Mini Earthquake - An 8" Cube of Bass
If you have been following me at all, you know I absolutely love the Tang Band W5-1138smf. It is an absolute masterpiece and a fine example of what a 5 1/4" driver should be capable of. This is the same subwoofer, that is getting national attention in the Dinas build. It isn't often you can tun a 5 1/4" subwoofer to have powerful bass down to 35hz. But what most people don't realize is that the W5-1138SM tunes almost identical, but has a much smaller neo motor and weighs much less. Yet it is just as powerful. It would be perfect for a small subwoofer that someone could use at a desk or for a bedroom.
However there is a problem with these subwoofers. They move a lot of air! And because of that it is hard not get them to chuff (create an unpleasant noise from the port). It definitely can be managed, but I really wanted to see if it was at all possible to create a smaller version with passive radiators.
If You aren't familiar, a passive radiator acts like a port, in that it tunes a speaker to a certain frequency. It differs in how it tunes. Instead of using a port, it uses what looks like a driver. But if you look at it closely, you will see there is no motor. Instead the motor is often replaced with some type of screw that you can attach weights to. This allows you to tune the subwoofer. By using these passive radiators, you will not get port noise. Unfortunately, finding passive radiators that work well with a particular subwoofer, is not easy to do. For now, I will skip on the why's. But instead, I will let you know that I was able to simulate some that should work well with the Tang Band W5-1138SM.
The Passive radiator that fit the bill was the Dayton Audio ND140-pr. In order for this to work correctly, it would need two of these passive radiators. And since passive radiators are tuned with both the size of the box and the amount of weight on them, I had to do some simulations. For this, I used WinISD. Now there were a few things I had to keep my eye on. The two main things were the excursion of the subwoofer and the excursion of the passive radiators. In order to simulate this, I had to input both the RMS and max power that subwoofer should use. Then had to check the excursion of both. On top of that, these will change based off the size of the box and the weight added to the passive radiator.
What you will see is that at tuning frequency and above there are no issues at RMS. The passive radiators do become problematic at max wattage just around 27hz to 43hz. And the subwoofer itself could use a second order high pass at 35hz. If using a computer this an easy fix with EQ. Of course, many people run subwoofers below their tuning frequency with no adverse issues. Just something to keep in mind. Now you are probably wondering why we haven't talked about tuning or frequency response yet. Let's take a look at it.
As you see, it doesn't tune as low as other W5 porjects, but it is significantly smaller. In fact, this subwoofer, is an 8" cube! It fits in the palm of your hand. It is incredible what it can do, in such a small enclosure. The response itself has an F3 of 50hz and has a rising bass extension centered at 80hz. This is a typical curve you find in a boombox style system. Perfect for music at a desk or small bedroom.
2 - ND140pr
1-Tang Band W5-1138SM
1 - Terminal Cup
Recommended Amplifier Options
Dayton 2.1 Desktop amplifier
How to Build it
It is literally an 8" cube. Here is the basic cutlist I used using 1/2" material..
Front and Rear Baffle
Top and Bottom
8" by 8"
8" by 7"
7" by 7"
I centered the Subwoofer on the front baffle and centered the cutouts for the passive radiators. For the Passive radiators, I did not like the look of their exterior basket. So I decided to mount them from the rear. For this I cut a 4 3/4" hole in each side to accommodate the nd140-pr. I also used a 3/8" roundover on them to make it look nice. However, I had to install these before it was all glued up. Once it is glued up, you cannot add the passive radiators. This also means, if you rear mount them, you cannot get them out without ruining the box. For this to be tuned properly, you need to install all the weight that came with each passive radiator (washers). Now to finish it off, you could add a 2.1 amplifier like this to the rear of the subwoofer or just make it passive by adding a terminal cup. Or if you want to use it with a desktop amplifier, you could try something like this.
