If you’ve ever dipped your toe into some form of high-performance motor sport, you know: The best race-car engines spin torque and exhale horsepower—with intoxicating ease. They’re engineered to be responsive. Depress the clutch, toe the throttle, and watch the tachometer instantly pin itself. Engage the clutch—your chest contracts and your head gets light. Then later . . .
Back in your Ford Fiesta, its revving engine sounds distant, muffled. Your body can’t feel the powerplant’s power. In gear, the Ford feels soft and hesitant, not responsive.
That’s how Klipsch’s highly responsive Reference Premiere RP-600M loudspeaker with its horn tweeter ($549/pair) compares to conventional box speakers with direct-radiating dome tweeters
I first encountered this affordable stand-mount at my friend Sphere’s house. When he played Miles Davis’s In a Silent Way (LP, Columbia CS 9875), I noticed all these formerly obscure musical happenings that made me love Herbie Hancock more than I used to. With the Klipsch two-ways, Hancock’s Fender Rhodes piano emerged from producer Teo Macero’s mix in a pronounced, über-electrified way. Every note felt statically charged. At one point I saw Miles, who’d introduced Hancock to the Rhodes, motioning to him, drawing him out, begging for more keyboard. Hancock’s notes revved and floated effortlessly, like orbs of light. My eyes followed his hands—they seemed lifelike, and at their proper height above the floor.
Sphere’s room is big—at least 35′ by 25′, with 10′ ceilings. He’d set up the RP-600Ms about 8′ apart and 10′ from the wall behind them. The next day, I contacted Klipsch.
Horns: A Brief Primer
1925: Chester Rice and E.W. Kellogg develop the first direct-radiating dynamic loudspeakers, based on principles that are standard-issue in most speakers made for domestic use today (footnote 1).
1926: First, Victrolas and radios, then motion pictures that talk. To service the emerging business of talkies, two Bell Labs engineers, Edward C. Wente and Albert L. Thuras, develop the Western Electric 555 compression driver: an extremely light, 0.002″-thin, aluminum diaphragm with a corrugated surround and a light, rigid voice-coil. This piston-coil assembly was set within a heavy, high-powered electromagnetic structure and designed to be easily mounted behind a variety of horns. Its bandwidth was about 300Hz–5kHz. Unbelievably, this ancient high-tech driver is still being used in many of the world’s finest audiophile playback systems.
Naked, the WE555 diaphragm looks a lot like a metal-dome tweeter, and almost exactly like the drivers in some of today’s best and most expensive headphones. I mention this because, without a horn, these aluminum domes become “dome tweeters” that convert less than 1% of the energy supplied them into acoustic output. With a horn attached, the WE555 converts more than 20% (footnote 2).
Horn loading accomplishes two things. First, a horn’s restricted throat mechanically loads the dome (or cone). This restrictive loading creates a region of high pressure that a horn whose flare is of a certain length and rate of expansion can effectively convert to a large, pulsing wavefront at normal atmospheric pressure. This elegant form of tuned acoustic impedance matching not only makes a horn speaker more sensitive to voltage, it reduces the amount of diaphragm excursion required to produce a given sound-pressure level (SPL), thereby linearizing the system and reducing distortion. Within their designated passbands, horns can be incredibly linear and low-distortion—especially at very low and very high SPLs, where conventional direct-radiating speakers compress and distort.
1946: Paul W. Klipsch founds Klipsch and Associates, and patents his design for the famous Klipschorn corner loudspeaker. This original design, along with Peter Walker’s original Quad electrostatic loudspeaker (1957), marked the beginnings of high-fidelity home audio as we know it today. The illustrious Quad ESL was discontinued in 1985. At the Klipsch factory in Hope, Arkansas, the legendary Klipschorn is still being manufactured, 73 years after its launch.
Description
The Reference Premiere RP-600M is Klipsch’s flagship stand-mounted speaker model. It’s small, at 15.7″ high by 8″ wide by 11.9″ deep, and the pair of them fit my Sound Anchor Custom Signature stands (24″ H by 8″ W by 12″ D) as if speakers and stands had been designed for each other. The RP-600M’s “Linear Travel Suspension” vented tweeter is built around a 1″ titanium diaphragm, loaded by a hybrid Tractrix horn whose mouth measures 5.75″ by 5.75″. The tweeter horn’s first expansion is circular and seems made of hard plastic; its second expansion is made of a soft, rubber-like material. The tweeter is crossed over at 1.5kHz to a direct-radiating, 6.5″ Spun Copper Cerametallic woofer with a rear-firing port with a flared, Tractrix profile. When I tapped the RP-600M’s enclosure with a knuckle, it sounded like a thinnish (15mm) particleboard drum with minimum internal bracing. My review samples were covered in a black ash vinyl that felt extremely durable and solidly applied.
The RP-600M’s sensitivity is specified as an extraordinarily high 96dB/W/m, its frequency response as 45Hz–25kHz, ±3dB.
Setup
Getting the RP-600Ms to serve up their full menu of pleasures required positioning them with care. The speakers’ off-axis response delivered a sweet spot at least two people wide, and generated satisfying instrumental tone everywhere in my room. At 10′ from the front wall in Sphere’s room, the RP-600Ms’ tonal character leaned toward lean, but so what? They made a mile-deep soundstage. In my room, moving them 3′ from the front wall reduced soundstage depth by at least 50%, but the bass and lower midrange were fuller—more to my liking. I also discovered that each inch I moved them farther from or closer to the front wall changed their tonal balance. With the Klipsches only 66″ apart and 75″ from my ears, their front baffles precisely 29″ from the wall behind them, and no toe-in, the weight and timbre of Alexander Melnikov’s piano as he performed Book 2 of Debussy’s Préludes (24-bit/96kHz FLAC, Harmonia Mundi/Qobuz) was just right for me.
I also noticed that when properly Blu-Tacked in place, the Klipsch boxes seemed to merge with my heavy, 24″-high, four-poster Sound Anchor Custom Signature stands. I have zero doubt that these heavy stands positively contributed to the quality of sound I achieved.
I had a slight preference for the sound of the RP-600Ms with their magnetically attached grilles in place, but my review observations were made without grilles.
Listening
Listening to soprano Elly Ameling sing J.S. Bach’s Cantatas 51 and 199, with the German Bach Soloists under the direction of Helmut Winschermann (LP, Philips LP 6500 014), I noticed how visceral and dynamic a human voice can be. With my First Watt SIT-3 power amplifier (18Wpc) driving the Klipsch RP-600Ms, the sound of Ameling’s voice was vibrantly present in the room—I repeat, vibrantly present, physically clear, and beautiful to behold. The only indication that I was listening to her through budget speakers was a moderate lack of soundstage width, and some decreasing imaging focus, as my attention wavered from the left to right of the stage.
Footnote 1: Mix Staff, “1925: Chester Rice & Edward Kellogg, General Electric Co. Modern Dynamic Loudspeaker.” Mix, September 1, 2007.
Footnote 2: Eberhard Sengpiel, “Loudspeaker Efficiency versus Sensitivity.”