[Lost81]

Hi guys,

I got my sound pressure meter back, so I am curious how many watts my amplifiers are putting out at normal listening levels.

I did a theoritical model based on a distance of 1 meter (3.28 feet), but I don't listen 1 m away from the speakers, so it won't work.

AKSA 100 Nirvana:
109.0W into 8 ohms
163.5W into 6 ohms
218.0W into 4 ohms

Mission 754 Freedom 5:
Nominal Impedence: 6 ohms
Sensitivity SPL 1m/2.83V:  90dB
Max SPL (per pair):            112dB
Recommended power: 30 - 250 Watt / Channel

Watt / dB@1m[/u]
   1 / 90
   2 / 93
   4 / 96
   8 / 99
  16 / 102
  32 / 105
  64 / 108
 128 / 111


My listening position is 8' 1" away from the speakers.
The speakers are 5' 9" apart.

Anyone have the formula for calculating the decrease in dB over distance in air at sea level ?

Thanks!


-Lost81

[doug s.]

for non-line-source speakers, rule of thumb is logarithmic spl loss as distance increases.  so, for 90db/1w/1m, ya lose 3db at 2m, (87db); 6db at 3m (81db); 12db at 4m (69db); etc...  

line source loss is linear, & a 90db/1w/1m speaker would be at 81db at 4m...

of course, in a smaller room, the drop offs may not be so bad, due to room loading.

doug s.

[Lost81]

Thanks, Doug!


-Lost81

[JohnR]

Um, for a point source in free space, the power drop will be 6dB every time you double the distance. Imagine that the sound is radiating in a sphere: double the size of the sphere, four times the area. Thus the power per unit area is one-quarter.

In a room, reflections and reverberation make this not really work.

[JLM]

Having two channels (stereo) will double the power and add 3 dB.  

In 1500 - 2000 cu. ft. (typical) rooms this added to room gain roughly balances with the distance losses from listening from across the room.

[Lost81]

Having two channels (stereo) will double the power and add 3 dB.

Good point. I overlooked that


-Lost81