Transcendent Sound

Making Music Better

 

Fostex Low Cost Satellite 

The design goals for this project were super easy assembly, small size, and dirt cheap with high performance.  All were obtained.   


The driver used is the Fostex  FF165WK.  To ease assembly, a pre-manufactured enclosure was used.  (From Parts Express) All that is required is to cut the holes for the driver in the front baffle.  The front baffle is held on by bolts.  After final assembly and everything checks out, glue it in place and use the bolts as clamps.  As an added plus, replacement baffles are available if one is ruined. 


The interior volume of the cabinet is 0.38 cu. ft.  External dimensions are 8 inches wide, 10 1/2 inches deep and 14 inches tall.  The port used is just a 1 1/2  inch hole in the 1 inch thick baffle.  The speaker is a 6 1/2 inch model that mounts in a 5 3/4 inch hole.  Don’t stuff or line the enclosure with anything.  Altering the internals and damping will have a severe effect on the midrange. 


The speaker is a bit bright and needs a notch filter to tame down a response peak at 2 kHz.  This circuit will compensate for nearly all of the peak.  Use an air core inductor with at least 20 AWG wire and a quality film capacitor.  
















The sound is razor sharp with incredible detail and openness.  They should continue to smooth out as they break in.  Full range drivers can easily need 100 hours to break in.  The F3 (-3dB) point is about 85 Hz.  That is quite acceptable as they are intended to be used with a subwoofer.  They can be driven full range but for maximum dynamics and volume at full power (22 watts), it is suggested that they be rolled off at about 100 Hz with at least a 6 dB/octave filter.  An active 12 dB/octave filter would give better results.  Transcendent amps with a 100K input impedance can be wired for a 6 dB/octave, 100 Hz filter by just inserting a .015 mfd capacitor in series with the input.  This is shown below on the 300B amp by adding a second input jack.



















With the second jack, a non-filtered input is always available.  That would be the lower jack in the photo.  The white wire is the amp input signal.  Connect the new RCA jack ground to the existing one.   


The speaker has a sensitivity of nearly 92 dB for one watt.  It sounds marvelous with the 300B OTL and plays nearly as loud as the Tang Bands.  The Son of Beast amp can drive this speaker to well over 105 dB, and is a perfect match for a top quality, low cost high-end system.  The Mini-Beast is also a good choice yielding great dynamics and smooth sound.   


In direct comparisons with the small box Tang Band, the Fostex has the edge in clarity and openness while the Tang Band has the edge in tonal accuracy.  Which is best is primarily an issue of personal taste.  With the small size of each, it’s easy to swap them out and enjoy both.      


The cabinets only cost $85 each and the drivers cost $80.  A pair can be built for less than $400 including shipping and miscellaneous parts.  Add $200 for a bucket sub with plate amp and you’ve got yourself a very high quality speaker system that takes up very little space.  The crispness and detail also make them superb for use in a home theater system as they can resolve the nuances of all those sound effects.  The are very non-directional creating the illusion that the sounds are emanating from the screen.


Using a 15 band graphic equalizer will allow the response to be perfected for watching movies.  These are affordable ($100 to $150) and available from professional sound equipment dealers.  They usually only have XLR connections but adapters to RCA jacks are inexpensive. One technique is to  adjust the 25, 40 and 63 Hz bands to -12 dB.  This will keep those large sub bass signals out of the speaker.  Then boost the 100 Hz band about +4 dB and the 160 Hz band about +2 dB.  That will level out the response in the upper base and give male voices body and weight.  Reduce the 1.6 and 2.5 kHz bands about -3 dB and the 1.0 and 4.0 kHz bands about -2 dB.  That will take out the last bit of brightness.  Couple with a properly adjusted subwoofer and your movies will come to life.