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Introducing Directiva - An ASR open source platform speaker project

Rick Sykora

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Towards the end of last year, @amirm and I started discussing a potential audio system project that would include an open source streamer and an active speaker design. I had already been working on a DIY modular speaker concept and planned to start a design based on it, but had some other projects that needed to be completed first. This allowed me to make some adjustments to my plans and reconsider some of my original ones. Here were my goals for the speaker:
  1. The speaker would be active and simple to build (for me, this meant no tools beyond a circular saw but for more optimal results is more like a table saw and router).
  2. The design tools would be free but flexible enough to allow external data import/export.
  3. The design would be openly shared but FOR NON-COMMERCIAL USE ONLY.
  4. The cost target for the drivers and crossover would be approximately $1000 US.
  5. Keep the cabinet size to around 15 liters or about .5 a cubic foot or smaller (allowing it to be reasonably shipped and Amir to test). The electronics would be external. (EDIT)
  6. The design would allow for modest flexibility and scalability so others could (eventually) modify and add value. So, here is where Amir intervened with his ideas/goals...
  7. The speaker should have good directivity. Note, this did force me to reconsider some of my (mainly cabinet) plans as we'll see later.
  8. The speaker should use the new Purifi 6.5 woofer. As it was not in my original plans, I was hesitant due mainly to cost. However, after working on the SPK5, had them in hand and agreed to use...
This put some pressure on the budget, but the tweeter candidates were not pricey, so on to the next task (getting some help)...
 
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Rick Sykora

Rick Sykora

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So, knowing that I did not have all the knowledge and/or experience to design this speaker on my own (at least not within this decade), started to seek out some help. ASR has many knowledgeable members, so started to put feelers out. You may have gotten wind of it earlier as I should have been more careful about establishing team rules. ;) My first rule is the initial team needed to have just enough qualified members to make good progress. The second was that they would be willing to share their effort under the guise of an open source arrangement. While wanting to be open and not overbearing, missed a key rule - willing to keep efforts within the team until we had sufficient concurrence on the design...

I already had experience with doing a cabinet design and some driver selection, so was looking for help with:
  1. Finalizing the tweeter selection
  2. Reviewing my proposals
  3. Validating the overall design
  4. Simulation and analysis
After having trouble with some of the Excel-based software for speaker design, I proposed the the team tool be VirtuixCAD. So team members would need to be comfortable with VirtuixCAD and or supplying data that could be used with it.

As SPK5 and other speakers based on the Purifi woofer were discussed on the forum, I had some input on the cabinet design from @DDF. After some rounds in that regard, we also discussed potential tweeters. He proposed the SB26ADC and so I added it to the list of considerations. As noted in the discussion on this forum, the Purifi woofer is best utilized in either a vented or passive radiator design, so my focus has been to evaluate those options (and I am still doing so). This did not hamper the progress on the overall cabinet design. As I have known Rick Craig for a few years, and he had just done his Purezza based on the Purifi woofer, decided I would seek his advice...
 

nm4711

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Great plan!

I planed and made a pair of pretty similar speakers back last summer/fall. It was tough to coose, but I went with the PTT4.0X04, to get smaller width. My speakers are around 12 litres (13,5 cm x 32 cm x 28 cm) and my goal was, to keep height and depth exactly the same as a standard DIN A4 folder, to get a "true" bookshelf speaker.
I chose the Seas DXT as tweeter, because it was an easy way to get a good waveguide.
Furthermore I went for a closed box design, because it is easier to design, and I planned to use a subwoofer anyways. With the 6.5 inch version on the other hand I would try to make a ported version, wich can be used without sub.
For the electronics I went with the FA122 modules. They just fit into the cabinets.

Feel free to ask questions and I can share my "plans" (or the size of the speaker and the parts) if you are interested.
 

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Rick Sykora

Rick Sykora

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Great plan!

I planed and made a pair of pretty similar speakers back last summer/fall. It was tough to coose, but I went with the PTT4.0X04, to get smaller width. My speakers are around 12 litres (13,5 cm x 32 cm x 28 cm) and my goal was, to keep height and depth exactly the same as a standard DIN A4 folder, to get a "true" bookshelf speaker.
I chose the Seas DXT as tweeter, because it was an easy way to get a good waveguide.
Furthermore I went for a closed box design, because it is easier to design, and I planned to use a subwoofer anyways. With the 6.5 inch version on the other hand I would try to make a ported version, wich can be used without sub.
For the electronics I went with the FA122 modules. They just fit into the cabinets.

Feel free to ask questions and I can share my "plans" (or the size of the speaker and the parts) if you are interested.

Thanks for sharing!

I suspect you will be quite interested in where this project is headed. ;)

Stay tuned!
 

nm4711

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Thanks for sharing!

I suspect you will be quite interested in where this project is headed. ;)

Stay tuned!
Yeah, you are so right. ;)

Will be interesting to see, what decisions you will make and why, during the design process. Also there is alot I and all the members can learn, if you share all steps and details and we get a proper measurement from amirm in the end.
 
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Rick Sykora

Rick Sykora

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After consulting with @Selah Audio, Rick liked the tweeter choice(s) and advocated for the passive radiator. Since Directiva is active, it does not compete directly with his current plans, he was willing to continue to participate in the effort. At this point, I needed someone that could pull some weight with simulation and analysis. There are several members that clearly capable and you likely know who they are. As was trying to keep the team smaller, I decided to consult with Amir. I proposed @ctrl and he concurred. Shortly after, I checked and @ctrl agreed to help as well. You will see he has been quite busy directing the outcome. I may need another member or two, so if you are interested, PM me.

