Zu Tone/Druid Tonal Anomalies

Gridlock · « **on:** 7 Dec 2005, 11:42 pm »

I'd like to hear anyone with Zu speakers if they have had a similar problem. I recently acquired a pair of Zu Tone speakers. Certain aspects about them are very good, such as soundstaging and speed, but it seems to me that unless my pair are defective, there is a serious issue with tonal accuracy. Right away when I set them up, I noticed that they sounded quite hollow. I then made a lot of measurements, both close miked and at the listening seat, with both a Behringer DEQ2496 and an RS sound level meter (using both pink noise and frequency generation). In both cases, it fairly closely matches what I am hearing, which is a severe rise in the upper midrange. I am trying to use a Z-Systems RDQ-1 digital EQ device to correct this problem, and have gotten much closer to a natural tone

and flatter curve. What this required was a 7.6 db cut centered at 1.4kHz at a width of 1.5 octaves. This is quite a cut! For reference, I've had two other sets of speakers (Monitor Audio GR60 and NHT ST-4) in the room at almost exactly the same position, neither of which had this problem. I spoke to Sean Casey at Zu about the problem, and he thought it might be room interaction, which might be true to a point, but the anomaly is just too severe, and makes this point less viable since my other speakers didn't show the problem. I noticed in another thread here, that a couple of people heard what seemed like a similar problem with the Druids.

I am very curious as to what others have experienced with any of the Zu speakers in this regard.

Thanks,
Stew

ooheadsoo · « **Reply #1 on:** 8 Dec 2005, 01:11 am »

No experience with the Zus, but I wanted to mention that IMO, this kind of rise or peak is certainly not too extreme for a room interaction.

Gridlock · « **Reply #2 on:** 8 Dec 2005, 01:23 am »

Quote from: ooheadsoo

No experience with the Zus, but I wanted to mention that IMO, this kind of rise or peak is certainly not too extreme for a room interaction.

Maybe, but two previous sets of speakers (Monitor Audio GR60 and NHT ST-4) had no such anomalies, and they were placed in the same position as the Zu's.

ooheadsoo · « **Reply #3 on:** 8 Dec 2005, 01:52 am »

I shouldn't be speculating because I know jack about this stuff, but I wonder if the top end dispersion has anything to do with it. Conventional speakers have a broader dispersion on the top end because of the small diameter tweeter, which would disperse more evenly throughout the treble, but the Zu's woofer will start to beam above the frequency you are boosting (until the super tweeter kicked in.) Perhaps those higher frequencies are now not being dispersed and reflected around your room to as high a level as those in the range you are boosting, and so you find a partial rise in frequency response around the 1.4khz region.

I have no idea what I'm talking about, do I?

audiojerry · « **Reply #4 on:** 8 Dec 2005, 02:54 am »

I'd buy that

miklorsmith · « **Reply #5 on:** 8 Dec 2005, 03:11 am »

I've had Fostex 206E speakers and will say those beam like crazy. The Druids are designed to point straight at the listener and are gentle in their off-axis behavior. Good theory, but I doubt it's the case here.

warnerwh · « **Reply #6 on:** 8 Dec 2005, 04:40 am »

Try different toe in/out and see what kind of readings you get. Different speakers will interact with a room differently due to dispersion and interactions with what's in your room. My own room which is a well treated dedicated room has a heck of a suckout at 500hz. Two different sets of speakers and the same thing. My point is that a room can affect different speakers differently.

How do you like that DEQ 2496? I"m surprised you also use the Z systems equalizer while also owning the DEQ 2496. I wonder if you can use one or the other and tell us if you can hear any difference in quality. I don't mean to hi jack your thread but if you'd pm me I'd appreciate it as I find the Behringer a wonderful tool. Thanks

Watson · « **Reply #7 on:** 8 Dec 2005, 05:51 am »

Someone posted measurements of the Druids a while back and they did indeed have very serious deficiencies. Soundstage has a more charitable set of measurements here:
http://www.soundstagemagazine.com/measurements/zucable_druid/

The thing with the Druids is they have a terrible power response (among the worst of any commercial speaker made in the last 10 years) because of the huge woofer and the high crossover point. That means unless you're listening on-axis in an anechoic chamber, there will be a big perceived peak around 1kHz.

The other thing about the Druids is they have no bass. The f3 is 200Hz (that's not a typo) and there is a total null at 150Hz. The bass comes back a bit at 100Hz (still about 3dB down), but it rolls off quickly again.

So if you're wondering why they sound hollow, there might be an explanation that's not just your room.

ooheadsoo · « **Reply #8 on:** 8 Dec 2005, 05:55 am »

Zu has disputed those measurements time over time. Apparently the design of their cabinet loading incorporates the floor, requiring a specific gap. Soundstage's anechoic measurement reveals what happens without a floor.

Response above 1khz is not unexpected for such a large woofer playing up to 12khz.

Watson · « **Reply #9 on:** 8 Dec 2005, 06:09 am »

With a full floor loading, there would at most be a +6dB difference. Not even close to enough to eliminate the total null, though perhaps enough to bring the 100Hz peak up a bit, and control the rolloff below that.

