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Speaker wattage question

I'm new here, so I hope I'm posting this in the appropriate forum.
I am running KEF LS50's with a Parasound Integrated amp. The amp is rated at 165 WPC @ 8 ohms. The speakers are rated for 25-100 watts (and are possibly lower than 8 ohms according to some sources).
If pushed, do I risk damaging a driver, or will I simply get clipping?
Any help appreciated and please pardon my ignorance on something I'm sure is common knowledge.
chrisg1000
erik_squires
16,821 posts
 
@inna

The SPL at a listening location is a function of the speaker sensitivity, room acoustics and distance from the source.

You could measure the SPL at 2.83 volts (1w/8 ohms) with the mic at the listening location and then do math from there if you really wanted to. :)

Divide your maximum RMS voltage by 2.83 and convert to dB. Add this to the SPL measured at the listening location and voila, you have your maximum SPL.

bombaywalla's avatar
bombaywalla
1,958 posts
 
inna
2,183 posts
08-11-2016 10:46pm
If the speakers are rated to be able to handle 200 watt/ch continuously and I am using 1000 watt/ch amp, how do I know where those 200 watts are, speaking of volume?
what erik_squires wrote is correct. 
Another method to do the calculation is as follows (you'll find this in several other of my posts in other Audiogon threads):

Say, your speaker is 90dB SPL at 1W, 1m & your speaker is 8 Ohms.
Since it's 8 ohms we are sure that 2.83Vrms into 8 ohms produces 1W of input power.
The SPL with drop by square of the distance from the speaker.
So, if you are listening at 3m (~10' away), the resulting SPL = 81dB.
There is approx 3db loss due to furniture, curtains, carpet, walls absorption.
There is a 3dB increase due to listening in stereo. So, the absorption & stereo effects essentially cancel out. 
You have 81dB SPL at 3m using 1W.
you have 91dB SPL at 3m using 10W.
you have 101dB SPL at 3m using 100W.
you have 104dB SPL at 3m using 200W.
you have 111dB SPL at 3m using 1000W.

using the metric above & your RadioShack SPL meter you can gauge when you have reached the 200W mark approximately (pretty decent approximation). Does this make sense?
larryi
4,327 posts
 

The power recommendation given by the manufacturer is just a rough guide of the kind of amplifier that should be used with the speaker.  Those numbers do not necessarily mean that the speaker is capable of operating at sustained levels as high as the top wattage rating.  The top end number is probably chosen to limit the possibility of damage even from short term events, such as a loud accidental pop, and I highly doubt that a speaker like the LS50 can take 100 watts for anything but the shortest period of time.  I would not want to put too powerful an amp on a speaker for fear that some event might cause such accidental large transients that could damage the speaker even though I would never actually try to run the speaker anywhere near the full output of the amp.

While it is most common to damage speakers with sustained levels of high output (overheating the voice coil), one can also damage speakers with very strong short-term transients.  I recently spoke with someone who damaged a tweeter by playing a classical recording that had extremely wide dynamic range (I have a few of these, and they come with a warning about the dynamic range), while not playing them at a very high average volume.

As to the idea that one is more likely to damage a tweeter with an underpowered amp driven into clipping than by excessive clean power from a too powerful amp, I spoke with a manufacturer who said that, by far, there are more instances of damage from use of too powerful amps than from clipping underpowered amps. 

I would personally stick with amps more toward the lower end of the recommended power range because I don't do that much loud listening and I find that lower-powered amps tend to sound better than higher powered amps, provided that the speakers are suitable for the lower-powered gear. 

inna
7,923 posts
 
My speakers are rated 15 watt - 200 watt. Before I was using 60 watt amp, now using 120 watt, and it is definitely better, though the quality of the current amp is higher as well. I sometimes listen to jazz/rock fusion at relatively high volume for couple of hours straight - nothing happens. The amp feels very relaxed and so do the speakers. In the case of the speakers that I have I wouldn't want to stay closer to the 15 watts than to 200 watts.
That math is too complicated for me. But the question was not about the precise figures but about real life situation and the position of the volume control. Anyway, I guess that this is the kind of situation when you cannot just rely on your hearing not to damage the speakers.
It appears that as it is often the case there is no general answer, it all depends on the particular application. One thing is certain though - when choosing speakers first choose quality drivers not nice cabinets and fancy crossover work.
bombaywalla's avatar
bombaywalla
1,958 posts
 
That math is too complicated for me. But the question was not about the precise figures but about real life situation and the position of the volume control.
sorry. I thought i had simplified it as much as i could. 
Well, one thing you could do it measure the SPL at your listening position with a RadioShack SPL (or any other) meter & see at what volume knob setting you are getting 91dB SPL average (which corresponds to 10W), 101dB SPL average (which corresponds to 100W) & what the peaks are at each of those volume knob settings. That will tell you how much you can crank it up & be safe with your speakers.

One thing is certain though - when choosing speakers first choose quality drivers not nice cabinets and fancy crossover work.
mostly true. Remember that cross-over networks can make or destroy your speaker. I.E. you could have quality drivers in your speaker but a really crappy, current hogging x-over driving those quality drivers & you will end up with an overall shitty speaker.
In the end, the quality drivers, the x-over & the cabinets are all tied together. It's difficult to separate them as individual pieces. Another example - you could have quality drivers, a 1st-rate x-over network but your cabinets side-walls could be weak & resonate too much w/ the music. Once again, the result will be shitty (with too much bass boom/overhang) & you would have wasted your $$ on quality drivers + x-over in an ill-designed cabinet.
All 3 items you wrote need to work in compliment w/ each other for the speaker to be sounding its best.
Yeah for sure don't buy a fancy speaker cabinet when you know that the drivers aren't top quality. 
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