I'm currently working on tweaking my Vifa P17 drivers, following instructions posted by Mark of McKenzie Acoustical Design
http://www.madspeaker.com
He wrote about the tweaks on this thread:
http://www.diyaudio.com/forums/showthread.php?postid=687719#post687719
Unfortunately the linked instructions are no longer on his site, but it involves removing the dustcap and adding a phase plug as well as glue rings to reduce vibration mode problems. He showed measurements of improved time domain performance and flatter response.
So far I have removed the dustcap and made a prototype phase plug. The real one will be solid copper. With dustcaps removed, it's hard to pick much difference, if it is there at all. I think I can detect some change in upper frequencies, but it's subtle.
Dustcap removed:
http://www.madspeaker.com
He wrote about the tweaks on this thread:
http://www.diyaudio.com/forums/showthread.php?postid=687719#post687719
Unfortunately the linked instructions are no longer on his site, but it involves removing the dustcap and adding a phase plug as well as glue rings to reduce vibration mode problems. He showed measurements of improved time domain performance and flatter response.
So far I have removed the dustcap and made a prototype phase plug. The real one will be solid copper. With dustcaps removed, it's hard to pick much difference, if it is there at all. I think I can detect some change in upper frequencies, but it's subtle.
Dustcap removed:
Attachments
Hi,
If the phase plug is turned, a steel screw in its centre
(from the back, countersunk head) should work a treat.
🙂/sreten.
If the phase plug is turned, a steel screw in its centre
(from the back, countersunk head) should work a treat.
🙂/sreten.
My concern is centring it correctly. In the magnet there is a 15mm deep hole in the centre drilled into the back of the magnet. Also I have concerns about changing the motor by drilling into the pole piece.
I've also thought about contact adhesive, but that could go wrong if not placed correctly as it tends to set quick!
I've also thought about contact adhesive, but that could go wrong if not placed correctly as it tends to set quick!
Hi,
I meant a steel screw in the phase plug not pole piece.
(Assuming a solid pole piece - not as you say hollow)
An accurately placed 15mm steel washer on the phase
plug will be centred and hold itself onto the pole piece.
🙂/sreten.
I meant a steel screw in the phase plug not pole piece.
(Assuming a solid pole piece - not as you say hollow)
An accurately placed 15mm steel washer on the phase
plug will be centred and hold itself onto the pole piece.
🙂/sreten.
Droping or placing a steel washer can be very dangerous . Alignining it while it's stuck to the pole piece might be really tough. In addition if it goes out of center while putting it in place you could ruing the top edge of the voice coil former.
Be careful. Use a slow ( or slower ) setting glue. Use some hand wound ( paper ) spacer to keep it centered with respect to the voice coil. You can pull it out after it sets.
Paulspencer: What solvent did you use to remove the dust cap ?
Thanks.
Be careful. Use a slow ( or slower ) setting glue. Use some hand wound ( paper ) spacer to keep it centered with respect to the voice coil. You can pull it out after it sets.
Paulspencer: What solvent did you use to remove the dust cap ?
Thanks.
Do you know of a glue that will work for this application? Metal to metal. The actual phase plug will be copper and I'm not sure what metal is used for the pole piece.
Solvent wasn't required to remove the dust cap. The cone is basically plastic, the adhesive is clear like silicone. It's a simple matter of getting a nail under the dust cap edge and gently working at it until it comes off. The dustcap comes off without damage and there are no marks on the cone.
Unfortunately the VC former is very thin and does not form a perfect circle. I'd like to trim it down if I could, but I think it could readily be damaged. I could fill the space around it with something to make a neater finish, but I suspect I might just have to not worry too much about it, as it's only visible very close up.
Solvent wasn't required to remove the dust cap. The cone is basically plastic, the adhesive is clear like silicone. It's a simple matter of getting a nail under the dust cap edge and gently working at it until it comes off. The dustcap comes off without damage and there are no marks on the cone.
Unfortunately the VC former is very thin and does not form a perfect circle. I'd like to trim it down if I could, but I think it could readily be damaged. I could fill the space around it with something to make a neater finish, but I suspect I might just have to not worry too much about it, as it's only visible very close up.
Hi Paul,
Thanks for the info about removing the dust cap.
If I were you I'd avoid any magnetic metal work on the pole piece or work with any magnetic pieces near the coil. If you have ANY magnetic metal scrapings it will become embedded in the air gap for ever ! There goes your speaker ! No magnetic screwdrivers either !!
Non magnetic is safest. Copper is great . You could use a VERY thin film of quick set Araldite epoxy glue. It hardens in an hour or so and then gets max strength in several hours. It is called Araldite Rapid over here.
