Converting 2 rear round ports to 1 front slotted port - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 8 Old 05-15-2019, 04:52 AM - Thread Starter
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Converting 2 rear round ports to 1 front slotted port

Howdy,



I recently just purchased 3 Helix Dome MTM's from DIYSG. I would like to convert the 2 rear round ports to a single front slotted port located at the bottom of the cabinet. The kit comes with (2) 2" diameter round ports that have the option to be telescoped. I am just assuming they are 5-6" in length when not telescoped based on the pictures from the website.



My thought was to just calculate the area of the 2" round holes and convert that area to slotted. The surface are of a 2" dia. circle is 3.1416 in^3, multiplied X 2 gives me roughly 6.3 in^3 total area. Convert that to a rectangle that is 9.5" wide (width of front baffle) and you end up with a rectangle that is 9.5" wide by roughly 0.66" tall. Then I figured I could just match the port length that is given at roughly 5-6" long. I would be rounding (fillet) the front of the port opening.



I want to front port them because my speaker placement seems to work better with front ported speakers. I have had 2 different sets in the past, first was rear ported and they were pretty boomy sounding and next I had a pair of front ported speakers and they sounded great in the same location. I would prefer to front port these based on those previous experiences.



Does anyone have any experience with this and could possibly help me out and tell me if I am doing this correctly?



Would really appreciate it.
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post #2 of 8 Old 05-15-2019, 10:11 PM
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Maybe just put the round ports on the top? If you're building to the same dimensions as the flat-pack, I'd think you'd have plenty of depth for them to run vertically behind the top midrange driver.

As to re-calculating the port size, just use WinISD... you don't need any driver info since box tune is purely a function of volume and port dimensions. Using the flat-packs internal dimensions and estimating a tune around 40hz (2x2" round ports at 6" long), I came up with a 9.5" x .66" slot port at ~5.4" long. Looking at the baffle, which I'm fairly certain is outset, I'm not sure you'd have enough height to work with... maybe just enough if you used 1/2" mdf for the top half of the port. You'll just need to dry-fit and measure when the baffle/drivers arrive to see.

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post #3 of 8 Old 05-16-2019, 09:10 AM
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How does this relate to a Transmission Line speaker. I believe there an actual path. The port is not just open to the speaker's interior. I sure more calculations are involved.
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post #4 of 8 Old 05-16-2019, 02:53 PM
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Quote:
Originally Posted by Rickreagan120 View Post
Howdy,



I recently just purchased 3 Helix Dome MTM's from DIYSG. I would like to convert the 2 rear round ports to a single front slotted port located at the bottom of the cabinet. The kit comes with (2) 2" diameter round ports that have the option to be telescoped. I am just assuming they are 5-6" in length when not telescoped based on the pictures from the website.



My thought was to just calculate the area of the 2" round holes and convert that area to slotted. The surface are of a 2" dia. circle is 3.1416 in^3, multiplied X 2 gives me roughly 6.3 in^3 total area. Convert that to a rectangle that is 9.5" wide (width of front baffle) and you end up with a rectangle that is 9.5" wide by roughly 0.66" tall. Then I figured I could just match the port length that is given at roughly 5-6" long. I would be rounding (fillet) the front of the port opening.



I want to front port them because my speaker placement seems to work better with front ported speakers. I have had 2 different sets in the past, first was rear ported and they were pretty boomy sounding and next I had a pair of front ported speakers and they sounded great in the same location. I would prefer to front port these based on those previous experiences.



Does anyone have any experience with this and could possibly help me out and tell me if I am doing this correctly?



Would really appreciate it.

Here are my rear ported c-notes converted to front slot port. I used all of the pre-cut parts but made a new front baffle and back panel. The first picture is the bottom of the slot port painted black. The middle (green) pic shows how to create the slot port internally and the last pic is the final product. Parts Express put them in the tech gallery so you can see the build there.
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Last edited by eriksells916; 05-16-2019 at 02:57 PM.
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post #5 of 8 Old 05-16-2019, 03:51 PM
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post #6 of 8 Old 05-23-2019, 04:53 AM - Thread Starter
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I ended up finding a couple different port calculators in the app store and found about what my slotted port needed to be according to the app. I ended up with a slot port of roughly . 625" tall and 6" deep. The calculator said it would tune my box to roughly 40 hz which is around what the speaker is tuned for. I understand that it's probably not perfect but I'm no speaker designer and just wanted to hopefully get it as close as possible to what I needed. Thx for the help. I have 2 of my 3 boxes glued up. I need to get the last one finished so I can start routing the edges and finish them. On mobile, hope these pics go through. I think they're gonna be pretty slick. Gonna chamfer all the edges.
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post #7 of 8 Old 05-24-2019, 06:15 AM - Thread Starter
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Quote:
Originally Posted by eriksells916 View Post


Here are my rear ported c-notes converted to front slot port. I used all of the pre-cut parts but made a new front baffle and back panel. The first picture is the bottom of the slot port painted black. The middle (green) pic shows how to create the slot port internally and the last pic is the final product. Parts Express put them in the tech gallery so you can see the build there.
How did you go about calculating your port length and height?
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post #8 of 8 Old 05-24-2019, 11:36 AM
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Quote:
Originally Posted by Rickreagan120 View Post
How did you go about calculating your port length and height?
Those look great, nice job.

I used the 12 volt site on my sub and then compared it to winisd and it was within .25in so I believe this tool to be the most accurate I have seen. https://www.the12volt.com/caraudio/boxcalcs.asp#porsq
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