Directiva r2 project: market requirements gathering

[McFly]

That Kimmo guy is one of the smartest people around and is the author of the Vituix software being used for simulation. Everything is achievable DIY if you have the vision skill and equipment or enough money to outsource the parts you can't. This was not always true but it most definitely is now.

True that, what with the rise of 3d printing in the last 5 years, and CNC machining 5 before that, DIY scope has expanded significantly. And the software available. Imagine if we could all get our own mini Klippel NFS's in the next 5 for $1000, or at least something that could measure LF in a standard room!

 

[TimVG]

That Kimmo guy is one of the smartest people around and is the author of the Vituix software being used for simulation. Everything is achievable DIY if you have the vision skill and equipment or enough money to outsource the parts you can't. This was not always true but it most definitely is now.

I think @amirm or @BDWoody needs to give @kimmosto the 'Technical Expert' badge

 

[sarumbear]

It's the closest mathematical explanation for part of the acoustics that I know of. Almost every person beyond Olsen who has gone through the required trial and error to come up workable theories has not shared them publicly.

Thank you for confirming that the math behind all those suggestions do not yet exist. This must be news to posters who had been telling me "its clear, what can't you understand".

I found Linkwitz's descriptions were valid when viewed through the lens of reproducing classical/orchestral music which was his goal. This does not apply to all music across the board and was the reason for me to move them on due to not being the right solution for me. It took me a long time to work that out though.

Siegfried have indeed a classical music lens on his auditions but his speakers can produce pretty decent bass if they are set up correctly. I like EDM and played many tracks on his speakers to him at his house. I can assure you we were shaking the windows. Dipoles work. However, they are very difficult to position in a normal domestic room to make them work and to me that is a big negative.

 

[abdo123]

I have an idea, why not make an open baffle speaker that would function in the future also as an in-wall mounted speaker (resembling an infinite baffle).

This way the DIY work is minimized, people who want low frequency controlled directivity know what to do, and we can focus on designing an optimal baffle for the tweeter and driver matching instead?

 

[fluid]

Thank you for confirming that the math behind all those suggestions do not yet exist. This must be news to posters who had been telling me "its clear, what can't you understand".

I think their point is that the cause and effect of the basic principles of a passive cardioid are known empirically if not mathematically.

Siegfried have indeed a classical music lens on his auditions but his speakers can produce pretty decent bass if they are set up correctly. I like EDM and played many tracks on his speakers to him at his house. I can assure you we were shaking the windows. Dipoles work. However, they are very difficult to position in a normal domestic room to make them work and to me that is a big negative.

I may not have been clear but I built the first generation Orion and the LX521 and had them both in many different rooms for a long time. EDM is not their downfall for me but almost any form of rock music I grew up listening to. I no longer believe that there will be one speaker to rule them all, but it is possible to get something acceptable to all genres if not outstanding for all.

 

[TimVG]

Thank you for confirming that the math behind all those suggestions do not yet exist. This must be news to posters who had been telling me "its clear, what can't you understand".

Well, the only thing that's clear is that side slots with a combined surface of about 1/3 of the drivers SD, combined with copious amounts of acoustic dampening material have the desired effect

Imo just because we don't have a predictive model yet, it shouldn't stop us from experimenting and attempting to make sense of it all.

 

[sarumbear]

Imo just because we don't have a predictive model yet, it shouldn't stop us from experimenting and attempting to make sense of it all.

I agree, DIY is for fun and learning. Maybe one of us will crack the code

 

[TimVG]

Since I have the first week of next month off, I could do some preliminary testing.. Any chance we'll settle on a mid/woofer in the next few days?

Otherwise I'll just have to find a cheap 8" somewhere (or 6,5)

 

[Rick Sykora]

From what I see below, Linkwitz had already worked out how to take a OB bass module from dipole radiation to cardioid. If we need an extra channel to do, not seeing this as a design constraint with the minidsp HD for design purposes.

If dipole bass is more ideal, than would like to have offer it for those who have the room to accommodate. While appreciate @TimVG willingness to iterate, would prefer to keep the slot approach as a subsequent cost reduction effort and not have it in the critical path.

 

[TimVG]

@Rick Sykora

That's alright for the bass. But what I'm talking about is figuring out how to keep directivity more constant from the midrange down to turn the horizontal polar from this:

More into this:

So my idea has (so far) nothing to do with the bass.

But no worries. Since this is physics I can use any 6,5 or 8" driver for this experiment.