You need just a thin film . It must not run when squeezed between the ploe top and the plug. You 'could' implant a SMALL steel screw ( 3mm ?) in the middle of the base of the copper plug. This should have enough magnetic pull to keep the plug in place while setting and low enough to move it around if required. The screw need not touch the magnetic pole piece .
I would like to use a glue with less strength so that the plug could be removed easily later on if required. Like plastic glue sticks ! If you heat the copper plug it should come off easily . If you are very sure of not removing the plug later on , the Araldite Rapid should be enough.
Alternatively, A 'right sized' steel screw in the base of the plug might be enough to keep it in place. A very "small" blob of epoxy at the joint will ensure that it really stays in place.
About the voice coil former. You will see that many other commercial drivers have coil formers that do not look centered exactly with respect to the center plug.
On my Mission 780 it is VERY noticeably off center. But not noticeable unless one looks at it up close. The edge of the former is too close to the plug to see if it is non uniform or not.
Cheers.
Thanks for the info about removing the dust cap.
If I were you I'd avoid any magnetic metal work on the pole piece or work with any magnetic pieces near the coil. If you have ANY magnetic metal scrapings it will become embedded in the air gap for ever ! There goes your speaker ! No magnetic screwdrivers either !!
Non magnetic is safest. Copper is great . You could use a VERY thin film of quick set Araldite epoxy glue. It hardens in an hour or so and then gets max strength in several hours. It is called Araldite Rapid over here.
You need just a thin film . It must not run when squeezed between the ploe top and the plug. You 'could' implant a SMALL steel screw ( 3mm ?) in the middle of the base of the copper plug. This should have enough magnetic pull to keep the plug in place while setting and low enough to move it around if required. The screw need not touch the magnetic pole piece .
I would like to use a glue with less strength so that the plug could be removed easily later on if required. Like plastic glue sticks ! If you heat the copper plug it should come off easily . If you are very sure of not removing the plug later on , the Araldite Rapid should be enough.
Alternatively, A 'right sized' steel screw in the base of the plug might be enough to keep it in place. A very "small" blob of epoxy at the joint will ensure that it really stays in place.
About the voice coil former. You will see that many other commercial drivers have coil formers that do not look centered exactly with respect to the center plug.
On my Mission 780 it is VERY noticeably off center. But not noticeable unless one looks at it up close. The edge of the former is too close to the plug to see if it is non uniform or not.
Cheers.
Ashok, thanks for the suggestions, very helpful.
Another challenge is putting rings of glue (PVA) on the rear of the cone. I need to put a ring which is close to the centre of the cone, and this is difficult as I need a long pointy nozzle which I don't have on this glue. I'm looking at making up some kind of nozzle for it ...
The ring needs to be 36mm in from where the surround rubber ends (on the back of the cone). I could do it on the front, but at the rear it will be hidden.
Another challenge is putting rings of glue (PVA) on the rear of the cone. I need to put a ring which is close to the centre of the cone, and this is difficult as I need a long pointy nozzle which I don't have on this glue. I'm looking at making up some kind of nozzle for it ...
The ring needs to be 36mm in from where the surround rubber ends (on the back of the cone). I could do it on the front, but at the rear it will be hidden.
Buy a disposable syringe at a medical store and attach a plastic straw to it. You'll have to pick the right size for both.
If the straw is too big or loose on the nozzle of the syringe , you could use quick set glue ( instant glue ) to glue it there.
Alternative slow method is Araldite ( "Rapid" if possible ).
You can clean out the pva with water after use . The injector could be of use later on.
Cheers.
Note : For a really thin tube you could use the empty plastic tube from a ball point pen refill . You could use " plastic shrink tube " used for wires , to join the plastic tube to the nozzle of the syringe. Use a long enough section to prevent slippage . There are some shrink tubes that also bond on the inside though I have never used them.
If its hard to get some shrink tube in small quantity , let me know. I can check if the size you want is available here. I can get them here by the foot.
If the straw is too big or loose on the nozzle of the syringe , you could use quick set glue ( instant glue ) to glue it there.
Alternative slow method is Araldite ( "Rapid" if possible ).
You can clean out the pva with water after use . The injector could be of use later on.
Cheers.
Note : For a really thin tube you could use the empty plastic tube from a ball point pen refill . You could use " plastic shrink tube " used for wires , to join the plastic tube to the nozzle of the syringe. Use a long enough section to prevent slippage . There are some shrink tubes that also bond on the inside though I have never used them.
If its hard to get some shrink tube in small quantity , let me know. I can check if the size you want is available here. I can get them here by the foot.
Hi Paul,
You might have to pick the fattest needle because the pva solution could be quite viscous . With a thin needle you will have to use a lot of pressure.
Incidentally even with a fairly thick pva solution will it not 'run' down the cone as it dries ? I guess you can check that by first applying on the front side of the cone.