Also @amirm is looking for volunteers to help with the streamer hardware and software. So if you are interested, please contact him.

Here is where things start to get more interesting and you will be seeing more from @ctrl. Have been rather wordy, but here is where we started. I wanted a simple box (like one of the Denovo cabinets sold by Parts Express), the Purifi 6.5 woofer and the SB26ADC tweeter. Since the passive radiator would add cost, the first proposal used a sealed cabinet. It looked like this...

1613415881013.png
 
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Rick Sykora

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Shortly after we did this first one, DDF discovered some distortion issues with the sealed box alignment and so we abandoned it. We initially considered using the SPK5 cabinet dimensions, but having graduated to more volume, the easier answer was to upgrade to the .56 cubic foot Denovo cabinet. I was also concerned about having the tweeter mounted so close to the top baffle edge and so this resulted in v1. @ctrl ran sims and here are the initial results...

1613417465273.png
1613417676155.png
1613417734010.png


Note, at this point, we have not transitioned to VirtuixCAD as yet. We are brainstorming over driver location and using @ctrl sims to compare iterations.
 

muad

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I really like the idea of the dxt tweeter. Would have been a great choice to get the directivity perfect
 

HooStat

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What is the ASR "position" on the use of subs? Should this design be predicated on the use of a sub or even two? If so, that might affect the driver choice (i.e., the 4" Purifi) and improve the budget.
 

ctrl

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I really like the idea of the dxt tweeter. Would have been a great choice to get the directivity perfect
Have some patience, Rick has just started his new novel ;)


If so, that might affect the driver choice (i.e., the 4" Purifi) and improve the budget.
See in the specs in post#1:
8. The speaker should use the new Purifi 6.5 woofer
 

HooStat

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See in the specs in post#1:
8. The speaker should use the new Purifi 6.5 woofer

This is why I am asking. It seems strange to have such a specific requirement when everything on this site about bass focuses on the importance of having 2 or more subs.
 

HooStat

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Maybe it should be called the ASR Purifi Open Source project just to be a little more clear.
 
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ctrl

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Rick wants to show the path we took to ultimately end up with the final design. Version v1 is the chassis arrangement a beginner might choose for aesthetic reasons.
1. sketch of the loudspeaker
2. frequency responses of the tweeter normalized to 15° (measurements simulated frequency response with 15deg steps, 0-90°)
1613420187231.png1613420216534.png
 
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headshake

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Maybe it should be called the ASR Purifi Open Source project just to be a little more clear.
It is a hard design choice for sure. It puts you into a few corners- bad 1-2k off axis. A need for more wattage,

I think basing it around a parts express box is a great idea. They are easy to build and don't require corner clamps.

I recently started my first speaker and used ponoko.com to cut the baffle. That was my way of getting around making cuts (pun intended). Lots of material/color choice too. Your end design could just be a couple of svg files to replace the front and back side of a PE box.

I'm with @nm4711 , the hypex plate amps are where to go.

Both of your drivers have been measured by hificompass. You could trace the off-axis and make vcad sims from that data too. Run it through the baffle sim and move the tweeter around.

Best of luck!
 
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Rick Sykora

Rick Sykora

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This is why I am asking. It seems strange to have such a specific requirement when everything on this site about bass focuses on the importance of having 2 or more subs.

Is part of the scalability requirement. But as cannot be readily tested by Amir, is not part of this initial design.
 
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Rick Sykora

Rick Sykora

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Maybe it should be called the ASR Purifi Open Source project just to be a little more clear.

The Purifi woofer is part of this implementation but not exclusive. This is what I intended as part of the flexibilty aspect. The idea is that others can use the initial work and apply the lessons learned. This is why it is an open source approach.

Hope this helps!
 

ctrl

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The problem with version v1 in post#14 is that the tweeter was placed so that the two side edges and the top edge are about the same distance from the center of the tweeter.
This adds up the edge diffraction. Even if one would optimize to 15° listening angle (shown in post#14) the design can not be saved - only in terms of directivity ;)

This becomes quite clear when normalized to the axial frequency response:

1613420966871.png
 
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Rick Sykora

Rick Sykora

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The problem with version v1 in post#14 is that the tweeter was placed so that the two side edges and the top edge are about the same distance from the center of the tweeter.
This adds up the edge diffraction. Even if one would optimize to 15° listening angle (shown in post#14) in the design can not be saved - only in terms of directivity ;)

This becomes quite clear when normalized to the axial frequency response:

View attachment 112757

This is comparable to when the corporate marketing guy (me in this case) thought he had a better idea, but actually it is not. The difference here is the better technical result will drive the design. ;)
 
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Rick Sykora

Rick Sykora

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This is comparable to when the corporate marketing guy (me in this case) thought he had a better idea, but actually it is not. The difference here is the better technical result will drive the design. ;)

...should add that the intent is the builder gets the choice to build despite possible drawbacks too. In engineering, there is rarely only one good outcome. Our goal was to show the tradeoffs and allow the builder to make his/her choice. If they are unable to build a fancy cabinet, they can still participate in the project at some level and will try to assist as best I and others can. :)
 
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