Sentinel Surround
by Keith Kidder 19/06/03

<note: most pictures have a larger one linked to the thumbnail>

Goal: I'm really kind of a two-channel guy, but I thought I'd give this Home Theater thing a try.  The Sentinel Surrounds were designed to provide rear ambience in my HT setup without ugly or bulky boxes mounted to the wall.  My wife has given them her full approval.

Drivers:  Vifa K10 4" woven fiberglass cone midrange.  Fs: 84Hz.  These drivers have a smooth response extending out past 15K. (Note: the K10 is out of production, a suitable replacement would be the Vifa MG10MD09-08)
Enclosure:  1/2" (12mm) MDF Transmission Line.  Taper ratio: 1.35:1.  External dimensions: 36" x 5" x 5".  Stuffing: 2 - 2.5oz.

Crossover:  None.

An angled internal baffle was added to create the taper

These plans are laid on their sides -- clik image for larger dimensioned plan.

Skipping ahead... Although I did try several RL circuits for baffle step compensation, listening tests showed that the Sentinels sounded best with no shaping circuits.  This is no surprise since the Sentinels were designed to up against the back wall of my living room.  Even in my living room the bass is impressive for such small drivers.  In order to achieve a more diffuse sound, one driver faces up (reflecting off the wall) and the other faces out (away from the couch).

Sure they're a tad bit soft on the top end... but who cares, it's just home theater.  Actually they sound decent for music and perfect for HT rear channels (in my opinion)
Sentinel Surround impedance.  I prefer to stuff the TL until things just start to smooth out.

I decided to experiment with pressure sensitive adhesive (PSA) veneer for this project.  Worked better than I thought it would.  The low initial tack is more forgiving than contact cement.  I used a warm iron to make sure the adhesive was good and set.  Everything seems to be holding quite well and I'm sure I wont have any problems in the future.  I may use this again for other quick and simple projects but if I'm going to be working on a larger more serious project I think I'll stick with the standard solvent-based contact cement and paper-backed veneer (less expensive too).

A coat of Danish oil and two coats of lacquer really made the figure on this cherry pop out.  For the fun of it I also knocked out a little center channel. Grills held on with magnets


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