2. tech-talk
  3. 1253939809

Amplifier Power Ratings & Speaker Sensitivity

We often hear comments about amplifier X does not have sufficient power to drive speaker Y or speaker Z requires minimum 200W to come alive. I am trying to figure out if there is a correlation between amplifier power ratings and speaker sensitivity in the prevention of over-driving of speakers when listening at high volume levels since stressing an amplifier beyond its intended output will cause the amp to clip that may subsequently cause damage to the coils of the speaker.

From what I have read, below is my understanding but please correct me if any of my interpretations are wrong.

1) For a manufacturer's stated sensitivity of say 86dB/W/m, 1W of power is required to produce 86dB SPL at a distance of 1m away from the drivers.

2) In the doubling of power, the SPL will increase by 3dB. For example :-
1W @ 86dB
2W @ 89dB
4W @ 92dB
8W @ 95dB
16W @ 98dB

3) For every distance added, the SPL will decrease by 6dB. For example :-
86dB @ 1m
80dB @ 2m
74dB @ 3m
68dB @ 4m
62dB @ 5m

4) Close placement to rear wall will boost 3dB in the bass

5) Close placement to a corner will boost 6dB in the bass

To determine whether an amplifier is capable of driving the speakers at a given loudness and distance without causing damage to either the speakers and/or the amp, can we use the power rating of the amp and the sensitivity of speakers as a basis in controlling the level of loudness we are getting from the system? Let say a 50W amp is used to drive a speaker with 86dB sensitivity and the listening distance is approximately 4 meters away. Can we work backwards from the peaks we are getting in the SPLs from the listening position? With the assumption of 90dB as the absolute peak SPL when listening at insane volume levels at 4 meters away(-18dB){at least in my case although I am aware some folks listen past 100dB}, the SPL at 1m away is 72dB.

At 4 meters listening distance,
1W @ 72dB
2W @ 75dB
4W @ 78dB
8W @ 81dB
16W @ 85dB
32W @ 88dB
64W @ 91dB

64W of power is required to produce 91dB SPL. If using lesser powered amplifiers of 60W and below, the amp will have potential to go into clipping. If listening at 88dB SPLs(peaks) and lower there would not be any concern on speaker or amplfier damage.

I do know that room conditions, amplifier gain, power supply and some other factors will play a part as well but the above should at least give a basic idea by providing a rough estimate on how loud should one be listening so as to prevent any damage to the components?

I understand that people with high-powered amps will not need to worry so much when cranking up the volume but it can be useful for some other folks who have flea-powered amps(especially tube amps), particularly those who like to listen loud.

Any advice or feedback would be most appreciated.
ryder
tvad
9,467 posts
 
09-26-09: Ryder
...the maximum SPL I have got when listening to very loud music is 88dB in the peaks as my ears often give up first before something blows up in flames of fire...My average SPLs are around 70-80dB when listening to reasonably loud music.

Everyone has his own definition of "loud", but these readings are pretty low, and I wonder if there's a glitch in the measuring method.

Do you have your Radio Shack decibel meter set to "C" weighting, and "Fast" response when taking your measurements? If not, consider changing to these settings and then testing again.
ryder OP
946 posts
 
Bob, I have not measured the in-room frequency response of the room since I am quite happy with the sound I'm currently getting from the speakers. Furthermore there isn't much allowance to move the speakers around and I have no plans to add EQ correction or a sub to the system. Nevertheless I will do a measurement someday and see how flat the frequency curve would be.

Yes, I have the Radio Shack SPL meter set to "C" weighting and "Fast" response when the measurements were taken. I am 100% positive it's my ears and nothing else. I have sensitive ears and suffer from mild hyperacusis hence cannot tolerate very high SPLs. My problem started during my younger days when I listened to very loud music(probably >90dB) and my hearing might have been damaged during that time. Since the symptoms have somehow diminished these recent years, I am trying to preserve my hearing by listening at low to moderate volume nowadays although I occasionally still crank up the music. I have to admit my ears are not as strong compared to a few others.
tvad
9,467 posts
 
Ryder, thanks for the explanation. I was just checking...
unsound
6,115 posts
 
Ah, that explains it better.
I often suspect that some who are not familiar with undistorted loud volume sound subconciously go into defensive mode in anticipation of pending distortion. To avoid distortion it helps to have plenty of clean headroom. Any one who attends live classical concerts and has sat fairly close to the stage can attest to the just how loud the music can become.
satch
329 posts
 
This is all done for one speaker (unless I missed that point. In that case: sorry!). Since most of use two speakers in the room, what does that mean? I seem to recall that you can add 3 dB (A) to the equation.

As for quality/quantitiy: 1 Watt is 1 Watt, from whatever amp it comes. Whether or not it will sound as good... that's an other debate.
More to discover