SDA 2B MW6503 Crackle with Heavy Bass

wwilbr · May 17

I've been running a pair of SDA 2Bs with original drivers, PRs, and crossovers powered by a Marantz 2270 for many years with no issues. Recently, the right channel MW6503 driver developed an intermittent crackle on heavy bass tracks at moderately high volume (>90 dB). Some tracks that produce the issue include: Jeff Beck - Serene (feat. Oliva Safe), Stevie Ray Vaughan - Tin Pan Alley, Kasia Lins -Liar, Harry Connick, Jr. - Ash Wednesday, several tracks on Eminem Curtain Call.

All driver and PR baskets have Dynamat applied. Mortite is in place to seal the outer basket ring to cabinet. The cone of the crackling MW6503 moves in/out normally and lightly thumping the cone with a finger sounds the same as the other 2B drivers. Visual inspection of the MW6503 removed from the cabinet showed no obvious issues except the slide-on connectors attached to the (+) and (-) terminals were a bit loose. Crimping them down a bit nicely tightened the connection but did not change the crackling behavior.

Replacing the "crackling" MW6503 with a spare MW6503 from backup inventory did not change the crackling behavior. The replacement driver crackles just the same as the original. Ugh! I am at a loss as what to do next to localize this issue. I'm starting to wonder if it could be a crossover issue, but have no experience to draw upon.

Any help or experience anyone can provide is greatly appreciated!

odcics2 · May 17

Check your upstream electronics.

nooshinjohn · May 17

Check the crossover, bench the MW to see if they are in spec. Push-test the cones of the speakers to see if you hear any scratching.

Gardenstater · May 17

Reverse the speaker cables L to R and R to L and see if the problem goes to the other speaker.

wwilbr · May 17

I just switched out the Marantz 2270 for a Peachtree Nova 150. The MW6503 crackle remains unchanged.

wwilbr · May 17

I don't know how to check the crossover yet but will search to see if I can find instructions and specs on the forum. I will check the impedance on the original MW, and the spare MW I used for testing, as you suggest.

wwilbr · May 17

I apprecaite everyone's suggestions. This is very helpful!

xschop · May 17

Rotate the driver 90 degrees and have a listen.

wwilbr · May 17

Will do. Thank you.

Gardenstater · May 17

Are you certain the sound is coming from the stereo midwoofer? Is it possible that it is the passive radiator? Seems unlikely that your spare midwoofer would produce the same crackle at the same times.

If the weight came loose in the passive it might make some funny noise, or even if the spider was cracked.

You could try swapping passive radiators.

pitdogg2 · May 17

While you're at it, take the time to get rid of the moretite. There is better stuff to use. I have used Armaflex with great results. You will need to cut to width, length plus burn holes for the screws to keep from twisting it up upon tightening screws.

F1nut · May 17

Among the other suggestions, check the spider where it is attached to the cone as they can separate. While it's unlikely that would happen on both drivers it's not impossible.

wwilbr · May 17

Great idea on testing the PR. Thanks! I'm pretty sure it's the MW but the symptoms are strange and definitely worth swapping the PR.

Thanks for the Armaflex rec. If I can get past this issue, I'll definitely look to replace the mortite.

wwilbr · May 17

Will do on checking the spider on both MWs. Thanks F1nut. I'll keep everyone posted as I get time to test during the coming week.

Gardenstater · May 18

And, just to eliminate the unlikely possibility that the spare MW you tried in that same position had the same defect, you could just swap the stereo MWs from L to R and R to L. Moretite makes it a PIA I realize.......

xschop · May 18

The 6503s are almost identical to 6510s minus a slighly different coil winding. Their suspensions are loosey goosey.
If you play them at loud volumes for long, then the coils impact and damage.

wwilbr · May 18

Findings so far ...
Reversing the speaker cables L to R - crackling remained on same side, didn’t switch to other speaker.
Rotating the cracking MW driver 90 degrees - no change in crackling.
Push-testing the cones - nice smooth movement throughout range, no scratching (both original and spare MW).
Checking of spider for separation from cone - no separation noted (both original and spare MW).
Checking of MW DC resistance - 6.8 ohm on original MW and 7.0 on tested MW; ~85% of nominal impedance.
Checking passive radiator - no weight on these, just the basket, the flat cone backed by styrofoam to spider.

Down to checking the crossover, and moving the known good MW from the R to L speaker just to be sure.

Is it possible to swap the crossovers from R to L and L to R speaker to test if the crackling moves from MW in R speaker to MW in L speaker, or is that not electrically possible? I guess what I am asking is are the crossovers identical in R and L speaker, or are they electrically dedicated to either the R or the L channel. Sorry, I am crossover ignorant.

Thanks for all the help!!

F1nut · May 18

Identical

The DC resistance is normal and correct. They are not supposed to measure 8 ohms.

Gardenstater · May 18

Unless swapping the crossovers is easier than swapping the stereo midwoofers, I'd just do the latter.

VR3 · May 18

Are you running room correction at all

VSAT88 · May 18

My Kenwood M2 (fully restored by Dan at DRM) would do that to my Polk SDA 2b's if I got to lively with the volume control. Sounds like a loud CRACK? Scary sound!! You swapped the amp and nothing changed? I went to a B&K and never had that problem again. It was me clipping the amplifier. That was long, long ago. I found that a really good amplifier was needed. But with you already swapping that out I do not know.... I have also found that a bad MW can cause it. Swapping side for side and seeing if the problem moves with the MW is sound advice as George said.

wwilbr · May 19

Well, I swapped crossovers R to L and L to R and the crackling on right MW6503 has resolved. Full testing with same songs at same (and higher) volume produces no crackling. System sounds great again.
Hmmm, while happy, still don't know the cause. Everything on the boards "looked good" - I did not bench test the caps.
Could it have possbily been a loose or slightly oxidized connection on one of the MW's +/- wires that terminate in the platic plugs at the crossover, or a blade connector from the crossover to the 16mH SDA inductor? The only thing I can think of is swapping the crossovers somehow improved a poor connection somewhere.
Many thanks to everyone again for your great support in working through this issue!

F1nut · May 19

Entirely possible.

Gardenstater · May 20

Kind of hammers home the point that avoiding contact resistance is super important. There was probably more current flow at those very low frequencies. You probably had a degradation in sound quality that you weren't aware of, at other frequencies. Maybe you should use DeOxit on all those connections at this point.

billbillw · May 20

I experienced something similar with my 2B in the first week I had them. It only showed up in one of the Focal Test Tracks for bass. I swapped drivers left to right and haven't heard it since. I think I also found the tweeter cables were stuffed in contact with the midwoofer and that could have caused some physical interference.

wwilbr · May 21

Thanks for your insights, guys. I like the DeOxit recommendation!

SDA 2B MW6503 Crackle with Heavy Bass

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