Jordan92790 Posted November 16, 2007 Author Report Share Posted November 16, 2007 Alright....so I've been trying to figure out displacement. I'm pretty sure my box is going to be a 14x35x35. my sub's displacement is .23f^3. I still need the volume displacement for a piece of 3/4 inch MDF bored that is 13.5x30 to seperate my sub from port. I've tried to figure this out, and I've came up with the following calculations. .75x13.5x30=303.75/1728=.18f^3 displacement. Can anyone correct me if I'm wrong on this? And since my box is going to be 14x35x35=17150/1728=9.92f^3. So subtracting the subdisplacement of .23 and my if my calculation on the 13.5x30 f^3 (.18volume) is correct that will gives me a 9.5F^3. If this is correctly calculated what would the demensions of my port have to be to tune my box at 34hz Quote Link to comment Share on other sites More sharing options...
andym85 Posted November 16, 2007 Report Share Posted November 16, 2007 u are figuring displacement wrong. you dont just figure the piece of wood used for the port for the displacement....u also have to figure all of the space in the port into the displacement equation also. so essentially it would be the height of your port x the width of the port (plus .75 for the wood) x the length of your port.... with that being said, if your port is 13.5"hx 7"w, then your port actually only needs to be 22" long to get ur tuning to 34hz. and the piece of wood for the port only needs to be 18.5" long (although the total port length is the actuall length plus half of the ports width (called end correction)...in this case 18.5+ 3.5 (<--half of 7)....which would give u an effective length of 22") box outer dimensions: 15h x 35w x 35d box inner dimensions: 13.5h x 33.5w x 33.5d (8.77cubes gross) port: 13.5h x 7w (gives u 94.5sq" of port area--12.74sq"/cft) x 18.5d port displacement: 1.12cft (13.5 x 7.75 x 18.5= 1935.5625/1728= 1.12cft) net box volume: 8.77 -.23 sub - 1.12 port= 7.42cubes tuning: 33.8hz Quote i likes me some audio stuff... Link to comment Share on other sites More sharing options...
andym85 Posted November 16, 2007 Report Share Posted November 16, 2007 again...the length of the wood for the port is 18.5" Quote i likes me some audio stuff... Link to comment Share on other sites More sharing options...
Jordan92790 Posted November 16, 2007 Author Report Share Posted November 16, 2007 (edited) u are figuring displacement wrong. you dont just figure the piece of wood used for the port for the displacement....u also have to figure all of the space in the port into the displacement equation also. so essentially it would be the height of your port x the width of the port (plus .75 for the wood) x the length of your port....with that being said, if your port is 13.5"hx 7"w, then your port actually only needs to be 22" long to get ur tuning to 34hz. and the piece of wood for the port only needs to be 18.5" long (although the total port length is the actuall length plus half of the ports width (called end correction)...in this case 18.5+ 3.5 (<--half of 7)....which would give u an effective length of 22") box outer dimensions: 15h x 35w x 35d box inner dimensions: 13.5h x 33.5w x 33.5d (8.77cubes gross) port: 13.5h x 7w (gives u 94.5sq" of port area--12.74sq"/cft) x 18.5d port displacement: 1.12cft (13.5 x 7.75 x 18.5= 1935.5625/1728= 1.12cft) net box volume: 8.77 -.23 sub - 1.12 port= 7.42cubes tuning: 33.8hz Wow...you are amazing, but I still have one more thing to ask. My box is going to be 33.5 inches deep inside. So is 18.5 long enough? Thats like 15 inches for air to travel into the port. Is this too much? and also How do you calculate the Hz of a port? You explained all your calculations but that one so that still confuses me just a lil. and also man I thank you soooooo much for the drawing you have given me. Did you use google sketch to draw that? It is amazing. If you ever need anything just ask Edited November 16, 2007 by Jordan92790 Quote Link to comment Share on other sites More sharing options...
andym85 Posted November 16, 2007 Report Share Posted November 16, 2007 (edited) im not amazing...just been on forums for a few years now and learned how to do things. and yea i did it on sketchup. as far as calculating frequency there is a big convoluted equation Fb = .159*((Av(1.84*10^8)/(Vb(Lv+.823*Av^.5))^.5 Fb = tuning frequency Av = vent area Vb = net volume in cubic inches Lv = effective length of vent effective length = physical length + end correction <---1/2 of the ports width although, like i always say, i know it looks intimidating but it really isnt if u are decent with math or any good with excel. (10^8 is 10 to the power of 8, and 10^.5 is the same thing as taking the square root of...i just did it like that in excel b/c i was unsure if there was a square root function) oh, it doesnt matter how much room you have between the back wall and the port. but u do want to keep the port at least the distance of the ports width off the back wall...for instance, in this case you wouldnt want your port to be any longer than 26.5" (33.5-7)...if it was any longer then would have to make a turn and do an "L" shaped port... Edited November 16, 2007 by amatt85 Quote i likes me some audio stuff... Link to comment Share on other sites More sharing options...
Jordan92790 Posted November 16, 2007 Author Report Share Posted November 16, 2007 (edited) You are amazing in my book. I'm decent in math, but when it comes to 3d objects..I just can't understand it. I think it's because I'm left-handed or something lol. Anyways I will be going to homedepot and lowes tommorow to check the prices on MDF. and I read on one of the post that lowes will cut the wood for you for little to no cost. so I would need 7 pieces of wood right? and please correct me if I'm wrong, but would I need (2) 13.5x35 cuts. (2)35x35 sheets. (1) 13.5x18.5 (1)13.5x33.5 and (1)13.5x26.5? Edited November 16, 2007 by Jordan92790 Quote Link to comment Share on other sites More sharing options...
andym85 Posted November 16, 2007 Report Share Posted November 16, 2007 that cut list is correct...and i have only had lowes cut wood once for me and they didnt charge me anything... Quote i likes me some audio stuff... Link to comment Share on other sites More sharing options...
Jordan92790 Posted November 16, 2007 Author Report Share Posted November 16, 2007 Well..I think I'm all set. I'm going to lowes tommorow after school to buy my wood. You have no idea how much of a help you have been. You've taught me alot. I knew nothing about volume or anything until I came to this site. I just went to radio shack and bought a box. It costed me 109 bucks! anyways thanks alot man. I'll post pics of the build, and will give you props for the help My friend and I are going to start it tommorow...He knows what he is doing. I'm not so sure about me though. Quote Link to comment Share on other sites More sharing options...
bigjd Posted November 16, 2007 Report Share Posted November 16, 2007 (edited) small error in the cut list u need 3 35 x 35 2 13.5 x 35 1 13.5 x 33.5 1 13.5 x 26.5 1 13.5 x 18.5 i have all the other shit so get the wood and bring it over and we will get it started... monday i will take the one peice to school and have wood shop cut the hole with the huge ass hole saw to make it perfect.. then ill work on the corners and shit.... tell ur mom u need to order the stuff in a week lol Edited November 16, 2007 by bigjd Quote Link to comment Share on other sites More sharing options...
andym85 Posted November 16, 2007 Report Share Posted November 16, 2007 no prob man! Quote i likes me some audio stuff... Link to comment Share on other sites More sharing options...
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