My first Infinity- RS4b- Need help!

Azriel

AK Subscriber
Subscriber
Hey guys,
I got my first set of Infinity speakers- RS4b's from a local record store. They were only $40, but you'll see why. Apparently the previous owner didn't feel like re-foaming the woofers. Instead, he chose to yank them, and rig a set of smaller woofers in. As you can see, the result was less than ideal.

Amazingly, they actually don't sound terrible. I think one or two may be out of phase, as it sounds odd in the bass. So, I'll have to pull at least one of the woofers and see what's going on. However, with the way he rigged them in there, I'd be afraid to try reinstall them, for fear of doing more damage.

Actually, as I type this, I'm listening to some jazz piano, and on the right speaker, certain notes have a really buzzy, metallic rattle kind of sound to them. The left channel doesn't do it at all. Also heard it on a Joni Mitchell disc. Could that be the mid dome? I turned the controls back and forth many times, and they aren't making static, so I don't think that's the issue. Sounds like something mechanical. When I put my ear to the speaker, I can clearly hear it's coming from the midrange. I can hear it with trumpet too.

Anyway, I obviously need woofers. So, what kind of damage can I expect for a set of woofers for these things? Anyone have any?

So, did I get a score, or am I screwed? Seems like there's more bad drivers than good in this pair. So far, it looks like I need 4 woofers and 1 midrange. Might as well buy a whole pair of speakers! For what it's worth, the cabinets are in beautiful condition.
 

Attachments

  • Front.jpg
    Front.jpg
    69.7 KB · Views: 113
  • Side.jpg
    Side.jpg
    62.7 KB · Views: 87
  • Woofer.jpg
    Woofer.jpg
    134.9 KB · Views: 84
you got a good deal, despite the woofers. just the tweeters are worth twice what you paid. the correct woofers are polycone 8". dump those undersized woofers and find some correct woofers. original part number is 902-4976. if you can't find originals, infinity's suggested substitute is 902-5030. replacements will turn up on ebay. lots of the polydome mids on there right now. here's the tech sheet.



.
 

Attachments

  • infinity_rs-4_b_150w_speaker_system_sm.pdf_1.png
    infinity_rs-4_b_150w_speaker_system_sm.pdf_1.png
    29.6 KB · Views: 56
Last edited:
Any midrange from RS-IIIa/b's to RS-6's will work in your RS-4b's. There's plenty available on eBay, just be patient and do not overpay. I think I got my spare pair of midranges for $60 total. The woofers are also luckily not that expensive, but be prepared to refoam (which is quite easy) them.

I really like the sound of my RS-IIIa's, and the RS-4b's are basically the same except the woofers are smaller. Just give them enough good quality clean power and they will sing like a bird. Your amp needs to be able to handle varying impedance loads from 8 Ohms to down to 4 Ohms, e.g. my Onkyo pushes 150 wpc at 4 Ohms which works great.

So IMO the 4b's are worth fixing and once done, you will be quite positively surprised how fantastic these relatively inexpensive speakers sound :)

Here a nice contemporary review of your 4b's:
View attachment RS_4b_review_Audio_1986.pdf
 
Thanks for the information. My biggest concern is the midrange. Is mine bad because it was overdriven, or just the plastic dome distorting in shape with age, causing a rubbing voice coil? If it's the latter, then wouldn't any replacement be just as vulnerable, since it's the same age?

I certainly hope I can get these sounding good again, since they sure sound like hell right now. That midrange driver just sounds terrible. I've never encountered anything like it.

I'll have to keep my eyes out for good drivers.

-Jon
 
What I have read and seen the polycell midranges in this RS IIIa to 6 range of Infinities do not degrade over time that much, that is, they do not show similar quick deterioration as e.g. the ones in the Kappa series.
 
I pulled the woofers, and they're Goldwood GW-8024. They're 4 ohm drivers, so the guy wired them in series! No wonder these speakers sounded so bad..LOL. Hmm, so what will I ever do with 4 8" 4 ohm woofers? Who knows...

Now to track down the proper woofers. I have a feeling this is going to take a while.

-Jon

EDIT: I looked at the wiring again, and I actually think they were NOT in series. Good lord, my poor Onkyo receiver was seeing a 2 ohm load. Oy. Glad I only played them softly. Needless to say, these speakers will be taken offline until I can get the right woofers.
 
Okay, so I think it was wired correctly then. There's so much fiberfill inside the enclosure, I couldn't see where the speaker cables were going. So, my top woofer had the red wire connected to negative, and the purple wired to positive. The bottom woofer was opposite that. I can see that the purple wire goes from one woofer to the other, while both red wires go back to the crossover.

Does that sound correct?

-Jon
 
I'm still confused, because when I look at the tech sheet for the 4b, it looks like they're in parallel.
 