 

[Rick Sykora]

@Rick Sykora

That's alright for the bass. But what I'm talking about is figuring out how to keep directivity more constant from the midrange down to turn the horizontal polar from this:

View attachment 161102

More into this:

View attachment 161103

So my idea has (so far) nothing to do with the bass.

But no worries. Since this is physics I can use any 6,5 or 8" driver for this experiment.

Gotcha. Seems this would potentially mean iterative design for both upper and lower modules?

Naturally am interested as I would need to be able to build and measure too.

 

[TimVG]

Gotcha. Seems this would potentially mean iterative design for both upper and lower modules?

Naturally am interested as I would need to be able to build and measure too.

That's correct. At that point one would have a semi-modular system to fit different needs. I for instance am happy with monopole bass and don't see the point to have a cardioid bass source in the modal region. So I could have the top module, with controlled directivity down to the modal region (for the average room), and simply combine it with a monopole bass source from 200-300Hz onwards (just spitting numbers). Another person could combine it with a dipole bass source, or a cardioid bass source.

 

[D!sco]

@TimVG Are you talking about potentially slotting the original purifi enclosure? Color me intrigued, but how would that affect the current low end? Agreed that this would require some significant handoff to the bass driver, which makes me question the use of a +10mm xmax perfect woofer as well.

Really excited to see where this is all going.

 

[ctrl]

@TimVG Are you talking about potentially slotting the original purifi enclosure? Color me intrigued, but how would that affect the current low end? Agreed that this would require some significant handoff to the bass driver, which makes me question the use of a +10mm xmax perfect woofer as well.

If you're willing to accept an unusual baffle design, you can modify the Directiva to control dispersion down to about 400Hz.
The Purifi woofer can be replaced by a cheap but also very good driver.

The horizontal -6dB limit could then look like this for the tweeter and woofer.

A crossover frequency around 1.8kHz would provide a very even dispersion down to 400Hz.

The normalized sonogram for the woofer alone, would look like this:

For even deeper control of radiation, one must resort to alternative concepts - such as slots, OB, ...

 

[TimVG]

@TimVG Are you talking about potentially slotting the original purifi enclosure? Color me intrigued, but how would that affect the current low end? Agreed that this would require some significant handoff to the bass driver, which makes me question the use of a +10mm xmax perfect woofer as well.

Really excited to see where this is all going.

It wouldn't work with the passive radiator in any case, but you could modify the enclosure, sure. It would absolutely kill the low end and a seperate (or integrated) bass module would be mandatory. I'm not sure if 'available flat pack' is a priority for R2, we'll see what Rick comes up with.

 

[Rick Sykora]

EDIT: This post has been deprecated. See one at top of thread for latest Requirements for Directiva r2

1. The r2 speaker should be active and simple to build. It will utilize a bass module and a upper monitor module. Use of commercially available cabinets (notably for the monitor) is preferred if possible.
2. The design should be reusable and extensible to allow for design variants. Minidsp 2x4 HD will be used as the active crossover for design and costing purposes. Seas DXT tweeter is to be re-used from r1 unless design team finds a less expensive substitute(s) with better performance.
3. Bass extension is targeted to be comparable to r1, but the bass module should provide additional bass output to allow for use in rooms up to 150 cubic meters. Listening distance is targeted to be 3-5 meters. The monitor module itself can have less bass extension than r1 to allow for use with existing subwoofers or other bass modules.
4. The bass module should be designed for accurate bass reproduction and low distortion. A sealed cabinet design is preferred.
5. The design may include passive crossover circuitry to help reduce the number of active channels and allow for a passive version of the monitor section.
6. Directivity should exceed r1. The primary requirement is for more consistent directivity over a more extended frequency range. Extensibility of bass module design may consider use of variable directivity, but this is NOT a primary requirement for r2. For the monitor, custom waveguides should be avoided.
7. The cost target for the drivers and crossover would be approximately $1600 US retail per pair. This cost includes the cabinets, and active crossover but NOT the amplification.
8. The combined cabinet volumes should be 60-75 liters or smaller. Combined height should not exceed 1.2m
9. The monitor module should be no wider than 50 mm more than the midwoofer used and the bass module should be wide enough to allow monitor to be securely fitted on top. The target width of the bass module is a maximum of 260 mm.
10. The electronics should be external, but the modules may consider added volume (above stated target) for those who prefer internal active electronics.
11. The design tools should be free but flexible enough to allow external data import/export. Plan to continue with VituixCAD and REW.
12. The design should be openly shared and FOR NON-COMMERCIAL USE ONLY.

