mods and alternatives for the P-CUBE subwoofer

remix.

This is not really a remix of the original P-CUBE, I'd rather call it mods and/or alternatives. The original design is great and works flawless as-is.

For the alternatives, I just didn't like the look of the Louvers, I'm probably broken by the whole covid pandemic but it gave me flashbacks of air-purifiers; I wanted to make it a bit different, also try something that is new to me, so I went with replaceable "windows" that are driven by the design of infill shapes.
Mod-wise, I have two things to add -

• in his original design, Paul Carmody planned with a 9"port, which translates to 228,6mm. By default, the P-CUBE sub has a port of 229mm - close enough of course, but the issue is with the flaring. The general consensus is that only half of the flaring is to be calculated into the effective length of the port, from my measurements that means it's effectively 18mm too short. Fortunately that is an easy fix, I just made the Port center section 20mm longer; this could also be just scaled in the slicer
• the reason for the additional 2mm is because I also wanted to use a different driver than the Tang Band.

drivers.

The Tang Band W5-1138SMF is a great little driver, no doubt about that. By pure accident, I discovered the Omnes Audio SW 5.01. Just comparing the TSP, it's ridiculous how much these two drivers are alike; to remove any doubt of the heritage though, they even said they had the TB as "role model" for this driver. Some even favour its "better" Qts value, but in the end they are very similar. For better or worse: it's just as terribly inefficient has the Tang Band as well :)
I attached a WinISD simulation comparing the drivers (with and without correction of the port length) - looking at the Transfer Function Magnitude the TB seems to go lower, however in the (IMO more important) SPL viewer we can see that the Omnes Audio goes even a bit deeper. With the additional 20mm longer port, we get an F3 of roughly 3Hz deeper sound - it's not much, but it's free :) we get a tad faster air velocity on the Omnes, but I don't feel like these subs are meant for very high volumes anyway.
Anyhow, an even more important reason is that the Omnes Audio is nearly half the price of the Tang Band (at least in my location), making it an interesting choice to save some money. Arguably though, the Omnes Audio is not as nice looking as the Tang Band, being not round and all - which gets mitigated by rear-mounting it.
As I wanted to build Paul Carmodys Isetta, I needed a 2nd Tang Band driver. Now having found the Omnes Audio, I can replace the TB inside the P-CUBE and use it for the new project now - as looks don't matter in the P-CUBE (I can't see the driver after all) and do matter a lot in the Isetta where rear-mounting is tricky.
The Omnes Audio SW 5.01 is a great way to make an already great and, relatively speaking, cheap subwoofer even more affordable (and a hair deeper).

mods.

The center port section is as easy as it can be - just print it and put it between the port tubes. The grip on the printed threads won't be ideal anymore, so make sure that the port joiner is properly centered between the two. I use a few strips of tape to make it a bit more secure.

Using the baffle for the Omnes Audio driver is also as easy as it can get, only difference to the original Tang Band driver is that it gets attached from the bottom (which shows the single downside during construction: you can't install the driver last). We don't need Blu Tack or similar, we use foam which is already installed on the speaker. Just install four M4 lock nuts on the top (for constructions like this, I find common nuts much more stable than heat inserts), screw on the driver with four 16mm M4 screws and you are golden. The screws should stick out just a tad, that way the driver is pressed firmly and the nylon inserts have enough grip. The rest is just the same as the the original baffle (just that you need four heat inserts less, the ones that were used for the driver).

alternative.

The Louver-alternative consists of three main parts: the columns, the windows, the accent lines. For a complete construction (top and bottom), you will need to print

• 4x the accent line
• 8x the column
• 8x the window

The accent line is just meant to close a gap in the design, I find that visually more appealing. It is meant to be printed in a contrast colour - or you do it like me, just (spray) painting it.

