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The acoustic response measured in nearfield is
superimposed over the model prediction below. The measured
response has been normalized to the maximum output level measured
Note that the measured frequency response drop-off, as frequency
increases, is artifact of the measurement method. For
this application, the
response below about 50Hz is of interest.
The acoustic response, using the near-field method
described by Keele , is shown below. The response was
measured using CLIO FW (v10.31).
Green diaphragm near-field, purple ducted port near-field,
red phasor summed response.
The impedance modulus, Z, of the system is shown below.
The measured Fb of 19.2Hz is somewhat lower than design intent and
is associated with a longer duct length than is required for an Fb
of 20Hz. Measured responses for area of
the ducted port, Sv, equal to 45.5in^2 with and end-corrected length, Lv,
equal to 13.75in. For preliminary testing, a duct length
approximately 5% longer
than prediction recommended. The duct length can be trimmed to adjust.
ENCLOSURE MODEL FROM
Modeling begins by first considering the
driver small-signal parameters  as specified by the manufacturer.
In our situation, a large extensively braced enclosure with Vb equal
to 0.48m^3 (16.95 ft^3) was available for experimentation. The
large size allows for adjustments to Vb (additional bracing or
adding solid volumes such as cellophane wrapped bricks).
A ducted port enclosure, with tuning ratio equal to unity (Fb=20Hz)
was modeled across a range of enclosure Quality factors (5-20) using
vented-box Excel spreadsheet. The predicted
responses, Eq. 58 in , are shown
The plot shows that F-3
will range from about 22 to 24Hz over a reasonable range of
enclosure Quality factors for the conditions specified.
The effect of variations in Qes, for fixed Vas (=25.9ft^3), Qms
(=2.90) and enclosure Q (=10), are considered and the results shown below.
The plot shows that magnetic damping
lower than about 0.45 will produce a reasonably "flat" magnitude
response for the conditions specified.
Our analysis of the small-signal parameters measured at 3.5Vrms
demonstrate that specification Qes and Qms are somewhat larger than
reported by the manufacturer. Here, the magnitude response for
the enclosure conditions specified is shown at the Qes, Qms and Fs
Qes, Qms, Qts (4-WIRE METHOD)
The magnet assembly is identified as a 6000 series assembly. The
structure is bolted to the basket by three long cap screws. The assembly is
located by the top plate, it fits into the counter-bore in
the basket (see below). The center plug is made of Aluminum and does not
alter the magnetic field. The center plug assembly is held in
place by two screws
which are magnetic (steel) and will alter the field shape.
The holes in the center plug accommodate air flow thus enhancing cooling.
The magnitudes of Qes, Qms and Qts are determined by using
a constant voltage approach. The parameters
required to determine the Quality factors are provided in the
developed specifically for this test.
The parameters were measured at two drive voltages, 3.0 and 3.5V. The test gear used to make the measurements:
FLUKE 8012A digital multi-meter > voltage drop across source
LEADER LMV-182A AC analog meter > voltage applied to driver
FLUKE 1910A digital multi-counter > frequency counter
KRON-HITE 6200A phase meter > phase angle
B&K 4010A function generator > sine wave generator
McIntosh MC2105 amplifier > voltage source
Source resistor > 10W non-inductive (7.45 Ohm)
The tables below (click on each) are the results of the 3.5Vrms (left)
and 3.0Vrms (right) measurements.
As evidence in the measurements, the magnitude of Qes measured is
essentially the same at each drive level (0.46). The value
reported here is somewhat higher than the magnitude specified by the
supplier for this driver (0.38).
magnetic assembly was removed from the basket and photographed. The loudspeaker
was purchased new from a
McCauley distributor. Note
factory application of adhesive (white material).
McCAULEY SOUND 18" LOW FREQUENCY TRANSDUCER MODEL 6174-8
DESCRIPTION (FROM McCAULEY SOUND WEBSITE)
The 6174 18" transducer is an ultra-high performance
woofer designed to reproduce low and extended low frequency
material at very high SPL's. The 6174's twin coupled magnet
structures increase the power handling to 800w RMS / 1600w
PROGRAM, while the system's convective cooling chambers actively
dissipate heat. The 6174 offers over 2" of controlled, peak to
peak cone excursion.
The unit examined here (S/N129911, Motor S/N14086) was purchased new in 2004.
The unit has seen light use in a residential environment
consisting of music and home theater sound (no touring, no
portable sound, no sound reinforcement, no musical instrument
Supplier specifications for the 6174 are