A Cardioid mid Coax 3 way speaker

[Vineeth Kumar V]

I built a 3 way speaker using a Sica 5.5C1.5CP coaxial driver in a passive cardioid configuration helped in the lows by a Wavecor SW 215 subwoofer in sealed box configuration. This will use a DSP crossover although there is potential for a passive crossover version as well. Here are some pics and other details

Initial prototype for testing cardioid mid. The space behind the Sica coax driver is filled with 50mm thick melamine foam sheets cut to shape

Final CAD design:

Build progress

Driver assembly (The space behind the coax is filled with melamine foam sheets and covered with a sock cloth for now)

Measurements

A linear phase crossover: V1 (Reference axis is 20 degrees off axis)

 

[heraldo_jones]

You just made me do a big jaaaaawwwwww drop . Beautiful design and good measurements. Would love to see a big cousing with XL sized cabinet and extended bass.

 

[Vineeth Kumar V]

This speaker is now alive and singing..
I tested this crossover first

Here is the reference axis (20 degrees off-axis) measurement I made of the speaker from 50 inches away.
It is almost exactly as per the predicted response in VituixCAD.
The blue line is what I took as the reference based on Vituixcad

Burst decay

So far I like it a lot.. But honeymoon days.. I Need to listen a lot more..
The vocals sounding special is one of the first feelings I got, while listening.
I am missing a bit of bass that I am used to with my big speakers but maybe more tuning & placement tweaks are needed..
More updates in the coming days as I listen more.

If anyone is wondering how the speaker looks like (sounds like ) while it is singing, and also wants to get some vague idea about the cardioid directivity, see the below video. Of course, these kind of recordings are pointless and the sound balance will just depend on what you play this video on & recording artefacts, but still...

 

[nerdemoji]

wow.... im lost for words

 

[kongkong]

I can't close my mouth... clapp clapp....

 

[abdo123]

How is this thing forward firing from 300 Hz!

Awesome work!

 

[voodooless]

Very unusual design, but it seems to suit the project well and the end result clearly speaks for itself! Very well done!

@amirm, promote to front page?

 

[Vineeth Kumar V]

@abdo123: Thanks
The coaxial driver at the top is in a passive cardioid "enclosure".
55mm thick basotect melamine foam rings surround the back of the driver (under a sock cloth)

Here is the absorption efficiency of basotect

 

[voodooless]

melamine foam

Also known as Miracle Sponge, available as a cleaning sponge. May not have very defined properties, but will probably work just as good and costs almost nothing.

I didn’t know this stuff was useful as sound absorption material. Great stuff!

 

[voodooless]

One small point of critique might be that I wonder how long it will take before you'll start seeing the MDF seems? Generally, if not plastered over liberally, they will become visible through the paint after a while.

I made a similar-shaped enclosure (without the extrusions), many, many years ago, and opted to plaster it with fiberglass to get it super smooth, and then spray painted it with metallic paint. All without using CNC Never again...

BTW, what amps and DSP are you using for this?

 

[Vineeth Kumar V]

One small point of critique might be that I wonder how long it will take before you'll start seeing the MDF seems? Generally, if not plastered over liberally, they will become visible through the paint after a while.

A friend of mine built these cabinets & painted them as per my design. He is a professional in this. I have similar layered MDF cabinets made by him for my main system about 1.5 years back and painted in black. To this day, it looks like the way it was when it arrived here. Here is a pic of it today (the top module in below pic)

So I hope these cabinets will remain as such too for some time to come

BTW, what amps and DSP are you using for this?

At the moment, I am using a Marantz PM 5005 for the woofer.
For the Sica coax mid, I am using this: https://www.audiosciencereview.com/forum/index.php?threads/allo-volt-d-amplifier-review.15539/
For the Sica Coax tweeter, I use this: https://www.allo.com/sparky/volt-amp.html

This system, at the moment, is designed for use with my PC. So, for implementing DSP, I am using Equalizer apo on my PC along with a 6-channel audio interface:

ESI - U86 XT

U86 XT is a versatile USB 2.0 Hi-Speed audio interface with 8 Inputs, 6 Outputs and...

www.esi-audio.com

This gives me great flexibility to implement even full bandwidth FIR filtering for each driver

 

[Vineeth Kumar V]

Here is how this project evolved
All Thanks to mabat's ATH software

Prototype-1

Polars

BEM sim-1

predicted polars'

Real world: measured polars

BEM sim-2 (with damping)

Predicted polars

Prototype-2

Measured polars

Prototype-3

Measured polars

This is where we decided that this concept is worth pursuing

Next came CAD design iterations

Design-1

Design-2

Design-3

Design-4

Design-5

Design-6

Design-7

Design-8

Design-9

With this I fell in love and decided to build

 

[Sokel]

Here is how this project evolved
All Thanks to mabat's ATH software

Prototype-1

Polars

BEM sim-1

predicted polars'

Real world: measured polars

BEM sim-2 (with damping)

Predicted polars

Prototype-2

Measured polars

Prototype-3

Measured polars

This is where we decided that this concept is worth pursuing

Next came CAD design iterations

Design-1

Design-2

Design-3

Design-4

Design-5

Design-6

Design-7

Design-8

Design-9

With this I fell in love and decided to build

A little TAD-ish,I love it!
Great built!

 

[voodooless]

I'm glad you threw out the Barpapappa designs

 

[thewas]

What a great feasible DIY alternative to the passive mid cardioid loudspeakers like from ME Geithain and Sigberg Audio, excellent work!

 

[voodooless]

I'd be interested in distortion measurements as well. Let's see how well the little coaxial can hold up in this cardioid setup?

 

[Vineeth Kumar V]

I'd be interested in distortion measurements as well. Let's see how well the little coaxial can hold up in this cardioid setup?

I will take it. But at the moment, I don't have an SPL calibration for my mic. I use a sonarworks sound ID reference XLR mic for measurements.
With relative SPL measurements based crossover design etc, I is ok. But for distortion I need to do SPL calibration. I am waiting to get something to do this first. The comes the distortion measurements

 

[MCH]

Foam speakers! Cool, I never thought it was possible.
I wonder if it would be feasible to 3D-print a mould coat it with something with the right chemical resistance and low adhesion and generate the foam inside. Not easy but would allow to make several identical speakers easily.
Question: I guess the drivers are heavy, how do you achieve a good structural stability, is there a "skeleton" inside? I can't see well in the pictures.

 

[Vineeth Kumar V]

Foam speakers! Cool, I never thought it was possible.
I wonder if it would be feasible to 3D-print a mould coat it with something with the right chemical resistance and low adhesion and generate the foam inside. Not easy but would allow to make several identical speakers easily.
Question: I guess the drivers are heavy, how do you achieve a good structural stability, is there a "skeleton" inside? I can't see well in the pictures.

The final speakers are made of 25mm thick MDF. Only the prototypes were made of XPS foam

 

[MCH]

The final speakers are made of 25mm thick MDF. Only the prototypes were made of XPS foam

Ahhh missed that!