December 1999

Klipsch Reference Series Model RP-5 Loudspeaker
Not quite up to the normal Klipsch standards.
Review By Dick Olsher

  The Reference Series represents brand new engineering from Klipsch aimed at both home audio and home theater applications. The model RP-5 is the top dog in a lineup that that leads off with the affordable RB-5 ($800/pr). The common denominator is a 1-inch titanium dome compression driver coupled to a Tractrix horn. Hey boys and girls, there’s absolutely no need to be afraid of horns. It’s basic utility was most likely first discovered many thousands of years ago by one of our early ancestors when he cupped his hands around his mouth to intensify a cry for help. Although the names may seem exotic at times, they simply refer to the horn’s geometric shape or flare rate, which may be conical, hyperbolic, exponential, or even Tractrix. You’re probably already familiar with a conical horn also known as a megaphone. Such a device efficiently couples vibrational energy to the air medium. The enhancement can be considerable – as much as 10 to 15 dB. However, unless the proper horn type is selected undesirable colorations are introduced by standing waves or resonances within the horn. Hence, you can appreciate the fact that the traditional knock against horns was that they squawk like a megaphone. Both research and praxis over the past ten years has shown that the Tractrix horn with its large flare rate is ideal for the reproduction of voice. With a Tractrix you can have your cake (i.e., increased efficiency) and eat it too!

The Klipsch Tractrix has been designed to be less beamy than traditional horns and achieves uniform directivity over a 90 by 60 degree field. If you peek inside the horn you’ll notice that the throat is slightly pinched off in the horizontal plane. This gives a more uniform illumination of the horn and a full 90-degree horizontal radiation pattern. It is still a good idea to toe-in the horn toward the listening seat, but small head movements do not produce image shifts. The soundstage remains stable with a much wider stereo sweet spot than I’ve experienced with other horn-based loudspeakers. Furthermore, the cutoff of this horn is sufficiently low that the tweeter is extended to about 2 kHz, making it much easier to blend in a mid-woofer.

For most of us "old timers," the Klipsch moniker is synonymous with the folded corner horn design – Paul Klipsch’s legacy from the 40s. Paul’s dictum that speakers belong in room corners makes a lot of sense whenever bass efficiency is a primary concern. And it usually is in the case of high-efficiency speaker designs where horn loading can push midrange or tweeter compression drivers to sensitivities well beyond 100 dB. The recurrent nightmare for all high-efficiency speaker designers is how to boost bass sensitivity to match that of the upper range. Bass horns with a cutoff frequency in the deep bass would have to be colossal in size and are therefore impractical. A bass horn with an exponential flare rate would require an overall length of 33.5 feet and mouth diameter of 17 feet for a response flat to 20 Hz. Now that’s bass horn with a wife acceptance factor of exactly zero!

One common compromise is to sacrifice bass extension by incorporating a modestly sized folded horn with a cutoff in the range of 80 to 100 Hz. Another approach is to use a powered woofer to cover the range below 100 Hz. The AvantGarde Acoustic Uno, Duo, and Trio loudspeakers introduced just such a configuration several years ago (Uno review coming soon! --ed). The advantage, of course, is lots of bass in a compact package. On the other hand, the bass quality may not necessarily be of horn quality.

In the case of the Klipsch model RP-5, a built-in powered subwoofer is used to cover the range below 90 Hz. An internal 150-watt power amp powers a 12-inch bass-reflex loaded woofer (yes, you do have to plug the speaker into an AC outlet).  An 8-inch aluminum-coned mid-woofer fills in the range from 90 Hz to 2 kHz. The subwoofer level may be boosted form its "flat" position several dB by the use of a rear-baffle pot. However, it isn’t possible to adjust the level of the tweeter relative to that of the mid-woofer.

This is certainly an impressive foundation for any speaker, let alone one priced at $2K per pair. It was precisely this product’s apparent value for the dollar that led me to it. Where else can you find a speaker that is 96 dB sensitive with bass extension to 25 Hz at even twice this price point? And since there are so few choices available to low-power tube aficionados, this promised to be a worthwhile addition to the Single-Ended Triode compatible field. The bottom line was that I could not turn down the temptation. After all, the RP-5 might just turn out to be a genuine Klipsch "Legend in Sound."

