Does iPhone 5S loudspeaker different to iPhone 5 loudspeaker?

I'm kind of curious. I have bought an iPhone 5S on 21st September and noticed that the loudspeaker produce different sound to the iPhone 5. The iPhone 5S loudspeaker seems to have better bass than the iPhone 5. I played the same exact song synced on both phones, but the sounds they produced are not the same. The 5S has much more bass sound than the 5. Also, the intrument sounds on 5S are much stronger than the 5. I can hear much more details of the instruments in iPhone 5S.

One thing I suspicious about is that some apps I used on the iPhone 5S produce pretty bad sound. For example, when I sent a message on Whatapps, you would normally hear the sound like soft pop, but on 5S you will hear the squeaky pop instead. This is kind of annoying to me. I wonderded my loudspeaker is a defect or that the sound quality of the pop sound in Whatsapp is bad.

Please advise. Thanks.