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Directiva r2 project: market requirements gathering

ctrl

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So, now it's time for the criticism of the targeted crossover frequency of the bass module or the bass module itself.

Roughly above 150-200Hz, the directional localization works quite well. That means at a crossover frequency of 500Hz, the three front woofers (W1-3) play with the same sound pressure level and the sound localization will most likely fall on woofer W2 - that's bad.

1635000823457.png
Therefore, the woofers W2 and W3 should actually play a bit quieter than W1 or show a steeper filter slope so that the localization is as close as possible to W1, i.e. the 2-way speaker top.

Update: I have deliberately not taken into account possible ground reflections - this makes the whole thing even more complicated.
 
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sarumbear

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Think about what happens to the speed of sound in different materials.
Think about how that speed change is linked to the compliance of the material, which change with frequency. Have you ever seen an absorber with a linear FR?
 

abdo123

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So, now it's time for the criticism of the targeted crossover frequency of the bass module or the bass module itself.

Roughly above 150-200Hz, the directional localization works quite well. That means at a crossover frequency of 500Hz, the three front woofers (W1-3) play with the same sound pressure level and the sound localization will most likely fall on woofer W2 - that's bad.

View attachment 160905
Therefore, the woofers W2 and W3 should actually play a bit quieter than W1 or show a steeper filter slope so that the localization is as close as possible to W1, i.e. the 2-way speaker top.

Update: I have deliberately not taken into account possible ground reflections - this makes the whole thing even more complicated.

the Kii (and BXT) do woofers on the side as well, would that make things simpler in anyway?
 

ctrl

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the Kii (and BXT) do woofers on the side as well, would that make things simpler in anyway?
Actually, the precedence effect should prevent what I described, because woofer W1 is always closest to the listener, on the other hand, one hear people say that especially with 2.5-way speakers certain frequencies move down and the speaker is not perceived as a point source.

With the Kii and the BXT module, the precedence effect should also take effect and the crossover frequency to the BXT module has to be well below 500Hz - or not?
 

sarumbear

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So, now it's time for the criticism of the targeted crossover frequency of the bass module or the bass module itself.

Roughly above 150-200Hz, the directional localization works quite well. That means at a crossover frequency of 500Hz, the three front woofers (W1-3) play with the same sound pressure level and the sound localization will most likely fall on woofer W2 - that's bad.

View attachment 160905
Therefore, the woofers W2 and W3 should actually play a bit quieter than W1 or show a steeper filter slope so that the localization is as close as possible to W1, i.e. the 2-way speaker top.

Update: I have deliberately not taken into account possible ground reflections - this makes the whole thing even more complicated.
Or you can EQ/filter W2 and W3 as done on so called 2.5 way systems. W2 and W3 can work to compensate the baffle step effect of the narrow baffle. I used a 2nd low frequency driver on Silver 5L for that. Baffle step effect is 6dB with a changeover of roughly 6dB/oct slope.
 

ctrl

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Or you can EQ/filter W2 and W3 as done on so called 2.5 way systems. W2 and W3 can work to compensate the baffle step effect of the narrow baffle. I used a 2nd low frequency driver on Silver 5L for that. Baffle step effect is 6dB with a changeover of roughly 6dB/oct slope.
It's not quite that simple here, because (the phase-shifted) woofer W4 that helps us to control the directivity somewhat is also still there. Therefore it has massive effects if W2 and W3 are reduced (and phase shifted) in the sound pressure level by steeper filters in advance.

Without filter
1635006947314.png

With steeper filter for W2 and W3 to reduce sound pressure above 200Hz.
1635006974917.png
 

sarumbear

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It's not quite that simple here, because (the phase-shifted) woofer W4 that helps us to control the directivity somewhat is also still there. Therefore it has massive effects if W2 and W3 are reduced (and phase shifted) in the sound pressure level by steeper filters in advance.

