DLHgn Posted December 1, 2015 Author Report Share Posted December 1, 2015 Ok, I will dabble with those equations after I get back from class (yay, more pointless classes that I have to take!). I want to know the how and the why because you can't know what you're doing until you actually know why it is the way it is. If I just asked you what dimensions to make the port and box for what ever sub I wanted, 1.) I wouldn't get the satisfaction of saying yeah, I designed this box and 2.) If I ever wanted to make another enclosure (which I most likely will) I would have to come on here again and ask someone to hold my hand again whereas learning what is actually going on and trying to soak up as much knowledge as possible, someone only has to hold my hand through it once. Plus, I like learning so it's no big deal for me Link to comment Share on other sites More sharing options...
DLHgn Posted December 2, 2015 Author Report Share Posted December 2, 2015 Ok so, for the first equation I got 52.59 inches for the length of the port. This was using the end correction of h/2 (1.25) at the website told me to use. For the second equation I got 40.97 using 2.227 for k. Do you average these two (~46.2) or what? Did I do something wrong? I just to be able to get this squared away and under my belt so I can do this on my own in the future. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted December 4, 2015 Report Share Posted December 4, 2015 Ok so, for the first equation I got 52.59 inches for the length of the port. This was using the end correction of h/2 (1.25) at the website told me to use. For the second equation I got 40.97 using 2.227 for k. Do you average these two (~46.2) or what? Did I do something wrong? I just to be able to get this squared away and under my belt so I can do this on my own in the future. So I don't use the "h/2" end correction technique, I don't think it provides enough end correction and you will end up being tuned lower than you want. So with with the first equation, we provide box volume, desired tuning frequency, K, and port area and it gives up a port length. 40.97" is what I got as well, so you did that one right. For the second equation, I modified it so I could input any value of K I wanted. With that equation you input box volume, k, port area, and length and it gives you a tuning frequency. I then play with the length until I get the tuning frequency I want. In this case it came out at 43", so pretty close to the first equation. You could average the two out and go come up with 42". The reason I said 45" earlier is I was using a slightly lower value for k (1.917 I believe), which is just something I've learned to do from experience. Also I always put a significant flare on the ends of my ports, which slightly shortens their effective length, so I like to add an inch or so to compensate. Really though a couple inches of difference is only going to amount to less than one Hz of change in tuning frequency, so don't worry about it too much. "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...
DLHgn Posted December 4, 2015 Author Report Share Posted December 4, 2015 So lots of flare reduces the amount of effective length? So if I were to say kerf it, would that change the length of port that the driver feels? Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted December 4, 2015 Report Share Posted December 4, 2015 Yup, that's right. I do a lot of kerf ports and I figure 1/4 the radius of the kerf bend is subtracted from the length of the port. So with a 3" radius kerf bend, the port loses 3/4" of effective length. This is assuming a kerf bend on only one side of the port, if you used one on both sides you'd subtract 1/2 the radius. "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...
DLHgn Posted December 4, 2015 Author Report Share Posted December 4, 2015 Yup, that's right. I do a lot of kerf ports and I figure 1/4 the radius of the kerf bend is subtracted from the length of the port. So with a 3" radius kerf bend, the port loses 3/4" of effective length. This is assuming a kerf bend on only one side of the port, if you used one on both sides you'd subtract 1/2 the radius. Oh that's not too bad. I was figuring it would be more complicated. So lets say, for example, you have a port that is 30" long before kerfing. If you added a 4" radius kerf to one end, your port would now need to be 31" to keep the same tuning. If you had two kerfed sides with 4" radius(how would you say radius in plural?)would your new total length be 32"? I know you said a few inches doesn't REALLY make all that big of a difference but lets assume I needed to keep it at exactly 30" effective port length. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted December 4, 2015 Report Share Posted December 4, 2015 Yup, you got it. Usually I put some kind of flare on both the outside and inside ends of the port, if you do the same you will want to account for both with your port length. "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...
DLHgn Posted December 4, 2015 Author Report Share Posted December 4, 2015 Yup, you got it. Usually I put some kind of flare on both the outside and inside ends of the port, if you do the same you will want to account for both with your port length. What do you mean by flare on the inside? Do you have a picture example? Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted December 4, 2015 Report Share Posted December 4, 2015 Yup, you got it. Usually I put some kind of flare on both the outside and inside ends of the port, if you do the same you will want to account for both with your port length. "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...
DLHgn Posted December 5, 2015 Author Report Share Posted December 5, 2015 Yup, you got it. Usually I put some kind of flare on both the outside and inside ends of the port, if you do the same you will want to account for both with your port length. What? Link to comment Share on other sites More sharing options...
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