The column has two little openings for M3 nuts (regular or quadratic), as the main-hole to attach it to the body was so close that a heat insert would not have had enough grip (I dislike the original idea of screwing into the plastic, but that just be my bad experience with that kinda connection); I found that using only one screw works also well enough, but as I wanted to alter as few items as possible I kept the two-screw-design.

The window is the only part that is "tricky". When slicing, the idea is to deactivate top- and bottom-layers, raise the wall number to 5 or 6, leaving effectively only your infill-pattern inside. I used Gyroid infill, around 10-12%, but you really have to play around with what you like visually. You can also rotate the window on the bed to adjust the orientation of the pattern. To give it a thicker look, I used an infill line multiplier of 2. I wouldn't make the window too dense as this could lead to chuffing noises. You could also deactivate the infill completely and glueing something in, like some foam; or you wrap the window in some acoustic cloth to get a modern look (in that case, the window would need to be scaled down a bit to account for the thickness).
Or you ignore the windows completely and leave it open, if you prefer that look. Make it yours!

Assembly is quite easy and is the same for top and bottom of the P-CUBE. You put on the accent line first, then screw in the columns; this sandwiches the accent line well. Put in the windows (you won't be able to adjust it later, so make sure the orientation is fine!). Right now it could seem that they sit losely, this will likely change once you top it off - so do just that, either with the end plate or end plate with port guide, depending if you do top or bottom. I had best success to install screws in the columns that are diagonally opposite to each other, sometimes needing to push one column towards the other a bit. If the windows have some play after you installed the end plate, something during the print might have gone wrong. In that case, you can disassemble it again and stack some tape on the edges that grip into the columns, to make it a bit thicker. Something like Blu Tack (or any other plasticine) could help too. After that's checked and you screwed all colums tight, install a 2nd accent line and top it off with the original end plate trim to sandwich it tight.

You might think that having so many single, now screwed down parts on a subwoofer lead to a lot of rattle. And I was afraid of that too. However, in the normal volumes where I see this subwoofer playing, I couldn't hear any rattle. Hell, even at the high volumes I tried out I only heard other parts of the appartement rattle around - so I'm quite confident with this.

BOM.

When you do all of my modifications, the only differences compared to the original bill of materials for the P-CUBE is

• 4x M4 lock nuts (the ones with nylon insert)
• 4x 16mm M4 screws
• 16x M3 nuts (regular or quadratic; effectively, I only use 8x though)
• also, you need 4x M3 heat inserts less, as well as the 4x M3 screws securing the driver

If you only do the Omnes Audio driver, you just need the M4 nuts and screws - if you only do the windows, it's just the M3 nuts. I strongly recommend nylon locking nuts for the driver: as it doesn't sit on top of the baffle and might rattle quite a bit (what else you need a sub for, huh :) ), there's a chance it "un-rattles" normal nuts over time; won't happen with the locking ones :)

printing advice.

All parts are oriented for their intended printing orientation - that means the new baffle needs minimal support for the screw holes and nuts. This is better than to get a rough surface on the recessed speaker section on the bottom, which is important to get a good seal. The columns don't need support, the minimal bridges will work on your printer :)
The driver baffle should be printed according to the original recommendations, with around 60% infill - I also recommend using five or six walls here. You can do the same with the columns, possibly reducing the infill a tad to 45% or so, but I wouldn't do lower. For the driver, I made some completely optional washers to not scratch its metal when installing the screws.
For the windows, read the section alternative.
The accent line and longer port section should both be printed with walls only, so you don't get any infill at all.

thanks.

They say "imitation is the sincerest form of flattery" - while I didn't immitate, didn't even alter exisiting files, and just build some new alternative parts for a terrific design, - I want say that this is indeed also just (my) form of flattery to honour the great effort that is the P-CUBE from zx82net. Paul Carmody designed a great subwoofer, but zx82net made it a slick, smartly designed printable version that has a small footprint and looks great as well as inconspicuous under my desk. So thanks, you two.

not really a remix, but mods and alternatives