Directiva r2 monitor prototype build

[Morpheus]

The bass module(s) are not a major show stopper but finalizing the monitor design specifics has been. One issue has been whether the final design will incorporate a woofer for bass without the bass module. If you want to simply build the original 2-way prototype, can post the specs for it. It could be used with subwoofer(s) for bass.

Hello Rick, firstly, thanks a lot to you, TIm, and everybody else involved in this project. We understand you are doing it for the community, on your little spare time, so things take a little longer that us, non technical endowed lurkers/curios would prefer..
As I see it, there could be 4 versions of this project, all of them catering to different needs and degrees of adherence to the cardioid design ethos: a single limited bass range cardioid monitor, a bigger bass driver augmented cardioid monitor, a limited bass cardioid monitor plus monopole bass module, and limited bass cardioid monitor with cardioid bass module for the top to down cardioid approach.
Right now, the clearly most important part seems to have been well finished, the top bass limited cardioid monitor. Since it works to well below Schroeder for most if not all of us, the major cardioid benefits are already there for the taking/experimenting with, so I think you should release that design, and roll the others as they come..
Many already have subs or bass capable modules, and may not use this at very high Spls, so this monitor is already a huge step up and a great experiment for a potential larger group of people. I myself would lke to try the whole cardioid setup, but since the SB and Seas drivers are the constant variable, even if later you want to try some of the variants, you can just add another box, or build a different one, repurposing the expensive bit.

 

[Rick Sykora]

Hello Rick, firstly, thanks a lot to you, TIm, and everybody else involved in this project. We understand you are doing it for the community, on your little spare time, so things take a little longer that us, non technical endowed lurkers/curios would prefer..
As I see it, there could be 4 versions of this project, all of them catering to different needs and degrees of adherence to the cardioid design ethos: a single limited bass range cardioid monitor, a bigger bass driver augmented cardioid monitor, a limited bass cardioid monitor plus monopole bass module, and limited bass cardioid monitor with cardioid bass module for the top to down cardioid approach.
Right now, the clearly most important part seems to have been well finished, the top bass limited cardioid monitor. Since it works to well below Schroeder for most if not all of us, the major cardioid benefits are already there for the taking/experimenting with, so I think you should release that design, and roll the others as they come..
Many already have subs or bass capable modules, and may not use this at very high Spls, so this monitor is already a huge step up and a great experiment for a potential larger group of people. I myself would lke to try the whole cardioid setup, but since the SB and Seas drivers are the constant variable, even if later you want to try some of the variants, you can just add another box, or build a different one, repurposing the expensive bit.

Understood. The team and I have just been working out how to best ensure reproducible results. This is notably important if I send to Amir as he has limited time to test too. Until recently, was not comfortable with how to tell others how to get a consistent result for the internal box damping. Either you will need to match the damping exactly or have the measurement capability to verify. Given the global membership, thought it would be restrictive to limit which damping material to use. I think we have a workable solution and once we confirm, will post.

 

[ta240]

Understood. The team and I have just been working out how to best ensure reproducible results. ..........

That is such an important factor that so often gets overlooked in DIY. I sometimes wonder how close each person's version of a design sounds. I've seen people comment that they didn't like a design but then mention that they altered it noticeably. Even without making changes on purpose, a lot of designs are pretty vague about bracing and damping. I love the ones that are like recipes "dampen to taste". Like I can really remember the sound before and after taking out a driver to add more damping; and that is if I listen to the exact right sound to highlight what may be right or wrong with it now.

 

[Nils.]

The bass module(s) are not a major show stopper but finalizing the monitor design specifics has been. One issue has been whether the final design will incorporate a woofer for bass without the bass module. If you want to simply build the original 2-way prototype, can post the specs for it. It could be used with subwoofer(s) for bass.

Has the 2 way prototype changed much since the original one from January 2022? Either way I'd love to have the plans for them.

 

[Markie Warkie]

Hey just wondering if there is any updates on the R2 ?

 

[Rick Sykora]

Have been buried helping my son renovate his new house. He has moved in and so will have more time speaker stuff. I need to modify the sealed r2 to be a passive resistance design. Am not the only busy team member as am waiting on Tim to supply the previously mentioned impedance measurement too.

I regret the slow progress as I thought r2 would proceed at r1’s pace and be done sooner.

 

[Markie Warkie]

Have been buried helping my son renovate his new house. He has moved in and so will have more time speaker stuff. I need to modify the sealed r2 to be a passive resistance design. Am not the only busy team member as am waiting on Tim to supply the previously mentioned impedance measurement too.

I regret the slow progress as I thought r2 would proceed at r1’s pace and be done sooner.

