How to make small room sound bigger

The only trick to make room acoustically bigger is to open the door & the windows, and that allows longer wavelengths to form, and pushes the Schroeder frequency lower.

«Back in 1954, Schroeder referred to the frequency at which rooms go from being resonators to being reflectors/diffusors as the “crossover frequency.” We now call it the Schroeder frequency.»

It is the reason why using a grid of tuned Helmholtz resonators and diffusers, i smooth out any disruptive modes, i have around 100 of them from the diameter in millimeters to few inches with various lenght from 8 feet to 6 inches, i dont need a subwoofer with my 7 inches speakers box, and i enjoy all acoustical cues optimally for my room : dynamic, timbre,imaging, soundstage, listener envelopment, intimacy ETC...

Dont buy anything experiment and have fun...

Study basic acoustic WITHOUT any tool save your ears... Train them...

Acoustic phenomenon are not mainly linear mathematical phenomenon.... They are  mostly non linear ....You ears are the best tool IN YOUR ROOM....

😁😊

If you're a DIY kinda person there's a whole series of U tube videos from a German acoustic engineer by the name Jesco. They are excellent. The videos on GIK are also informative. If you're not interested in learning how to fix the acoustic short coming in your room and build treatments yourself, there's a whole world of companies that will be glad to help at a cost, but hey it's part of the hobby for me. Good luck, it can be a rabbit hole if you get into it.

sure modify your components  begin with power supply capacitors, install better resistors like Audio Note non-magnetic silver, add filter chokes to the AC and inputs, etc.  

Happy Listening.

Use small speakers on low stands like Isoacoustics with upward tilt to effectively make the room sound larger.