Vernneal - That's subject to personal circumstances. My horns are 24" wide by 21" deep by 52" tall. Not small and not enormous. Because they are back near the front wall, their space consumption isn't particularly egregious, however, the 18" diameter horn mouth is pretty eyecatching. In other words, the aren't really too big but they are pretty conspicuous.
Given the need for space behind them, I would say that most panels are effectively larger.