2. amps-preamps
  3. 1082152469

enough watts to drive these speakers? Help?

Greetings all,

I've got a friend with 89db efficent speakers playing in a 12'x15'x8' bedroom. He's looking at getting a 8 or 10 watt, low powered SET amp and is concerned if his speakers will play "loud enough".
He usually listens to classical and jazz at "moderate" levels at the loudest.

I compute that he should be getting 95db using only 4watts and the room should give a little more, perhaps 2db.

Are my calculations correct?

Anyone else that has a similar setup and can comment if it's loud and dynamic enough?

Thanks and happy listening!
myraj

Showing 2 responses by bombaywalla

bombaywalla's avatar
bombaywalla
1,958 posts
 
Your calculations assumed that your friend would be listening at 1m (3.3ft) from the speaker in his bedroom. Would that really be the case?
If not, one loses 6dB when one moves back from 1m to 2m. Then one loses 3dB when one moves back from 2m to 3m. If your friend is 3m (~10ft) from speakers, the 89dB efficient speaker yields 80dB SPL at his listening position using 1W. To get 90dB SPL, he'll need 10X the power i.e. 10W. At this pt. the amp runs out of gas. There'll be a 3dB increase in SPL owing to 2 speakers i.e. stereo music. Room can re-inforce to some degree but it is hard to tell.
Ill designed xovers in the speakers can eat up some watts.
If he's willing to not crank it up, 8-10W/ch should be fine if everything else has a reasonable design (a bit nebulous but I hope that you can understand what I mean).
bombaywalla's avatar
bombaywalla
1,958 posts
 
Fatparrot,

Just saw your comments.
6dB loss in SPL per doubling of distance is correct! We are not talking about a power measurement here; rather, a voltage measurement when we read off SPL on a meter. Hence, 20*log() rather than 10*log(). Another thing is that since it is a ratio (SPL at 1m vs. SPL at 2m) when we do a divide operation, the impedance cancels out.
Hope that this clarifies.
More to discover