Met Posted March 12, 2015 Author Report Share Posted March 12, 2015 your port area per foot seems fairly low at 9.7?? Just in reading most lean towards a minimum of 12 up to 15. Im by no means a huge box designer, but I was curious as to how that may affect the box? From what I've read, you need 8 - 12 per cube for areo port, 12 - 15 for slot port. I know these subs love a lot of port, but for everything to fit properly, I've ended up with 8.5 per cube. If I have any port noise, I can rebuild it with more port area. I'll just have to move my spare tire and the tools as I won't be able to access the door. We'll see! Link to comment Share on other sites More sharing options...
Krakin Posted March 12, 2015 Report Share Posted March 12, 2015 port per foot is an absolutely useless number. If you see someone recommend this unit then you need to disregard what they are talking about, because they clearly are lacking in their understanding of ports. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
Met Posted March 12, 2015 Author Report Share Posted March 12, 2015 port per foot is an absolutely useless number. If you see someone recommend this unit then you need to disregard what they are talking about, because they clearly are lacking in their understanding of ports. Could you elaborate? This is my third build. I didn't know much, I've just done a ton of research to figure it out .. but I could have found incorrect information. These are my dimensions and calculations so far. H - 17.5 (18.25 after double baffle, max height before rear view starts getting blocked) D - 22.5 (this is the the max depth before blocking access to the spare) W - 38 (max width is 40 inch) So, airspace: Inner dimensions - 16x36.5x21 = 7.0972 cuft before port/driver displacement. Driver displacement - 7.0972 - .36 = 6.737cuft (.18 per sub, .18x2 = .36) Port displacement - 6.737 - .494 = 6.243cuft math: 3.14(2*2) (17) = .494 Net volume: 6.243cuft PSP Calc: 4in port x 4, 17in length : 33.8hz (I'm keeping it at 17in as im lazy to cut) So, 6.24cuft @ 33.8hz I'm really hope I did all that right. Link to comment Share on other sites More sharing options...
Krakin Posted March 12, 2015 Report Share Posted March 12, 2015 For a fluid to flow properly through a vent, the vent must contain the necessary amount of area, not surface area -even though that will play a factor in area needed *explained at end of post-. Think of sucking up water in a straw then spewing it out. If you do it slow the water stays together. If you do it fast it spreads apart and becomes 'ugly'. This is because the speed of the water through the straw was much to fast for how small the straw is. If you tried the same thing with the same water but you were trying to blow it out of something with as much cross-sectional area as a cup or something else large, the water would once again just kind of spill out no matter how hard you blow. When relating this back to box designing, you need to account for the amount of air being pushed/pulled and how fast. You want to keep the speed of the air down to a speed that won't cause the air to become 'ugly' like the water in the straw. However, since this is audio and loud=good for most people we rearrange what we are looking for to how big of a port do I need to be able to push/pull this air at full power without making it 'ugly'. For our case when finding the area needed for a vent for a ported enclosure we need to know a couple of variables. The amount of surface area from the speakers being used. The Xmax of the speakers in use. Last we need to know what tuning frequency is being sought after. If it wasn't almost midnight I would write more but what it'll end up being after me explaining much math is to use this calculator to find a number close enough. http://www.carstereo.com/help/Articles.cfm?id=31 Now to readdress the surface area variable that I mentioned at the beginning of the post. Surface area does play a factor in how much cross-sectional area is needed. An ideal port will have the least amount of surface area as possible to lower he affect of boundary layer -the affect of surface area slowing down/otherwise deteriorating airspeed in a determined direction-. If you have a real skinny port with a large height you will have a large amount of surface area. The closer you get to a 1:1 ration of length vs height the less surface area you will have and the only way to have less than a 1:1 ration is to have a circular port. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
Met Posted March 12, 2015 Author Report Share Posted March 12, 2015 For a fluid to flow properly through a vent, the vent must contain the necessary amount of area, not surface area -even though that will play a factor in area needed *explained at end of post-. Think of sucking up water in a straw then spewing it out. If you do it slow the water stays together. If you do it fast it spreads apart and becomes 'ugly'. This is because the speed of the water through the straw was much to fast for how small the straw is. If you tried the same thing with the same water but you were trying to blow it out of something with as much cross-sectional area as a cup or something else large, the water would once again just kind of spill out no matter how hard you blow. When relating this back to box designing, you need to account for the amount of air being pushed/pulled and how fast. You want to keep the speed of the air down to a speed that won't cause the air to