This page presents information about a 3-way loudspeaker that was designed using the Virtual Crossover to develop the passive crossovers for the system. This information is presented to give you an idea of the kind of development and testing that can be done with the Virtual Crossover.
The most important design goal in the development of this
loudspeaker was to optimize the early arrival sound.
The direct sound heard in the first few milliseconds
from a speaker is extremely important to its overall subjective
quality. The response of this speaker
is highly accurate in both amplitude and phase. Achieving this level of
accuracy requires careful attention to the time alignment
of the drivers and to the development of the crossover circuits.
Each channel of the speaker consists of two separate enclosures, a satellite enclosure and a low-frequency enclosure. Each satellite enclosure contains one tweeter (Vifa H26TG-35) which is surrounded by two midrange drivers (Vifa P13WH) in the vertical direction; this arrangement minimizes frequency response variations. Since the tweeter and midranges are mounted on the same baffle, time alignment for these drivers is obtained using an L-C delay line network in the tweeter crossover circuit. An all-pass network is employed so that the tweeter response is not attenuated in amplitude. Time alignment between the satellite and low-frequency drivers (Meniscus W0838) is achieved by physically offsetting the satellite enclosure behind the low-frequency enclosure, which is one reason for separating the drivers in different enclosures. Other reasons for this separation are to isolate the drivers and to simplify the design requirements for the low-frequency enclosure. Yet another reason is that by adjusting the relative positions of the satellite and low-frequency enclosures, the midrange level can be tuned.
There are many different ways to approach crossover design. The method I used was to begin by looking at the individual driver responses, while mounted in the actual speaker enclosures to be used. For the satellite (midrange-tweeter) enclosure, the drivers were measured approximately six feet from the enclosure, on axis with the tweeter. For the woofer, since it is extremely difficult to obtain low-frequency information this far away from the speaker unless you have an anechoic chamber, the method of close-miking was used. I then incorporated circuits in the crossovers to compensate for some of the non-ideal characteristics observed for the drivers. Next, components must be included that implement the basic function of transitioning from one driver to the others; since I wanted to achieve excellent pulse reproduction, I basically used first-order crossover filters. Passive crossovers are used so that the loudspeaker requires only a single amplifier to drive it.
I used the Virtual Crossover in the initial development and testing of the crossover circuits; this allowed me to determine a close approximation to the final crossover circuits without having to construct any actual circuit prototypes. This procedure dramatically reduces the number of required circuit prototypes. In the final stage, circuit prototypes were made and final adjustments were made, which were necessary because the circuit models provided to the Virtual Crossover were not perfect.
At this point I want to make a comment about implementing these circuits using the Virtual Crossover. First of all, the Virtual Crossover can only do as good a job modeling a real crossover as the model that you provide for it. In my experience, inductors are the most problematic circuit elements to model. Their series resistance must be included, and it is not always sufficient simply to measure their DC resistance, because the AC resistance of inductors can be significantly greater than the DC resistance; this problem gets worse as the frequency goes up, so it is especially important for the tweeter crossover circuit. If you have coupled inductors in your circuit, the coupling coefficient must be determined, which is sometimes a difficult task. And at higher audio frequencies, parasitic capacitance between the windings of an inductor may become important. Here I simply present the nominal crossover circuits for the speaker system, without getting into these issues of component modeling.
The following photo shows the assembled crossover boards for one channel, before being mounted in the satellite and low-frequency enclosures: