To Doug Schneider,
As per Philip Beaudette's review of the Monitor Audio GX100, these new MA speakers are great and the review is one of the reasons why I’m getting a pair. But could you give a little bit of explanation on the NRC measurements for the speakers? To tell you frankly, I know nothing about the parameters being mentioned. But I feel this is one of the opportunities to learn more about hi-fi.
The measurements we perform on speakers at Canada's National Research Council (NRC) show on- and off-axis frequency response, sensitivity, and distortion, as well as other things such as impedance, electrical phase, and if the frequency response deviates as SPL increases. More measurements could be done, but these do tell quite a bit about a speaker's sound and if it meets the manufacturer's specs.
In the case of the Gold GX100, the various frequency-response charts show a relatively linear balance from about 70Hz up past 20kHz (+/- 3dB), with useable bass to below 50Hz, which is good for a compact design. Dispersion is very well controlled right up to 75 degrees off the tweeter axis, which is as far as we measure, indicating that the designers did an admirable job of blending the ribbon-based tweeter with the cone-based midrange-woofer. Given these specs, GX100 should sound fairly full, and because its dispersion is well controlled, it should be quite tolerant of room placement. Sensitivity is almost 87dB, which is average for a speaker of this size and type, and the impedance stays mostly above 8 ohms, meaning that the GX100 is fairly easy to drive and shouldn't require too powerful an amplifier to work well.
But the GX100 isn't completely neutral -- the frequency-response measurements indicate that the speaker will have some character. The "listening window," which is an average of five measurements taken around the front of the speaker, shows some emphasis from 3kHz to 10kHz. This could make the GX100 sound a little bit forward, which will likely appeal to some listeners and not to others. There's also a bit of emphasis between 500Hz and 1000Hz, which might add some fullness to the midrange -- likely a good thing overall. The slight dip at 3kHz indicates the region of the crossover, but it's not likely to be audible. The region above 12kHz is down slightly, but not overly so -- the GX100 should sound extended in the highest frequencies, but not bright.
The most concerning thing in the measurements is the distortion that shows up between about 2.5kHz and 5kHz, something that's common with ribbon-tweeter-based designs and, if audible, would likely manifest itself as a hard, edgy sound, particularly at higher listening levels. Why this occurs is pretty straightforward -- the ribbon must extend to below 3kHz in order to blend properly with the midrange-woofer. However, as it extends below 3kHz, the distortion rises due to the diaphragm's limited excursion. (Good-quality dome-type tweeters can extend to about 2kHz without undue distortion, but Monitor Audio's designers used a ribbon because of other benefits this type of driver can provide.) Obviously, that's one of the tradeoffs the designers made in the GX100 in order to achieve a well-controlled dispersion pattern.
Measurements can be a bit tricky to understand if someone isn't well-versed in reading them, but I hope this helps you along. . . . Doug Schneider