As far as everyone's aware, there are 2 kinds of gong culture found in the Philippines:  
The Cordilleran Flat Gongs and the Visayan-Palawan-Mindanao Knobbed Gongs.

In Vietnam's "Space of Gong Culture" (UNESCO MOIHH 2005), both knobbed and flat gongs are played by South Vietnam's Montagnards/Highland peoples, who are Austronesian/Cham speaking peoples + Austroasiatic/Katu & Bahnar peoples.

There is a notable similarity in construction and polyphony when you compare flat gong culture of Vietnam and Cordillera. Not completely similar in technique but it's still there. 

Natandaan ko kasi na people attribute the flat gong to China. I feel like it isn't that "simple" given China's use and context of flat gong is very different (not hand beaten + no polyphony).

So, would the Sa Huynh-Kalanay connection be a more plausible connection for the gongs? Especially since the jade artifacts in both Vietnam and Cagayan+Batanes already strongly imply that historical trade connection and potential similarities in native material culture.



\+ Flat gongs are also played in Cagayan Valley among the Agta and Gaddang and by very very few Ibanag and Itawit ritual officiants.  Would it be out of the realm of possibility that the flat gongs were played by the Ilocano and Pangasinan, maybe even a bit further south of them?

  
\*I think a caveat would be how come knobbed gongs didn't make it to Northern Luzon. Maybe knobbed gongs came later? 

Knobbed gongs are also played by the Suludnon/Panay Bukidnon people on Panay. And I was wondering how it got there if they were surrounded by lowland Christian peoples, unless it was already there before the Spaniards came. 

Maybe instead of the knobbed gong coming from Sa Huynh, it may have been transmitted through later trade from other cultures (Indonesians)? 

Also notably, free reed mouth organs were not transmitted to the Philippines through the Sa Huynh Culture. 

Roger Blench speculates that free reed mouth organs were an Austroasiatic invention, and there are free reed mouth organs being played now where Sa Huynh would have been, and mouth organs are also currently found in Borneo among the Dayak Iban of Sarawak and Sabah Dusun. 

 Austronesians certainly came to Indochina later as they are outnumbered by the existing Austroasiatics. So mouth organs had not yet become part of their organology, whilst Austroasiatic may have been a possible substratum in Borneo (D Kaufmann 2018)

Would the Sa Huynh-Kalanay Culture explain how flat gongs reached Northern Luzon?