Directiva r2 project: market requirements gathering

[fluid]

I was just realizing that. So how does the Genelec system work? Is there a directivity mismatch between the W371 and the monitor on top of it?

There are two steps in the directivity related to baffle size and box size. The first step is when the baffle is no longer constraining radiation and the second related to the width and depth of the cabinet combined. In a rectangular box with no passive or active radiation control on the sides or rear these steps are inevitable.

The Genelec Ones use a coaxial driver with the front baffle contoured as a waveguide to control the directivity of the mid and tweeter, the woofers exit through slots spaced apart to narrow the radiation either vertically or horizontally depending on how they are placed.

The larger 14" woofer in the W371 naturally has narrower radiation higher up in frequency, the crossover point is chosen to match that of the monitor above. The rear woofer narrows the pattern through cancellation at the upper end before transitioning back to omni below 100Hz or so to not lose all the bass.

Not all of that is possible in an off the shelf box. Don't forget that the Ones and W371 are big speakers in comparison to the R1.

Active side woofers are a more practical option to create similar directivity in an off the shelf box but the cost has to be considered.

 

[Rick Sykora]

I was going to say that the Directiva R1 cabinet is the Denovo 0.56 cu. ft. box and it will perfectly match the Denovo 1.16 cu. ft. box you linked to but actually the bookshelf is 1/2" wider unfortunately. So they might not look very appealing when stacked.

I think someone already mentioned this but I like the idea of the 1.16 cu. ft. cabinet made into a bass module for the 2-way bookshelf R2 design to sit on top of. Something like the W371 or Kii BXT would be ideal. I don't know if the dimensions of this cabinet would be conducive to a W371 style design and I imagine a BXT style design would be more expensive and complicated so maybe it doesn't make sense.

In any case I like the design direction I have seen expressed a few times in this thread which seems to be a bass module, possibly with directivity control down to "x" frequency, along with a 2-way bookshelf design similar to R1 but with a less expensive woofer.

Yes, the baffle width mismatch between the 2 Denovo cabinets is unfortunate. Notably since the tower is narrower where wider would have been more aesthetically acceptable at least. I wanted to see how the thread continued while I was away. Particularly to see how much a poll might be needed. At this point, I see enough convergence to put together some r2 requirements. I think the only major question is whether a wide baffle should be used to help control directivity...

Sticking with the extensible approach, the major ramification is how wide the bass module might need to be to allow a monitor to match up with it. Am going to resolve this by shooting down a wide baffle design as a directivity control approach. Even if I could get over the marginal appearance, pretty sure my wife will not! Wide panel speakers also have much more constrained room placement options. I would like to opt for more flexibility rather than less. In walking before we run, better low frequency directivity could be a design option. Without the wider baffle, it is likely to require using more midwoofers or a fancier cabinet design.

Will give this a couple of days for members to consider this approach. Then will hopefully be ready to solidify requirements by the end of the week.
Thanks!

Rick

 

[ctrl]

They have extension to 500hz and have an operating mode specifically to maintain constant directivity when used with Ones with that high crossover point. Presumably the monitors are high passed to match. We think of the W371 as a subwoofer but they are much more than that.

An abrupt change in directivity will probably be unavoidable for the 8341A and 8351A with the W371. This is simply due to the dimensions of the speaker cabinet as @fluid described and the crossover frequency of the W371 bass modul.

Due to the slightly larger enclosure than the 8341A (or Directiva, for example), the 8351A can probably avoid the unavoidable for a bit longer, but the first widening in dispersion occurs above 500Hz from 100° dispersion to 220° dispersion at 700Hz (compared to Directiva at 800Hz).

At lower frequencies, the W371 module prevents the further increase in dispersion.

 

[abdo123]

An abrupt change in directivity will probably be unavoidable for the 8341A and 8351A with the W371. This is simply due to the dimensions of the speaker cabinet as @fluid described and the crossover frequency of the W371 bass modul.

Due to the slightly larger enclosure than the 8341A (or Directiva, for example), the 8351A can probably avoid the unavoidable for a bit longer, but the first widening in dispersion occurs above 500Hz from 100° dispersion to 220° dispersion at 700Hz (compared to Directiva at 800Hz).
View attachment 160353 View attachment 160354
At lower frequencies, the W371 module prevents the further increase in dispersion.

This is very interesting, so basically with the W371 the 8641A becomes the most linear speaker, while without it the 8341A is the most linear.

 

[sarumbear]

Edit: I just saw the post that TimVG wrote about confusing terminology, and I agree.

I'll do my best to clear up what seems to be a slight disconnect/confusion about the "cardioid" talk (from both sides, not just you).
Directivity control to a low frequency is achieveable by using a cardioid design, either by woofers wired out of a phase with a time delay on the side and/or back, or by passive means using a leaky slot. I am assuming you know this, but it's worthwhile context for other readers.

