Ultimax 18 down-vented sub - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 6 Old 05-24-2019, 03:46 PM - Thread Starter
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Ultimax 18 down-vented sub

I didn't see an on-going "help me with my sub design" thread, but feel free to merge this as necessary.

This design was inspired by the MiniMarty, but I wanted the port to be on the bottom of the box. Here's the current design:

Dayton Ultimax UM18-22
Two ports
Each port is 7-5/8" x 3" x 44-3/4"

I calculated the box volume as follows:
9.969 CF minus 1CF of bracing and 0.37 CF for the driver = 8.6 CF

WinISD puts the box tuning at just over 17 Hz.

The plan is to have a pair of them (hopefully front left and front right, but right and left rear are also options) driven by a Behringer NX6000D.

My question is - what am I missing before I start cutting MDF?
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Last edited by saf-t scissors; 05-24-2019 at 04:35 PM.
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post #2 of 6 Old 05-24-2019, 07:02 PM
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FWIW, my down firing Marty Cube has been doing great. Tonnes of tactile feel on suspended floor.
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Last edited by Zarkoff500; 07-18-2019 at 06:42 PM.
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post #3 of 6 Old 05-24-2019, 07:03 PM
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How tall are the feet?

The closer you place the port to a boundary (within the box itself, against a wall or floor) the longer it's effective length. Likely not an issue here as your feet look to be fairly tall, but if going for a specific tune something to consider.

Other than that, should be no problem.

Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

Speaker builds: DIYSG HTM-10 build | DIYSG Volt-6 build | DIYSG Fusion-8 builds
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post #4 of 6 Old 05-24-2019, 09:25 PM
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My feet are approximately three inches.
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post #5 of 6 Old 07-18-2019, 06:27 PM - Thread Starter
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I've been busy with other things and haven't started on this yet, but I recently went back and looked at a previous iteration, and now I'm wondering if it might be the better option. It's the same basic design, but with the following specs:

Dayton Ultimax UM18-22
Two ports
Each port is 7-5/8" x 3-1/2" x 44-3/4"

9.768 CF minus 1CF of bracing and 0.37 CF for the driver = 8.4 CF

WinISD says the box tuning is about 18.6 Hz. If you assume the feet are about 4" high, that might lower the tune closer to 18 Hz.

Any thoughts on this one vs the one in the first post?
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post #6 of 6 Old 07-18-2019, 06:36 PM
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What does port velocity look like in WinISD? If it's 25m/s or lower, and you have similar graphs as those in your earlier post, should be good to go.

I don't believe you'll see any change to tune with 4" feet.


ETA: If the port is going to be built like that in your first post, you can model it as a single port instead of 2.

Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

Speaker builds: DIYSG HTM-10 build | DIYSG Volt-6 build | DIYSG Fusion-8 builds
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