I am a 50-year pro recording engineer. I have 2 iPads, Gen. 1 and new M4 model.
There is no question: the so-called 'improved' speakers in the 2024 iPad M4 are far inferior to my Gen 1.
I've already had it for more than 14 days, and there's so many reports of this, I don't think comparing it to other M4 iPads at the Apple Store will reveal any especially wrong with mine. They're just crap speakers delivering significantly less dynamic range. Luckily I purchased extended Apple Care.
I still love the new iPad, and for me this isn't a deal-breaker, because I almost never listen to music straight thru the iPad speakers; I almost always send the signal to good speakers or headphones.
Still, what's up with the claim, Apple, that these speakers delivered 'better' more-spacious sound than previous iPad models??