If you're a Simpsons fan, surely you remember the scene where Bart found ten megaphones, and lined them up to see what would happen.
While this was an awesome prank, The Simpsons isn't exactly known for being scientifically accurate. Which is why TheBackyardScientist decided he'd replicate it to see what happened.
He set up ten megaphones in a row, and used a Sound Level Meter to determine how loud they actually were, compared to just one megaphone.
And the results were... disappointing.
Using one megaphone gave a sound level of 79.7 decibels, while using TEN only raised the sound level to 81dB. For reference, the average vacuum cleaner is around 87dB. Not quite enough to shatter windows...
They then placed all the microphones in a circle which made a literal feedback loop. You know that high-pitched squealy noise that microphones make? Imagine that but super super loud.
That gave off a reading of nearly 120dB.