The Klipsch RB-81 II is a rather large bookshelf speaker featuring a horn loaded 1" compression driver and an 8" cerametallic cone woofer in a front ported enclosure. Retailing for $850/pair, the RB-81 II has a rated frequency response of 44Hz-24kHz (+/- 3dB) and a sensitivity of 97dB with a 2.83V input at 1m. With a number of competitors to choose from at this price point, does the largest bookshelf in the Klipsch Reference line deserve a look (or a listen)? Read on to see what I think.
Executive Overview
The RB-81 II is a bit of an abnormal sight these days, being a basic two way bookshelf speaker sporting a big 8" woofer. Generally this type of layout presents a problem; crossing over the woofer at a higher frequency means beaming will be a problem and consequently it will create a big directivity mismatch when the tweeter takes over. Cross at a lower frequency and the tweeter runs into trouble at higher output levels. Fortunately, Klipsch's use of a horn loaded tweeter should help ameliorate the problems on both sides of the equation, as it will provide both pattern control and improve the efficiency (and reduce distortion for any given output level) of the tweeter.
Other than this one interesting tidbit, the overall design of the RB-81 II is relatively unremarkable. It is a standard box with a black ash vinyl veneer that isn't going to win any awards, though it isn't terribly offensive either. The front baffle is a single piece of molded plastic, including the horn and front firing slot port. Given my experience with Klipsch Reference speakers, I'd expect the RB-81 II to be reasonably well built, and the 27.5 pound weight is a good indicator in this regard as well.
Moving on to the numbers, things get a little more interesting. The RB-81 II has a rated sensitivity of 97dB and a low end extension of 44Hz, which taken together is likely to be an optimistic appraisal of the situation. Klipsch is known to rate both figures as "in room", meaning if you were to compare these specs with that of another manufacturer that rated their speakers under anechoic conditions, you'd need to knock off about 4dB of sensitivity and 10Hz of extension to get something approaching an apples to apples comparison.
It's unfortunate in my opinion that Klipsch feels a need to do this. Even assuming the RB-81 II's sensitivity is closer to 93dB w/ 2.83V @ 1m rather than 97dB, combined with an 8 ohm nominal rating, it should still be very easy to drive for a partnering amplifier. Extension in either case should be well suited for a typical 80Hz XO, and the 8" driver should be capable of delivering strong dynamic output in all but the largest of rooms. Overrated specifications aside, Klipsch seems to have the makings of a competent speaker, which really negates the need for overrated specs in the first place.
Summary
If you're in the market for a high output bookshelf speaker in the sub $1,000 mark, the Klipsch RB-81 II might be right up your alley. An initial glance at the design doesn't reveal any massive faults, and on the up side the RB-81 II shouldn't require an ultra-high powered amplifier to get going. My only big gripe from a quick glance is that I'm not fond of how Klipsch rates their speakers, particularly since it doesn't seem necessary here.
So what do you guys think? Anybody own a pair?
Anybody interested in Joel putting a pair through the wringer?
Quick Specs
Dimensions: 19" H x 9.3" W x 12.3" D (with grille)
Weight: 27.5lbs (12.5kg)
Frequency Response: 44Hz-24KHz ± 3dB
High Frequency Crossover: 1400Hz
High Frequency Driver: 1" (2.54cm) Titanium diaphragm compression driver mated to 90° x 60° square Tractrix® Horn
Low Frequency Driver: 8" (20.3cm) Cerametallic cone woofer
Nominal Impedance: 8 ohms compatible
Sensitivity: 97dB @ 2.83V / 1m
