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Post by subbass32 on Jan 25, 2021 21:41:24 GMT -7
Why aren't accelerometers common on IB subwoofers? Both Miller & Kreisel and Velodyne saw great success using these simple devices as a means of controlling distortion in their servo-subs. But it would seem to me, given the criticality of limiting driver excursion in I/B subs, that an accelerometer would be safer, simpler, and more effective than any electronic limiter, equalizer, or dsp in preventing a driver from crashing through it's Xmech! In fact, wouldn't an accelerometer-linked limiter allow the use of less aggressive spiders, thereby increasing efficiency and by extension, headroom? Used in conjunction with a Hall-Effect sensor mounted safely away from the voice coil assembly, accelerometers seem tailor-made for I/B sub applications, and could be cheaply included in drivers that are ideal for this application, such as FI Car Audio drivers. Indeed, power amplifiers could be built with an accelerometer input jack, electronically interfacing with the clipping eliminator circuit to virtually eliminate over-excursion! I really admire how Harman has pre-programmed their Crown power amplifiers with the profile of most of their JBL Professional subwoofers to optimize amplifier DSP functionality for the characteristics of the subwoofer being driven. However, just as electric motor Variable Frequency Drives have largely shifted from using mechanical encoders to open-loop vector control out of expediency, audio engineers in the subwoofer design realm seem to have trivialized the "concrete" benefits of servo-drive technology in I/B subwoofers. In multi-driver applications (like I/B subs), only one of the drivers need be interfaced with the amp since like drivers in the same baffle will behave identically to each other. Voice coil temperature monitoring and protection can easily be accomplished through computer modeling in DSP, but the many variables of electro-mechanical excursion limiting do not lend themselves to such modeling...
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Post by ThomasW on Jan 26, 2021 17:54:41 GMT -7
It's my experience that servo mechanisms are pretty good for lowering distortion when used in smallish sealed box systems. Gived how we use drivers in our IB systems servos would be added expense with minimal benefit
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Post by subbass32 on Jan 27, 2021 11:25:51 GMT -7
Thank you Thomas. Short of the reckless "back up until it sounds expensive" method, how does one get maximum SPL (within the excursion-limited frequency band) out of their I/B sub without driver damage? High pass filters are useful, of course, but they are still arbitrary, in that program material often contains brief, very high amplitude passages that cannot usually be anticipated before watching a film. Very aggressive high pass filter slopes adversely affect transient response and can leave a lot of usable excursion on the table. Electro-mechanical excursion monitoring and protection would allow a user to get ALL of what they paid for out of their sub while providing peace of mind. Few things ruin an immersive film watching experience as much as a horrible clattering noise emanating from your expensive subwoofer! Moreover, when you have invested in four drivers, the cost of one single "whoops" can greatly exceed the initial capital investment of one accelerometer/hall-effect sensor team and the associated electronic interface inside the driving power amplifier. This could be viewed as the next evolutionary step after McIntosh's "Power Guard", Carver's "Clipping Eliminator" and modern digital signal processing in commercial power amps. Persuasive argument; done. I invite any and all to (respectfully, like Thomas) shoot holes in my theory.
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underthebottom
New Member
System is operational but incomplete - it is temporarily an open baffle.
Posts: 42
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Post by underthebottom on Feb 3, 2021 11:12:34 GMT -7
Years before I found this site, I was planning an infinite baffle sub - even though I didn't know then what it was called. I guessed that the bigger the box, the better. So using the basement as the box would be best. It seemed that using multiple drivers would spread the load. AKA "divide and survive". Same reason why a heavy truck has multiple tires. The 6 Fi drivers I used have a 30mm Xmax, and during initial testing as an open baffle, their excursion was no where near that much. Even while the room floor was moving up & down enough to interfere with my sense of balance. To quote Mythbuster Jamie: "Overkill is underrated". I concur. Accelerometers seem like a complication that just isn't needed.
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Post by subbass32 on Feb 6, 2021 14:01:02 GMT -7
This is intriguing; how did you gauge their actual excursion vs their excursion limit?
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underthebottom
New Member
System is operational but incomplete - it is temporarily an open baffle.
Posts: 42
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Post by underthebottom on Feb 6, 2021 19:00:39 GMT -7
No instrumentation. Grille over drivers is expanded steel with holes big enough to stick a finger through to cone (carefully). Compared to no signal, displacement felt like less than a quarter inch out from rest position. Xmax of 30mm implies that there was still an inch of headroom remaining. And I am assuming that displacement will be slightly less when the cabinet is finally closed in. Pipe organs can be fun (evil laugh). I may need to add some bracing to the floor.
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