The Absolute Sound posts a video about a new product development from Magnepan, but...
...fails to give any mention of the impetus for the development, for which Tom Martin has coined the term "Open Architecture". Here’s the full story:
Danny Richie of GR Research offers this service to his customers: Send him a loudspeaker you want him to evaluate, and he will put it through all his tests at no charge. He takes measurements of frequency response (on and off axis), cross-over characteristics (and the quality of the cross-over parts), individual driver responses, a spectrogram/waterfall plot, evidence of comb-filtering, impedance, sensitivity, etc. He evaluates any failings he finds, to see if he can develop measures to remedy those failings. Danny is a well-known expert at cross-over design, and if he feels the loudspeaker has the required potential he puts together one to "fix" the failings he finds in the speakers sent to him, selling the x/o in DIY kit form.
Over a year ago he received a Magnepan MG3.7i for evaluation, and ran it though his full battery of tests. In the video he posted on YouTube (see below), he describes his findings on that model Magnepan. He came up with a major redesign of the cross-over, to eliminate what he considers the MG3.7i’s failings. Finding fault in the measured frequency response of Magnepans is not new, but before dismissing what I just wrote, consider watching the video.
What he found was that the Magnepan cross-over slopes results in the three drivers (bass, midrange, tweeter) over-lapping each other, reproducing the same frequencies at the top (bass driver), top and bottom (midrange driver), and bottom (tweeter) of their ranges. That can cause comb-filtering, which is exactly what Richie found in his measurements of the MG3.7i. A lot of it. That filtering wreaked havoc on the response of the speaker, with lots of phase cancellation occurring due to the same frequency reaching the listening position from different drivers at different times (the definition of comb filtering).
Danny also found the cross-over to be comprised of absolute junk parts---push-on connectors, steel nuts and fuse assembly, electrolytic capacitor, iron-core inductor, etc. But THAT was already well known about Maggie cross-overs, with many after-market products offered to replace the stock parts.
So Danny created a new cross-over, which you will hear about in his video. What I want to highlight here is that he made a new cross-over plate to install in place of the stock one, but that plate merely holding three sets of connectors for the three drivers. Those inputs are fed from a new, separate x/o box, with all new x/o filters designed to---amongst other things---eliminate the comb-filtering, allowing the three drivers to create a beautiful frequency response. Danny suggests anyone considering the purchase of a pair of the MG3.7i to ask Magnepan if they are willing to make a pair without a x/o, in it’s place three jacks connected directly to the three drivers.
In his video, Danny also mentions how his GR Research/Rythmik Audio Open Baffle/Dipole Sub makes a great partner for use with the MG3.7i, or any other dipole planar for that matter. I’ve been touting that combo for years here on Audiogon.
So, I see the heading of the TAS video (posted below, if all goes well), and start watching it. One of the first pics I see is a pair of MG1.7i, with three sets of jacks where there is normally those crappy Magnepan speaker cable binding posts! I guess Magnepan has also watched Danny’s video 😉. On top of that, standing next to the MG1.7i’s are open baffle/dipole woofers!
Magnepan has been talking about offering an OB/Dipole sub for use with their planars for several years now, but there is already a dipole planar-magnetic loudspeaker with integral dipole (though not open baffle) woofers---the Eminent Technology LFT-8c. One can also add a pair of the GR Research OB/Dipole subs to the ET LFT-8b, using the OB sub in place of the LFT-8b’s monopole woofer. Just leave the 8b’s connecting strap off the woofers binding post.
While Danny’s x/o keeps the single-amp design of the 3.7i intact, Magnepan’s design requires three separate power amps, one for each driver.
