alaskanzx5 Posted January 12, 2015 Report Share Posted January 12, 2015 I've thought about but never found anything on it. I know that it is needed info to help determine port area and port velocity. I can't seem to find a formula for it or a calc online. A question for the pros with out a doubt. t1500bdcp 2 t2d4 15" 1 t600.4 1 t400.2 1 set p1 tweets singer alt, tons of wiring, smd vm-1, 80prs, back seat delete, still in the works, aiming for a 145-147 with the ability to play 25hz up to 50hz. Link to comment Share on other sites More sharing options...
Jessica Posted January 12, 2015 Report Share Posted January 12, 2015 i am 90% sure that most "displacement" has nothing to do with the space the sub takes up. It is more about xmax. From what i have read, unless your sub has a really huge motor, dont worry about it when figuring box volume. I may be wrong though Rest in peace, walled 87 accord build log 03' Corolla build with AA Mayhem inside. My super random youtube channel and terrible camera work. Wiring comparison by CaptainzPlanetz Wire and fuse guide by Guest SyKo13 Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 12, 2015 Report Share Posted January 12, 2015 Driver displacement is usually referred to as Vd. Its generally measured in cubic centimeter (cc). To get it you take Sd (cone area) x Xmax (in mm) and divide by 10. So your average 12" sub with 480 sq cm of cone area and 18 mm of xmax will have a Vd of 862.2 cc. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
Jeff4661 Posted January 12, 2015 Report Share Posted January 12, 2015 i am 90% sure that most "displacement" has nothing to do with the space the sub takes up. It is more about xmax. From what i have read, unless your sub has a really huge motor, dont worry about it when figuring box volume. I may be wrong though I disagree with us in my opinion all subs take up volume inside of enclosures.. Depending on how big your sub is could make or break your tuning point... Example? 4 hdc3 15" subs take up .2 cubes per sub so if I built a 10 cubic foot box tuned to 35hz with out considering that volume those take up In an enclosure.. I would actually end up at only being a 9.2 cubic foot box bringing Ur tuning up to around 37hz Current build 05 Yukon SLT http://www.stevemeadedesigns.com/board/topic/195350-jeffs-05-yukong-wall-build/ Link to comment Share on other sites More sharing options...
alaskanzx5 Posted January 12, 2015 Author Report Share Posted January 12, 2015 So what I could find is Vd = sd x Xmax. Didn't see anything about divide by 10. So when doing this from what I can see sd comes in cm squared and Xmax in mm obviously. When doing it I'm assuming you use one way Xmax as that is the standard for Xmax. However are you suppose to convert any of the measurements? If not awesome this keeps it simple. t1500bdcp 2 t2d4 15" 1 t600.4 1 t400.2 1 set p1 tweets singer alt, tons of wiring, smd vm-1, 80prs, back seat delete, still in the works, aiming for a 145-147 with the ability to play 25hz up to 50hz. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 12, 2015 Report Share Posted January 12, 2015 So what I could find is Vd = sd x Xmax. Didn't see anything about divide by 10. So when doing this from what I can see sd comes in cm squared and Xmax in mm obviously. When doing it I'm assuming you use one way Xmax as that is the standard for Xmax. However are you suppose to convert any of the measurements? If not awesome this keeps it simple. The divide by 10 part comes in because your final unit is cubic centimeters and you are inputting square centimeters (Sd) and millimeters (Xmax). One cubic centimeter = one square centimeter x 10 mm (or 1 cm). If you converted the xmax from mm to cm first you wouldn't have to divide by 10. Either way you end up at the same place. The xmax input is the standard one way measurement. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
alaskanzx5 Posted January 12, 2015 Author Report Share Posted January 12, 2015 Ok, I got this down. That was easy enough. Now part 2 of this question. How do you use vd as a determination factor of port size? I know there is more to it then this. I also realize that this is the amount of air the sub can move if pushed to full Xmax which is box and power it seeing dependant. I found 2 different formulas and I feel as if I'm doing it wrong. Wish someone would create a calc where you could enter in you vd, desired tuning and what ever else was needed to figure in port velocity. Them again knowing how to do it by hand is nice to. t1500bdcp 2 t2d4 15" 1 t600.4 1 t400.2 1 set p1 tweets singer alt, tons of wiring, smd vm-1, 80prs, back seat delete, still in the works, aiming for a 145-147 with the ability to play 25hz up to 50hz. Link to comment Share on other sites More sharing options...
