Sorry for the stupid question but
Bigger speakers also sound bigger to me than smaller ones even at the same volume.
I've been told this is not correct and impossible but i still feel that way, and also other people do because I read the cliche of "these speaekrs sound much bigger than they are" Pretty much everywhere.
What is the cause of this phenomenon?
This is a quite complex matter, but it can be broken down in a few parameters that can not individually be quantified. Here are a few:
1: Intermodulation distortion is probably the largest factor. A non linear motor, suspension, radiating area etc will give us clues that reveals to our ears that "this is a bit difficult" for the speaker, and that takes away the "lightness" and "effortlessness" of the speaker.
Typical factors that does cause high IMD are large and heavy surrounds, high inductance, non linear motors, motors that are too weak and has to deal with high mass. Especially if the voice coil has many turns (which often can be seen from the inductance).
2: Sensitivity is not a factor that by itself is possible to hear. But as the amplifier does not have to work as hard, it means it will distort less. If the voice coil heats up, it will affect the frequency response of the speaker. It can also give us a slow modulation effect. So unless you have a big enough amp and the coil does not heat up much, this is an audible parameter.
3: A speakers directivity is one important factor unless the room is very big or semi anechoic. For example, if the speakers are located in the dead end of a LEDE-room, directivity is not as important as if they are placed in a small non treated room. For a typical room, we face problems in the transition zone called the Schröder frequency. This can typically be 100-500Hz. This is where a room causes lots of high Q problems. In other words, this is where we typically have some hard midrange resonances caused by the surfaces near the speaker, and we often have to dial back this area a bit for those frequencies not to over power the experience completely. This problem is significantly smaller if we can reduce the dispersion of the loudspeaker.
4: And that leads us to the frequency response. We can not design a speaker that hits the room response precisely, so the frequency response will be a result of what typically works across many different rooms. Small speakers for small rooms needs to be dialed back more in the lower midrange. They also lack the capacity to keep high SPL, so by dialing back the mid bass/lower midrange a bit, and keep it at a higher level at Fb, we can get slightly more total SPL, and have less problems in a common room.