Woofer Impedance (Cont.')
Significant
factors (especially near the free air resonance frequency) of inductive and
capacitive reactance are left out for simplicity. These measurements didn't
resolve well with the printing on the sub's magnet, which claimed "4//4
Ohm, 26W//26W." I would rate the woofer as a 7 Ohm unit for testing purposes.
It should be any easy load to drive for the dual TDA8510J amp setup.
The Satellites
Like the subwoofer, the
satellite specs are not specified by the manufacturer. The satellite cases
were screwed and glued together, so I left them intact for fear of cracking
a case or two.
Satellite
Impedance
|
Frequency
(Hz)
|
Voltage
(mV)
|
Current
(mA)
|
Impedance
(Z)
|
|
315
|
120
|
25.0
|
4.80
|
|
1000
|
104
|
28.6
|
3.64
|
|
3150
|
109
|
24.7
|
4.41
|
Affecting power measurements,
and thusly power ratings, I will assign a nominal 4 Ohm rating for this review.
Similar to the easy going nature of the subwoofer, the sat drivers will be
an easy load to drive for it's quad amp IC, a TDA8510J.
Frequency Response
The unintentional bass
hump is moderately narrow in frequency range, but very pronounced. Remember,
a 10dB boost essentially means a relative doubling of loudness for sounds
produced in that affected frequency area. The low frequency cutoff in room
measured an below average-for-size 54Hz, with a small rolloff beginning at
58Hz.
The midrange response
was a disappointment. In two critical ranges, the curve shelved upward in
one region and downward in another region. This had a dramatic effect on the
perceived sound quality.
In-Room
(2 Walls) Frequency Response
|
Bass
(rel. 100Hz)
|
Midrange
(rel. 1kHz)
|
Highs
|
|
64-78Hz
= +3 to +8dB
|
4.7-6.3KHz
= +3 to +8dB
|
14.5KHz
= -3dB
|
|
58Hz
= -3dB
|
7.5-11.5KHz
= -3 to -8dB
|
17.5KHz
= -6dB
|
|
54Hz
= -6dB
|
|
|
The on-axis response clearly
shows quite a nasty boost in the 4.7-6.3KHz range, which almost necessitated
that the satellites must be listened to 15-30 degrees off-axis. But, if they
are angled to that suggested range, the extreme upper midrange and high end
roll off dramatically. All
listening tests were performed with the satellites angled approximately 15
degrees off-axis to avoid the dreaded audio "headache."
The
bass response was the most disappointing. The engineers just couldn't seem
to take advantage of the dual port design of the enclosure and create a LF
cutoff at least in the sub-50Hz range. This is nearly one full octave short
of the 28Hz spec.
Rated
R.M.S. Power Output
As I griped
earlier, a high distortion power rating is nearly useless when contemplating
higher end audio. Possibly a few teenagers, especially those with some hearing
to spare might enjoy massively distorted sound, but this reviewer cringes
at anything much over the 1% mark (which is plenty detectable). For
the purposes of all my audio reviews, I chose the generous 3% rating, which
was traditionally utilized for cassette deck/reel-to-reel testing until the
early 1990's. At 3%, the waveform when viewed on an oscilloscope starts to
visually "flat-top" or clip.
The main
voltage rail to the minuscule DC filter cap, a 3300uF 25V unit, measured 16.3
VDC at no load. Direct measurements confirmed a satellite power of 4.64 Watts
per channel, so the total across all four channels adds up to just over 18
Watts. The satellite with both amps at 3% distortion, reached 5.47 Watts per
channel or a total of almost 11 Watts. I am rating the Xtrusio's as a 29 Watt
speaker. This is far lower than the 100 Watt claim, but remember that the
distortion figure is more than one-third lower than Logitech's 10%.
