TL for a pair of 8's..... ?
... what program is that? I've always had to use the old fashioned (mathematical) trial and error....
10-18-2009, 12:17 PM
#14
500 Watt CAFz'r
Join Date: Jan 2008
Posts: 537
That copy of MathCAD is the oldest that will still run the work sheets. Fortunately it's free, but Martin's sheets are $25. Once you pay you can download them and save them on your hard drive. There are examples and a tutorial to help learn to use them. I rarely bother with the bottom half of the work sheets. They are only for baffle effects and I believe room effects.
10-18-2009, 12:23 PM
#15
Thanks man, I have no idea how your attaching these... 
Anyhow, would you happen to have a link to where I can buy the sheets? I'm going to be reading this for hours...
EDIT: SORRY JORDY!! Not trying to hijack your thread...
Anyhow, would you happen to have a link to where I can buy the sheets? I'm going to be reading this for hours... EDIT: SORRY JORDY!! Not trying to hijack your thread...
Last edited by DeadlySones; 10-18-2009 at 12:32 PM.
10-18-2009, 08:07 PM
#16
500 Watt CAFz'r
Join Date: Jan 2008
Posts: 537
Here is the Link to purchase a one year subscription to Martin King's work sheets ($25, scroll to bottom to pay). They are required along with MathCAD to simulate transmission line performance. There are also worksheets for other enclosure types including everything from sealed boxes to horns. Once he gives you the password you can download them to your hard drive (permanent). You can use them for ever as long as it's not for commercial gain. There is another membership for commercial use.
10-18-2009, 09:31 PM
#18
Here are some plots of different TL's using your woofer. The blue broken line is the response that would be expected if the woofer was in a sealed enclosure. The red line is the expected TL performance. The first plot is a tapered tube with the driver at the big end and the opening at the small end. The second is a mass-loaded type where the small end is closed off and a port is added. The mass loaded type will integrate with a midrange easier due to reduced ripple above 110Hz at the expense of a peaky bottom end. The tapered open ended line has a broader gain region but sacrifices the region above 110Hz to ripple. The performance of both these designs can be manipulated to reduce peaking and ripple but at the expense of size and efficiency. Currently they are both in the 60-70 inch length range and a little under a square foot cross section at the big end. The idea is to fold them of course.
For the first plot a LPF of about 100 Hz with a steep slope would be best. It would benefit from the dip immediately after the corner frequency and be well into the stop band before the response kicks back up at 200 Hz. For the second plot a more moderate slope would be fine with a corner frequency as high as 400 Hz. Obviously the closer to the first nasty ripple at 500 Hz, the steeper the slope should be.
The nice thing about a TL is the gain achieved at low frequency (10-15dB!). The problem is the cabinets tend to be very large, especially when getting into drivers 8" and larger. They are really best used to help out systems with small woofers since the cabinet will end up "normal" sized and they can still run with the bigger systems (at moderate power levels).
For the first plot a LPF of about 100 Hz with a steep slope would be best. It would benefit from the dip immediately after the corner frequency and be well into the stop band before the response kicks back up at 200 Hz. For the second plot a more moderate slope would be fine with a corner frequency as high as 400 Hz. Obviously the closer to the first nasty ripple at 500 Hz, the steeper the slope should be.
The nice thing about a TL is the gain achieved at low frequency (10-15dB!). The problem is the cabinets tend to be very large, especially when getting into drivers 8" and larger. They are really best used to help out systems with small woofers since the cabinet will end up "normal" sized and they can still run with the bigger systems (at moderate power levels).
10-19-2009, 03:53 PM
#19
500 Watt CAFz'r
Join Date: Jan 2008
Posts: 537
Seriously once you have the dimensions of the line you have to fit it to your space. You will likely want to fold them since a tapered line will end up a rectangle once folded back on itself. Where you fold it makes little difference. Here's an example of a folded mass-loaded line. The port intruding into the small end of the line is no big deal.Edit: forgot to mention I'm at work, I'll post the line dimensions when I get home.
Last edited by kevmurray; 10-19-2009 at 03:55 PM. Reason: goofed
10-19-2009, 08:31 PM
#20
500 Watt CAFz'r
Join Date: Jan 2008
Posts: 537
For the simple tapered line:
Length=78"
Big end area=132 sq in
Small end=18 sq in
Opening at the small end
Simplest design is 12 wide with 1.5 inch opening at the bottom (18sqin) and 11 inch deep at the top. Driver center is 12.5 inches down from the top. By moving the driver down the line a little I was able to quash the first peak at 200 Hz. The usual approach is to play with the MathCAD simulations for several weeks until happy with the cabinet size. This is a quick design based on my experience. If you spent more time with the simulations you would probably come up with a design more to your liking. I'll include the MathCAD parameters in case anyone would like to take this further...
Length=78"
Big end area=132 sq in
Small end=18 sq in
Opening at the small end
Simplest design is 12 wide with 1.5 inch opening at the bottom (18sqin) and 11 inch deep at the top. Driver center is 12.5 inches down from the top. By moving the driver down the line a little I was able to quash the first peak at 200 Hz. The usual approach is to play with the MathCAD simulations for several weeks until happy with the cabinet size. This is a quick design based on my experience. If you spent more time with the simulations you would probably come up with a design more to your liking. I'll include the MathCAD parameters in case anyone would like to take this further...
