Jungle Drums is the 2nd upgrade for the Monkey Beacon in BTD4 and is is the second upgrade of path 1 for the Monkey Village in BTD5. In BTD4, Jungle Drums cost $1275 on Easy, $1500 on Medium, and $1600 on hard. In BTD5 it also costs $1275 on Easy, $1500 on Medium, $1620 on Hard and $1800 on Impoppable. It increases attack speed for all towers in its radius by 15%. Towers that attack every four frames or faster, like Spectre, Sun God, and Ray of Doom are unaffected.
It's a good idea to combine this with extremely powerful towers such as the Destroyer or the Spiked Mines.
To fit maximum temples, this upgrade should not be purchased as the previous upgrade increases the Sun God's range, thus increasing the range for sacrificing towers. However, the increased range also makes it easier to max a TOTMG. A maxed TOTMG does better than 2 Sun Gods.
In Bloons TD5 Mobile, fully upgrading Attack Speed in the Monkey Lab will allow all towers to "be under the effect of Jungle Drums". This can stack with this tower upgrade, making it very efficient (and even more efficient with a Specialty Building upgraded to Tier 2, if it increases attack speed).