Check my calcs?
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 132 Registered: Oct-05 | Will someone check and see if this is right? This is my first box design. 5.4 ft^3 before disp? 3.83 ft^3 after. This is for two RE SX 12s, Xmax 21. Port is 25.8 long, Area is 5x14.5 External Dim (36x23x16) One sub on incline, one facing up, port firing into back wall.  |
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Silver Member Username: DrivingrecklessNear tampa, Florida United state... Post Number: 208 Registered: Apr-06 | DID YOU USE AUTOCAD OR MICROSTATION???OR..... |
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Silver Member Username: Thomas_gNM Post Number: 417 Registered: Oct-05 | Not sure so i dont fu*kin know. That design looks pretty kool though. |
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Gold Member Username: Tdeaton1021Near Tampa, Florida USA Post Number: 2833 Registered: Sep-04 | a box with 3.83cuft net tuned to 32 hz needs a 35.5inch port length for a port of 14.5x5 inches that box, given that it is 3.83net and a 25.8inch port length and 5x14.5 port is tuned to appx 36hz. ^^pretty sure im REALLY exhausted. |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 133 Registered: Oct-05 | I wasn't sure about that either. When you put your net in the calc i didn't know if you did before or after port disp. How do you know how much net you have beforehand? You dont. You cant really figure net w/o knowing how much port volume you have. This has always boggled my mind, and is the reason for no attemp at building a box. I could always run the port back up the box, but that COULD restrict airflow with that angle... |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 134 Registered: Oct-05 | Thats AutoCAD reckless. |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 135 Registered: Oct-05 | WIth a port that big the volume of it knocks my Net down to ~3.5, which is too small. Are you sure that is right? |
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Gold Member Username: Tdeaton1021Near Tampa, Florida USA Post Number: 2842 Registered: Sep-04 | net volume is the volume minus sub and port displacement. its really simple, just work backwards... if you want a 4 cuft net box just type in 4 net and your tune and then mess around with different port sizes. each time calculate the port volume and add the port volume and sub volume to the net volume until you have the right amount of gross volume you are looking for. also, to use your first idea, just reduce that port area some and your port will become smaller. thus giving you more net volume and less port disp. try something like 4x14.5 that should reduce your port length quite a bit. maybe even 3.5x14.5 even 3.5x14.5 gives you appx 50 sq inches of port area. thats plenty for 4 cuft net. |
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Silver Member Username: DrivingrecklessNear tampa, Florida United state... Post Number: 222 Registered: Apr-06 | AutoCAD is a crazy program u did it at school??? |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 137 Registered: Oct-05 | Okay recalced, check my crap again please lol. Seems to me like the port is too short... but then again I messed up the first time :-/ And reckless, CAD is amazing, but nothing compared to SolidEdge. I just can't find a cracked version of SolidEdge. I have AutoCAD on my comp. Grr, isnt letting me post a pic, but the new volume is 4.6 and port is 14.5x3.5x15.91 and tuned to 32 hz. 5.4 -.32 sub disp, -4.7 port volume= 4.6 net, |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 138 Registered: Oct-05 |  |
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Silver Member Username: DrivingrecklessNear tampa, Florida United state... Post Number: 226 Registered: Apr-06 | my favorite program is microstation its ezier to use thn autoCAD even though its still easy |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 139 Registered: Oct-05 | I had CAD I and CAD II at my old school. For two years I had it as a class. We used CAD first year and SolidEdge second year. Look up SE, its studly. |
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Silver Member Username: DrivingrecklessNear tampa, Florida United state... Post Number: 227 Registered: Apr-06 | iight i will cuz i took the same courses u did but thn used microstation at my job so i kinda lost my abilities in autoCAD but ill look it up |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 141 Registered: Oct-05 | :-/ bump |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 82 Registered: Jul-05 | You want something crazy look up Autodesk 3ds Max. That things capabilities just amaze me. |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 83 Registered: Jul-05 | And btw i don't think that box will be tuned right because that port's effective length is 17.66" long, not 15.91". |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 142 Registered: Oct-05 | But you have built them before... so tell me what to do to fix it please?  |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 143 Registered: Oct-05 | what if i did port dims 14.5x3.75x18.82? 4.48 ft^3? |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 84 Registered: Jul-05 | When you have a vented port along a wall the wall has an effect on the ports effective length. It extends the ports effective length one half the distance of the ports width. So in your last example the side of the port was 15.91" and your port was 3.5" wide. 15.91+0.5*3.5=17.66". This extra bit of port air volume should also be subtracted from you box's net volume. I hope i didn't confuse you too much. If you want i could prolly calc you up a box if you want. I'm guessing you want those outside dimensions that're in your drawing. How wide do you want your port, and what do you want to tune it to? |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 144 Registered: Oct-05 | Well I was really trying to do this on my own, but I really do need the help, so thank you a ton. I want the port anywhere from 3.5x14.5 to 4x14.5 And I need to keep the net above 4 ft. Tuned to 32 Hz. So would I just do 3.5x14.5x(length+1.75)? Or do you add the length at the end? |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 145 Registered: Oct-05 | Disregard that last statement.... I must have been out of my mind. So if i have a port, for a 4.55 ft^3 @ 14.5x3.5, I'd originally have a 16.22 length port. I'd add 1.75 to it (half of 3.5inch port width), to make it 17.97, close enough to 18. So an 18 inch port, .528 volume. 5.4 before minus .528, minus .32 sub disp, = 4.552. Perfect @ 32hz? Am I right? |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 86 Registered: Jul-05 | Hmmm. I'm not sure if that's right. With those dimension I got a tuning of 35.15 Hz. Here's what i got.  