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Duntech's reputation has been built on technical excellence and international leadership in audiophile quality loudspeaker design. In a highly competitive international market place, an ongoing investment in research and development capability is considered vital to increasing market share and winning new markets.

Duntech design philosophy involves a combination of technologies specifically:

  • symmetrical arrangement of loudspeaker drivers
  • time alignment
  • first order crossovers
  • a patented, acoustic, sound absorbent felt material of critical size, shape and placement, designed to reduce diffraction distortion
  • high quality drivers

DUNTECH loudspeakers are 'pulse coherent' - i.e. a combination of technologies that will reproduce complex musical waveforms with minimum distortion or alteration to the shape.

The company's technical objective is to develop loudspeakers which have the following attributes:

  • The ability to reproduce individual frequency components which arrive at the listening position at the same time, and with the correct relative phase to each other.
  • Reproduction of a spectral balance approximating that of the original performance.
  • Arrival of the amplitude and phase components of the sound reproduced by each speaker at the ear in a manner which recreates an accurate sound stage with good location and depth.
  • Inaudible levels of non-linear distortion, viz. harmonic, intermodulation or vibratory.
  • Presentation of a reasonably consistent and resistive load impedance to the amplifier, so as to avoid amplifier-induced distortion.

Performance requirements for each of these attributes are known quantities and are built into the design of every DUNTECH loudspeaker.

Unique driver arrangement.

Duntech employs a unique physical arrangement of drivers that permits the realization of several design goals important to the accurate reproduction of complex musical sounds. These may be summarized as follows:

  1. Accurate alignment of path lengths between individual drivers and the preferred listening position.
  2. Symmetrical radiation patterns.
  3. Simulated point source radiation.

To assist in understanding how this arrangement works, Figure 1 provides a sequence of drawings which illustrate the concept of apparent sound centre and effective source of radiation. In Figure 1, the drivers are depicted from both the front and side. A dot is used to indicate the location of the sound source within each driver, with respect to the initial time of radiation.

The centre image that occurs when monaural sound is fed to a pair of stereo loudspeakers can illustrate how the pair of woofer drivers also yields a centre image, that is, creates an illusion of a sound source mid-way between them. Thus, a listener some distance in front of the loudspeaker will perceive sound radiated by the two woofer drivers as if it emanated from a single driver, shown by dotted lines, located in the same place as the tweeter.

In the same way, bass and mid-range drivers create an accurate illusion of a single driver located in the same place as the tweeter. Therefore, the combined radiation from all of the drivers results in a listener hearing sound which appears to originate from a single, point source radiator, located on the tweeter axis.

Also, because all of the drivers have their effective source of radiation arrange along an imaginary, equidistant, vertical arc, the sound energy from each of the drivers arrives simultaneously and in-phase at the ears of a listener located at a distance of three to four metres (9-13 feet), on the tweeter axis.

First order type crossover network

The crossover, or frequency dividing network, is the very heart of a loudspeaker system. Its purpose is to divide the electrical input signal from the amplifier into separate, overlapping frequency bands. This is necessary because no single loudspeaker driver exists which can reproduce sounds over the entire audio spectrum, with acceptable accuracy and loudness to meet the criteria for true high fidelity reproduction. By utilizing separate drivers to cover each of the ranges, it is possible to individually tailor them to meet the often divergent needs required for different portions of the spectrum.

Replication of highly complex waveforms with the highest possible precision requires that considerable attention be given to the design of the crossover network, along with properly time aligned drivers as mentioned earlier. Figures 2 and 3 provide a comparison of the results obtained when using first order and second order networks to reproduce a 1 KHz square-wave signal with a time aligned, bass and treble loudspeaker system. The crossover frequency is 1 KHz. The separate outputs of the high pass, treble, and low pass, bass, sections of the first order crossover network are shown in Figure 2A, along with the input signal. The combined waveform, the sum of low-pass and high-pass sections, appears in Figure 2B and may be seen to be a nearly perfect replica of the original square-wave. By contrast, Figure 3 illustrates the very serious waveform distortion which results when a second order crossover network is used, a popular second order Butterworth design. Higher order networks, such as third and fourth order types, produces an even greater degree of waveform distortion.

