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Discussion Starter · #1 · (Edited)
Hey all, just moved into a new place with a pool and wanted to install a good sounding setup. In researching subwoofer options, decided to go the DIY route. Came across mark Henninger's "Sump Sub" which peaked my interest (very cool design mark!) Seems like a very affordable way to create a waterproof enclosure. Need some help with selecting port size/length. Plan to power with a Crown XLS 1502.

My Plan:
2 Sump basins
1 sump lid as outer baffle
1 plywood inner baffle in sealed portion to give the mounting screws something to bite.
1 15" Dayton HO

Home depot sells 2 sealed sump basins that look like they would work. A 17x16 at 2cf and an 18x22 with approx 3cf. Both are around $23-$27 each.

Planning a 4th order BP with 1:1 ratio for sealed and ported sides with the sub placed in the middle between the two basins and a PVC pipe protruding out the end or the top. I would use PL premium and silicone to seal the baffle to the sealed basin chamber. Once the sub was installed I would install the top chamber similar to how mark did in his design.

Now to my questions, I plan to use a single PVC pipe for the port. My vision is to bury the enclosure and have a single 4" pipe coming out with a 90 deg elbow and a 4" to 6" increaser as a flare at the end. Sort of periscope looking. Seems like most direct burial subs have mushroom caps on the top, I think I would prefer the directional periscope design so that I could direct the sound towards the pool area and away from my neighbor.

For the modeling: which cf should I shoot for in each basin? 2cf or 3cf? And what port length and size (3,4 or even 6" pvc) would be best?

I am also not stuck on the driver just seemed like a good option since it has an aluminum cone, would also be open to running a 12" or building a second 12" if sound quality was good but I need more output.

Thanks all!


2cf Sump Basin

3cf Sump basin
 

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I would recommend aiming for a tuning at or above 30hz as anything lower will be rather difficult to hear in an outdoor hemi-anechoic environment or a large indoor pool room.
It also keeps the port length and size to reasonable dimensions that have a hope of fitting in the box.

As for what dimensions to use, plop the driver values and box volume into winISD and let it calculate it for you. It can be a square box as long as it has the same enclosed volume. (There are online calculators for cylinder volume vs cube volume.) i.e. h*pi*r^2 vs w*d*h (inside dimensions)
 

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I haven't modeled that driver for a 4th order BP, but pointing your port at you isn't going to give you any directivity. It may as well point at the house across the street, at a neighbor or the sky. Low frequencies ( and a small radiator, a port ) are omnidirectional.

The only way you can get some slight directivity in your use case is to have your device outlet very close to a wall ( garage or house wall ) where the distance to the wall is under 1/8th wavelength at the highest frequency of interest. At 100 hz, this would be less than 17" at 16.95", preferably closer to maximize bandwidth.

Diameter of the port should be as large as practical to minimize self noise, length will dictated by manipulation of front and rear volumes and port tuning frequency when simulating.
 

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Discussion Starter · #5 ·
Thank you all for the insight and pointers! I made some tweaks in WinISD and think I found a viable option (also decided to go with the 15" Dayton HF (RSS390HF-4) since it models better in a BP enclosure vs. the HO. I'm new to using winISD. does my graph look reasonable?

Going with a 2 cf / 2 cf option tuned to 42hz as it seems to model a bit better in the > 50hz range vs. the bigger enclosure. I also like the idea of using the house for directivity. I have the perfect spot where my brick fireplace bumps out 2' from the foundation wall. I can get the port 12" from both walls.

And yes, re: critters. I plan to use a mesh screen on the end. Should I be concerned with humidity? My plan was to completely seal the front plastic baffle so only the rubber surround and aluminum cone would be exposed.

It also looks like i will need to go with a 6" pipe for the entire length. 4" with that tuning only left me with a 7" port which isn't quite enough to bury and then elbow 90 degrees above grade. The 6" gave me a longer vent with the added benefit of a lower port velocity.

Looks like the HF will be back in stock at the end of the month, will post pics of the assembly process.
3115061
 

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Depending on where you place it, mud and leaves too.
Also thermal stress: full summer sunlight vs cold winter nights. The expansion / contraction will add just as much wear as physical debris or humidity would.

Stainless steel mesh will easily keep the physical things out like bugs and small rocks and offer shade from UV rays.

UV rays will rot rubber or foam surrounds in no time.

Any humidity will cause black mold. House insulation has VB's for this very reason. The voicecoil will get warm/hot, and the outside air will be colder. Things could start sweating.

Worst-case: you just replace the driver I suppose.
 

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I'm sure that what you have modeled is going to be better than a commercially available product. Try and keep the outlet no more than a foot to 18" above the ground as well. I'd suggest picking up a small 2x4 foot size handi panel of baltic birch to mount the driver, it takes screws well and uses waterproof glue. I would not recommend using MDF or OSB for mounting the driver.

Regarding the wire connection, you can drill a hole in the sump and install a non-metallic cable entry bushing, basically a PVC pass through fitting before final assembly. I'd still utilize a secondary sealing method around the outside of the fitting and the cable, as a back up to the rubber gaskets for the cord and the body to the sump.

I'd suggest a good quality polyurethane sealant like Sikaflex-221 for sealing the cable entry bushing and cable. It's mechanically tougher than a silicone after curing and thick, non sagging during application. Sika lists it's elongation at 500% before failure.
 

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I should have mentioned to do a 'locate' on the property before digging, but this should by now be common sense.
 

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Discussion Starter · #10 ·
Ok, build is complete! I will write everything up with a how to at some point. This being my first build, I'm not entirely sure that it sounds as good as I would have hoped. A little boomy. I set the LP on the Crown 1502 @ 85 hz and that seems to help.

The sealed baffle should be right around 2cf minus the sub displacement. The ported side i would guess is right around 1.95cf. I used a 6" vent at 17.75" long. About 2" is inside the basin and the rest potrudes out the top.

So before I bury this thing, wanted to make sure I tweak all I can hardware wise...

Questions:
Should I add any type of filler? Rockwool or similar? both sides or just the sealed? The ends seem to move quite a bit since there is no bracing which probably creates some unwanted noise. Thinking the dirt will keep this from happening once it is in the ground.

Should I be running this through some type of dsp? My current setup is a chromecast audio to a niles whole house amp, with a Y connector for the L side going to the crown amp. The sound seems to be a little 'off' like delayed from that playing through the mains. wasn't sure if I needed to do some correcting outside of just the LP filter from the amp.
3119657


3119654
 

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Looks good. You could put a small piece of rockwool in the sealed section if you so desire. Depending on how far the sub is away from your typical listening area and the other outdoor speakers, you may need to add delay so that they work well together.

If the sub is farther away from your intended listening area, you will likely need to delay your other speakers.
 
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