I need help with this assignment on gain structure. I have attached it for better viewing. Thx

Mic Sensitivity

Sensitivity: –54 dBu (1 Pa input). Our microphone will have a given sensitivity, which is a measure of what electrical output level will be generated given a known acoustic input level. The greater the sensitivity, the greater the output level for a given input signal. This might be presented as follows:

Sensitivity: –54 dBu (1 Pa input). This means that given an acoustic level of 1 pascal (≈94 dB SPL), the microphone will generate a voltage of –54 dBu. This is nearly 1000 times (or 60 dB) smaller than a line level of about 1 volt. Hence, the need for a mic preamp!

Mic preamp

At each of the gain stages to follow, levels of gain are set in dB (unitless), and we can simply add or subtract dB from our signal level, since dB is always dB, a common ratio of powers or voltages. So, if our preamp is set to +60 dB, it means we are adding 60 dB to our existing signal of – 54 dBu (or 54 dB below 0.775 V, right?). That would yield –54 + 60 = +6 dBu = 0.775 x 2 (remember, +6 dB = 2 x voltage?) = 1.55 V, a nice, healthy, average signal level.

Power Amplifier Sensitivity

Sensitivity: 100 W into 8 Ω (2 VRMS Input). Our signal stays in the line-level realm, until we have to play it back, at which point it needs to be amplified to speaker level, a much higher level required to properly drive a loudspeaker. Most commonly nowadays, this amplification stage lives within the speaker cabinet itself, in the form of a powered speaker. Again, we have an input sensitivity, yielding a specified output level given a certain input-signal level, such as:

Sensitivity: 100 W into 8 Ω (2 VRMS Input). This means the amp will put out 100 W into a speaker rated 8 Ω, given a 2 VRMS input voltage. What if the speaker is not 8 Ω? Well, the speaker's impedance, which you can think of as a type of resistance is essentially inversely proportional to power. The lower the impedance, the greater the resulting power, and vice versa, all other things being equal. Halve the impedance of the speaker, and you will get double the power, barring any real-world limitations. Thus, assuming the amp can handle it, 100 W into 8 Ω will become 200 W into 4 Ω.

Loudspeaker Sensitivity

Sensitivity: 90 dB SPL (1 W input; @ 4 feet on-axis). Finally, our loudspeaker will also have an input sensitivity, written as follows:

Sensitivity: 90 dB SPL (1 W input; @ 4 feet on-axis). This means that given a 1 W input signal, the speaker will generate an acoustic signal level of 90 dB SPL measured at 4 feet on-axis from (directly in front of) the speaker.