Simaudio N HT's Xd User Manual

Page 10

ed on the XdA amplifier’s front

panel. Turning off the amplifier and

turning it on again fixed the prob-

lem.)

Repeating this torture test with

the 150Hz crossover filters didn’t

result in any shutdowns with the

Clarke solo, and the chord that

begins “In the Flesh,” from Pink

Floyd’s Is There Anybody Out There?

(The Wall Live) (CD, Columbia C2K

62058), sounded positively cata-

clysmic. The low-frequency crash of

the wall being demolished on this

album gave the XdW subwoofers

one heck of a workout. However, the

drum-and-unvoiced-guitar intro of

Eric Johnson’s “East Wes,” from his

live Austin City Limits CD, still man-

aged to shut down the left XdS

woofer amplifier if I wasn’t careful

with the volume control. (Setting the

NHT PVC’s control to –6dB, equiv-

alent to an in-room SPL of around

108dB, could trigger an amplifier

shutdown with this track.)

I listened again to the half-

step–spaced tonebursts on Editor’s

Choice. Despite the revised filters, I

could still hear the slight modula-

tion noise accompanying the

tonebursts. Probably not too much

should be made of this phenome-

non; I mention it only because I

had never heard it before with con-

ventional loudspeakers.

What about the high frequen-

cies? The veiling that had bothered

me was much reduced, the top

octaves having more air apparent.

Perhaps more significant was the

minimizing of a slight mid-treble

“shoutiness” that had limited maxi-

mum volume with the original fil-

ters. The presentation was first-rate

in its lack of coloration, superbly

stable and detailed imaging, excel-

lent retrieval of subtle reverbera-

tion tails, and overall top-to-bot-

tom integration. Wow!

Measurements: Fig.1 shows the

response of the Xd satellite (black

trace) and the XdW subwoofer

(green), as well as the individual

responses of the Xd tweeter (red)

and woofer (blue), with the XdA

crossover running the original digi-

tal filters. The crossover points lie

at 110Hz and 2.3kHz, and the

Linkwitz-Riley filter slopes are a

very steep 48dB/octave. A touch of

excess energy can be seen in the

mid-treble, and the top octave is a

little shelved off both on axis (red)

and in the 30° averaged response

(black). It also looks as if the tweet-

er’s ultrasonic dome resonance has

been notched out.

By contrast, fig.2 shows a similar

set of response curves taken with the

revised filters (NHT’s “150Hzcross-

over.flt” file). (Because of continued

wind and torrential rain during

October, the responses above 300Hz

were taken indoors at 40" instead of

outdoors at 50"; this affects the accu-

racy of the measurements in the

midrange but is otherwise inconse-

quential.) The filter slopes are still

48dB/octave, and the crossover

between the XdW subwoofer and

the XdS satellite can be seen to have

been shifted up to 150Hz, as speci-

fied. While the upper crossover

point looks very similar to that in

fig.1, the XdS drivers look better

integrated overall, with a flatter mid-

treble. There is also now slightly

more energy apparent between

7kHz and 15kHz, and the tweeter’s

ultrasonic resonance is unfettered by

a notch. The response on-axis (red

trace) now extends flat to the tweet-

er’s resonance at 27kHz, though the

HF unit’s limited dispersion above

15kHz results in less energy in this

region in the 30°-averaged curve

(black).

But it is the response in the room

that matters most. To investigate

how the Xd system behaved in my

listening room, I ran my usual test of

averaging 120

⁄3-octave power spec-

tra taken individually for the left and

right speakers in a window centered

on the position of my ears. The blue

trace in fig.3 shows the in-room

response of the Xd system with dual

subwoofers and the XdA’s original

digital filters. The lack of energy in

the 50Hz and 63Hz bands is endem-

ic to my room and

seating position.

But note the exten-

sion to 20Hz and

the very flat mid-

range, meeting

±1dB limits from

250Hz to 16kHz—

superb perfor-

mance for an in-

room, listening-

position measure-

ment. There is a

slight lack of

upper-bass energy,

though not nearly

as much as I was

expecting from my

auditioning.

The red trace in

fig.3 is the in-room

response taken in

an identical man-

ner with the 150Hz

c r o s s o v e r / E Q .

Overall it looks

very similar, but

there are detail dif-

ferences that corre-

late with the listen-

ing impressions.

There is more

energy in the

80Hz, 100Hz, and

125Hz bands, indi-

cating better inte-

gration between

the subwoofers and

satellites. That

www.Stereophile.com, January 2006

F O L L O W - U P

Fig.1 NHT Xd system, original XdA crossover filters, anechoic response on

axis at 50", averaged across 30° horizontal window and corrected for
microphone response (black), with the nearfield XdS woofer (black)
and XdW subwoofer (green) responses plotted below 300Hz, and the
individual XdS woofer (blue) and tweeter (red) responses.

Fig.2 NHT Xd system, revised XdA crossover filters, anechoic response on