B&G Neo3 custom waveguide testing

[dlneubec]

This thread is to report on an attempt to make develop a waveguide for use with the Neo3pdr and/or Neo3w. DanP and I worked together to come up with the specs for 4 waveguide prototypes, which he then produced and sent to me. I ordered a Neo3pdr and a Neo3w to test in the waveguides. I received the PDR, but the W is on backorder and I should be here next week.

All tests were done using Jeff B’s method of placing the tweeter face up on the floor. These are therefore quasi infinite baffle measurements. I placed a cardboard baffle over a piece of 2x6 with an opening cut in the 2x6 large enough to house the tweeter. All measurements were taken at 69mm from the center of the driver face. A 2.7ms gated window was used to keep out as many reflections as possible. Flat baffle measurements were done by doing a cutout in the cardboard baffle to simulate a flush mount. For measurements with the waveguides, they were placed on top of the tweeter and held only by gravity. Insulation was placed around the WG edges to try and reduce any diffraction from the WG edges, should there be any.

Obviously, these are not high quality measurements or ones that can be used for design purposes. The sole purpose was to do some quick and easy evaluation of these waveguides.

These are the Waveguides used:

1. 132mm H x 165mm W x 39mm D with 90 degree throat termination
2. 132mm H x 165mm W x 39mm D with 61 and 71 degree throat terminations
3. 105mm H x 140mm W x 25mm D with 90 degree throat termination
4. 105mm H x 140mm W x 25mm D with 56 and 71 degree throat terminations

All have 54mm H x 35mm W throat openings and a 13mm lip for mounting





The first measurements were taken on a flat baffle. Shown is 0-15-30-45 horizontal off axis.



I also took measurements at 20mm, 40mm, 69mm and 123mm of the same tweeter and one of the waveguides, to see if the infinite baffle fell apart as you changed distance from the tweeter to the mic. As you can see, all the measurements track very well at all distances, so I stayed with 69mm.



I will post the individual results next. The results for the Neo3w should be completed next weekend and I will post the results here at that time.

[dlneubec]

I’m undecided whether they are worth pursuing further. There is a definite boost provided, even in those that are only 1” deep, but the FR is a bit rough and there is a concentration of energy in some locations, which is a concern. It may be that they will perform better with the Neo3w. I should be able to post results from it next weekend.

Here is the flat baffle response again:



Waveguide 1: 132mm H x 165mm W x 39mm D with 90 degree throat termination

0-15-30-45 degree horizontal off axis measurements:



no vertical were done:

Waveguide 2: 132mm H x 165mm W x 39mm D with 61 and 71 degree throat terminations

0-15-30-45 degree horizontal off axis measurements:



0-15-30-45 degree vertical off axis measurements:



Waveguide 3: 105mm H x 140mm W x 25mm D with 90 degree throat termination

0-15-30-45 degree horizontal off axis measurements:



no verticald were done:

[dlneubec]

Here is the flat baffle response again:



Waveguide 4: 105mm H x 140mm W x 25mm D with 56 and 71 degree throat terminations

0-15-30-45 degree horizontal off axis measurements:



0-15-30-45 degree vertical off axis measurements:

[cjd]

I'll see if I can get measurements of the hack-job dipole waveguide I threw together the other day, just for the heck of it. Though I plan to hack some of the other things I've wanted to try into this test. I also don't have the PDR - mine is the plain vanilla version.

2 and 4 look best to me of this bunch? I think.

[dlneubec]

I'm interested to see your results. Post a photo if you can. I'd like to see what you are trying.

I suspect a shallower WG would have less negative impact on the off axis response, but it would not provide as many potential benefits either. I hope the plain jane Neo3w does better in these WG's than the PDR did. We'll see.

I thought it was interesting that the vertical off axis, which has a significantly sharper taper to the profile, actually looks a little more WG-like in its response. Also, even the shallowest WG's have a fair amount of boost at the low end.

[dlneubec]

Sorry for the messed up photos. I think I have it corrected now!

[cjd]

Did you use any type of gasket (i.e. felt) at the interface?

[dlneubec]

No gasket, they were just set on the top of the driver.

[cjd]

So I did some preliminary measurements today. I get down to about 1kHz, though there's a bit of wobbling through that range to get there. And, as expected, a crazy peak at about 14kHz. These are RS-180 cutouts laminated, split, and shaped to squeeze the Neo3 at the middle, so pure circular and almost 90 degrees at the throat. More mini-horn than waveguide.

The peak I was able to largely mitigate with a very simple trick, but other issues remain. Given the VERY little time I spent, I'm quite happy with stuff already. Finishing up an equipment rack, some January cleaning, and cooking all take priority just now, but I'll keep plugging.