I've been a dipole speaker enthusiast for many years. I suspect that I've owned as many as 7 pairs of Magnepan speakers over the years including the outrageous Tympani IIICs with their 8 panels. A number of years ago, I reviewed a pair of MartinLogan Aeon-i electrostatic speakers and never looked back. I purchased the review samples and still have them. So happy have I been with the M-L speakers, which have never given me a moment's trouble or regrets in all the years I've owned them that when I got the chance to review the company's small near-field speakers called the Motion 4i, I jumped at the chance.
Motion 4i Description
These small speakers are designed to set on a pair of stands, or perhaps a bookshelf or, in my case a desktop. These speakers are 12.6" x 5.6" x 5.7 (32cm x 14.3cm x 14.5cm) and weigh 6 pounds or 2.72 Kg each. The front of these tall, narrow, piano-black speakers is straight with a metal grille held on the front of the cabinet by magnets. From the rear, the cabinets are curved in a concave fashion and are ported with a Helmholtz resonator. Also on the back is a captive threaded sleeve for mounting on a wall with the included wall mount plate.
The Motion 4i is a fairly straightforward small speaker with a 4-inch “woofer” giving response to 70 Hz ± 3dB. The system crosses over to the tweeter, which is absolutely most interesting feature of this speaker system at 2900 Hz. The 4i has what M-L calls a Folded Motion Transducer of 5.25” X 1.75” (2.6cm X 3.6cm). This tweeter is, in reality, an adaptation of the famous Heil Air motion Transformer first invented by engineer Oscar Heil at ESS Systems, Inc. This transducer works very differently from a normal cone or domed tweeter in that it works like an accordion in that the “diaphragm” is pleated and works by squeezing air out from between the pleats as they compress together and expand at an audio rate. The advantage of this system is that it is very low in distortion and doesn't have the modal breakup that often plagues normal apex driven piston-like tweeters. The result is a small system with a frequency response of 70 to 23,000 Hz ±3dB. Interestingly this is almost identical to the frequency response of the famed BBC/Rogers LS3/5a. Sure, the top end of the M-L goes a tad higher, but the main difference is that no LS3/5 from any company licensed to make it has a tweeter as good as that of the Motion 4i!
When seen with the metal grill removed, one will notice, that below the woofer, there is a strange looking plastic disc poking through the cabinet. This is not another driver, but is, in reality, the back of the unique Helmholtz radiator and allows the resonator to act as a semi-folded horn. Behind that plastic disc, the low frequencies make a 180 degree turn on their way out of the box. I've never seen a Helmholtz resonator that worked this way in any other speaker.
MartinLogan recommends powering the 4-Ohm Motion 4i with between 20 and 150 WPC. I use a Napa Acoustics NA208A hybrid tube/solid-state integrated amplifier of 25 Watts/channel and this seems to be plenty for these speakers (I don’t know whether or not the Napa amp doubles its power at 4 Ohms as opposed to eight Ohms.). The amp is sourced from China by the San Francisco Bay Area Company Napa Acoustics and though small, it performs admirably for its size, cost and power. It has vanishingly low distortion and very flat frequency response. The amp is connected to the Motion 4i speakers with Sewell Direct's excellent “Silverback” 12 Ga 6 ft speaker cables terminated in very high quality banana plugs (http://tinyurl.com/yxmvbj9t). The Motion 4is have unique banana jacks which are mounted flush with the back panel and “grab” the plug when inserted. There is no provision for spade lugs or bare wires.
The Sound: Bass
It should be apparent from the specs that these speakers aren't great shakes in the bass department. Being 3 dB down at 70 Hz and 6 dB down at 60 Hz tells us that the low frequencies drop like a stone below 70 Hz. However, this is somewhat misleading. The bass on these speakers is very well defined and very well controlled. Low frequency transients are fast with little or no hangover. When playing something like Saint-Saens' Symphony #3, “The Organ Symphony” (Reference Recordings (RR-136), the organ comes through loud and clear. While not very deep, the bass is taut and clean and in the final analysis quite satisfying, especially for a desktop computer speaker. But if you are a bass freak, I'd suggest you augment these speakers with a good pair of subwoofers or go another route.
The Sound: Midrange and Tweeter
AS Mentioned earlier, the glory of this speaker system is the Folded Motion Transducer tweeter. Starting at just below 3KHz, this tweeter is simply amazing. It reminds me so much of MartinLogan's electrostatic “house sound” that it's uncanny. As I write this I'm listening to Jascha Heifetz playing the Rozsa Violin Concerto (Miklos Rozsa wrote this superb concerto especially for Heifetz in 1956). This recording was made in that same year for RCA Victor in the “golden era” of stereo. It sounds magnificent and images like gangbusters because, like all early RCA Victor Living Stereo recordings, it was made with a minimal microphone technique of two or three microphones only. Heifetz’ violin, a 1714 “Dolphin" Stradivarius, heard through these speakers is uncanny and sublime. It sounds so clean and articulate, that I must credit the M-L's tweeter for this superb high-frequency performance. The orchestral background with Walter Hendl and the Dallas Symphony is simply gorgeous with these speakers, each instrument is in its proper place and size. The sound is simply sublime and it just sings via the Folded Motion Transducer on the MartinLogan Motion 4i speakers.
These speakers are moderately priced at US$249.99/ea and may be the least expensive speakers on the market to sport an air motion transformer type tweeter. For that reason, they are bargains that punch quite a bit above their weight. If you are looking for a really good, affordable pair of speakers for the desktop, the vacation cabin, or for a small stereo system in a dorm room or small apartment, I haven't heard anything that comes even close to sound quality of the MartinLogan Motion 4i at anywhere near their price poiint. I would say that except for that last octave of bottom-end, that these modest speakers are pretty much perfect for their intended application. That they beg comparison with the latest incarnation of the BBC/Falcon Audio's LS3/5a (US$2995/pair) is just gravy. Believe me the MartinLogans sound quite a bit better than this famous Brit from “Auntie Beeb*”. I once worked for a radio station that used the Rogers version of the LS3/5a as studio monitors, so I'm quite familiar with them.
However, if you are bass freak, you're gonna need to add subwoofers or try another speaker. MartinLogan has an entire line up of the Motion series of speakers at all price-points up to around $3000. All of these use the Folded Motion Transducer tweeter and have the same effortless top end that the Motion 4i's exhibit. Of course the bigger speakers have more bass and all sound superb. I hesitate to recommend the top-of-the-line Motion 60XT because of its price (US$2999.95/). For that money, one can buy a pair of MartinLogan's ElectroMotion electrostatic hybrid speakers, and I have friends who own these and I think they are a better buy for less money. Besides the US$500.00 difference between the 60XT and ElectroMotions can buy an awful lot of music! The Motion 4i is highly recommended and might just be the most articulate small speaker one can buy for the money.
* “Auntie Beeb” is the nickname that the British gave their beloved BBC many decades ago, and it has stuck.