Understandable thanks for the update I'm ot sure if you saw my post but il looking at building a pair of new speakers and I'd love to build a pair of r2s

 

[Rick Sykora]

Original VCAD project (@ctrl design) using @TimVG data...

 

[Rick Sykora]

Quick measurements at 0, 30 and 60 degrees at ~1m with 4ms gate...

Am getting better bass, so this is using same filters without the 3 dB attenuation on the tweeter. More work to do...

 

[Rick Sykora]

You may have noticed a few things about my first set of measurements. Am just doing these in preparation to send to another team member. They will do testing with better test equipment. The first suspect was the jag at the end of the 60 degree measurement. My second was the 0 degree one being flatter at the end of the on-axis measurement. These indicated I may have been too sloppy in set up of my measurement rig.

My first suspicion was that the platform had veered from level as I rotated the platform. This was confirmed with a level. The normal center pillar of the stand is a cardboard tube and it has gotten loose over time. I replaced it with a PVC pipe, and it is now much better (although slightly higher than earlier). A quick check confirmed it improved. Along with the new pipe, I got out my wife's Leica laser measurer and check every key dimension to ensure better alignment. Another check showed the on-axis had a more expected droop as expected after 15 kHz.

So, here is the update set. Now at the same angles, but really at 1m and the gate is 3.8 ms. The gate worsening slightly is likely due to the longer PVC pipe increasing the platform height by a few inches.

As you can see, the 30 degree response is almost the same as on-axis and the 60 degree tracking is much better.

 

[Rick Sykora]

Here is a look at impedance change from sealed to slotted cabinet. This measurement is just the woofer in the box using a laptop PC and a new Dayton Audio DATS v3 (my old test fixture required a desktop PC). First sealed...

Fs is around 88 Hz and impedance peaks at about 15 ohms.

Now slotted...

The fs is much lower and around 38 Hz and the impedance has increased to around 27.5 ohms. You can see some slight rippling between 50-100 Hz. Not sure if this is due to the slots or the prototype cabinet sides. The sides are removable and are not as secure as they would be if glued. The amount of damping is the same is both cases and is a combination of some small foam sheets lining the sides and Acousta-stuf in the middle.

I share this info for a couple of reasons. The first is trying to ensure the Directiva team is creating a consistent design by establishing a more readily reproducible baseline. The second is learning about the tuning of the slots to achieve a cardioid response. This a work in progress and new to most of the team. As you might expect, the slots allow much more air flow and so the impedance shifts closer to the free air resonance of the SB15NBAC30 woofer - 33 Hz. Also note it is more like an open baffle as it is not like the expected closed box or bass reflex impedance behavior.

As we continue to refine the cabinet tuning, impedance measure will help track how damping changes affect the cardioid performance. As with any other DIY build, it will help others determine how well their build matches the reference design too.

 

[somebodyelse]

Do you have an understanding of how consistent the damping can be made between builds yet, or is that still to come?

 

[Rick Sykora]

Do you have an understanding of how consistent the damping can be made between builds yet, or is that still to come?

Still working on it. The original proto used different material than I used. I expect consistency between builds to be fairly easy if using the same material. Since we have a global audience, am considering that folks may use different materials. Our hope is that by closely matching impedance, other builders can match the final design.

I use acoustic foam sheet to keep the Acousta-stuf from leaking out the slots but thinking may be better using grille cloth instead. Glad you asked me as can try it before I ship.

 

[Rick Sykora]

now with grille cloth liner rather than foam...

looks a bit worse to me, but as I took off stand to change lining, may not be identical alignment. Impedance changed slightly, same fs but slightly higher peak.

One more reason to ship it to professional environment!

 

[somebodyelse]

See https://www.audiosciencereview.com/forum/index.php?threads/a-cardioid-mid-coax-3-way-speaker.49096/ using basotect melamine foam in a similar application. If it works in this design it might be easier to make repeatably, and should be globally available.

 

[Rick Sykora]

See https://www.audiosciencereview.com/forum/index.php?threads/a-cardioid-mid-coax-3-way-speaker.49096/ using basotect melamine foam in a similar application. If it works in this design it might be easier to make repeatably, and should be globally available.

Thanks, but this is quite a bit more dense than we anticipate needing for r2.

 

[Rick Sykora]

The r2 prototype has left the cold north coast for warmer temps on the west coast. Will take all week to get there.

Will update the thread once we have some more useful progress to share.

 

[Rick Sykora]

Prepping to resume testing r2 this weekend!

 

[Jinjuku]

By the way: Thanks. And is there anyway I or the community can help?

 

[Rick Sykora]

By the way: Thanks. And is there anyway I or the community can help?

Thanks, nothing comes to mind but can ask the team.

This is the first Directiva prototype to be measured in an anechoic chamber and the team is mulling over the measurements and then will share. Still looks pretty good but still refining the damping material.