Hi DrStrangeQuark,
I will see if I can answer some of your questions and add some insight into the design behind the M80 and M100. I will start by digressing a bit to establish the design goal.
It has been refreshing as of late to see Dr. Toole’s video of his speech in Montreal making the rounds:
Dr Floyd Toole Video It contains much content on the topic we call the “family of curves” (Floyd calls this the “Spinorama”) and its importance to sound quality. To put it simply; it is the family of curves that predicts how well a speaker will perform in subjective listening. The more interesting question is why the topic is so rarely discussed compared the volumes put into topics that have little to no impact on sound quality. I can only surmise as to the reason for this but here are two likely candidates:
1. There is nothing visual on the product itself to point to that demonstrates a differentiator affecting the family of curves; making the topic somewhat boring when compared to say a cone material or even a crossover part.
2. Most manufacturers and reviewers do not have the equipment to measure the family of curves. This is especially true with all the curves required to create the sound power curve.
The relevance of the above is to show a key design goal in all of our speakers. This graph
M80 Graph shows the Listening Window and Sound Power curves for the M80. When deciding on the crossover points, crossover slopes, and driver design there are two main things to consider:
1. To not have audible distortion up to the maximum SPL of the speaker system where compression occurs.
2. To achieve the desired Listening Window and Sound Power response curves.
Given these dual goals we are not in any way attached to a particular slope or frequency point for our crossovers; there is no benefit in holding onto a goal such as “only using 24 dB per octave filters”. The only purpose the selected slope serves is the end measured benefit to the family of amplitude response curves as measured in the finished speaker design (design goal 1 above excepted). In the case of the M80 there are four woofers and two tweeters per speaker. We often call the two 5.25” drivers mid-ranges, in fact our spec sheet shows them as such, but in reality they are woofers and should really be referred to as “smaller woofers” as opposed to midranges (perhaps I will change our spec title). When used in the M22 they are, of course, called woofers. The reason this is important is because of how we treat the lower crossover point of these 5.25” woofers. They are mounted in small sealed chambers of their own that cause a natural slow roll-off starting at 170 Hz. For reasons that benefit the family of curves substantially we do not put any electrical high-pass filter on these woofers. The 6.5” woofers use a combination of the woofer design itself and their low-pass crossover to create a slow almost shelf like roll-off at the 160 Hz crossover point.
