Here is a set of measurements I made of the Truextent Be4016 beryllium dipahragn (16ohm version) in a 2450SL core (1.5") on the rectangular 90x50 PT waveguide (PT-F95HF).
For comparison purpose the measurements also include other JBL OEM diaphragms.
All measurements were taken under the exact same conditions:
- dayton mic calibrated by cross spectrum
- mic at ~40cm from the horn mouth (not far enough to get a meaningful response curve, but ok for comparison purpose), exact same position for all measurement
- Studio Projects VTB1 V preamp ("tube blend" turned off)
- creative labs sound card (line level), not calibrated
- holmimpulse software in sweep mode
- Ev dx46 active crossover in digital input mode, no eq or filter except a FIR HP at 600Hz (no influence on phase)
- Ram-audio S4044 power amp set to a very moderate SPL
- 75uf protection capacitor (shall not have much influence on phase above 1.5khz, even for the 8ohms diaphragms)
- PTF-95HF horn (no really usable under 1khz, so only the HF response can really be compared)
- 2450SL core (1.5" coherent wave phasing plug, 4" diaphragm, neodymium motor)
The diaphragms under test are:
- JBL D8R2450SL (2450SL): 8 ohms 4" Titanium diaphragm without ribs but with aquaplas, used in the 2450SL, 2452H-SL, and 475nd
- JBL D8R2450 (2450Ti) : 8 ohms 4" Titanium diaphragm with ribs, used in the 2446H/2450H/2451H
- Truextent Be4016 (2450Be) : 16 ohms 4" Beryllium diaphragm
The 16ohms truextent diaphragm was of course given 3dB more level in the active crossover, so every diaphragm received approximately the same wattage, as is confirmed by the fact that the levels are matched in the low end.
As you will see the measurements do track the ones found in the Truextent white paper quite well:
In a second set of measurements, post #4, the 2450Be is compared to a 2435HPL