Zu Druid questions

I have built underdamped pipe speakers, and speculate that the Druid's enclosure may be a variation on an underdamped pipe.

The 150 Hz notch would indicate an internal path length of about 90 inches. When the path length is equal to one wavelength, the backwave energy emerging from the end of the pipe is 180 degrees out of phase with the front wave of the driver, so cancellation occurs. The depth of the notch makes me suspect the line is underdamped. Note that the ear is much more tolerant of frequency response dips than it is of peaks; without that SoundStage measurement, I bet very few people would know it's there.

Brave move on the part of Adam and Sean, sending their speaker to be measured when I'm sure they knew full well that its measured response would raise eyebrows.

If the 90 inches ballpark path length is correct, we'd expect to see a local response maximum at about 75 Hz, with response rolling off slowly to about 37.5 Hz and then falling off rapidly below that. This is reasonably consistent with the SoundStage measurements.

To my ears, the Druids sound like they have much more bass than the SoundStage measurements indicate is possible, even optimistically factoring in boundary reinforcement.

Normal boundary reinforcement will of course bring up the response in the lower octaves, but not all that much. I do not understand why the gap between the vent and the floor is so critical, but can accept that it is. Zu claims to use muffler technology invented by a man named Griewe, which I have been unable to find details of so presumably it's not patented. Mufflers.... hmmmm.... Jackson Browne.... hmmmm....

There are two ways to bring up the apparent loudness of a signal. The most obvious is to increase the intensity, or sound pressure level, of the signal. A less obvious way is to make the signal last longer. If presented with two brief signals of equal intensity but different duration, the ear will perceive the one lasting longer as being louder. Perhaps the muffler-like characteristics of the Griewe enclosure take advantage of this psychoacoustic phenomenon, filling in the perceived bass a bit by sustaining bass energy for just a little bit longer. "Oh won't you staaaaaay, just a little bit longer...." This is just a SWAG on my part, and I invite clarification and correction from anyone who knows better.

Duke

jack,,you still have great speakers

What is the value of all this speculation about whether of not the Druid design should work? It clearly works for a lot of people. "Science Says" is a fun game for awhile for a certain sort of person but the proof is in the listening.
I have no expertise in speaker design but I have wondered if the unusually short excursion of the full range driver could explain anything about the success the Druid enjoys. The driver movement is not visible until you reach very high listening levels and then only slightly.
Also, why should the diameter of the driver be a limiting factor? The QUAD 57, to which I hear the Druid compared sometimes, has a much larger radiating surface. Does it also defy the calculations of our critics? Or does it also benefit from very short excursion? Is it transitional speed that benefits both in defying projections that should limit them?
Maybe it is possible that Zu started out with a design that should not be able to work and manipulated it in such a way that it works quite well. I don't know their secrets but I remember being told that they took old technology and found ways to improve upon it using modern tools and materials. Maybe they did that. Maybe not. Still, the speaker is a marvel and deserves investigation. If it turns out you don't like it, you will have had some fun experimenting and you will be able to provide us with an educated and informed opinion.

Bob_reynolds, you are exactly right.. pretty little hardware, big snake like power cables... much is just marketing hype in the audiophile world, that is the good thing about Zu actually as you point out,, They are directly derived from the PRo arena and concepts used in live pro equipment, and the designs use Pro drivers, designed for a purpose period, without all the extra frills and correction circuitry needed with mainstream audio drivers. But of course they had to break down and start adding pretty colors, machined custom plates etc, to look like a hi end product, but all the money is put in the right place with Zu designs, the Performance, reliability, and sound.