Dear Community,
I recently watched a video about the B&C coaxial compression drivers. After looking them up i was shocked how pricey they are. Then i saw the diagram below and thought: can't we make our own coaxial compression driver with conventional cheap drivers/parts?
When thinking about the concept i became more and more excited to try.
Directivity control provided by a horn + point source behaviour like a full range/coaxial driver = why not?
Let's discuss the possibilities and try to succeed!
So here is my fist take on a design concept of a DIY coaxial compression driver (will name it CCDIY):
In light blue: HF dome tweeter;
In orange: basic shape of the midrange driver with cone;
in dark blue: phase plug for both drivers (is not finished, need to implement the B&C patented method for blending the HF with the MF);
in grey: front and inner channels in a housing.
Thinking about 3D printing the parts after first design prototype is ready.
Also, the dome tweeter has to be able to dissipate some heat. still thinking about solutions for that.
I recently watched a video about the B&C coaxial compression drivers. After looking them up i was shocked how pricey they are. Then i saw the diagram below and thought: can't we make our own coaxial compression driver with conventional cheap drivers/parts?
When thinking about the concept i became more and more excited to try.
Directivity control provided by a horn + point source behaviour like a full range/coaxial driver = why not?
Let's discuss the possibilities and try to succeed!
So here is my fist take on a design concept of a DIY coaxial compression driver (will name it CCDIY):
- HF: 1 inch dome tweeter like the Dayton Audio ND25FN-4 or Peerless by Tymphany OC25SC65-04 etc.
- MF: full range/ midrange driver. about 2.5 or 3 inches, like pdf_dayton audio_PC68 or a pro driver from Faital etc.
- using B&C phase plug design, more info in the link of the video.
- all in a tight package:
In light blue: HF dome tweeter;
In orange: basic shape of the midrange driver with cone;
in dark blue: phase plug for both drivers (is not finished, need to implement the B&C patented method for blending the HF with the MF);
in grey: front and inner channels in a housing.
Thinking about 3D printing the parts after first design prototype is ready.
Also, the dome tweeter has to be able to dissipate some heat. still thinking about solutions for that.
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The B&C diaphragms are annular and the mid-range is behind the treble and both are compression drivers.
I believe that it's absolutely possible to make a passable DIY version given a well-equipped machine shop and the knowledge to use what's in it. If you set aside, say six months to a year of spare time and are prepared to build half a dozen prototypes as you narrow in to the final design through extensive testing, I'm sure that the parts and material prices will be less than B&C's or BMS's offerings.
Back in the day, yes. I think you are looking in a different direction than i am. For pro and absolute best audio, go for the b&c or go your route. For home use, 3D printing and off the shelf parts will suffice.
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The spirit and cause of diy! If we combine our knowledge, positive vibes and provide good feedback we could reach more than you would think. So please before commenting, read the first post carefully and think of any possibilities and limitations of said idea/design problem. If you think it is impossible or far out of reach, give constructive reasons why or be more inviting to discuss your statement.
If you see possibilities or a different solution to the (design) problem, be my guest!
The problem might be that non-compression drivers are not up to the task because diaphragms are not stiff enough.
It might work for lower (hifi) levels, though.
It might work for lower (hifi) levels, though.
A synergy (MEH) horn arrangement would be a lot easier I think.
Well this kind of looks like @perrymarshall's horn addition (trace back and forward) to my reflector-coaxial point-source PrimeRadiant Axia (summarized in the Fullrange Photo Gallery).
I agree. Have more confidence in the midwoofer than the dome tweeter because of use of midwoofers in MEH designs where a compression ratio of >5:1 is usual.
I agree! I love the simplicity of meh and the ability to diy them with basic tools.
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Thinking about ways to test a concept of the CCDIY before manufacuring a prototype. Would AKABAK be good for simulating the acoustic behaviour of the phase plug and transition from CCD to horn?
If yes, what would be key parameters to get right in the simulation?
If no, what would be another way to test the concept without 3D printing dozens of iterations?
Also, for testing the limmits of the drivers, varable compression ratio would be nice to implement in the prototype. For example using shims.
If yes, what would be key parameters to get right in the simulation?
If no, what would be another way to test the concept without 3D printing dozens of iterations?
Also, for testing the limmits of the drivers, varable compression ratio would be nice to implement in the prototype. For example using shims.
Overall project update
Bought a 3D printer for manufacturing prototypes and testing.
Will start prototyping later this month.
Basic design is pretty much done.
Prototype design (goal: design for printing and testing) will start this week.
Update basic design
I’ve made several updates to the CCDIY design, starting with the tweeter. I replaced the Dayton Audio ND25FN-4 (dome type) with the Peerless XT25SC40-04 ring radiator. This change introduces an annular-style phase plug like the B&C coaxial, thanks to the ring radiator's geometry. Additionally, I opted for a 1.4-inch horn entry size (before 1 inch).
Here’s a section view comparison showing the old (left) vs. new (right) version:
Also, the XT2524SC40-04 works great under compression, according to Hornresp.
For the midwoofer section, I redesigned the ports that merge into the HF path within the expanding horn segment. I studied the design principles outlined in B&C’s coaxial driver patents and found that the MF path can blend into the HF waveguide with minimal diffraction and/or reflection if the junction occurs in a region where the HF waves are traveling through a relatively straight section.
