The spec is pretty pointless a person with perfect hearing has a range of 20hz-20khz. This is often quote by most, some manufactures seam to quote stupid numbers for some reason known only known to them.
Sony do make some very good speakers, these thu I have no idea about and in the price bracket I would be look at wharfdale speakers.
Frequency Response: 45 Hz–50 kHz
The problem is, that response is unqualified. That is there is no reference to compare it to. For example, if it said - 45hz to 50hz ±3db, that would mean something.
These Sony speakers are good for the money, the problem is, they simply aren't that much money.
In a very broad context, if the frequency response is very high, then down in the hear-able range, the Tweeters are straining to a lesser degree. If the Tweeter goes to 50khz, then at 20khz, it is cruising. If the limit is 20khz, then at 20khz, it is at its limit.
But, that alone can not be used as a metric. Good speakers are good regardless of the spec, and bad speaker are bad regardless of specs.
For very low cost speakers, the Sony Core Floorstanding speakers are OK. Though I'm not sure where you are, or how much you are paying.
To make any judgement, we would need to know where you are, and how much you are paying, and what other options are available to you.
Sony has always made good speakers ... for the money.