Help me understand how to optimize bass on the Zu Definition Mk IV

My Def4s are 6" from the back wall, and the floor is wood glued to reinforced concrete. Sean delivered the speakers, dialed in the bass amps, and the output curve is flat (see the owner's manual):

Volume=9
Low pass=45
PEQ Gain DB=3.0
PEQ frequency=35
Phase in degrees=0
Gap=1-1/4"

Bass is tighter and more cohesive than either the 1.5s or 2s. You can always call Sean for suggestions.

GSM, I've just tried yr settings and really quite like the sound.

For the OP,

Are your Def 4s new or did you buy them used and they're simply new to you? There's a reason I'm asking. What are your room dimensions? Which 300B tube are you using in your SE amps?

I started with Def 1.5 back in early 2005. Then Def II, then (and still) Def 4. All three have been placed in exactly the same location. With the 4x10" back firing arrangement, I did have speakers placed close to the wall behind, but no corner loading. Under normal circumstances, the Def 4 12" sub should easily outperform the older 4x10" array, in bass depth, quality and amplitude. The old plate amp on the 4x10" wasn't as powerful as the sub amp in the Def 4. However, with 6" clearance to the back wall and 2' to the side, with the backfiring array you certainly had corner loading with the Def 1.5 that has gotten you accustomed to exaggerated bass. You might just have to wean yourself off some of that, because you are not going to get the same amplitude of corner loading from the downfiring sub in Def 4. Particularly with your 300B SET amps. You'd have corner reinforcement of rising THD bass.

On the other hand, Def 4 gives you control that laughs at the simple level knob on Def 1.5 / 2. So alot can be accomplished by getting the controls combination settings optimized. But first I need the answer to the questions whether your Def4 are new from Zu or used. Then I'll have more to suggest.

Phil

Again, thank you guys for the contributions. Please keep sending along any thoughts you have. So far they are exactly the kind of answers I was hoping for from current owners. Wish I could invite you all over for a drink and a listen!

So I played around for a few hours tonight and managed to improve the bass presentation on the speakers significantly. I've had to find my own settings, as the examples posted above just haven't done it for me, in my space, with my tastes. I would still say that these MkIV's in their current configuration here are outputting only maybe 70% of the bass quality I was getting from the Mk1.5's. But steps forward for sure. 

I've definitely had this realization.... I lived (very happily!) with my previous Zu's for 12 years here and had them dialled in just perfectly. I probably had somewhere around 5000 hours of listening bliss with them. Then I found these used MkIV's locally for a good price and decided to make the leap. Somehow I thought I could just slot them in just where the others were and figured it would be instant love. Now I get it... they are a different speaker, with a different solution for transducing bass frequencies, and I'm going to have to play around and get to know them in time... 

I was struck by reading this thread --https://forum.audiogon.com/discussions/zu-definition-4-height -- where 52tiger says he "was running out of options and really wasn't sure if the Def 4 was better than the def3," but after raising the height off the floor "the bass is tight and amazing, the downfiring design is so much better than the rear firing its no comparison." Clearly I have some experimenting to do. 

I'm having faith in the last line of that thread by dentdog: "With my Def 4s I worked them around quite a bit to optimize... For me it was well worth all the effort." 

Just saw your reply Phil. My MkIV's are new to me, bought used locally. I wasn't really looking to upgrade, but stumbled upon them and... well... you know how this hobby is. They look to be the first version (not rev B, if that makes a difference). My room dimensions are 13' wide by 22' deep, with the speakers on the short wall. They are 8 feet apart, tweeter to tweeter, with the listening position 8 to 9 feet from each tweeter. Almost a nearfield setup, which might be part of the issue in the way the bass is sounding in the sweet spot. Despite the size of the room, these positions can't really be changed, as the other half of the room is a music studio for playing and recording. 

My 300b tubes are Full Music 300b/n mesh plates. I've always loved them and they churned out mind-bending bass with my previous mk1.5s. 

However, you are right that I may need to wean myself off some of the exaggerated bass from the 1.5s. Being a bass player and a lover of some bass-heavy genres like reggae, those deep frequencies just floated my boat, even if it resulted at times in some smearing of the midrange. That said, I could barely turn the amplitude knobs past 12 o'clock without blowing my head off, while now I'm struggling to get enough bass out of the MkIV's. I do listen to a wide variety of music, so I'd like to get the balance correct!