Zu Druid questions

Ait,

Thanks for the input from your perspective - that of someone with a professional scientific background.

Here's a link that talks about an effort to better correlate measurements with perception in audio by means of a psychoacoustically-weighted metric derived from several different measurements, but focusing on the shape of the transfer function rather than on spectral changes:

http://www.audiomasterclass.com/learn.cfm?a=3651

See also Audio Engineering Society preprints number 5890, 5891, and 6888.

Duke

Duke,
Please take note that people ate before they began tinkering with agriculture. I'm not sure my correction is any more pertinient than your analogy attempt but I felt like pointing out that discrepancy.
Now, as for science, I am well aware that scientific data and techniques were applied to the creation of the Zu designs. What I am mocking is the ongoing second guessing so many of you feel qualified to apply to other peoples designs. Jack is asking for fellow members to share any experience they have with two specific speakers. He is not seeking prognostication. I've reread his post and he has not asked for opinions of what the speaker SHOULD sound like based upon an educated guess. The whole laboratory/measurement debate is stupid but if you are one who values those numbers, hell, it's your money , do your thing. I'm sure a lot of people will jump to your defense at this point and Tvad will surely scold me. Nonetheless, I maintain that the lab talk should be witheld until requested. It muddies too many discussions and hijacks too many threads.

Shardone - Some of this or that might be related to rainbows and puppydogs. If the driver is breaking up anywhere in its band I can't hear it. You couldn't either.

When the frequency response becomes very spikey above a certain frequency cone break up is often the explanation. The fall off in off axis response is probably beaming. IMHO the "whizzer" cone is there for a reason.

As Duke points out...our hearing is remarkably well able to deal with notches in the frequency response (spikes are actually much more acceptable than sustained drops)

So the break up may not be audible.

The uneven power response: Although the "whizzer" fixes the on axis to a large extent....I expect that the roll off in off axis response above 2 Khz will be clearly audible. The speaker will probably sound different as you walk from directly in front to 45 degrees off axis - this is not a bad thing - just the way it will behave and will make speaker positioning/toe-in quite important - thats all.

Duke,

I agree with you. Underdamped/high Q design is a much better explanation for the severe notch at 150 HZ. The cone will respond to cabinet resonance.

Here is another example PMC GB1 of a speaker with a similar notch.

There is a superficial similarity in the tall narrow cabinet dimensions and overal response, however the GB1 is crossed over on the tweeter much lower and therefore has a more even off axis response at higher frequencies.
PMC = 6.1"W x 9.21D x 34.25" H
Zu Druid = 10 1/2"W x 6 3/8"D x 50"H

I agree that the notch at 150 Hz will likely be inaudible - many rooms may have sharp notches like this anyway from wall reflections/modes - so no big deal.

However an underdamped design will differ quite audibly from a critically damped design. As you suggest, longer oscillations in the low end may give more of a bass impression than the frequency plot alone may suggest.

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All goes to show that measurements are meaningful and do tell us something about the design and the performance.

Of course, I would NEVER recommend to select a speaker based on measurements alone. Nevertheless I would not recommend to stick ones head in the sand and totally ignore meaurements either.

Let me finish by saying Zu Druid's are undoubtedly good speakers. The high efficiency and dynamics from this design is likely to be extremely impressive even with very modest amplification power. My intent was never to bash these great speakers. Sorry if it sounded that way...but I was only trying to defend the value of measurements.

Macrojack,

The issue of the SoundStage measurements came up. I posted a possible explanation. Note that Zu hasn't really described what their enclosures do, so we are left to surmise - and note also my request for clarification and correction on the specifics. Is trying to understand the SoundStage measurements and correlate what little we know about the encloure design with subjective impressions really so out of place as to be called "hijacking"?

I'm going to do it again, just so you know. Shadorne commented on a similar-looking frequency response curve in a PMC loudspeaker as possibly shedding light on the Druid's design. I'm going to reply to him.

Also, just so you know, it's not the numbers themselves that I value. It's the knowledge and insight that can be conveyed if you understand what the numbers are saying. I wish to understand loudspeaker design (and the Druids are a particularly interesting design), and I wish to share my understanding with others who are interested in loudspeaker design. If you feel I have mischaracterized the Druids in some way, by all means take me up on my request for correction. If you just object to my interjecting numbers and science in general, I invite you to start another thread and we'll discuss it.

Shadorne,

Thanks for bringing up SoundStage's measurements of the PMC speaker. I think there's some information there that may shed light on the mysterious Druids.

The PMC is clearly a tuned pipe enclosure - in this case a transmission line having a factory-specified line length of "2 meters". The midbass notch location would lead me to expect a line length of about 2.15 meters, so the specified line length corresponds pretty darn close with the location of the notch. I think the notch is too severe and too low in frequency to be related to an internal resonance. It looks like what I used to get in some of my transmission line designs. I'm pretty sure the PMC woofer has a higher Qts than the fullrange driver in the Druid, which would be consistent with the PMC's measured response holding up better below 100 Hz.

From the location of the notches, we can conclude that the PMC and Druid have similar path lengths. The PMC uses a three-fold transmission line. We don't know what's inside the Druid yet. Maybe one of these days I'll try to map out the internal partitions by knuckle-rapping.

There's something else we might gain insight into from a comparision with the PMC measurements. Take a look at both impedance curves. You see how the Druid's impedance peaks rise up much higher in the bass region? My guess is that's partly due to the Druid having relatively little damping material in its enclosure. Now some of the difference could also be due to high a high mechanical Q (Qms) of the Druid's driver, but even a little damping material in a tuned pipe should bring those peaks down considerably. I'm not saying there's no damping material in the Druid, but what's there is evidently not very effective at low frequencies (intentionally, I would guess - the impedance curve may be an indication of the design's muffler heritage).

By looking at both speakers' frequency response and impedance curves, I think you can see a family resemblance. Something similar to the PMC's transmission line - but obviously not identical - seems to be going on in the Druid's enclosure.

Duke

Sorry, guys. I didn't mean to attack anybody but time and again I have seen these simple requests turned into engineering dialogues which completely abandon the original poster. I suppose if he were to come on board and request clarification this might make sense. As it is, I believe he has been left high and dry.
For a few of you, the emphasis seems to be on what went into the speaker but you may be surprised to learn that most of us only care about what comes out of it.