SDA-1C Speaker Troubleshooting

[TKotL]

I recently purchased a pair of SDA-1Cs to upgrade my system (previously SDA-2Bs). I was expecting a minor difference, but the new speakers are superb.

That said, when playing back some reference tones through the speakers, they sound quite different. The Right speaker is noticeably "flat" (even with the test tone), with less bass. Testing with the SPL meter, it is coming out ~2dB less than the Left speaker.

I have tested with an alternate set of speakers to verify the problem is not with my amplifier, and I don't have an interconnect cable. (I intend to build one given some free time).

It's going to be a couple of weeks before I can break out my toolbox to open it up so I can examine the internals. So in the meantime, does anybody have any suggestions as to where the problem may be and where to focus my troubleshooting?

(Side note: DarqueKnight, if you happen to read this, how do I go about ordering a copy of the SDA Compendium if I can't PM or e-mail you?)

[Ricardo]

You have a multimeter? I would start checking each speaker according to the measurements in the document you'll find in post #13 here:

http://www.polkaudio.com/forums/showthread.php?t=48018

Welcome...and good luck.

[anonymouse]

If the issue is mostly with the bass, you most likely have an air leak in the one with weaker bass. Check the box seal and redo with caulk, make sure the passive radiator, all drivers and the binding post cup are all well seated.

[TKotL]

HTrookie: I grabbed my meter and did some testing, though I couldn't find any specifications for the SDA-1Cs.

Interestingly, though, the results were completely symmetric -- both speakers got almost the same results -- but the specifications in that document for similar speakers are asymmetric -- some measurements should be different between the left and right. (Yes, I did check that one is marked Right and the other left. :) )

Of course, I have no idea what this actually means in practice.

Measurements for anyone who is interested:

Test:                     Left: Right:
IC Pin #2 to Black        2.4Ω  2.4Ω
IC Pin #1 to Black        0.2Ω  0.2Ω
IC Pin #1 to IC Pin #2    2.4Ω  2.4Ω
IC Pin #2 to Red          3.5Ω  3.6Ω
Red to Black              4.1Ω  4.2Ω
IC Pin #1 to Red          4.1Ω  4.2Ω

[TKotL]

If the issue is mostly with the bass, you most likely have an air leak in the one with weaker bass. Check the box seal and redo with caulk, make sure the passive radiator, all drivers and the binding post cup are all well seated.

Doing a simple test of the seal, I gently pushed in the passive radiator, and on both speakers, all four of the drivers move as a result. If there's a bad seal, then it's going to be pretty minor.

[F1nut]

Without the cable connected, nothing is going to sound right or test correctly. Having said that, I suspect you may have a bad mid driver.

[Ricardo]

You are right that the 1C's are not there, hadn't noticed. Anyway, measurements are the same for both speakers, and for pin/blade connectors they should be. The ones you were looking at are blade/blade.

I thought about the bad driver, but I would expect that these measurements would tell you if you had one....and everything looks good; air leak was a good idea also, but seems that's not the problem either. I cannot think of anything else right now.

[Polk65]

It's going to be a couple of weeks before I can break out my toolbox to open it up so I can examine the internals.

A Phillips screwdriver will do.

(1) Make an interconnect for your SDA 1C's with a speaker wire or an RCA cable ( peel the ears off ) and place into your interconnect round sockets. If you use only one speaker wire, tape the ends of the unused wire. Use a common ground amplifier.

(2) Check the screws and seal on the right rear terminal where the wires connect.

(3) Open the cabinet and wiggle each speaker connection.

(4) Swap crossovers. They are getting tired and one might be failing. While you're in there, check the mid-woofers. With SDA's getting older it's not unheard of finding cabinets with ganked drivers. There should be mw6510's on the outside and mw6511's inside. Write some notes of what goes where.

[TKotL]

Without the cable connected, nothing is going to sound right or test correctly. Having said that, I suspect you may have a bad mid driver.

I agree that without the interconnect the speakers won't sound quite right, but I would expect them to misbehave in an identical fashion... which they're not doing. One speaker is clearly performing differently to the other.

What is the best way to test the individual drivers for correct function? Is it as simple as removing them, visually inspecting them and looking for telltales that would indicate a problem? (Incorrect part numbers, detached magnets, fluid leakage (?)) Are there electrical tests I can perform?

[Auraka]

I use a quick test with a 1.5V battery (C or D type) intermittently connected to the input of the speaker, noting correct polarity. All mid/bass drivers should project out with the + connected to the positive terminal. This test will tell you if the drivers are functioning and in phase.

