Quick way to make an effective phase plug

[ashok]

I tried out a quick and easy way to make a phase plug. It is not long lasting I guess but enough to make some tests . You can also shape the plug as you want it.

First make a small paper ring by wrapping some thin paper around a suitable former . Use a former slightly smaller than the diameter of the required plug. If your former is much smaller , you will need to wrap several layers of paper.

Then put in a small iron screw into the bottom of the paper ring and pour a little molten wax into it. Place the whole thing on a smooth metal surface.Let it harden fully. Then after it has cooled pour in some more. Not enough to melt all of the first layer. If that happens all the wax will flow out the bottom. Keep adding two three times till it is full to the top.

The initial paper cylinder should be just high enough to protrude out of the voice coil of the speaker.
After the wax cools , wrap another layer of paper around this wax filled paper cylinder to get a new longer cylinder which is the height of the full plug. Then pour in more wax a little at a time. This time you could do it a bit faster . Let it cool slowly. If you put it in the fridge to cool the center will sink and you will get a huge depression.

After it is cool , you can unwrap the outer paper layer and then use a sharp knife to chip / scrape away the wax to get a conical plug with the shape you want. It takes a while for the insides to solidify. If its soft you will have to do it all over again !

The plug will sit easily on th epole piece due to the metal screw. Do not use a 'big' screw as you don't want it 'magnetically locked' in place.

Here are some basic measurements I made on a 4 inch driver.

The data appears as follows.
Parameter - stock driver - driver without dust cap - driver with phase plug

Resonance freq ( Hz ) 121.2 - 131.0 - 131.0
Qms 5.4 - 6.26 - 6.25
Qes 2.38 - 1.92 - 1.93
Qts 1.65 - 1.47 - 1.47

[ashok]

Plug installed in one speaker. Second former without wax.

[ashok]

Driver with dust cap and dust cap removed. Bottom of phase plug with ms screw just visible through the wax.

[ashok]

Another picture with phase plug and stock driver.

[marchel]

nice work, bt while you're at it , Why not add copper or aluminum ring in the plug, It might lower the distortion of the driver.

[ashok]

Hi Marchel , that's a good idea . It never occured to me. Maybe I can just use some thin foil . I have some aluminum foil I bought years ago to make coil formers. I could use that.
Hmm........... this might be really interesting. Easy to do with the wax and Al cylinder .
I can measure distortion but it means a lot of setting up to do.
We'll see. If I do get round to it I'll post some results.
Cheers.

[chrisb]

just pray the voice coil/pole piece doesn't get warm enough to radiate or conduct heat through the mounting screws to the wax..........

and at least 2 small screws (i.e. #4 or #5) will tend to keep the plug more stable