Hi All,
I have been doing some testing with shallow waveguides for my BaSSlines project that I thought you all might be interested in. These are more thorough results than I have posted before. I created an insert into the baffle that would allow me to make multiple WG's and insert them into the same baffle, with same tweeter, same mic setup, position, etc. The tweeter is the Peerless HDS with the face plate removed. The tweeter is mounted by pressing it to the back of he WG cutout, held by a woof fixture. The measurements were all taken at 1 meter, with the mic 80" high, in the center of a room with vaulted ceilings probably 15' high at that point and with a 4ms gated window.
All the WG's were created from mdf by boring a hole with a forstner bit, then rounding over the appropraite amount and then routing from the back for the palnned depth of either 1/2" deep or 3/4" deep in these cases. These are something just about any DIYer can build petty easily, which was the idea. There are a few tricks to doing this, most notably, when using a 3/4" rounvoer bit, you have to have a backer piece to you mdf baffle that you also bore a hole through. This backer piece is needed for the bearing of the deeper 3/4" roundover bit to ride on. All the bore through holes on these were adjusted so the final throat sizes are about 1-1/4" +- 1/32" at the final size.
Most of the plots show the waveguide perfomance at 0-15-30-45 and 60º of axis horizontally, so you can see the effect on axis and the directivity off axis. The first plot is the HDS with a standard flush mount. My goal with the waveguide is to get some boost at the low end so that when qualized out in the crossover you get the possible benefits of lowered distortion, slighly higher sensitivity, better off axis directivity and a counter to the typical rising responce of the HDS tweeter on axis, which might be fatiguing to some over time. Also included are some comparisons of the favorite WG results on axis with each other.
HDS mounted Flush: 0-15-30-45-60º
1/2" deep WG, 1/2" roundover: 0-15-30-45-60º
1/2" deep WG, 3/4" roundover: 0-15-30-45-60º
3/4" deep WG, 3/4" roundover: 0-15-30-45-60º
3/4" deep WG, 3/4" roundover, with 1/2" deep 45º chamfer after, sharp edges sanded round by hand: 0-15-30-45-60º
3/4" deep WG, 3/4" deep 45º chamfer, sharp edges sanded round by hand: 0-15-30-45-60º
Here are the flush mount (red), 1/2" deep/1/2" roundover(pink), 1/2" deep/3/4" roundover (blue) and 3/4" deep/3/4" roundover (black), all on axis.
My conclusion is: it depends on what you are looking for. The deeper wavegides have more boost, but all peak at about 4kHz on axis. The 1/2" deep waveguide, with 1/2" roundover has the flattest FR on axis from 4kHz and up on axis. The 1/2" deep/3/4" roundover WG and the 3/4" deep/3/4" roundover WG have the best off axis responce when you get out to 30º and beyond and the most directivity. I'm now leaning toward either the 1/2" deep/3/4" roundover of the 1/2" deep/1/2" roundover WG's from a raw response point of view. I will see how they look in the crossover design.
I hope these results will encoorage some of you to experiment with this concept. I think it has a lot of merit and is not at all hard to do with just a router and standard bits. It helps if you have a drill press and a router table as well.