Without filter
View attachment 160920

With steeper filter for W2 and W3 to reduce sound pressure above 200Hz.
View attachment 160921
Who said it’s simple. But it’s doable.
 

voodooless

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There is another way to enhance the effect of the rear woofer: mount it much more inside of the enclosure, so closer to the front woofers. That way you extend the path length, and thus enhance the effect. You will create a kind of cavity though, which may have it’s own set of problems.
 
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sarumbear

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sarumbear

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Lbstyling

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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
It's worth noting that his comments are generally spoken from the perspective of enhancing his speaker design (I.E the Orion /LX 531.
His speakers are heavily optimised to be placed quite far out in the room. As wonderful an engineer as he was, his speakers do not score well on the Spinorama' that ASR is biased towards because he had different design goals.

D+D/Kii are the opposite of linkwitz in part because they are optimised to use the cardioid polar to make use of being almost against the front wall.
 
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sarumbear

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It's worth nothing that his comments are generally spoken from the perspective of enhancing his speaker design (I.E the Orion /LX 531.
His speakers are heavily optimised to be placed quite far out in the room. As wonderful an engineer as he was, his speakers do not score well on the Spinorama' that ASR is biased towards because he had different design goals.

D+D/Kii are the opposite of linkwitz in part because they are optimised to use the cardioid polar to make use of being almost against the front wall.
Very correct observation and a fact.

Siegfried was a close friend. We knew each other since late 70s. Spinorama was never a criteria for either of us. However, since studying reviews on ASR, I now believe it to be an important virtue.
 

Lbstyling

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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.

View attachment 160873

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 :)
So think we are at opposite ends of the spectrum of approach.


In practical terms, I have removed Various sized and shaped Sections of the side panels of small bookshelf designs, and wrapped the driver in ever increasing layers of wool a la the early attempts tried in the above link.

I measured significant improvements in spl 'null' for the bass driver behind the speaker when placed in an open field. I did measurements at the time and improvements over a ported box really were that simple. Perfect? No. The width of the null increased as I moved the wool away from the driver, but response became more irratic, and the null shallower.

The large drop in efficiency and bass was very clear. You want a sub driver under it to pull it off, even if using the Purifi I would imagine.

Anecdotally, I also remember at the time others were finding that in room it didn't work to control below 100hz but in a field it does.

We need to see it as an evolution rather than expect to find the math and just do it first time. The point I'm making is that you really don't need to fully optimise anything when you have no opposition! Your nearest competitor is circa $20k.

IMO people are expecting too much from a first go at it. A DIY cardioid design even half baked would be the most interesting DIY design in the last 10 years.
 
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sarumbear

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Morpheus

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Was researching more of Linkwitz's studies on directivity. Notably how he changed a OB woofer design from a dipole into a cardioid.

An open baffle concept, is a non starter as is for the majority I would think, as I can't move the speakers much into the room, and reflections land right where they shouldn't..So, for me only the low bass open baffle bass is a possibility, although what I would I actually would rather have a sealed box, That is what almost invariably sounds best to me, and is getting rarer even with the equing and power options we have these days..Linkwitz himself lamented that there were no constant directivity SOTA designs using sealed alignments at all when he was alive, at least to lowish frequencies..Although, I think the Grimm, and DD actualy are sealed implementations , and give you that..
 

sarumbear

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fluid

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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.
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.

The other part of the delay comes from the low pass filter effect of the basket, materials and venting. The group delay of the filter extends the overall delay and refining this is what takes the cut and try. An active cardioid is simpler purely because all of the parameters can be adjusted through the position of the cancellation driver and the filters applied to it. There's no amp channel available for it in this project unfortunately as it would make ctrl's modelling work much easier.

Along the way, I found some of his observations on many of the designs we are discussing here. so thought I would share

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.
 

fluid

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That guy, Kimmo has seems to have tried practically every possibility. Very impressive work. I can just about imagine how Geithain‘s design works. Very complicated as I expected. I cannot imagine it to be achievable on a DIY project.
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.
 
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