Re: Why Do TEF Systems read 3-5 dB high ?
Ivan,
As far as I’m concerned, the jury is not out regarding whether JBL’s SRX 718 or 728 are half space measurements, it is confirmed with JBL’s measurements of the same speaker used in the SRX cabinets measured in half space on the roof of one of their buildings.
I have also measured the 728 side by side with my ported dual Lab 12, the relative measurements confirm that the JBL measurements are half space, or that my 2x12 cabinet has magically gained 6 dB over what Eminence sensitivity specifications show it to be.
Regarding near field vs. far field differences in measurement, this effect may be noticeable at one meter if the horn mouth was significantly larger than the front loaded speaker’s cone area, say a 4 x4 foot horn mouth compared to a single front load 18.
But the TH-115 has a similar mouth area to the EV2118 cone area.
Having done a quick test with horn loaded vs. BR cabinets to see if there was a change at distance relative to near feild results, using relatively small cabinets, the one meter results held up to far field results. Phil Lewandowski repeated my experiment in better conditions (no nearby buildings), comparing a Growler to a JBL SRX 718, his test confirmed that both cabinets followed the inverse square law near perfectly from one meter to 30 meters.
I do agree that a comparative testing of subs (especially large units) at 10 meters is better than one meter, looking forward to those tests when you get a chance.
Art Welter
