Stereophile – August 2019

stereophile.com n August2019 115

KLIPSCH FORTE III

that the more clay I put into the corners

of the horn, that tended to eliminate

that beaming. Usually you avoid that by

raising the crossover point, which isn’t

the most efficient use of the horn. The

Mumps allow me to use the horn in a

wider bandwidth.”

Like versions I and II, the Forte III

couples to the floor via a 1" wood base

to which four^1 / 8 "-thick round metal

footers are attached, one for each corner.

Setup

The Forte III is the most amplifier-

sensitive loudspeaker I’ve reviewed:

Careful upstream choices were essential.

The Kuzma Stabi R turntable^5 and

4Point tonearm/Hana EL cartridge

handled analog; the Tascam CD-200iL

CD player with BorderPatrol DAC SE

spoke digital, connected by a 1m run of

Triode Wire Labs Spirit II interconnect.

The Kuzma 4Point’s dedicated Crystal

Cables tonearm cable connected to a

Musical Surroundings Phonomena II

phono stage, its signals flowing to either

Helmholtz resonator. You cause the air
to resonate at a certain frequency and
that extends the bottom end. A drone
does the same thing.”
At a time when the US is experienc-
ing an outbreak of measles, the Forte
III remains au courant by having—you
guessed it—Mumps. Literally named
for the swollen salivary glands they sort
of resemble, Roy Delgado’s patented
Mumps are curved 1" ridges that round
off the interior corners within the throat
of the K-703-M midrange horn. The
goal, according to Klipsch’s website, is
“to improve coverage and control of the
key mid-frequency band.”
“Studying various data,” Delgado
noted, “I noticed that when the directiv-
ity index tends to drop, right before
the horn starts to lose control of the
coverage pattern, it beams, the coverage
pattern becomes narrower and starts
to wrap around itself like a cloverleaf
effect, and the output comes down. I
wanted the waves to stay in contact with
the horn walls so that when they exit
the horn that beaming is eliminated.
Working with modeling clay, I noticed

the rear panel, these modes shouldn’t

color the Forte III’s midrange.

The crossover between the woofer’s

farfield output on the tweeter axis

(fig.3, blue trace above 350Hz) and

that of the midrange drive-unit (green

trace) occurs slightly higher than the

specified 650Hz. The filter slopes

are asymmetrical, the output of the

horn-loaded midrange unit rolling off

very rapidly. The farfield response of

the midrange unit and the horn-loaded

tweeter, taken without the grille, has a

flat trend but with some small peaks

and dips, a suckout centered on the

5.2kHz upper crossover frequency,

and a slight excess of energy in the top

audio octave.

The black trace below 300Hz

in fig.4 is the complex sum of the

nearfield woofer and passive radiator

responses taking into account acoustic

phase and the different distances of

the two diaphragms from a nominal

farfield microphone distance. The rise

in the mid- and upper bass is primar-

ily due to the nearfield measurement

technique, which assumes that the

drive-units are mounted in a true

infinite baffle—ie, one that extends

to infinity in both the horizontal and

vertical planes. But this rise does

suggest that the Forte II’s maximally

flat low-frequency alignment will give

a lot of bass in all but large rooms.

Note that, despite its size, the Klipsch

doesn’t offer a lot of bass extension, it

being tuned for sensitivity rather than

extended lows.

Higher in frequency in fig.4, the

black trace shows the Klipsch’s farfield

response, averaged across a 30° hori-

zontal window centered on the tweeter

axis. Although the overall balance is

even, several small suckouts and peaks

are still evident between 1 and 20kHz.

The plot of the Forte III’s horizontal dis-

persion (fig.5) suggests that the suck-

Fig.3 Klipsch Forte III, acoustic crossover on

tweeter axis at 50”, corrected for microphone

response, with the nearfield woofer (blue) and port

(red) responses, both plotted below 350Hz.

Fig.4 Klipsch Forte III, anechoic response on

tweeter axis at 50”, averaged across 30° horizontal

window and corrected for microphone response,

with the complex sum of the nearfield woofer and

port responses plotted below 300Hz.

Fig.5 Klipsch Forte III, lateral response family at

50”, normalized to response on tweeter axis, from

back to front: differences in response 90–5° off

axis, reference response, differences in response

5–90° off axis.

5 See our review in the July issue of Stereophile.

Frequency in Hz Frequency in Hz

Amplitude in dB Amplitude in dB