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. 

First of all, your listening position need to be 5 feet closer. Things are actually worse then they seem. The Y axis is in 20 dB increments. Most systems I have seen use 5 dB increments. This is a very shouty curve with the bass lagging 10 to 15 dB behind the midrange. From 200 Hz up things are actually quite good except for that dip at 12KHz. You need to measure each channel separately and compare. 

The ideal in room curve starting at 20 Hz which should be 5 to 10 dB above baseline sloping down and reaching baseline at 100 to 120 Hz, then flat out to 1 kHz then a steady slope downwards to 6 to 12 dB under baseline at 20 kHz. Bothe channels should mirror each other directly. I would like to see if that 12 kHz dip is in both channels. Any difference between the two channels will screw up your imaging. 

You need to deaden the front and side walls at the first reflection point which may calm your midrange and I would remove the bass traps. After that your best option is a digital preamp with EQ and room control. Subwoofers and digital bass management would give you much more control over the bass. 

Don't feel bad. I have measured many systems worse than this. I just measured a system with Magico S7 loudspeakers. The imaging was pitiful for speakers of that caliber. Low and behold one channel had a 10 dB dip centered on 300 Hz. He is ordering a DEQX Pre 4 which will fix the problem. This is like a photograph out of focus. You use digital EQ to focus the system and you can see the results with your measurement system.  

@lanx0003 

If you have a good floor the last thing you want to do is decouple the speaker from the floor. Ideally you would bolt it down to the floor. Spikes are the usual option. Why? Newton's 3rd law. You need a very massive, fixed mass (the floor) to control the reactive forces or the speaker shakes. Play a 20 Hz test tone and put your hand on the speaker. What you feel = distortion. Now spike the speaker to the floor and you will feel less shaking. You might also notice more aggressive bass. I'm afraid this whole speaker decoupling gig is an example of lay intuition. If a floor is so bad that it resonates in the audio band then fix the floor. Most floors dampened by carpet might only resonate in the 5 to 10 Hz range, great for causing footfall problems with turntables but not a problem for loudspeakers.

You might want to consider a MiniDSP SHD Studio. This assumes you have your own DACs. It uses Dirac Live which is similar to ARC. This unit is $1,300 and includes streaming. Benchmark Media Systems uses a Studio with their own DACs and is super pleased with the results. It also includes subwoofer crossovers and bass management. 

@lanx0003 

It is always best to use three spikes. They should be driven clean through any carpet and padding into the plywood. Three spikes on tile is OK as long as you lower the speaker gently. 

The best digital signal processing units sound like whatever you make them sound like. You can create any target curve you like within certain limits. After 25 years of doing this I can look at a curve and tell in a general way what the system will sound like. You can not determine imaging this way. I have to see measurements on each channel separately to get an idea, again in a general way. The best units are now using 64 bit floating point systems with powerful processors. They run at a minimum of 24/192. There is no characteristic sound. It all depends how you program it. Most system like Dirac Live run on their own algorithms leaving you little room to play. You have to accept whatever they do with minor adjustments. With my old Tact and the new DEQX units you can let them do their thing and walk away or you can grab the bull by the horns and program the unit yourself which IMHO produces the best results once you learn what you are doing.  

@lanx0003 

What you are listening to is distortion, bass resonance. Little loudspeakers do this all the time intentionally to give the impression of bass. I can understand wanting more bass power and weight. The best ways to do this are Digital Signal Processing and subwoofers.