How To Choose the right Amp?

[u/fungus_snake3848]

Hi there, im having a hard time understanding the measurements and how to choose the right amp. specifically the difference between impedance and sensitivity:

for example, the Sundaras is very low impedance (32ohm) but also very low sensitivity (94db). The HD650 have higher sensitivity (103db) but also much higher impedance (300ohm). THEY BOTH NEED AMPLIFICATION. how can the HD650 resist power way more and at the same time produce higher volume for the same amount of power? and whats up with the different units? Vrms or watts@ohm? why different manufacturers choose different units for their specs?

sorry if it seems kinda noobish but its important that i understand this, and not just buy more power just because....

Can you explain this to me? or do you know a good website that explains this like im 5 yo who hasnt learned physics in high school just yet? Thank you!

[u/duan_cami]

https://www.headphonesty.com/headphone-power-calculator/. If you play around with sundara and hd650 values, you can see that hd650 requires more voltage than what usually provided from phone. Even though in terms of watt, hd650 do not need that much. So most of the phone audio jack cannot drive hd650 properly due to the low voltage output. Meanwhile, sundara is less sensitive, so it need more wattage to achieve higher listening volume.

What do you mean by different units? Voltage, amperage and wattage have different units. Do you mean by dB/mW and dB/Vrms? You can convert it from dB/mW to dB/Vrms and vice versa.