Sunday, January 10, 2016

Bespoke Aria/Monacor RBT-95 Mod

I have used this driver as a super tweeter in my system since March of 2015 and I have fought a sibilance issue with this driver ever since the very first day. I have tried literally over a hundred different things to tame this nasty issue - new crossover components, new crossover alignments, shifting crossover points dozens of times, over 30 different series notch filters, etc. - all with zero success. Some changes made things better but caused other problem like sporadic oscillations, mid-bass dips, and combing issues. Things were so frustrating I considered tossing the driver and chalking it up as a costly and time-consuming experience.

However, this morning I disassembled the box trying to recall if the driver was bipolar (it is not) suspecting it may be a cabinet-induced resonance. While inside, I removed the driver from the front baffle board (two center screws are all that hold it in place; the two top and two bottom screws sandwich the driver together and should not be loosened), removed the driver from the baffle board, and removed the protective screen by lifting the edge with an X-Acto knife. WARNING: The risk of removing this screen is huge: anything of ferrous composition coming close to the face of the driver will instantly be sucked through the thin planar diaphragm destroying it in an instant. But how often are steel or iron things flying through the air in my listening room? Never! So what did I have to lose? Nothing...I was going to put the driver in the spare heap anyway so I decided to give it a try.

Stock RBT-95

Long story short, this is a very positive modification and one that is incredibly easy to do and undo. After removing the screen you must tighten the two screws a little more so that the face of the driver is flush with the phase plug/baffle. This was about an extra 1/4-1/2 gentle turn (and I stress the word GENTLE since stripping out these screws ruins the baffle board).

Modified RBT-95

So what did I hear? First, the nasty resonance is almost completely gone (YAY!!!!) and the overall sound of the driver is vastly improved. What I once thought was a metallic sounding super tweeter, similar to that of a well-designed titanium bullet tweeter, has now approached similar low-sonic colorations that a good AMT or other planar driver does. It truly is magic and well worth the risk and effort.

My first impression of Nils Lofgren's Acoustic Live - Kieth Don;'t Go was jaw dropping. The overall timbre of the guitar previously sounded great but un-homogenous sort of  like several instruments combined in one with weird overtones to fundamentals. Now, all of this weirdness is gone and the strings resonate properly pulling out the fundamental sounds of the guitar body along with it. In Iver Klieve's performance of "Bridge Over Troubled Water" on his deUSYNLIGE album clearly reveals the position of the organ ranks in the church. In Patricia Barber's Regular Pleasures you can hear the strings of the double bass buzz against the finger board and the drummer tap the high-hat cymbal that is recorded in amazing clarity and detail. In the Bill Evan's Trio album "Walts for Debby" the My Foolish Heart cut exemplifies the superb talent of Paul Motian pushing brushes on cymbals and snare drums. Listen here for the incredible inner detailing captured in this recording of the metal wires slowly chaffing against the instruments - it is hard to believe that this high-quality recording was made in 1962, a mere 54 years ago.

Since my driver is outboard of the satellite box, I can move it forward/backward to time-align the sound. Now instead of chasing down the cause of this annoying sibilance, I can focus on the best possible sound stage. I can personally attest to the positive benefits of minor forward/backward movements where at some point the depth of the sound stage just comes alive. Ambient clues from rear-wall reflections in the original recorded room contribute a spaciousness to live performances you may never have experienced before.

Outboard Super Tweeter

Another thing you may note in the above picture is that I added felt to the face and sides of this speaker. This modification was already done as was the removal of the stock network (see this blog entry for other details about this speaker). I also tried swapping speaker polarity to assure myself that the absolute phase of this driver matched that of the others (it is correctly labeled).

All I can say is WOW!  Persistence and perseverance prevailed and I now have a harmonious and seamless top octave that I can easily live with. As it is when climbing the audiophile ladder, once one issue is resolved it reveals other shortcomings. But hey, that's the fun of this hobby, right? What flaws did it reveal? Stay tuned and find out!

Yours for higher fidelity,

Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate by purchasing one of my eBooks or through a PayPal donation, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style (like that of the Discovery Channel), it targets one star that has never been considered before and builds a solid case for its candidacy.

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