If you would have seen the numerous unboxing videos and press images of the Nexus 5, you would have noticed that the handset has dual speaker grilles at the bottom. Sadly, if you went through the device service manual, you would have realized that only the left one is the actual speaker, with the right grille being their only for the secondary microphone and cosmetic purposes.
To make matters worse, initial reports from new Nexus 5 owners suggest that the phone’s speaker is invariably quiet while playing back music using certain apps. Its not a hardware fault though as confirmed by Google to the folks over at Android Central. Turns out there is some underlying issue in Android 4.4 KitKat, due to which the Nexus 5 speaker is not working at its optimal best.
A fix for this issue should be coming soon, perhaps, with the rumored Android 4.4.1 KitKat update.