WinISD Vent way too long - Subwoofer for 1Dayton Audio TCP115

Beginner here... I'm trying to design a small subwoofer box for a 4" Dayton Audio TCP115-8 using WinISD. I added the speaker in the database and created different projects using this speaker, but the port length is absurdly long (0.6 meters, or 1.3 meters for two vents). What am I doing wrong?

Thank you for your time and patience.


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Not doing much wrong
Just happens with small boxes.

Slot ports are common.
Sharing 3 walls will shorten the port.
But allows 90 degree shape if needed.
Or as mentioned Passive radiator.
General rule thumb is radiator be 2x larger
than driver depending on weight and cone
travel needed.

Or use larger box/driver
6.5" or 8"
Thank you all for your valuable information. I was worried that the data I entered for the speaker was incorrect, causing WinISD to generate wrong dimensions.

After you confirmed that this is the "normal" behavior, I noticed that if I increase the volume of the enclosure, the vent length is reduced. I'll try to find a compromise between size, vent and response for a small under-seat subwoofer.

I chose this speaker because I saw it used in a 3D printed 7th order bass enclosure made by HexiBase on YouTube. My 3d printer footprint is not that large and I don't have the knowledge to mod or redesign that kind of enclosure to fit my small wood CNC (I don't even understand what "4, 6, 7th order" means.)
Also, I saw a Fiat 500 (2007) under-seat subwoofer that uses a 5" speaker in a plastic box and still delivers sufficient bass to complement the other speakers.

Again, many thanks!


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3D printed subwoofers are pretty fun. I have a thread over on Diyma where I 3D printed a midbass about ten years ago. I used a three inch woofer(!!!) and it hit about as hard as a 7" woofer in a door.

My hunch on why this was:

1) I used a bandpass box, and bandpass boxes can achieve higher output than a sealed or infinite baffle

2) By 3D printing, you can make the box really rigid, especially if you use walls with a fairly large diameter

3) Bandpass boxes can handle a lot of power because the enclosure reduces excursion, whereas an "infinite baffle" midbass has uncontrolled excursion

EDIT: I forgot one thing: bandpass boxes might work better for your application. Basically, you can move the vent of the box to the outside of the cabin. That was the main reason I went with bandpass over ported. The width of a car audio soundstage depends a lot on where the midbass is located, and in a bandpass box, the apparent source of the sound is the port itself. So with a bandpass box, you can put the port on the side of the box, maximizing stage width.

Also bandpass boxes don't require ports as long as ported boxes do. This is because a bandpass box can achieve the same response shape as a ported box, but the port itself is tuned to a higher frequency.
Consider it a Midbass not subwoofer.
Tuned around 55 to 60 Hz it is where accuracy ends
and unloading begins.

Subwoofer starts at 60 Hz not ends.

Pretty normal high Qts speaker designed for doors will do same thing.
no ports needed.

Doesnt matter if its 4th 6th 7th order.
60 Hz is 60 Hz
Only has possibility or slightly improving efficiency in a narrow bandwidth.
AKA one note wonders.

Typical car cabin 45 to 55 Hz
So midbass isn't to hard to get from cabin gain.