I'm not sure if you can read it but the port wall is 24.15" long. giving you an effective port length (the cyan colored line) of 25.9". the volume of the box (the yellow line) is 4.52 cu.ft. after sub displacement that leaves 4.2 cu.ft. I used Autocad to calc the volume so i'm pretty sure that's right. The tuning on this box is 32.0 Hz. |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 147 Registered: Oct-05 | I'm still not understanding your effective port length. I can see where you add the extra 1.75... I guess i see it now... I used autocad for my drawing too, and its 5.4 total. Is that what you started with? When I'm done eating I'll come refigure it. Can you think of a better design for this? Or a better place for the port? |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 92 Registered: Jul-05 | I didn't really "start" w/ any volume per se. i drew up the outside dimensions then offset .75" for the walls. to get a volume i simply listed the yellow line, multiplied it by 14.5, and subtracted 552.96 (sub displacement in cu. in.) this is what i used for the net volume. calculating the port length was tricky because if i changed the port length, this changed the net volume and vice versa. i had to guess and check a few times until i got it right. I don't really know how to explain a ports effective length except that a sub can't "see" your port size. all it can do is "feel" the effect it has on it. That's why when you do round ports you need to put them a certain distance away from any wall or it'll mess with ther tuning. As for a better design i couldn't really say unless i saw waht sapce there was to wok with. i'm pretty sure this one would work well. You're gonna make two chambers exactly alike right, one for each sx? |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 148 Registered: Oct-05 | How could I do two chambers? If you noticed, it only has one port lol. And this is for a dual SX setup, one on the incline, one on the top side. 16 inches wide only fits one. I have to figure my volume here. I was doing it like 5.4 total vol, -.32 sub disp,-port disp = net. And I was guessing and checking. I just didnt do effective area. I didn't know you ahd to do that. |
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Gold Member Username: Tdeaton1021Near Tampa, Florida USA Post Number: 2853 Registered: Sep-04 | seth- on the program he was using you select if its slot or just a regular square port. by doing so it automatically changed the port length. with a straight port its easy because the port length is measured down the center of the port and so you jus have to make the port wall to the length it gives you. also, 4.2 cuft net tuned to 32hz with a 3.5x14.5 port needs to be only 18.67" long. im pretty sure everything above is correct... |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 95 Registered: Jul-05 | I wasn't sure if you were calc'ing this for one sx, but gonna make your box 32" wide, with two exact chambers, ea. one side by side with the subs firing the same direction as your port. (in other words this box was only for one sx). And trevor, i don't use any programs. i do it all with the equations by hand so i have to do a little bit of guess and check. I'm pretty sure i'm right, but i could be wrong. if u go to www.the12volt.com, under their port calculators enter 8.03846 for the diameter (the equivalent of a 50.75 sq. in. square port if it was round), 4.2 for the volume, and 32 Hz for the tuning. you'll see it comes up with something quite close to what i calc'ed. |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 149 Registered: Oct-05 | This looks wrong to me... But I guess I'll try and try until I get it. I was trying to get a little more volume out of the box... :-/ I kept forgetting to subtract sub disp, which was buggin me out.  |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 151 Registered: Oct-05 | grrr. Now that you say that, is my second one correct? |
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Silver Member Username: Talon_es93Post Number: 201 Registered: Mar-06 | hey i need some help.. ik this ain't gotta do nothin with this and sry but its the only way i can get ppl to listen.. i needa know how to hook up a second battery.. and again.. sorry |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 97 Registered: Jul-05 | Okay, here's another calculation that i got off off diy subwoofer. the address is www.diysubwoofers.org/misc/portcal.htm Port Length The port length required to tune a volume of air to a specific frequency can be calculated by using the following equation: Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv) where, Dv = port diameter (cm) Fb = tuning frequency (Hz) Vb = net volume (litres) Lv = length of each port (cm) Np = number of ports k = end correction (normally 0.732) I did some conversions and... Dv = 20.42 Fb = 32 Vb = 118.93 Np = 1 If you plug it all in you end up with 65.711cm, which is 25.87", i'm tellin you man, your ports effective length needs to be about 25.9". |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 154 Registered: Oct-05 | :-/... I calced it in the calc... its on carstereo.com... Are you positive? Trevor and I are coming up with very similar answers... and yours is the odd one. Did you do the volume in liters or feet? |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 98 Registered: Jul-05 | pretty sure i'm right but i don't wanna f up your box man. i've calc'ed it using diy subwoofer, jl audio, and the12volt as sources to check my numbers and it all checks out for me. Anyone else wanna input. i guess i gave it a shot but it's your box so it's your call man. i really hope it turns out great, those are some nice subs. |
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Bronze Member Username: Seth_walkerU.S.A. Post Number: 100 Registered: Jul-05 | Oh and btw .D. for a second battery what u need to do is use a battery isolator to separate the battery u use for starting, from the ones you use for audio. After you got that just connect them in parallel where ever u wanna mount them. |
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Silver Member Username: Talon_es93Post Number: 203 Registered: Mar-06 | THANK YOU man.. i been trying to figure it out all day and no one would respond me...i needed to know b/c on thursday i'm throwin 5 15"S and 4 12"S in my suburban for a compitition and runnin 2 amps so i kinda needed that... thanks tho |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 155 Registered: Oct-05 | :-/ I'll refigure more. |
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Gold Member Username: Tdeaton1021Near Tampa, Florida USA Post Number: 2859 Registered: Sep-04 | all i can say as proof is the programs i use are correct... the hand calculating stuff is too tough for me... |
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Silver Member Username: Demon_prideCrowder, Oklahoma USA Post Number: 156 Registered: Oct-05 | Thanks for the help both of you. When I'm ready to build this box I'll post again with my final dims. Should be sometime in the next few weeks. School's getting out and I don't have much to do. |
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