Thursday, May 28, 2015

Bozak Rebuild Project - Part 11

It's been over three years (Yikes! How time flies) since I started this quest to rejuvenate my 1958 Bozak 302-A speakers and slowly but surely things have gotten better. New satellite enclosures, new network designs, new drivers, new inductors, and new capacitors have all improved the original sound that today rivals the best of the best high-end designs. Along the way I have shared what I discovered with you in hopes that your own learning curve for improving your own speakers will be shortened.

This segment of my ongoing saga recaps the current thoughts on the redesign of this classic loudspeaker. I will share with you the driver complement, constraints, and challenges in maintaining a high 1-watt sensitivity loudspeaker while still maintaining excellent accuracy in both the frequency and phase domains.

First, I wanted to share with you why I chose the Bozaks over other models: their high sensitivity. This translates into loud music with modest amplifier power. The Bozaks have a 1-Watt sensitivity of about 97dB/W/m meaning that it takes A LOT less power to drive them to the same SPL as an 87dB/W/m loudspeaker. (I’ll talk about the pros and cons of low and high efficiency loudspeakers in another segment since that’s another can of worms.)

I started with the philosophy of making as few changes to Rudy Bozak’s original 1958 design as possible but rather applying current technology to a dated approach. I initially tried the well-regarded “Pat Tobin Mod” of upgrading capacitors with positive results. However, measuring each individual driver with its original first-order network revealed each driver severely “bleeding” beyond its desired operating band. So higher-order crossover networks seemed to be the solution.

Second and third order networks were tried with mixed results and finally I settled on fourth-order Bessel networks for the M-T and T-ST but a second-order Butterworth from the W-M. Along the way I discovered that my Bozak tweeters had a lot of holes in their diaphragms and these tweeters gently rolled off at about 8KHz. So replacement tweeters with the same high sensitivity were sought out. This proved to be a long process since most drivers in this range were PA speakers that were not what one would consider high-end.

I finally came across the Peavy Versarray that used a planar tweeter with very good sensitivity, the RD-1.6. After many attempts at taming this driver, I abandoned the work. The next choice was the Mundorf AMT 164UM2.1 that is still in the system today. It performed much better than the Peavy however it still had issues with the top octave. Using a forth-order Bessel LPF to limit the HF content turned out to be a good choice but that meant searching for a super tweeter.

Again the search mainly found PA drivers and exotic compression horns that – while they may have sounded good – were beyond the reach of my wallet. Using Panasonic EAS-10TH400A leaf tweeters in a previous loudspeaker with fantastic results I decided to search for something using leaf technology.

I purchased a pair of Bespoke Aria tweeters (these folks use the Monacor RBT-95 true leaf super tweeter) but I never liked the way they sounded. This has been my main efforts over the entire year: taming the Monacor. I had faith that all I needed to do was to persist and persevere and things would work out. But until I made some near-field measurements, I did not completely understand why the sound was so weird. Anyway without belaboring the point, the solution was to cross this super tweeter REALLY high (currently it crosses at about 34KHz) to control the Monacor's contributions below the crossover frequency that really screwed up the sound of the stellar Mundorf AMT tweeter.

Monacor RBT-95 Leaf Diaphragm

Below is a photo of the final crossover network (as of today) and here is the configuration:
  • Super-Tweeter high-pass filter (HPF) uses Russian Teflon capacitors shunted with Corning glass capacitors with wire-wound ground-path (shunt) chokes
  • Tweeter uses a combination of Mundorf, Audyn, Russian Teflon, Obbligato, and Corning glass capacitors with ribbon signal-path chokes in the low-pass filter (LPF) and wire-wound chokes in the HPF. A sort of "Zobel network" is also used to minimize T-ST interactions.
  • The midrange uses Mundorf, Russian Teflon, Clarity, and Corning glass capacitors with a Solen capacitor for the notch filter. The midrange network uses ribbon chokes in the signal path and wire-wound shunt chokes. The midrange uses a notch filter at about 3KHz to help smooth a mechanical resonance. A Zobel network is also used.
  • The woofer (actually two woofers in an isobaric arrangement to improve bass response in a small cabinet) uses a low-loss toroid inductor and Clarity caps for the crossover and the Zobel network uses Clarity and Audyn caps.
  • All signal-path resistors are Mills non-inductive.
  • The midrange and tweeter are T-pad attenuated. All attenuators are better than 1% hand-matched.
  • All capacitor and inductor values in the network are spot-on hand-measured.
  • All impedances of drivers at the crossover points were confirmed via LRC resonant measurements with my HP 465 oscilloscope and function generator.
  • All network LPF/HPF performance was verified with near-field measurements of each individual driver and then its partner to assure minimal driver interaction.
  • All point-to-point network wiring is #14AWG stranded silver-plated OFHC copper, Teflon insulation.
  • W-M crossover is -6dB BW2; all others are -6dB Bessel4 (hence the high parts count for this 4-way system).
  • Each driver has its own network board and speaker terminal pair.
  • The satellite box is now a truncated trapezoidal-pyramid design with curved front edges and adhesive felt on the face
  • Presently each speaker is tri-wired (one amplifier, two channels, six speaker wires total). Wiring varies in material content but all are star-quad.

