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A Cardioid mid Coax 3 way speaker

Joined
Feb 23, 2021
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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
prototype.jpg

Final CAD design:
cad_render.jpg

Build progress
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IMG-20230828-WA0011.jpg
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Driver assembly (The space behind the coax is filled with melamine foam sheets and covered with a sock cloth for now)
IMG20231027164545.jpg
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Measurements
1698483409787.png
sica_mid_polars.jpg
1698483347152.png


A linear phase crossover: V1 (Reference axis is 20 degrees off axis)
cardioid_mid_3way var7 XO-schema-7.png

cardioid_mid_3way var7 Six-pack.png

cardioid_mid_3way var7 Impulse+ETC+Step.png

linear_phase_pref_score.png
 

Attachments

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OP
Vineeth Kumar V
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Feb 23, 2021
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This speaker is now alive and singing.. :D
I tested this crossover first
1698771126547.png



1698771135887.png




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
ref_axis_measurement.png



Burst decay
1698833925613-png.1229754


So far I like it a lot.. But honeymoon days.. :D 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... :)
 
Last edited:

nerdemoji

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wow.... im lost for words
 

voodooless

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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?
 

voodooless

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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

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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... :facepalm:

BTW, what amps and DSP are you using for this?
 
Last edited:
OP
Vineeth Kumar V
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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)
1698915191886.png


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:
This gives me great flexibility to implement even full bandwidth FIR filtering for each driver :)
 
OP
Vineeth Kumar V
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Here is how this project evolved :)
All Thanks to mabat's ATH software

Prototype-1
1683044060436-jpeg.1170481


Polars
1683045824668-png.1170488


BEM sim-1
1683083565604-png.1170649


predicted polars'
1683083630955-png.1170650

Real world: measured polars
1683083672941-png.1170654


BEM sim-2 (with damping)
1683083798055-png.1170655


Predicted polars
1683083860705-png.1170657


Prototype-2
1683122669736-png.1170757


Measured polars
1683122460632-png.1170755


Prototype-3
1683133795544-png.1170828


Measured polars
1683133842026-png.1170829


This is where we decided that this concept is worth pursuing :)

Next came CAD design iterations

Design-1
1683467500380-png.1171890


Design-2
1683644328016-png.1172574


Design-3
1683646240892-png.1172580


Design-4
1683651675776-png.1172598


Design-5
cardiod_speaker_side-png.1172856


Design-6
full_speaker-png.1173651

Design-7
red_black_front-png.1173731


Design-8
cardioid_poor_mans_full-png.1174911


Design-9
img-20230520-wa0014-jpg.1175810


With this I fell in love and decided to build :D
 

Sokel

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

Prototype-1
1683044060436-jpeg.1170481


Polars
1683045824668-png.1170488


BEM sim-1
1683083565604-png.1170649


predicted polars'
1683083630955-png.1170650

Real world: measured polars
1683083672941-png.1170654


BEM sim-2 (with damping)
1683083798055-png.1170655


Predicted polars
1683083860705-png.1170657


Prototype-2
1683122669736-png.1170757


Measured polars
1683122460632-png.1170755


Prototype-3
1683133795544-png.1170828


Measured polars
1683133842026-png.1170829


This is where we decided that this concept is worth pursuing :)

Next came CAD design iterations

Design-1
1683467500380-png.1171890


Design-2
1683644328016-png.1172574


Design-3
1683646240892-png.1172580


Design-4
1683651675776-png.1172598


Design-5
cardiod_speaker_side-png.1172856


Design-6
full_speaker-png.1173651

Design-7
red_black_front-png.1173731


Design-8
cardioid_poor_mans_full-png.1174911


Design-9
img-20230520-wa0014-jpg.1175810


With this I fell in love and decided to build :D
A little TAD-ish,I love it!
Great built!
 

voodooless

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

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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.
 
OP
Vineeth Kumar V
Joined
Feb 23, 2021
Messages
35
Likes
175
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 :)
 
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