Interesting new speaker tech from KEF - Page 1
Forum section: electronics / general

author: AVGresponding
author_rank: Super Contributor
timestamp: July 13, 2025, 09:43:42 am
content: Using a flex-pcb orthoganally oriented wrt the voice coil to provide real-time voice coil velocity monitoring, with all that implies:

author: madires
author_rank: Super Contributor
timestamp: July 13, 2025, 11:13:10 am
content: Philips Motional Feedback active speakers from the 70s: Philips RH-544 Electronic Speakers!They use piezoelectric sensors.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 13, 2025, 11:54:43 am
content: That should avoid the induced current that the orthogonal windings in the KEF are also intended to do. I wonder at the relative merits; I suspect the coil method works better at lower frequencies

author: Zero999
author_rank: Super Contributor
timestamp: July 13, 2025, 11:55:29 am
content: I've thought about this before, but never seriously.The idea was to use two voice coils and magnets, which will screen them from each other, preventing transformer action.Here's a rough sketch.

author: madires
author_rank: Super Contributor
timestamp: July 13, 2025, 12:12:41 pm
content: Quote from: AVGresponding on July 13, 2025, 11:54:43 amPeople owning Motional Feedback speakers say that the speakers have a nice and solid bass.

author: tooki
author_rank: Super Contributor
timestamp: July 13, 2025, 12:16:58 pm
content: I wonder how much improvement this has compared to the widely used approach (in small gadgets with integrated speakers) of carefully characterizing a speaker model in a lab, then using those parameters and a “smart amp” (TI Smart Amp, ADI Dynamic Speaker Management, etc) that monitors voltage and current, and uses the parameters to know exactly how it can and can’t drive a given speaker.

author: langwadt
author_rank: Super Contributor
timestamp: July 13, 2025, 12:43:52 pm
content: Quote from: madires on July 13, 2025, 12:12:41 pmmotional feedback only really works at low frequencies, so it makes sense, it is also where most speakers distort most

author: Zero999
author_rank: Super Contributor
timestamp: July 13, 2025, 01:09:29 pm
content: Quote from: tooki on July 13, 2025, 12:16:58 pmThat's why I didn't seriously consider pursuing my idea. A speaker model can also take into account the enclosure, which feedback fails to do.

author: langwadt
author_rank: Super Contributor
timestamp: July 13, 2025, 01:16:50 pm
content: Quote from: Zero999 on July 13, 2025, 01:09:29 pmit sorta can, if the speaker(driver) does what it supposed to do because it is closed loop, the enclosure will do what it is supposed to do

author: nctnico
author_rank: Super Contributor
timestamp: July 13, 2025, 04:48:38 pm
content: In the end the the real problem is small speaker enclosures and their lousy efficiency. A couple of decades ago I bought a piece of test equipment from a guy who built his own loaded horn speakers. He built these literally from scratch. A 6W class-A tube amplifier was all he needed to make the mugs dance on the table. And because the (single) voice coil in the speaker didn't need to move much, the distortion of his speakers was also extremely low. It was a very impressive demonstration.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 13, 2025, 06:02:47 pm
content: Quote from: Zero999 on July 13, 2025, 11:55:29 amSo isn't your idea basically a servo mechanism?Looks pretty good to me, but have no idea how it would work in the Real World®™.

author: thm_w
author_rank: Super Contributor
timestamp: July 14, 2025, 09:04:53 pm
content: Servo dual voice coil subwoofer has been around for a while, but sounds like it has some limitations.Article with a list of a few of the technologies used:https://audioxpress.com/article/servo-control-in-mainstream-audio-from-motional-feedback-to-the-bend-sensorhttps://www.audiosciencereview.com/forum/index.php?threads/servo-speakers.18247/So many options here for feedback: piezo (the philips one mentioned above), optical, microphone, force sensor, accelerometer, etc.