BBP is F*cked, WinISD

[MisterE 10+ year member]

Using BBP6 I entered a box for a 12 Type R and used the parameters for the old model. I entered the external dimensions, the tuning I wanted, 2 round ports flared on both ends, 4" diameter..... 253 inch long port?? Am i doing something wrong?

Also, on WinISD i keep forgetting what volume to enter for the box. Before driver and everything? After? But if its after and I have to subtract port calculation.... how do I know how big the port is if i havent calculated the volume of the box yet?? get what im saying? lol WinISD Alpha

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[Volenti 10+ year member]

re-BBP6, you either have the wrong unit somewhere or a decimal place in the wrong spot, go through and double check everything, either that or your trying to tune a 1/2 cuft enclosure to 15hz //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[MisterE 10+ year member]

Crazy. Tried it with another sub and it did the same thing? I havent used BBP for that long....

i select a subwoofer (that shouldnt matter for this exercise unless i want to graph, correct?) and i change the shape to PRISM, SQUARE.

External Dimensions

Wall Thickness front and sides .75 in

A 19 B 18 C 14.5 in

Fb: 30 Hz

Use classical damping

No of Vents 2

Round

Two flared ends

Diameter 4 in

and the length for this sub pops up 371.8 in??

im just trying to find the port length with smallest possible area w/o noise for a 12 type R!

i think my program is just F-ed because if i change the number of ports to 1 instead of 2 the vent length stays the same

 

[Volenti 10+ year member]

I tried it as you described and my BBP did the same thing, must be something with the calculation for the flared ports and low tuning, a smaller port or slightly higher tuning worked, ironically the "suggest minimum vent area button" came up with 3.919'' dia...

 

[DBfan187 5,000+ posts]

http://www.psp-inc.com/psp-inc.com/public_html/..%5Ccgi-bin%5Cport_length_calculator.cgi

 

[xpl0it 10+ year member]

BBP6 knows what it's doing when it comes to port calculations.

 

[Tempe 10+ year member]

Also, on WinISD i keep forgetting what volume to enter for the box. Before driver and everything? After? But if its after and I have to subtract port calculation.... how do I know how big the port is if i havent calculated the volume of the box yet?? get what im saying? lol WinISD Alpha

The number you enter of course is your net volume. The program cannot account for bracing volume as it does not know what you will use . It cannot account for port displacement as a port can be internal, external, or both, and it does not know the thickness of the port material. It does not account for enclosure material thickness as it does not know this. Also bracing and sub displacement are variables. The only constants are the net volume (Vb), tuning (Fb), and port area.

Pick your constants. Pick ideal enclosure W x H x D. Subtract 1.5" from each number (2.25" from the corresponding measurement if a double-baffle is used) to get your internal measurements. Use this formula to get your gross volume: ((W - 1.5) x (H - 1.5) x (D - 1.5) / 1728).

Your gross volume is normally 25 - 33% more than your net volume. If you want 2 cubes try for 2.66 gross cubes. Enter 2 cubes tuned to 30 in WinISD Pro. Pick two 4" vents to get their length. I am GUESSING the ports to be like 25" long. The port displacement is like 0.48 cubes. Assume the sub takes up like 0.15 cube. You could use some mdf scraps for bracing to make it up to 2.66 cubes.

19 x 18 x 14.5 is 2.17 gross cubes. That is 17.5 x 16.5 x 13 are the internal measurements. Fidget with them to 1) get to 2.66 cubes internal and 2) be small enough to meet your requirements and fit.

/class //content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif

Tempe