# A make shift ported box for a sub in way too small enclosure



## oabeieo (Feb 22, 2015)

if you are building a box and insist it be ported
Or if the sub simply models better and has more output with a port here’s a trick I’ve been doing lately and having absolutely fantastic results


1. Use winisd and load speaker parameters into winisd

2. Get your gross volume. It needs to be at least the size of a good sealed box for that driver for this to work. A QTC under .9 is kinda a must and a F3 at 50 or lower. (55 60 is the bleeding edge so pay attention to what your doing and understand the spirit of what we’re doing here)

3. Now open a new project and do the same box volume. You will have to ajust the box volume to be the net volume to account for port and sub displacement)

4. Select a tuning frequency for the ported box. Look at spl graph and tune above fs but as low as can to fit the port in the box. Find a tuning frequency between 25-40hz. Which ever gives the best extention on sub bass.
At some point you will start to tune lower and the spl graph won’t change that much. Stop and go higher if tuning too low. This takes some common sense. Not much music is below 30hz so if your tuning in the 20s your just wasting output from the port. Remember, your goal is to get more low end and deport bass than you would if went sealed, and need to just be able to fit port in box that’s all.

5. The proper size port for sub will probably be too long to fit in box. Here’s where my trick comes in. In winisd start to go with a smaller round port. For a 10” a 2”ID port is about max small and for a 12” a 2.5”ID port is about as small as I would go. If your box is too small for one of those , your sealed QTC is too high and or the sub your using probably needs to be IB maybe because QtS is too high so not ported is the best choice in that. In that case use the sealed box. This works with midQ and lowQ woofers. A small round port works great if port length is under about 18” so pick the right port size and tuning frequency. Don’t put bends in port of choose a very very long port. Keep it short and tune between 30-40 ideally. If tuning in 40s you will need some eq to control excursions below tuning. A subsonic filter will work also. But I hate the way they sound , eq works much nicer. 

6. So now you have a box and a port designed, your common sense has guided you the rest of the way through it. That small port will have a port velocity in the 3s or 4s at tuning. That’s okay. Build your box or port your sealed box that you have built that sucks and has barely any output. Lol

The next step You won’t gain enormous amounts of power handling at tuning because the sub will still have excursions at tuning, because it’s is still more on the sealed size vs ported. But excursions should still be less, just not ideal. But the trade off is still worth the added power. It will still gain power handling and lower excursions, it will not be like a normal ported alignment with optimum volume and post area.

7. Now stuff the port with sheet polyester polyfill or fiberglass. Start with a light stuffing and play a test tone that matches the tuning frequency. Stuff the port until port noise is mostly gone and you beginning to hear bass instead of wind. Once you put box back in car the loading effect from the car will load the port the rest of the way so it won’t make noise. Even if port fires somewhere that’s not a boundary. The wavelength is so large the car will still load and quiet the port down that last little bit (try it it works)

By stuffing the port your not changing the tuning frequency, your slowing down and restricting the air from passing through the port. Your trying to slow it down just enough so the amount of air in the port is equivalent to the amount of air that would be made from a much smaller sub in that same box. Perhaps a sub that that box size and port size is ideal. Like a 6.5” for a 10” or a 8 or 10” for a 12”, etc.

Now enjoy the added bass output from that pathetic underseat truck box that is way way too small for that sub you have loaded into it. It’s not leaps and bounds more bass , but it’s an improvement from what it was before. You probably won’t see 20-30s loud but you should definitely be enjoying the 40s (hz) that you simply didn’t have before.


Enjoy


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