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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

Showing 6 responses by bombaywalla

bombaywalla's avatar
bombaywalla
1,958 posts
 
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?
yes, if pushed, you risk damaging your tweeter (before you damage your woofer). The amp will not clip since it has 165W/ch & plenty of current drive (that's usually the case for Parasound amps). The speaker will start distorting indicating it's been over-driven &/or broken. 
I'm thinking that you are not going to use more than 10W/ch from your amp at usual listening levels. The transients will be much higher but for much shorter duration. SO, then, it becomes a question of reliability - in how much time will your LS50 fail when you keep pushing more than 100W into your LS50 repeatedly over a period of time? I don't have an answer for you other than a fuzzy "long time".
Don't get too enthusiastic with the volume knob & you should be fine, I believe.  
bombaywalla's avatar
bombaywalla
1,958 posts
 
paraneer
639 posts
08-10-2016 5:09pm
Speaker wattage ratings are generally meaningless. The two key specs are impedance and sensitivity when matching an amp to a pair of speakers.
I wouldn't say that speaker wattage rating is generally meaningless - it does have a function. And that function is to generally make the user aware how much wattage the cone drivers can handle before they start distorting. Even tho' one is going to hit those max wattage numbers infrequently, one needs to be aware of the max wattage handling or one is going to break/fry/destroy the driver(s) with too much power. Personal experience confirms this. If the max wattage handling of the speaker was not mentioned one could do a lot more damage more quickly than if this spec was stated - i.e. you know whether you can go all out with your amp or not. For example - my DMT10 speakers can handle 350W & they are connected to a 120W/ch amp. I know that even i crank the volume to max, i will not destroy the drivers. OTOH, my Scintillas can handle 200W max so I cannot crank the volume to max as my amp can output 1100W into 1 Ohm. If I didn't know this I'd have fried the ribbons by now....

I agree with you that speaker wattage handling spec is not what one uses to match amps to speakers.
good additional point by georgelofi.  
bombaywalla's avatar
bombaywalla
1,958 posts
 
Harmonic distortion is present in all equipment to a (hopefully) small extent but in most clipped amplifiers this distortion increases dramatically. Your speaker’s crossover dutifully routes any of these signals higher in frequency than the crossover point to the tweeter, increasing the likelihood of damage.
well explained djohnson54. One point that djohnson54 made that i’d like to elaborate on - when the amp goes into clipping, the output music signal looks like it has lopped off tops & bottoms. The lopped off top comes from the fact that the output voltage maxed out to the B+ power rail. Anytime you have a music signal with sudden changes in amplitude it is like having a high frequency content in that signal. Sudden changes in amplitude = amplitude changes happening fast = high frequency content. So, it is this high frequency content that is dutifully passed onto your speaker’s tweeters (x-over is simply just doing its job). And, like djohnson54 wrote, the tweeter is not designed to handle high(er) power as there is not much hi freq energy but the clipped signal from the power amp does have high(er) power. And when this hi freq distortion power exceeds the tweeter’s power handling capacity, you fry your tweeter.....
bombaywalla's avatar
bombaywalla
1,958 posts
 
inna2,182 posts08-11-2016 5:49pmWhy do speaker manufacturers put it in the specs when you can possibly drive anything with 1000wt of clean power?

Inna, i think that you misunderstood. You can drive any speaker with 1000W/ch but it does not mean that you can crank up the volume indefinitely. If you do, you will fry the tweeter & eventually the woofer. So, you can use a 1000W/ch amp, just be careful of where the volume knob is & do not exceed the manuf's speaker wattage upper limit. it's not so much about "clean" power i.e. just because it's clean it wont damage the speaker. No, not true.

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?
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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