There are no two ways about it: you’re either going to love or hate this speaker. Its tonal balance is forward, in your face, and about as lively as they come. If that’s your cup of tea, then you’ll be dancing a jig of joy in your listening room. I liked the clarity and focus of the upper mids and lower treble, but I constantly wished for a more natural blending of the tweeter and mid-woofer. The entire range covered by the tweeter is tipped up and after a while I felt my auditory system synapses become saturated. It was like being in the middle of a spectacular pyrotechnics display! In addition, resolution went off the scale. Both the tweeter and mid-woofer sounded as fast and precise as only metal drivers can. The combination of speed and upper range emphasis did wonders for the resolution of low-level detail. Transient nuances and the subtleties of each recording’s acoustic were laid bare. It was all very impressive, but totally unnatural, as if harmonic overtones were magnified under a microscope.

About this time I was scrambling to find a brilliance or treble control. Unfortunately, none were to be found. An in-room frequency response measurement (with the grille off) at about 3-feet from the tweeter yielded the result shown in Fig. 1 below. Only the range above 200 Hz is presented here, as it is relatively free from room reflections. Often measurements don’t tell the whole story. In this case, what you see is basically what you get: a 2 to 3 dB emphasis (relative to the lower midrange) above 2 kHz – the range covered by the tweeter. The tweeter’s response is reasonably smooth; it’s just that there’s too much of it. A treble control would have been a lifesaver in a situation like this. It would have allowed me to voice the treble to my liking, while permitting a different set of ears the latitude to go "hog wild."

The grille provided with the RP-5 is a pretty elaborate plastic lattice with a thick cloth cover. The situation with the grille on is shown in Fig. 2. The extreme treble takes a hit, and the lower treble exhibits a few more bumps. But the presence region emphasis centered at 5 kHz is still there in its full glory.

Figure 1.

Figure 2.

There was also an audible discontinuity between the subwoofer and the mid-woofer. The two didn’t appear to blend very well. Part of the problem was due to fundamental differences in character between these drivers. The mid bass of the subwoofer wasn’t as detailed and precise as the upper bass of the metal-coned mid-woofer. There was a lot of mid bass and deep bass, and one could always crank up the output of the subwoofer to floor shaking levels. But the definition through this range suffered in comparison with the upper bass. The result was the realization that the drivers weren’t working together harmoniously.

The Klipsch’s soundstage was wide and reasonably deep and mage outlines were nicely focused. I had no difficulty in being drawn into the original acoustic perspective. The relative distance to each instrument, however, was a bit distorted by the heightened brilliance. In the end, the biggest obstacle for me was the tonal balance. After being blown away for 60 seconds, I was sufficiently "metal-fatigued" to want to leave the room. Too bad: a $4 treble control might have turned this speaker around for me.

Specifications
Sensitivity: 96dB @ 1 watt/1 meter
Frequency Response: 25Hz-20kHz, ±3dB
Nominal Impedance: 8 Ohms
Crossover Frequency: 1950Hz and 90Hz
Power Handling: 150 watt maximum continuous (400 watt peak)
Enclosure Type: sealed - Mid Bass; subwoofer - Bass reflex via wide flare, rear-firing port

Drive Components: Three-way system using one 1" (2.54cm) K-105-K titanium dome, magnetically shielded compression driver with a 90°x 60° Tractrix Horn, one 8" (20.32cm) K-1084-S aluminum cone, magnetically shielded mid-bass and one 12" (30.38cm) K-1087-K subwoofer

Net Weight: 72 lbs. (32.7kg)
Dimensions: 42.5" (107.9cm) High x 9" (22.9cm) Wide x 20.3" (51.6cm) Deep
Finish: Black Ash vinyl veneer 
Cabinet: Medium density fiber board construction (MDF)
Subwoofer Amplifier: Peak output power: 400 watts into 4 ohms 
Auto Power On: 2 second ON delay, 15 minute OFF delay

Inputs: High level speaker terminals via binding posts; two line-level terminals including a variable line input and a dedicated LFE input (non-filtered) via RCA phono jacks

Outputs: One line level and one LFE output via RCA phono jacks (pass through from line in and LFE input)

Voltage: 110/120VAC 60Hz (Export version: 230VAC 50/60Hz)

Manufacturer
Klipsch
8900 Keystone Crossing #1220
Indianapolis, IN 46240

Phone: (317) 581-3185
Fax: (317) 574-3870
Website: www.Klipsch.com