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Help please in debugging RS IIIb's

G

GardenGate

New Member
Hello - hoping folks can give me some help here figuring out what's going on with a pair of RS IIIb's which I inherited from my late Dad who purchased them new in the early 1980's. Overall, they have been well kept for ~40 year old speakers, but of course the foam surrounds for the woofers were shot, so I just replaced them with the kit and directions from Simply Speakers. The bass sounds fine now but above once I get past a moderate volume level, I hear some distortion that sounds like something is vibrating or buzzing in the speaker - for example, if it's piano music, it kind of sounds like as if something that is sitting on top of the piano is vibrating.

Any thoughts to offer on figuring out the cause and how to fix it? Everything seems solidily screwed together on the speakers themselves. A bad EMIT or Polydome midrange? Something bad in the crossovers? What else can I do to debug what's going on?

Thanks in advance!
 
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Typically going to be one of four possible causes, especially right after a refoam.

1) Voice coil rub. If the voice coil isn't properly centered it will rub against the magnet. You should be able to feel it by hand and/or hear it if you depress the cone. Only way to fix it is to refoam again.

2) Loose dust cap. If you removed the dust caps and didn't fully reattach them they will rattle at higher volume/ cone movement. Hopefully you didn't remove the bullet cone center caps if the woofers are still original.

3) Loose/detached spider. When reforming it is not unusual to extend the cone further than normal and pull on the spider. I have had this happen on a couple occasion after a refoam.

4) wires are hitting the back of the cone. With the clear poly cones you should be able to see thru them and see if any of the wires are laying against the cones.
 
I would guess a voice coil as well. If it was played with no surrounds they could be damaged, might try rotating 180 degrees. Unconnect drivers one at a time to identify which one is bad and find someone who knows how to fix. If you have never refoamed or repaired drivers before it’s easy to get one out of alignment or gunk in a gap
 
I agree with the above. Have you ever refoamed woofers before? What do the woofers sound like out of the cabinet played in "free air"? Any noise? Is it coming from both speakers or just one? How did you make sure the voice coil was center when you were refoaming? Did you use the test tone style or another method?

Then again, it could be those old Polydome mids on their last leg. You might try removing and disconnecting the 4 woofers (take the bare leads) and see what the mids and highs sound like by themselves. Those mids are problematic now that they are 40 years old.

Yeah, lots of questions but it's basically a game of darts right now.
 
What those guys said.
Except the part about the polydomes.
The RS series including the IIIb have the polydome that doesn't suffer from hardening and cracking, as far as I know.
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The "other" Kappa series polydomes do have well known hardening and cracking issues.
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It could be a rubbing voice coil or vibrating dust cap. Could also be a portion of the surround that's not glued down fully, or even a spider that's become torn or partially detached. We'd need to know more about how you did the refoaming.
 
Could the wires be reversed on the lower woofer? The speakers have to be running in parallel (or is it serial?) to sound correct. Help me out here.
 
Thanks for all the replies so far - a few pieces of info in response:
- voice coil rub: it was the first refoaming I've tried, following the directions and YouTube videos that SimplySpeakers.com provided which said to center the cones by hand while the glue is drying, no need to remove the dust caps to shim. It seemed pretty straightforward, and after all the glue cured, I detect no rubbing at all on 3 of the 4 woofers, and on the 4th, perhaps slight potential rubbing only when moving the woofer cone to an extreme deflection by hand (> 1/2") I'm not driving anything to that level of volume, so my strong suspicion is that it's not a woofer voice coil rubbing that causing the distortion?
- loose dust cap(s): per above, I didn't remove the dust caps - they seem to be perfectly fine and not loose
- loose/detached spider: is the spider the yellowish/orange portion that suspends the voice coil and cone to the metal frame of the woofer? If so, I can try and look to see whether any of them are detached anywhere. If so, is that fixable with glue or something else?
- wires hitting the back of the cone: that was almost a problem when I reinstalled one of the woofers, but did see that through the polypro cone, took the screws out and reinstalled
- gunk in the gap: is that possible if the dust caps have never been removed? If it is possible, as the foam was really deteriorated, and so there's a decent chance some old foam may have fallen in there either before or during my refoaming process. I assume then there is no way to figure that out without removing the foam and/or dust caps?
- polydome mids: per what goodolpg said, my speakers have the clear ones in the upper photo, everything visually looks great. Having said that, to my ear at least, the vibration/resonance/distortion I hear and moderate to higher volumes seems to be in the mid range, not from the frequencies I would normally associate with the woofers or twetters.
- woofer wiring: when I first (re)wired the woofers, I connected red to red, black to black on each speaker, but realized that the original wiring where red was connected to black and vice versa was correct to get the woofers in series and actually play (after the initial rewiring, the woofers in parallel did not play at all)

My next step is to look for a loose/detached spider, but any other thoughts would be very welcome - thanks!
 
My recommendation would be to hook one woofer up at a time directly to the speaker wire from the amp (you can remove the tweeter and run the wire through the hole) and see if you can detect any rattling when playing at the same level. This will allow you to determine which woofers are causing the problem. From there you can investigate further. Note that you should disconnect the crossover wires from the woofer being tested after noting which wire is connected to which terminal.

Personally I think that SS's advice to center the VC by hand is questionable at best. The AK recommendation is to play a bass frequency (frequently mentioned is 30hz) through the woofer to center the coil, if you're not going to shim it. Many Infinity woofers are notorious for their narrow VC gaps (although I'm not sure if yours is one).
 
To test the Polydomes, use the toilet paper tube method. While playing some music that has caused your noise/vibration issue, place one end of a cardboard toilet paper tube (a paper towel tube works, too) over the Polydome. Place your ear at the other end of the tube and listen. This method allows you to isolate the sound of the Polydome from all of the other drivers, permitting you to definitively determine if the midrange driver is working property (this method works for tweeters, too).
 
Coming back to this - the buzz-like distortion is definitely coming from the Polydome mids on one of the two speakers. No visible damage - I assume I should be looking for a replacement?
 
Have you swapped the poly dome from speaker to speaker to see if the buzz follows the polydome?
They do show up on ebay fairly often. Some have blue lettering, some have a red/orange lettering, as far as I know they are the same electronically.
It might be possible to change the faceplates, I don't know if that involves messing with the dome and wiring, or if the faceplate easily pulls off the assembled unit.
 
Thanks to everyone who helped on this thread! I did get a Polydome off of eBay for not very much money - cosmetically not perfect but no way to tell once the fabric is back on the front of the speaker. The pair sound great again!
 
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