The Klipschorn bass unit acoustic response, located in a
corner position, is shown in the plot below. The horn
responses, measured at the left side mouth opening (purple) and
right side (red) are shown. The microphone is placed in the geometric center of each
mouth opening (19.5" from the floor, 4.5" from the wall). The
green plot is the phasor sum (derived by post processing) of both
left and right responses. The two responses are derived
using DFFT on MLS impulse using a rectangular window.
The on-axis response of the
horn loaded with the BMS driver is shown below (green). The
response of the Beyma CP-25 tweeter is also provided
(purple). The responses derived using DFFT
on MLS impulse using a rectangular window. Microphone placed
MID-RANGE AND TWEETER CROSSOVER QUASI-ANECHOIC RESPONSE
The measurement microphone was placed 1.3 meters from the center of the
V-Trac horn mouth section and an MLS impulse applied and
response recorded. The mid-range and HF units were both connected to
the network. The quasi-anechoic, frequency response for
frequencies >1kHz is shown below. Purple curve is mid horn
response, green is high frequency response and blue is total
response. Frequency domain information derived from DFFT of
MLS impulse. Red plot is excess phase determined by
subtracting numerically derived minimum phase response from total
CUMULATIVE SPECTRAL DECAY
The Cumulative Spectral Decay (CSD) plot of the V-Trac response shown above
is provided and shown in the plot, top. Below is the CSD of the current
production Klipschorn midrange (K55/K401) and high frequency unit
systems operating with 4th order bandpass, 4th order high pass
filters. Decay shown is over entire length of impulse
response (4.1ms). As evidenced in a comparison of the two, decay
rates are higher and exhibit better uniformity in the V-Trac system with no particular
frequency demonstrating excessive overhang. Note also the
exceptionally smooth decay at the V-Trac crossover frequency
(~4500Hz). The data demonstrates that the V-Trac system
exhibits better transient behavior.
EXCESS GROUP DELAY
Excess group delay plots provide a quantitative assessment of the
time dispersive characteristics of a multi-way loudspeaker system.
For example, if a loudspeaker system is claimed to be "time
coherent" what that implies is a flat excess group delay
plot across the useful bandwidth of the system. Here, for
comparison purposes, we provide excess group delay plots of both the V-Trac
with the KV1 network (red) and
a stock Klipschorn operating with a A-type network (green). The KV1 is
a 4th order band-pass on the MID and 4th order hi-pass on the HF.
The A-type utilizes a first order high pass on both the stock Klipsch MID and HF units. As is evident in
the plot comparing the two, the
magnitude of the excess group delay errors associated with the
A-type network are considerable and are responsible for distortion. The KV1
less phase error resulting in better imaging and enhanced
stereophonic effect. Excess phase derived from DFFT
of MLS impulse.
THE V-TRAC KLIPSCHORN NETWORK (KV1 & KV2)
A three-way crossover network for the
modified Klipschorn loudspeaker
system has been developed and is described here. The V-Trac consists of a large
format wood construction tractrix horn
manufactured by Greg Roberts
at Volti Audio
It is driven by the
BMS ND4562 MID
neodymium, 2" throat,
polyester diaphragm, compression driver. High frequency content is handled by the
. The network has been developed by
between computer model simulations using both LTSPICE and MATLAB
simulators and experimentally determined acoustic
responses. The design approach considers
acoustic response limitations of each component and
seeks a network configuration that establishes as near a flat, on-axis,
response as is possible within the design practice allowances
for useable bandwidth, phase distortion, physical size, part
count and cost.
Network simulations are terminated with loads that accurately
capture both impedance magnitude and phase information of the
bass, mid and high frequency horns
providing accurate predictions of purpose
design revisions. Near and far-field impulse, frequency and phase data files
and curves are
generated using CLIO (v.7.3 and 10.31) acoustic analyzer.
Note regarding acoustic response curves - Real, unsmoothed acoustic
response curves are not always pretty and are almost never shown
simply because the data likely fails to substantiate the performance claims made by the manufacturer. We
have characterized, in great detail, the acoustic response of this
system. We have used computer simulation to develop the
crossover network. The computer models were then calibrated to
the actual acoustic response measurements. This provides us
with a powerful tool to refine the networks and establish the
desired acoustic response. The only thing that matters is the
acoustic response of the system. We have refrained from showing
the predicted response from simulation software because
predictions have no value to the end user. That said, all
claims are substantiated with performance data.
The KV1 consists of two sections, a bass horn filter and a
V-Trac filter. The bass horn filter
section sends low frequency signals to the Klipschorn folded bass
unit whilst the
top section filter sends signals to the BMS midrange and Beyma high
frequency drivers. Capacitors and inductors are Janzen
manufactured (Capacitors: polypropylene Cross-Caps, Inductors:
#18 air-core and #15 iron-core). Additional we have incorporated one
design feature found on the current factory network, a large
notch filter in the bass horn section. We have however, altered
the shape of the response to suit our design requirements.
The filter with the LF notch
filter is designated the KV2.
Midrange horn output level user modified by switching out
Midrange filter is 4th order band-pass, establishes well-defined acoustic
center of mid-range.
High frequency filter is 4th order high-pass.
Bass horn filter is low-pass available either without the notch
filter (KV1) or with (KV2).
A singe KV2 network is shown below. The low frequency filter
section (left) is shown with notch filter.