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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
ryder OP
1,690 posts
 
Thanks for the advice Shadorne. It was useful and much appreciated. Regarding listening to LOUD music up to 100dB SPL or higher, I have measured the SPLs from 4 meters away at the listening position using a Radio Shack SPL meter and the needle has never gone past 90dB in the peaks during fluctuations when listening at insane volume levels. In fact 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. In this sense I am little amazed when reading about folks listening up to 100dB or beyond that. Maybe my ears are less tolerant compared to others with stronger immunity to high SPLs. My average SPLs are around 70-80dB when listening to reasonably loud music.

Yes, I am well aware that Harbeths are not designed to play at high SPLs and as such have practiced caution as to prevent any excessive over-driving to these delicate speakers. The perception of loudness varies with different individuals as I personally find the Harbeths are able to cope up with my expectations when I crank up the volume and blast the music. Most often my ears give up first(90dB peaks) before my speakers(or ear drums) blow up. My amp is rated at 80W so I guess I have got everything covered in my listening habits. By the way, the listening position is not against the wall as there is a 3' space from the chair to the back wall. I do know the effects of placing the chair directly against the wall and I don't like the results either.
ryder OP
1,690 posts
 
Thanks for the link Tvad. I have gone through the document and it seems to make more sense now. I particularly agree with the statement that loudspeaker sensitivity ratings are often overstated by a few dBs. That is the reason it is always prudent to practice extra caution by allowing some buffer to account for all these anomalies by means of listening at lower volumes several notches below the ultimate output of the amplifier, or by getting a substantially higher-powered amp.
elevick
2,636 posts
 
Power isn't everything. 30 watts from a Pass Labs may be sound louder than 60 watts from a cheap yamaha receiver. It's quality vs quantity.

Keep in mind that your 80 watts will be hard to beat without going to a massive amp. 80 watts to 160 will only gain you 3db. To double the perceived volume you need to increase by 10db. In other words, you need to get to 200+wpc to really hear a difference with a similar quality amp.

My final input with your calculations is placing speakers against walls or in corners to gain bass volume/db. No 2 speakers will gain the same benefits or problems by moving them closer to a wall. Almost every time though, you will lose a lot of imaging by doing this and probably get "boomy" bass.
ryder OP
1,690 posts
 
Yes, I forgot to mention about quality power between a good amp and a cheap receiver. The same goes with power differences between solid-state and tube amps. Both my Plinius and Rega amps rated at 100W and 80W respectively sound much louder than my top model Sony 5-channel amp AV rated at 130W. Not only that, using the BTL function of the Sony amp can increase the power from 130W to about 210W in 2-channel mode. Even at this power output the Sony amp sounds substantially "weaker" than both my 2-channel audiophile amps. Until now I don't have any clue to explain this in a technical perspective although price-wise the cheap Sony is taken for granted to sound softer. Due to this experience I have lost respect in the Sony brand in coming up with inferior mass-market amps although they seem do much better in other areas.

Another issue I read for years is tube amps sound substantially more powerful than a solid-state amp with both having similar power ratings ie. a 20W tube amp can sound much more powerful and louder than a similar 20W solid-state amp, or an 8W tube amp sounds more powerful than a 30W SS amp. Yet again I don't know how to explain this phenomenon. It would be good if someone with technical knowledge and experience can clarify.
shadorne's avatar
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shadorne
7,477 posts
 
In fact 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.

At 4 meters this requires 88 + 12 = 100 db SPL from the speakers. From the amp this requires 32 watts. So you should be easily OK to reach these peak level without any problems of any sort from your amp or speakers.
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