Frying SDA drivers...

smglbrth

Here's my story and I'm sticking to it... Anyway, listening to some music this am (that crazy NAD CDP is working like a champ again, go figure), Lord of the Rings "The Two Towers" CD, specifically the 3rd song "Riders of Rohan". When the horns come up around the 2-3 minute mark I tend to turn it up since it sounds so good. I tend to keep the volume in check pretty good but guess I got carried away this time. There was no distortion that I heard and no warning. I turned it back down then I heard that dreaded, very noticeable, crackling sound coming from my left speaker, damn. After inspection both stereo and dimensional drivers are shot. Did the push test and the stereo driver never came out. The dimensional driver did go out, albeit unwillingly and with noticeable noise. Weird, both voice coils are gone I suppose. The tweeter is fine (never tripped). I did JB weld the magnets on the drivers years ago.

I checked the crossover to see if anything was burnt and didn't notice anything unusual, no weird smells either. Pulled two working drivers out of my 8t's and popped them in. Wala, everything is back to normal. Played various music, including what I was listening to, and all seems well.

I'm no stranger to blown drivers in older Polk speakers. They usually give some sort of warning that something is wrong early on, these didn't. Both bad drivers do have an electrical burnt smell but you really have to put your nose up to them. I have blown one driver at a time in multiple driver Polks but never two at the same time and never with this woofer cone effect. Most all the time this effect is from magnet shift.

Would both drivers going bad at the same time have something to do with how the SDA circuits work? It got me wondering since they both went bad at the same time. If, in fact, the smaller SDA's tend to do this then it gets expensive, quick. I did take a serious look at the amp as well and I can see nothing wrong with it.

Ya, ya, you can keep the ear bleeding jokes. This is the first time in several years I've had the volume where it was. No wife or kids home, he, he. Now the 8t's are in limbo and the 7C's are doing front theater duty. I know, sacrilege, but a man's gotta do what a man's gotta do to keep his SDA's going...

nooshinjohn

They did give you a warning, but you had it up too loud to notice it...

leftwinger57

No sig so I have no idea what model SDA you have. There was a come clean thread on stupid sh$t people did to there prized speakers and gear. Me I tried to set my new x-overs w/ one hand and it didn't quite set right. Gravity took over and the x-over slid across the coil and shorted my 6503. I was very lucky it got replaced w/ an E-BAY driver for $19, you should be so lucky. For me I can't go past 9 o'clock on my pre or the walls start to shake and bad things can happen.

westmassguy

smglbrth wrote: »

Here's my story and I'm sticking to it... Anyway, listening to some music this am (that crazy NAD CDP is working like a champ again, go figure), Lord of the Rings "The Two Towers" CD, specifically the 3rd song "Riders of Rohan". When the horns come up around the 2-3 minute mark I tend to turn it up since it sounds so good. I tend to keep the volume in check pretty good but guess I got carried away this time. There was no distortion that I heard and no warning. I turned it back down then I heard that dreaded, very noticeable, crackling sound coming from my left speaker, damn. After inspection both stereo and dimensional drivers are shot. Did the push test and the stereo driver never came out. The dimensional driver did go out, albeit unwillingly and with noticeable noise. Weird, both voice coils are gone I suppose. The tweeter is fine (never tripped). I did JB weld the magnets on the drivers years ago.

I checked the crossover to see if anything was burnt and didn't notice anything unusual, no weird smells either. Pulled two working drivers out of my 8t's and popped them in. Wala, everything is back to normal. Played various music, including what I was listening to, and all seems well.

I'm no stranger to blown drivers in older Polk speakers. They usually give some sort of warning that something is wrong early on, these didn't. Both bad drivers do have an electrical burnt smell but you really have to put your nose up to them. I have blown one driver at a time in multiple driver Polks but never two at the same time and never with this woofer cone effect. Most all the time this effect is from magnet shift.

Would both drivers going bad at the same time have something to do with how the SDA circuits work? It got me wondering since they both went bad at the same time. If, in fact, the smaller SDA's tend to do this then it gets expensive, quick. I did take a serious look at the amp as well and I can see nothing wrong with it.

Ya, ya, you can keep the ear bleeding jokes. This is the first time in several years I've had the volume where it was. No wife or kids home, he, he. Now the 8t's are in limbo and the 7C's are doing front theater duty. I know, sacrilege, but a man's gotta do what a man's gotta do to keep his SDA's going...

