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.

128x128bdp24

Most of the Acoustat panel speakers can be modified to use the Acoustat servo amps. Roger Modjeski did some mods to my servo amps, but unfortunately he passed away before we could implement the tube input stage. I modded my Model 2s with help from Roger where we implemented his mod to increase treble dispersion to greatly widen the sweet spot. The challenge with the Model 2s is when you remove the interfaces to connect the servo amps the speaker is challenged to stay upright. Rob from Magna Risers made me custom feet similar to what he makes for Magnepan speakers and they work just great. I assume they work great on Maggies as well.

 

@clio09: I remember that Roger often extolled the virtues of the Acoustst panels themselves, but considered the transformers absolute junk. Do you have the only pair of Model 2’s he worked on?

By the way ESL fans, Roger advised me to cross-over my Quad 57’s (originals) to subs at 100Hz using 4th-order filters (24dB/octave), as he found the bass panels to be unacceptable below that frequency. He deplored resonances, whether electronic or acoustic.

 

@bdp24 I believe I do have the only Model 2s that are modded by Roger. My experience with Acoustat came from the fact that Roger had a pair of Xs. He used (actually butchered) the cabinet so that he could test his own ESL panel and power supply. I was using that pair of speakers in my system when until I spotted the Model 2s for sale locally. At which point Roger told me to grab them and we went to work on those. Sadly I will need to sell them and the servo amps, as well as two pairs of my 57s (including Rogers own pair that I had Sheldon Stokes restore). Other than running RAM Tubes I'm retired now and I just have too much stuff. I also do still have Roger's own ESLs with his direct drive amps which I will keep.

Crossing over ESLs at 80 to 100 Hz depending on the speaker makes a lot of sense. I wish more people would try it out. I think one of the more interesting developments in ESLs these days is David Janzen's reworking of the KLH 9 which his father originally designed. If I could only have a pair of those.

 

@clio09: The KLH 9, another ESL I’ve never heard. I think that model never made it to the West Coast (in 1972 the leading high end shops were in the North, East, and South. Guys like Paul Heath in Philadelphia.).

When I discovered J. Gordon Holt and his Stereophile Magazine in 1972, he had double-KLH 9’s as one of four loudspeakers comprising his list of Class A Recommended Components. The others were the new Magneplanar Tympani T-I (in it’s revised incarnation, which improved the T-I’s high frequency extension), the Infinity Servo-Static 1 (which I did manage to hear, but at $2,000/pair---in 1972 that was lot of dough---were out of reach for me), and the Hartley Concert-Master. He had the Quad ESL in Class B.

Another ESL I was interested in was the Dayton-Wright, made in Canada. I went up to a new hi-end shop in Berkeley to give them a hearing, the shop owned and operated by David Fletcher, who later gaining notoriety as the designer of the Sumiko "The Arm" and the SOTA turntable. David struck me as an extremely intelligent fella, and when I couldn’t hear the Dayton-Wright (I don’t recall why he couldn’t demo the pair he had), I asked David about the Tympani’s (which were at the top of my list to audition). He was unusually candid when he said "I’m pushing the Dayton-Wrights." 😉

 

I did dannys upgrade, lrs plus, and its much much improved. They still soak up loads of power but they are so clean you dont realize how loud they are actually playing. i got some $30 tv stands off amazon and used them as stands, they look and work perfect. i also made wood 'feet' for the bottom of the stands for more stability. i lift them up and move them into the room when i want to listen. magenpan would be better of leaving out the x over unless they want to do it right. fwiw i have a medium sized room and use an svs sub and its very full range. i pass the signal thru the sub at 70hz and that goes to the maggies.