Crossover Network as of 5-23-15

Remember that in my world things routinely come and go but I can report that I am pretty happy with the way they sound, and that is saying a lot. To give you an idea of what they sound like, give a listen to the outstanding Vapor Sound Joule. The Joule has much better bass control and my Bozaks have a better top octave. The lower mid-bass between the W-M is the other noticeable difference but this difference depends a lot on room resonances and speaker placement.

There is one other change that I am in the process of implementing: better crossover-to-speaker wire terminations. It is well known that ferrous terminations (steel nuts and bolts) will magnetize slightly as the signal passes through. Magnetizing the nuts and bolts steals some of the energy that really should go to the speakers. Using stainless steel versions changes all of that since stainless steel has no appreciable magnetic properties (see below). As you can also see, I continue to use star-quad stranded silver-plated-copper wiring throughout making the biggest difference in the size of the sound stage and other differences in transient response.

Stainless Steel Nuts and Bolts

Also evident in the above image are the numerous holes from countless failed attempts at a HPF design, redesign, re-redesign, re-re-redesign...for the super tweeter. One day I will replace that board and make it at least look better. And some other day I will design and build a better woofer enclosure (it's already on the drawing board waiting for spousal approval).

BTW, many of the ideas I used in this redesign you can also use on any design. Here is a brief summary of generic mods:
  • Take out your crossover network and go through it by using better wire in a point-to-point method abandoning those puny copper PC board traces.
  • Use good wire everywhere and orient the chokes 90 degrees to each other (horizontally, vertically, or laterally) and don’t place two similarly oriented chokes near each other.
  • Use good quality capacitors in the crossover network
  • Use three screws (wherever possible) in a triangular pattern to mount the drivers. BTW, you can test this on your woofers by loosening all but three screws are still in the holes but not touching the basket. Give this one a shot and be amazed.
  • Put felt around the midrange and tweeter drivers and make sure that the screws used on them are as flat with the baffle board as possible
  • Use separate ground runs from the back speaker terminals through the crossover network and then to the driver
  • Try bi-wiring or even tri-wiring and experiment with wire designs of your own. I prefer star-quad with silver wire; you may have a different preference since this is a pretty lively wire and may cause your mid/tweet to sound harsh or metallic.
  • Put your speakers as far into the room as aesthetically possible without breaking up your relationship (1/3 of the way toward the listening chair is a good number)
  • Move your speakers around a little here, a little there, and see if the bass or sound stage improves
  • When finished moving them around, put your speakers on spikes (three if possible; two in front and one in back). If you have hardwood floors, slip three pennies underneath (again two in front, one in back) and be amazed! I call this “Phil R’s patented 6-cent fix.” Catchy, right?
  • Buy a really good power conditioner and plug all of your equipment into it (no sharing of outlets). Isolation transformers are not enough; RF filtering is absolutely essential.

I’m sure there is more but this should keep you busy for a while (maybe three years or so ;). Tweaking is part of the fun of this hobby and every point of the playback chain has the potential to be tweaked. Remember that swapping out speakers will give you the biggest change in your system. If you are not happy with them, start there.

So how does it measure? I knew you were waiting for this. Well this was a surprise to me: it measured - from the same listening position I have made all of my other measurements - rather disappointing since the microphone I used suffers greatly above 6KHz and below 300Hz. Many of the 3,000 or so measurements I made over these three years looked great on paper but sounded absolutely awful. This one shown below measures fair but it sounds truly amazing. To give you an idea of how the sound changed, the oldest surviving RTA measurement (hard drive crash at fault here for eliminating older measurements) using the original four-tweeter design and the Pat Tobin network is shown for comparison. Also shown in green on the graphs are the approximate crossover points for each of the two systems.

The characteristic sound of the original Bozak is gone except for the captivating midrange of the B-209B. The woofer box is now ported so the bass is quite a bit deeper; it also has a slight “tubed” port characteristic. While the flared port is not objectionable, it is another area of interest to me. A tapered port design may be in the distant future. For now, I am pretty happy with the way it sounds. With the exciting dynamics and deep bass my wife is also. So stay tuned and see what pops up out of my head next in Part 12?

See also Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9, and Part 10

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 © 2015 by Philip Rastocny. All rights reserved.

