Sunday, January 24, 2016

Big Change Coming to this Blog


IMPORTANT

Soon, this blog
http://Audiophile-Musings.blogspot.com

will be renamed to

because of an issue with a registered trademark  in the UK of which I have only recently become aware.

The owner of this trademark and I have come to a win-win agreement without the need for involving other actions. I personally feel that this is an excellent resolution. As a respected author, I have no desire to infringe upon this trademark and I completely understand this trademark owner's position. If the shoe were on the other foot, I would be doing the same.

All of my previous posts will be moved to a new blog site that is currently under development called "Audiophile-Muzings," a variant of this original name intended to be inspirational as my blog was originally conceived to be. The trademark owner has also agreed that this is an acceptable name change. However, this will take some time to implement since there are about 200 posts involving numerous links and external sites that must also be informed and coordinated about this move.

I will post updates to my progress as they become available. No new postings will appear on this site other than these updates. Please be patient with me since this is indeed a monumental effort.

To minimize confusion at this point, let me clarify something.

If you are looking for the blog AudiophileMusings, you have reached the wrong blog.

Click this link to take you there.

I publicly apologize for any inconvenience and confusion this may have caused.




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.

My other titles include:




Copyright © 2016 by Philip Rastocny. All rights reserved.

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.

http://www.amazon.com/dp/B00QFIAC3G

My other titles include:




Copyright © 2016 by Philip Rastocny. All rights reserved.


Thursday, January 7, 2016

The Golden Ratio

OK, I get it. It's been several months since I've posted and many of you suspect I've fallen off the face of the earth -- NOT! Many excuses surface in my mind but know this: I have not died nor have I become a zombie. I have been busy with my new solar panels building a 2.7kW system above our carport (believe me, this was a serious undertaking, not for the faint of heart). And now guess what: as our friend Arnold is fond of saying,  I'M BACK!


I have been fussing with that silly crossover point with my super tweeter and made good progress although I am still unhappy with the way it sounds. It is far better than it ever has been but you know how golden-ear types are: mercilessly critical. So the journey continues.

To refresh your memories, I use a Mundorf AMT for my tweter and a Bespoke Aria for my super tweeter. After countless attempts at a revised crossover point I have narrowed down the cause of the sibilance issue on the ST to a cavity resonance in  its enclosure. This combined with a mechanical resonance of the planar suspension of th ST at this same frequency proves to be a real nightmare.

At this point, I have been experimenting with series resonance filters (near 8KHz) to tame the wild beast and I have been marginally successful in doing so. But when I get the sibilance under control, the bass response goes out the window and vice versa. Now that the design has matured, I hear an occasional sporadic electrical resonance that is driving me literally bonkers. I tried not to redesign the enclosure (I like the way it looks) but alas, at this point I must yield to common sense.

So two things must be addressed: 1) the enclosure dimensions, and 2) the mechanical resonance of the diaphragm. Since this mechanical resonance is impacted by the enclosure resonance, it makes sense to redesign the enclosure first before tackling the mechanical issue.

Since their introduction in 1993, I have admired the design of the Bowers and Wilkins Nautilus speakers with their ground-braking logarithmic spiral woofer enclosure (also the Golden Ratio M,T,ST enclosures). For the Golden Ratio, the enclosure dimensions continuously converge in a1.618:1 ratio as shown below. BTW, the Nautilus speaker borrows its name from the sea creature whose shell also conforms to this same logarithmic spiral.


What interests me are the M-T-ST enclosures, what appears to be a unique tapered transmission line (TTL). Their super tweeter crosses at 3,500Hz. But the wavelength at 3500Hz is less than 4" so they must be using a multiple of that frequency (i.e., an inter-modular) for that enclosure. Interestingly, the model 804 uses a TTL enclosure for its ST of the 4" length.

So the next tale in the ongoing saga will be this new super-tweeter enclosure. I am uncertain as how I will go about this but old trumpets, horn flares, and waveguides come immediately to mind. We will see...


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.

http://www.amazon.com/dp/B00QFIAC3G

My other titles include:




Copyright © 2016 by Philip Rastocny. All rights reserved.