Help building a ported box!

[Ketsueki]

I have a infinity kappa 10.1 driver and i was looking into building a ported box for it. I use it mostly for playing games and watching movies, but from time to time it gets some music use. However ive never built a ported box before, and i dont have a whole lot of money to spend on a port. I do have 2 4'x8' sheets of mdf and lots of glue and screws laying around so if it would be possible to use a slot port in place of round port? I have some decent wood working skills and im willing to try anything, i just dont know where to begin...

Any help or advice would be greatly appreciated!

 

[annunaki]

First you need to model the driver with the T/S parameters to get an idea of what the proper volume should be as well as response & tuning frequency.

Once you have that you then simply use some good old fashioned math. Use L x W x H (in inches)/1728 to come up with cubic footage or ft^3 with a rectangular prism that has the correct amount of internal volume for the the woofer, port, & bracing.

 

[jamie2112]

I would listen to Annunaki he just built an amazing sub......

 

[Ketsueki]

is there any advice you could give me on how to actually build the box, how much internal bracing i should use, where to place it, any thing in specific i should know about using a slot port?

 

[TLS Guy]

I have a infinity kappa 10.1 driver and i was looking into building a ported box for it. I use it mostly for playing games and watching movies, but from time to time it gets some music use. However ive never built a ported box before, and i dont have a whole lot of money to spend on a port. I do have 2 4'x8' sheets of mdf and lots of glue and screws laying around so if it would be possible to use a slot port in place of round port? I have some decent wood working skills and im willing to try anything, i just dont know where to begin...

Any help or advice would be greatly appreciated!

Here is a vented alignment for you Infinity Kappa 10.1 driver. It is a ported alignment with slot vent as you requested.

The box volume is 1.6 cu.ft. When you add the driver volume, bracing port volume and amp you will likely end up with a total internal box volume of around 2.2 to 2.5 cu.ft.

The slot vent is quite long for the cabinet volume, so you will have a few turns to make. Brace the cabinet well with boards with big openings dattoed in every 6 inches or so and the vertical and horizontal bracing inter locking.

Cover half the surfaces with sound absorbing material, such as Rockwool. Make sure there is material behind the driver.

 

[WmAx]

is there any advice you could give me on how to actually build the box, how much internal bracing i should use, where to place it, any thing in specific i should know about using a slot port?

Some simple cross bracing every 7 or 8", if using hardwood ply 3/4" material, is sufficient, to push panel resonances well over the band a subwoofer will operate within.

For the port, it is critical that you use the large cross section area possible, to minimize port output compression. But don't go so large that the port resonance goes below about 115-120Hz. But 115-120 Hz is fine if you are crossing this subwoofer at about 80-85Hz with a 4th order crossover slope. Some people may claim the port resonance may be an issue, but in reality, the Q(bandwidth) of this resonance will be so narrow, that it can not possibly be an audible issue(according to credible perceptual research on resonance audibility) at the actual SPL it will occur in relation to the main signal, when crossed as specified above.

You should use a broadband internal acoustic dampening material. Most people use worthless materials, such as 2" foam or some poly. While poly is fine for changing the tuning aspects of a cabinet, it is not very good at actually preventing acoustical reflection based resonances at the frequencies of interest. Use 4" of high density fiberglass or rockwool board(4-8lbs per cubic foot) on one side of the longest dimension, and directly behind the driver, and 2" elsewhere in the cabinet, if you want the most effective acoustical dampening mechanism.

-Chris

 

[annunaki]

Check out my build thread HERE to get some possible ideas. There are other build threads as well that you can get some good input from also.

 

[Ketsueki]

wow! do i really need THAT much internal bracing! also would fiber glass insulation work? how important is it to line the box with material? how does lining a box with material effect sq, and spl?

sorry for all the questions, thanks for helping me guys!

 

[TLS Guy]

wow! do i really need THAT much internal bracing! also would fiber glass insulation work? how important is it to line the box with material? how does lining a box with material effect sq, and spl?

sorry for all the questions, thanks for helping me guys!

Yes, you do need that kind of bracing, the internal pressures are enormous. You do not need to add the fill volume to the box volume, just the items I mentioned previously.

Fiber glass house insulation is not good. Half the internal surfaces should be covered with rockwool like product, especially behind the driver. Do not use excessive fill or you will "kill" the box.

You have fun project, now is the time to get your feet wet!

