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Triticum Agricolam

6th Order Port Area Experiment

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UPDATE 2/5/18:
The first set of impedance measurements are on page 2, post #17
The first set of SPL measurements are on on page 3, starting at post #28
The second set of impedance and SPL measurements are on page 4, post #40
My analysis and conclusions are on page 5, post #42.
 
The common practice with series-tuned 6th order bandpass enclosures has been to make the inner (rear) chamber port area small compared to the front chamber port. The reasons I've seen given for doing this range from "better cone control" to "wider bandwidth" to "it's just better".  I've always been skeptical that making the rear port so small is beneficial.  From a physics standpoint it doesn't make any sense to me, it seems like doing this would be very detrimental to low frequency output.  I've certainly been wrong plenty of times before though, and lots of people have built enclosures that way and have had good results. The purpose of this experiment is to see what effect changing the rear chamber port area has on performance. 
 
For this experiment I'll be using a Sundown SA-12 sub. I came up with a tentative design in HornResp. It has a 1.0 cu ft rear chamber tuned to 32 Hz and a 2.2 cu ft front chamber tuned to 64 Hz. All ports are going to be completely external and attached to the removable top panel so I can change their dimensions without changing the chamber volumes.  I'm going to have two port configurations to test. One will have a rear port with 6 sq in of port area, the other will have a rear port with 25 sq in of port area. The front port for both configurations will be 40 sq in. Here is my proposed design, this is the 6 sq in port config:
BP6-1.PNG.122d90563f0e6e52656e753c50ed0308.PNG
 
And this is the 25 sq in port config:
BP6-2.PNG.bd65681638e374eed98e313c7aa03ce5.PNG
I'm hoping to keep the tuning as close to the same a possible with both configurations,  won't know until I build it though. 
 
After the enclosure has been built I intend to test it by measuring the SPL output and impedance curve at various different power levels with both of the different port configurations. 
 
Thus far I haven't cut any wood yet. Before I do I would love to get people's input about what I intend to build and test. If there is anything I can do to make the test better or more relevant please let me know. 
Edited by Triticum Agricolam
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That's awesome Triticum! Seems higher powered parallel 6th's have issues with needing ALOT of port area and other nuances. Maby your idea will alleviate some of that. Fingers crossed lol. 

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Badass man, tuned in for data!

The low tuned 'jumper' port is a great novel idea. Although, knowing the velocity is going to already be high in that port, i would make extra sure that all transitions are extra smooth in that region. Im sure that level of detail was already in mind and just unnecessary to show in the model, but i figured its worth mentioning. 

EDIT: maybe a U-shaped PVC?

Edited by WalledSonic

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5 hours ago, WalledSonic said:

Badass man, tuned in for data!

The low tuned 'jumper' port is a great novel idea. Although, knowing the velocity is going to already be high in that port, i would make extra sure that all transitions are extra smooth in that region. Im sure that level of detail was already in mind and just unnecessary to show in the model, but i figured its worth mentioning. 

EDIT: maybe a U-shaped PVC?

I thought about using PVC, but its costs money and the small port is only just over 9" long.  That might be tough to do.  

For sure I'm going to round over all the edges well and I'll put 45s in the corners to try and let the air flow as smoothly as possible.  

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Tuned in. this is a really interesting test

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From fiddling around in hornresp I think a smallish inner port area is often required to create good efficiency, response, and displacement predictions. I have theorized that inner port loading and how it interacts with the other chamber is very important. It will be interesting to see the findings of the experiment. Your other thread on series 6th's was loaded with practical info, thank you for testing the theory.

 

I myself have a series 6th in the works for a first gen alpine type-r that I have laying around, might be some time till I can actually get to box building, have made some good designs, though.

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Got started on the test box.  I'm using OSB because its cheap, and I had a sheet lying around.  Its not pretty, but it is effective.  :-)

 

597d6fcfc6b02_2017-07-2922_06_00.jpg.2c46cc937dca9788ae3f6e7f225f4a2c.jpg

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2 hours ago, Triticum Agricolam said:

Got started on the test box.  I'm using OSB because its cheap, and I had a sheet lying around.  Its not pretty, but it is effective.  :-)

 

597d6fcfc6b02_2017-07-2922_06_00.jpg.2c46cc937dca9788ae3f6e7f225f4a2c.jpg

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