When you are using WinISD go to the signal tab and change the input power to 1200 watts. Dan Wiggins adivsed to also change the series resitance but I can't remmber the number he recommends for the Brahma. Regardless we can get some good information once we change the signal power. Now go to cone excursion. This is the two way excursion so Xmax is about 56 mm. Look at what the sub does below the tuning frequency. You can also look at the max power tab. You are above max power at roughly 21.4 Hz and lower. This is the mechanical power limit with the box at 2.75 cubic feet and the sub tuned to 30 Hz. When the sub goes beyond the mechanical Xmag it breaks. Then finally look at group delay. At and below tuning group delay is too high. That is the slow sound of ported boxes. Hella loud, but after the rest of the music is done with the note. Per Dan Wiggins, "a good rule of thumb is less than 25 ms at 20 Hz). This is typically NOT a concern with sealed systems."
- http://adireaudio.com/tech_papers/sub_gd.htm
Apparently with the 30 Hz tune group delay is still acceptable, just no where close to sealed.

Lastly look at the "rear port air velocity." Above 17 m/s is audible. I am using a 4.5 inch by 5 inch rectangular port. In my box 15.5 inches tall the port is 4.5 inches tall and 5 inches wide. 15.5 inch box height minus o.75 inch wood thickness two times = 14.0 inch internal height. I wrap my port three times and use 0.5 inch baltic birch to seperate the sections of port. Now my middle section of port is only 4.0 inches height. This is acceptable, will give an advantage of lower tune for same port length and should not be audible. At the point that the port reaches the outside edge of the box it is flared to the full thickness of the wood giving an exit dimension of 6.0 inch X 6.5 inch. I will round this down slightly because the BB is not truly 3/4 inch thick but 18 mm instead. Also because it is better to have an idea that it won't work quite as well as planned. So for the port noise I will use the dimensions 5.75" X 6.25". Without the flare we have obvious port noise below 45.5 Hz. With the flare the clean low end is extended to 37.7 Hz. Now let's do two things. First lets change our tune to 28 Hz. Now our port noise is not audible until we get to 33.4 Hz. Now we also know that music is very dynamic and it is seldom at peak power of 1200 watts. So let's drop our signal to 600 watts and look at our port noise again, below 17 m/s all the way down to 20 Hz. Even acceptable with the 30 Hz tune.

I am going to guess you want to go with 28 Hz for your box. I will use the 4.5" X 5.0" port dimensions to calculate the length and then add 2.0" for the flared end. 26.1" vent length. I will try to draw this up today / tonight. and hope that this box that should be able to get in the 4th gen will also work in the 5th gen. I suggest getting some cardboard and making a box model to determine for certain that it will be able to get into the trunk as well as be able to fit where you want it. Figure about 15.5 - 16.0 inches tall, 21 inches deep, 30 - 34 inches long. We may have to crop a rear corner to clear a strut if we need the max width.

 

For free air break in use the wooden frame the driver was shipped within. Turn teh driver upside down and remove the free "doggie frisbee" from the back of the magnet. My dog loves those frisbee's!

Now if you have a home sub amp and a warble tone track on a CD use that to break it in. Otherwise you can use any amp stable to 4 ohms and use the tone generateor on WinISD. Or just don't worry about it at all, push the cone with your hands to near X-max a few times and put it in the enclosure. Pushing the cone down can help loosen a bit the initial suspension tightness. And D.W. uses the technique himself or I wouldn't mention it.

And send me an email in case I lost it!

j_grieve33@hotmail.com

 

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