okay so a friend asked me if its possible to just drill/make the ports afterwards out of his current sealed box. I told him no, cuz sealed and ported has different measurements and what not..who wins the $5?
You can place a port in your now sealed box. A simple hole saw and drill will do the trick nicely. Youll have to determine the net cubic air space. (net= space left after the subwofer is in) Then determine what tune frequency you want to port the subwoofer at. As far as space you can increase the space without building a new box simply by adding poly batting and glueing it to the walls of the enclosure. The basic rule of thumb is 1 inch thick gives about a 10 percent increase in box volume seen by the subwoofer. (2 inches max is what most usually use.) When you addim the batting into the equasion make sure you add that to your net box volume. To determine port width and length needed for a desired box volume and tune frequency of your subwoofer for a given power amount use (pvc tubing being the choice for your round ports) The only possible snafoo you could run into is port depth but there are ways around that. Also your ports will take up a little airspace.
Do not convert sealed box into vented. It doesn't have enough cu ft of space. Pollyfill will help somewhat, but only up to 10%. Take a look at vented box spec, it is almost 2x the volume of sealed. No matter how much you stuff it, you won't make up for the difference. Not only that, the vents are tuned to specific frequency. It has direct relation with the box's volume. If you just drill a hole, it'll sound like a $10 box/sub.
Well as far as the 2 x the volume comment isaac you broght up a good point but just because they recommend that it doesnt mean you have to use that amount of airspace. Also we dont know how large this sealed box is and with polyfill it could be large enough that placing fiberfill in will bring the box size to the right amount for a goosd sounding ported box Also heres a site showing test results that ive showed before showing that you could actually boost a box over 30 percent depending on the enclosure size.
ps...I cant find the site right now but ill look for it
Make a small box act like a larger one with polyester fiberfill by TOM NOUSAINE
The word "FIBER" is turning up in a lot of hip conversations these days -- you know, the ones that take place in art galleries, bistros, and install bays. In the galleries, they're talking about the fiber-optic conduits through which compressed digital audio and video will travel when the Intergalactic Superhighway concludes the long and winding road to our homes. In the bistros, they're talking about the colon-scrubbing glory of fiber-rich delicacies like oatmeal quesadillas and bran flan. But, to us -- the few, the proud, the mighty Box Builders -- fiber means dacron-polyester fiberfill, that magic and powerful ingredient that helps deliver maximum bass from a tiny space.
SEALED ENCLOSURE 1.4-ft3 Box
Stuffing Density (lb/ft3 )
System Resonance (Fsb)
Effective Size
Percentage Gain
0
56.6
1.4
--
0.70
53.0
1.6
14%
0.75
52.7
1.7
21%
1.50
51.7
1.8
29%
1.75
50.8
1.9
36%
2.60
50.4
1.6
14%
3.10
52.6
1.2
-14%
It's no secret that you can use fiber- fill to make low-end magic; clever installers have been using it for years Take two boxes of the same size and type, insert the same woofer into each one, and stuff one with some fiber-fill -- the one with the stuffing should kick out lower bass.
In simple terms, it works like this: The fiberfill fools the woofer into thinking that it's in a larger box (one with more air, or internal volume, in it). than it really is. And, in general, the larger the box, the lower the bass you can get out of it.
Fiberfill stuffing is a popular alternative for people who can't or don't want to allot a lot of space for a subwoofer box. A compound or Isobarik configuration, which pairs two woofers in one box, is another popular option, though it has some considerable downsides: For one thing, you have to buy two woofers. There is also a theoretical sensitivity loss (on the order of 6 dB) because you end up with twice the cone mass, though you can cut your losses -- losing only a few dB SPL -- by running a pair of the drivers in parallel.
SEALED ENCLOSURE 5.1-ft3 Box
Stuffing Density (lb/ft3 )
System Resonance (Fsb)
Effective Size
Percentage Gain
0
42.0
5.1
--
0.25
42.0
5.1
0%
0.50
41.2
5.8
14%
0.75
40.3
6.2
22%
1.00
39.4
6.5
27%
1.25
38.6
6.5
27%
1.50
40.2
5.6
9%
The particulars of fiber stuffing are pretty interesting: The air inside your enclosure actually heats up as your woofer moves, making the air stiffer. (I'm absolutely serious.) When the enclosure is stuffed with fiber, the fibers wiggle, dissipating some of the heat and making the system work as though the box were larger. Theoretically, your woofer/box bass system can act like a system that's a maximum of 40 percent larger when you've latched onto the right stuffing recipe -- in other words, if you have an enclosure that offers 1 cubic foot (1 ft³ ) of internal volume, in a perfect world a good stuffing job will make it perform like an enclosure that offers 1.4 cubic feet of internal volume.
