There are, as several of you have commented, many parameters that work together (or against each other) to generate the total or overall acoustic response of a speaker system. Each parameter has both positive and negative associations with the overall acoustic response, the design goal being to maximize the positives while minimizing the negatives and also to understand the specific contributions that each parameter contributes.
Some general parameters that were considered when designing the cabinets include the following:
1. The response of the 12” driver, considering the low end, the low mid voicing, crossover and then the impedance curve including both acoustic and electrical loading and phase response. These parameters must be suitable for combining with a midrange section without accentuating objectionable artifacts, while adding to the perceived feel of warmth and thickness yet not being overwhelming.
2. The response of the midrange section was the most difficult because the low mids must retain a reasonable phase relationship with the 12” driver throughout the crossover overlap range. This was accomplished with both acoustic and mechanical means to insure that there was minimal time offset between acoustic sources as frequency increases (to minimize midrange smearing effect) while maintaining adequate sensitivity. Additionally, we wanted to be sure that adequate loading was present on the drivers to allow them to be driven harder than a typical 3 way design if a little (speaker cone) overdrive harmonics was desired. This, of course, required a rather substantial overdesigning if the midrange section to insure adequate capacity when driven hard.
3. The tweeter section’s crossover works in conjunction with the low pass response of the midrange section and resulted in a higher crossover frequency to get desirable acoustic response. This, or course, can be adjusted to taste or turned all the way down without danger of damage to the crossover components.
4. Being as much an amp designer as a speaker designer, and knowing of the problems that some of the 3 way cabinets on the market presented to amplifiers (sub-nomimal impedance curves, inadvertent resonant excitation of class D residuals, large capacitive impedance zones), we were particularly sensitive to these issues and considered how the various crossover elements worked together to avoid the pitfalls that I have seen in (some) other designs. These interactions can play a big part in how a cabinet sounds, particularly when driven hard. In some cases, when a linear amp clips and the internal feedback control is lost, or when protective VI limiting occurs, these hidden issues can cause problems and in some instances amplifier failure. I have worked with several of you on TB with these specific issues.
5. By necessity, much more work was done with this cabinet analyzing, testing, playing, listening and adjusting various parameters so that the system would work together with a minimum of negative artifacts. We found that phase and time offsets were much more important in this kind of design, and as a result, a focus on the overall system phase and TOC response was more challenging than originally assumed. We had to approach this design a little differently than a more traditional cabinet, and used parameters that otherwise could have been ignored or discounted on other topologies to our advantage. I also researched back over 30 years to such topics as mechanical low pass filters, mechanical aperture acoustic filters, secondary TOC considerations, electro-mechanical contributions, total impedance response (including electrical, electro-mechanical and purely mechanical) and their resulting phase shifting contributions. Yes, pretty geeky stuff but ultimately fascinating too.
