JesseyMclame Posted November 3, 2013 Report Share Posted November 3, 2013 Okay so I've got An M1 XL 18 with psi soft parts, ittl be getting right around 1800-2000 watts, I'm gonna do 5.5 cubes after all displacement, (came from rusty), I'm gonna do aero ports, I just have no idea how much port area to give it. I'm thinkin like 10-12 SQ inches per foot ? Any input would be awesome, thanks guys! Current setup in my 96 Hoe Hu - Pioneer DEH-80prs. Amps - (4) Crossfire C5 1700D's, MTX Thunder 5604(mids), PPI Art 300.2 (tweets) Batts - 4 91ah rear batts, 50ah batt up front. Subs - 2 Crossfire XSv2 18's Alt - Singer 330A Front stage - Random JL & Eclipse mids, Eclipse tweets Link to comment Share on other sites More sharing options...
Rail Posted November 4, 2013 Report Share Posted November 4, 2013 Do yourself a favor and forget about the sq in per cube "rule", because it is a complete myth. Port area does not relate directly to volume of the enclosure. Factors that do matter are the tuning frequency of the enclosure (Fb), the xmax of the sub, cone area of the sub (Sd), and of course the number of subs. You know the T/S parameters of a speaker? Created by A.N. Thiele and Richard H. Small? Small derived a formula to calculate the minimum port area required to avoid port noise and compression. Following his formula you get MINIMUMS of: 77 sq inches at a tuning of 20Hz 115 sq inches at a tuning of 30Hz 134 sq inches at a tuning of 35Hz With your "rule", 5.5 cu ft with 12 sq in per cubic foot would only get you 66 sq inches of port. This is far too small for an 18" subwoofer, its not even enough area if you were to tune to 20Hz which I doubt you are planning. Chevrolet Tahoe Crescendo PWX6 (2) and FT1 (2) Fi Audio SP4 15" (1), AQ3500D.1 (1) Enclosure: 4th Order (Ported) 4.5cu ft @26Hz Mechman Elite 370A & Kinetik HC2000 Sky High 2/0 Wire Future Plans: (2) 18" @25Hz Link to comment Share on other sites More sharing options...
CleanSierra Posted November 4, 2013 Report Share Posted November 4, 2013 You're a new member, but I like you already^^^ Great info and I agree we need to throw the "per cubic foot" rule out the window. Im not the one you want to try to troll. Just a fyi for you. Link to comment Share on other sites More sharing options...
JesseyMclame Posted November 4, 2013 Author Report Share Posted November 4, 2013 Okay so pretty much, no matter the net volume of the box, those are the minimums I need to make the speaker sound it's best at that tuning frequency? Current setup in my 96 Hoe Hu - Pioneer DEH-80prs. Amps - (4) Crossfire C5 1700D's, MTX Thunder 5604(mids), PPI Art 300.2 (tweets) Batts - 4 91ah rear batts, 50ah batt up front. Subs - 2 Crossfire XSv2 18's Alt - Singer 330A Front stage - Random JL & Eclipse mids, Eclipse tweets Link to comment Share on other sites More sharing options...
JesseyMclame Posted November 4, 2013 Author Report Share Posted November 4, 2013 Or more so, let the woofer work proper in said enclosure. Current setup in my 96 Hoe Hu - Pioneer DEH-80prs. Amps - (4) Crossfire C5 1700D's, MTX Thunder 5604(mids), PPI Art 300.2 (tweets) Batts - 4 91ah rear batts, 50ah batt up front. Subs - 2 Crossfire XSv2 18's Alt - Singer 330A Front stage - Random JL & Eclipse mids, Eclipse tweets Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted November 4, 2013 Report Share Posted November 4, 2013 To expand on what Rail said, the formula I use is: Vd (Volume of the driver in cubic inches) * Tuning Frequency (In Hertz) * .02 = Area of the port (In square inches) This formula is pretty conservative and should keep your port velocity under 10 meters/sec. If you don't know the Vd of your driver you can calculate it, its Sd (Cone area in square inches) * Xmax (In inches) * 2. "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...
john253a Posted November 4, 2013 Report Share Posted November 4, 2013 To expand on what Rail said, the formula I use is: Vd (Volume of the driver in cubic inches) * Tuning Frequency (In Hertz) * .02 = Area of the port (In square inches) This formula is pretty conservative and should keep your port velocity under 10 meters/sec. If you don't know the Vd of your driver you can calculate it, its Sd (Cone area in square inches) * Xmax (In inches) * 2. using sd you'll be looking around 130sq" and thats just crazy in 5.5 net 3x 6" at 17 long (psp) is what idd use and block 1 off for daily edit: that is if you don't want low 30's tune, you will get better performance form you equipment with a larger port, just you'll be hard to get 3x 6" 41" long @30hz in a 5.5net box Link to comment Share on other sites More sharing options...
Rail Posted November 4, 2013 Report Share Posted November 4, 2013 You're a new member, but I like you already^^^ Thanks! New member, but not new to car audio Okay so pretty much, no matter the net volume of the box, those are the minimums I need to make the speaker sound it's best at that tuning frequency? Yes, in order to avoid port noise and port compression due to high air velocity. To expand on what Rail said, the formula I use is: Vd (Volume of the driver in cubic inches) * Tuning Frequency (In Hertz) * .02 = Area of the port (In square inches) This formula is pretty conservative and should keep your port velocity under 10 meters/sec. If you don't know the Vd of your driver you can calculate it, its Sd (Cone area in square inches) * Xmax (In inches) * 2. Small's formula is actually: 39.37 * (Fb*Vd)^(1/2) Fb is the tuning frequency of the enclosure Vd is the amount of air that the sub can displace (which is cone area times the xmax, so Vd = Sd*xmax) This will get you the minimum diameter of the port in inches, so if you divide by 2 to get the minimum radius, you can then use pi*r^2 to find the minimum area of the port. Edit: To make this more clear, you must convert both the Sd and Xmax to meters, so that for the Vd you get cubic meters. Chevrolet Tahoe Crescendo PWX6 (2) and FT1 (2) Fi Audio SP4 15" (1), AQ3500D.1 (1) Enclosure: 4th Order (Ported) 4.5cu ft @26Hz Mechman Elite 370A & Kinetik HC2000 Sky High 2/0 Wire Future Plans: (2) 18" @25Hz Link to comment Share on other sites More sharing options...
Brandonbkd Posted November 4, 2013 Report Share Posted November 4, 2013 The setup in my sig only has 86 sq in of port and it sounds great. No port noise whatsoever. FI BL18 Build Log: CLICK HERE!! 2003 Explorer Sport: FI BL18 SoundQubed 2200 at 0.7ohm Pioneer DEH-2500UI Pioneer 6 x 8s Rockford Fosgate 6 x 9s 5 ft^3 box at 35hz Lots of Mega Mat Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted November 4, 2013 Report Share Posted November 4, 2013 Small's formula is actually: 39.37 * (Fb*Vd)^(1/2) Fb is the tuning frequency of the enclosure Vd is the amount of air that the sub can displace (which is cone area times the xmax, so Vd = Sd*xmax) This will get you the minimum diameter of the port in inches, so if you divide by 2 to get the minimum radius, you can then use pi*r^2 to find the minimum area of the port. The formula I gave is Small's formula, its just been worked around to use Vd in cubic inches instead of cubic meters and to give you your result in square inches of areas instead of the diameter of a round port. Also to calculate Vd you have to multiply the Xmax by 2 since it is a measurement of travel each direction. "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...
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