There are three types of stuffing that are commonly used for this purpose: fiberglass insulation, long-fiber wool, and polyester fiberfill. Fiberfill is the best choice because it doesn't come loose and fly around and irritate your skin or lungs like fiberglass, it works as well as either of the others, it's a lot cheaper than wool, and moths hate it. I recently bought five 20-ounce bags of it at $1.99 a pop (a total of 6.26 pounds for $9.95) at Minnesota Fabrics; that turns out to be about $1.60 a pound. You should be able to find some at any fabric store or in the bedding section at friendly stores like K-Mart or Home Depot.
To evaluate the effectiveness of box stuffing, I used an MLSSA analyzer to measure the impedance of three enclosures -- 5.l-cubic-foot sealed, 1.4-cubic-foot sealed, and 1.4-cubic-foot ported (the port measured 3 inches in diameter and 6 inches in length) -- with various densities of stuffing. For the sealed boxes, I was able to determine the effective box size -- as enhanced by the stuffing -- using the system's resonant-frequency and Qes values. For the ported box, I compared the tuned frequency of the empty enclosure to the tuned frequency of the stuffed enclosure, using the Speak for Windows computer program; this enabled me to find the effective box size that fit the actual resonant frequency I'd measured.
PORTED ENCLOSURE 1.4-ft3 Box
Stuffing Density (lb/ft3 )
System Resonance (Fsb)
Effective Size
Percentage Gain
0
42.0
1.4
--
0.40
39.1
1.6
14%
0.85
37.2
1.8
29%
1.25
35.2
1.9
36%
1.40
34.2
2.0
43%
1.75
35.2
1.9
36%
In each case, the news was good -- make that very good. With all three boxes, I enjoyed roughly 25 to 35 percent of "space gain" by using stuffing at a rate of 1 to 1.75 pounds per cubic foot of internal volume.
When making system performance predictions, be aware that the Qes figure -- and, therefore, the Qts figure -- of the sealed boxes dropped. And with the ported box, the peak of the impedance curve on the lower side of the tuned frequency became heavily damped below the box's point of resonance. I also found that there is such a thing as too much of a good thing: System resonance (Fsb) rises again, beginning with densities of around 1.5 pounds of stuffing per cubic foot of box volume; this happens because the fibers are jammed so tightly together that they stop wiggling and, consequently, stop dissipating heat.
I also found that stuffing gets less effective as box size increases. The morale: The bigger your box is, the harder it is to fool your woofer.
A few rules of thumb: Stuff small enclosures -- those with up to about 3 cubic feet of internal volume or less -- with 1.5 pounds of fiberfill for each cubic foot of internal volume and you should get about a 30-percent increase in box volume without seriously affecting other performance variables. For larger enclosures, add stuffing at a rate of approximately 1 pound per cubic foot and you should get a virtual-space boost of about 25 percent. One thing's certain: You'll impress the heck out of your friends at the art gallery and bistro.
"In each case, the news was good -- make that very good. With all three boxes, I enjoyed roughly 25 to 35 percent of "space gain" by using stuffing at a rate of 1 to 1.75 pounds per cubic foot of internal volume."
Pollyfill for a sealed box works. However, for vented boxes, not very ideal since air gets pumped in and out. The pollyfill will fall apart over time and get blown into cabin space/trunk. This is why you hardly see vented boxes with any stuffings. The specs listed by the manufacturers are not mandatory, but for getting maximum efficiency and SQ, it is highly recommended.
the ideal volume between a sealed and ported box for the same sub usually differs by up to 50%, so generally speaking you can't just slap a port into a sealed box and have it sound decent.. you win.
tell your friend to just hop on ebay and order a prebuilt ported box for that size sub for $50. it's not that expensive for a prefab MDF box these days. $15-20 for the box, and add shipping
Recommended sealed enclosure: 1.0 Cu.Ft. - 1.3 Cu. Ft. Recommended ported enclosure: 2.0 Cu.Ft. - 2.72 Cu. Ft.
about 54 percent difference so at 35 percent increase in a sealed box you would be up to 1.755 cubic feet close enough to give it a try if the box was built larger than factory recommended sealed to start with
