I've been chatting with a few PE guys. The double hump in the impedance seems to be due to stuffing behind the dome and in the pole piece. The comments were that the double hump version has a lower FS over the non-double hump. Some liked the lower FS with the double hump
You can tell after opening these the stuffing behind the dome has a hard cap and is not your typical material. I'll be playing as well. Lots of fun.
I'm using number 2 as the guinea pig, but it should work on both. The key is to attack from the rear. I heated up a small screw-driver to slowly pry off the back cup. In most cases, this will likely chew up and ruin the cup. I found some Ball baby-food jar caps at Walmart to facilitate the replacement parts. They are a touch loose, but will work. 2" PVC flat caps are a touch too small, but would also likely work.
Initial:
No back cup:
Removed the foam plug:
Pulled out string of black adhesive (that was across the front of the pole) from the rear using needle-nose pliers, and then inserted a 1" ball of cotton to flush with backplate. There is still no back cup installed:
And finally added the Ball-back-cup with a thin layer of wool batting over a material similar to Ultratouch, slightly overstuffing the cup, and then wrapping with masking tape to hold and seal the assembly for testing:
I did absolutely nothing in front of the felt pad that covers the vented pole piece, and this looks really good!
I hope those of you with bad RST-F tweeters feel that fixing these will be of benefit. I do at the moment.
Ben, is it possible to get a FR sweep? after and before (with the other non modified Tweeter), but still looks a lot of work, for something that should have just worked off the box...
Mine were free in the bag from MWAF, and it took about an hour of playing around. I can see what I get in reference of the other unmodified but I never took one of the unmodified number 2. The Qts is higher than spec, but I even managed to best the spec impedance ripples. There is no ripple above resonance now.
Okay, did as asked. Not cool enough to do much else today. I had to shut off the ceiling fan and the box fan for these, and the family was nice and kept totally quiet for the 10 minutes it took.
I attempted what I call the 'Jeff Bagby driver measurement setup sans cabinet'. I set the tweeters on a sheet of egg-crate on the carpeted floor, then laid a circle of open-cell 1/16" sheet (with center cut out for the driver) atop of it. Then I surrounded the foamed face with 3-4 pieces of Sonic-Barrier. Jeff uses felt, but I had this handy. The mic was about 2 feet from the driver facing down. A 70uF cap was used in series for driver protection.
Bstock1, unaltered:
Bstock2, modded, same levels and setup:
I think that is a NOTICEABLE difference. Granted, I'll also oblige a graph of the modded Bstock1 when I get there. Ben
Well, I as able to get them a lot closer to each other, and reduce the number of problems they had initially. I have a bit of audible 3rd order and a corresponding broad impedance bump around 250Hz in the Bstock1 driver, but everything else is pretty close. I don't know what is causing it, but it didn't look to be there before. Being I'll roll it off long before there, I'm not worried about it. I also took an HD pop of an old RS28A-4 in the same setup, just for fun. Mod1 then Mod2 for all below...
RS28A-4 HD :
The FR of the Bstock modded drivers is now pretty similar, as is the T/S, impedance, and HD. That's all I was really hoping for. Being that the FR is pretty close, but only applicable to these tests, I'll omit those for the sake of not being notable information.
Lot's of strangeness in business practices that PE would/could screw up a flagship product like the RS28. Probably they were prohibited from using specific features by Usher and have not found a good workaround. The old RS28 looks just it always has - a total mutha value for <$100
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
Apparently this mix up was from the manufacturer changing specs without telling PE of the change. Even so, I bested the stock Z curve, and dramatically reduced the HD from how they came to me. I have not seen the HD curve of one that was supposedly good from the manufacturer. Yes- the old venerable RS28 is still a leader in good specifications.
Nice work Ben! I'll keep this in mind for the future... I can see a pair of one-off rear home theater surrounds getting these tweeters from the goodie bag, so making them as good as can be would be advantageous. Did you happen to snap any pictures? I've never torn into the rear of a tweeter like this before, so knowing (and seeing) what to expect ahead of time would be a big benefit.
I did not, but what I did I thought would be self explanatory. The #1 unit did not have a strung piece of adheasive across the pole, so that might not be a common issue. Basically; pop off the cap, pull out the foam plug and replace it with a 1" cotton ball flush with the backplate, then recap and have ultratouch in the cup instead of the bonded felt that came with it. Just fill the cup to just beyond the rim, and glue it back on. The batting I used in between isn't really necessary, but I did it to cover the pole.
About 3-4 layers of a thin white felt, made stiff by the gluing in of the layers. It's 3/16-1/4" thick or less. The cup itself is pretty thin, and not all that strong.
Hey Ben, just wanted to let you know I just did your mod to one of my grab bag rst28fs with the same result as far as correcting the z to factory spec. The only thing I did different was used a layer of foam rebond carpet padding with a layer of fiberglass insulation in front of it in the jar lid instead of ultratouch, only because it’s what I had. Thanks again for your research into fixing these.
I just thought there was some way to improve them that most who received them would also like to know about. I managed to do it without much effort or time, and the improvement was pretty impressive. You are very welcome!
Don't have any ultratouch that will fit into the cup so left the stock felt padding in place, replaced the foam plug with the obligatory 1" cotton ball, and sealed the cup back to the tweeter with a couple rounds of black tape.
Not quite there yet.
Use the entire 1" cotton ball? It fits pretty tight.