[TKotL]

(1) Make an interconnect for your SDA 1C's with a speaker wire or an RCA cable ( peel the ears off ) and place into your interconnect round sockets. If you use only one speaker wire, tape the ends of the unused wire. Use a common ground amplifier.

Given that I am using a common ground amplifier, you're saying that the blade connection on the interconnect cable is redundant (i.e. it's the ground pin, which is common with the ground pins on the speakers and Amp)?

If both speakers are passing signal information back and forth (L -> R and R-> L), how is that possible on a single strand of cable?

As to your testing suggestions, I'll work through those once I get time to work on the speakers. (Next week, I expect).

Thanks for your suggestions!

[DarqueKnight]

I agree with F1 that you may have a bad driver. I would also ask you to check the following things:

1. Check to see that you have the proper type of drivers. It is not uncommon to find that a previous owner replaced a defective or blown driver with the wrong type. They all look alike.

The driver model number should be written on a sticker on the back of the driver magnet. For the SDA 1C, each cabinet should have two MW6510 dimensional drivers (stacked vertically) and two MW6511 stereo drivers (stacked vertically).

2. You could have the correct complement of drivers, but the positions may have been switched or could even have come from the factory in the wrong positions.

3. You may have one or more defective components in one or both of the crossover circuits. I know you said you noticed a difference in the bass, but one of the most common culprits in volume differences in a pair of SDA's is the tweeter protection polyswitch. These can get more resistive with age. Even if you are having no problems with your polyswitches, it is a good idea to switch out the old ones with the new, improved version, which is available free from Polk.

I have sent you a PM with Compendium ordering info.

[TKotL]

1. Check to see that you have the proper type of drivers. It is not uncommon to find that a previous owner replaced a defective or blown driver with the wrong type. They all look alike.

That is pretty high on my list of things to check -- when I was inspecting the speaker last night, I noticed that the "top left" driver appears slightly different to the others... all seven other drivers look pretty much identical, but that one has a subtly different shade. It may be nothing, but it has me suspicious.

3. You may have one or more defective components in one or both of the crossover circuits. I know you said you noticed a difference in the bass, but one of the most common culprits in volume differences in a pair of SDA's is the tweeter protection polyswitch. These can get more resistive with age. Even if you are having no problems with your polyswitches, it is a good idea to switch out the old ones with the new, improved version, which is available free from Polk.

Any idea what the base resistance of the polyswitch should be under no load (or, rather, multimeter load). For testing purposes, is it safe to bridge the polyswitch?

I have sent you a PM with Compendium ordering info.

Thanks very much, I get the feeling it'll be coming in handy sooner rather than later. I can't reply to your PM, but you should have an e-mail from PayPal with delivery address and payment confirmation.

[DarqueKnight]

Any idea what the base resistance of the polyswitch should be under no load (or, rather, multimeter load). For testing purposes, is it safe to bridge the polyswitch?

I measured the six polyswitches (blue ones in attached pic)that came out of my three pairs of CRS+'s and obtained readings of 0.4, 0.5, 0.5, 0.5, 0.6. and 0.7 ohms. The large yellow devices in the attached pic are the new poly switches. I have four of those and they measured from 0.5, 0.5, 0.5, and 0.6 ohms.

The two polyswitches that came out of my SDA 1C's measured 1.2 and 1.1 ohms.

For testing purposes, is it safe to bridge the polyswitch?

No problem. Some people have replaced their polyswitches with a wire jumper and others have left the polyswitches in place and soldered a wire jumper across the polyswitch terminals. I have used both methods.

Your Compendium will ship out tomorrow.

[Dennis Gardner]

My guess is the replaced mid driver is out of phase or not even hooked up. In an open cabinet design, it is really hard to tell by sight if one of the drivers isn't working as the good driver will move the dead one easily unless it is frozen.

[Auraka]

Back in the day, I saw two separate failures with my original drivers. On the mid/bass I broke two cones on one channel, somewhat near the voice coil and the failures were very obvious at volume (replaced under warranty).

The second failure was more difficult to diagnose as the SL2000s were making sound though muffled. The dome at the point where the coil and dome are attached had melted effectively cutting the center dome away from the suspension. To look at them they looked normal but if you lightly touched the dome it would hinge off the suspension (also replaced under warranty).

[Auraka]

As to your testing suggestions, I'll work through those once I get time to work on the speakers. (Next week, I expect).

