user18436572 Posted November 20, 2014 Report Posted November 20, 2014 Pretty self explanatory. New here. Not to car audio, although compared to a lot of you guys, I could definitely be considered a n00b. Anyway, I am wanting to get back into it. I am good with Sketchup. I'm good with math. I have been playing with winisd. Seems pretty simple. I've just never actually designed my own ported box before. I've either had other people from forums do it for me, or used the box calculator on the RE website, which is very limited to one design style, and I'm not very confident in its accuracy. The only thing I'm really lacking here to really get the ball rolling on designing some legit enclosures is the fact that I have no idea what end correction is or how to use it. I watched a youtube video created by Mark at C.A.F. to teach myself how to use Sketchup, and he mentioned adding half the port width to the length of the port, which is what got the ball rolling in my head that I need to learn what this is and how to use it in order to design and create a properly tuned enclosure. Thanks in advance!
Krakin Posted November 20, 2014 Report Posted November 20, 2014 This is a quick little image that shows the values of some common end corrections. The commas are used as decimal points. Rough translations. 1. Tube, single flush. 2. Converted into channel. 3. Prolongs channel bottom from the ground. 4. Prolongs channel along both the ground and one sidewall. 5. Prolongs channel along both the ground and the sidewalls This is the formula if you want to use it. Lv=length of vent in centimeters Dv=diameter of vent in centimeters Vv=volume of enclosure in liters fb=tuning frequency in Hz Np=no. of vents k = correction factor For square port(s) sum up the total port area and convert to a circular port area. For rectangular ports with large ratios of width vs height there are other terms that are needed that I don't know of right now. Edited to make the formula more comprehensive. 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.
Krakin Posted November 20, 2014 Report Posted November 20, 2014 Bumping this because I edited the post 35 minutes after posting. 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.
user18436572 Posted November 20, 2014 Author Report Posted November 20, 2014 This might make more sense if I could read German. lol So, you actually are supposed to subtract end correction? Not add it? And are the values for K given in these drawings just examples or constant values depending on enclosure design? So...if it's a stand alone port sharing no walls with the rest of the enclosure, K=0.732? And if it shares one wall, K=1.23? And if it shares 2 walls in the corner, K=1.728? And if it shares 3 walls like most simple vented designs, K=2.227? These are constant values? What if the vent has to round a corner like an L as in many vented designs? Does that change the value of K, or is it still just 2.227?
Krakin Posted November 20, 2014 Report Posted November 20, 2014 This might make more sense if I could read German. lol So, you actually are supposed to subtract end correction? Not add it? And are the values for K given in these drawings just examples or constant values depending on enclosure design? So...if it's a stand alone port sharing no walls with the rest of the enclosure, K=0.732? And if it shares one wall, K=1.23? And if it shares 2 walls in the corner, K=1.728? And if it shares 3 walls like most simple vented designs, K=2.227? These are constant values? What if the vent has to round a corner like an L as in many vented designs? Does that change the value of K, or is it still just 2.227? I've continued to update that post, see if it has answered any of your questions. 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.
user18436572 Posted November 20, 2014 Author Report Posted November 20, 2014 Ahh, I didn't see the German to English translations. Okay. I'm pretty sure I understand. These ARE, in fact, constant values? And, I'm assuming it doesn't matter whether the port has a bend in it or not? Just tell me if I'm correct, so I know for sure. lol. One more question.... I remember reading somewhere a long time ago that if there is any type of flaring of the port, the usable length of the port ends at the point where the wall is no longer straight. Is this correct? And if so, let's say I am going to use a router bit to put a small rounded edge at the mouth of the port and around the inside end of the wall to remove the sharp corners. Let's say the rounded edge has a half inch radius. Do I need to add an inch of port length to compensate for my slight flaring on both ends?
Krakin Posted November 20, 2014 Report Posted November 20, 2014 I'm not sure as to the accuracy of the numbers or if they stay constant, however, I know I've seen the circular vent number multiple times, as I've not needed to know much of this since I avoid vented enclosures. As for the usable length of a flared port it is generally accepted to subtract half of the flare radius from the physical length to obtain the effective vent length. This holds true whether you only have a single end flared or both ends. This is a great site on flaring ports and ports in general. http://www.subwoofer-builder.com/port-flares.htm 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.
user18436572 Posted November 20, 2014 Author Report Posted November 20, 2014 Awesome, dude! Thanks so much! Now if someone could just confirm that these are definitely constant values, I can get down on some designs. I will definitely be giving that website a read. Probably tomorrow at some point. But for now, I must sleep. Thanks again!
Krakin Posted November 20, 2014 Report Posted November 20, 2014 I got the formula rearranged to find just the end correction factor. It does not appear to be constant as of a couple of practice examples. This is what one of my source sites says on the subject. The value for k, the end correction, can be fine-tuned by using the following values to derive the appropriate end correction figure for each end of the port, then adding them together Flanged End: 0.425 Free End: 0.307 e.g. if both ends were flanged, k = 0.425 + 0.425 = 0.850 if one flanged, one free, k = 0.425 + 0.307 = 0.732 if both ends were free, k = 0.307 + 0.307 = 0.614 Normally, k=0.732 is assumed 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.
Triticum Agricolam Posted November 20, 2014 Report Posted November 20, 2014 ... Now if someone could just confirm that these are definitely constant values, I can get down on some designs. ... So the values for K are constant. If you look back at Krakin's first post where he give the formula for port length based on volume, port area, and tuning you can see that the port is shortened by K multiplied by the round diameter of the port. So your larger area ports will get shorted a greater number of inches/cm and smaller area ports less. Since slot ports aren't round you have to figure out what diameter a round port of equivalent port area would be and then plug that number into the formula. I have a spreadsheet that I've put all the formulas into to make this easier, I can link it if you are interested. One of the short comings of WinISD is it only allows you to choose between end correction values of .614, .732, and .850. Its still a very useful program though and I use it often. In my own work I use the formula Krakin listed and the one that JL audio has published. They both do the same thing and give almost the same answer. I can tell you from personal experience though that port length and tuning are not exact sciences. There are lots of other things that influence tuning that are not factored into the formulas. Where it really gets fun is when you start doing things like large kerfed port mouths. The good news is the formulas will generally get you close enough. If for some reason you really need to be right on pretty much your only option is to make your port long, test it, and then trim down until you get it where you want it to be. "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:
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