Silbatone Box Adventures

from Western Electric Oscillator July 1947

Whether it's an open baffle as conceived by G.A. Briggs or an enclosed box like the Western Electric utility boxes above, I've always been an advocate for a wide baffle design. The wide frontal area serves as an acoustic reflector that helps propagate sound toward the listener instead of escaping to the sides and back. Somehow the wide baffle, whether open or closed, always makes reproduced music sound more alive to my ears!

A notable exception is the narrow front baffle Silbatone box designed by Dr. Stefano Bae for the Western Electric/Altec 755A. Since I uploaded the cabinet project under the auspices of Joe Roberts, it has garnered a following amongst DIYers who've reported successful results mounting other 8' drivers like the Altec 755C, 755E and the Lafayette SK98/Pioneer PIM8L. 

I finally got a chance to mount and listen to my 755Cs and PIM8Ls + other 8" wide band drivers. Hopefully, this article will encourage readers to DIY this mini-monitor sized box because it really offers a lot of musical pleasure per cubic inch!

To recap, let's start with the...

Altec 755A

Ever since I started dabbling in DIY audio, I've been enjoying my treasured pair of Altec 755As. Whether it's mounted in an open baffle, 2 cf box and now, the Silbatone box, IMHO and experience, I have yet to find an 8" wide range driver which can equal its midrange sound quality, especially its ability to reproduce vocals with remarkable realism. 

Silbatone box + Altec 755A

FWIW, here's an iPhone RTA of the Altec 755A in the Dr. Bae/Silbatone box.

Although my buddy J-Rob hasn't been writing much these days, I highly recommend his Junkyard Jukebox blog for his musings about the Western Electric/Altec 755A, while good ole Frank does the music making here.

Since I didn't want to risk damaging my irreplaceable Altec 755As by constantly changing them in and out of their Silbatone boxes, I commissioned my friend at Hommage Audio to build another pair. This time, I specified a rough and ready version with extra blank front baffles so I can configure them for other 8" drivers. I had to learn how to cut a recess with my Jasper router jig because I decided to rear mount the drivers.

Altec 755C

 

I have a close affinity to this driver because it made me realize that there's a vast horizon of hifi beyond BBC voiced LS3/5As driven by PP EL84s and EL34s. The 755Cs were my gateway to high sensitivity speakers driven by flea powered SE-DHT amps.

Silbatone box + Altec 755C

In spite of the greater top end specs, to my ears, there is less energy in the higher frequencies and less presence in the midrange compared to its older brother, the 755A. Although I'd agree with the improved bass extension, IME, 40Hz is a bit optimistic in this box, the 2 cf cabinet or the open baffle. The 755C retains much of the 755A character, with a bit less snap and sparkle.

If you don't have a 755A to compare it with, you'll already be impressed. Admittedly, comparing hifi components is a really fun aspect of this hobby. But what's the point of comparing something you can't find and afford vs. something more realistically attainable?

Although the 755C sounds perfectly fine without a super tweeter, the Altec 3000H adds that last bit of ambience and air. Unfortunately, 755C + 3000H doesn't = 755A.😞

Doesn't the IKEA blue Knarrevik look spiffy?😉

Pioneer PIM8L

I discovered this 8" duo-cone at a radio show in Lansing, MI in the 90s in the more deluxe Lafayette SK98 guise, which I deeply regret trading.😞 It can also be found branded as Pioneer PIM8L, PIM20 or Hamlin with either 8 or 16 ohm voice coil. Regardless of what brand it sports, I regard this wide band 8" very highly! 

Silbatone box + Pioneer PIM8L

High frequencies can beam, but on-axis it has more HF energy than the 755C and possesses a similar 3D midrange. Just watch out for rubbing voice coils, damaged/torn suspensions and heed the Pioneer specified 6W maximum rating! 

Unfortunately, both Altecs and the Pioneer are no longer easy to find and when available, are very costly! So what are the alternatives?

The following drivers don't have the gravitas of the Altecs and the Pioneer. But they are easier to find and more affordable. They all offer great musical value for the money, IMHO!

Motorola Golden Voice 8 

This Alnico 8" paper cone driver sounds fast with lots of snap from the bass to the top end with a vibrant midrange. But as I listened further, I became aware of a slight whizzer cone tizz. It projects a very lively and exciting sound, which reminds me of Lowthers!

 

Silbatone box + Motorola Golden Voice 8"

Could the spikes above 2 kHz a manifestation of that tizz? It's not offensive but I just wish it wasn't there.

Electro-Voice Wolverine LS8

The EV Wolverine LS8 is a very smart looking vintage driver. It's very dynamic with a warm and dark-ish tonal balance. Definitely the most laid-back presentation from this trio of whizzies, yet still very engaging.

Many years ago, my friend Ding had a pair of EV SP8Bs mounted in open baffles and those sounded very similar to this LS8.

Beyma 8AG/N

Here's a modern and affordable 8" wide bander that's available from US Speaker Parts. While I was based in Manila, I became good friends with the Beyma importer and distributor and got a chance to play with a few of these drivers.

 The 8AG/N (top left) performed very well in the open baffle and likewise, in the Silbatone. It's a very smooth sounding driver. The tonal balance is similar to the Motorola GV8 without the whizz tizz. 

Silbatone box + Beyma 8AG/N 

However, if I split hairs, the midrange isn't quite as vivid as the Motorola GV8. Could that be an Alnico vs. Ferrite thing? That said, I wholeheartedly recommend this modern 8" wide band driver, which seems to have had some following in Germany but still under the radar stateside.

CODA

In my comments above, I focused on midrange and upper frequency musical performance because in this survey, I realized that 8" wide range drivers, which worked well in my G.A. Briggs inspired open baffle, also produced satisfactory bass response in the Silbatone box. Therefore, it's safe to assume that 8" drivers with a Qts value close to 0.7 or greater, are suitable candidates for the Silbatone box. 

Instead of obsessing with T/S parameters, be adventurous, have fun and experiment like my Instagram friend Andrew did below. Anyway being empirical is very much in line with this excerpt from J-Rob's comment in the original Silbatone 755 box article, "... My analysis of this untuned little cabinet is that it falls under the 'small box with a hole in it' design paradigm."

Lii Audio 8" in DIY Silbatone boxes

I highly recommend visiting and following Andrew's IG feed!

Happy tinkering and listening!