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Introducing Directiva - An ASR open source platform speaker project
- Thread starter Rick Sykora
- Start date
OP
- Thread Starter
- #942
Ok, but for me, Amir has hosted the project on his site and helped with r1's development. Agree there is no stopping someone else from sending to Erin, but as mentioned, he could test much more popular speakers and benefit more people than testing Directiva. His other risk is to open door to requests from other DIY efforts. I foresee less incentive for Erin to get involved IMO.
For me, have heard both active and the passive versions at point with much the same music. I still have passive testing to do, but have not heard anything that would make me pick one over the other to date. Am in the same room, with the same amplification and the main diff so far is the passive has no hiss. I expect this could be remedied with a hybrid crossover, but that is another project still in my queue. Am also in the middle of Directiva r2 design, so if anyone wants to build their own and can get Amir or Erin to test, fine by me! I could use a bit more time to get back to more listening.
Don't want to speak for @hardisj but he has recently stated that he is more than happy to help out DIYers refine a design.
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Michael
Revel M105 Copy DIY build
This is a really nice build. 3D printed components are on the level of active crossovers for new school cool. Can't wait to see the finish!
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Michael
Great work so far! Long thread (and a fascinating one), so I may have missed it. When you found out the SB15 could not go low enough to meet a typical sub, what was the reason for not going up a size? Does the cardioid design have a bandwidth restriction?
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To be honest, I never expected it would - the design goal was always to couple it with a bass module. In fact it performs as I expected it would. Effectively you have to consider R2 as a 3-way system, of which the prototype is only the top module. One of the design goals was better and more extended directivity, and in that respect we have succeeded. Going up a size would not have cut it. Even the 8" midrange of the venerable D&D 8C cannot be crossed at 80Hz. So you're looking at quite a large monitor if you want (passive) extended directivity control and be able to directly cross to a subwoofer.
Now, if you plan to cross at 80Hz - you simply don't need a very powerful bass module. That's one advantage of having a modular system - you don't have to leave anything on the table and spend your money where you need it.
There are talks of an alternative R2 top module, without the extended directivity behaviour, but as a standard ported enclosure.
Might this work? (Not a recommendation - never tried one.) Claimed f3 of 78 Hz in less than 1 ft3.
Ignore the pumped-up Xmax spec. The copper cap and sensitivity make it interesting to me.
Why? No offense but the world doesn't need another regular DIY 2-way speaker.
The current top module can be relatively easily crossed (actively) @100Hz with a subwoofe specially with 4 Ohm version. It won't be optimal but it won't be that much worse than a regular sealed speaker.
For those who don't want to use a subwoofer are more than welcome to build the much easier R1.
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Rick suggested it. At that point (post R2) it would be a relatively straightforward design to execute. So not as much as a why but rather a why not.
At this point however, it's just talk. Rick is still working on R1 (passive) and I am focussing on R2 along with another (unrelated) build. I wouldn't have the time if I wanted to.
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I see no reason why it wouldn't. Make it side firing and you can even have it match the width of R2 visually.
I would suggest however to wait and see what the design team comes up with.
Point taken. Maybe i should have been more precise.
Napilopez shows the way it can be done with success without Klippel NFS. His restriction is too short gate time, which isn't a problem for me. I have done ,and still can, over 10ms gated measurements and merge it with groundplane at 150-200Hz to get the effective result of 50ms reflection free window.
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OP
- Thread Starter
- #951
Have to agree there are fair number of 2-way DIY speakers out there. I am not sure how many have good directivity and a number of folks have asked for a cheaper r1. Maybe will just replace the woofer in R1, redo the crossover and call it done. Will see, am still trying to get a passive crossover done for r1 and we are in the middle of the r2 effort, so the cheaper 2-way Directiva is still on the back burner.
Making the phase response the same in passive and active is very hard. Crossover slopes will be different because drivers interact with passive components and it will make for different frequency response if you use the same transfer functions. Acoustic slopes should be as close as possible regardless of crossover slopes.
Other than that, you can introduce a protection, say high pass filter at 20Hz to reduce the woofer excursion and low pass filter to filter out the breakup of tweeter - both things influence distortion profile and can sound quite different when listening a bit louder. Not to mention adressing smaller nuances in frequency response with DSP active which isn't always economic/practical with passive crossovers.
