When I had my Manger drivers I experimented with some phase plug designs to improve off-axis response. It worked quite well 
Off axis, there seems to be a sharp suck-out that ranges from around 15KHz to 10KHz depending on the angle you measure from (which is what suggested to me it was destructive interference in the first place)
By implementing the phase plug this suck-out (around 13KHz IIRC, at about 15-20 degrees off axis) was reduced by about 6dB-8dB!
I have lost the measurements I had to show this working but I still have the design for the phase plug. So, I submit it here for the benefit of anyone with Manger drivers. There seemed to be no negative effects to note.
The most important part is the width of the base, which is 19mm. You need to place this as close to the centre of the diaphragm as possible. I left about 2-3mm for excursion. The profile of the body was found through experimentation and did make a difference, but not huge. So don't worry if you can't make it match the diagram exactly.
I suspect the 19mm diameter phase plugs from Planet10 Hi-Fi may work very well (maybe better!) but you want to take those screws out the bottom or the magnetic force will pull the plug in to your mangers!
Here is the plug design I used to good effect.
http://www.audiosmile.co.uk/images/phase-plug.jpg
I hope someone finds this useful.
Off axis, there seems to be a sharp suck-out that ranges from around 15KHz to 10KHz depending on the angle you measure from (which is what suggested to me it was destructive interference in the first place)
By implementing the phase plug this suck-out (around 13KHz IIRC, at about 15-20 degrees off axis) was reduced by about 6dB-8dB!
I have lost the measurements I had to show this working but I still have the design for the phase plug. So, I submit it here for the benefit of anyone with Manger drivers. There seemed to be no negative effects to note.
The most important part is the width of the base, which is 19mm. You need to place this as close to the centre of the diaphragm as possible. I left about 2-3mm for excursion. The profile of the body was found through experimentation and did make a difference, but not huge. So don't worry if you can't make it match the diagram exactly.
I suspect the 19mm diameter phase plugs from Planet10 Hi-Fi may work very well (maybe better!) but you want to take those screws out the bottom or the magnetic force will pull the plug in to your mangers!
Here is the plug design I used to good effect.
http://www.audiosmile.co.uk/images/phase-plug.jpg
I hope someone finds this useful.
If you use 3 MSW per channel, are the side two not meant to be low-passed?
I used blu-tak to make my phase plugs. But I only took it as far as an experiment, I didn't run them with the plugs as I sold the Mangers soon after to try other things. I'm sure it would have improved them though.
Sorry I lost all the pics and measurements I took of them in a computer crash.
I used blu-tak to make my phase plugs. But I only took it as far as an experiment, I didn't run them with the plugs as I sold the Mangers soon after to try other things. I'm sure it would have improved them though.
Sorry I lost all the pics and measurements I took of them in a computer crash.
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