Directiva r2 project: market requirements gathering

[voodooless]

Yup, the Monacor waveguide performs quite well and is something worth considering. I was aware of the soundimports link, but we're not at that point in the design phase yet

The point was that routing should be easy and custom modification should not be needed. The links shows both do not need to be an issue with a generic waveguide.

 

[Tangband]

Yup, the Monacor waveguide performs quite well and is something worth considering. I was aware of the soundimports link, but we're not at that point in the design phase yet

My own DIY active HYBRID had a monacor waveguide.
Its a custom adaptor for the waveguide. Measurements where very good, but the sound slightly worse, not as detailed than Genelec 8340 wich I bought after doing measurements on that speaker.

 

[Tangband]

The point was that routing should be easy and custom modification should not be needed. The links shows both do not need to be an issue with a generic waveguide.

My own experience is that a really good waveguide shouldnt be symmetrical, as the monacors are.
I would look at how Genelec does it and also Revel.

 

[TimVG]

The point was that routing should be easy and custom modification should not be needed. The links shows both do not need to be an issue with a generic waveguide.

Absolutely true. One more aspect is availability. Since the members are literally all over the globe, it's important that parts are easily obtainable. I'm not sure how readily available the Monacor brand is in the USA for example, it's all stuff we need to consider.

 

[RickS]

Is a dome tweeter a requirement? Otherwise that would open additional options.

As for a generic waveguide: turns out they fit quite af few tweeters without modifications. Check out this article: https://www.soundimports.eu/en/blogs/blog/wave-guiding-your-favorite-tweeter/

No, tweeter does not have to be a dome. I may use the BG Neo as I have a bunch around here.

While there should be a primary offering, do not want to get too wrapped up in just one answer. A waveguide is not off the table either, but the design team needs to demonstrate why it will be needed AND it better be as simple to do as most other drivers. This is comparable to why truncated frame drivers are not acceptable. Do not want cutouts or mounting requirements that are complex.

Expect the design teams to formally start over this weekend. If you are not on a team, then expect the team leads or I will report progress over time.

Thanks!

Rick

 

[gy-k]

One of the R2 requirements is that the system should be relatively easy to build - that will include routing. This means elliptical waveguides and the likes will be hard if not impossible to implement in a flush mounted configuration.

Another requirement is that the parts need to be readily available and usable without further modifications. I know a lot of waveguides require further adapter plates and the likes to be used with otherwise readily available tweeters.

Also I believe 6,5" for the woofer is not set in stone, since this will be a 3-way system - it's a possibility, but not a certainty.

Not sure I'd set high hopes on the availability of a waveguide part either. By the way, just putting a dome inside a waveguide isn't necessarily a great match. The oblate spheroid waveguide assumes a flat wavefront of a compression driver. (I'm just an amateur, but I beleive this much I can repeat.) Mabat's waveguide is one, it's freestanding and needs no baffle/cabinet woodworking effort, it needs to be (ordered as) 3D printed but the plans will always be available.

 

[voodooless]

No, tweeter does not have to be a dome. I may use the BG Neo as I have a bunch around here.

Hey, I still have several of those as well

This is comparable to why truncated frame drivers are not acceptable. Do not want cutouts or mounting requirements that are complex.

I would not totally rule them out, you can mount them on the rear of the baffle and do with a circular whole.

 

[TimVG]

By the way, just putting a dome inside a waveguide isn't necessarily a great match.

Absolutely. If I implied as much, please blame the language barrier.

 

[sarumbear]

This all matters most to the design team...

Are the team members announced?

 

[Nwickliff]

My 2c, which is probably more like .001c, Or more of a question is why are people so obsessed with getting bookshelves (or any speaker, for that matter) to play the lower notes and octaves that generally don't disperse evenly from the main position in "normal" rooms. If properly time-aligned and crossed to a sub and preferably multiple subs, won't you get much more even bass in "most" rooms? It frees up the box design for much more headroom and I would guess fewer issues with resonances too, no? Isn't it better to have each driver do less work in order to get maximum performance? I understand it as an exercise and perhaps that's the main purpose here. Anyhow, happy building.

 

[voodooless]

My 2c, which is probably more like .001c, Or more of a question is why are people so obsessed with getting bookshelves (or any speaker, for that matter) to play the lower notes and octaves that generally don't disperse evenly from the main position in "normal" rooms. If properly time-aligned and crossed to a sub and preferably multiple subs, won't you get much more even bass in "most" rooms? It frees up the box design for much more headroom and I would guess fewer issues with resonances too, no? Isn't it better to have each driver do less work in order to get maximum performance? I understand it as an exercise and perhaps that's the main purpose here. Anyhow, happy building.