First order type crossover response Second order type crossover response
Figure 2A
Shows seperate low pass and high pass outputs and the 1 KHz square wave input.
Figure 3A
Shows seperate low pass and high pass outputs and the 1 KHz square wave input.
Figure 2B
Shows the sum of the high pass and the low pass outputs laid over the 1 KHz square wave input.
Figure 3B
Shows the sum of the high pass and the low pass outputs laid over the 1 KHz square wave input.

 

It may be argued that such a deterioration in waveform and pulse quality is unimportant with respect to producing a loudspeaker that sounds good. There is an element of truth in this. It is possible to design a 'good-sounding' loudspeaker which exhibits inferior phase response and pulse dispersive properties. It is not possible to produce an accurate sounding loudspeaker unless it is meticulously designed to exhibit minimum phase and pulse coherent characteristics. The real difference is between good or pleasant sound quality and truly accurate sound quality.

Further, only aircore, low loss inductors and very low distortion, polypropylene capacitors are used in the crossover network. All resistors are high quality, precision, high power types. Such components are far more costly than the iron core inductors and electrolytic, paper, or mylar type capacitors found in most other loudspeaker systems. However, the added cost is well repaid by the achievement of better musical accuracy and an almost unlimited life expectancy.

The drivers are connected to the crossover using high-purity, copper wire containing up to 648 individual strands. The outer insulation is almost acoustically dead and was chosen for its outstanding electrical, mechanical and acoustical properties. Special solder containing silver is used for making all connections to the crossover. The input terminals for the loudspeaker are heavily gold plated to reduce distortion that can occur by the formation of oxides on contact surfaces.

The loudspeaker can be operated in all of the following modes, easily selectable from the back panel:

  1. Normal mode using a single stereo amplifier for each pair of loudspeakers.
  2. Bi-wired mode using a single stereo amplifier with dual connecting cables for each pair of loudspeakers.
  3. Passive bi-amping mode using two amplifiers for each loudspeaker.

Minimising diffraction distortion

A form of audible and measurable distortion arises when the sound energy radiated by a loudspeaker driver is diffracted from an external edge of a loudspeaker enclosure.

The level of this distortion becomes particularly serious when an offending edge is at a distance from a driver which exceeds about one quarter of a wavelength at any frequency within the intended range of the driver.

Such diffraction causes an audible smearing of musical transients, a degradation in definition and ambience, and generally alters the amplitude versus frequency properties of the system, either on-axis or off-axis.

It explains why many designers choose to arrange drivers in an asymmetrical grouping along the front panel of the loudspeaker, mistakenly believing that they are counteracting the effects of diffraction. However, while the scheme may be used to remove some of the bumps and drop-outs in the curve of amplitude versus frequency, it does not materially improve the ability of the system to accurately reproduce the fine detail of many musical passages. Perhaps even worse, such loudspeakers usually exhibit a grossly asymmetrical radiation pattern, one of the chief contributors to poor stereo imaging.

An obvious solution to the problem would be the elimination of sharp edges by rounding them in a manner reminiscent of early 1930 designs. A little rounding is not sufficient. Minimum radii of several inches are necessary to alleviate the problem.

A better and more cosmetically acceptable solution is to apply an effective sound absorbing material between the drivers and the relevant edges. Properly executed, the sound waves reaching the edges will be attenuated to a level resulting in inaudible and virtually immeasurable distortion, as in Figure 4.

Duntech has solved the problem by covering all relevant surfaces with a highly efficient, sound absorbing, natural felt.

The density, thickness and shape of the felt is matched to the specific requirements of the loudspeaker to reduce the diffraction to an insignificant level.

This technology is protected by U.S. Patent #4,167985, issued in 1979

Other Features

A close look at the loudspeakers will reveal many other unique features. Among them are: optimally damped enclosures for each of the drivers; internal bracing, where required, to increase the rigidity of the enclosure; and high quality drivers, incorporating high temperature voice coils, specially treated cones, and innovative magnet structures.