a.palfreyman
pfm Member
We I have some AR2ax speakers that I've never used. I refoamed the bass units some time ago with Boston Acoustics foams but never settled with them. Anyway that's another story.
The tweeters on these had both been blown and were O/C. I'd previously tried to remove one of the domes but destroyed it... so a few weeks ago I bought a set of 4 off 19mm tweeters (from China) and measured these. Thankfully there were 2 which measured identically, 5R7 and 50uH. I'd also bought some magicians foam balls but couldnt cut them reliably so I nicked a used dish-foam from the kitchen, removed the Scotchbrite and cut some slices circa 5mm thick with some big scissors:
I'd spun a copper coupler on the lathe by hand using a tungsten carbide planer blade to create a sharp edge and I used this to cut some foam discs from the slices. I then trimmed one corner with curved nail scissors to create a dome-shape:
This was glued in place using a clear plastic ruler to ensure it didn't move and weighted:
Giving:
Note that there is a thin paper gasket glued to the metal where the old dome was removed. Dont want any shorted terminals...
I then played around with a spare tweeter dome which was difficult to align, so I made this tool from thin ply with a hole cut to clear the tweeter surround, and 0.5mm cable sheathing:
In the end, I struggled with manual alignment so much that I cut three strips from a Heinz bean can label, inserted these into the magnet gap, put three small patches of PVA between the strips and dropped the tweeter in place. I firmed it down slightly with the tool above, taped it down where glued and then slid the paper spacers out. I then fed it with my low distortion oscillator via a lm3886 amp module and using a small DIY mic preamp and Teac module, minimised the distortion by using the tool to manipulate the position slightly. Once dried, I fed some glue under the gaps with a tooth pick and firmed it down. Didn't take any pictures as I was sweating it too much! Anyway, this is a finished tweeter:
I need to mount it to a board to measure it properly, because standing waves in-room give a bit of a false impression but during the process, and once dried, it appears as though it is better than -70dB distortion residual at 3.13kHz.
I'll have a break before attempting the second one.
The tweeters on these had both been blown and were O/C. I'd previously tried to remove one of the domes but destroyed it... so a few weeks ago I bought a set of 4 off 19mm tweeters (from China) and measured these. Thankfully there were 2 which measured identically, 5R7 and 50uH. I'd also bought some magicians foam balls but couldnt cut them reliably so I nicked a used dish-foam from the kitchen, removed the Scotchbrite and cut some slices circa 5mm thick with some big scissors:
I'd spun a copper coupler on the lathe by hand using a tungsten carbide planer blade to create a sharp edge and I used this to cut some foam discs from the slices. I then trimmed one corner with curved nail scissors to create a dome-shape:
This was glued in place using a clear plastic ruler to ensure it didn't move and weighted:
Giving:
Note that there is a thin paper gasket glued to the metal where the old dome was removed. Dont want any shorted terminals...
I then played around with a spare tweeter dome which was difficult to align, so I made this tool from thin ply with a hole cut to clear the tweeter surround, and 0.5mm cable sheathing:
In the end, I struggled with manual alignment so much that I cut three strips from a Heinz bean can label, inserted these into the magnet gap, put three small patches of PVA between the strips and dropped the tweeter in place. I firmed it down slightly with the tool above, taped it down where glued and then slid the paper spacers out. I then fed it with my low distortion oscillator via a lm3886 amp module and using a small DIY mic preamp and Teac module, minimised the distortion by using the tool to manipulate the position slightly. Once dried, I fed some glue under the gaps with a tooth pick and firmed it down. Didn't take any pictures as I was sweating it too much! Anyway, this is a finished tweeter:
I need to mount it to a board to measure it properly, because standing waves in-room give a bit of a false impression but during the process, and once dried, it appears as though it is better than -70dB distortion residual at 3.13kHz.
I'll have a break before attempting the second one.
