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Fostex 168S with BS-168

by Godzilla

As speaker builder hobbyists, we know the cost of drivers, crossover components and cabinetry. Buying new from the local Hi End shop seems ludicrous because we know those 8” Vifa’s cost $25 and that Morel tweeter is $28. Connect it to $6 worth of caps and wrap it in a crappy 3/8” particle board box (with very nice veneer) and price it at $1,000. Sometimes I wish I never knew what was in those lovely veneered boxes.

The Full Range Driver Forum is an excellent source for information. Most everyone there has been through the frustration of building a multi-way system with parts quality equal to or better than what is commercially available.

In fact, most all of them – myself included – have decided to do things a little bit differently. Elaborate front or rear loaded horn cabinetry, single, ‘full range’ drivers, ‘helper’ tweeters, birch plywood or real wood are the norm. Why? Better sounding speakers, that’s why!

The focus of this project is the Fostex 168S.

This is not a cheap driver at around $115 US. But since I already had excellent results from much cheaper full range drivers (Radio Shack 1197, 1354. Pioneer B20 and the neat little TB 3” drivers – both aluminum and paper) I thought I might as well splurge.

Wifey and I finally purchased a new house with a large living room. The 168S will be going in there. All I had to do was decide which cabinet to put them into. No easy task, there are several choices all with unique flavors of their own. So off I went to the local Home Depot with measurements in hand. Here are links to the designs I tried.

I started with the smallest cabinet then went for the difficult to build back horn and finally the ported design. Ultimately, I felt the ported design, called the bs-168 was clearly the best sounding. I modified the dimensions a little to better fit the decor of my living room and made the cabinet taller and less deep. Special thanks to ‘LageB’ a member of the Full Range Driver Forum for posting this design. I will refer to my cabinet as the bs-168 Mod not because I would like to lay claim to a great new design, but because it is different from the original and some may want to build from the original measurements. In reality, the dimensions used are approximately 3” taller and 3” less deep. All walls, including the top and bottom are nearly doubled up to form a solid cabinet. That’s it.

All measurements were done with the most sophisticated equipment known to man, the human ear. All comments and criticisms are subjective and basically my humble opinion. My intentions are to alert anyone interested to this easy to build, excellent sounding, relatively high efficiency, tube amp friendly speaker design.

Parts:

  • Fostex 168S: $112
  • Radio Shack 40-1310 super tweeter: $30
  • Capacitor - .47uf: $.99
  • Pine: $20
  • Cup: $3

Parts total: $165.99 for one. Parts total for pair: $331.98

Dimensions:

  • 12" x 28.5" x 13.5"

Construction:

The pine was cut at Home Depot. All of the boards were 12" wide.

Titebond wood glue holds like a vice. After applying I clamped for a tight seal. Clamps are so important! I remember first buying them and thinking I would never use them more than once - hahaha. When clamping use another piece of wood where the clamp pads rest, this way they don't come in direct contact with your cabinet and you can tighten until the glue squishes out without worry.

Sanding was easy with the Mouse Sander by Black and Decker.

I was amazed how nicely the wood looked!

Tweaks:

  • Wool between wizzer and main cone.
  • Stuffing.

Sound:

This is an excellent speaker! From top to bottom and everywhere in between. I have spent a lot of time trying to get the Fostex 168S to sound as good as I have read it could sound. I am so glad LageB posted the plans from the late Mr. Tetsuo Nagaoka. His research and experimentation resulted in a beautiful sounding speaker. It is my opinion, modifying the dimensions of the cabinet slightly will not drastically change the basic goodness of this design. It's obvious Mr. Nagaoka knew what he was doing after the first few notes.

I did not write a review on the bk-161 back horn with the 168S because I couldn't bring myself to write a review of a compromised combination. I did not want others to build this elaborate cabinet only to be ultimately disappointed with the sound. With the bs-168 there is no compromise. Everything is balanced. The overall character of the sound can be described as follows:

  • Midrange: Fast, clear and detailed. Organic and natural.
  • Bass: Fast, clear and detailed. Bouncy and rhythmic.
  • Treble: Extended and crisp.

Overall, the presentation is tilted slightly forward. Upper mids are pronounced. But there is an ease in the presentation that is rare in any speaker. Without strain, you hear detail. An instrument's decay as it fades away is portrayed nicely. You don't even hear some of these details on lesser speakers. You also get a sense of scale and breadth about the performers and their instruments. Everything sounds larger and more real. Eva Cassidy, Holly Cole, Diana Krall and Ella's voice FILL the room. Their band's size and physical depth are easily recognized and never blur their lovely vocals. Instruments are easily discernable as well as recognizable. On some of my older Stan Getz CD's a trumpet can sound like a sax. Not with the bs-168. Pianos sound as large as they should, not like tiny little toys and they resonate like the giant instruments they are (I grew up with a baby grand piano in the house). Strings float in mid air - maybe they shine a little too much - but no speaker is perfect. Bass is detailed and bouncy. Every note, except for the lowest, is clear and punchy. There is a bloom to the sound that is very real and satisfying that I attribute directly to the box/driver combo. Treble is extended - thanks to the super tweeter on the back of the cabinet. Without the tweeter, all of the treble is there just not as wonderfully shimmery. Brush work on cymbals sounds almost 'scary' real.

Tubes work best and provide an even more holographic image than solid state. Efficiency was never an issue with my 30 watt amps. I have a tube Cary Audio and a solid state Rega for comparison.

As you can tell, I am very satisfied with this speaker. From the easy to build cabinet to the quality of the components the entire experience was very rewarding.

I recommend this project for anyone interested in bringing the band into their listening room!

Godzilla

A few months later…

I am still happily listening to my bs-168 Mod's. I feel they are a reference other speakers can be judged by. But I do have a few warnings and reservations for folks thinking about building. The balance is forward. No amount of break in changed this. On small scale music this balance lights up the performers in an amazing way. On large scale music this balance could be considered too have more than enough upper midrange. Bass is excellent in my opinion and amazingly tight and focused but could still be considered light considering the size of the cabinet. I like the bass but feel a subwoofer provides the lowest octave or two. Treble is excellent and much better than I've heard from almost every other design. I love the detail and clarity. But remember, I mounted the tweeter on the rear when voicing the speaker, so depending on the room, your results may vary.

If I had 3 wishes I would ask for a slightly warmer tonal character, fuller bass and less sheen on violins. If I had a fourth….I would wish for less congestion in the midrange - but I am really asking for perfection. Everything is really great.

The speakers are excellent for all types of music and very satisfying. I listen a lot and am consistently amazed at the way they produce sound.

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