Tuesday, May 19, 2015

Tributaries 4K UHDMI Cable Review - Part 3

In Part 1 of this series, we tested the tester to assure that what I assumed about my system was true and it was NOT. Rest assured that now all is now well with my system and, BTW, if you haven't rechecked your own calibration settings in a while you should probably do so.
In Part 2, we saw how a NULL test reveals any differences in photographs and that photographic images of the same images revealed visual differences between HDMI cables. This evidence debunks the debunkers, something most of us already knew but could not prove - no more! I hope that the word finally gets out, that the folks who believe that wire is wire read Part 2, and for anyone to try that experiment for themselves. It is a simple to confirm by even the most casual photographer with a modest camera - but it must be done at night so the ambient light level remains the same. I would love to have a better camera that did not compress the video data so that I could see more differences.
Here in Part 3, I will try to subjectively assign visual differences between these cables. And based on a recommendation from a good friend at, I will refer to these cables by simpler, less confusing names rather than their product numbers. So to refresh your memory, there are four cables under test:
  • UHD HDMI (UHD-010b) I shall call the BASIC cable
  • UHD Slim (UHDS-010b) I shall call the SLIM cable
  • UHD Slim Active (UHDS-020b) I shall call the SLIM-A cable
  • UHD Pro (UHDP-010b) I shall call the PRO cable
The Cables Under Test
The comparisons will all be made against my trusty 1080p SERIES 8 cable. Are you with me? Good. Let's get to it.
Now choosing a video sequence worthy of repetition is a challenge since I must do this all during one setting otherwise my video memory fades and I am unable to make fair comparisons. So for this test, I chose the already well-regarded and well-reviewed movie Avatar 3-D version. I chose to watch the scene where Jake and Neytiri cross a log (scene 11, time: 40:30-41:50) and seeds float down from above. This scene segment is where Jake asks, “What are they?” and Neytiri responds, "Seeds of the Sacred Tree...very pure spirits" (aka the Tree of Souls). The Seeds magically settle on Jake's body and then drift away.
Most mystifying about this particular scene is not only the floating and spinning of these Seeds themselves but also the various camera angles from which this scene is simulated. Even distortions from simulated camera-lens swaps (shorter-focal length and lower f-stop versus longer-focal length and higher f-stop) are faithfully reproduced at the outset of this scene giving you a feeling of looking at a background in the shape of a “curved sphere” rather than the more-frequently-used “flat field.”
With a fresh set of batteries in the glasses and a bookmark (OPPO's AB Replay function) noting the start/end of that scene, I am ready and will make progressive comparisons to two cables. BTW, to assist myself in complete attention to the video, I decided to mute the audio during their review. And to eliminate influences from changes in ambient room lighting, I performed this part of the evaluation at 3:00 AM.
Series 8-to-Basic
This was a tough one. Although I preferred the Basic over the Series 8, I have a difficult time sorting out how to tell you why. These two cables are strikingly similar both revealing full rich colors and fantastic contrast. But the Basic cable edged out the Series 8 in what I may call video fatigue: things just looked a bit more spatial. Specifically, small improvements in detail to the bottom two “arms” of the seed were noticed with the Basic and less defined in the Series 8. And the sense of the size of the forest felt “different” meaning the 3-D perception was a little better. There is not much more I can say other than these two cables are remarkable with only minor differences.
Series 8-to-Slim
Here is where things start to get exciting. With the Slim cable, the blood on Jake’s right upper arm is much better defined and perceived in greater contrast than with the Series 8. Also better defined are the blood vessels in Neytiri’s sclera (the white area of the eyeball) along with the radial lines of the iris (limbus, stroma, and colorette). The animation art of making inanimate things look real by the addition of lighting and shadow can better be appreciated with the Slim cable.

Neytiri’s Eye Detail
Additional detail in both the upper and lower arms of the Seeds is evident with the Slim cable over the Series 8. Background images believed to be blurry in the Series 8 are now clearer with greater-perceived three-dimensionality. The luminous moss on the background logs now hints at some edge detail where with the Series 8 this level of information is completely lost. Jake’s brow wrinkles show depth and convey emotion veiled until now. The dark pigment lines in Naytiri’s face show they are just below the top layer (epidermis) of her skin rather than on its surface.
Series 8-to-Slim-A
OK, now this is getting a little tougher again. The differences noted with the SLIM cable over the Series 8 are also present in the SLIM-A cable. The only additional perceived difference is in thin lines such as the top “arms” of the Seeds at their edges. From inside to tip, the arms widen, then taper to a point, then widen again finally tapering to a single tip. As the seed spins, you can see how thin this line is between the upper and lower parts. Also, the green glowing specs on both Jake’s and Neytiri’s faces are brighter than in the Series 8.

