Stereophile – August 2019

I heard new

coughers in

audiences.

I spotted a

squeaking

church-bell

support.

stereophile.com n August2019 69

MAGNEPAN LRS

W

hen a loudspeaker

is measured, the

underlying assumption

is that the distance

from the speaker to the microphone is

significantly greater than the largest

dimension of the speaker’s drive-unit

array.^1 With conventional moving-

coil loudspeakers, this assumption is

almost always correct: The microphone

is in the speaker’s farfield, where any

differences in the path lengths from all

the drive-units are negligible. However,

with a panel loudspeaker such as the

Magnepan LRS, this becomes difficult

to arrange. The LRS’s Magneplanar

panel is 38" tall by 10" wide, which

means that, at my usual microphone

distance of 50", the farfield assump-

tion is incorrect. The resulting proxim-

ity effect will tilt up the response at

low frequencies^2 —as it will when the

loudspeaker is listened to at the same

distance.

So with that caveat, I used DRA

Labs’ MLSSA system and a calibrated

DPA 4006 microphone to measure the

Magnepan LRS’s frequency response in

the farfield and an Earthworks QTC-40

mike for the nearfield response.

Magnepan specifies the LRS’s sen-

sitivity as 86dB at 500Hz with 2.83V.

I don’t like specifying a sensitivity at

just one frequency, as this could be

misleading with a speaker having a

nonflat response (as they all do). I

prefer to use a wideband noise signal

and a B-weighting filter; this filter

reduces the effect on the measured

value with speakers having extended

highs or lows. Taken in this manner, my

estimate of the Magnepan’s sensitivity

was almost 6dB lower than specified,

at 80.1dB(B)/2.83V/m. Because a

panel speaker has a dipolar radiation

tweeter 8'0" from my listen-

ing seat, and the woofer at

7'10" away. (The speakers

were 6'10" apart.) With my

ears about 40" above the

floor, the sound was pre-

cisely focused and natural-

toned.

In that position, I noticed

that bass began rolling off

around 60Hz, and the treble

appeared to fade quickly

above 10kHz. (A pair of 1.2-

ohm resistors are included

to attenuate the tweeter,

but I never felt any need

to use them.) From 200Hz

to 6kHz, this new Maggie

The second step was
trickier. The speaker’s
response in both the verti-
cal and horizontal planes
appears more directional
than it is with most box
speakers. This directionality
is exacerbated by the LRS’s
two-way design—it employs
a first-order crossover—and
its side-by-side placement of
the woofer and tweeter.
“Whether the tweeter
is on the inside or outside,
the tweeter should not be
closer to the listener than
the bass section,” Wendell
Diller told me. “Measuring
from your seated position,
if the bass panel is 10'6"
[away], the tweeter should
be at least 10'7".” Think
in terms of mid-to-treble
balance and remember to
not place the LRS parallel
to any walls.
Of course, you can use a
tape measure to certify the
aforementioned woofer-
tweeter relationship. I used a Bosch GLM 20 Compact
Blaze Laser Distance Measure—which worked perfectly
while making the setup process fun. I ended up with the

delivered flat response with minimal room-added fluff or

brightness.

I caution readers not to judge these speakers on a single

MEASUREMENTS

1 See my article on measuring loudspeaker fre-

quency response: stereophile.com/features/103/

index.html.

2 See the measurements accompanying my

November 1991 review of the Magnepan MG2.6/R:

stereophile.com/content/magnepan-mg26r-loud-

speaker-measurements.

Fig.1 Magnepan LRS, electrical impedance (solid)

and phase (dashed) (2 ohms/vertical div.).

Fig.2 Magnepan LRS, anechoic response on

midpanel tweeter axis at 50", averaged across 30°

horizontal window and corrected for microphone

response, with nearfield panel response plotted

below 300Hz.

Stereophile Magnepan LRS (R) Impedance (ohms)

& Phase (deg) vs Frequency (Hz)

Frequency in Hz

Amplitude in dB