What's up guys, i emailed the technical support of BBP6 to ask them about the accuracy of their vent length (Lv) number and whether or not you can use this number in a regular slot (L-shape) port. Doing some comparisons, the vent length (for a square vent) of the BBP6's number is on average 3-4" longer than other vent length calculators (such as the12volt.com AND carstereo.com's). This is why i asked him this question, because the value they give you is always so much larger than other vent calculator's.
What I mainly wanted to know is how other people on this forum use BBP6 to calculate their vent lengths for slotted enclosures? do you just measure the port using the given (Lv) or what???
Here is the email from them:
BassBox Pro does not calculate slotted vents. Because a slotted vent uses one or more box walls as vent walls, the airflow becomes very complex and the mass of air that vibrates as part of the vent is difficult to predict (it would require calculations similar to advanced fluid dynamics which are beyond the scope of BassBox Pro). In fact, we are unaware of any speaker enclosure design program that attempts to accurately calculate the required length (or conversely, Fb) of a slotted vent. These kinds of vents are usually designed by building and testing prototypes and adjusting the vent length until the desired resonance (Fb) is achieved.
When one or more box walls are used as vent walls, the result is an increase in the air mass that resonates with the vent. In effect, the vent appears to be longer than it really is and this lowers Fb to a lower frequency. As mentioned above, this is difficult to calculate because it is very complex mathematically. So, how are these kinds of vents designed? Using BassBox Pro, you could design the vent as a standard rectangular vent as you started to do in your example with the understanding that the program will suggest a vent length (Lv) that is longer than you really need. You could think of it as a rough or "ballpark" estimate. Next, you would build a prototype of this box, mount a driver to it, and measure its impedance. The minima between the two resonance peaks of the impedance response will be the Fb or box resonance (see page 281 of the BassBox Pro User Manual). Shorten the vent length until the measured Fb equals the desired Fb. This is usually done by shortening the shelf piece of the slotted vent. (Naturally, this will not be possible if the required vent length becomes less than the box wall thickness. In this case you'll need to start over and either reduce the size of the vent opening or reduce the box volume---and either of these can mess up your design---this is the nature of vent design.)
What I mainly wanted to know is how other people on this forum use BBP6 to calculate their vent lengths for slotted enclosures? do you just measure the port using the given (Lv) or what???
Here is the email from them:
BassBox Pro does not calculate slotted vents. Because a slotted vent uses one or more box walls as vent walls, the airflow becomes very complex and the mass of air that vibrates as part of the vent is difficult to predict (it would require calculations similar to advanced fluid dynamics which are beyond the scope of BassBox Pro). In fact, we are unaware of any speaker enclosure design program that attempts to accurately calculate the required length (or conversely, Fb) of a slotted vent. These kinds of vents are usually designed by building and testing prototypes and adjusting the vent length until the desired resonance (Fb) is achieved.
When one or more box walls are used as vent walls, the result is an increase in the air mass that resonates with the vent. In effect, the vent appears to be longer than it really is and this lowers Fb to a lower frequency. As mentioned above, this is difficult to calculate because it is very complex mathematically. So, how are these kinds of vents designed? Using BassBox Pro, you could design the vent as a standard rectangular vent as you started to do in your example with the understanding that the program will suggest a vent length (Lv) that is longer than you really need. You could think of it as a rough or "ballpark" estimate. Next, you would build a prototype of this box, mount a driver to it, and measure its impedance. The minima between the two resonance peaks of the impedance response will be the Fb or box resonance (see page 281 of the BassBox Pro User Manual). Shorten the vent length until the measured Fb equals the desired Fb. This is usually done by shortening the shelf piece of the slotted vent. (Naturally, this will not be possible if the required vent length becomes less than the box wall thickness. In this case you'll need to start over and either reduce the size of the vent opening or reduce the box volume---and either of these can mess up your design---this is the nature of vent design.)