Which Model do you have? Odd that both stereo and dimensional drivers in the same cabinet would go. They're on quasi-separate circuits.

boston1450

Are the drivers now the correct drivers ? Sorry for your loss

Schurkey

What speakers?

What amp?

Cabinets sealed so the driver excursion isn't excessive?

smglbrth

nooshinjohn wrote: »

They did give you a warning, but you had it up too loud to notice it...

Probably right...

SDA 2A's, B&K Reference 200.2, cabinets are good, 6510's, same as the 8t's. I just thought it strange since I've never had a Polk driver go bad that particular way, so fast. They were made in 2001 (Mexico models), same year I purchased them. They were replacements in the 8t's but when I bought the 2A's I swapped them thinking newer was better. What comes around goes around as I put the original 1986 drivers back into it!

The drivers that blew look exactly like the originals except the contacts on the cone are hidden on the rear, not seen on the front.

F1nut

That is an odd one. I'm inclined to agree with Schurkey about the excessive driver excursion being the likely cause.

I've played various models of SDA's at stupid loud levels many times over a great many years and have never blown a mid-driver. The fact that you have says something that you need to look into, IMO.

nooshinjohn

I finally clipped my Carver tubes last night and did not harm any drivers, nor the amps...

westmassguy

I've had my 2As at deafening levels, even ran them with my home theater full range, never had anything like that happen.

PolkieMan

Yea I had a carver tfm-15 never could find anything wrong, me or the warranty repair shop but every once in a while it would blow a speaker, some sort of voltage spike or something. The fact that you were stressing it may have caused it. hook some junk up to it and try it again.

deronb1

Maybe one channel of the amp went to **** and dumped too much dc to the drivers?

Schurkey

Thinking some more--in specific about the post where the weight fell off the 3.1 passive radiator--I'm sure this is more "mechanical" than "electric". What the drivers have in common aside from their age and construction is their location in that cabinet.

I'd look again for air leaks, and for a defect in the PR...anything that would cause a loss of "air-spring" in that cabinet and therefore promote excess excursion of the midwoofers.

westmassguy

Schurkey wrote: »

Thinking some more--in specific about the post where the weight fell off the 3.1 passive radiator--I'm sure this is more "mechanical" than "electric". What the drivers have in common aside from their age and construction is their location in that cabinet.

I'd look again for air leaks, and for a defect in the PR...anything that would cause a loss of "air-spring" in that cabinet and therefore promote excess excursion of the midwoofers.

On the 2A/2B, the PR is a large chunk of Styrofoam. There's a hole for hot glue to be added for counterweight. Check if the spider has detached.

smglbrth

When I checked the PR there was no detachment from the spider. I'll definitely have the check something soon (away from home right now for work). After this all happened I did the push test again on the right speaker and noticed, more like heard, an air leak coming from the dimensional driver. I thought it was around the screws but was actually coming directly from the dust cover. This is the first time I've ever heard it from that specific area. I realize there is some air movement from the dust cover since it's mesh but this was pretty noticeable. The same sound never came from the stereo driver. The driver still has good movement. Maybe the voice coil is getting loose as well?

So..., "maybe" whatever caused all this in the first place came from the amp, fried the left drivers and the back fed through the SDA cable to the right speaker? That would seem really strange since I've never had a problem with the amp before. However, I never got carried away with the volume that much either. It still works the same as all the years I've had it since this "incident".

I'll take closer look for air leaks when I get home. From what I'm hearing this particular situation is strange indeed...

smglbrth

Back home, went over just about everything. Took the passives out and saw a very few places which "might" have been leaking air. Patched those up and used the lighter test (albeit very carefully) around all the seams for the cabinet, used my ear for the drivers/screws. I have a test CD which pumps out a very low frequency and all you can see is the drivers/passives move, you can't hear much anything. Nothing, nada. I could hear no air and the flame never showed any variation from any of the seams. Push test was the usual 3-4 seconds for each speaker.

So..., guess I can chalk this up to knowing the limits of the amp and speakers. I still it's strange but stuff happens. Now I have to order a "few" replacement drivers, get those dang crossovers redone and stop procrastinating about it! Once I get that done, amongst the other upgrades they will be done, at least for the rest of my life...

PolkieMan

Don't abuse vintage stuff that you really like and love and make sure every time the volume is set to a very low level at power on and power off. Don't use a lighter :-).

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