Okay, so I think it was wired correctly then. There's so much fiberfill inside the enclosure, I couldn't see where the speaker cables were going. So, my top woofer had the red wire connected to negative, and the purple wired to positive. The bottom woofer was opposite that. I can see that the purple wire goes from one woofer to the other, while both red wires go back to the crossover.

Does that sound correct?

-Jon

In short yes.

Your woofers are wired correctly, in series and are in-phase (i.e. purple wire going from plus to minus).

Notice that one of the red wires has a black stripe, indicating negative. You want to hook it up to a woofer terminal that has no red stripe painted next to it (indicating negative). Conversely, the solid red cable hooks up to a woofer terminal that has red stripe painted next to it.

The above is based on how the woofers in my RS-IIIa's are connected. I had to figure all this out back in March/April when I got my speakers, as the previous owner had wired them incorrectly.
 
Cool, thanks a lot for that. It looks like the right speaker is wired correctly. I'll have to pull the woofers in the left and see what's going on. I imagine they're probably wired out of phase to the right speaker. Doesn't really matter though, as I'm replacing them anyway.

Still, good to know for when I hopefully get to install the right drivers.
 
Well, I've made more progress over the last 24 hours. I removed the midrange, and took the front plate off. Inside, I saw some dust, debris, and fine metal shavings around the perimeter of the dome.

I also removed the woofers from the other speaker, corrected the reversed wiring, and reinstalled carefully. The fruit of my labors seems to be functional speakers that sound surprisingly good. Especially considering the wrong woofers.

Is there any harm in using these woofers until I can find the right ones? Were the original woofers 4 ohm or 2 ohm? If they were 2, am I risking changing the crossover frequencies to the midrange and tweeter by running 4 ohm woofers?

Thanks,
Jon
 
Great speakers, the Goldwood woofers are good quality woofer and will be fine until you find some originals. They should bring $ on ebay and maybe even pay for your originals.

On the buzzing mid, check to make sure there are no wires laying against the walls of the cabinet or resting on something else which would cause vibrations. You could also switch drivers from left to right and see if the issue travels with the mid to the other speaker.
Jim
 
I am pretty sure that / if my memory serves me right, the original woofers are ~4 Ohms each.

You should check the Ohmic resistance over both midranges (and the tweeters too while you are at it :) ). The samarium EMIT tweeters measure Ohmic resistance (DC) of around 3.0-3.1 Ohm. The polydome mid-ranges measure Ohmic resistance of around 3.8-3.9 Ohm. These numbers were measured by me last spring.
 
Last edited:
Jim,
I did check for loose wires when I had the mid out, and everything looked ok. Even after cleaning it, the anomaly persists.

The weird thing is I only hear it with piano. I've tried numerous albums with well recorded pianos, and it's always around the same note range. It's centered on the D in the octave above middle C. Regardless of the album, anytime someone plays that note, or others close to it, it sounds like the piano's got a cracked soundboard. Can you tell I'm a pianist? LOL. The sound is metallic, buzzy, and the decay is dead.

However, if I play something more poppy/compressed, like The Killers- Human for example, everything sounds fine. You only hear it only simple acoustic recordings. I also hear it strongly with trumpets. Winton Marsalis's horn is quite unlistenable in the right side, while it's fine on the left.

I'm thinking a replacement driver must be in order. Ordinarily, I'd want to replace the diaphragm, but since they're obsolete, that's not an option. Here's hoping the replacement isn't just as bad.

-Jon
 
yep, a replacement is necessary, IMO.


Don't forget to check that a connection wire isn't vibrating against the enclosure inside, I had that happen a couple of years ago, and it was only on ONE specific frequency, around the range your talking. opened the speaker back up, moved the wire away from the side wall, and sound gone.

being a 'sort of' pianist myself, I can tell you you're gonna be really happy once you get these Infinity's back to operating state.
 
Make sure to try swapping the mids between the speakers. If the distortion swaps with the mid, then the mid is definitely bad. If the distortion stays with the original speaker, your mid is OK, and you still have an internal issue. Maybe with the crossover?

Good luck!
 
I'm playing an organ cd now, and just about every note sets the midrange off to buzzing. I noticed that if I gently touch the dome, the buzz goes away immediately. As soon as I release, it's back. So, that pretty much nails it down.
 
I wonder if the mid got overdriven? Overheated? If so, it sounds like the voicecoil might have gotten warped, and is rubbing. I'd try removing the diaphragm and inspect the coil, to see if it's out of round. Check the voicecoil coating for burns or bubbling. Clean the magnet gap too, while it's apart. It's not like you can hurt anything, at this point!
 
I was thinking the same thing, which was why I pulled it initially. However, when I took the front plate off, I couldn't find a way to open it up without ruining it. The diaphragm is glued on and appears very fragile. I figured if I tried to remove it, I'd risk tearing it. Plus, I don't have any glue to re-install it.

I just ordered a replacement on ebay for $35 shipped. Here's hoping it works out. Now, if only the woofers were so easy to find.

-Jon
 
Back
Top Bottom