MWAF contestants, B-Stock RST28F-4 info...

[4thtry]

That corrosion is no joke..geez. Glue must have been made with water from the Dead Sea.

I looks worse that it actually is. The corrosion layer is very thin. I did not scrape it off because I did not want to accidently push anything down the pole piece hole. I had a vacuum cleaner running when I pulled the cup off so that any small particles were immediately sucked safely away.

[dynamo]

That corrosion is no joke..geez. Glue must have been made with water from the Dead Sea.

[4thtry]

Here are a couple pics & a curve from my testing work. As you can see in the photo, I left the thin white felt pad glued to the plastic cup in place, then added a small 1/4" thick piece of denim insulation over the pole piece hole, sandwiched between the thin white felt pad and the pole piece hole. Prior to creating this sandwich, I put the original foam plug back in place. I taped the cup back on with blue masking tape. I also tested with a washer pushed underneath the original white felt pad with no denim and the original foam plug in place. The Z curve was identical for both tests. The key seems to be getting the amount of stuffing in the pole piece and the tightness of the stuffing in the rear chamber "just right." Notice that my Z curve peaks out a little above 6 ohms with a slightly lower Q than the "golden" or good sample curves. I will keep experimenting until I get my Z peak to hit about 8 ohms or so by changing the stuffing ratios, then glue the cup back on.

[4thtry]

That's amazing Bill. I would have thought it was junk. Do you have the tuner working?

Yes, both AM & FM sections working well: pulls in tons of stations. Once I get it completely aligned, it will be even better.
As they say, one man's junk is another man's treasure. (Sorry for the hijack. Back to the tweeter discussion).

[jhollander]

John, the Claritone is now up and running and sounds great!!!.

That's amazing Bill. I would have thought it was junk. Do you have the tuner working?

[4thtry]

Interesting observations. I will remove the felt pad and try the metal washer mod and report back. I was going to post some pics, but I've been sidetracked lately working on my Claritone restoration project. John, the Claritone is now up and running and sounds great!!!.

[GTPlus]

GT, your second post's images are broken. Good work what I can see.
Wolf

They should be fixed now, LMK if not.

Here are a few pictures. While I saved the cup, the glue plus small size really makes this unappealing to reuse. The felt pad is junk imo. It looks like the glue corroded the coating on the magnet. Judge's score this a "2".

Mine look much the same, looks like the glue causes some corrosion. One of mine was worse than the other.

I am hoping I can get some measurements soon, but my theory is the back cup is probably doing very little. I noticed I could get impedance curves to look best when the vent was blocked. Also, if you look at the cup design, it is dimpled behind the vent. I think the intent is to get the felt to be clamped tight to and at the vent.

I ran a test by taking the stock cup and felt, with the foam in the vent, then putting a metal washer between the felt and cup to press the felt closer to the vent. The results looked close to published spec, and also came close to the tight packed cup. Maybe the spec change on these was just too thin of felt.

[Wolf]

I also felt the 'felt' was not worth reusing it. My magnet in the first one actually had a bit of rust on the steel plate- I'm with you there....
Looks like you need some Ball lids,
Wolf

[jhollander]

Here are a few pictures. While I saved the cup, the glue plus small size really makes this unappealing to reuse. The felt pad is junk imo. It looks like the glue corroded the coating on the magnet. Judge's score this a "2".

[4thtry]

Did you change the cup stuffing or remove the felt?
Just curious,
Wolf

No, I left the thin white felt pad, which was glued onto the the back of the cup, in place. So I did not replace it with Ultratouch, as shown in your diagram. I will give this a try later and report back. But what I did was to simply pull off the plastic back cup and remove the small piece of tapered foam in the pole piece with a forcepts tool. I replaced the small foam plug with a cotton ball, re-installed the back, and then re-measured. I did not remove the front faceplate. I did everything from the rear end.

[Wolf]

GT, your second post's images are broken. Good work what I can see.
Wolf

[jhollander]

I did the same with the heat gun an pried the back cup off. It looks reusable. It does look like the pole foam might not be needed which matches what I heard elsewhere. Unfortunately my felt is in a storage unit box that I'm not getting to any time soon so my testing is going to be limited.

[GTPlus]

Tight packed cup foam in vent


Vent taped off(blocked), no cup with no foam in vent


Taped off Vent(Blocked) with foam in vent



That's it for tonight. If I can get some time I'll try to take some response graphs of the same variations.

[GTPlus]

This thread is way too tempting to not be apart of, so I had to tear into my set as well.

I was able to get the back cups off without too much damage. I started by warming up the sides of the cup with a heat gun on low to soften the glue. I then pinched the sides of the cup in a vise (red arrows in pic, Hope you don't mind me borrowing the pic Wolf)



This causes the edge of the cup to deflect out and create a gap where the cup meats the magnet. I could then slowly work my way around the circumference and pry it away from the magnet. So the cup is still usable and in not too bad of a condition

So far I have only run some impedance sweeps in DATS, using different variations in pole stuffing, cup stuffing etc...

Here are a few results.

Stock...



No cup or foam in vent




Stock Felt in cup, no foam in vent


Tight packed cup with no foam

More to come

[Wolf]

With something that is less than 1" away from the acoustic origin, I'd think that absorption and damping is the best bet.
Later,
Wolf