Help with a Dual SA8 box?

[SuperDaveTX 0]

I didnt think my post was that unclear.

My driver has an Xmax of 16.5mm with up to 24mm something possible or so. My box plan shows a cone excursion of 13.5mm.

So, I was curious if any part of the box design would affect the amount of cone excursion. I am using winISD and it is showing my 13.5 based on what I give it.

I will post my numbers later. gtg

[SuperDaveTX 0]

So this is what I have come up with:

Outside box dimensions 28x14x14.

Port 2 x 14 x 32 Tuned to 34Hz

Should yield internal free space ( port already subtracted ) of 2102 inches cubed = 1.78 ft cubed. - .1 for each sub => 1.6 ft cubed for .8 per sub.

velocity is around 19.5, cone excursion is about 13.5. SPL peak is 112 at 39 Hz

[NB50 206]

So this is what I have come up with:

Outside box dimensions 28x14x14.

Port 2 x 14 x 32 Tuned to 34Hz

Should yield internal free space ( port already subtracted ) of 2102 inches cubed = 1.78 ft cubed. - .1 for each sub => 1.6 ft cubed for .8 per sub.

velocity is around 19.5, cone excursion is about 13.5. SPL peak is 112 at 39 Hz

Are you doing a slot port?

[SuperDaveTX 0]

I guess. Basic L port. and I subtracted that volume from the volume of the box.

[NB50 206]

Your port can't be 14" H if your box is 14" H then.

[SuperDaveTX 0]

True.. port will be 12.5 x 2 x 28 Thanks for the catch!

So that makes my port velocity 21.5 m/sec. Is that still OK?

Recalculating volume shows total space is now 1.67 ft cubed total or .93 per sub.

Also, one question. By just shortening the port, I see that it increases the velocity of air. If I don't shorten the port, would that make the tune higher or lower? Using WinISD, I don't see how to let the tune change

Edited September 12, 2011 by SuperDaveTX

[duanebrow 6]

True.. port will be 12.5 x 2 x 28 Thanks for the catch!

So that makes my port velocity 21.5 m/sec. Is that still OK?

Recalculating volume shows total space is now 1.67 ft cubed total or .93 per sub.

Also, one question. By just shortening the port, I see that it increases the velocity of air. If I don't shorten the port, would that make the tune higher or lower? Using WinISD, I don't see how to let the tune change

Hi Dave,

The longer the port the lower the tuning. The bigger the port the longer it will need to be to tuned the same. Select the "box" tab and you can change tuning to what ever you want. (you can use the arrow keys to change values once you click on it.)

You can also open up a second project using the same drivers. then play with that to see what is changing. (you will want to change the color of the plot line in the "plot" tab)

Port velocity should be kept under 17 m/s if possible. This often results in very long ports that are not practical. 21 is still very good. I'd try rounding over the edges of the port to help eliminate port noise.

Dave - how much power did you model these at? I entered 800 for system power. I am seeing 30 m/s at 34hz.

Duane

[SuperDaveTX 0]

Hi Duane,

I used 400 watts. Remember I have two subs in this box. I guess I can increase the width of the vent to 2.25, but that will put my length back to 32" That would put velocity just over 19.

Edited September 12, 2011 by SuperDaveTX

[duanebrow 6]

Winisd uses system power. Or total power going to the box. I entered 800 figuring 400 to each. Because the box will be in the back port noise shouldn't be a big deal. Small boxes need longer ports than larger boxes to be tuned the same. It's a compromise. Use the biggest port you can make work. Point the Port away from the people in the car. Flare or roundover the port ends to help.

Edited September 12, 2011 by Duane

[SuperDaveTX 0]

Oh heck.. So I think that is another mistake I made. I only put in 400 watts where it really will be 400 x 2.