Introducing Directiva - An ASR open source platform speaker project

[Rick Sykora]

Further improvement for your consideration:


P.PS There is already a ASR speaker under development that many of us came to similar design conclusions as this, is this a continuation of the same one? Have you asked the developers of that one what their thought are?

I think there is room for more than one ASR speaker as the designs have different end goals. As I stated earlier, my plan is to create a pattern that could be followed to create a variety of (likely derivative) speakers. Hopefully this helps both efforts. I look forward to seeing both efforts come to fruition.

 

[Rick Sykora]

Getting back to the Directiva journey...

After some more iterations that were trying to use the Denovo cabinet and tradeoffs with the bracing and other extensive modifications, @ctrl proposed a new cabinet. Now known as version 8, it reminded me of the Salk Veritas HT1 (which I happen to like and so we progressed with it). One of the primary questions was about beveling and whether the top of the front baffle needed to be beveled.



If you look at the frequency range of 2-5kHz and compare the versions, you will see that version 9 (top edge beveled) has slightly wider radiation. While this difference is slight, would not have expected the result. Since it is better and a bit less work, the vote goes to version 8.

A couple of side comments. Small differences are a good sign as they suggest you are getting towards a point of diminishing returns. The other note is a shout out to @ctrl for getting us this far this fast. Between expending his effort and computer time, we are much further along than if I had to build and measure all these alternative designs. If that were the case, you likely would not have heard from me until next year and/or would have a less optimal design!

 

[Lbstyling]

Getting back to the Directiva journey...

After some more iterations that were trying to use the Denovo cabinet and tradeoffs with the bracing and other extensive modifications, @ctrl proposed a new cabinet. Now known as version 8, it reminded me of the Salk Veritas HT1 (which I happen to like and so we progressed with it). One of the primary questions was about beveling and whether the top of the front baffle needed to be beveled.
View attachment 112921View attachment 112923
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If you look at the frequency range of 2-5kHz and compare the versions, you will see that version 9 (top edge beveled) has slightly wider radiation. While this difference is slight, would not have expected the result. Since it is better and a bit less work, the vote goes to version 8.

A couple of side comments. Small differences are a good sign as they suggest you are getting towards a point of diminishing returns. The other note is a shout out to @ctrl for getting us this far this fast. Between expending his effort and computer time, we are much further along than if I had to build and measure all these alternative designs. If that were the case, you likely would not have heard from me until next year and/or would have a less optimal design!

So as described before, the round over version has narrowed pattern control (around 7-8k) but if you show the full polar (out to 180degree and vertical) you usually find the energy has smoothed off axis, and filled in a little.

If you look at impulse, you will see a second source of the tweeter has been removed with the round over version as the sharper edge will otherwise work as a second tweeter (diffraction point).

The perception of this is that the tweeter may sound a little more 'exciting'.

Another thing to consider, the distances between 3 of the 4 edges of the cabinet front the center of the tweeter are very similar. This can come out better when you creating bigger differences.

What frequency is the graph showing up to?

Another thing to consider- Elipical waveguide may help for the same reason given as the cabinet dimensions above. Best of current tech now includes possibly creating equal path lengths for the wavefront to reach the mouth of the guide (this is why JBL waveguides look funny for instance)

To be clear, these are not criticisms. Not at all. And are small things in the grand scheme of things!
Overall, looking great!

 

[Rick Sykora]

As our story unfolds further, I made clearer some of my design philosophy and wanting to be able to range from a simple cabinet to a more complex one. So we returned to the .56 cu ft. Denovo and modeled it replacing the original tweeter with the Seas DXT. Here are the results comparing the latest set of variations...

v12 - Unmodified Denovo cabinet



v11c - Modified Denovo with major bevels



v8 - custom cabinet



With the Seas's waveguide, you get a significant improvement over the SB26ADC. Beveling the Denovo cabinet yields another significant improvement in directivity. Finally, the v8 custom cabinet yields a slight improvement over the modified Denovo cabinet.

In this same vein, I mentioned that I aimed to have a version of the cabinet that might be built with just a circular saw. So, next we will look at what that means for directivity....

 

[Chromatischism]

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°)
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Not a speaker designer but as a user I know I would end up padding that tweeter by a couple of dB. Looks good otherwise.

 

[HooStat]

Is the narrowing toward the top of the speaker (option 8) accomplishing a similar goal as a wave guide that is sized to match the woofer? Is it narrowing the dispersion of the woofer to match the tweeter near the crossover? I can't quite tell from the graphs, and I don't have the experience to understand exactly what is going on.

 

[_thelaughingman]

@Rick Sykora Are you guys factoring in affordability for the end user of this kit speaker? Having good sounding speakers with good speaker cabinet is a must and not a tradeoff but I am curious as to what would the ballpark for the price when this is finally pitched for orders.

 

[hex168]

Did you folks consider a wider cabinet a la GGNTKT M1 at all?

 

[Rick Sykora]

@Rick Sykora Are you guys factoring in affordability for the end user of this kit speaker? Having good sounding speakers with good speaker cabinet is a must and not a tradeoff but I am curious as to what would the ballpark for the price when this is finally pitched for orders.

Yes, but not done as yet. Drivers are about $800 + $64 for Denovo cabinets + $200 for minidsp 2x4 hd + misc connectors and wire is about $1100 before any discounts or shipping. Would be less if you build cabinets yourself. Finally, you need 4 channels of amplification, would be another $400 or more. Call it around $1500 for active vented version.

Not sure how affordable that seems, but is intended to be a good value. Does that help?

 

[jtwrace]

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

Not sure if he has the time but @tomchr would be great for this.

 

[Lbstyling]

Not a speaker designer but as a user I know I would end up padding that tweeter by a couple of dB. Looks good otherwise.