I guess there are many reasons: some people don’t want subs or don’t have room for many. Two additional speakers that have the bandwidth can already act as two subs. Some don’t like the bookshelf design, others don’t like speaker stands.

 

[Lbstyling]

My own experience is that a really good waveguide shouldnt be symmetrical, as the monacors are.
I would look at how Genelec does it and also Revel.View attachment 162197View attachment 162198

The elliptical waveguide is to allow the c to c space to be as close as possible. If waveguides alone are considered in isolation, conical is more optimal.

 

[Tangband]

The elliptical waveguide is to allow the c to c space to be as close as possible. If waveguides alone are considered in isolation, conical is more optimal.

Might be. But, the lateral and horisontal dispersion gonna be slightly different with an elliptical waveguide. Genelec uses this shape even in the big studio monitors they make . Is it only for making the c-to c closer ?
JBL also uses a different non-symmetrical shape in their waveguide for their professional speakers. I dont think its a coinsident.

Here is Genelecs paper on their waveguides. There is no information about making c-c shorter as a benefit.

Directivity Control Waveguide (DCW™) Technology - Genelec.com

Directivity Control Waveguide (DCW™) for flat on- and off-axis response.

www.genelec.com

 

[Tangband]

Here is interesting reading about Revels waveguide, in this Harman paper:

https://www.excelia-hifi.cz/revel/data/revel-concerta-2-tech.pdf

”
Conventional waveguide theory states that broadband pattern control (i.e. directivity control) is best achieved by a large straight (conical) section in the waveguide, and that transition design at the entrance and exit of the waveguide are critical to prevent high frequency narrow-band directivity and frequency response problems. Finally, the size of the waveguide determines how low in frequency the waveguide can control pattern.
With previous generation waveguides, although the directivity was well matched at the crossover frequencies, they tended to have excess directivity and lower output above 9kHz.
A new generation slender wave guide along with an acoustic lens was developed for the Concerta2. The wave guide uses a large gentle blend radius at the exit of the waveguide. The directivity is now well matched to the midrange drivers of the Concerta2. The output is improved above 9kHz by adding an acoustic lens in front of the dome (Figure 7).”

 

[bigjacko]

I rememer that if waveguide is in perfect circle, the wave will be coherant and make on axis dip somewhere. The dip goes away at off axis so if the speaker is not pointed towards listener the on axis dip does not matter. Genelec sure does not want that, so not surprised if they don't use perfect circle.

 

[Lbstyling]

Might be. But, the lateral and horisontal dispersion gonna be slightly different with an elliptical waveguide. Genelec uses this shape even in the big studio monitors they make . Is it only for making the c-to c closer ?
JBL also uses a different non-symmetrical shape in their waveguide for their professional speakers. I dont think its a coinsident.

Here is Genelecs paper on their waveguides. There is no information about making c-c shorter as a benefit.

Directivity Control Waveguide (DCW™) Technology - Genelec.com

Directivity Control Waveguide (DCW™) for flat on- and off-axis response.

www.genelec.com

Yup. Pattern control at crossover is better when drivers are closer together (under 1/4 wavelength at cross is ideal). This problem doesn't go away when you make bigger speakers, it gets worse.
RE JBL, if your refering to the modern waveguides like the M2, they are symmetrical, yes.

If you mean they are not conical, well they sort of are actually. The odd shape with the narrowing corners in the throat is a mathematical calculation where you make the shape of a circle (the driver) match the shape of a square (the box) while keeping its Path length the same through the 360 degree radius of the horn. This is the closest you can go to replicate a conical pattern control with a rectangle mouth.
Move the material of the extra path length towards the throat, and you can also use it as a semi diffraction Device, fixing/helping the dispersion issue of the top octave with drivers of over 1" width exit.

 

[tuga]

Might be. But, the lateral and horisontal dispersion gonna be slightly different with an elliptical waveguide. Genelec uses this shape even in the big studio monitors they make . Is it only for making the c-to c closer ?
JBL also uses a different non-symmetrical shape in their waveguide for their professional speakers. I dont think its a coinsident.

Here is Genelecs paper on their waveguides. There is no information about making c-c shorter as a benefit.

