Usher Audio Technology Compass X-719 loudspeaker Postscript
I felt that the measurements of the Usher's treble correlated with Bob Reina's subjective findings. However, concerned about the fact that our review samples of the Usher X-719 had arrived at my place with shipping damage, and that that might have affected my measurements, Joe D'Appolito sent me his own measurements of the X-719, with the following comments:
"Fig.1 shows the full-range frequency response of a production X-719 selected at random for testing. No special trimming was applied. Response below 200Hz was obtained outdoors using the ground-plane technique and spliced to the quasi-anechoic response above 200Hz. The microphone used is a ACO Pacific 7016 which is accurate to ±0.3dB below 20kHz. Fig.2 shows the response of the system and individual drivers on an expanded frequency scale. Note the smooth woofer roll off above 2kHz. [Joe's measurements, like my own, were taken with DRA Labs MLSSA system. Though he has averaged his data on a 0.1-octave basis, this will not affect the differences described.—JA.]
Fig.1 Usher Compass X-719, full-range frequency response.
Fig.2 Usher Compass X-719, responses of the individual drive-units.
"Referring to fig.1 you can see that there is neither a low-frequency suckout nor a tweeter peak in this response. I have tested over 50 of the T9550 production tweeters during the design of several of the Usher speakers and never seen a 10kHz peak. The tweeters in the tested samples appear to be defective, possibly damaged in shipment. They are being shipped to me for further examination.
"Regarding the woofer suckout there are two possibilities. The nearfield technique used to get low-frequency response often produces low-frequency response irregularities that do not show up in the far field. Additionally, the X-719 is sensitive to internal placement of the crossover components and enclosure lining, both of which appear to have been disturbed by rough handling during shipment. We have not seen the suckout in any of our testing."
My thanks to Joe D'Appolito for supplying these measurements and for allowing them to be published in this postscript. I am at a loss why my measurements are different from his. I measure a 1977 sample of a BBC LS3/5a at regular intervals to ensure that a systematic error has not crept into my test set-up. I also check against other sources; for example, the exact same sample of a speaker I recently measured had also been measured in the NRC in Ottawa, and other than the 2-pi correction for my nearfield LF trace, my curve overlapped that one.
One factor that may have affected my measurements was that it was unexpectedly cold on the day I measured the Usher X-719, around 45 degrees F. (While I perform the nearfield, vibration, and impedance measurements indoors, the far-field measurements are performed outdoors on a high stand, so that I can minimize the effects of boundary room reflections.) I kept the Usher speaker indoors until the last moment before measuring it, as well as running high-level noise through it continually when it was outdoors, except when I was taking a measurement. I did the waterfall and on-axis responses first; the off-axis measurements in both planes last. I don't think, therefore, that the measurement would have been unduly affected by the ambient temperature.
However, the microphone (a calibrated DPA 4006), having considerably less thermal mass, might have been affected, though it is fair to point out that other speakers I measured on the same day did not display the 10kHz response peak.
I look forward to finding out if, in fact, the review samples' tweeters had been damaged in shipping.—John Atkinson