Another key consideration: the width of the MF ports at the point where they meet the HF waveguide should not exceed 1/4 of the wavelength of the tweeter’s highest operating frequency. This keeps HF diffraction to a minimum.
For the midwoofer i changed driver. I chose the peerless TC7FD00-04 for the nice extension to the HF and decent sensitivity for the relative low compression ratio (5.82:1).
would love to hear your 2 cents!
Bought a 3D printer for manufacturing prototypes and testing.
Will start prototyping later this month.
Basic design is pretty much done.
Prototype design (goal: design for printing and testing) will start this week.
Update basic design
I’ve made several updates to the CCDIY design, starting with the tweeter. I replaced the Dayton Audio ND25FN-4 (dome type) with the Peerless XT25SC40-04 ring radiator. This change introduces an annular-style phase plug like the B&C coaxial, thanks to the ring radiator's geometry. Additionally, I opted for a 1.4-inch horn entry size (before 1 inch).
Here’s a section view comparison showing the old (left) vs. new (right) version:
Also, the XT2524SC40-04 works great under compression, according to Hornresp.
For the midwoofer section, I redesigned the ports that merge into the HF path within the expanding horn segment. I studied the design principles outlined in B&C’s coaxial driver patents and found that the MF path can blend into the HF waveguide with minimal diffraction and/or reflection if the junction occurs in a region where the HF waves are traveling through a relatively straight section.
Another key consideration: the width of the MF ports at the point where they meet the HF waveguide should not exceed 1/4 of the wavelength of the tweeter’s highest operating frequency. This keeps HF diffraction to a minimum.
For the midwoofer i changed driver. I chose the peerless TC7FD00-04 for the nice extension to the HF and decent sensitivity for the relative low compression ratio (5.82:1).
would love to hear your 2 cents!
I don't have a lot to add but I encourage you to continue. I've always been curious about this type of experiment. I do wonder whether your positioning of the tweeter ports could be moved a bit closer to the middle of the tweeter, rather than landing at the edge of the surround. Perhaps the ports could also be angled inward a bit so they don't take such an immediate and abrupt 90° turn. But you may need just to try to print to see how much difference that might make. In any case, best of luck.
I've made my own compression drivers before, and I learned a lot, and don't regret it.
But when everything was said and done, it just made me realize that "real" compression drivers are worth the expense.
But when everything was said and done, it just made me realize that "real" compression drivers are worth the expense.
For what it's worth, I've heard those B&C Coaxials in a large format line array and they perform better than anything else I've experienced. Distortion is lower and the phase was much flatter. They are really, really good.
@Patrick Bateman thank you for all your work on diyaudio. You have inspired me to start this project by showing creativity in waveguide concepts. Especially MEH and combining waveguides with regular tweeters like the SB19STC000-4.
I’d be honored to hear your thoughts and insights in the thread as the project develops.
I’d be honored to hear your thoughts and insights in the thread as the project develops.
Thanks for your reaction. I placed the HF port so it faces the ring where the voice coil and former join the membrane. The reason for this is that it maybe would load the flexible membrane parts less. Also, the sudden 90 deg bend is there tho provide ample straight section for the MF to join.
Moving the HF ports more to the middle could give more room for the MF ports wich could provide the posibility of using a bigger MF driver while keeping compression ratio <7:1. Im limited to an sd of about 22 cm2 for the MF with the current design.
Ill report back on this!
I evaluated this on the current design. The reason i have not placed the port more to the center of the tweeter is that the distance between the outer edge to the port is way longer than 1/4 wavelength of the max frequency. Im currently drawing a version where the HF port is split in two entries. This to spread the port surface area over the sd and ensure short distances from rhe membrane edges to the ports. This also lowers the throat chamber volume which helps with spl above 8k hz.
Will test both the single port and split port phase plug in the prototype.
Design Update
I made a lot of changes in the design. Thanks to @Wright for the input on the phaseplug of the HF section. I changed it from a single anulair channel to a twin channel. Also, this made it possible to integrate a 3 inch mid driver (sd of arroud 32 cm2) which gives many more options to sellect. I have changed to LaVoce FSN030.72 for the mean time. Here is a cross section view.
First prototype and preliminairy test
I 3D printed the parts to test the HF. No mid and mid ports included in the print. I only had time for a short listen on a SB H280 horn. No obvious defects in the sound were noticable. Im planning to use a plane wave tube to evaluate the HF and MF section. Here is a picture of the "listening test".
I made a lot of changes in the design. Thanks to @Wright for the input on the phaseplug of the HF section. I changed it from a single anulair channel to a twin channel. Also, this made it possible to integrate a 3 inch mid driver (sd of arroud 32 cm2) which gives many more options to sellect. I have changed to LaVoce FSN030.72 for the mean time. Here is a cross section view.
First prototype and preliminairy test
I 3D printed the parts to test the HF. No mid and mid ports included in the print. I only had time for a short listen on a SB H280 horn. No obvious defects in the sound were noticable. Im planning to use a plane wave tube to evaluate the HF and MF section. Here is a picture of the "listening test".
DIY at its core! I applaud your dedication and hope it achieves your goal. Fantastic project!
Fantastic! Will be really curious to see how things change as you add the mid ports. Keep up the good work and let us know how you get on.