Besides EQ/DSP, what are some other ways that can significantly change sound quality?

[Tangband]

You are using EQ so you are using no room correction software? If not did you ever consider using room correction software like mathaudio room eq It is free with Foobar 2000 An i have great results with it. In 45 jears time buying a 40,- euro measuring mic was the best investment i ever did in audio gear. My sound is atleast with 70% improved considering my horrible room acoustics.

My room measurments. The white Line (neutral targetcurve) is used to make it a level playing field really a hugh improvement.

https://imgur.com/T0I1hrT

I use GLM in the bass region and some mild shelving in tweeter area ( - 1 dB from 3 KHz ).
What I have found - Correct location of the loudspeakers in the room is still more important than roomcorrection and eq .

 

[Snarfie]

I use GLM in the bass region and some mild shelving in tweeter area ( - 1 dB from 3 KHz ).
What I have found - Correct location of the loudspeakers in the room is still more important than roomcorrection and eq .

The speaker placement was in my room let say 30% of the result 40% room correction but could differ for each room i guess. Measuring is knowing.

 

[Tangband]

The speaker placement was in my room let say 30% of the result 40% room correction but could differ for each room i guess. Measuring is knowing.

If you use really good loudspeakers correctly in the room, and have a very good room you dont need any eq at all.
Needing eq is a symptom of substandard :

1. Placement of loudspeaker or listener.
2. Bad or suboptimal room acoustics.
3. Bad loudspeakers.
4. Bad recordings

Changing the direct sound from the loudspeakers ( as you always do with roomcorrection and the use of eq ) always makes some things in the sound slightly worse .
So its all about compromises.

I use GLM because I have a less good listening room.

My brother has a very good listening room and after extended changes of loudspeakerplacement , the result was - best sound without any correction at all.

 

[Snarfie]

If you use really good loudspeakers correctly in the room, and have a very good room you dont need any eq at all.
Needing eq is a symptom of substandard :

1. Placement of loudspeaker or listener.
2. Bad or suboptimal room acoustics.
3. Bad loudspeakers.
4. Bad recordings

Changing the direct sound from the loudspeakers ( as you always do with roomcorrection and the use of eq ) always makes some things in the sound slightly worse .
So its all about compromises.

I use GLM because I have a less good listening room.

My brother has a very good listening room and after extended changes of loudspeakerplacement , the result was - best sound without any correction at all.

Agreeing with you that a room with good acoustics does not need any correction. But i can asure you that a quite bad room acoustics like mine ( as you could see with sometimes more than 13 db difference) with room correction like mathaudio will make any song sound better not worse. For instance after 45 i hear the Abbey Road recording completly balanced for the first time. After correcting my room acoustics i hear a band playing with al interaction between the band members close to a intimate experience.

 

[JWAmerica]

Let's not forget listening location. Sitting too close to the back wall is a common problem.

I was under the impression that sitting against the back wall, not simply close to it, eliminates some problems, similar to placing the mains against (or within 2" of) the front wall.