One day my buddy asked me what he could do with a pair of 4 inch Pioneer car audio coax speakers he got at Walmart for $55.  They had been lying around for awhile and he wanted something he could use in a house, not in a car.  He had already measured the t/s parameters with LIMP (ARTA) and the first thing that caught my attention was the high qts, weighing in at 1.3.  With a workable 113 hz fs, the only alignment I considered seriously was open baffle. 

 

 

We modeled it quickly with XLBaffle to make sure it would actually work (shown compared to the OB friendly Eminence Alpha 15A loudspeaker on a 20 inch baffle just for comparison).  I was surprised at how well it modeled and it only needed an 8 inch wide baffle.  It's a given that these speakers can't do bass at all but we were pleased to see response low enough to blend with a carefully placed subwoofer or two.

 

 

 

Then I did a much more exhaustive simulation with MJK's Mathcad Single Driver OB worksheet.  Note that neither of these graphs take the tweeter or crossover into consideration and the midwoofer is modeled as a rigid piston so the models won't match the measurements exactly.

 

 

 

Both models clearly show the problematic first diffraction peak at around 700 hz.  There's a couple of things you can do to deal with the diffraction but that's not a big concern at this point.  The important thing is that both models predict strong output down to around 150 hz.

 

 

 

 

The models looked good so he built them.  Then I measured them with Room Eq Wizard (below).  I use my laptop as source and uncalibrated mic which is fine for getting a good idea of what's going on but obviously not the last word in accuracy.  Measurement was taken at 1 meter, power level unknown, in the middle of a room, a few degrees off axis, ungated, smoothed 1/3 oct to make the hf easier to read.  As you can see, the simulations accurately predicted trouble around 700 hz.  We haven't bothered to fix that yet since he hasn't complained about it.  The big hole at 5 khz is a result of poor integration of the cheap midwoofer and tweeter.  The crossover - probably a single small capacitor - is hidden somewhere in the plastic molding so there's nothing that can be done with that.

 

 

 

He uses these speakers with a subwoofer and he's pretty happy with them.  I like them well enough although I've never had a chance to get really critical with familiar music in a room that I'm familiar with.  It's clear that these are not top shelf audiophile quality but it was a quick, easy, inexpensive and satisfying project.  I would have liked to see a more ambitious driver chamfer but even as is the price/performance ratio is great and it's hard to imagine a simpler build.