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Shaped Ports


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  • 11 months later...

I liked this port so much I'm basically copying it for my 12TBX100 sub.  The height wasn't listed so I guessed it as 44mm from the pictures (3*18mm boards with 10mm of rebate).  Tuning came out at 38Hz.  How close did I get?

image.png

I'm also guessing from how your Hornresp response compares to mine that you used complex inductance parameters?

 

 

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I did use complex Le and my vent area are more than yours, even if you double the numbers to combine the two ports. I will PM you my HR inputs, but I usually manipulate the inputs there in a way to get results closer to real-world expectations.

My thoughts on the design after a while:

-I've used them at a few weddings and the performance was great. I have a sub-octaver on the cajon, which adds a nice 40-45Hz low end to the kick drum, which would be hardly achievable with run off the mill 12" PA designs tuned to 55Hz and what not.

-They can take a lot of power and I've never noticed port noise, but theres some early compression creeping in, which is just natural for a design this size

-The expansion of the port towards the outside is too much I think. It might cause separation (and turbulence) there, which could be remedied by an extra element to guide the air, but I'd maybe just make the expansion less logarithmic... I'm learning a bit from a youtube channel called Kyle Engineers, which is an ex-mercedes F1 engineer

-A bigger port gives you more performance of course, but the goal here was space-efficiency obviously, and it needed to be a one man setup which won't break my back.

The design is lacking a bit of punch compared to my 21ds115 cabs, but I guess that's only natural since those are front loaded and.. well 21"

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Thanks for the info! I had already designed a sub with just pipe ports to try and get something built quickly, however I needed to redesign it as my model would break on changing the material thickness parameter and it was overweight for the application (ultra portable human carried ~5km) resulting in a change from 18mm to 12mm (yes I know 12tbx100 is heavy, but I got them cheaply and this is the easiest thing to change).  But then I realized how much output at tune I was potentially giving up (JBL HLA port design information indicates around 9dB at tune).  In the future I would be interested in a even more port optimization but its a bit outside my area of expertise as I'm an electronic engineer and my only physics is in electromagnetics.   From the off the shelf options ( https://www.l-acoustics.com/en/product/ks28/# ) it looks like your on the right track.  If you wanted to try lots of port designs the best approach for testing would be to have a box that allowed attaching ports to the outside so that each test only required building the port and not a whole box.

Size is very constrained for these subs as they have to go on someones back and also fit under my desk at home.

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  • 2 months later...

Thanks for the paper, I've been looking for some more info the topic!

If you had access to a flow sim software, you could probably get some decent info out of that, even if it works with (non compressible) liquids.

 

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