New box time!

William from NOLA · Post by **William from NOLA** » Mon Dec 06, 2004 1:32 pm

Ok, I'm going to start building a new box this wednesday (I hope). This box will be for competitions. I have a 4.5 cubic foot, slot ported (30 hz) box right now that I can hit 140.3 dB on. I want to create a new one to try to hit 145.

I'm planning on making a 6-7 cubic foot slot ported enclosure. I'm not sure what to tune it to. I'm thinking about 45 hz. I'm not quite sure how much port area I should try for either.

I'll post again later with my hatch area's dimensions.

Ryan from Ohio · Post by **Ryan from Ohio** » Mon Dec 06, 2004 1:45 pm

Make an adjustable port.

In other words make one wall moveable in length so you can change frequencies...

Changing ports at competitions at the last minute seems to be popular.

If its strictly for competition design it so you can tune from 50-70 Hz areas...

:s_thumbup

Justin from Detroit1 · Mon Dec 06, 2004 3:20 pm

Just use aeroports as they are considered better then slot ports. Make a few different ones so that you can change frequencies on the fly. Like Ryan said, go 50-70hZ for competitions.

William from NOLA · Post by **William from NOLA** » Mon Dec 06, 2004 10:39 pm

Aeroports would be cool. Right now I have a guy who has a termpro mic and is willing to help me along and find the best frequency and whatnot. This will be next week sometime. Should be interesting!

Ryan from Ohio · Post by **Ryan from Ohio** » Tue Dec 07, 2004 4:01 am

Did you compute the resonat frequency of your van?

I dont have the forumla handy, but its a good starting point.

William from NOLA · Post by **William from NOLA** » Tue Dec 07, 2004 10:18 am

No I didn't, I don' know what it is. I just used the USACi sine wave sweep.

William from NOLA · Post by **William from NOLA** » Wed Dec 15, 2004 10:46 pm

Okay, I went and had a date with a termlab mic. I hit 141.1 dB when I laid on the roof. Turns out it flexes a LOT. I also found out my resonant frequency is about 50 hz.

For my current box, I can do 42 hz sine waves and hit 140.x easy.

We used a W3v2 10" in a sealed box (prefab) to find the frequency of the van (did every frequency from 35-70). Then again with the sub out of the car in free air testing and compared the two numbers. The little 10 managed to hit 131 dB in the small sealed box with 300 wRMS.

Plans for the new box:
7.5 cubic foot
47 hz
~120" of port area

I'm going to double the wood on each side (two sheets of .75 on every side) and brace it.

This shall be loud!

William from NOLA · Post by **William from NOLA** » Wed Dec 15, 2004 10:54 pm

Here's an excel spreadsheet of the data:
Transfer Function Data

Ryan from Ohio · Post by **Ryan from Ohio** » Thu Dec 16, 2004 4:27 am

double the wood on the sub mounting face aswell.

Liquid nail the boards together.... Screw together let cure.

Then cut it all apart...

Take pics also...

William from NOLA · Post by **William from NOLA** » Tue Dec 21, 2004 11:38 am

Mmmkay... finally got around to making the calculations. Think 189.75 cubic inches of port area is too much?

Box dimensions and calculations:
--Exterior Box--
Depth: 24"
Width: 36"
Height: 22"
Wood thickness: 1.5" (two .75" MDF boards)

--Volumes--
Before driver: 7.62 cubic feet
Driver displacement: 0.18 cubic feet
After driver: 7.44 cubic feet

--Port--
Height: 5.5"
Width: 34.5"
Length: 2.49"
Tuning ~47 hz
Port area: 189.75 square inches