Not wise.
The subwoofer generates strong low-frequency energy and vibration, which can transfer to the speaker and create additional resonances that interact with the speaker’s own natural resonance. Additionally, the La Scala is 40 inches tall, with the horn located around 33–34 inches—right at typical ear level when seated. Placing it on top of a subwoofer would raise the tweeter and upper midrange horn above the ideal listening height, potentially affecting the speaker’s imaging and soundstage precision.
Over time, the continuous vibration can compromise the structural integrity of the speaker cabinet. By the time cracks appear—either internally or externally—it may already be too late to prevent damage.
Thank you for the reminder. This makes me realize that next time I’m considering a used pair of speakers, I should ask the seller whether they’ve been placed on top of a subwoofer for an extended period.
Lastly, the ideal placement for a subwoofer is not necessarily directly beneath or near the speakers. Experimenting with different positions is key to seamlessly integrating the sub into your system. Limited space should not be an excuse — it may even be possible to place the subwoofer along a side wall.