Hi ssoleymani,
"Laid-back" means a prominent dip or "suck-out" in the midrange--likely about 3 dB or greater (verrry laid-back would be 6 dB or more)--which has the effect of making the speaker sound rather dull or distant, as if you had thrown a blanket over the speaker.
Our ears are acutely sensitive to midrange sounds, and in controlled listening tests, we can sometimes detect differences of 1 dB. Variations in midrange frequency response of 3 dB or more are easy to hear. Male and female vocals will sound more removed (behind the plane of the speakers), or farther back and less detailed when there's a 3-dB+ dip in the mids. "Laid-back" is a polite term for saying a speaker lacks clarity and presence or has poor linearity in its frequency response, especially in the critical midrange.
Regards,
