The Nightmare Before Labor Day

[Kravchenko_Audio]

I think that if you can figure out how to accomplish it, narrow vertical directivity is ideal.

Basically any reflections off of the floor or ceiling are no good.

To me, one of the most dramatic examples of this is the Gradient Helsinki:

I heard these a few years back, and the near absence of sound from the floor and ceiling was eerie. I heard them at CES, where the acoustics are fairly awful. Yet even though the ceilings are "only" nine feet tall, the Helsinki sounded noticeably different than a conventional speaker. And I think a lot of that is because the first reflection is aimed so that it occurs quite a bit after the initial wavelaunch.

In other words -

In a conventional speaker, the midrange is mounted vertically, and the sound that's radiated into the floor and ceiling is fairly similar in output level to what's going FORWARD. Because of this, sound is radiating into the floor before it even reaches the listener.

Sound radiates into the floor, ceiling and back wall before it even reaches the listener.

With the Helsinki, there isn't much sound radiated into the floor at all, and the sound that hits the ceiling takes a while to get there. By angling the baffle it increases the pathlength by about 41%.

The subwoofer is a dipole, and the dipole's null is aimed right at the back wall, with an intention to reduce excitation of that surface.

But before anyone runs out and makes a Helsinki clone, keep in mind that it has an Achilles Heel, which is that the maximum output is not great. It has a sensitivity of 84dB and a power handling of about 100 watts iirc: https://www.stereophile.com/content/gradient-helsinki-15-loudspeaker-measurements

I have always used a planar in my high end work. One reason is low distortion. The other is controlled vertical directivity. I agree with you. You don not have to worry so much about floor and ceiling bounce when you are using a planar. With a hemispherical radiating driver it is much more of an issue. What you are doing with your horn design can accomplish vertical directivity in a much wider bandwidth. I know I'm preaching to the choir. But it should be said.

 

[tmuikku]

By angling the baffle it increases the pathlength by about 41%.

This is misconception I think, the mid radiates sound to all directions no matter the tilt angle, and path length to listening position directly or through boundary doesnt change at all with the tilt. What changes is the radiation pattern towards the boundaries (spe ular reflection points) and towards the listener.

mid seems to be some kind of cardioidish arrangement and tilting it so perhaps reduces sound for some bandwidth towards floor but increases it toward ceiling. Or perhaps tries to balance both to have similar response, similar radiation angle. It would also reduce sound towards front wall if the speaker is not toed in like many hifi setups seem to be for some reason. Assuming its not cardioid but supercardioid for example. Maybe it is just to mate the waveguide and sideways dipole nicely. Or all of them and or something else. front wall reflections are reduced though for the whole system, aboxless system that works near wall even. The dipole bass wont have much of first frontwall and vertical reflections, nice.

It would be nice to see measutements and hear it in action, is there any interviews woth the designer?

 

[Patrick Bateman]

The Genelec 8030A has surprisingly excellent directivity control, especially for it's size. I think much of that is because of good engineering and that enclosure that's shaped to reduce diffraction. Here's a pic of the speaker, and it's horizontal and vertical directivity.

Although the Gradient Helsinki is very strange looking, it maintains it's directivity to a lower frequency than the Genelec. You can see there's significant directivity control all the way down to 600Hz. We probably won't see many more designs like this, the designer died in 2018: https://www.theabsolutesound.com/articles/jorma-salmi-1948-2018-1

Gradient has always been fascinating to me. Back when Geddes did his original "shootout" against various speakers, IIRC the Gradient Revolution came out a little bit ahead of the Summa. (I bought the Summa.)

Gradient has been quietly introducing things to the audio field way ahead of it's time; Linkwitz popularized the use of dipoles beginning about 25 years ago, but Gradient was selling them in the 80s!

I am far from a fanatic about amplifiers, but in my office I'm running a pair of single ended Class A amps. My setup in the living room uses Class D.

When I'm designing a loudspeaker, I really put an effort to keep it passive, because I figure there's lots of people out there who prefer to use their favorite amp.

From that perspective, the Gradient stuff is really interesting I think. It's nearly as good at directivity control as some of the modern DSP designs, but it does all of it's magic using passive component and careful manipulation of the driver geometry.

Having said all that, if you want the absolute best performance, products like the Genelec 8351A are tough to beat. The Gradient Revolution performs surprisingly well for such a modest passive design, but it's tough (maybe impossible?) to best the brute force of DSP and multiple amps.

Measurements courtesy of Princeton University: https://www.princeton.edu/3D3A/Directivity/

 

[tmuikku]

Thanks for the link to Princeton University measurements, there is even an electrostat in the set!

 

[Patrick Bateman]

Leveraging some inspiration from Dave Smith's thread (https://www.diyaudio.com/community/...heir-behavior-through-simple-modeling.388279/) I came up with this shaded array that might work well with a tweeter in the center - as long as the vertical directivity of the tweeter is very narrow. A ribbon or planar might work.

The first file that's attached is a zip file with the VituixCad project, along with the ZMA files for the drivers. For the frequency response, I just modeled the Dayton ND64 midranges as if they were ideal pistons, since I'll be using them below a frequency where they beam. (They start beaming about 6khz.)

Random observations:

1) I intentionally left a gap in the center of the array. The idea was that a tweeter or a Unity horn with narrow vertical directivity would go there. I was pleasantly surprised by how high the array can play; I'd estimate that it can play up to about 2500Hz using 2.5" midranges, which is pretty good performance I think. I think I'll actually modify it to use larger woofers than 2.5", on the assumption that there are plenty of tweeters that can play down to 1500Hz.

2) There's a gnarly off-axis null between 600Hz and 1khz. Not sure if this is a concern. I tried messing with the polarity of a few elements, and was able to make the null go away, but when doing so, it makes the vertical directivity too wide, which probably isn't what I want. Basically you can get response that's a bit like a Bessel array by flipping the polarity on one of the fourteen elements.

3) I used a mix of 2.5" (Dayton ND64) and 5" elements (MCM 55-3870.) The idea is basically that the outer elements in the array don't need to play above 500Hz, so why bother using an expensive 2.5" woofer? A single MCM 55-3870 has more output than two Dayton ND64s and costs half as much.

4) I intentionally did everything using passive components. I'm not keen on paying for ten channels of DSP and amplification. The cost of inductors gets ugly in a hurry and is one of the reasons I'll probably redesign this project. For two speakers, the inductors alone cost about $100.

 

[sap2212]

Hello, I don't speak your language, and I hope my translator will do a good job.

I use a waveguide inspired by the "DOSC" invented by Mr Christian Heil.

My prototype is equipped with a 4" loudspeaker with a waveguide. I obtain at the output a cylindrical wavefront with a regularly decreasing amplitude in the high frequencies. The directivity is 180° on the horizontal plane and very low in the vertical plane.

The loudspeakers are stackable to cover the desired height. There is no interference between the speakers, because it is a cylindrical wave stacking. The height of the speaker is 8 ".The floor and the ceiling are not affected by the sound waves. To further reduce reflections with the side walls, I place the loudspeakers face to face in recessed from the back wall.

 

[Patrick Bateman]

How does it measure?

I've built a few of these, my latest one is documented here:

https://www.diyaudio.com/community/threads/square-pegs.217298/post-6972282