tuga
Major Contributor
Is that a PA model? How big is the woofer (can't find it on your website)?
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Directiva r2 project: market requirements gathering
- Thread starter Rick Sykora
- Start date
Is that a PA model? How big is the woofer (can't find it on your website)?
I remember a member sharing an in-room response measurement of the Kii 3 and a regular omni-speaker (Devialet Phantom). they said that cardioid wasn't worth it while clearly the Kii 3 had a much much lower response error rate. It was very confusing to read. One might argue that whatever benefits are there above 200Hz are the same below 200Hz. For example with a cardioid down to 200Hz you're limited in placement with regard to the front wall, if you want to avoid SBIR it has to be closer than 0.4 meters, which pretty means shove it to the wall.
I don't know if this will be of assistance taken from a link posted above
"Acoustic resistance enclosure or sometimes referred to as a leaky sealed box, can be an alternative to open baffle. The acoustic resistance enclosure can be implemented with filter like material that is porous with air flow resistance. Then the ratio of acoustic resistance of the vents, R (Ns/m^3) relative to the acoustic stiffness of the box, K (N/m^3) will add delay, T, where T = R/K (s). So in theory, the out of phase acoustic AC pressure from the back of the transducer diaphragm is delayed and leaked from the enclosure such that the rear directed sound pressure is cancelled. This sometimes referred to as passive noise control. Figure 6 below contains generalized illustrations of rear and side vented acoustic resistance enclosure examples. Where R is the acoustic resistance (Ns/m^3 or MKS rayl); ℓ is the minimum front to back or back to front path length (m); S is the total exit area of the vents (m^2); Vol is the internal volume of the enclosure (m^3); and B is the adiabatic bulk modulus of air, 142,000 (N/m^2 or Pa), then K = BS/Vol (N/m^3). Energy is dissipated in the vents et al.; thus the leaked radiation is attenuated and damping is increased".
There are many examples of the point ctrl is trying to make. This is why ported boxes are only minimally stuffed as a general practice and usually at the edge of the cabinet. If you stuff more you damp the resonance and lose the bass that you were trying to get with the port. Damp the resonance, lower the Q sounds very similar to me.
Akabak and ABEC are pretty much the same thing now, just depends on whether you like scripts or point and click.
I only just posted a link where a lot of this is covered
https://www.audiosciencereview.com/forum/index.php?threads/directiva-r2-project.27212/post-948566DIY)
Without plane wave tube impedance measurements or the properties of the filling material in the appropriate format (neither of which are yet available DIY) then what can be simulated is varying amounts of damping. This has some use but is doesn't take away some cut and try. The basket of the driver used also has an effect on the low pass filter and all of these things are difficult to account for outside of FEA and full models of everything. Vent sizes and positions can be done in Vituix quite quickly to see the effect and avoid having to make lots of sawdust. The cardioid effect works best over a limited bandwidth and needs different solutions depending on which bandwidth is targeted.
Is that the Sica 5.5" coax stacked on an 8" woofer of some sort? Looks really nice!
All the experiments for Designing the 8c cardioid cabinet have been linked to by me earlier in the thread (DIYaudio). You have what you need. It's really not that complicated.
It's under development, and only exists as an early prototype so far. It's intended for home/consumer use. It's roughly the size of the the JBL L100 Classic (slightly smaller). The woofer is a 12".
On the picture below it's next to our SBS.1 for scale.
Yes, only the driver is 12". Thanks!
tuga
Major Contributor
It's under development, and only exists as an early prototype so far. It's intended for home/consumer use. It's roughly the size of the the JBL L100 Classic (slightly smaller). The woofer is a 12".
View attachment 160830
I'll start saving!
Crowdfunding available?
No, we considered crowdfunding in the early days, but there are not a lot of audiorelated crowdfunding projects. Also in general the most successful crowdfunding projects are low / moderately priced items, it's rare for higher priced products to succeed. So not sure if it's realistic to get traction on crowdfunding for something like this.
What I saw an experiment where someone blocked the back of an open baffle speaker and instead of a figure-of-eight polar diagram that you expect from a dipole speaker he got a cardioid like response. That is neither knew nor ground breaking. They were open baffle speakers where the rear sound was blocked. There was no compliance change for the driver, its Vas stayed the same. In other words there was no enclosure. As it is with microphones, by controlling rear sound of a transducer you can change its polar diagram. See below. Mathematics of this clear and well understood.
So far I looked at two examples of measured cardioid polar patterns on a manufactured speaker. D&D 8C and the active models of German Geithain. They both use a single driver to achieve the cardioid like response. Kii3 for instance is different; they use multiple drivers driven separately and facing all around the cabinet.
D&D 8C has a cardioid like polar response above 100Hz. Geithain works down to around 50Hz.
D&D 8C has two simple slots on either side of what otherwise looks like a closed box. I can only think them to act as ports. However they seem to do something else but I have no mathematical explanation for it.
