Stereophile – August 2019

stereophile.com n August2019 97

DUTCH & DUTCH 8C

I

used DRA Labs’ MLSSA system

and a calibrated DPA 4006 mi-

crophone to measure the Dutch &

Dutch 8c’s frequency response in

the farfield and an Earthworks QTC40

mike for the nearfield responses.

Before I took the measurements, I

connected the speaker (serial no.

8c-515) to my network and and visited,

lanspeaker.com, in order to defeat the

settings Kal Rubinson had used during

his auditioning. These were compensa-

tion for the distances to the room’s

front and side walls; the levels of treble

and bass; and the two parametric

filters he’d used to compensate for his

room’s low-frequency modes. I left the

volume setting at –20dB, selected the

“Analog Low Level (–10dBV)” input

setting, and disconnected the speaker

from my network. (The network con-

nection is necessary only for setting

the controls; the 8c is fully operational

without it.)

As the 8c is an active loudspeaker,

no sensitivity is specified. However,

with a 1V RMS pink-noise signal, the 8c

gave a B-weighted SPL of 84dB at 1m

on the HF axis, which suggests that the

speaker has plenty of gain in reserve.

When I investigated the enclosure’s

vibrational behavior with a plastic-

tape accelerometer, I found a resonant

mode at 363Hz on the centers of the

side panels (fig.1), with another at

551Hz on the top. These modes were

very low in level, however, and the 8c’s

enclosure felt reassuringly inert when I

rapped it with my knuckles.

The green trace above 200Hz in

fig.2 shows the D&D speaker’s farfield

response with an analog input signal,

averaged across a 30° horizontal

window centered on the tweeter axis.

The response is superbly flat, remain-

ing within ±1.4dB limits from 200Hz

to 15kHz! However, the output rolls

off sharply above 20kHz, reaching

full stop-band attenuation just above

direct output of the rear drivers is acoustically coupled to

the energy reflected by the wall such that they act as a single

source. The potential downsides of positioning the speakers

so close to the front wall are midrange colorations, but those

are minimized by the highly

controlled cardioid dispersion of the front drivers.

cies, from 100Hz down, sent to them
by the 24dB/octave Linkwitz-Riley
low-pass filter.
On each side panel is a small (ca
5" by 2") rectangular port covered
with a metal grille. These ports
provide precise acoustical venting of
the back radiation of the front-firing
8" driver, to cancel much of that
driver’s forward radiation and shape
it into a cardioid pattern. Thus, the
front driver, with a bandwidth of
100–1250Hz, radiates most of its
energy forward, and minimal energy
to the sides and rear, where it would
reflect off and interact with walls
and other room structures. This
dispersion pattern is similar to that
created by the 1" tweeter and its
acoustic waveguide.
On the 8c’s underside are a small
vent and a variable-speed fan that
kicks in when needed to ventilate the amplifiers. I never
heard it.
While the 8c is big for a stand-mounted speaker, its cabi-
net isn’t big enough to develop a lot of bass; Hofmann’s Iron
Law has not been repealed.^4 The 8c’s bass amp is specified
to output 500W, but if your goal is to fill a large room with
a lot of bass energy, a pair of 8" drivers presents displace-
ment problems.
D&D takes advantage of placing the speakers close to
the front wall with what they call Boundary Coupled Bass.
When the 8c is positioned from 4" to 20" from the wall, the

MEASUREMENTS

Fig.1 Dutch & Dutch 8c, cumulative spectral-decay

plot calculated from output of accelerometer

fastened to center of sidewall (measurement

bandwidth, 2kHz).

Fig.2 Dutch & Dutch 8c, anechoic response on

tweeter axis at 50", averaged across 30° horizontal

window and corrected for microphone response,

with nearfield woofer (blue) and subwoofer (red)

responses and their complex sum (green), respec-

tively plotted below 300Hz, 350Hz, and 300Hz.

4 Josef Anton Hofmann (1924–2010), the H in KLH Audio Systems, defined three

desirable parameters in speaker building: bass extension, efficiency, and small

enclosure. He demonstrated that any one or two of these can be optimized only at

the expense of the other(s): If you want a small enclosure and high audio output,

you pay for it with limited bass extension. If you want a speaker with high output

and extended bass, you better build it big.

Frequency in Hz

Amplitude in dB