdf. Someone please help me calculate net cubes before sub displacement and port area. Thanks

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[blkvenm97]

Btw this is an L slot port on the side....here is a link to a picture of it on my facebook page...

https://m.facebook.com/?hrc=1&refsrc=http%3A%2F%2Fh.facebook.com%2Fhr%2Fr&_rdr#!/photo.php?fbid=613155872101696&id=100002218656203&set=a.242037642546856.59274.100002218656203&source=43

 

[bbeljefe]

Not knowing if the baffle is doubled or what bracing is in the cabinet I can only assume it's ~4 cubes and with that vent it's tuned at 34.5Hz.

 

[blkvenm97]

Thanks a lot for that info. I was thinking it was around 4 cubes. How do you calculate it to come up with that answer? To get the net cubes after displacement of the subs you simply take whatever the subwoofer displacemment is and subtract that from it is that correct?

 

[Kangaroux 5,000+ posts]

Volume before sub displacement is about 4.4 cubes...assuming each sub is 0.15 cubes that gives you 4.1 net. With the port dimensions you have (and if I'm understanding it correctly, with the port just going down the right side of the box) then you're tuned to about 35-36hz.

 

[Kangaroux 5,000+ posts]

Thanks a lot for that info. I was thinking it was around 4 cubes. How do you calculate it to come up with that answer? To get the net cubes after displacement of the subs you simply take whatever the subwoofer displacemment is and subtract that from it is that correct?

Your dimensions are 37 x 16 x 18

3/4" wood all around means subtract 2x that for either side from each dimension

35.5" x 14.5" x 16.5"

Multiply all the dimensions together and then divide by 1728 (12 * 12 * 12 = 1728 in^3)

= 8493.375 in^3 / 1728 = 4.91 ft^3

That's your gross volume (before port and subs).

Your port is 3" (+ 3/4") x 14.5" x 17.5"

= 951.56 in^3 / 1728 = 0.55 ft^3

Now subtract port displacement from the gross volume:

4.91 - 0.55 = 4.36 ft^3

And assume subs are 0.15 each:

4.36 - (0.15 * 2) = 4.06 ft^3

Then to calculate the port you use this calculator: Subwoofer Enclosure Calculators, Parallel, Series, Port Length and Volume

Enter in 3" and 14.5" for the port dimensions and 4.06 ft^3 for the volume. Keep adjusting the tuning until the port length matches what you have. In this case it's about 35-36 hz

 

[blkvenm97]

Your dimensions are 37 x 16 x 18
3/4" wood all around means subtract 2x that for either side from each dimension

35.5" x 14.5" x 16.5"

Multiply all the dimensions together and then divide by 1728 (12 * 12 * 12 = 1728 in^3)

= 8493.375 in^3 / 1728 = 4.91 ft^3

That's your gross volume (before port and subs).

Your port is 3" (+ 3/4") x 14.5" x 17.5"

= 951.56 in^3 / 1728 = 0.55 ft^3

Now subtract port displacement from the gross volume:

4.91 - 0.55 = 4.36 ft^3

And assume subs are 0.15 each:

4.36 - (0.15 * 2) = 4.06 ft^3

Then to calculate the port you use this calculator: Subwoofer Enclosure Calculators, Parallel, Series, Port Length and Volume

Enter in 3" and 14.5" for the port dimensions and 4.06 ft^3 for the volume. Keep adjusting the tuning until the port length matches what you have. In this case it's about 35-36 hz

That actually makes a lot of sense. I thought it was over 4 cubes although it was supposed to be built to rockford p3 specs (1.79 per sub) and it was supposed to be tuned to 33 but I called the box builder yesterday and he rememmbered building the box...he said it was built to p3 specs tuned to about 35. Is there a way to add to the sides of the port to lower tuning? Pretty sure I've seen that done. Is that a good idea to do or not so much? Also I wanna run a pair of sa12s and id like to use this box....based on these specs would the sas perform pretty good in it or would I be better off building another enclosure? Id rather use this one if possible but I want the sas to perform as good as I can and if that means building another box that I will do. A lot of people I see run around 4 cubes for their sa12s. Either way ill probably be running them in this box anyways to start until I get the other box....do you guys think they will do good in this box? They will run off a rockford t1000-1bdcp until I get a high output alt and second battery then I will add a second t1000 that I already have and run one on each sub. The amps will be run at 2 ohm with gains set low so they won't even be breaking a sweat meanwhile the sa12s will be slamming. Any ideas? Thanks for the help guys

 

[Kangaroux 5,000+ posts]

That actually makes a lot of sense. I thought it was over 4 cubes although it was supposed to be built to rockford p3 specs (1.79 per sub) and it was supposed to be tuned to 33 but I called the box builder yesterday and he rememmbered building the box...he said it was built to p3 specs tuned to about 35. Is there a way to add to the sides of the port to lower tuning? Pretty sure I've seen that done. Is that a good idea to do or not so much? Also I wanna run a pair of sa12s and id like to use this box....based on these specs would the sas perform pretty good in it or would I be better off building another enclosure? Id rather use this one if possible but I want the sas to perform as good as I can and if that means building another box that I will do. A lot of people I see run around 4 cubes for their sa12s. Either way ill probably be running them in this box anyways to start until I get the other box....do you guys think they will do good in this box? They will run off a rockford t1000-1bdcp until I get a high output alt and second battery then I will add a second t1000 that I already have and run one on each sub. The amps will be run at 2 ohm with gains set low so they won't even be breaking a sweat meanwhile the sa12s will be slamming. Any ideas? Thanks for the help guys

It wouldn't really be worth going through all the hassle to change everything. Do you still have the receipt for the box build? You could tell them that the box they made for you wasn't what you asked for. With the box being so big there's a good chance you might blow a sub by giving it too much power (bigger box = more efficient).

 

[ancorp 10+ year member]

The SAs (granted that the cutout diameter is same or almost identical) should be fine in that box if its built solid. The port area is on the low size though. I would consider rebuilding the box, but they should still play fairly well.