It all started with a desire to dust off the top of my Klipsch type corner horns.  That's when four drivers were discovered on top of one horn, the D1, D2, D3 and D4; the 1824M and the 54-060 were on then other.  Well, my curiosity got the better of me so the 8 drivers were put on the work bench.  Then I had to rummage through the house looking for the D5, the brown one, which I knew I had but couldn't remember where it was.  After several minutes of searching, I found it in the corner of a bedroom aside a pair of   JBL 2397 horns   each with 2328 and 2327 adapters.

One of the Electro-Voice drivers, the D3, had very high resistance to the coil, like greater than 200 ohms.  That fault was traced to the solder junction connecting the braid to the terminal inside the head.

All are Electro-Voice T25 drivers collected over the years.

In the rear are two 54-060 driver units I bought many years ago in my search for a driver that would go as low as 400hz.  After adding a 0.050" shim to the gasket, that was achieved but at a loss of about 3dB in output which wasn't really a problem.  Non-linearity in the diaphragm excursion could create distortion but not having a distortion analyser at the time, that information wasn't measurable. Purported to have a frequency response from 100hz to 8khz, no mention was made that it's about -14dB down at 300hz and 4khz, (see Fig 4)  They were probably intended for use in  public address systems and used as such, they'd do extremely well

Later acquisition of the1824M units (center row) proved satisfactory.  Twenty or more years later, acquisition was made of a pair of Klipsch K55V drivers which were already modified to go down to 400hz  efficiently.

The D5 is the brown one in the foreground.

Response and impedance curves can be seen in Figs 1 through 4.  Those curves were run on the exponential horn shown in photo 3 with exception of the set of curves in fig.3

A note about other stuff in this photo.

The amplifier (at right) is an H.H.Scott 99B dating to 1954 and in almost perfect working condition.

The 4 knobbed device in the rear is a true RMS wattmeter using a Motorola MC1594L multiplier chip. Using a scope as a monitor, it will show instantaneous peak watts regardless of frequency and speaker impedance fluctuations.  An engineer friend designed it and taught me how to use a wire wrap tool to do the wiring.   This is a prototype and was never soldered.  It still works.

The 500hz horn with adapters. The first converts the 2" diameter throat of the horn to a throat of 1.4" diameter.  This is reduced again to a throat of 1 inch diameter.  the top adapter converts the 4 bolt pattern to a 1.375"-18 hole and thread, the standard size.

The horn is ABS material and if you're curious:

Acrylonitrile butadiene styrene

The testing setup.  The 54-060 driver is on the horn

A closeup of the horn with adapters and the Electro-Voice T25 driver, the oldest one in the collection

QTR watt 1m on500hz horn RED=D1; GRN=D2; ORN=D3; BLU=D4 THD pink=D1 yel=D2 grey=D3 blk=D4

Note that these curves were run at 1/4 watt, so increase the curves by 6dB.  This was the result of the 108dB SPLs while running at 1 watt

There was a D5 response but the file somehow disappeared, probably an overzealous directory cleanup.  However, the response of that driver on the diffraction horn in fig 5 shows that the response on the ABS horn should be similar to these

If those ABS horns weren't currently in use, another response would be performed.  

The RED curve shows the effect of the horn on the driver's impedance,

The brown T25 driver on the diffraction horn.  The responses were run with the horn's long axis vertical (43 RED on axis and 44 PINK 30 degrees off axis)  and horizontal (45 DARK BLUE on axis and 46 LIGHT BLUE 30 degrees off axis)

All responses are gated (quasi anechoic) to remove room reflections 

As can be seen, the on axis responses are nearly identical.  One would expect the off axis response to improve with the long axis vertical but the opposite shows.  This result was double checked.

QTR watt 1m 54-060 on 500hz horn GRN=1 RED=2 BLUE=THD-1 PINK+THD-2

These response curves show that the 54-060 driver is intended for PA use.

PHOTOS 6 & 7

The oldest EV driver I have.  It's 16 ohms and of the four EV T-25 units, it has the best response, see fig 4, black trace.  The diffraction horn shown below  measures 19" x 3" x 12".  It's made of fiberglass and I had to wedge a 1" dowel about three inches in to stiffen the sides.  It's barely visible in the right photo below.  The oak beams clamped to the perimeter were added to further stiffen the horn since it's not mounted on a baffle.  The dowel had the most effect.

This horn & driver assembly has been lying around here since the late seventies.  The diaphragm is the original one.

The magnet assembly is chromium plated.

These two photos show the horn horizontal and 30 degrees off axis, LEFT and vertical on axis, RIGHT.  These were taken in Sept., 2022.  The response curves are those in fig 3 above