Sonic Boom

Sonic Boom is a Tier 2 perk in Call of Duty 4: Modern Warfare that increases the damage (and consequently the killzone radius within the blast radius) of all explosives used by the player. Explosive weapons that are affected by Sonic Boom are fragmentation grenades, launched grenades, Composition-4, RPG-7s, and Claymore mines. Sonic Boom is canceled out by the Juggernaut perk and will not affect flashbangs, stun grenades, or smoke grenades.

In Game
Sonic Boom increases damage just enough for hand grenades to kill at the very edge of its blast radius. Other explosive items' kill radius are nearly doubled, but the increased blast radius of any of them aren't nearly as large as the hand grenade. This perk is not commonly used due to the availability of more versatile Tier 2 perks, but can be useful, as this perk may be used by players who mortar frags or use grenade launchers. Players may also combine this with claymores on objective based game modes. This perk is also useful because it may help to kill more foes in a large firefight or in a small map.

Some players make a class around this perk. They use a gun with a Grenade Launcher, and use the perks Sonic Boom and Martyrdom. This is very effective on small maps like Shipment. Sometimes the Grenade Launcher is replaced by the Frag x3 perk.

If a reference for distance is needed, look for the boxes on Shipment. The large cargo crates that you see many of in Shipment and Wet Work are exactly 256x100 units in size. 256 being 6.5 meters, the same exact range of the Frag Grenade's max blast radius.

Sonic Boom is the Call of Duty 4 equivalent of the Fireworks perk in Call of Duty: World at War and the Danger Close perk in Call of Duty: Modern Warfare 2.

It is interesting to note that in S.S.D.D., the picture to the left and above the live firing range words, it is the same picture, only sideways.

Trivia

 * In Modern Warfare 2 the Danger Close V challenge awards you with a title "Sonic Boom", referring to the previous name given by Infinity Ward