I've been working with the team sort of keeping track of things. When the project is mature, I intend to create documentation answering most of these questions.
Regarding the passive crossover -
Making a fully passive 3 way cardioid is not practical, and so you can expect that this speaker will need an active filter between the W and M/T drivers. However, I believe that a passive network between the M/T with DSP will work well, potentially just as well as a fully active 3 way design. The reason for this is that the effects of the cardioid radiation on the woofer output are fairly benign, simple, and occur far from the crossover region of c. 1.8 khz. In addition, the drivers selected for the M and T blend together very well. As someone who has been designing crossovers for conventional speakers for a long time, it's honestly amazing how easy crossover design is when diffraction is taken care of and the tweeter has modest waveguide behavior.
This makes the speaker more practical, since the DSP can be enacted with a single minidsp unit, or even a two channel Hypex Fusion plate amp (this would be my choice).
Regarding the bass unit -
While the team has converged pretty well on the mid/treble box, with drivers being selected after a lengthy process taking both value and performance into consideration, the bass unit is less developed. I think the reason for this is that while the bass unit is not simply a subwoofer (needing response into the 100-300hz region, distortion testing should tell us), it's a fairly simple exercise to get adequate bass spl.
My own feeling is that cardioid bass is probably not advantageous in domestic spaces, but would be nonetheless very cool to try to pull off. As a result I could see several bass unit alternatives, and the builder can select the one which best fits their needs:
- A slim, economical bass unit which has output that complements the treble unit
- A deeper, probably fairly expensive cardioid output bass unit, for those who are naturally curious to the benefits of cardioid bass.
- A larger bass unit for those who want high output, lower distortion, or just want a big speaker. Think something like the Genelec W371A - big ass woofer in a tall box.
Regarding the passive crossover -
Making a fully passive 3 way cardioid is not practical, and so you can expect that this speaker will need an active filter between the W and M/T drivers. However, I believe that a passive network between the M/T with DSP will work well, potentially just as well as a fully active 3 way design. The reason for this is that the effects of the cardioid radiation on the woofer output are fairly benign, simple, and occur far from the crossover region of c. 1.8 khz. In addition, the drivers selected for the M and T blend together very well. As someone who has been designing crossovers for conventional speakers for a long time, it's honestly amazing how easy crossover design is when diffraction is taken care of and the tweeter has modest waveguide behavior.
This makes the speaker more practical, since the DSP can be enacted with a single minidsp unit, or even a two channel Hypex Fusion plate amp (this would be my choice).
Regarding the bass unit -
While the team has converged pretty well on the mid/treble box, with drivers being selected after a lengthy process taking both value and performance into consideration, the bass unit is less developed. I think the reason for this is that while the bass unit is not simply a subwoofer (needing response into the 100-300hz region, distortion testing should tell us), it's a fairly simple exercise to get adequate bass spl.
My own feeling is that cardioid bass is probably not advantageous in domestic spaces, but would be nonetheless very cool to try to pull off. As a result I could see several bass unit alternatives, and the builder can select the one which best fits their needs:
- A slim, economical bass unit which has output that complements the treble unit
- A deeper, probably fairly expensive cardioid output bass unit, for those who are naturally curious to the benefits of cardioid bass.
- A larger bass unit for those who want high output, lower distortion, or just want a big speaker. Think something like the Genelec W371A - big ass woofer in a tall box.
With the woofer module playing up to 300hz, would that negate the cardioid behavior of the M/T? Would we still get cardioid behavior down to 100hz, ala D&D 8C? Does this even matter?
Sorry... I'm probably asking questions that will in your documentation. Just really excited for the possibility of hearing cardioid without spending $10K
It's a matter of tradeoffs. The sb15 exhibits outstanding cardioid behavior down to 200hz or perhaps below (I don't think we've measured any lower.) However, distortion becomes a factor when you take into account the 4db cancellation loss embodied by the cardioid radiation. The D+D uses a much bigger midrange with a lower crossover point and has high distortion for an 8" midrange speaker, so we can expect distortion (or excursion, really) to be the limiting factor for our design.
