Anthallo asked in Cars & TransportationCar Audio · 10 years ago

# RMS Power Output of 4-channel Deck to Two Speakers?

I have a deck that provides "22W x 4" RMS power. If I only hook up two speakers to the deck (no amp), will the power still be 22W per channel, or will it be more?

(I don't remember the ohms of my speakers, so if you need that, sorry. They're 6.5" Hertz DCX 165)

Relevance
• Steven
Lv 7
10 years ago

It will be about 22W per channel no matter how many are connected. The thing to remember is that sound is logarithmic so half power is -3dB, ie just barely noticeable. Unless you use really bad speakers, 44 Watts is plenty.

The RMS rating is the maximum undistorted sine wave that the amplifiers can produce. Combine this spec with the speaker impedance and you can estimate the rail voltage used by the amplifier:

Lets assume your amp is bridged and using a 4 Ohm load. 22Watts RMS is 44 Watts peak. RP=V^2 so V= root(4x44)= 13.27V. Sound familiar? So 22Watts assumes your running battery voltage is like 14.5Volts since the output transistors have a saturation voltage that wastes about 1 Volt.

Each channel has it's own circuit that can deliver on peaks the battery voltage less a bit to the attached speaker. If you do not connect to two outputs, the battery voltage limit remains the same for the other speakers.

Amplifiers that convert the battery voltage to something higher are required to get more than 22W per 4 Ohm speaker. Even 22W requires a bridged output, ie each channel is actually two amplifiers.