 

[WmAx]

You absolutely do not need that level of bracing for the normal operating band of a subwoofer. The only thing you need to do is use enough bracing to push panel resonances well past the bandwidth you use it within. If you cross your sub with a 4th oder crossover at 80Hz, you only need top push your panel resonances over about 120Hz; the signal will be attenuated enough by that point that the panel resonances will be of no audible consequence. To effect this, you only need to use a 3/4" hardwood plywood with basic cross bracing every 8 to 10" point. Quality plywood is far stronger than the common MDF material that is commonly used in speaker construction. The average price for a 13 ply 3/4" thick hardwood birch is about $50 per 4' x 8' sheet in my region. The ideal acoustical absorption material is a high density rockwool board or fiberglass board, as TLS guy specified. Use 4" in one side of the longest dimension parallel surfaces, and 4" thick immediately behind the driver, and 2" elsewhere. This assumes an average sized 2.5-4.5 cubic foot volume of average proportions. With significant dimension deviations or larger volumes, some adjustments should be made to the dampening to accommodate the circumstances.

-Chris

 

[Ketsueki]

so how would i go about making a port that long, would i simply have it go the full length along the bottom then up the backside then along the top? also, i subtract all the volume the port takes up from the 1.6 cu ft right? i think im going to have a 12 or 14" face on the box and just have the sides of the port be a part of the internal bracing. so as far as this rockwool material goes, where might i be able buy it?

 

[TLS Guy]

so how would i go about making a port that long, would i simply have it go the full length along the bottom then up the backside then along the top? also, i subtract all the volume the port takes up from the 1.6 cu ft right? i think im going to have a 12 or 14" face on the box and just have the sides of the port be a part of the internal bracing. so as far as this rockwool material goes, where might i be able buy it?

I would run the port tunnel around the sides, like you first suggested. The port volume needs to be added to the internal volume not subtracted. Vb is the volume of air that must load the speaker cone. Anything that takes away from the volume, like drivers, bracing, amps, and the port must be added back.

I would go to your local lumbar yard for help getting Rockwool products. Make sure you use gloves and mask while handling it. This usually means adding 15 to 20% to Vb to get Vt. (total internal volume)

 

[Ketsueki]

wouldnt the port be around the side if i layed the box on its side?, or do i need to specifically build the port a long a certain side?

 

[TLS Guy]

wouldnt the port be around the side if i layed the box on its side?, or do i need to specifically build the port a long a certain side?

No just wind it round the most convenient surfaces. Make sure it is the correct length and cross section. Smooth the turns with 45 pieces in the corner turns. Flare both ends.

 

[Ketsueki]

if i use one out the outside walls of the box as part of the port, i would just round off the exposed edge inside the box and leave the outside wall alone right? also back to the port, just to double check, i subtract all the wood used to make the port, and all the internal braces, and however the airspace inside of the port is considered to be a part of the internal volume and is not subtracted?

also how do i find the volume the drive takes up?

thanks again for helping me!

 

[TLS Guy]

if i use one out the outside walls of the box as part of the port, i would just round off the exposed edge inside the box and leave the outside wall alone right? also back to the port, just to double check, i subtract all the wood used to make the port, and all the internal braces, and however the airspace inside of the port is considered to be a part of the internal volume and is not subtracted?

also how do i find the volume the drive takes up?

thanks again for helping me!

I don't understand about using one on the outside walls. The port should be inside the box. Yes, it is the volume of the wood used to make the port you add back. You should flair both ends, that creates least turbulence. I calculated the port on the basis the ends would be flared.

For the volume of the driver you make an educated guess. I would just add 20% to Vb to account for the whole works. That will be close enough for speaker, braces port and amp. You could add what you can calculate, and add another couple of % for the driver volume.

 

[Ketsueki]

i have an external amp, and is what i mean by using an outside wall (i hope this isnt against the rules) http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/std_adp.php?p_faqid=26

the slot ported picture is what i was planning (but with internal bracing)

 

[TLS Guy]

i have an external amp, and is what i mean by using an outside wall (i hope this isnt against the rules) http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/std_adp.php?p_faqid=26

the slot ported picture is what i was planning (but with internal bracing)

Yes, you have it correct. That slot vent is internal. Just round the edges both ends, so there is not a sharp transition. Also in the corner is where you need the 45 to round the turn. You want to keep the cross section constant even in the turns. The length of the vent is measured down the middle of it.