What you see on the readout is the amplifier gain.
The sound level will increase or decrease due to 2 things; the gain setting and the input voltage to the unit.
You can set the gain to 0db, and that means unity gain. If 500 millivolts RMS is the average input voltage from some source, then the output voltage to the speaker will also be 500 millivolts. Some sources may have different output levels than others, so the even though the receiver gain says the same the volume will change.
A CD player may also have different output voltage levels depending on the CD being played. There are huge differences in the levels on CDs, so that will also change the volume with the same gain setting.
A setting less than 0db gain (-)on the amplifier will mean the output voltage to the speaker is less than the input voltage from the source component. A setting over 0 db (+) means the output voltage is higher than the input.
When the amplifier is set to 0 db, there is unity gain, which means the amplifier is not amplifying the input voltage, but it IS putting out a lot more CURRENT (to the speaker) than is coming in from the signal source, so it is acting as a POWER amplifier nevertheless.
The sensitivity of the speaker also has a big effect on the volume, without changing the gain setting of the receiver (amplifier).
Speakers are rated in db per watt. A speaker that is rated for 90 db per watt will do exactly what that implies; it will produce a sound level of 90 dbA at a distance of one meter when one watt is supplied by the amplifier.
For an 8 ohm speaker, It takes 2.83 volts across the amplifier output to drive the speaker with one watt of power.
For a 6 ohm speaker, it takes 2.45 volts to produce one watt. The voltage is lower, but the current will be higher. Power is voltage times current.
Now suppose we still have the amplifier set at that same level, but we change to a speaker with a sensitivity of 84 db per watt. The sound level produced by the speaker at one watt will be 84 dbA.
84 dbA is ONE-Fourth of the sound level compared to 90 dbA. Each 3db is a factor of 2 up or down.
90 dbA is a moderately loud sound level, but not REAL loud.Another way to look at it is that the speaker that has a sensitivity of 84 db/watt will need 4 watts to produce a 90 dbA sound level. The one with a sensitivity of 90 db/watt only needs one watt to produce the same sound.
A 6db difference in sensitivity between 2 speakers means the less sensitive one needs 4 times as much power to get the same sound level. each 10 db is ten times as much.
Did I mention that speakers with sensitivity that low really really suck?
With speakers that have a sensitivity of 84 db/watt, you will have to set the gain of the receiver much higher to get a given volume level compared to more sensitive speakers. It takes more gain to get more output voltage to get more power to the speakers.
What you need is some speakers with a sensitivity of 89 db/watt or higher. Then you will need a lot less power to get a given volume level and your amplifier will be much less likely to distort on peaks.
An analogy would be two wagons; one with a 4000 pound load and the other with a 1000 pound load.
Your speakers are like the 4000 pound load. It's going to take a lot more power for a given speed than if you were pulling the 1000 pound load (which represents the 90 db/watt speakers).Memo
; I had some of the numbers totally wrong here before I corrected them today (2/23); that's what I get for doing something too fast and not checking; my apologies for the confusion.
Originally Posted by themow
Can you elaborate on this statement? It would seem that as volume control increases, the amp output would increase thereby working harder. Im not disagreeing, I just want to understand.