Friday, May 17, 2019

A visit to J-Rob's and the Silbatone 755A box by Dr. Stefano Bae

OB/755A


Despite the fact that Joe Roberts and I both revere the 755A, he never thought highly of my open baffle set-up. To this day, I'm still baffled as to why he featured my home-brewer article in Sound Practices. 😉 I enjoy the engulfing planar-like airiness of the 755A/OB combo which Joe finds lifeless, boring and lacking in snap. 


OB + 755A

Could the dip in this RTA trace be indicating a lack of snap? 😜


Custom-built Altec 618 + 755A


J-Rob custom 618 cabinet

  Back in the mid-90s, I owned a pair of original Altec 618s. Those sounded boxy and colored, perhaps due to their lightweight construction. So I traded them for a pair of early sand casted 811 horns...😧 Oh well, live and learn. 😁

When my friend Chong gave me a pair of well braced vintage DIY 618 boxes (allegedly built by an ex-WE engineer and used to house a pair of WE755As), I understood the snap that ticked the Joe-man.


ex-J-Rob Altec 618 + 755A

This is the nicest and most modern looking RTA trace in this survey! Loaded with Altec 755As, the sound is snappy and dynamic while retaining that warm and realistic sheen in the midrange, which evades most speakers marketed in the past 50 years. Although some listeners may still find that quality a vintage coloration...

A visit to J-Rob's


People don't always have to agree to remain friends


Case in point: Joe seems to prefer the Japanese 755 - Lafayette SK98/Hamlin/Pioneer PIM8L - over the ferrite 755C. However, if push comes to shove, I'd take the 755C over the various permutations of the PIM8/20L even if I played a role in reintroducing its virtues to the world. Maybe it's just my sentimental attachment to the 755Cs since they were my very first high-efficiency drivers?

J-Rob sez, "I shouldn't even be talking to you since you like 755Cs." 😆



When I visited Joe in the summer of 2018, he had a pair of 4 cubic foot WE753A look-alike cabs that house Western Electric WE728Bs driven by a spruced up Dyna SCA35 which was recently replaced by a J-Rob cloned Peerless A100 PP 6A5G amp built during the Sound Practices era. Signal source is a Mac Mini>Tidal>Audirvana>Wavelength Audio Brick DAC.

Despite the natural high frequency roll off of the 12" WE728B, it sounded very full-range because of its rich overtones. That is, overtones as musicians use it to describe musical instruments. A high quality violin, piano, or any musical instrument for that matter, possesses rich overtones and this has nothing to do with high frequency extension. Even FFT analyses have failed to identify why del Gesus and Strads sound harmonically richer and have greater carrying power in a good acoustic space compared to a painstakingly crafted modern violin.

I was looking forward to hearing the Silbatone SE300B amp on the floor but Joe hasn't gotten around to re-wiring it for 120V, and also to LPs, but the Gates CB500 was waiting for a resurfaced idler wheel. Then he showed me his next project - Klangfilm horn repros (center background) + Altec and JBL large format compression drivers.



Finally, I was introduced to the pair of Altec 755As perched on top of the WE753C-like cabs. I was quite impressed with the sounds emanating from the 755As!

This 755A/box combo was featured in the Silbatone exhibit at the Munich High-End 2018 Show. Prior to that, Joe spoke fondly about the box and gave DIY hints in this Audiokarma thread. I was hoping that he'd be inspired to update his Junkyard Jukebox blog for a formal presentation of this cabinet design before he went on a sabbatical from the internet.

Since there's no sign that he'll be back anytime soon, with his permission, I took it upon myself to write about this 755A cabinet breakthrough.


Silbatone/Dr. Bae WE/Altec 755A box plan
Copyright Silbatone Acoustics


I re-drew the box plan based on a quick sketch Joe uploaded in the Audiokarma thread. Please note that this cabinet plan is published solely for the Audio/DIY community as a public service of Silbatone Acoustics. 

Under no circumstances should this be used for commercial purposes! 

Let's see if that works...truth be told, I am well aware that there have been a few enterprising individuals who have benefitted commercially from projects published in this blog. So I'm not holding my breath.


John Piro Clone Build
Interior walls + back lined with two layers of Kimpak

I sent the drawing to my buddy John Piro shortly after my Altec 753C cabinets were delivered.



Can anyone distinguish JP's clone from the original Silbatone box? 


Dr. Bae designed Silbatone box + 755A

J-Rob comments:

"The cabinets were designed by genius Silbatone engineer Dr. Stefano Bae as a group project for the Silbatone-sponsored DIY/Western Electric forum in South Korea. 100 pairs were quickly sold out, immediately driving up the world price for 755As. The original uses Silbatone's custom silver litz wire, which is said to be an essential ingredient of the original recipe, and top shelf WBT connectors.

