Active 4 way with MiniDSP and UCD

Hi everyone,

After quite a few years not building any speakers anymore it started to itch again recently. With DSPs getting more affordable I wanted to try building some active speakers. I own a Sonos Connect so my idea was to connect 2 MiniDSP 2x4HD with a Toslink Optical splitter to the Connect. In that way I’d try to create some sort of high end Sonos speaker :) So I started drawing something in Fusion 360.

For the look and feel of the speaker I took some inspiration from an existing German brand of speakers. I like the slightly angled baffle look and I wanted something that could cover the full range so it needed to be large enough to fit a decent subwoofer. My living room furniture is made of white oak and I have a black leather sofa, so this made up the choice of materials for the outside. Baffle with waveguide milled out of solid oak and panels with leather polstering.


Choice of drivers:
I personally like the sound of soft dome tweeters. I also wanted a good controlled directivity so I decided to integrate a waveguide. I went for the Scanspeak D2604/833000 after seeing the test results here. I intend to cross over at around 3 Khz
For high mid I chose Wavecor WF152CU14. I liked the low distortion of the driver and the look of the phase plug :). If it helps in directivity we will see later. It should handle the range down to 500 Hz. For low mid I designed in 2 x Wavecor WF152BD03 in separate closed chambers of around 3.5 liter. They should handle down to around 125Hz.


For the low end I was looking what I could do with a volume of around 40 to 50l behind the drivers and came across this which I could integrate. So a 26W/4558T00 close to the floor on the one side and a passive radiator 26W/0-00-00 higher up on the other side to make it fit in the narrow housing. With the MiniDSP I will have the flexibility to adjust the response to the room a bit.


The setup is made of separate sections, which are screwed together with threaded inserts, so it is easy to take apart and tweak. Most of the walls are double MDF with some damping in between.


The amplifier is made of 4 UCD400OEM modules together with a SMPS1200 and is mounted with heatsinks underneath in the base of the speaker. I created a PCB with a simple gain stage to connect the amplifier modules and to fit some connectors for the drivers. Cooling air can enter from the bottom and exit on the side through venting holes which are covered by the cloth hiding the subwoofer.
I’m still looking to find a way to connect the baffle without the visible screws. I might try to do it with supermagnets. If anyone has other ideas how to do this, please let me know.
Next is starting to build something. I might do some youtube videos on progress if people are interested.


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Very nice concept! Only thing I could suggest is use the NCore amps rather than UcD. I have UcD180s and NCore 252s and there is no comparison. However the 252s pop on turn off.

The NC252MP + NC100HF would give you 3 channels and maybe an NCore 500 for the bottom.
An option would be to swap the 26W/4558T00 with say 2 shallow subwoofers like the SW26DBAC76.

Then you could put one on each side and wire them to push outwards at the same time. This cancels the mechanical forces which means no box vibration. Even better if you inverted one of the drivers as it would cancel a lot of even order distortion.

Also I think you could get away with turning it into a 3-way instead of a 4-way. The bottom woofer part should be able to handle up to 200 without problems.

EDIT: I plugged the WF152CU14 into Linkwitz spl-max spreadsheet and SD = 93 cm^2, xmax = 4.5 mm will get up to 107 dB @ 200 hz. That should be plenty enough. It has a fairly low of 53 hz so I would wager it would perform excellent down to 200 hz on the distortion side of things too.
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Thanks for your suggestions. I also thought about the fusion modules but I wanted to keep the amplifiers invisible. On top of that I found a very good deal on the ucd400 modules on ebay. I fully agree it is the more complex and risky way but for me this is a hobby so I like a challenge :). It's about the journey and not about the destination.

The double woofer also crossed my mind. Indeed the cancellation of reaction forces would be nice. However I opted for the PR one as I could get a very nice low tuning frequency and did not need a port opening. Also cost of the PR was lower than an extra driver. Might be a version I can try to design too.
I'm not sure if it will fit in the with of the base, but otherwise you could just mount the fusion amp pointing down to the ground. It would probably yield a better quality product than a miniDSP + UcD. Probably less fun though ;)

For your original idea: I see lot's of heatsinks, but nowhere for the heat to go. Only a metal base will probably not be enough. I'd make some slits in the base to help convection.
Hi all, in these strange corona times we need to keep ourselves busy indoors as much as possible, so I made a start on the amplifier section of this project.

I soldered the connection and gain PCBs:

I milled the amplifier base plate out of 3mm Alu:

I milled the heatsinks for the UCD modules and the SMPS:


And finally assembled all together with the MiniDSP2x4HD:


It is all build quite compact to fit into the base of the speaker but went together pretty well. I powered it up and all seems to work fine for now. Stays really cool but will get hotter once it is inside the enclosure I think. It idles at around 35W in total, not too bad for a 4 x 400W amp.
Next up are the feet as my garage is now already full of Alu chips :)


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Yes, I use a single SMPS1200 for the 4 modules. I did not have any issues with high inrush currents. The smps has an ntc inrush current protection and soft start so that seems to work. In the datasheet it even shows examples of up to 6 UCD180 modules connected to it. I use the UCD400 versions as the distortion level is not so different from the smaller ones and it gives me much more headroom. Plus as said before I bought 10 pieces on ebay cheaply.

The PCB contains 2 channels gain stage with a LM4562 opamp similar as on the NC500 evaluation board.
The MiniDSP is capable of correcting time delays between drivers. A slanted front baffle is not necessary. Naturally, styling also plays a major role in form and function.

High functionality designs like the Magico G5 use large radius quarter-rounds on the front baffle edges to reduce distortion, and a simple rear construction.
@LineSource, I googled Magico G5 but did not find it. I did find the Q5 which has a slightly rounded baffle, I assume this is what you meant. I did something similar to help with edge diffraction. It starts with a chamfer at the edge of the drivers and then goes into a radius near the edge.

@grahamgraham, to get the waveguide profile I just bought a WG300 and traced it on paper first and then converted into CAD. To check it I printed it again and looked wit a torch if it fitted.


@pguerin, I designed the PCB myself. Here is how it looks:

From the description above I understand you had a W300 profile 3D routed. Have you found an affordable workshop in Belgium that is capable of doing that? So far the companies I found in the Netherlands are asking outragious prices for one off projects, that take less than an hour to finish. So, just curious to learn from your experience.