Sonic Boom

Sonic Boom is an upgrade for the Boomerang Thrower that appears in Bloons TD 2, Bloons TD 3, Bloons TD 4 and Bloons TD 5. This upgrade allows the Boomerang Thrower to pop frozen bloons. Just for that reason, Bloons TD 2 states that Ice Towers work the best with Bomb Towers or Sonic Boom Boomerang Throwers nearby.

The upgrade picture is shown to be of either three yellow boomerangs gradually increasing in size or sonic waves.

Update History (Bloons TD Battles Mobile)
Besides accessing Red Hot 'Rangs and Bionic Boomer, the Sonic Boom upgrade is rarely used. A slight price drop to Sonic Boom has been made due to its really niche purpose.

4.1

Sonic Boom price decreased ($100 → $50).

Trivia

 * In Bloons TD 5, when the tower throws the boomerang with this upgrade, a sonic wave can be seen briefly.
 * With Double Ranga, only one sonic wave is shown, even though there are two boomerangs being thrown.
 * With Red Hot 'Rangs, no sonic waves are shown. (BTD5 iOS only)
 * In Bloons TD 2, the description for the Boomerang Thrower says Sonic Booom instead of Sonic Boom.
 * The BTD5 Artwork shows a Boomerang Thrower with Multi Target unlike BMC, it has the correct mark on the tip of the head.
 * The BTD5 Artwork shows that he is happy and opening his mouth. In BMC, he does a surprised face.
 * The Sonic Boom upgrade does not make a return to BTD6, most likely because it was considered useless due to its extremely high niche, especially when Red Hot 'Rangs is easily purchasable anyway. Instead, Long Range Rangs replaces the prior upgrade to the Red Hot 'Rangs.
 * In Bloons TD 5 Flash, the artwork is 3 rings but ingame its one ring, but Multi-Target fixes the problem.