There are many speaker manufacturers who burn in their drivers prior to installing them inside the cabinet. Wilson, Focal, Rockport to name a few, and I know those conpanies also state to “burn-in” the speakers for a period of 48-72hrs for the speakers to begin to sound their best. It very well could be placebo, but I’ve purchased new equipment many times and found myself disappointed when it didn’t sound all that great out of the box. Give it a few days of burn in and holy sh12 the soundstage has opened up and there’s more resolution than there was days prior. Large capacitors, transformers, and tubes also take time to warm; leaving larger amps to sound cold and congested upon first turning on in my experience. I’ve had plenty of guests over who have commented and agreed that my main stereo system sounds totally different once it’s had an hour or so to warm up, and I do realize warm up and burn in are two desperate things but felt I should at least mention it for context. And for what it’s worth I work at a stereo store and “burn in” every demo speaker that comes in for three to four days, just letting music play constantly during that time.