Modding the Zu Omen MKII

@kevinjkim So glad I can be of help! I made comments on some of the photos on dropbox, providing more context and detail where I could. Feel free to ask questions. DIY will change your life. :)

Just chiming in here. I today finished up all the mods that @slowlearner28 mentioned. First, several months ago, I inserted the dowel bracers and applied the auto sound deadner. That tightened up the bass somewhat.

Last month I replaced the stock drivers with the 103ND. That brought greater clarity and dynamics to the mid-range.

Over the past few days I installed the Radian 475 aluminum tweeters (I couldn’t afford to spring for the beryllium versions). I did an A/B test with installing a Radian in one speaker and going back and forth with the balance control on my amp. It seemed to my ears that the new tweeter adds more presence to the high end. I have to listen a bit more - there’s definitely a difference, but I can’t pin down what it is yet, as dumb as that sounds. Today I put the remaining Radian tweeter into the other speaker.

Some advice:

If you can afford it, I’d go with the Acoustic X coating instead of the auto mat stuff. I’m sure they both worth fine, but I think applying the coating might be easier and cover every square inch. The auto-mat stuff is heavy, can get in the way of the dowels, and takes a while to flatten completely out with a roller. I know Zu uses the Acoustic X type stuff. 

Be very careful with installing the t-nuts if you’re adding those to the mix. Make sure the t-nut cones fit properly in the drill holes and accept the screws without locking up before you put them in the cabinet. I had one t-nut get stripped or something when I screwed in the 103ND and it was a huge headache - the screw got 3/4 of the way down the t-nut but then would turn continually without tightening or loosening. I had to get a pair of bolt cutters to snap the screw head off and ended up scratching the aluminum perimeter ring that goes over the driver. I had a similar problem with one of the smaller t-nuts for the tweeter, but at least that time I had learned my lesson and tried them all out before installing them. Frankly, the t-nut installation was by far the biggest PIA of this project.

Finally, the theaded steel studs that came with my tweeter-to-dome adapter were 1/2" too long. They stuck so far out of the tweeter that I couldn’t screw the Radians into the Zu tweeter dome. You need to get 1/4-20 threaded studs that are 1" long, something like these.

Anyway, the project is now finished. I’m hoping to put in some serious listening time in the next day or so.

How does it sound with the Radian 475 Aluminum tweeters?  

I want to provide a follow-up to my November 2020 post on the modifications I performed on my Omen Dirty Weekend Mk.II and detail some discoveries I have made since then. It has been 3 years since I completed those mods and the speakers still continue to amaze me. In that time I have gradually upgraded nearly every component upstream and the speakers have allowed me to hear every change—the Zu 103 full-range drivers in combination with the Radian 475 beryllium supertweeters are very revealing and I learned that your upstream components need to be up to the task. I love the tone density and “shove” of the modded speakers—qualities Zu speakers are best known for—but wanted to further push my system to achieve greater transparency, realism, resolution, and holographic imagery through upstream components.

In the past year I have dove into the world of L-pad calculators, first order crossover calculators, and the software Room EQ Wizard (REW). The reason being that while the modded speakers are thoroughly engaging, I have noticed that on some music I was missing a bit of upper-midrange and above “presence” especially in female vocals. Measuring the speakers with REW confirmed my suspicions, and I could see a gradual decline in the frequency response starting at 1.5kHz out to 20kHz. The L-pad I used with 3ohm and 4.7ohm resistors calculates to about 6dB of attenuation to the tweeter, so my hunch was that this was the cause. I suspected that by removing the L-pad and having just the 1uF capacitor (like in a stock ODW) would solve this. Bear in mind that a stock ODW Mk.II uses Zu’s 206 full-range driver and Eminence ASD1001 tweeter. In addition, the L-pad used in a Zu Soul Supreme with the 103 driver and Radian 850 supertweeter also provides about 6dB of attenuation, which lead me to the conclusion that the Radian 475 beryllium is just a very different animal than an 850 aluminum, so using a 475be in combination with the 103 driver requires a different filter network.

While I could have re-purposed the 1uF Duelund tinned-copper capacitors I used in my 2020 mod, I didn’t want to take apart the filter network I soldered together in case my hunch was wrong. So when a discounted pair of V-Cap ODAM 1uF caps popped up on PartsConnexion, I jumped on them. Everything I read about the ODAM caps, with their characteristic grain-free sound quality and holographic imagery appealed to me and I was very curious how they would compare to the Duelunds.

With just the 1uF ODAM cap hooked up between the 103 driver and Radian 475be, built similarly to Zu's stock Erse caps or upgraded Clarity caps, they are simply a revelation. They sound just like people have described—utterly grainless, holographic, and oh so smooth. I thought the Duelund tinned-copper caps sounded wonderful, but the ODAM caps really are on another level. I measured the speakers again with REW and was very relieved to see that the frequency response from 1.5kHz to 20kHZ was now nearly ruler flat. Female vocals now have greater presence, and because of the reduced “grain” sound spooky real. I close my eyes, and my brain is tricked into thinking the singer is in the room. Success!

I uploaded a graph comparing the frequency response of the speakers with the Duelund caps/Path Audio resistors versus only the ODAM caps (measured using a miniDSP UMIK-1 mic at 1 meter, volume set to 75dB SPL, with Psychoacoustic smoothing). I am quite satisfied with how smooth the graph is considering my listening room is untreated. There is a slight dip at around 150Hz, so I’m currently considering why that might be and ways to alleviate it. I suspect there might be some phase cancellation due to my untreated room at the first reflection. Or perhaps I'm just at the DIY limit to what can be improved upon with the ODW's cabinet to reduce resonance.

https://www.dropbox.com/scl/fi/airbm18g0rmltcstowiaf/Zu-Omen-DW-Mk.II-103nd-475be-no-sub-duelund-vs-odam-Psy-average-1m-0-deg.png?rlkey=qp28gaz2cu0nrrnnofemmfzre&dl=0

I will end this post by re-stating something I wrote in a post several years ago: DIY will change your life. It literally changed mine. Thanks for reading.