Cj Kumz Posted January 12, 2015 Report Share Posted January 12, 2015 Yah this is a very complex topic. And involves a lot of calculations.. I have also tried and ended up with dead ends lol. Obviously the rate at which the cone is moving combined with the time and distance the air covers will need to be factored in too. Hopefully someone will chime in soon. Vw Polo Pioneer Deh-6050UB Sundown Saz-3500d DD Audio 9500 15'' 5.5 cubic feet box with 10 inch port @ 38hz I live to hear the Bass drop!!! Link to comment Share on other sites More sharing options...
kirill007 Posted January 12, 2015 Report Share Posted January 12, 2015 Ok, I got this down. That was easy enough. Now part 2 of this question. How do you use vd as a determination factor of port size? I know there is more to it then this. I also realize that this is the amount of air the sub can move if pushed to full Xmax which is box and power it seeing dependant. I found 2 different formulas and I feel as if I'm doing it wrong. Wish someone would create a calc where you could enter in you vd, desired tuning and what ever else was needed to figure in port velocity. Them again knowing how to do it by hand is nice to. Why not just use WinIsd? You model the port velocity for your sub in your enclosure and much more Thinking is the root of all problems... You ALWAYS get what you pay for. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 12, 2015 Report Share Posted January 12, 2015 Ok, I got this down. That was easy enough. Now part 2 of this question. How do you use vd as a determination factor of port size? I know there is more to it then this. I also realize that this is the amount of air the sub can move if pushed to full Xmax which is box and power it seeing dependant. I found 2 different formulas and I feel as if I'm doing it wrong. Wish someone would create a calc where you could enter in you vd, desired tuning and what ever else was needed to figure in port velocity. Them again knowing how to do it by hand is nice to. Once you have Vd you can determine port size using Small's formula, which is: dv = 39.37 * (Fb x Vd)^.5 dv = diameter of the port in inches Fb = tuning frequency in herz Vd = driver displacement in cubic meters Since this formula uses Vd in cubic meters you have to take your Vd calculation in cc and divide it by 1,000,000 to get cubic meters. Also the number is gives you back is the diameter of a round port, so to get sq in of port area you have to take dv and divide by two to get the radius and then use your normal area of a circle formula (Pi r^2). I put all of the above math into a spreadsheet so all I have to do is enter in cone area, xmax, and tuning frequency and I get my answer in square inches. The problem with all of this is it is based on the assumption that you are going to push the sub all the way to Xmax. A lot of today's subs have such huge Xmax that you are going to run out of power handling capacity long before you get anywhere near Xmax. This is one of the reasons why determining optimal port area is no easy task. I've put a lot of mental energy into this problem and I'm yet to come up with a system that I'm 100% satisfied with. These days I usually start out with Small's formula and then put that area into WinISD like kirill007 suggested and see what port velocities it gets me. Of course once you get your data back from WinISD you have the question of how much port velocity is too much? I'm of the belief that lower is better, so I like to keep things below 20 m/sec, but often that isn't practical, 30 m/sec is my hard limit, but even that number is situation dependent. Assuming you do determine what the optimal amount of port area is, if you are going to be using a slot port, they are less efficient than round ports of equal area so you have to take that into consideration as well. It all adds up to "how much port area?" being a very complex question. The good news is if you have access to an AMM-1 you have the ability to find out if your port is undersized. Using an AMM-1 you can check to see if you are getting port compression. If you play a tone through your system at your box tuning frequency and watch the impedance as you turn the power up, if you are getting port compression the impedance will start to climb as power increases. I just got my AMM-1 and this is something I've been experimenting with. The only caveat to this technique is power compression will also increase the impedance as power increases so you have to test for that separately. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.