Greater Thin-line Detail
Series 8-to-Pro
It is obvious that the full quality of the Pro cable is beyond the ability of my 1080P playback system to reproduce. The only differences I noticed in addition to the aforementioned improvements were the in Neytiri’s eye lashes. With the Series 8 (or any of the other cables), her eye lashes were blurs or completely unresolved. Some additional contrast was also noticed in the folds of the clothes in Jake’s pants and in Neytiri’s loin cloth. Beyond this, it is difficult to detect any additional improvements with my 1080P system.
Follow-up Observations
After this 3:00 AM evaluation, I forgot to swap the Pro cable out of my system and went back to bed. A few hours later, I transcribed the notes from this review into meaningful and coherent grammar. The entire day passed without watching any television until that evening when my wife put on the latest Survivor episode. I am glad she did.
Because of the limitation in the number of colors used in the Avatar scene, a full appreciation of the Pro cable was overlooked. Once watching other material with the Pro cable, colors – especially the greens – took on a new level of accuracy. When watching the few seconds of introductory scenes to Survivor of the Nicaraguan coast with its already enhanced and over-saturated colors, additional contrast improvements were obviously observed with the Pro cable over the Series 8. There is richness that rivals good plasma television sets (note that I am not comparing LEDs as an equivalent to a plasma screen, just another movement in the “right” direction).

Deliberately Enhanced Green Colors in “Survivor” Episodes
Further observations of other program material show skin tones reproduced more faithfully with greatly enhanced contrast especially in low-light situations. Over the next few days, I really began to appreciate what I was missing with the Series 8 cables. The Pro model outperformed the Series 8 in just about every way you can imagine. It was like buying a new television set where even the commercials became more enjoyable to watch (well, not really “watching” the commercials as much as enjoying the striking improvement in video quality).
For me, this was a revealing adventure in appreciating (and demonstrating) the technological advancements in interconnecting wires. In other words, it is evident that all HDMI cables are not created equal especially given the measured results in Part 2 of this series. HDMI cables indeed are different but which is best? That is for you to decide.
The Series 8 cable was pretty darned good for its time but as it goes with inevitable technological improvements, any of these four new cables from Tributaries would be a welcomed addition to your own system. The level of diminishing returns applies to HDMI cables as it does for any other piece of audio/video gear. Personally, the best bang for the buck came from the SLIM model and additional, more subtle improvements came with the SLIM-A and PRO models. If my video system were 4K-capable, I am certain that even more differences would be noted.
The old saying of “garbage in – garbage out” applies to every link in the audio/video chain. Cables are a “low-hanging fruit” way to improve your existing system. Unlike springing hundreds if not thousands of dollars for a new Blu-ray player, a modest investment in cables can provide more enjoyment at a far more reasonable price point. Determining which cable is best for you is part of the fun of this hobby.
Buying an expensive cable and installing it in your system may or may not give you the results you expect. Much like learning how to listen to music to appreciate its plethora of intricate nuances, you must be similarly skilled in video nuances to appreciate minor changes in color accuracy, clarity, contrast, and dynamic range. Like hearing a floor-standing speaker compared to a sub-compact bookshelf model, some video differences are striking but others can be overlooked.
I do not consider investing in a cable and then finding another more to my liking as a waste of money but rather an investment in education. Without taking the time to personally observe that cable X is visually different from cable Y, how would you know for sure? How would you develop your visual acuity? Reading reviews such as mine can give you an idea where to begin and what to look for but the final call comes down to your system and what you prefer. My wife prefers a lot of bass to “feel” the impact of an explosion in an action/adventure movie; I do not. Being an artist, she is also far pickier about color accuracy than I am. Your taste in video performance is similar where specifications can guide you to a choice but your eyes must weed out the “sheep from the goats.” Know that any of the Tributaries HDMI cables will definitely be in the “sheep” category.
The Tributaries line of audio/video cables are high quality products providing vast improvements to your video enjoyment compared to those supplied with your equipment or available at those “big box” stores. Any of these four reasonably-priced HDMI cables also gives you far more entertainment value than reaching for the esoteric sky. Remember this: When looking to upgrade your system, think of your cables first as a possible weak link in the “source-to-destination chain.” Swap out your cables and then sit back, put on your favorite movie, and enjoy things you may have never noticed before. Any of these four cables are truly “eye candy!”
If your local dealer does not handle these fine Tributaries HDMI cables, you can purchase them directly from the manufacturer in various lengths at Tributaries Cable, 6448 Pinecastle Blvd., Suite 101, Orlando, FL 32809; Phone: (888) 554-2514. See their web site at for information about all of their audio/video cables and any of their other fine products.
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: