The new RST28F-4 tweeters???

PWRRYD

I just purchased a pair of the new RST28F-4 tweeters because they are on sale and I happen to have I pair of the Visaton round waveguides I want to use them with.  Right out of the box these are no RS28 tweeters that we use to know and love...

1)  Visual inspection of them, their faceplates are not centered or clocked correctly.  The 4 attachment screws heads are not centered in their counter bores, not even close.

2)  These are the fabric dome version, not the aluminum dome version, yet they have a phase shield.  Why?

3) I did a DATS impedance sweep of them.  They aren't even close to the published curves that show a single well defined impedance peak at Fs.  Both of the tweeters that I got have a double peak Fs curve that peaks at 425 Hz and then again at 1100 Hz, but the peaks are only 5 ohms.  There is another blip at 1500 Hz.  

Anyone else measure a RST28F-4?  Does their .zma measure close to the published curve or are they more like the pair I got and measured?  I'm not going to monkey around with these (i.e. try to center the domes) because I plan to return these as defective.  Just curious if this is just bad luck on my part or if we have truly lost an old go to product.

Kornbread

I've got 4 of them laying around from the last sale.  Now you got me worried. 

jhollander

As soon as they went NLA I think we lost a go-to tweeter.  I'll reserve judgement until after I get to listen to them (I have the Al version).  I think it still takes years of reviews to get the reputation back.

Sound like you got the ported version   

Nicholas_23

Hey Craig , I ran a sweep on the pair of aluminum dome I have. Lets just say they didnt overlay very well. Ill run another sweep later tonight and post what Im talking about. 

jr@mac

Yep, saw that too in my quad. RIP RS28.

Nicholas_23

Actually , these look better than when I first ran the sweeps. I did let both burn in for a couple hours FWIW. They were all sorts of wonky initially.

jr@mac

It's 2019, no need for 90's Morel level of poor tweeter chamber design. 

Nicholas_23

I agree 

Nicholas_23

Im half tempted to dissect one 

Nicholas_23

First blush , face plate screws took nothing to take out. No resistance at all

Nicholas_23

Impressed ,there is some heavy felt like , wool maybe in the rear chamber? Maybe some asian pubicles in the mix too ?  Seeing black kinky hairs . It is damped though and nicely done from what I can see. 

PWRRYD

I've never broken in a tweeter before.  I'll run some sine sweeps through them and see if it makes any improvement.

dcibel

It's not bad at all, especially given the cost. The impedance bump is reflected in the frequency response, depending on your crossover point and baffle design it may help the final response or make things difficult. The generous pole vent is nice to see, however it looks like there is felt in the back, and a felt pad behind the dome, but nothing in between. Stick some cotton balls in there, couldn't hurt.

PWRRYD

I don't know what I should do.  Here is the DATS impedance sweep of the pair I got:



And of course here is a link to Dayton's spec page:

https://www.parts-express.com/pedocs/specs/275-141--dayton-audio-rst28f-4-specification-sheet.pdf

I hate to take a chance and screw up me being able to return them. 

Nick, looking at the Dayton spec page they say this tweeter has ferrofluid.  I can't tell from your pics.  Do your's have ferrofluid?

PWRRYD

Also Nick (or anyone else) do your's have any clear markings as to which terminal is positive or negative?  Mine only have a sloppy red Sharpie marker swipe on one terminal.

Nicholas_23

Whoa , those dont look right at all Craig , mine were off but not like that .... eeeash . I have a red sharpie marker that indicates + on the terminal. I do not see any film or residue on the coil that would indicate ferrofluid was applied.  Man , that sucks those sweeps are waaaaay off. 

Nicholas_23

Tom_S

Mine don't look too bad - seems I got lucky.

jr@mac

I love how PE calls these PoI tweets an upgrade over the Usher originals.

Nicholas_23

Note : If someone wanted to test these with some cotton in the pole piece , you will have to peal the felt pad from the top of the motor and glue it back in after the fact. 

Gowa

I'm happy that I went with the SB SB26STAC-C000-4 over the Dayton now.

dcibel

PWRRYD, send yours back, they no good.

https://www.audioxpress.com/article/test-bench-two-28-mm-dome-tweeters-from-dayton-audio-rst28a-4-and-the-rst28f-4

dynamo

It’s been my experience with PE that they may just let you keep the defective ones instead of them having to pay shipping, so if so you might be able to dissect them to find the problem.

PWRRYD

I'll be calling PE customer service first thing tomorrow morning.

dcibel

jr@mac said:

I love how PE calls these PoI tweets an upgrade over the Usher originals.

Yeah, those original RS28 never had any consistency issues or little bumps in the impedance...

http://techtalk.parts-express.com/forum/tech-talk-forum/65371-dayton-rs28f-4-testing-anomoly

I remember back in the day we'd just be happy just to have a motor with copper in it at USD$30 price point.

jr@mac

Come on...

Nicholas_23

Nicholas_23 said:

Whoa , those dont look right at all Craig , mine were off but not like that .... eeeash . I have a red sharpie marker that indicates + on the terminal. I do not see any film or residue on the coil that would indicate ferrofluid was applied.  Man , that sucks those sweeps are waaaaay off. 

I stand corrected , I was for whatever reason thinking ferrofluid would be white in color. I ran my pinky finger across the coil and there is indeed fluid there. 

PWRRYD

PE gave me a RA number to return them and then will send me a new pair.

Tom_S

I hope you end up getting a good pair in the end. Maybe this will cause them to pay a little attention to QC.

Gowa

Tom_S said:

I hope you end up getting a good pair in the end. Maybe this will cause them to pay a little attention to QC.

That's where all the cost cutting is.

jhollander

Rush to fill the void by the demise of the RS28.  Kind of sad, but understandable. How do you create something as good with a short deadline?  I still need to spend some time with them in a decent design. I think Chuck has used them so I'd like to hear want he thinks.  I finished a remote design with them and the RS180 but may not get to hear them any time soon.