Hi John,
One thing I learned with my diffusers was that mdf can't be milled to a very small, sharp point. There is not enough structure and it will break off easily, so be very careful with the tip of the cone, if you use all mdf. What I ended up doing was adding a piece or two of hardwood for the tip section which allowed for a sharper cone tip. The change of material is a bit of a challenge, because mdf is so soft and the hardwood is not.
Good luck.
One thing I learned with my diffusers was that mdf can't be milled to a very small, sharp point. There is not enough structure and it will break off easily, so be very careful with the tip of the cone, if you use all mdf. What I ended up doing was adding a piece or two of hardwood for the tip section which allowed for a sharper cone tip. The change of material is a bit of a challenge, because mdf is so soft and the hardwood is not.
Good luck.
I needed a cone, so laminated up some scraps of particle board and mdf of various types in a vertical format. Big mistake. First the differences in hardness made it very difficult to turn evenly. The tool chattered. Second, not all the mdfs turned nicely. One in particular made of very fine material, had a "grain" believe it or not, and taken the wrong way, tore rather than cut cleanly.
A horozontal lamination of identical materials should be easier.
A horozontal lamination of identical materials should be easier.
rjb said:
"Rj", I'll try to keep this in mind as well, and ensure that I use the material from the exact same sheet of MDF, so there will not be any differences. And the only additions will be the wood for the point of the lense, which will be out of softer wood.
Dan is right about MDF being a problem when trying to turn a fine point. I am pretty much required to use wood here. But I will also keep your tip in mind while I am turning the lense.
Thanks for the tip. I'm not sure when I will be heading back, but it may not be this week, as I am pretty busy with business. If I can find some time open, I will make the blanks and set them aside.
Meanwhile, I will probably be starting to work with the B20s, by removing the dust cap, and at least trying to drill through the center of the magnet assembly, using my drill press. And I'll be taking pictures.
John L said:
Meanwhile, I will probably be starting to work with the B20s, by removing the dust cap, and at least trying to drill through the center of the magnet assembly, using my drill press. And I'll be taking pictures.
Hi John,
Guide bearing came off the router bit? Ouch. I haven't had that particular pleasure yet.
Hope all goes well with drilling through the pole of the speaker. My fingers are crossed for you.
MJL21193 said:
It's no fun, believe me. Fortunately, it only came loose, and didn't fall off. Just enough to ruin my day.
I had forgone the solid bit because it had gotten filthy and needed a good cleaning, and I was lazy. I'm sold on that particular bit, because I never allow the bit to stay still in any one spot, so it never has a chance to burn things. But in this case, I let myself get in a hurry, and did not wish to lubricate the portion of the wall where it would run. I won't do that again.
And thanks for the well wishes.
Ed LaFontaine said:
Thanks Ed. The instructor has a huge vacuum system under the floor of his shop, and hoses running all over the place, and into the floor. I suspect he will have a set-up for this huge OneWay lathe.
I'd love to have one like this in my shop, but it obviously costs several thousand dollars.
Today I started modifying one of the B20s. Even though I understand Dave, about getting metal shavings in the voice coil, I decided that it was still worth the experiment. Besides, it is not like I am performing surgury on a Fostex, or a Feastex. If it does not work, I can always order another one.
The first thing I did was to make an "X" slit across the dust cap. Then I gently pulled the cap off the cone, which was straight forward.
Using the same proceedure for replacing voice coils, I inserted a heavy duty sheet of paper between the coil and the magnet assembly.
Here is what it looks like with the insert pushed completely down into the coil.
Then I applied painter's masking tape in pieces until the voice coil was fairly secure from shavings.
Then I applied grease with a small brush until it covered the area where the drill bit would exit. This would help keep the metal shavings from being forced to the voice coil magnetically.
I carried the speaker to the drill press, and set a piece of plywood on the base, but could not find the key for loosening up the existing bit within the press. No matter where I looked it could not be found. So I was forced to take it to my work table and do it by hand.
Before applying the bit, I dropped some sewing machine oil into the recess where the bit would begin drilling. This made it much easier to keep the shavings attached to the bit or right around the hole.
Before each time I would drop more oil into the hole and then drill until I had accumulated a bunch of shavings. Then I would remove the bit and carefully wipe away all the shavings by following the flute of the bit. Then I would do it over again. I did this about eigth times until I finally reached the other side.
The grease on the other side managed to keep most of the shavings away from the coil, so I was able to clean up most of the speaker and remove almost all the shavings. However, I could not remove all of it, and a couple of small pieces managed to migrate to the coil. I think that there is virtually no way to completely remove ALL of the metal, but there are ways to clean up after yourself.
Keeping the insert in place is important, but also the insertion of a piece of clear plastic helped remove the two small metal shavings. Here is what it looks like with the clean-up. There is absolutely no obstruction of the voice coil, and it moves smoothly up and down.
After this I started looking around the shop for a large dowel that would fit in the pole piece. And sure enough, a 1 1/3" dowel is perfect for making a phase plug on which the tweeter will set. Here is what it looks like.
