How large should be my port

Hi my friends! I am complete new into this hobby of building speaker boxes and after making a lot of research I still couldnt discover how to solve this question.

I have 2 speakers (125w RMS - Taramps 7driver HD 250S) which have a really really really nice sound (from low-high). I built a box with the following inner dimensions: 30 cm wide, 20 cm tall and 15 cm depth = 9 liters. The wood is 1cm thick however the front panel is not thick so I could easily cut the holes (it's 3mm and I will surely improve the thickness of the front wood in the coming days). Picture below:

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I know I should use a much larger box with these speakers, however I dont have any space left for the place where this box will be placed in my house.

My question is this: I already made a hole in the box with a diameter or 6cm to put the port. My question is: how long must be the tube that I will insert into this box in order to get a good low bass (30 hz? maybe 40?). You can see in the picture below I 3D printed a tube with 6cm diameter and 10cm long, but I still dont like the bass (it does not improve much when compared to have the box sealed).

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Useful link: https://www.tarampstore.com/taramps-hd-250s-rms-loudspeaker-pair/p

Suggested cabinet volumes and port dimensions for both the 5" and 6" versions of this driver are given in the pdf documents in the link.

You can not expect to obtain "good low bass" by randomly selecting a box volume and reflex tube dimensions.

The best results with your cabinet would probably be obtained by completely sealing it and filling it loosely with absorbent material, such as wool or synthetic pillow stuffing material.
 
P.S. For future reference, the pdf documents give the suggested cabinet volume and port dimensions for one driver.

For two drivers in the same cabinet, you would double the suggested cabinet volume and use two ports.
 
My friend @Galu thanks for your attention. So I will seal this box and remove the port since you said it's gonna be better. But I would like to ask you one thing: in the link you provided (directly from the Taramps website) I cant find the recommended enclosure volume. I just found the volume occupied by the speaker itself (0.4 Liters). Could you please tell me where is the recommened volume of the enclosure, please?