What happened to my room acoustics

@lanx0003 ,

Then you would know every bass guitar sounds different.

This issue is not up for contention. It is an easily measurable phenomenon and not a matter of my opinion.

Porting woofers is a design principle destined for the bowels of some museum. It is an antiquated method of pushing the frequency response of a woofer lower and then cutting it off abruptly in the context of a wooden box which in all respects is a musical instrument masquerading as a pipe organ. Only tightly sealed boxes need apply. Edgar Villchur knew this in the late 50's. Today, given enough power and within the physical constraints of the driver, we can tailor the amplitude response of a woofer or subwoofer to do anything we want without any added limitations or distortion. The quality of the sound depends primarily on the construction of the enclosure, how to not make a musical instrument, and that folks is a trade secret. 

@mahgister 

In the late 70's Randy Hooker aka RH Labs. Made a subwoofer that was a helmholtz resonator. It was a passive subwoofer down firing into a slot. It was huge in comparison to modern subwoofers, about 3 feet by 2 feet by 2 feet. They made beautiful if somewhat colored bass. Inside the enclosure the driver was housed in a larger compartment which was slot loaded into a smaller compartment. It resonated at 20 Hz forcing the driver to go down low. It was a pleated 12" paper driver, nothing special. There were no subwoofer drivers back then. 

Helmholtz resonators are the basis of mechanical acoustics...

As you know i used them in my first room a lot ...

Distribution and location matter ...

Now in my second room with smaller speakers , i designed a new porthole for them using different straws tuned for this goal exactly as when we compute the right size of the neck volume and diameter of the resonator body ...

Then you understand my perspective ...

My goal was first learning acoustics then improve my sound without cost ...

Thanks for the information...

My best to you ...

@mahgister

In the late 70’s Randy Hooker aka RH Labs. Made a subwoofer that was a helmholtz resonator. It was a passive subwoofer down firing into a slot. It was huge in comparison to modern subwoofers, about 3 feet by 2 feet by 2 feet. They made beautiful if somewhat colored bass. Inside the enclosure the driver was housed in a larger compartment which was slot loaded into a smaller compartment. It resonated at 20 Hz forcing the driver to go down low. It was a pleated 12" paper driver, nothing special. There were no subwoofer drivers back then.

the simplest solution is usually the best.

I would pull the speakers forward 1 foot and move closer 3-4 feet.

What are your speaker stands and height? To me the gel seems an ok solution

The stand is 32-inch high, placing the tweeter below ear level, but the 5-degree tilt of the front baffle on the S400 compensates for this gap.

Lanx0003,

I also have a pair of Buchardt Audio S400 MkIIs, and just a couple of recommendations based on experience.....though I have never measured the room. I am building a new audio room, and have a DSPeaker Anti-Mode to install at that time.

(1) In my experience, 3 feet into the room for the Buchardts is too much, I found the cleanest and most accurate bass at about 20 inches from the front wall; Buchardt recommends closer placement to the front wall.

(2) I'd reach out to Mads Buchardt for his opinion, I have found him (along with Don Sachs and Alvin Chee at Vinshine) to be most generous with his time and help. He  frequently posts and answers questions on the Buchardt Audio Worldwide Owners Group.....or just email them, you will definitely get a response.