And next I drilled a hole through the dowel.
And here is the ND20FA-6 on top of the dowel, but I will probably use the ND20FB-4.
The next thing for me to do is to modify both drivers, paint the phase plugs, run the wire, and epoxy the plug to the speaker, and then seal the hole with hot glue.
The first thing I did was to make an "X" slit across the dust cap. Then I gently pulled the cap off the cone, which was straight forward.
An externally hosted image should be here but it was not working when we last tested it.
Using the same proceedure for replacing voice coils, I inserted a heavy duty sheet of paper between the coil and the magnet assembly.
An externally hosted image should be here but it was not working when we last tested it.
Here is what it looks like with the insert pushed completely down into the coil.
An externally hosted image should be here but it was not working when we last tested it.
Then I applied painter's masking tape in pieces until the voice coil was fairly secure from shavings.
An externally hosted image should be here but it was not working when we last tested it.
Then I applied grease with a small brush until it covered the area where the drill bit would exit. This would help keep the metal shavings from being forced to the voice coil magnetically.
An externally hosted image should be here but it was not working when we last tested it.
I carried the speaker to the drill press, and set a piece of plywood on the base, but could not find the key for loosening up the existing bit within the press. No matter where I looked it could not be found. So I was forced to take it to my work table and do it by hand.
Before applying the bit, I dropped some sewing machine oil into the recess where the bit would begin drilling. This made it much easier to keep the shavings attached to the bit or right around the hole.
An externally hosted image should be here but it was not working when we last tested it.
Before each time I would drop more oil into the hole and then drill until I had accumulated a bunch of shavings. Then I would remove the bit and carefully wipe away all the shavings by following the flute of the bit. Then I would do it over again. I did this about eigth times until I finally reached the other side.
The grease on the other side managed to keep most of the shavings away from the coil, so I was able to clean up most of the speaker and remove almost all the shavings. However, I could not remove all of it, and a couple of small pieces managed to migrate to the coil. I think that there is virtually no way to completely remove ALL of the metal, but there are ways to clean up after yourself.
Keeping the insert in place is important, but also the insertion of a piece of clear plastic helped remove the two small metal shavings. Here is what it looks like with the clean-up. There is absolutely no obstruction of the voice coil, and it moves smoothly up and down.
An externally hosted image should be here but it was not working when we last tested it.
After this I started looking around the shop for a large dowel that would fit in the pole piece. And sure enough, a 1 1/3" dowel is perfect for making a phase plug on which the tweeter will set. Here is what it looks like.
An externally hosted image should be here but it was not working when we last tested it.
And next I drilled a hole through the dowel.
An externally hosted image should be here but it was not working when we last tested it.
And here is the ND20FA-6 on top of the dowel, but I will probably use the ND20FB-4.
An externally hosted image should be here but it was not working when we last tested it.
The next thing for me to do is to modify both drivers, paint the phase plugs, run the wire, and epoxy the plug to the speaker, and then seal the hole with hot glue.
Hi John,
Nice job! I would guess that the ND20-FB will be better in your application because of the smaller flange and also due to its rising frequency response, which should be helpful in getting a flatter 90º off axis FR.
FWIW, another very nice, inexpensive neo tweeter you might try is the Aura NT-1. If you haven't seen it, you can at Madisound. It has the same body as the FB, but a titanium dome and is consideraly lower in distortion and can cross lower for that reason. I'm comparing it to the NB in my current project, and to my ears, it is much cleaner and more detailed and only $3 more.
Aura NT1
Nice job! I would guess that the ND20-FB will be better in your application because of the smaller flange and also due to its rising frequency response, which should be helpful in getting a flatter 90º off axis FR.
FWIW, another very nice, inexpensive neo tweeter you might try is the Aura NT-1. If you haven't seen it, you can at Madisound. It has the same body as the FB, but a titanium dome and is consideraly lower in distortion and can cross lower for that reason. I'm comparing it to the NB in my current project, and to my ears, it is much cleaner and more detailed and only $3 more.
Aura NT1
Fantastic work, John. The smaller Dayton tweeter (of which I have a pair) would probably work a bit better for you (could probably be press fit directly into the dowel instead of having any exposed back side causing reflections), but that wouldn't exactly be a difficult change down the line. You'll be able to see how viable this is quickly enough, and I'm excited to see how it goes.
Kensai
Kensai
John L said:
Nice work... The only thing I would do differently than you're suggesting is use flush mounted flat head screws on the back of the plug to magnetically adhere the plug in place. You can get a hint of how it ooks by looking at some of the phase plug pictures on the planet 10 site. It's not my idea
It might be that the weight is too much for the plug to hold... but I'd certainly try it before expoxying something in place.
Unless youre' talking about expoxying the supertweeter to the plug... in which case, ignore everything I just said
GB
I'm amazed you got thru with a hand drill -- what kind of bit? How hot did things get? I may try that now.
