Fostex 168z – A Wonderful Full Range Driver

The Fostex 168z (older style with whizzer) is one of my favorite full range drivers. I’ve tried it in several cabinets but enjoy it most in a large ported box. It has a midrange heavy sound but when you bring the bass in line with the midrange it sounds beautiful. It doesn’t need a tweeter on axis but I prefer the sound slightly off axis and with a rear mounted tweeter.

Fostex 168z in Large Ported Box (42L)

Nagoaka Tetsuo designed a 46 liter cabinet for this driver and even tho it doesn’t simulate very well (not flat) it sounds great! Years ago I built the 46 liter cabinet but lost them during my divorce. Fortunately, I came across a pair of large AR cabinets left out for trash, brought them home and refinished them. You can see the shape they were in. With a little elbow grease I was able to restore them. They look great sitting in the corner of my apartment. They are 42 liters but certainly close enough. They are tuned to 59Hz.

As for the sound, it’s just as I remembered. The bass really bounces along. It’s full and rich without any strain. They are not perfect but always make me smile and produce an engaging sound. It’s a bit full in the bass (which can be adjusted to taste with more stuffing) but everything else is wonderful up until the treble where they roll off. I may put a tweeter on the rear to add extra sparkle. Otherwise, these are great examples of how a full range driver can sound in a simple ported box. If you already have these drivers, or come across them used, I can’t recommend them highly enough in large ported boxes.







Fostex 168z in a Back Horn (BK161)

My son, Jeremy, standing beside a not too successful back horn project.

Pros: Jump factor, big sound.

Cons: Hollow sounding, impossible to move around due to the MDF construction and sand filled voids. I’ll never do this again.




Fostex 168z in a BIB

Much better sounding than the back horn above. The BIB sounded great in corners retaining all of the drivers positive traits. It’s certainly one way to go with this driver but I prefer the large ported box because it’s smaller and has a bouncier, more fun bass. The BIB is dryer sounding and probably more accurate (flatter).


My boys, Jeremy and Jason, helping me build a BIB!




Fostex 168z in Ported Box (24L)

It sounds good up against a wall or in a corner but never fully satisfies since bass extension isn’t great. It’s ok and can be satisfying but does not allow this excellent driver to reach its potential. Build it if you lack space and can’t build the larger box otherwise, I’d say the overall performance is only average. The box is tuned to 62Hz.




Fostex 168z on Open Baffle 

Certainly a good performing speaker. It satisfies on many levels but can sometime sound dry. Although I like this speaker I still prefer this driver in the large ported box. Here I have mine set up on top of H-frames (Alpha 15). Just about anything sounds great on top of H-frames! The baffles are 18″ squares. Using Thorsten Loesch’s Open Baffle Spreadsheet (speakers two feet from the rear wall) my simulations predict a rolloff around 250Hz (the red line is for the Fostex 168z). Clearly there are better choices for open baffle but I was curious and happily listened to these for months before taking them apart.

OB-freq-18x18-baffle fostex-168z-open-baffle



2 thoughts on “Fostex 168z – A Wonderful Full Range Driver

  1. Dear Zilla:

    I just put together a BK-16 with FE168 Sigmas. I’m pretty happy with them- though I need to tune them somewhat. Based on your findings, sounds like I might be happier with them in an approx 46 litre Nagaoka (or similar) ported box you mentioned above. I would like to build these; however, I was hoping to find some specific dimensions and info as I am not yet a cabinet designer. Can you point me to specifics on this speaker box? I have woodworking tools so can build the box myself. Meanwhile, I’ll keep looking. Thanks, Kip.


    • Kip, the original website with this design does not specifically provide dimensions. It just says “Inner cavity 46 litter”. To calculate the cubic feet for a cabinet simply multiply LxWxH and divide by 1,728. This gives you the cubic feet for the cabinet. Next go to Google and look up “cubic feet to liters” which will bring up a simple conversion calculator. Enter the cubic feet to convert to liters. I hope this helps.


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