As for Zu's claim that the microphone was positioned incorrectly for the tweeter's crossover point, that's either wishful thinking or damage control. They could have put the microphone anywhere and the power response would still be terrible -- the 12khz crossover point guarantees it.

ooheadsoo · « **Reply #10 on:** 8 Dec 2005, 06:54 am »

The 6db you mention is nominal room gain. Zu is talking about a fundamental change in the tuning of the enclosure, similar to changing the length and diameter of a port. By removing the floor, you are throwing off the enclosure's tuning. It's a different beast, not just a boundary effect. At least that's how it seems to me, not having heard the thing.

Watson · « **Reply #11 on:** 8 Dec 2005, 07:23 am »

If you look at pictures of the NRC setup, they do measure on a platform. The speaker isn't suspended in midair (despite what the space cadet over at 6moons writes), so what's left is boundary reinforcement.

What I'd really like to see is measurements of the Zu Definition. An MTM with huge drivers and a high crossover point will have nulls from comb filtering all the way through the upper midrange and beyond.

I don't want to sound like I'm bashing Zu. I'm sure the speakers sound very dynamic and many people probably like how they act as tone controls.

What I don't like to see is people blaming the room, the amp, the source, the cables, etc. when a person doesn't like how they sound. That's just a typical audiophile wild goose chase, searching for an elusive cable that will make everything better, when it's the speakers themselves that are totally nonlinear.

ooheadsoo · « **Reply #12 on:** 8 Dec 2005, 07:37 am »

Yes, that is a very good point - but I still don't see how it's possible for a null of that shape to be created without intent, if it is indeed electronically induced. The driver won't do it all by itself. You can see from the impedance plot that the fs of the driver appears to be 90hz. One can only guess what that blip above 150hz is, and Zu's response fits from an amateur's point of view, assuming Zu are not morons.

miklorsmith · « **Reply #13 on:** 8 Dec 2005, 03:28 pm »

Watson - you haven't heard any of the speakers and you haven't followed the threads enough to know about the problems with the Soundstage! measurements.

Speculative musings are one thing, statements about how fans probably appreciate their properties as tone controls are another thing entirely. Please leave appraisals of how they sound to people that have bothered to listen to them.

Watson · « **Reply #14 on:** 8 Dec 2005, 06:36 pm »

Quote from: miklorsmith

Speculative musings are one thing, statements about how fans probably appreciate their properties as tone controls are another thing entirely. Please leave appraisals of how they sound to people that have bothered to listen to them.

Note that I didn't say tone controls are a bad thing. There are manufacturers who deliberately aim for a non-flat frequency curve (e.g. Totem). If that's the sound a person likes, that's great. If not, moving on to another speaker makes more sense. No amount of burn in or room treatment or cable rolling will make a large speaker with a 12 kHz crossover have a flat polar response. The Definitions, being an MTM, will have even larger problems.

I find your post on the Audiogon forums fairly enlightening, actually, as it confirms subjectively what the measurements and physics predict:
"Well, the Definitions in my room currently are showing a 12 db rise in the same area you're talking about and higher. I'm measuring from the listening seat and the rise is obvious there. In fact, it's so obvious that I can hear it ringing off the glass bar and window that my listening seat are between. It is not pleasant and is something I'm working on through acoustics and will be aquiring a TacT to help as well.
With most music, the notes are not prolonged enough to pressurize that frequency. Piano and blazing guitar do light it up though. I assure you it isn't something I prize."

miklorsmith · « **Reply #15 on:** 8 Dec 2005, 06:47 pm »

True. Yet, my situation is so obviously a room issue that it isn't fair at all to hang it on the speakers. If you read the text, I can hear those frequencies literally bouncing off the glass of my bar and opposite window. It sounds like there's another pair of speakers spitting out those frequencies with certain kinds of music with slow decays at those Modes. Most music doesn't activate the room modes at all. Translation: Read what I actually said and recalculate.

Your theoretical complaints are not borne out by first-hand observation.

Watson · « **Reply #16 on:** 8 Dec 2005, 06:50 pm »

It's so obviously not a room issue. It's entirely predictable based on the physics of MTMs.

This picture shows how the polar response of an MTM deteriorates when run with a very high crossover point:
http://www.zaphaudio.com/audio-speaker16-XG18-MTM-offaxis.gif

BTW, for those who haven't seen it, the rest of the Audiogon thread is good reading:
http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1133903740&read&3&4&

miklorsmith · « **Reply #17 on:** 8 Dec 2005, 06:58 pm »

Actually, the MTM is run with no crossover.

Watson · « **Reply #18 on:** 8 Dec 2005, 07:02 pm »

According to Zu's web page, the Definitions are crossed over at 10kHz.

miklorsmith · « **Reply #19 on:** 8 Dec 2005, 07:05 pm »

The full-range drivers are run completely XOverless. The supertweeter uses a very simple hi-pass network at its lower range.