3D printed sphere speakers with Sica 5.5" coax drivers

[ppataki]

Long time no project so I thought it would be high time to share a new one
....this time plunging into the world of 3D printing!

In the last 6 months or so I have been taking a course in 3D printing and 3D design so the idea came naturally to design and print some speakers using 3D printing technology

I was so happy with my previous sphere speaker projects that I decided to continue on that path but this time instead of using bamboo salad bowls from Ikea I used some corn-based bio PLA

This time I opted for a 25cm sphere with ported design - usually I don't fancy those but 'variety is the spice of life' as they say.
The drivers are the Sica 5,5 C 1,5 CP speakers from one of my earlier projects
I cross them to my subs at 80Hz so I wanted to keep them as linear as possible until 80Hz with the port tuning; here is how the simulation looks like:

70W would be the xmax limited maximum input power at 80Hz, providing an SPL of 114.5dB for two speakers at 1m

Then I designed the cabinet:

The design includes a disc-shaped base, flush for the driver, a reinforcement ring behind the driver mounting area and a two flared-end reflex port
Wall thickness is 15mm

After some failed attempts with the printing I decided to cut the model into two hemispheres and print them separately with my Bambu A1 printer

And the result:

(my daughters are holding the two parts together)

The rear hemisphere is not perfect but 3D printing has a pretty steep learning curve so I hope the next one will look better

On the inside - as always - I have applied 4mm butyl sheets and 10mm felt

Here is a knock test video without the butyl vs with the butyl:

New video · Friday, Jun 20

Tap to view!

photos.app.goo.gl

With this method of adding damping butyl, you can totally build speakers using plastic - it is definitely not inferior to traditional materials but the measurements will also prove this below

The final look:

There is an 'adapter stand' piece missing to elevate them to ear-height, I will post that too once printed
Also the second speaker will be printed next week

Btw. printing takes an awful lot of time; one hemisphere takes about 24 hours to print (and around 600-700gr of PLA)

I will share the measurements in the next post very soon!

 

[ppataki]

And now the measurements!

All taken in the MLP, approx. 250cm from the speakers

First let's see the frequency response using the same driver in a sealed cabinet vs. in this ported sphere with no DSP whatsoever:

Clearly we can see that the port is doing what it should do
Between 150Hz and 300Hz there is an area with lower energy anyway - I will measure the speaker from 1cm to see of this is speaker or room related

Now let's continue with some slight adjustments to reflect reality: from now I will compare the sealed cabinet EQ-d vs. the reflex spheres EQ-d too since that is how I listen to them

Frequency response:

I had to apply a +12dB low shelf from 700Hz to the sealed cabinet and in case of the reflex spheres I added two bell filters: +5dB at 225Hz and +3dB at 700Hz - clearly way lower stress on the amp and on the driver itself

Distortion:

Really interesting to see this! The ported design has lower distortion in the 100-200Hz region - I would appreciate some comments/ideas about this
Can it be because of the port?

Phase:

This is clearly where the sealed box wins (although not sure how audible it is.....)

IR:

This is the next surprise - at least for me. The ported design seems to be much cleaner in the first 1ms timespan. The pre-impulse part seems to be faster-rising too
Again, any explanation would be welcome here as I was always under the impression that IR shall look much nicer in a sealed cabinet
One idea I have is that the difference might come from the fact that the FR curves are a bit different above 1kHz too

Step response:

One thing to note here: the pre-impulse part (pre-echo or pre-ringing) looks cleaner with the ported design but here I think I know the reason: the +12dB low shelf must be causing it in case of the sealed design - correct me if I am wrong

Group delay:

Here the sealed design wins, but again, audibility is questionable....

And finally the Wavelet diagrams:

The Peak Energy Time (delay) is the same for both and there is a bit more post-ringing in case of the sealed design - again I find it a bit strange but hopefully somebody can explain this

I am attaching the mdat file for your scrutiny

Subjective comments will also follow once the second sphere is also completely printed and assembled

Stay tuned!

 

[JohnnyNG]

They just keep getting better - nice!

 

[ppataki]

The 'adapter stand' is done too so the tweeter is at ear height now

I think it would look better with the same black paint as the tripods, so next week I will paint them black

 

[Salt]

Is that 'cat protection' around the wire? Or any other reason? (Just curious 'cause neve seen that indoors).
Beside that, my first optical impression was Minion .
Enough of joking: Great work, respect

 

[ppataki]

Enough of joking: Great work, respect

Thank you, appreciated!

Is that 'cat protection' around the wire? Or any other reason?