Since I know someone will ask, yes I did use a small hand full of polyfill. This was only because everything is so tight in there. This prevented the wires from hitting against the subwoofer or the passive radiators. You could easily just glue the wires, but having the passive radiators already installed, it was hard to get back in there, so I just used the polyfill I had on hand.
There is no right or wrong way to finish this subwoofer. However, if you do rear mount the passive radiators like I did, make sure to apply some finish to the roundover before mounting the passive radiators. Once these are rear mounted, it will be very hard to finish this area. I like to use a furniture wax on something like this. You can always add more at anytime and it finishes quickly. You just rub it on and buff it out until you get the sheen and color you desire.
If any of your veneer gets scratched or chipped, you can make an easy fill using Timbermate products. I typically mix Cherry and Maple together until I get the color I am looking for. Once this is applied, you just quickly sand it off. It is also water based, so if you want to thin it, you just add water. I must admit, this stuff, when used correctly, will last you a very long time.
Can I use W5-1138SMF?
This is a good question. I actually had both on hand, so I easily could have used the W5-1138SMF...except for one issue. The W5-1138SMF's motor won't fit between the Passive radiators. So if you want to use the W5, you would need to modify the box. A double or triple front baffle should work. That would give you enough space to have the motor in front of the frame of the passive radiator.
I think it came out really nice and is really fun to listen to. If you try you can overpower it, but for the most part it is a really fun subwoofer, that I plan to enjoy having at my desk.
Any further questions, ask at the forum.
*These plans are free for personal use. These are not to be used commercially. If you want to use these commercially, contact me first.
Just for fun video. This is the beginning of Live Die Repeat. This is way below tuning frequency, but fun to see.
Yep that must be it, I was wondering if you made 2, then I saw your build thread and see it was repainted white. So I just need an SA100 amp, and I already have another "extra" subwoofer, still interested in the 8" one it just seems like such an awesome idea to be able to fit a subwoofer on a bookshelf, even if it knocks the books off. I'm a bigger fan of speakers than books =)
Do you (or anybody else here) see a problem with making the internal box volume about 5 or 6 percent bigger?
I calculate your internal bare box volume at 343 cu. in.
My slightly modified design comes out to 361.70 cu. in.
That calculates out to 5.4533% larger.
I'm trying to tweak the box design a bit to make cutting the material with less saw fence setup.
I also am moving the material up to .75" MDF.
All six panels would have .375" rabbets all the way around to help with alignment during assembly with the added benefit of an airtight seal and additional strength.
Let me know your thoughts...
This is an 8x8x8 using 1/2" material for a total internal volume of .198 cubic feet. If you wanted to use 3/4" material, you can make it an 8.5x8.5x8.5 . That will keep the internal cubic volume the same. If you want to go a little bigger, you should be fine, but it will hit the mechanical limits of the passive radiator sooner. Not by much, but just something to think about.
Your original design measure 7"x7"x7" internally.
My tweaked design measure 7.125"x7.125"x7.125" internally.
So, an eighth of an inch bigger internally in each dimension.
I am unclear what you mean by:
it will hit the mechanical limits of the passive radiator sooner.
Can you explain that, please?
Also, do you use SketchUp or something similar for woodworking design?
The larger the box you build, the lower the tuning frequency will go which will in turn change the the way the passive radiators and subwoofer work together. So the bigger the box you go, the sooner the passive radiators will hit xmax. That means that you can't put as much wattage through it. You're not doing a lot more, so it's not going to have a dramatic change, but it will be a change.
Makes perfect sense now, thanks to the explanation!
I tweaked my design a bit to get it within one third of a cubic inch (Close enough!) of your original design. 😉
It's not quite a perfect cube anymore, but now I only have three table saw fence setups I have to do.
Two for cutting the six panels to size and one setup for the rabbets.
Let me know if you would like me to share the SketchUp files. Note, I don't use "SketchUp for Web", I am still using the old 2016 version. :/
Just a heads up for anyone looking to build this the passive radiators are on sale today at parts express and it should save you ~$11 on a pair.