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.

Parts Used

Necessary Parts
2 - ND140pr
1-Tang Band W5-1138SM

Optional Parts
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.

Finish Tips

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.

For glue on a project like this, I will always use Titebond II. But any Titebond wood glue should work well.

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.

Final Thoughts

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.

Like Free Plans?

Feel Free to tip the designer: This help me to continue to give away free plans.

*These plans are free for personal use. These are not to be used commercially. If you want to use these commercially, contact me first.

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  1. Just for fun video. This is the beginning of Live Die Repeat. This is way below tuning frequency, but fun to see.



    1. @123toid Looks good!  I really don’t need another subwoofer, but this looks awesome being so small, and like a good project to start with.  I don’t plan on making one just yet, but the use cases for this seem endless as it would let you fit a sub in almost any area.

      1. @123toid I don’t know what you mean, also I think one of them might be an alpha version of this…
        (also pictured: sub12 and a powered intinity sub hiding in the back)

  2. 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 =)

  3. @123Toid
    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…

    1. @scotty

      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 8.5×8.5×8.5 . 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. 

      1. @123Toid
        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:

        Posted by: @123toid
        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?

      2. @scotty

        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. 


      3. @123ToidMakes 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. :/

  4. 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.

  5. Hi!
    I just found your Mini Earthquake video and am trying to use that as a starting point for a subwoofer build.
    My issue is that I want to use a bigger driver and bigger PRs.
    I am planning on using the Dayton Audio DSA175-8 6-1/2″ driver and DSA175-PF 6-1/2″ radiators.
    I also plan on using 3/4″ MDF for the box.
    I tried to use WinISD to plan my build, but I am a complete n00b at this. I absolutely and completely do not understand the tuning freq stuff.
    With a box volume of .198 ft.³ (5.6 L), the Fh (?) is 87.29 Hz.
    The F3 (again ?) appears to be approx. 78.79 Hz.
    Is this good/bad?
    Will I need to change box volume or will tuning the radiators be necessary?
    I am including the driver/radiator info, just in case.
    Any help will be appreciated!!!

    1. @shredi-master

      Some great questions.  The one issue with Passive Radiators in WinISD is that it does not predetermine box size or weight for optimal tuning.  You really need to mess around with the box size and weights on the passive radiator to figure that out.  I notice you are using a woofer, versus a subwoofer.  IS this for a speaker project?  Or is this to be used as a subwoofer?  If this is to be used as a subwoofer, you would be better off to try a different driver.  Why don’t you give us some ideas of what you are trying to do, so we can better help. 

  6. @shredi-master

    A couple basic things to note.  First just because a subwoofer is bigger, doesn’t mean it will go lower.  Second, a passive radiator system acts like a ported system.  So if you are modeling a sealed cabinet, that will not be accurate.  I went ahead and modeled a PR (green), port (red) and sealed (blue) with that subwoofer to show you what I mean.
    As you can see using two of the DS175-pr it will only have an f3 of 42hz.  However, it will probably be louder and you might make some of the extension up with room gain. Is this closer to what you are looking for?

  7. Yes! Thank you!!!
    I created a model using the DCS165-4 with an enclosure volume of .355 (internal volume of a 10 inch cube made with 3/4 MDF) and two DSA175-PR radiators with 40g of weight (I am assuming 40g weight on each PR). 
    I got an F3 of 42 Hz, and an Fh of 45 Hz. 
    I found a bunch of your WinISD tutorials on YT and they answered a bunch of my questions.
    Still have two more:
    1. I used 60 watts as the system input power on the Signal page, as the Lepai amp has 60 watt output to the sub. Is this okay to do?
    2. When I check Cone Excursion (PR) for this model, the line peaks above my radiator Xmax. I read that I could actually exceed Xmax by no more than 10%. My model peaks at about 8.6mm at about 40 Hz. Moving towards the lower frequencies the peak decreases a little, then increases up to just over 9mm at 10 Hz. 
    Would this be an issue?
    I also created another model using same sub driver and same enclosure, but with two DCS215-PR 8″ radiators.
    I got an F3 of 40 Hz, and an Fh of 43 Hz using 50g of weight, with no excursion issues.
    I want to take time to thank you again for indulging my effort, here. I know you are busy and I am asking a lot of n00b questions, so…
    Thank You!!!

    1. @shredi-master

      It will probably be fine.  However, if you want, you can decrease the volume to 0.29 and the weight to 50g.  IF you do this you shouldn’t have any issues at all.

  8. Hello! New here. Would you recommend this design or your cube-cube for a desktop setup paired with Overnight Sensations and the 2.1 Arylic amp you reviewed recently? This will mostly be to fill out the low end for moderate near-field listening, but I definitely want something that can kick when the housemate leaves and I can crank up my bass-heavy electronic music!
    If you would recommend the former… Any 2021 updates you would make to that design? I can definitely spend more on the driver since I’ll be using the 2.1 amp in place of the low-pass and plate amp.
    Sources are FLAC/Spotify from Laptop > Schiit Modi Multibit or a vintage philips TT > Parks Audio Puffin.
    Side note: how will the OS’s sound with the Arylic 2.1? I’m coming from a ’79 Vintage JVC integrated I found at goodwill for $20 ( removed link ) does a fine job but I think the OS’s will benefit from some new components feeding them. Some of the caps were looking pretty bulgy the last time I had it open.
    Thanks! Great channel. I’ve got a whole list of DIY projects in the pipeline now, starting with getting the amp and building a sub!

    1. @spacejams


      Honestly, this should probably be a separate topic.  But I’ll try to answer it.  If you have more questions, it would be better to start a new topic and tag me in it. 

      Having said that, the mini earthquake is great for it’s size, but it is still limited in it’s size.  IF it was me, I would go with the cube cubed.  I am not sure, what all I will design for 2021, yet.  I will probably do some passive radiator builds, but I haven’t decided yet. 

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