I think that might come down to the beam width. Current version is showing about 65deg. If that was significantly more, total energy in the top octave would be too high. Depends what the final version ends up at I would expect.

 

[Lbstyling]

Not sure if he has the time but @tomchr would be great for this.

Surely a JohnYang job? No?

 

[Rick Sykora]

Did you folks consider a wider cabinet a la GGNTKT M1 at all?

TBH no, but once the design and derivative process is proven out, the platform was meant to be extensible.

 

[Colonel7]

Yes, but not done as yet. Drivers are about $800 + $64 for Denovo cabinets + $200 for minidsp 2x4 hd + misc connectors and wire is about $1100 before any discounts or shipping. Would be less if you build cabinets yourself. Finally, you need 4 channels of amplification, would be another $400 or more. Call it around $1500 for active vented version.

Not sure how affordable that seems, but is intended to be a good value. Does that help?

Thanks to you and the team for doing this. Does this include a well-documented write-up complete with lessons learned and how-to in one dedicated place? That would be great. If so folks can truly learn and modify (or just straight on build and set up miniDSP 2x4 to spec). One of the source of frustrations for anyone new (and not so new) to DIYing is the real lack of documentation or even accuracy about a given final design and build, followed by using idiosyncratic or obsolete software or spreadsheets that rely on Windows 7 or somesuch , plus references to 30-page threads that are left dangling...

 

[_thelaughingman]

Yes, but not done as yet. Drivers are about $800 + $64 for Denovo cabinets + $200 for minidsp 2x4 hd + misc connectors and wire is about $1100 before any discounts or shipping. Would be less if you build cabinets yourself. Finally, you need 4 channels of amplification, would be another $400 or more. Call it around $1500 for active vented version.

Not sure how affordable that seems, but is intended to be a good value. Does that help?

Definitely helps, seems to me that it’s a better all round solution.

 

[Lbstyling]

Yes, but not done as yet. Drivers are about $800 + $64 for Denovo cabinets + $200 for minidsp 2x4 hd + misc connectors and wire is about $1100 before any discounts or shipping. Would be less if you build cabinets yourself. Finally, you need 4 channels of amplification, would be another $400 or more. Call it around $1500 for active vented version.

Not sure how affordable that seems, but is intended to be a good value. Does that help?

Once you add the amplification your in Hypex money, so why not use a Fusion FA122? Your using a bass driver with -60+ dB distortion, so you will need somthing good. This is a DAC, pre and power amp with digital active EQ and measurement software, ADC and even a remote for a few $more. The DAC is a really good one SINAD is 100db or thereabouts, and the amplification is load independent. SQ is as good or better than anything for any money.

I would be happy to offer support and EQ etc for using one (have several projects using them)

 

[ctrl]

Is the narrowing toward the top of the speaker (option 8) accomplishing a similar goal as a wave guide that is sized to match the woofer? Is it narrowing the dispersion of the woofer to match the tweeter near the crossover? I can't quite tell from the graphs, and I don't have the experience to understand exactly what is going on.

Okay, this is not going to be easy.

The small waveguide of the Seas-DXT controls the sound radiation only at high frequencies. In the manufacturer's measurements (quasi half-space measurements) you can see that the waveguide controls the radiation well down to about 5kHz (constant directivity CD behavior when comparing on-axis and 60° measurement).


By "removing" the baffle from the tweeter as early as possible, it radiates wider than with a baffle (which acts like a simple waveguide).
Simulated Seas-DXT in cabinet v9 without XO (10° steps):

This allows us to significantly expand the CD behavior of the waveguide in conjunction with the baffle. The 60° frequency response (FR) now runs more or less parallel to the on-axis FR down to about 1.5-2kHz.

This can be better seen by looking at the graph normalized to the on-axis FR.
Simulated Seas-DXT in cabinet v9 without XO (10° steps) normalized to deg0:



The situation is somewhat different with the woofer. There, the cone acts as a waveguide at higher frequencies.
What we want here, however, is that the transition from the 2pi behavior (the baffle influences the radiation) to the 4pi behavior (the wavelength is so large that the baffle has no influence on the radiation) starts as late as possible and the transition takes place as evenly as possible.

Therefore, (in very simplified terms) the woofer should have as much baffle around it as possible. Because the baffle also acts here like a simple waveguide focuses the radiation at low frequencies.

 

[ctrl]

What frequency is the graph showing up to?

In most cases up to 13kHz, sometimes 15kHz.
But the simulation will not match reality even earlier.

Without a sectional drawing of the tweeter, the accuracy of the simulation is limited.

Especially since the ideal behavior of the simulated tweeter cone naturally also deviates from reality. It also depends on the "resolution" of the simulation (the computation time increases exponentially with the number of boundary elements).

With a little luck the simulation is accurate up to about 8-10kHz for on-axis and angular frequency responses with an accuracy of +-1dB
In another project (using the Seas-DXT) where I helped optimize the baffle, the comparison of real measurement ("Messung") to simulation looked like this:

 

[Rick Sykora]

Once you add the amplification your in Hypex money, so why not use a Fusion FA122? Your using a bass driver with -60+ dB distortion, so you will need somthing good. This is a DAC, pre and power amp with digital active EQ and measurement software, ADC and even a remote for a few $more. The DAC is a really good one SINAD is 100db or thereabouts, and the amplification is load independent. SQ is as good or better than anything for any money.

I would be happy to offer support and EQ etc for using one (have several projects using them)

Thanks for the offer.

Intended the design to allow for amplifiers of choice, but does not exclude having the FA122 as an option. Without major modifications to the current cabinet, it would have to be mounted externally though.

 

[McFly]

Harman? I think you mean ASRman. Keep up the good work team love seeing these kinds of projects.