No, it is just 'aesthetics'
There are two different types of speaker cables coming from the cabinet (since there is no passive crossover involved but PC-based DSP, multichannel processing) so I wanted to 'group' the cables + have something that is white to somewhat match with the living room design

 

[kemmler3D]

This is awesome! I've had a very similar project in mind languishing in my to-do list for a long time.

Printing spheres is tough because it ends up being effectively a lot of overhang/bridging near the top. You can mess with cooling, speed, and layer height to improve this, but it looks like your infill is already pretty dense so that's probably not the issue.

Results look pretty decent... Thanks for sharing all these!

 

[JohnnyNG]

Really interesting to see this! The ported design has lower distortion in the 100-200Hz region - I would appreciate some comments/ideas about this
Can it be because of the port?

I would think so since the port damps the motion of the woofer near Fb.

 

[EERecordist]

Very impressive! Thanks for the detailed build posts.

How did you get from print to polished and painted?

It would be interesting to do a resonance study.

I've always been interested in sintered metal printing and wonder how it compares acoustically to die-cast metal as seen in the KEF Blade. That metal printing should drop in price as the patent expired.

 

[ppataki]

Very impressive! Thanks for the detailed build posts.

Thank you!

How did you get from print to polished and painted?

I have neither polished nor painted it
Just PLA as I mentioned above and that's it

 

[ppataki]

Quick update:

The rear hemisphere of the second sphere looks way better than the previous one

ű

It is definitely a learning curve and an evolution

 

[Todd k]

wow. Impressive. The members continue to amaze me with their skills. Very cool.

 

[ppataki]

Finally, the 'raiser adapter' is now painted in black using the same paint that I used for the tripods (matte eggshell chalk paint)

Overall I am really satisfied both with the looks and the sound - from now on I will be printing all my future DIY speakers (if size permits, of course)

Next steps:
- print and finish the right sphere and the raiser
- do a round of DSP optimization (manual + Dirac)
- will post my subjective thoughts on how it sounds
- print two more spheres replacing my current rear speakers - those will have the exact same Sica drivers but using their manufacturer-recommended passive crossover instead of driving them fully actively with computer-based DSP (of course Dirac optimization will be performed). I will post these as well later on

 

[hex168]

I look forward to your results, great work! BTW, have you seen the new Celestion coax?
Looks interesting, easier to get than the SICA. Don't know if it is close to as good.

TFX0515 - Celestion

A 6.5-inch pressed steel chassis, ferrite magnet coaxial driver with silk dome tweeter and 100° nominal HF coverage.

celestion.com

 

[ppataki]

I look forward to your results, great work! BTW, have you seen the new Celestion coax?
Looks interesting, easier to get than the SICA. Don't know if it is close to as good.

TFX0515 - Celestion

A 6.5-inch pressed steel chassis, ferrite magnet coaxial driver with silk dome tweeter and 100° nominal HF coverage.

celestion.com

They look great! - unfortunately I could not find any off-axis/globe/etc. manufacturer measurements about them

 

[voodooless]

Nice that these finally work out. I'm not surprised these work better in a reflex enclosure.

Given the simulation, you might benefit from a slightly longer port, or maybe just stuff some polyester filling lightly in the port to make it virtually longer. It may also remove some port resonances in the process.

I like the look of these very much!

 

[Looneybomber]

I've always been interested in sintered metal printing and wonder how it compares acoustically to die-cast metal as seen in the KEF Blade. That metal printing should drop in price as the patent expired.

The KEF blade enclosure is plastic, not metal.

“Made from an ultra-high density polyurethane composite”

https://images.salsify.com/image/upload/s--KRS_G-t8--/e00836ec314dbfd4f29903c8baf3944efd2be684.pdf

 

[EERecordist]

The KEF blade enclosure is plastic, not metal.

“Made from an ultra-high density polyurethane composite”

https://images.salsify.com/image/upload/s--KRS_G-t8--/e00836ec314dbfd4f29903c8baf3944efd2be684.pdf

Thanks!

 

[ppataki]

Here is how it sounds, with some caveats:
- I am using brand new, zero burn-in drivers
- Dirac was not re-run yet
- the adapter on the right is not yet painted in black

New video · Tuesday, Jul 1

Tap to view!

photos.app.goo.gl

If you use headphones you will get the idea anyway

I personally love it, the speakers totally disappear (you can hear that in the video too), very nice airy & detailed sound - really enjoyable!

 

[ThatSoundsGood]

This is a really cool project! Nice one!