Wish you all the best.
Ashok.
You might have to pick the fattest needle because the pva solution could be quite viscous . With a thin needle you will have to use a lot of pressure.
Incidentally even with a fairly thick pva solution will it not 'run' down the cone as it dries ? I guess you can check that by first applying on the front side of the cone.
Wish you all the best.
Ashok.
I wasn't planning on using the needle actually, perhaps I should consider it.
There was no problem with running with my test. The only problem was getting even thickness, but that's not critical, just the perfectionist in me talking.
There was no problem with running with my test. The only problem was getting even thickness, but that's not critical, just the perfectionist in me talking.
If you use the needle be sure to grind or file off the sharp needle point. very easy to get hurt with such a sharp point.
Cheers.
Cheers.
I have 4 vifa PJ17's out of an old pair of duntech viscount speakers.
the 4 drivers are matched pairs.
will fitting a phase plug upset the matching?
also are the phase plugs specially made for the driver?
or are they available somewhere?
allan
the 4 drivers are matched pairs.
will fitting a phase plug upset the matching?
also are the phase plugs specially made for the driver?
or are they available somewhere?
allan
I'm not sure about the phase plug side of things however in terms of being matched pairs, if all modifications are done in the same way on each driver, then they will remain matched, just work carefully imho.
I'm not aware of phase plugs made specifically for this driver, however I have seen them for sale from Planet audio and other sources online. If you have access to a lathe you can make your own and it is not difficult. You can make them out of wood which is cheaper and easier, although in my case I have copper that I'm going to use.
I have put glue rings on one driver, and removed dust caps from two drivers of my four. I have not really had a chance to closely assess the difference at this point, but I haven't noticed anything particularly obvious.
Revmoving the dust cap reveals vents in the VC former which contribute some turbulent noise at high excursion. This problem may be reduced with the phase plug, although I may have to tape them up.
I have put glue rings on one driver, and removed dust caps from two drivers of my four. I have not really had a chance to closely assess the difference at this point, but I haven't noticed anything particularly obvious.
Revmoving the dust cap reveals vents in the VC former which contribute some turbulent noise at high excursion. This problem may be reduced with the phase plug, although I may have to tape them up.
paulspencer said:Prototype Phase plug added
The tricky part will be attaching it to the pole piece. I think I will have to use glue, but care will be required to get it right. I don't want to glue the VC former to the pole piece!
Any suggestions anyone?
You could just use 3M double sided tape. If using wood phase plugs, because tape doesn't stick to wood very well, just be sure the bottom is smooth and sealed with either wood glue or some type of finish.
And a question: now that it's been some time (more than a year) that you've gotten to spend with the modified drivers, do you have some more detailed impressions about the improvement to the sound?
It's funny to get a response 2 years later, especially since I haven't really finished the mod but recently have been finding bits of time to work on it!
They will be solid copper with clear finish on them.
I intend to attach with a threaded rod, then use locktite to secure.
The last two weekends (Sunday arvo is all I seem to be able to use), I've been turning up wood prototype phase plugs. 4 attempts and I haven't got one yet which is just right - correct diameter, length and profile.
As far as the sonics go, I haven't done a test since I first tried this. In truth I haven't really done a decent test. Two drivers have the dust caps removed and the glue mod done. They are rolled off at 200 Hz 1st order.
I suppose the way these things are supposed to work is that I do a test and then gush audiophile adjectives to describe how everything you can imagine improved! However, I'm not sure if I will actually be able to hear the difference in a blind test. That remains to be seen.
When it came to applying the glue, I rigged up a device to do it with some tube, also used a nail. I put it on the back of the cone so it doesn't have to be neat. Much harder but worth it to keep the front clean.
I now have these in open baffle so the turbulence issue isn't there. In the future I may use them as surrounds, then it might be an issue.
They will be solid copper with clear finish on them.
I intend to attach with a threaded rod, then use locktite to secure.
The last two weekends (Sunday arvo is all I seem to be able to use), I've been turning up wood prototype phase plugs. 4 attempts and I haven't got one yet which is just right - correct diameter, length and profile.
As far as the sonics go, I haven't done a test since I first tried this. In truth I haven't really done a decent test. Two drivers have the dust caps removed and the glue mod done. They are rolled off at 200 Hz 1st order.
I suppose the way these things are supposed to work is that I do a test and then gush audiophile adjectives to describe how everything you can imagine improved! However, I'm not sure if I will actually be able to hear the difference in a blind test. That remains to be seen.
When it came to applying the glue, I rigged up a device to do it with some tube, also used a nail. I put it on the back of the cone so it doesn't have to be neat. Much harder but worth it to keep the front clean.
I now have these in open baffle so the turbulence issue isn't there. In the future I may use them as surrounds, then it might be an issue.
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