Mass loading my speaker stands with sand resulted in a significant tightening of bass. And it is a close to free as you can get.
Speaking of free, and I know this going to sound trite to some, the single tweak that results in the most significant improvement in my personal experience is to simply close my eyes, or listen when it's dark outside (my listening room has windows). Whether we want it to or not, our brains are always at work processing information trying to make sense of the world around us, and I find that every bit of information being processed by any of the other senses reduces my auditory experience. It is not always easy or possible for me to isolate just my sense of hearing, but when I can it makes for the most engaging sessions.
Speaking of free, and I know this going to sound trite to some, the single tweak that results in the most significant improvement in my personal experience is to simply close my eyes, or listen when it's dark outside (my listening room has windows). Whether we want it to or not, our brains are always at work processing information trying to make sense of the world around us, and I find that every bit of information being processed by any of the other senses reduces my auditory experience. It is not always easy or possible for me to isolate just my sense of hearing, but when I can it makes for the most engaging sessions.