One of the most often overlooked benefits of in-wall speakers is that the in-wall mounting takes the guess work out of the speaker voicing (so called baffle step) by giving very predictable low frequency behavior for the half space (2 pi) mounting of the wall. A free standing speaker, depending on the distance from the rear wall and side walls has a complex interference of their direct and reflected sound, causing dips in the response around 200 Hz, the so called “Allison effect”.
The other benefit of an in-wall mounting is much reduced diffraction. This reduction of early reflections helps both the imaging (localization of the phantom images created by multichannel audio) and the tonality (timbre) of a speaker system.
Our auditory systems “fuse” sounds which happen within ~3 ms of each other: the so-called “Haas effect”. In essence, we hear the direct sound and reflection (diffracted sound) as the same sound event. As these sources are coming from different positions, this smears localization and imaging cues. This is partly why you see all of the main monitors (not near fields) in a recording studio are soffit mounted in the walls and why the practice of mounting speaker no closer than 3-4 feet from the side walls should be adhered to.
The reflected sound also effects the tonality of the sound because it acts as a virtual source delayed in time from the original signal, creating comb filtering artifacts (successive peaks and dips in the frequency response) from there interference. This alters the perceived tonal balance of the system, depending how closely these dips fall in our “critical bands” of hearing.
So, when talking to customers, remember, high performance in-walls speakers don’t have to be a compromise in performance, they can actually be an advantage. They have predictable low frequency response and better imaging and tonality due to less diffraction.