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  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  (System | Reviews | Threads | Answers | This Thread)

  Responses (1-24 of 24)
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09-26-09   Your back of the envelope calculations are roughly correct. ...   Shadorne

09-26-09   Fwiw - i looked at your setup and the living room is a lot o ...   Shadorne

09-26-09   One other point i noticed - your listening position appears ...   Shadorne

09-26-09: Tvad
I believe you've done a very good job of capturing the essentials.

On this Daedalus Audio webpage, there is a link titled ".....more...(reprint on loudspeaker sensitivity from Musical Fidelity)."

It has some very helpful information along the lines being discussed here, IMO.

Tvad  (Threads | Answers | This Thread)

09-26-09   Thanks for the advice shadorne. it was useful and much appre ...   Ryder

09-26-09   Thanks for the link tvad. i have gone through the document a ...   Ryder

09-26-09   Power isn't everything. 30 watts from a pass labs may be so ...   Elevick

09-26-09   Yes, i forgot to mention about quality power between a good ...   Ryder

09-26-09   at 4 meters this requires 88 + 12 = 100 db spl from the spe ...   Shadorne

09-27-09   "09-26-09: ryder thanks for the advice shadorne. it was ...   Acoustat6

09-27-09   everyone has his own definition of "loud", but th ...   Tvad

09-27-09   Bob, i have not measured the in-room frequency response of t ...   Ryder

09-27-09   Ryder, thanks for the explanation. i was just checking...   Tvad

09-27-09   ah, that explains it better. i often suspect that some who ...   Unsound

09-28-09   This is all done for one speaker (unless i missed that point ...   Satch

09-28-09   Hi ryder, i just looked at your system page and noticed all ...   Acoustat6

09-28-09   Satch, re: watt quality; yes, no one is arguing the criteri ...   Unsound

09-28-09   Only 1 fly in the ointment. if you need say .... 100 watts ...   Magfan

09-29-09   Magfan, that's certainly a plan. fwiw, and with all due resp ...   Unsound

09-30-09   Un: also fwiw, it seems that people rely on 'cheap watts' to ...   Magfan

09-30-09   Interesting link, thanks.   Unsound

11-06-09   shadorne, there has been some changes. the peak spl i am get ...   Ryder

11-07-09   The designer for harbeth, alan shaw cannot factually answer ...   Ryder

11-07-09   i would be pretty sure it can handle that spl at 1 meter. m ...   Shadorne

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