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Directiva r2 project: market requirements gathering

Tangband

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


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.
Thanks for the paper ! Its interesting reading. The only way to have a good sound with coaxial design is to cross it high, about at least 400 Hz or higher with sharp filtering. What Genelec dont say is that the IMD even then, doesnt go away like magic , its still there but its much less severe for the soundquality. This IMD problem does not show up at sine-sweeps when measuring loudspeakers, but its easy to hear when playing music in a fullrange coaxial construction. Loudpeaker construction is all about compromises….
 

Tangband

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A little bit off topic but….This amplifier module with two tpa3255 ( 4 channels ) seems really good value to use if going active and have the poweramps inside each of the loudspeaker cabinet. About 65 dollars at Amazon including taxes.
A meanwell power supply 36 V 6 A seems also good. The small picture is a new tpa3255 board for only 25 dollars, 2 channels.
A40DDC85-A999-422D-8815-3604A677D879.jpeg
 

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voodooless

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gy-k

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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

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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.
 

Joe BKNY

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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
Hello all -
Rick (or others) can you please give an update on where this project stands?
Thank you for all of your work!
 

Trouble Maker

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The design should be openly shared and FOR NON-COMMERCIAL USE ONLY.

I don't know realistically how much moral or legal teeth they have, but have you/the team considered covering or publishing these (Directiva projects) under some Creative Commons or Open Source licensing?

Separately, a huge thanks to everyone working on these projects and being so open with the process here. I've loved following and learning from it.
 
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