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An encounter with Inductor Saturation
Just this past week I encountered something that I'd never experienced before, and through researching it came to the conclusion that inductor saturation is a real thing and what may have worked for a few days won't necessarily work forever. Follow along if you will:
I've been putting the finishing touches on the Iowa 2016 project. Through the initial PCD modeling the software suggested a 3.5mH inductor along with a healthy cap for the woofer roll-off at about 375hz. Upon application it sounded just about right. In fact the bass was strong enough to investigate the possibility of a sealed enclosure. After a couple more weeks of experimenting and modeling it was determined that a sealed enclosure was the right way to go. I dis-assembled the project, closed off the original port, then began the finishing phase. Little did I know that an electronic storm was brewing in the crossover.
About three weeks ago the cabinets were finished, the crossovers soldered and installed, and I happily anticipated the hearing final product. I popped in the test disk and fired 'em up. The first indication that something was amiss was a grungy sound, apparently from one of the woofers. I was certain I'd blown one of the venerable Usher 8955's. Fortunately I had a spare and after swapping out the 'bad one' tried again. This time I noticed the same crunchy sound coming from both woofers. It sounded like the drivers were being blown out of alignment and were exceeding their listed 5.5 mm of xmas, yet I was not applying much power from the amp. Something was very, very, wrong here. (BTW, if you're interested the Signal Path is a Panasonic DMP-BDT500 into an Emotiva USP-1 and XPA-2.)
My initial thought was a mis-wired crossover (but two mis-wired??) yet upon checking the wiring appeared fine. Next up, verify the enclosure specs because...well, I didn't know why; I was grasping at straws. Why was something that worked fine two weeks ago now completely messed up? A driver with a Vas of 133 liters in a sealed 37 liter enclosure is just about ideal (once again, according to PCD). But I couldn't think of another reason that these seemingly fine drivers were behaving so inappropriately. So I took a leap of faith and re-ported the enclosures with the original 2x8" ports. They worked before, so why not now? Unfortunately the result didn't change - same grungy/crunchy output from the woofers. Nothing about this made sense.
After ruminating on this for a couple days with no fresh ideas I consulted Chris Roemer, but he had no answer, and a 15 minute conversation with JR yielded no new insight either. Back to the drawing board - it's time to get creative. So I swapped in a different pair of drivers just to see what might happen. No change. I tried a 10" subwoofer too because at this point there was nothing to lose, with no noticeable difference. The old adage of doing the same thing over and over kicked in, so it was time for a change in direction. At this point the only thing that made sense was to reverse engineer the crossover, in other words start replacing pieces part-by-part in hopes of finding....something? The thing is that all the parts were brand new, so what were the odds that I'd have two flawed pieces causing the same issue with both drivers? But sure enough, the first part I swapped out held the answer.
Late last winter I purchased some of PE's closeout inductors - those little 'bobbin' inductor selling for about $6.00 each. The intention was to use them in a couple of small surround speakers for a friend. Apparently they are woefully inadequate for long-term application on a robust woofer. A switch from the closeout bobbin to a full size Jansen inductor immediately resolved the problem. No grunge and no crunchy, just pure sound. Problem resolved! (Celebratory beer consumed!)
After resolving this issue and researching inductor saturation I discovered that a small, ferromagnetic core, inductor can have an extremely low saturation point that can lead to abrupt saturation (versus gradual saturation), signal/voltage clipping, and odd harmonics. Apparently that's what was happening here. Who knew you could ruin these little guys with a couple volts of electricity?
Lesson learned? No more tiny inductors on beefy woofers!
I've been putting the finishing touches on the Iowa 2016 project. Through the initial PCD modeling the software suggested a 3.5mH inductor along with a healthy cap for the woofer roll-off at about 375hz. Upon application it sounded just about right. In fact the bass was strong enough to investigate the possibility of a sealed enclosure. After a couple more weeks of experimenting and modeling it was determined that a sealed enclosure was the right way to go. I dis-assembled the project, closed off the original port, then began the finishing phase. Little did I know that an electronic storm was brewing in the crossover.
About three weeks ago the cabinets were finished, the crossovers soldered and installed, and I happily anticipated the hearing final product. I popped in the test disk and fired 'em up. The first indication that something was amiss was a grungy sound, apparently from one of the woofers. I was certain I'd blown one of the venerable Usher 8955's. Fortunately I had a spare and after swapping out the 'bad one' tried again. This time I noticed the same crunchy sound coming from both woofers. It sounded like the drivers were being blown out of alignment and were exceeding their listed 5.5 mm of xmas, yet I was not applying much power from the amp. Something was very, very, wrong here. (BTW, if you're interested the Signal Path is a Panasonic DMP-BDT500 into an Emotiva USP-1 and XPA-2.)
My initial thought was a mis-wired crossover (but two mis-wired??) yet upon checking the wiring appeared fine. Next up, verify the enclosure specs because...well, I didn't know why; I was grasping at straws. Why was something that worked fine two weeks ago now completely messed up? A driver with a Vas of 133 liters in a sealed 37 liter enclosure is just about ideal (once again, according to PCD). But I couldn't think of another reason that these seemingly fine drivers were behaving so inappropriately. So I took a leap of faith and re-ported the enclosures with the original 2x8" ports. They worked before, so why not now? Unfortunately the result didn't change - same grungy/crunchy output from the woofers. Nothing about this made sense.
After ruminating on this for a couple days with no fresh ideas I consulted Chris Roemer, but he had no answer, and a 15 minute conversation with JR yielded no new insight either. Back to the drawing board - it's time to get creative. So I swapped in a different pair of drivers just to see what might happen. No change. I tried a 10" subwoofer too because at this point there was nothing to lose, with no noticeable difference. The old adage of doing the same thing over and over kicked in, so it was time for a change in direction. At this point the only thing that made sense was to reverse engineer the crossover, in other words start replacing pieces part-by-part in hopes of finding....something? The thing is that all the parts were brand new, so what were the odds that I'd have two flawed pieces causing the same issue with both drivers? But sure enough, the first part I swapped out held the answer.
Late last winter I purchased some of PE's closeout inductors - those little 'bobbin' inductor selling for about $6.00 each. The intention was to use them in a couple of small surround speakers for a friend. Apparently they are woefully inadequate for long-term application on a robust woofer. A switch from the closeout bobbin to a full size Jansen inductor immediately resolved the problem. No grunge and no crunchy, just pure sound. Problem resolved! (Celebratory beer consumed!)
After resolving this issue and researching inductor saturation I discovered that a small, ferromagnetic core, inductor can have an extremely low saturation point that can lead to abrupt saturation (versus gradual saturation), signal/voltage clipping, and odd harmonics. Apparently that's what was happening here. Who knew you could ruin these little guys with a couple volts of electricity?
Lesson learned? No more tiny inductors on beefy woofers!
Comments
http://www.parts-express.com/35mh-20-gauge-ferrite-bobbin-core-inductor--269-2134
http://www.parts-express.com/30mh-23-gauge-ferrite-bobbin-core-inductor--269-2260
And, uh...yeah, that search went awry a bit.
Chuck was helpful in solving and issue with woofer bloom these experienced. With the center-point of the Usher 8955A eight inches above the floor I was experiencing an annoying low frequency howl - floor bounce. He suggested lifting the center of the woofer up six inches or so and see what happens. Chuck for the Win! The howl is gone and the soundstage blossomed! One of my test tracks has an annoying howl to begin with and in its original form the speaker would drive me out of the room. Now, it's gone. Thanks Chuck!
18AWG or higher, trusted brands are the way to go.