DESIGNERS’ BENCH Issue #3 - FILTER DESIGN and DSP
Of all the challenges that we face every day like product design and fabrication, marketing and just running our businesses one stands out as most demanding of our skills, most fun and most gratifying: filter design. Now, if you didn’t already know this about him, Dad likes to take chances, likes to push his luck, likes to find out where the limits are.  Of course that has to backfire once in a while, right?  Get over it, that’s the cost of exploration.  But when he started drawing a twin woofer two way my eyes crossed! Come on, Dad, you taught me this stuff when I was a kid.  Remember the wave kinetics demonstations in the bathtub? Twin woofers decouple at the wavelength of the distance between their centers.  It’s nature. The idea is fine for a three way where the woofer cut off is pretty low. But for a two way? When has that ever worked?  Haven’t you’ve heard it when the other guys try it?  Plus you’ll have to run the tweeters down so low - POP!  How much did you pay for those tweeters? Anyway, what would you gain in the bargain?  Twice the output. Or much more bass extension. Or some combination.  So there is an allure, I’ll give him that. Dad figured we could use our DSP smarts and the right tweeter to limit the  woofers’ band all the while protecting the tweeters.  This strategy would not have stood a chance with old fashioned passive filters.  I have to remind myself we’re not in Kansas anymore. And we’re using a great new woofer that, with its huge coil, can really dish it out. It’s just begging for some serious DSP equalization at the bottom and we are certainly using enough juice to bang out the kind of bass energy that I demand. All right, what the heck.  We can always back off to a single woofer design.  So, OK. Go for it. Right away we realized that DSP was opening yet another door to the next level up.  How far could we take it?  Off and on between our other work we keep returning to the Kestrels and each time they get better.  You know, filter work is kinda like an eye exam: you keep making changes until you can’t get any more improvement.  So, in a funny sort of way, when it goes on and on for weeks that’s a really good thing. So, where are we now? Not only did the decoupling issue yield to my attack and the tweets are happy, but the big coils and big, smartly EQed power really delivered the kind of power-band guts and resolve that puts a smile on my face.   AC DC from a two way? No way, right? Hells Bells Yes!  Today Dad the insomniac snuck in for an early session before I got in. As I climbed the stairs to the lab he was playing Duke Ellington’s Indigos album.  It was beautiful. Gobs of energy, wide open dynamics. Timbrel detail top to bottom. Real real horns. Midrange-orama. The stuff that most people just don’t get. This little speaker punches way, way, way above it’s weight. I can’t believe I’m saying this: but they really do use the whole Kilowatt! Kestrel indeed! Are we done with the filter? Probably, I’m already pinching myself; we could be at the limit. We’ll see.  But we’ve sure pushed that limit back a step or two.  And the beauty of DSP is that, should we take another step, say, a year from now, we just email the new file to our Kestrel owners, keeping them up to date. Try doing that the ‘old way’. Ha!
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DESIGNERS’ BENCH Issue #3 - FILTER DESIGN AND DSP
Of all the challenges that we face every day like product design and fabrication, marketing and just running our businesses one stands out as most demanding of our skills, most fun and most gratifying: filter design. Now, if you didn’t already know this about him, Dad likes to take chances, likes to push his luck, likes to find out where the limits are.  Of course that has to backfire once in a while, right?  Get over it, that’s the cost of exploration.  But when he started drawing a twin woofer two way my eyes crossed! Come on, Dad, you taught me this stuff when I was a kid.  Remember the wave kinetics demonstations in the bathtub? Twin woofers decouple at the wavelength of the distance between their centers.  It’s nature. The idea is fine for a three way where the woofer cut off is pretty low. But for a two way? When has that ever worked?  Haven’t you’ve heard it when the other guys try it? Plus you’ll have to run the tweeters down so low - POP!  How much did you pay for those tweeters? Anyway, what would you gain in the bargain?  Twice the output. Or much more bass extension. Or some combination.  So there is an allure, I’ll give him that. Dad figured we could use our DSP smarts and the right tweeter to limit the woofers’ band all the while protecting the tweeters.  This strategy would not have stood a chance with old fashioned passive filters.  I have to remind myself we’re not in Kansas anymore. And we’re using a great new woofer that, with its huge coil, can really dish it out. It’s just begging for some serious DSP equalization at the bottom and we are certainly using enough juice to bang out the kind of bass energy that I demand. All right, what the heck.  We can always back off to a single woofer design.  So, OK. Go for it. Right away we realized that DSP was opening yet another door to the next level up.  How far could we take it?  Off and on between our other work we keep returning to the Kestrels and each time they get better.  You know, filter work is kinda like an eye exam: you keep making changes until you can’t get any more improvement.  So, in a funny sort of way, when it goes on and on for weeks that’s a really good thing. So, where are we now? Not only did the decoupling issue yield to my attack and the tweets are happy, but the big coils and big, smartly EQed power really delivered the kind of power-band guts and resolve that puts a smile on my face.   AC DC from a two way? No way, right? Hells Bells Yes!  Today, Dad the insomniac snuck in for an early session before I got in. As I climbed the stairs to the lab he was playing Duke Ellington’s Indigos album.  It was beautiful. Gobs of energy, wide open dynamics. Timbrel detail top to bottom. Real real horns. Midrange-orama. The stuff that most  people just don’t get. This little speaker punches way, way, way above it’s weight. I can’t believe I’m saying this: but they really do use the whole Kilowatt! Kestrel indeed! Are we done with the filter? Probably, I’m already pinching myself; we could be at the limit. We’ll see.  But we’ve sure pushed that limit back a step or two.  And the beauty of DSP is that, should we take another step, say, a year from now, we just email the new file to our Kestrel owners, keeping them up to date. Try doing that the ‘old way’. Ha!
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