Used the dremel with one of those cutting wheels that shatters if you look at it wrong and cut at the junction of the cup/magnet just cutting through the plastic cup. The cutting wheel lets you know when its through the plastic cup. The cup then came off with just a little prying and it's easily reusable.
If it's bigger than 1" squished, it's too much. It really was about 1" diameter when compacted, and yes it fit tightly. Football and twist as you insert it.
I know this is a really old thread but I thought I'd revive it. I've had this week off and had lots of time in the morning to work on stuff while everyone is still sleeping. I was able to successfully remove the back cups without destroying them. I did Ben's mods and got them back together and remounted to the Visaton waveguides. Their impedance curves are now identical and more closely match PE's. I'll take some FR and distortion measurements when I get some boxes built.
I ended up donating my set unmodified. Friend was building an LCD based pin ball machine. I had enough junk to supply the sound system. I used those tweets and some Audax mids for the satellites. I used an MCM 8" subwoofer for bass duties in ported box tuned to 38hz.
I was going to do the crossover and I happened to see a set of Boston Acoustic car audio xovers laying on the shelf, thought...what the heck and slapped them in there. Much to my surprise that's the FR curve. Bonus! A bit hot in the middle, but just fine for pinball duty. A tent sale 2.1 plate amp finished it off.
Basic boxes are built. Need to machine the driver rebates and cutouts on the baffles, attach, flush trim, then roundover with 3/4" bit. More to follow...
Comments
You can tell after opening these the stuffing behind the dome has a hard cap and is not your typical material. I'll be playing as well. Lots of fun.
InDIYana Event Website
I'm using number 2 as the guinea pig, but it should work on both. The key is to attack from the rear. I heated up a small screw-driver to slowly pry off the back cup. In most cases, this will likely chew up and ruin the cup. I found some Ball baby-food jar caps at Walmart to facilitate the replacement parts. They are a touch loose, but will work. 2" PVC flat caps are a touch too small, but would also likely work.
Initial:
No back cup:
Removed the foam plug:
Pulled out string of black adhesive (that was across the front of the pole) from the rear using needle-nose pliers, and then inserted a 1" ball of cotton to flush with backplate. There is still no back cup installed:
And finally added the Ball-back-cup with a thin layer of wool batting over a material similar to Ultratouch, slightly overstuffing the cup, and then wrapping with masking tape to hold and seal the assembly for testing:
I did absolutely nothing in front of the felt pad that covers the vented pole piece, and this looks really good!
I hope those of you with bad RST-F tweeters feel that fixing these will be of benefit. I do at the moment.
InDIYana Event Website
InDIYana Event Website
I attempted what I call the 'Jeff Bagby driver measurement setup sans cabinet'. I set the tweeters on a sheet of egg-crate on the carpeted floor, then laid a circle of open-cell 1/16" sheet (with center cut out for the driver) atop of it. Then I surrounded the foamed face with 3-4 pieces of Sonic-Barrier. Jeff uses felt, but I had this handy. The mic was about 2 feet from the driver facing down. A 70uF cap was used in series for driver protection.
Bstock1, unaltered:
Bstock2, modded, same levels and setup:
I think that is a NOTICEABLE difference. Granted, I'll also oblige a graph of the modded Bstock1 when I get there.
Ben
InDIYana Event Website
RS28A-4 HD
The FR of the Bstock modded drivers is now pretty similar, as is the T/S, impedance, and HD. That's all I was really hoping for. Being that the FR is pretty close, but only applicable to these tests, I'll omit those for the sake of not being notable information.
InDIYana Event Website
Yes- the old venerable RS28 is still a leader in good specifications.
InDIYana Event Website
InDIYana Event Website
The cup itself is pretty thin, and not all that strong.
InDIYana Event Website
InDIYana Event Website
InDIYana Event Website
I know this is a really old thread but I thought I'd revive it. I've had this week off and had lots of time in the morning to work on stuff while everyone is still sleeping. I was able to successfully remove the back cups without destroying them. I did Ben's mods and got them back together and remounted to the Visaton waveguides. Their impedance curves are now identical and more closely match PE's. I'll take some FR and distortion measurements when I get some boxes built.
What you don't own a camera?
Glad to hear it, Craig! I still have to use my pair...
InDIYana Event Website
I ended up donating my set unmodified. Friend was building an LCD based pin ball machine. I had enough junk to supply the sound system. I used those tweets and some Audax mids for the satellites. I used an MCM 8" subwoofer for bass duties in ported box tuned to 38hz.
I was going to do the crossover and I happened to see a set of Boston Acoustic car audio xovers laying on the shelf, thought...what the heck and slapped them in there. Much to my surprise that's the FR curve. Bonus! A bit hot in the middle, but just fine for pinball duty. A tent sale 2.1 plate amp finished it off.
https://www.dropbox.com/s/2vc1o7wb5iwp8hx/IMG_9078.mov?dl=0
https://www.dropbox.com/s/i1rc3wsu8cghoff/IMG_9105.mov?dl=0
I hope these work, he did a fantastic job on it!
...and of course the best game on it....
https://www.dropbox.com/s/zj0ifxnd398segi/IMG_9140.mov?dl=0
Where did you get the grills for the Audax on the sats? Those are cool!
InDIYana Event Website
Basic boxes are built. Need to machine the driver rebates and cutouts on the baffles, attach, flush trim, then roundover with 3/4" bit. More to follow...
I think he had a buddy print them.