Geithain on the other hand use a round side "opening" which the designer says is an acoustic filter and is cagey about how it works. What I saw was certainly didn't look like a normal port. Their system also is not explained mathematically. The designer considered patenting their design but not done it.
In short, we have no understanding of how either D&D 8C's or the German speaker's slots work. @Lbstyling says it is not complicated. I wish it to be true. It must be bliss to assume acoustics and physics are simple to understand. They never are. I do however, wish everyone to enjoy their hobby. You don't have to understand the math behind certain phenomena to enjoy your hobby. Stay in bliss
Looks almost identical to one of the Geithain models I mentioned on my earlier post.
https://de.wikipedia.org/wiki/Musikelectronic_Geithain (in German, use Google translate)
Getting state of the art quality and directivity control down to the lower ranges in DIY with a middle class budget, or a fraction of the finished standard bearers price ( for me, Grimm 1st,, especially with the sub, Ki 2nd, DD 3rd )..Take the best evidence an the ideas like those implemented by Grimm, DD and Kii and deploy them in the best way to get us DIYers a no holds barred, best of those implementations speaker, but without their retail cost..They explored different doable approaches for this goals, and only the very lowest bass at the highest output could have to be sacrificed, or made modular/ scalable, to get us in that boat....Not to disrespect the teams knowledge and innovative thinking and ability to come up with alternative or complimentary solutions, but those, plus Ggtk's, readily point a lot of solutions on how a practical home friendly approach can be made to work, at a lower price point...None of them even uses inordinately expensive drivers, at least nothing compared to our Directiva r1 ( well, the excel woofer is up there too..).The fact that we can mix and match those ideas and others, not strictly bound by brand and patent infringment in DIY vs commercial use, could probably even lead to bigger achievements than what they got, for a sane pricepoint, if we are willing to go the distance in building them, and the team on managing to engineer this "SOTA for a price" marvel...That's why I didn't jump on the R1..Its great, but I think better is still to come from this team, and I rather spend once, and for good ..
R and K range of available acoustical materials is known. By roughly guessing the values and using the actual measurements of the 8C, you can calculate T. Try if you can get a delay long enough to cause cancellations above 100Hz. The wavelength of 100Hz is almost 3.5 metres and the 8C slot to driver distance (ℓ) is at most 0.2m?
The important word in that text is "in theory". In practice I cannot see how it works using the math described above.
Not sure if it was already posted here, but it does contain quite a bit of information on cardioids: https://www.audiosciencereview.com/...about-cardioids-but-were-afraid-to-ask.10359/
Some more interesting info: https://projekter.aau.dk/projekter/...ol(6e5295bf-c2df-44b6-976a-173e8a842c8a).html
Especially the part from chapter 7 on is interesting.
Especially the part from chapter 7 on is interesting.
It appears that at least for a passive approach, we're a bit in the dark on the math. Which means in effect there's a lot of trial and error involved. Which in turns means the right way to do it can't be immediately transferred from project to project. But I guess there are opportunities to share some results and what parameters seem to have a lot of impact.
We'll start a development thread for the new speaker relatively soon, and will share at least some of what's going on with the vents on the sides, depending on how it goes. The vents are connected to the chamber housing the coax (the 12" driver is in a separate chamber), so there will be a traditional approach to the lowest frequencies.
We'll start a development thread for the new speaker relatively soon, and will share at least some of what's going on with the vents on the sides, depending on how it goes.
The vents are connected to the chamber housing the coax (the 12" driver is in a separate chamber), so there will be a traditional approach to the lowest frequencies.
OP
- Thread Starter
- #399
Was researching more of Linkwitz's studies on directivity. Notably how he changed a OB woofer design from a dipole into a cardioid. He considered the cardioid bass inferior to the dipole. I do note that dipoles are not for everyone and even my decent-size listening space is smaller than what Linkwitz suggests for his designs. As it turns out, Linkwitz was a bit skeptical how beneficial a cardioid might be. Here is quote from his website...
"A cardioid or U-frame woofer would exhibit characteristics of both monopole and dipole. It is not clear what the room acoustic benefits might be. Unlike the H-frame with its 90 degree nulls, these types of mixed radiators can excite room modes at ALL angles. Even the null towards the rear of a pure cardioid woofer does not prevent the excitation of the room mode along the 0 degree to 180 degree axis."
Along the way, I found some of his observations on many of the designs we are discussing here. so thought I would share
Enjoy!
Rick
"A cardioid or U-frame woofer would exhibit characteristics of both monopole and dipole. It is not clear what the room acoustic benefits might be. Unlike the H-frame with its 90 degree nulls, these types of mixed radiators can excite room modes at ALL angles. Even the null towards the rear of a pure cardioid woofer does not prevent the excitation of the room mode along the 0 degree to 180 degree axis."
Along the way, I found some of his observations on many of the designs we are discussing here. so thought I would share
Enjoy!
Rick
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dc655321
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Think about what happens to the speed of sound in different materials.