You have correctly noted that directivity control this way is challenging (impossible) to do high in frequency, primarily because of the width of the baffle. There are limits to how slim you can make the baffle, and the baffle necessarily needs to be small relative to the wavelength of the frequency we wish to cancel.

However; directivity control by the means of a waveguide, if looked at with a polar plot, will have a shape that is not too unlike a cardioid solution: low pressure 180 degrees from the front, and gradually sloping before that as you move off-axis. Attached is an image of a polar plot of the gradient helsinki 1.5, as measured by Princeton University (scroll down). This is a design with a passive cardioid midwoofer and a waveguided tweeter. At 5khz (the lowest frequency the tweeter was measured at before being crossed over to the woofer) we can see that the tweeter, as you move very far off-axis, drops by close to 20dB.

But a 20dB drop is not an infinite drop, which is what a theoretically ideal cardioid should have 180 degrees off-axis. "Luckily" for us, we won't get a perfect cardioid performance from the actual cardioid aligment either, due to various losses. I believe the designer of the dutch and dutch has mentioned that he can get a passive cardioid down to about -20dB attenuation at the back. More is possible with active solutions of course, and the passive gradient seems to have about 30dB of attenuation at 500hz (no measurements below that).

The end result, if we combine these two techniques to control directivity, is a speaker that has a "cardioid-ish" response over a wide bandwidth. In the case of dutch and dutch, about 150 to 20khz. Technically it isn't a cardioid across the whole bandwith (or, if we're being pedantic, at any point), but the behaviour is similar enough. You don't have to take my word for it, Erin of Erin's audio corner has measured it, as can be seen in this polar map:

Gradient measurements by Princeton U:

Very interesting speaker. I have never seen such dispersion on a speaker. Bravo!

I read a few magazine articles but still not sure how the speaker nor the high frequency drivers operate. Is there anywhere I can read about the tech? If you have it patented may I know the number so that I can read, please?

 

[abdo123]

Very interesting speaker. I have never seen such dispersion on a speaker. Bravo!

I read a few magazine articles but still not sure how the speaker nor the high frequency drivers operate. Is there anywhere I can read about the tech? If you have it patented may I know the number so that I can read, please?

I think he’s talking about the Dutch & Dutch 8C

 

[sarumbear]

I think he’s talking about the Dutch & Dutch 8C

On his post he mentions Gradient Helsinki 1.5, which was reviewed here:

Gradient Helsinki 1.5 loudspeaker

A clever engineer with an interest in home audio says that the real obstacle to high-fidelity sound is the adverse and unpredictable way in which speakers interact with most domestic rooms. To address that need, he brings to market a loudspeaker that disperses sound in a new and original way...

www.stereophile.com

 

[abdo123]

On his post he mentions Gradient Helsinki 1.5, which was reviewed here:

Gradient Helsinki 1.5 loudspeaker

A clever engineer with an interest in home audio says that the real obstacle to high-fidelity sound is the adverse and unpredictable way in which speakers interact with most domestic rooms. To address that need, he brings to market a loudspeaker that disperses sound in a new and original way...

www.stereophile.com

Yes but I know the Dutch and Dutch uses a constant directivity waveguide exactly like he says.

 

[sarumbear]

Yes but I know the Dutch and Dutch uses a constant directivity waveguide exactly like he says.

The topic is about cardioid dispersion, he said “Attached is an image of a polar plot of the gradient helsinki 1.5, as measured by Princeton University” and the title of the polar diagram clearly says Gradient Helsinki 1.5.

 

[sarumbear]

Please read the whole topic then instead of being a cynical snob.

Please mind your manners. You are on a public forum. I’m continuing on this post for the benefit to other members of the forum. I wI’ll no longer reply to you.

This is what the poster said. Emphasis is mine.

The end result, if we combine these two techniques to control directivity, is a speaker that has a "cardioid-ish" response over a wide bandwidth. In the case of dutch and dutch, about 150 to 20khz. Technically it isn't a cardioid across the whole bandwith (or, if we're being pedantic, at any point), but the behaviour is similar enough. You don't have to take my word for it, Erin of Erin's audio corner has measured it, as can be seen in this polar map:

Above you see the D&D 8C response. It is clearly visible that it is not a cardioid dispersion. It’s a controlled directivity speaker. A very good one but not even close to a cardioid one. However, Gradient Helsinki 1.5 below has a cardioid design. It’s like cardioid microphone! I have never seen a speaker like that. If anyone knows I appreciate if they let us know.

Gradient measurements by Princeton U:

 

[ctrl]

Above you see the D&D 8C response. It is clearly visible that it is not a cardioid dispersion. It’s a controlled directivity speaker. A very good one but not even close to a cardioid one. However, Gradient Helsinki 1.5 below has a cardioid design. It’s like cardioid microphone! I have never seen a speaker like that. If anyone knows I appreciate if they let us know.

I don't get it. What is so extraordinary about the directivity of the Gradient Helsinki 1.5? Unfortunately, there are no normalized frequency responses or normalized sonograms at princeton.edu.

