The Impact of Taller Waveguides on HORIZONTAL Beamwidth

[Patrick Bateman]

As usual, I'm trying to come up with a speaker design that will have narrow vertical directivity and wide horizontal directivity.

I built some CBT-ish things, and I made a Unity horn that worked pretty well.

The issue I had with the CBT was that the top end wasn't great (a known issue with all types of line arrays, even curved and shaded ones) and the Unity horn I made had a very low WAF score

This got me looking into Horbach Keele arrays, which are basically a refined version of a WMTMW

While working on that, I realized that I had very very little width to play with (due to WAF) but a lot of HEIGHT to play with (also due to WAF)

So I wanted to learn: Does making a waveguide taller change it's horizontal beamwidth?

IE, we definitely change the VERTICAL beamwidth of a waveguide when we make it taller, but is there a change to the horizontal beamwidth?

Let's find out...

 

[Patrick Bateman]

I want to make the speaker look a bit like the KEF speakers. High WAF and all that.

Attached are the KEF speakers, and my two designs. One design uses a waveguide measuring 140mm x 140mm, the other measures 140mm x 227mm

Last pic is my living room; I basically have nearly unlimited height to work with. To give an idea how big that wall is, the TV is SEVEN FEET in diameter.

 

[Patrick Bateman]

Here's the horizontal beamwidth of the 140mm x 140mm waveguide, the 140mm x 227mm waveguide, and the two measurements overlaid on each other

As you can see increasing the height of the waveguide makes virtually no difference on the horizontal beamwidth whatsoever.

But it does reduce the throat impedance. That probably has some value I think.

A lot of this would depend on whether you have any limits on the height of the baffle. In my case, I really don't, the speaker could be ten feet tall and that would probably be OK. The main limit for me is the width, due to WAF.

 

[Michael C]

I suggest you sit down with your other half and get the specs she will be happy with/acceptable/and go from there.

 

[Patrick Bateman]

Here's the vertical beamwidth of the 140mm x 140mm waveguide, the 140mm x 227mm waveguide, and the two measurements overlaid on each other

This one's a lot trickier.

Vertical beamwidth IS wider, but only at lower frequencies.

At higher frequencies, beamwidth is narrower.

The smaller waveguide has narrower beamwidth overall, but the beamwidth is more consistent. The larger waveguide has a big 'step' in the beamwidth.

Mabat has argued for symmetrical waveguides, and this tends to echo that idea. The only significant advantage I can see from the larger/asymmetrical waveguide is that the impedance is lower and broader. But that's only on the horizontal axis; on the vertical axis it's the opposite.

Seems to indicate that the symmetrical waveguide is the winning option.

Part of me wants to repeat this experiment with a vertical diffraction slot, but I wouldn't expect any real improvement from that either. I can't think of any situation where a diffraction slot improved smoothness or beamwidth. My various experiments tend to demonstrate that the only real advantage of a diffraction slot is if you need low frequency loading AND you want a wide beamwidth. For instance, the JBL M2 has a beamwidth of something like 100 x 100. If it used a conventional waveguide, it would be very shallow, and wouldn't load the diaphragm down to a low frequency. The addition of the diffraction slot in the M2 increases the throat impedance.

 

[Cooper60hz]

Maybe take a look at the jbl 4632 it's a super tall wave guide 90 horizontal 20 up 30 down if I remember correctly

 

[cowanaudio]

LOL! Do you think John would be better off single?

BTW, I still think this room is screaming out for a built in >2m tall planar line array.

 

[Cooper60hz]

😂😂woah woah I'm not trying to get involved in that

 

[newvirus2008]

Maybe take a look at the jbl 4632 it's a super tall wave guide 90 horizontal 20 up 30 down if I remember correctly

I think the OP is talking about waveguides that're 'taller than they're wide' rather than a multi-way stack that is super tall.