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The R(ight) loudspeaker on my AKG-K99 headphones stopped working. I bought a replacement (x2) 'mini' loudspeaker.

After soldered the replacement the sound was "weird". No problem. I predicted that. Different loudspeakers, different sound! For that reason I already had the second sp-39 loudspeaker. So I went to solder the second replacement. But after I opened the L(eft) AKG loudspeaker, to my surprise I saw more pads than the R(ight)!

BUT I have three problems.

To my surprise the cables are four instead of three.

To my knowledge:

  • 1 = common ground [Gold color ]
  • 2 = positive (L channel) [Red color ]
  • 3 = positive (R channel) [Red color ]

(end of TRS story) Problem #1

  • 4 = WTF? (What's The Fing?) [Green color]

I made some continuity test's. (I de-soldered the monacor / replacement before testing - more for that later)

Problem #2. Continuity partners (check picture for numbers: AKG-L loudspeaker connection ): 1 [green] + 2 [gold] (!), 3 [red] + 4 [red] (!!). How's that possible?

Problem #3. Continuity partners mini jack (TRS) vs cables (factory soldering) TRS connection 1 [Sleeve] with Green AND gold (!). 2 [Ring] with BOTH reds (!!), 3 [Tip] with Green AND Gold (!!!).

Also to my surprise #2 Monacor has 4 tabs probably to cover the 'host' situation L. I was expecting 2 pads per loudspeaker but I have 4. I have some lack of knowledge here. How to solder the monacor as host (L) and as client (R)?

This is my soldering (weird sound - more loud, but adjusting the balance is not helpful) My monacor soldering for R channel

Problem #4: In monacor ALL pads have continuity (!!!!).

Similar threads - but for some reason didn't help. Sorry. Headphone wire color coding Fixing headphone jack

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    \$\begingroup\$ Just a note - many multimeters treat low resistances (say, under 50 ohms, more or less) as a continuity (and beep). This value may vary between multimeters, so check the actual resistances instead of relying just on the continuity beep. Your speakers are 32 ohms, so it's likely the multimeter will still beep when you put the probes across the speaker (or even both in series, as would be the case when probing from L to R, as the GND is common to both) \$\endgroup\$
    – Richard the Spacecat
    Commented Jul 15, 2021 at 12:31

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#1 of 3: You get confusing results just because you assumed the pinout wrong. Since you have a multimeter, you can just measure which goes where instead of assuming which goes where.

#2 of 3: There is again no problem. If you look at the picture, you will see that pads you marked 3 and 4 are connected together by the printed circuit board on the speaker. Therefore, it is expected to measure direct connection between pads you marked 3 and 4.

#3 of 3: There are three wires so there would be one wire for each of the T, R, and S connection. As each of those wires are connected to a speaker, a continuity test will show continuity between all of them.

#4 of 3 (you said 3 but asked 4): I think you must stop measuring with continuity testing because it will tell you everything has so low resistance it keeps beeping for continuity. It's the wrong tool. Use resistance measurement as it is the correct mode for measuring to distinguish between wires and speaker coils.

So, from what I decipher the TRS cord goes to LEFT speaker first, which connects all wires, and from there, two wires go to RIGHT speaker. It would be a good assumption that since only gold and red goes to the right speaker, they are ground sleeve and ring, and since gold and green goes to left speaker only, they are ground sleeve and tip.

I'd say TRS are green, red, gold. That is why gold and red are looped through on the left speaker to go to the right speaker.

If you used continuity test mode, it will also say that a speaker has continuity, not only wires. That's why you measure continuity between green and gold, while you should measure about 32 ohms. The two red wires are supposed to be connected together, that't the link from cable to right speaker, so it should measure 0 ohms. That's why the gold ground wire also goes to both speakers.

If you did not measure continuity between red and gold, it might indicate that either the red or gold wire between left and right speakers is broken and has no continuity, so changing the speaker elements won't fix the wire. Most likely the speaker elements are fine and the wire between is broken. Unless you seriously overloaded the right speaker so it actually is the speaker that's damaged.

I hope this helps.

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  • \$\begingroup\$ After I posted the four questions (sorry) I was puzzled about the continuity and I had the idea that its a "looped" system the loudspeaker, not a switch, so a continuity is a normal thing. Thank you for clarifying this and your time to decipher all the four questions. Still I am puzzled about the twice RED pads. I don't find purpose on that, but I will think more about it. THANKS! \$\endgroup\$
    – krg
    Commented Jul 15, 2021 at 23:30
  • \$\begingroup\$ I made it! Thank you again. a) I ignored the extra tabs from monacor. b) I used the green side of monacor as positive and the other side as common ground. c) I soldered the remaining RED wires. I suppose the extra pads on AKG was for convenience with no connection to speaker. \$\endgroup\$
    – krg
    Commented Jul 16, 2021 at 13:42
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In headphones where the cable only goes in one side, there must be some loop-through to the other side. There should be L, R and ground on the wire. It's easiest for the manufacturer if a circuit board has a loop-through pad to allow the speaker wires being looped to be soldered.

Check both speakers are wired the same way round. I can see a "+" symbol next to one of the pads in the picture.

Check one of the speakers isn't connected between L and R, because that produces a very odd effect.

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