Sidetracking into small ...

[ergo]

While my Wavecor Ardents keep playing themselves in in family room and I listen to them daily I've been dabbling on a quite different field. My friend needs new back speakers for his new flat. Something that goes right on wall and would have as minimal visual impact as possible. So I've been digging into my small driver stach I've gathered over time but never got around to use.

First one to try was this Tectronic BMR unit. Looks very nice on paper... sort of too good




As I've also been messing with my 3D printer and upgraded the Prusa mk2 to Prusa mk2.5 it's been interesting to give that one some jobs. So a first attempt was printing out some front panels for very simple quick mdf test boxes. As each of these units is barely 2'' and even feels very small and fragile indeed I added 4 per box.

[ergo]

Some initial listening was done during the week by me and my friend and we arrived to a similar conclusion... they have some interesting aspects of sound, but it does not sound quite right and there seems to be some midrange distortion both of us noticed... What they did well was off axis performance. One could really move in wide window and the sound barely changed.

So today I did some measurements... thats why the box is safety strapped up there.

This is all 4 speaker units horizontal 0 to 60deg


And this is a 4 driver full polar (horizontal 0 to 180 and vertical 0 to 180)


The frequency response and power response do explain some of our unhappiness. But this config might still have potential if I would mate it with a small 19mm or so mini tweeter as well and perhaps also experiment LP filtering the outer pair of drivers.

I did run THD test also with 2.83V input... this one reveals an issue the datasheet does not show. There is quite a nasty distortion peak around 700Hz


Somewhat interesting driver still. So I might play around with these a bit more.

[ergo]

In parallel I also had a pair of these


With quite good luck with the 3D printed front panels I decided to make a much bolder move and try printing the whole box. So on to the Fusion CAD it was... This driver seemed to have promise with an inverter port added. So decided to try that too.


I've never tried this big a job on my printer, but the mk2.5 upgrade better show it's worth it


Some stringing on top of the speaker hole, but I was still quite amazed that it worked at all without any support structures.
Right way to do it would be either to split box right at driver center and print it in two halves so that hole never grown narrower. Or then to print the front panel as a separate piece so it can lay flat on print bed... that what I did with the Tectonic front panels above.

[ergo]

At end of the day this is what I've been listening to while writing all this


Sounds much better than Tectonic without any tweaks... but measurements to prove that will come some days later as it is past midnight here

3D print have some issues with some layers, so have to figure out what causes that. First few cm off the bed turn out petty good most of time, but as said it was a first to try something this big.

Still sorta wonderful this new world where speaker building can be indoors without any dust and material coming as a string of a roll.

[ergo]

As expected the responses look quite nice as is. Some peak around 1.3k but a series notch could take care of that.


Distortion is also rather ok on this one (same condition 2.83V at 315mm)


With a series notch like this


It could reach these response curves


So I'll try to find components to make this and give it a listen next. Seems quite a promising little thing and with approx 70EUR per box or so it would be a nice value for money.

[ergo]

Performance when speaker is on wall with ARTA Dual Gate (horizontal 0, 10, 20 to both sides and vertical -10 and -20)



This is with the slightly adjusted midrange notch that I'll be trying out

[TEK]

Thats very cool Ergo!
Found the speakers for sale several places, for example here: http://www.lautsprechershop.de/index...io-bb-3_01.htm

Would you be willing to share the
3D-models? I have a MK3 printer - might be fun to try something like this for desktop speakers.
Guess others might be interested as well!

[ergo]

Yes - that's the plan. I'll make the Fusion file available as well as the STL files.

I'll need to find time to make a small tweak and separate the inverter tube to a separate piece and add a small countersink in base to fit it into for glue in. The design above has the base and inverter as a single piece. While it did work sort of ok I think it will be better on most printers to place the bottom piece to the printer bed the other way around because of the rounded over corners.

I should hopefully get new rolls of the grey PETG by the weekend. Then I can do the second one and hopefully get to listen to them in stereo.... I'll also do some more experimentation with print settings. Especially the top layer quality was poor due to some settings probably as seen above.

It seems the 3D printing with the mesh core (I used 25% GRID infill) is actually quite good from acoustic aspect. A 'knock test' gives back a much lower frequency thump than similar box in MDF for example. I do have the accelerometer kit I haven't really used much yet. This seems a perfect candidate to try that out. Of course most interesting would be to create a replica from layers of MDF glued together to really have an A/B comparison to prove or disprove the assumption. We'll see if I have the time and drive to pull that off

[ergo]

Some progress with the Omnes project. I've now printed two boxes.. what solved all my layer peeling issues appeared to be using 0.2mm layer instead of the 0.35mm layer. Print time increased from 19h to 26h each for the main bodies and to about 4.5h for each cover. But then again that's just time and unless one would need to pay by hour it's not really that important.



I've now shared the Fusion file as well as all STL-s here

I've separated the inverter tubes from the bottom plates as then one can print the bottom plate upside down and the curvature on edges will print with better quality.

Both speakers are singing now and my friend is listening to them. I forgot to make a picture of an assembled pair, but will do so soon.

[Steve Manning]

Very cool Ergo. :T:T