Directivity Control Waveguide (DCW™) Technology - Genelec.com

Directivity Control Waveguide (DCW™) for flat on- and off-axis response.

www.genelec.com

This paper is also worth a read, with interesting considerations regarding 3-way design:

Genelec_coaxial waveguides.pdf

Audio Engineering Society. Convention Paper Presented at the 142nd Convention 2017 May 20–23 Berlin, Germany This Convention paper was selected based on a submitted abstract and 750-word precis that have been peer reviewed by at least two qualified anonymous reviewers. The complete manuscript...

docdro.id

The Acoustic Design of Minimum Diffraction Coaxial Loudspeakers with Integrated Waveguides
Aki Mäkivirta, Jussi Väisänen, Ilpo Martikainen, Thomas Lund, Siamäk Naghian
Genelec Oy, Iisalmi, Finland

ABSTRACT
Complementary to precision microphones, creating an ideal point source monitoring speaker has long been considered the holy grail of loudspeaker design. Coaxial transducers unfortunately typically come with several design compromises, such as adding intermodulation distortion, giving rise to various sources of diffraction, and resulting in somewhat restricted maximum output performance or frequency response. In this paper, we review the history of coaxial transducer design, considerations for an ideal point source loudspeaker, discuss the performance of a minimum diffraction coaxial loudspeaker and describe novel designs where the bottlenecks of conventional coaxial transducers have been eliminated. In these, the coaxial element also forms an integral part of a compact, continuous waveguide, thereby further facilitating smooth off-axis dispersion.

 

[voodooless]

Since we're back at spewing random things, let me do that as well. Might be of interest: https://store.miscospeakers.com/6-5-xbl-2-high-excursion-ultra-low-distortion-woofer-82141, also tested here. Might be an interesting candidate for bass drivers. Distortion down low is quite excellent and the cost is quite low. Worldwide availability might be a bit tricky though, but at least in Germany, one can buy them.

 

[gy-k]

Point 13 says "the target width of the bass module is a maximum of 260 mm". Using readily available flatpack kits to build it is a great idea, quite fundamental even, I think. As I understand it's going to be a floorstander. (Point 12: "The combined cabinet volumes should be 60-75 liters or smaller. Combined height should not exceed 1.2m.") But I can only find one flatpack kit for a floorstander, the '1.16 cu. ft. Tower Speaker' kit. This one has ~32l volume and its width is less than 10" or 260mm. What I can think of for more volume is stacking 3x '0.67 cu. ft. Subwoofer' kits or 2x '1.0 cu. ft. Subwoofer' kits. (The former is cheaper but maybe it'd be a bit front heavy? The latter has more bracing.) Such a thing would have ~56l volume, but its width would be 12" or 14.25". That cabinet width would allow for a 10" driver. I thought the Beyma 10iX looks interesting, the size means it has ~2.8x Sd of a 6.5" driver, but its 13mm Xmax spec is comparable to the Purifi. I think it models nicely in a 56l cabinet: "https://imgur.com/lU5vX2F" (At a SPL when driven to below Xdamage below port tuning.) I guess one of the SEAS L26ROY models could be a benchmark for 10" drivers, personally I like this Beyma driver more because of its somewhat lighter paper cone and flat surround.

 

[fluid]

The elliptical waveguide is to allow the c to c space to be as close as possible. If waveguides alone are considered in isolation, conical is more optimal.

It may be a consideration but having an asymmetric waveguide is often used because of the idea to narrow the vertical directivity. This doesn't always work as the vertical loses control earlier than the Horizontal and this creates waistbanding in the polar response. What is best and right is really quite complicated and dependent on other factors in the system design.

A conical waveguide allows a spherical wave at it's throat to continue and not disrupt the pattern. An OS throat allows for a flat wavefront to expand to a spherical one.

I rememer that if waveguide is in perfect circle, the wave will be coherant and make on axis dip somewhere. The dip goes away at off axis so if the speaker is not pointed towards listener the on axis dip does not matter. Genelec sure does not want that, so not surprised if they don't use perfect circle.

This is also not entirely true. If the DI of an axisymmetric waveguide is made to be as flat as possible there will be some disturbance to the on axis. This can be mitigated either by using a large termination flare or allowing the directivity to rise slightly and combining both gets a very minor on and near axis change with very smooth and even off axis response.

RE JBL, if your refering to the modern waveguides like the M2, they are symmetrical, yes.

It might look that way but it isn't quite the same. The Horizontal is 120 and the vertical is 110.

https://3e7777c294b9bcaa5486-bc9563...038/m2_makingmonitor_mix_oct2013_original.pdf

What is sometimes forgotten when making a waveguide with an asymmetric pattern is that it cannot match the directivity of a round cone driver in both the horizontal and vertical, you trade one thing for another.

If you mean they are not conical, well they sort of are actually. The odd shape with the narrowing corners in the throat is a mathematical calculation where you make the shape of a circle (the driver) match the shape of a square (the box) while keeping its Path length the same through the 360 degree radius of the horn. This is the closest you can go to replicate a conical pattern control with a rectangle mouth.
Move the material of the extra path length towards the throat, and you can also use it as a semi diffraction Device, fixing/helping the dispersion issue of the top octave with drivers of over 1" width exit.

Not much in this is completely right but it would take a lot to unpack it all and put it back together.