In the voltage summation tool enter 1 V and 1 V. The result will be 1.4142. Convert this to dB and you will have 3.01 dB (the same result we calculated in Example 3).
When driving an 8-ohm load, the output noise of the AHB2 power amplifier is -112 dBW. If we run the amplifier in bridged mono, we have two output channels driving a single speaker differentially. The two output channels of the AHB2 produce uncorrelated white noise, so we can use our tool to sum these noise signals. AC line hum and buzz would be not be uncorrelated, but these are absent from the noise floor of the AHB2.
The two white noise sources (formed by the two output channels) are in series and can be summed using our tool. Enter -112 dB for both noise sources and the result will be -109 dBW at the bridged mono output. The 8-ohm bridged mono output of the AHB2 is 380W which is 26 dBW. The difference between 26 dBW and -109dBW is 135 dB. This number, 135 dB, is the signal to noise ratio of the AHB2 when it is running in bridged mono mode driving an 8-ohm load. In bridged mono mode, the signal level increases by almost 6 dB, but the summed noise only increases by 3 dB. This means that the SNR of the amplifier is actually 3 dB higher in bridged mono mode (135 dB mono, 132 dB stereo). The total output noise coming from the speaker will be 3 dB higher, but the music can play 6 dB louder.