rwacka
31-10-2012, 19:06
Evening all. I have been trying to get my head around the relationships between amplifier input sensitivity, amplifier power and range of volume control. And of course there is also speaker sensitivity to consider.
I understand that input sensitivity, quoted in V, indicates the input required for full amplifier output (W). The relationship between input voltage and input sensitivity can be used to calculate the excess db for a given input (approx db=20*log(v1/v2) where v1 is the input voltage and v2 is the input sensitivity).
So, for a Leak Stereo 20, input sensitivity is 100mV and power is 10 wpc. So for a CD input at 2V full power from the Leak (10 wpc) is reached with the volume control at -26db attenuation.
On the basis of a halving of power reduces the volume by ~3 db you get a relationship like this:
http://i1218.photobucket.com/albums/dd410/rwacka/ampsens.png
What's the point of this? It means (I think) that if you know the sensitivity of your speakers (say 88db at 1 W) you can read across to find out the volume attenuation (and hence position of the volume control) for a reasonable listening volume. So for sensitive speakers (say 100db/w and assuming a passive pre) a Leak Stereo 20 is not a good match - you get 1 W of power (100 db of volume - loud in a domestic setting) at an attenuation of ~ -36db. So only a small turn of the volume control and it is too loud.
How correct this logic is I am not sure and as for relevance.... well it kept me amused for a while and I like to think I might understand these complex black boxes a wee bit. Would welcome any thoughts.
I understand that input sensitivity, quoted in V, indicates the input required for full amplifier output (W). The relationship between input voltage and input sensitivity can be used to calculate the excess db for a given input (approx db=20*log(v1/v2) where v1 is the input voltage and v2 is the input sensitivity).
So, for a Leak Stereo 20, input sensitivity is 100mV and power is 10 wpc. So for a CD input at 2V full power from the Leak (10 wpc) is reached with the volume control at -26db attenuation.
On the basis of a halving of power reduces the volume by ~3 db you get a relationship like this:
http://i1218.photobucket.com/albums/dd410/rwacka/ampsens.png
What's the point of this? It means (I think) that if you know the sensitivity of your speakers (say 88db at 1 W) you can read across to find out the volume attenuation (and hence position of the volume control) for a reasonable listening volume. So for sensitive speakers (say 100db/w and assuming a passive pre) a Leak Stereo 20 is not a good match - you get 1 W of power (100 db of volume - loud in a domestic setting) at an attenuation of ~ -36db. So only a small turn of the volume control and it is too loud.
How correct this logic is I am not sure and as for relevance.... well it kept me amused for a while and I like to think I might understand these complex black boxes a wee bit. Would welcome any thoughts.