But what is clearly indicated is that below 700Hz, the loudspeaker widens considerably in dispersion and the directivity is a little bit uneven. This can be seen nicely on the frequency response measurements.



So what makes the Helsinki a "cardioid typical" speaker and the 8c not? Here are both horizontal sonograms with approximately the same scaling and the same angular range (-90° to 180°).
The Helsinki has more and more pronounced side lobes as the 8c, which are untypical for perfect cardioids.

 

[sarumbear]

I don't get it. What is so extraordinary about the directivity of the Gradient Helsinki 1.5? Unfortunately, there are no normalized frequency responses or normalized sonograms at princeton.edu.

But what is clearly indicated is that below 700Hz, the loudspeaker widens considerably in dispersion and the directivity is a little bit uneven. This can be seen nicely on the frequency response measurements.
View attachment 160373


So what makes the Helsinki a "cardioid typical" speaker and the 8c not? Here are both horizontal sonograms with approximately the same scaling and the same angular range (-90° to 180°).
The Helsinki has more and more pronounced side lobes as the 8c, which are untypical for perfect cardioids.

View attachment 160371

View attachment 160372

The bottom charts are cropped. Can you try again so that both angle and amplitude axis are visible?

Can you also post the link to the Princeton test?

Thank you.

 

[ctrl]

The bottom charts are cropped. Can you try again so that both angle and amplitude axis are visible?

Can you also post the link to the Princeton test?

All princeton sonogram are cropped. But since both speaker are horizontal symmetrical it doesn't matter.
I cropped the sonogram of the 8c too, so now both are comparable.

The 3D3A Lab at Princeton University

www.princeton.edu

 

[Spocko]

Please mind your manners. You are on a public forum. I’m continuing on this post for the benefit to other members of the forum. I wI’ll no longer reply to you.

This is what the poster said. Emphasis is mine.


Above you see the D&D 8C response. It is clearly visible that it is not a cardioid dispersion. It’s a controlled directivity speaker. A very good one but not even close to a cardioid one. However, Gradient Helsinki 1.5 below has a cardioid design. It’s like cardioid microphone! I have never seen a speaker like that. If anyone knows I appreciate if they let us know.

I don't know if it's "like that" but doesn't the Kii3 specifically claim to be a cardioid speaker?

 

[sarumbear]

All princeton sonogram are cropped. But since both speaker are horizontal symmetrical it doesn't matter.
I cropped the sonogram of the 8c too, so now both are comparable.

The 3D3A Lab at Princeton University

www.princeton.edu

I’m sorry but without seeing the axis how can one understand any data?

 

[sarumbear]

I don't know if it's "like that" but doesn't the Kii3 specifically claim to be a cardioid speaker?

If you know any measurement about them please show us.

 

[ctrl]

I’m sorry but without seeing the axis how can one understand any data?

I have corrected post#171, the sonogram now has a frequency axis. You also have access to both original sources Erin's 8c measurements and Helsinki measurements.

Now can you please explain what makes the Helsinki a "cardioid typical" speaker and the 8c not?

 

[Spocko]

If you know any measurement about them please show us.

A few I found here:

• Audio Express
• 
• https://www.kiiaudio.com/media/GENERAL/docs/reviews/vumetre26kiithree.pdf
• French Review
• 
• Sound on Sound
• 
  
  

 

[fluid]

Above you see the D&D 8C response. It is clearly visible that it is not a cardioid dispersion. It’s a controlled directivity speaker. A very good one but not even close to a cardioid one. However, Gradient Helsinki 1.5 below has a cardioid design. It’s like cardioid microphone! I have never seen a speaker like that. If anyone knows I appreciate if they let us know.

A normalized polar plot doesn't make it as easy to see as a line based polar chart at specific frequencies but in Dutch and Dutch's own polar plots from 500Hz down to 150Hz and from approximately 120 degrees off axis to 180 the 8c is 20 dB down from a normalized zero which is exactly what Martijn claims. In Erin's Kilppel measurements in that same range the DI is just under 5dB constantly which by any reasonable definition makes it cardioid (4.8dB) there, which is the only range that it is claimed to be.

There is a nice overview of these sort of speakers here

https://www.linkedin.com/pulse/directivity-control-part-1-survey-loudspeaker-systems-steve-mowry

and a follow up page with a design

https://www.linkedin.com/pulse/dire...se-article_more-articles_related-content-card

If rear rejection is not the most important aspect then a supercardioid has a higher DI in the forward direction and is what you tend to get with a rear cancelling driver like the W371.

 

[hex168]

How about a fully-realized version of this:

Big 2-way - cardoid

Just trying out some stuff with some scrap wood as due to the covid situation, all of my hobbies are gone for the time being and I need something to do. Parts: XT1664 horn and 18Sound NSD1480N, Faitalpro 15FH500 Midrange/bass cabinet: Top cabinet Naturally, I put in a quick...

www.audiosciencereview.com

It looks like it has a lot of potential.