As the main Directiva r2 stakeholder and project lead, questions or comments should be directed to me.

The deadline for comments is October 31 and plan to finalize the requirements by November 1.

Thanks!

Rick

 

[briskly]

If dipole bass is more ideal

A dipole drives the gradient of the pressure mode, unlike the monopole. A pressure node is antinodal to velocity. In plainer words, the worst place to place a dipole is the best place to put a monopole. If you don't commit to a full dipole loudspeaker, the idea of a dipole bass bin seems like a bad idea.

 

[voodooless]

A dipole drives the gradient of the pressure mode, unlike the monopole. A pressure node is antinodal to velocity. In plainer words, the worst place to place a dipole is the best place to put a monopole. If you don't commit to a full dipole loudspeaker, the idea of a dipole bass bin seems like a bad idea.

Besides, looking at the 26cm maximum width requirements, that will be hard to do.. on the other hand, I’ve build a open baffle speaker with about that width. It even included a 15” bass. Bass performance wasn’t actually very bad. So it is possible.

I think the requirement list so far is quite clear. For me there are several deal breakers, but that was clear from the start. It’s not really an issue though. The general design idea and direction is still very close to where I’d like to go. So from that point of view I can still benefit from a contribution.

 

[TimVG]

Requirements for Directiva r2

1. The r2 speaker should be active and simple to build. It will utilize a bass module and a upper monitor module. Use of commercially available cabinets (notably for the monitor) is preferred if possible.
2. The design should be reusable and extensible to allow for design variants. Minidsp 2x4 HD will be used as the active crossover for design and costing purposes. Seas DXT tweeter is to be re-used from r1 unless design team finds a less expensive substitute(s) with better performance.
3. Bass extension is targeted to be comparable to r1, but the bass module should provide additional bass output to allow for use in rooms up to 150 cubic meters. Listening distance is targeted to be 3-5 meters. The monitor module itself can have less bass extension than r1 to allow for use with existing subwoofers or other bass modules.
4. The bass module should be designed for accurate bass reproduction and low distortion. A sealed cabinet design is preferred.
5. The design may include passive crossover circuitry to help reduce the number of active channels and allow for a passive version of the monitor section.
6. Directivity should exceed r1. The primary requirement is for more consistent directivity over a more extended frequency range. Extensibility of bass module design may consider use of variable directivity, but this is NOT a primary requirement for r2. For the monitor, custom waveguides should be avoided.
7. The cost target for the drivers and crossover would be approximately $1600 US retail per pair. This cost includes the cabinets, and active crossover but NOT the amplification.
8. The combined cabinet volumes should be 60-75 liters or smaller. Combined height should not exceed 1.2m
9. The monitor module should be no wider than 50 mm more than the midwoofer used and the bass module should be wide enough to allow monitor to be securely fitted on top. The target width of the bass module is a maximum of 260 mm.
10. The electronics should be external, but the modules may consider added volume (above stated target) for those who prefer internal active electronics.
11. The design tools should be free but flexible enough to allow external data import/export. Plan to continue with VituixCAD and REW.
12. The design should be openly shared and FOR NON-COMMERCIAL USE ONLY.

As the main Directiva r2 stakeholder and project lead, questions or comments should be directed to me.

The deadline for comments is October 31 and plan to finalize the requirements by November 1.

Thanks!

Rick

1/8/9) Let's just use the Denovo bookshelf & tower cabinets then - they tick all the boxes.

2) If the design is meant to be scalable, more then 2 DSP channels would be handy. The original design, imo, still benefits from using 2 DSP channels over a passive crossover, and since at leas part of the design is being recycled this would be handy. I also believe for this cabinet there's better out there than the DXT tweeter, but I doubt one can could do it for the same, let alone less money.

7) Again, if the design is meant to be scalable $1600 may work for one version, but not for another. If you need a lot bass output and extension, and also want a cardioid dispersion pattern, that alone will set you back 3-5 capable drivers and two DSP channels.

 

[Rick Sykora]

Should have stated earlier, I (mainly) wrote the requirements in the spirit of market requirements.

While the earlier thread discussion did go beyond what the speaker could be, please try to keep review comments about what r2 will be rather than how to do it.

I realize this may be a challenge for some, but I will hand off the task of how to implement r2 to design team(s). At some later point, may hold a design review if we feel further feedback is needed.