I do not know where the cardiod/monopole crossover frequency will end up, but it will around or below the schroeder frequency of most rooms, while maintaining what we determine is acceptable levels of distortion.
If you want full range cardioid and it's going to be an expensive proposition, for the same reasons dipole bass is expensive - tons of output being cancelled out by itself. I do not know what the team's feelings towards the cardioid bass module are, but I hope someone develops it simply for people who want something special.
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It would negate the effect, yes. However the question remains how beneficial cardioid behaviour will be in the modal region. A crossover somewhere from 200 to 300Hz is still in the modal range of the average room. This would mean that you'd only ever have to EQ the bass module in-room, no need to tamper with the top module.
Instead of thinking cardioid you could also look at it as controlled directivity over a wider range. This means that the off-axis sounds remain timbrally close to the direct sound, and consequently the crucial early horizontal reflections are as well. If we look at the horizontal behaviour (shown here down to 200Hz) of R2 compared to the well measuring (and much larger) Genelec 1032A, it's easy to see just how much more consistent R2 radiates sound. These things tend to not be very pronounced in a spinorama, but it's there nonetheless.
I thought it might be helpful to describe what is special about these directiva projects, what they offer, what they do not offer.
Traditional DIY designs tend to target all-around performance, with the same compromises that commercial speakers have. In other words, you set a budget, you set a size, and you make the best speaker you can within those specifications.
The directiva projects offer something a little different - they seek to achieve performance characteristics which are rarely available in DIY or commercial designs. They give you a taste of state of the art performance, but this comes with certain costs.
In the first speaker, the cost was complexity and expensive, esoteric drivers. What you got in return was probably the best performing small speaker on the planet, with limited bass performance.
This second speaker I offers better value, but it is still a complex design. What you get in return is a very special radiation pattern which is similar to a large waveguide speaker like a Gedlee Abbey or something. The bass and overall output is dependent on how much you are willing to spend, and although I hope the team develops a few bass modules, in reality any DIYer can make an active bass speaker.
In both cases, you get a design validated by careful measurements and a degree of customization - want 3db less treble? You can dial it in according to your room and your taste.
There are outstanding speakers on the market these days, and I believe the value proposition for DIY has weakened. Why DIY when Elac, KEF, Harman and Arendal make such good passive speakers? Why DIY when you can get a whole active system from Kali, Neuman or Genelec? Except in the case of very large speakers, DIY doesn't offer a ton of value, unless it does something special. That's where these speakers excel.
Traditional DIY designs tend to target all-around performance, with the same compromises that commercial speakers have. In other words, you set a budget, you set a size, and you make the best speaker you can within those specifications.
The directiva projects offer something a little different - they seek to achieve performance characteristics which are rarely available in DIY or commercial designs. They give you a taste of state of the art performance, but this comes with certain costs.
In the first speaker, the cost was complexity and expensive, esoteric drivers. What you got in return was probably the best performing small speaker on the planet, with limited bass performance.
This second speaker I offers better value, but it is still a complex design. What you get in return is a very special radiation pattern which is similar to a large waveguide speaker like a Gedlee Abbey or something. The bass and overall output is dependent on how much you are willing to spend, and although I hope the team develops a few bass modules, in reality any DIYer can make an active bass speaker.
In both cases, you get a design validated by careful measurements and a degree of customization - want 3db less treble? You can dial it in according to your room and your taste.
There are outstanding speakers on the market these days, and I believe the value proposition for DIY has weakened. Why DIY when Elac, KEF, Harman and Arendal make such good passive speakers? Why DIY when you can get a whole active system from Kali, Neuman or Genelec? Except in the case of very large speakers, DIY doesn't offer a ton of value, unless it does something special. That's where these speakers excel.
dc655321
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That is an interesting question, for sure.
I would think that maintaining cardioid directivity down through frequencies that are traditionally problematic could only be a good thing (say, ~100Hz).
But engineering seldom admits "a good thing" without also introducing something "less good"
OP
- Thread Starter
- #960
Will just add that @617’s ”limited bass performance” is a matter of taste. Directiva r1 measures down to low 40s by Amir’s spin data. For many listening to music in apartments, condos and smaller rooms that is plenty. For low bass or HT special effects, few speakers are capable and you will need a subwoofer anyway.
