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Micro Speakerpeteraczel | 22 July, 2009 15:54
Powered Micro Loudspeaker Soundmatters International, Inc., Reno, NV, USA. Voice: (775) 981-1460. Fax: (775) 981-1465. E-mail: support@soundmatters.com. Web: www.soundmatters.com. “foxL” powered stereo loudspeaker, $199.00. Tested sample on loan from manufacturer.
It’s the size of a Baby Ruth candy bar, maybe just a little bit thicker. It’s stereo. It’s self-powered—there are amplifiers in it. It’s a full-range high-fidelity loudspeaker system, for crying out loud! Who would want a loudspeaker that small, designed to be listened to at a distance of 20 inches or so? Let’s go to the source, designer Dr. Godehard Guenther, physicist and former NASA engineer: “Music is a big part of my life, yet so is travel. There weren’t any really small hi-fi-quality portable loudspeakers—so, utilizing a number of our patented and proprietary technologies, I developed one myself. A true labor of love, I named it after Fox, my first grandson.” So it’s for travelers, frequent fliers, joggers, hikers, bicyclists, anyone on the move who doesn’t like those earbuds in his ears (and I can’t blame them). Yes, it will play louder when plugged into the wall than in its portable mode, but I’m getting ahead of myself. The Design The “foxL” is a small slab of metal, 5.6 by 2 by 1.2 inches in size (that’s 142 by 51 by 31 millimeters). It houses the following components: (a) for the left and right channels, two 25-millimeter dual-voice-coil full-range drivers, called “Twofers” because they tweet and woof; (b) for both channels, a so-called BassBattery that is both a rechargeable lithium battery and an acoustic bass radiator (clever!); (c) four digital amplifiers with a total specified power-output capability of 8 watts at <0.1% THD; (d) on/off switch, volume control, various input jacks, etc. One of those jacks is actually for an optional powered subwoofer (Soundmatters offers one named SUBstage) to extend the range of the foxL below the BassBattery’s specified low-frequency limit of 80 Hz—but then of course the system is no longer very portable. The portability factor has to be further qualified by the power supply options. The wall wart that comes with the foxL and is used to recharge the lithium battery delivers 5 volts to the digital amplifiers. When it’s plugged in, the maximum SPL of the speaker is considerably higher than in its portable mode on battery. The battery’s output is only 3.6 volts. Setting a sufficiently loud listening level is a little bit tricky with the foxL because of the interaction of the power supply, the listening distance, the setting of the volume control, and the input level. With everything trimmed in, the unit can produce a sound level totally disproportionate to its size. Dr. Guenther apparently knows something that others don’t. Soundmatters also offers the foxL with Bluetooth option for wireless streaming, at $249.00. I haven’t tried that one. The Measurements The most interesting measurement in this case seems to be the maximum obtainable SPL. The published specifications claim 95 dB at a distance of 50 centimeters (19.7 inches) with the AC adapter plugged in and delivering 5 volts. I found the limit to be just short of 90 dB with the most favorable frequencies, the SPL being highly frequency-dependent. At shorter distances it’s possible to hit 95 dB. On battery, with 3.6 volts, the SPL limit is proportionately less. I don’t want to make too much of an issue about the discrepancy between the specs and my results because Soundmatters doesn’t specify the exact physical and electronic conditions of the SPL test. Maybe I didn’t do it their way. Frequency response is the other major question when it comes to a micro loudspeaker, and it’s reasonable to measure it in the nearfield because that’s where the listening takes place. Quasi-anechoic (MLS) measurements at 1 meter or 2 meters are not really relevant here. Fig. 1 shows the small-signal nearfield response of the right-hand Twoofer (which is a somewhat smoother version of a very similar response obtained when trying to sum the nearfield output of both Twoofers). Between 200 Hz and 5 kHz the response is reasonably flat, ±2.5 dB; then it rolls off slightly, and quite smoothly, to 15 kHz; the small 18 kHz resonance is normal. Fig. 1 is not valid below 200 Hz; you have to go to Fig. 2, which shows the small-signal nearfield response of the BassBattery. The curve indicates strong response down to 80 Hz and useful response down to 60 Hz, a profile similar to that of a typical minimonitor (just scaled down). The published full-range spec of 80 Hz to 20 kHz is not very meaningful because no ±dB range is given, only an obscure (possibly incorrect) DIN number. Overall, I would call the frequency response of the foxL remarkably good, considering the extreme miniaturization and special purpose of the design.
Fig. 1: Small-signal nearfield response of right-hand 25-mm driver.
Fig. 2: Small-signal nearfield response of the BassBattery. I thought I heard some low-frequency distortion in my SPL tests, so I ran a not particularly challenging harmonic distortion test of a 150 Hz tone, with the microphone measuring the BassBattery at a 50-centimeter SPL of 80 dB. (I couldn’t make it any louder without buzzing.) Fig. 3 shows the result. The FFT indicates 2nd harmonic distortion of –23 dB (7.1%), 3rd harmonic distortion of –28.5 dB (3.8%), 4th harmonic distortion of –41 dB (0.9%)—shall I go on? Those are pretty awful numbers for a far from stringent test, even allowing the possibility of somewhat better results if the test had been structured differently. At the end of the day, it appears that the foxL is a very clever little gadget rather than a full-fledged high-fidelity device. There are no miracles.
Fig. 3: Nearfield spectrum of a 150 Hz tone reproduced by the BassBattery, at a 0.5-meter SPL of 80 dB. The Sound This is obviously one of those quirky electroacoustic components that stand or fall on the perceived quality of their sound, regardless of measurements. I approached the listening evaluation with skepticism and I was rather pleasantly surprised. The foxL has sufficient range and dynamics to produce a surprisingly lifelike sound. If your face is close enough to it, it sounds like a grownup loudspeaker, not like an amplified candy bar. To be sure, the sound is a little bit thin and pinched as the music gets louder, and there is audible bass distortion from time to time (depending on the program material), but the overall impression is one of realism rather than sonic miniaturization. The stereo effect is minimal; there is no “air” around the sound; but what do you expect, with the left- and right-channel drivers 4 inches apart? Also, strangely enough, I sometimes heard more distortion with the AC adapter connected than on battery power, but the effect wasn’t consistent. I could start speculating about the cause of this anomaly but I won’t. When all is said and done, the foxL is somewhere near the edge of the category famously characterized by the great Samuel Johnson: “[It] is like a dog’s walking on his hinder legs. It is not done well; but you are surprised to find it done at all.”
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