I finally got around to a final modification to the “built-in” speakers of the entertainment center (AKA Speaker IV).  The way the speakers sit in the cabinet leaves a gap of about an inch between the baffle and the door.  That gap is an acoustic mass that has to interact with the speaker output, creating resonances.

Solution: add some acoustic foam around the front of the speaker to seal the gap.  So the foam cut-outs for the drivers are something of a hatchet job.  It works.  Well.  The mid-range, such as voices, are so much clearer, more intelligible.  Little details that were masked before are now discernible.

Drivers are a 2″ G2Si ribbon tweeter and Peerless 6.5″ HDS series mid-bass.  Cross-over is acoustic 4th order LR at 2.5 kHz.  The mid-bass is in a sealed cabinet tuned to 80 Hz.  Why so high?  The intention is for these to be crossed over to a subwoofer at 80 Hz as “small” speakers.

Response tested sitting about 32″ off the floor – pre foam.  (I’ll do an update when I do a post-foam test.)  Test level is 1 watt, measurement distance 18″.  Measurement window is about 3.5 msec, so the response is smoothed.

The distortion levels are respectable.  The distortion above 1 kHz is mostly 3rd harmonic (green) which suggests the ribbon tweeters would sound best crossed over above 4 kHz, as well as the mid-bass could be crossed over lower as part of a 3-way design.  (Will have to confirm with additional measurements of the individual drivers.)  Alas, not a big enough opening in the entertainment center for 3 drivers.