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New Woofer Box & Circuit Designer 4.2
After the thread a couple weeks ago regarding the affect of stuffing ports I decided to modify my box model in the Woofer, Box, and Circuit Designer to include Qp for port losses. The basis for it was already in the program but I was using a constant for the value when it was in vented mode, simply becuase most standard ports do not change Qp enought to really matter.
The interesting thing about this Benson Box model is that I am using the same math table for vented, sealed, and passive radiator. The program just changes certain parameters when you switch modes. (Qmp of the passive radiator is the equivalent of Qp for ports). After I added the ability for the user to change to Qp as a variable I found the program could do some things I hadn't really considered. For example, if you lower Qp down to a value like 0.001, meaning nearly infinite port losses, the box model's results will match that of a sealed system, even in vented mode, without changing any of the other parameters. This makes sense, but I didn't anticipate that the program would do it on this alone. If you consider that a mass-load transmission line's terminus is generally stuffed creating a low Qa and low Qp, and you enter low values for these in vented mode, the impedance begins to look a lot like a TL (there is a tight relationship between vented and Transmission line anyway).
The program is fairly powerful now. I probably should have done this sooner, but that's the way development works. :rolleyes:
I also added some clarification to the pop-up comment boxes for the box Q's. Make sure you have comments activated in the Tools, Options, in Excel or you will miss the built-in User Guide. For the sake of further clarity I have added here the text from these guides:
For Ql: Ql is the Q at Fb due to box losses from leakage. As Ql approaches infinity losses will approach 0. A system with no leakage will have a Ql of about 50. Very small leaks will have a value of 30, small minor leaks will be about 20, and significant leaks will have values of 5-10. Normal values will range from 40 to 10, with 20-30 being a fairly typical system. Values in the range of 10 will represent many porous cabinets and cones, 5 will represent leakage like you would see when using an Aperiodic vent. Use these numbers as a guideline for adjusting these values.
For Qa: Qa is the Q at due to box losses from Absorption. As Qa approaches infinity losses will approach 0. High values >100 will represent very low losses. Normal values will range from 120 to about 5. As a guideline, an enclosure with no fill at all would have a Qa value of 120, a small amount of dacron in the box would bring it to about 100-80, walls covered with foam would be about 40, covered with thick fiberglass or a heavy damping pad would bring it to about 20. A fully stuffed box would be 5-10 depending on stuffing density.
For Qp: Qp is the Q at Fb due to frictional losses within the port. As Qp approaches infinity losses will approach 0. A straight port with one flush end will have a Qp of about 80. Two flush ends will be about 90. A port with one flared end will have a Qp of 120. Two flared ends will be 140. If a port is covered with grill cloth it could drop Qp to 60-70. If a port is filled or stuffed with damping material Qp could drop as low as 5-20. Use these numbers as a guideline for adjusting these values.
As always, make sure the Analysis Toolpaks are loaded in Excel through Tools, Add-ins. This is the answer to the most common question I receive.
Enjoy, I hope the program works out for you. (It is available at the link below).
Now, if I can figure out how to accurately model a full transmission line....
Jeff B.
The interesting thing about this Benson Box model is that I am using the same math table for vented, sealed, and passive radiator. The program just changes certain parameters when you switch modes. (Qmp of the passive radiator is the equivalent of Qp for ports). After I added the ability for the user to change to Qp as a variable I found the program could do some things I hadn't really considered. For example, if you lower Qp down to a value like 0.001, meaning nearly infinite port losses, the box model's results will match that of a sealed system, even in vented mode, without changing any of the other parameters. This makes sense, but I didn't anticipate that the program would do it on this alone. If you consider that a mass-load transmission line's terminus is generally stuffed creating a low Qa and low Qp, and you enter low values for these in vented mode, the impedance begins to look a lot like a TL (there is a tight relationship between vented and Transmission line anyway).
The program is fairly powerful now. I probably should have done this sooner, but that's the way development works. :rolleyes:
I also added some clarification to the pop-up comment boxes for the box Q's. Make sure you have comments activated in the Tools, Options, in Excel or you will miss the built-in User Guide. For the sake of further clarity I have added here the text from these guides:
For Ql: Ql is the Q at Fb due to box losses from leakage. As Ql approaches infinity losses will approach 0. A system with no leakage will have a Ql of about 50. Very small leaks will have a value of 30, small minor leaks will be about 20, and significant leaks will have values of 5-10. Normal values will range from 40 to 10, with 20-30 being a fairly typical system. Values in the range of 10 will represent many porous cabinets and cones, 5 will represent leakage like you would see when using an Aperiodic vent. Use these numbers as a guideline for adjusting these values.
For Qa: Qa is the Q at due to box losses from Absorption. As Qa approaches infinity losses will approach 0. High values >100 will represent very low losses. Normal values will range from 120 to about 5. As a guideline, an enclosure with no fill at all would have a Qa value of 120, a small amount of dacron in the box would bring it to about 100-80, walls covered with foam would be about 40, covered with thick fiberglass or a heavy damping pad would bring it to about 20. A fully stuffed box would be 5-10 depending on stuffing density.
For Qp: Qp is the Q at Fb due to frictional losses within the port. As Qp approaches infinity losses will approach 0. A straight port with one flush end will have a Qp of about 80. Two flush ends will be about 90. A port with one flared end will have a Qp of 120. Two flared ends will be 140. If a port is covered with grill cloth it could drop Qp to 60-70. If a port is filled or stuffed with damping material Qp could drop as low as 5-20. Use these numbers as a guideline for adjusting these values.
As always, make sure the Analysis Toolpaks are loaded in Excel through Tools, Add-ins. This is the answer to the most common question I receive.
Enjoy, I hope the program works out for you. (It is available at the link below).
Now, if I can figure out how to accurately model a full transmission line....
Jeff B.
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