Over the years Silbatone designed and made literally dozens of experimental boxes, including back horns for up to four (755A) drivers per side. This was probably the most successful, although rather modest.

My analysis of this untuned little cabinet is that it falls under the 'small box with a hole in it' design paradigm."



Unlike before when I felt the need for at least SE300B power to make the OB/755A sing, now I'm enjoying near-field sounds from my JP cloned Silbatone/Dr. Bae boxes + Altec 755As driven by an SE46 amp with tiny Noguchi FM6WS Finemet OPTs.



The SE2A3dx which normally drives the Altec 753Cs in the main listening area had no trouble driving the Altec 755As in Silbatone boxes to moderately high SPL levels.

 Even without the silver litz wire and high tech WBT connectors, I heard all the virtues of the slant 618 box + open baffle combined = detail, snap, macro and micro dynamics from the 618 box + airiness and lack of vintage boxy colorations from the open baffle.

The Dr. Bae/Silbatone cabinet transported the 70 year old 755A design to the 21st century in a monitor-sized package!






14 comments:

  1. Hurrah! This is just the kick I needed to get my own Silbatone/Bae cabinets rolling! Nice writeup sir, and thanks! -Nate

    ReplyDelete
    Replies
    1. Hey Nate,

      Once you get your Sil-Bae/755A going, send a picture. Happy listening!

      JE

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  2. Thinking I might have to try this box with my Pioneer PIM-8 drivers. Could never get the best behavior from the PIM-8s when using the Altec 618 cabinets, but there was a definite *something* there with those drivers...

    ReplyDelete
    Replies
    1. That is in my "to-do" list. I just have too many things lined up. Keep us posted!

      JE

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  3. I keep on trying to comment but it deletes them. Anyway, I built these for my Altec 755A speakers. I kept on bugging Joe Roberts until he took some measurements. I thought they made the 755A's sound great. A very modern type of sound with a studio monitor clarity in many ways. But alas, the bass was not enough for me.
    I had previously only tried the speakers with some smaller vintage cabinets as well as a 1 cubic foot simple aperiodic box. They sounded boxy and stuffy in the vintage cabinets and a bit muddier in the 1 cubic foot cabinet. Anyway, I sold the 755A's but I'd like to try another speaker in these cabinets, which I still have. Any other suggestions?

    ReplyDelete
    Replies
    1. Even if J-Rob has no love for the 755C, IMHO, it works very well in this box also. A friend in Manila confirmed this. In fact due to "less snap" there seem to be greater perceived bass response. At some point I'd like to try the SK98/PIM8/2L even if I know that requires an even bigger box than the 755s. I can't think of any vintage 8" or for that matter, any modern 8" which can produce more bass in this small box. It's physically just not possible.

      Thanks for dropping by!

      JE

      Delete
  4. Hi,
    Can it be used on other brands of 8” fullrange speakers? eg:Philips 9710.

    Thx

    ReplyDelete
    Replies
    1. So far I've only tried them with Altec 755As and got a very positive reaction from a friend who is a 755C user. If you get good results from the 9710 or any other 8" driver, please let me know.

      JE

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  5. Hi, have you tried a 755E in this cabinet? Would you mind share your impressions? Thank you!

    ReplyDelete
    Replies
    1. I left my pair of 755Es in the attic. ;( But based on audio buddies whose ears I trust and are currently enjoying 755Cs in these cabs, I don't see any reason why it won't work just as well for the 755E.

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  6. Any guidance as to the diameter of the internal wiring? I'm using a 755C in my build. I looked in the Colloms book (High Performance Loudspeakers, 7ed) and he'd doesn't address the issue in any detail. Reading on-line provides more opinion that science. Any thoughts are greatly appreciated.

    Thanks,

    /d

    ReplyDelete
    Replies
    1. I use 16 AWG tinned stranded copper wire for internal wiring. Something like this - https://shorturl.at/wyBI9

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    2. Great, thanks. I just checked to see if I have a leftover 16 AWG tinned copper wire and I happen to have a few feet of leftover silver wire (Mundorf?) at 18 or 20 AWG. Aside from trial-and-error is there any way to determine if 18 or 20 would be appropriate (I'm thinking math here)? Or should I get off my lazy butt and buy 16 AWG tinned copper? Thanks again, /d

      Delete
    3. I sense that you're overthinking. Use your leftover silver wire so you can listen to music ASAP! That's the bottom line!

      Delete