become 'ugly' like the water in the straw. However, since this is audio and loud=good for most people we rearrange what we are looking for to how big of a port do I need to be able to push/pull this air at full power without making it 'ugly'. For our case when finding the area needed for a vent for a ported enclosure we need to know a couple of variables. The amount of surface area from the speakers being used. The Xmax of the speakers in use. Last we need to know what tuning frequency is being sought after. If it wasn't almost midnight I would write more but what it'll end up being after me explaining much math is to use this calculator to find a number close enough. http://www.carstereo.com/help/Articles.cfm?id=31 Now to readdress the surface area variable that I mentioned at the beginning of the post. Surface area does play a factor in how much cross-sectional area is needed. An ideal port will have the least amount of surface area as possible to lower he affect of boundary layer -the affect of surface area slowing down/otherwise deteriorating airspeed in a determined direction-. If you have a real skinny port with a large height you will have a large amount of surface area. The closer you get to a 1:1 ration of length vs height the less surface area you will have and the only way to have less than a 1:1 ration is to have a circular port. Thanks for the info, I understand port area a lot better. Using the calc you linked, I got this: Drivers:2 (15in) Xmax:23 (DC level 3 = 23mm Xmax) Tuning: 34hz Min diameter: 14.4 Min area: 162.79 I have ~50in total. So I need 162in? I'm wayyyy off. And as far as the diameter, how do you calculate the minimum diameter when using multiple ports? I have a total of 5 PSP "4 ports @ 17in length .. adding the fifth port requires more length than I have. I would need to order more extensions if so, and I would definitely need to brace the ports I'm sure. Link to comment Share on other sites More sharing options...
Met Posted March 12, 2015 Author Report Share Posted March 12, 2015 Also, when I calculate the port length, I get a different outcome than PSP's calc. PSP: 17in @ 6.24cuft = ~33.8 hz Carstereo: 15.85 @ 6.24 = 34hz The PSP port is 18in total, but 17 usable. (I measure the port myself, it's slightly under 17, about 16.7. I can adjust this I think with the cup link) I don't know which calc to believe at this point haha Link to comment Share on other sites More sharing options...
Krakin Posted March 12, 2015 Report Share Posted March 12, 2015 I believe that psp account for their extended port attachments only now. I believe the carstereo sites is accurate, but to be absolutely sure I would download WinISD and use that. WinISD will also tell you the air velocity through the port so you can see the affect that different areas have. You figure out the affect of multiple aeroports by just summing up the areas of each one. I suggest using the same radius for each port. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
Met Posted March 12, 2015 Author Report Share Posted March 12, 2015 I believe that psp account for their extended port attachments only now. I believe the carstereo sites is accurate, but to be absolutely sure I would download WinISD and use that. WinISD will also tell you the air velocity through the port so you can see the affect that different areas have. You figure out the affect of multiple aeroports by just summing up the areas of each one. I suggest using the same radius for each port. I completely forgot the PSP calc is for the total length. So I have 6.24cuft @ 33hz, with a total length of 18in. As far as area goes, according to carstero I would need 5 x 6in ports, or 3 x 8in ports O.o Is this correct? I'd have to make my own 8in ports, and The box would probably need to be taller so the subs have clearance. I have winISD, but I can never figure out how to use it correctly. They have a ton of parameters, and DC doesn't give all of the ones winISD asks for. I'm not sure if all of the patameters matter, as I think it calculates the other ones if you don't have a value .. but I wasn't sure how accurate that would be. Do you know of any read ups on winISD? I've looked and have never found anything really. Link to comment Share on other sites More sharing options...
Krakin Posted March 12, 2015 Report Share Posted March 12, 2015 When entering parameters on WinISD don't change any that the program predicts. Also, since we are in car audio you don't have your box in a direct line to see you. This makes it hard to hear negative effects of a small port. This means you can cut off a little bit of the area and be okay. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
Met Posted March 13, 2015 Author Report Share Posted March 13, 2015 When entering parameters on WinISD don't change any that the program predicts. Also, since we are in car audio you don't have your box in a direct line to see you. This makes it hard to hear negative effects of a small port. This means you can cut off a little bit of the area and be okay. Awesome, I entered in what DC gives. It's awesome, I didn't realize it graphs your frequency response. According to winisd, I shouldn't have any port noise. I read to stay below .16 vent mach .. I'm at .02! With 4 x 17in ports, I should be sitting in between 33-34 hz. I'm gonna build it this weekend, pictures incoming! Link to comment Share on other sites More sharing options...
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