Not sure who that quote was directed towards, however the battery test I mentioned can be performed on the entire speaker, i.e. connecting to the input of each complete speaker, not just individual drivers. No need to disassemble, truly a quick test of function and phase. The tweeters will show no movement but will emanate a scratching sound as the battery connects/disconnects.

[opsman35]

Hello all,

I have a pair of SDA 1-C's. It appears that the stereo drivers on the Left speaker are not functioning. I have checked the wiring to make sure it is correct, additionaly if I move the Stereo drivers from the left speaker to the right they function properly. I feel that I might have a problem with my crossover. I pulled it out and the soldering is very sloppy. I think the previous owner attempted to fix the same problem, but instead made a big mess. Any ideas on the best approach to get these functioning properly again? I had a set of SDA's previously and miss them a great deal! Any help would be appreciated.

Thanks

[ben62670]

One thing that can be confusing about Polk's is that they use the black wire as positive, and the white as negative. Most people think of black as ground. Seeing that amps put out AC currant it is actually correct for the black to be "hot". This does not apply to the external wiring.

Ben

[ben62670]

Hello all,

I have a pair of SDA 1-C's. It appears that the stereo drivers on the Left speaker are not functioning. I have checked the wiring to make sure it is correct, additionally if I move the Stereo drivers from the left speaker to the right they function properly. I feel that I might have a problem with my crossover. I pulled it out and the soldering is very sloppy. I think the previous owner attempted to fix the same problem, but instead made a big mess. Any ideas on the best approach to get these functioning properly again? I had a set of SDA's previously and miss them a great deal! Any help would be appreciated.

Thanks

Welcome to Club Polk OOPS.
I would take a multi meter and check the resistance from point to point on the crossover. The stereo drivers should not be affected by bad components as far as being able to play. There is a small inductor in series with the positive lead from the speaker terminal that should have slight resistance. Try also measuring from the positive input terminal to the black wire that connects to the stereo drivers. There should be a small amount of resistance between these 2 points.

Ben

[TKotL]

1. Check to see that you have the proper type of drivers. It is not uncommon to find that a previous owner replaced a defective or blown driver with the wrong type. They all look alike.

Bingo. One of these drivers is not like the others... The upper stereo driver (the one I noted looked a little "different") is a MW6502, not a MW6511. That seems to be a smoking gun.

From what I've been reading, it sounds like I can source a new driver direct from Polk?

[TKotL]

I measured the six polyswitches (blue ones in attached pic)that came out of my three pairs of CRS+'s and obtained readings of 0.4, 0.5, 0.5, 0.5, 0.6. and 0.7 ohms. The large yellow devices in the attached pic are the new poly switches. I have four of those and they measured from 0.5, 0.5, 0.5, and 0.6 ohms.

Would those "new polyswitches" be present in a set of SDA 1Cs circa 1989? Because the polyswitch on my crossover looks like the large yellow type, not the small blue.

I haven't been able to get the crossover board out to read the markings on the polyswitch -- my eyesight isn't good enough to read it where it's sitting at the moment. One of the standoffs is inaccessible beneath the large coils leading to the drivers, and I'm hesitant to cut it off.

Anyway, the switch tests at 0.7Ω, which would appear to be within range. I'm going to hold off replacing it for the moment -- that can wait until I get up the courage to overall the crossovers entirely.

Your Compendium will ship out tomorrow.

It arrived today, thanks very much. It's going to come in very handy very soon, I think.

[ben62670]

Take a reading of both speakers, and post the ohm rating.

[TKotL]

Take a reading of both speakers, and post the ohm rating.

Sure. The MW6511 measures 3.4Ω, the MW6502 3.7Ω.

[F1nut]

No need to cut the standoff. Using a thin blade screwdriver, push the tab in while applying upward pressure on the board.

[ben62670]

OK they are close. the issue here is that the 6502 likes a smaller cabinet. I would call customer service and order another 6511. It will help with the bass. I am not totally sure that is the only issue, but I think it is definitely one.

[TKotL]

No need to cut the standoff. Using a thin blade screwdriver, push the tab in while applying upward pressure on the board.

Yeah, the problem is finding the tab to push. Three of the standoffs are easy to locate and remove, but there's one hiding under the coils and I can't find the head of it.

[ben62670]

You can't squeeze the prongs with needle noses from the top?

[F1nut]

Just spread the inductors apart a bit, it's located closer to the caps.

[F1nut]

No Ben, not enough room for them.