I got 1 1/4" dowel for my experiment. The little dayton fits perfectly on the end. A piece of 1 1/2" heat shrink will go over this to make it look seemless and add a bit of girth,
I don't think screws will be enuff to hold the plug if the driver is mounted normally, but facing up it will probably be sufficient. A tiny bit of ductseal or bluetack to keep the plug from walking might be helpful.
dave
Thanks Guys! I had not shown you all how I got the tweater to fit snuggly on the phase plug, so I went back down to the shop and took some more pictures. Here is what the top of the plug looks like after I cut away with the top, using my table saw. Please note that I did this in a hurry. I was in a rush to get the pictures, and I have lots of 1 1/3" dowel, which is a perfect fit for phase plugs to be used on these B20s. They are a pretty tight fit, and I wouldn't want to go any larger since they may tend to rub against the voice coil.
I went back and checked things out and noticed a little piece of lint at the eleven o'clock position.
I took out my trusty piece of cut sheet plastic, I guess somewhere around 8-10 mil thickness, and ran it under the lint and played with it until it moved up to the corner lip. Then I took one of those round metal pieces that are used to keep insulation in place in roof joists. Let me go back down stairs and take another picture of it. If you get any lint between the voice coil, this works wonders. I'll be right back.
An externally hosted image should be here but it was not working when we last tested it.
I went back and checked things out and noticed a little piece of lint at the eleven o'clock position.
An externally hosted image should be here but it was not working when we last tested it.
I took out my trusty piece of cut sheet plastic, I guess somewhere around 8-10 mil thickness, and ran it under the lint and played with it until it moved up to the corner lip. Then I took one of those round metal pieces that are used to keep insulation in place in roof joists. Let me go back down stairs and take another picture of it. If you get any lint between the voice coil, this works wonders. I'll be right back.
Ok, here is what I am talking about. I had learned about how to repair speakers some years ago, had actually worked with reinstalling surrounds and voice coils and spiders, so I remembered how to use inserts to hold the voice coil in place while making changes and repairing drivers. That is how I remembered to insert a paper layer between the coil and magnet.
Also, to remove lint, a plastic insert is pretty good at removing the little critters that get lodged between the coil and magnet. All you have to do is cut a piece that is easy to use and just insert it between the paper and the coil. Then just pull up until the lint moves to the top of the magnet. Then take a sharp object, such as a long needle, and gently work with it until the lint sticks to the needle.
In this case, it was a piece of fine metal shaving, so it did not want to move away from the magnet once I had moved it to the top of the magnet. I accomplished this by taking the metal rod in the picture. Note that it has a point on the ends.
You can find these thin rods at any hardware store, and they are used for keeping insulation in place once they are installed within trusses or joists. If your basement has an unfinished ceiling, they should be there in great numbers. All you have to do is take one down and use it, before replacing it. I keep one in my parts drawer all the time. In this case, it becomes magnatized and will tend to pick up the lint fairly easily. Once it is gone, just wipe it off the rod, and the lint is history.
Here is a picture of the plastic placed down in the coil/magnet assembly.
By using this technique, if you ever get lint between the coil and the magnet, and it affects things, just stick a piece of plastic between the two and gently force it up to the top of the magnet for removal.
I do have some worries about having a phase plug attached on these drivers, and it works with all drivers having PPs. It is very easy to get lint between the coil and magnet, because it is slightly open all around. Am I missing something here? Do these modified speakers have a tendency to pick up crud? After all, that is the purpose of the dust cap.
Also, to remove lint, a plastic insert is pretty good at removing the little critters that get lodged between the coil and magnet. All you have to do is cut a piece that is easy to use and just insert it between the paper and the coil. Then just pull up until the lint moves to the top of the magnet. Then take a sharp object, such as a long needle, and gently work with it until the lint sticks to the needle.
In this case, it was a piece of fine metal shaving, so it did not want to move away from the magnet once I had moved it to the top of the magnet. I accomplished this by taking the metal rod in the picture. Note that it has a point on the ends.
An externally hosted image should be here but it was not working when we last tested it.
You can find these thin rods at any hardware store, and they are used for keeping insulation in place once they are installed within trusses or joists. If your basement has an unfinished ceiling, they should be there in great numbers. All you have to do is take one down and use it, before replacing it. I keep one in my parts drawer all the time. In this case, it becomes magnatized and will tend to pick up the lint fairly easily. Once it is gone, just wipe it off the rod, and the lint is history.
Here is a picture of the plastic placed down in the coil/magnet assembly.
An externally hosted image should be here but it was not working when we last tested it.
By using this technique, if you ever get lint between the coil and the magnet, and it affects things, just stick a piece of plastic between the two and gently force it up to the top of the magnet for removal.
I do have some worries about having a phase plug attached on these drivers, and it works with all drivers having PPs. It is very easy to get lint between the coil and magnet, because it is slightly open all around. Am I missing something here? Do these modified speakers have a tendency to pick up crud? After all, that is the purpose of the dust cap.
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