Sensitivity and Wattage, Amps and Speakers

[operaman]

I have Polk Audio 2 way towers, RT-400, 8ohm, Sensitivity:1 watt at 1 meter: 89 dB

What is the idea amp wattage to power these? Current amp is a Kenwood rated at 100w, probably putting out 30wpc. I have read on here that it's better to have an amp that is rated for much higher wattage than your speakers. Am I going to get much better sound if I have an amp that is pushing 50-100wpc?

 

[MeatInStereo]

I noticed a difference when I have my NAD 7600 (150Wpc RMS...dynamic 300wpc) connected to my PSB alpha B's which are rated at 100w sensitivity 91db compared to my Yamaha HTR-5940 (says 105wpc RMS but it sounds more like 50w RMS) My NAD also has about 60 amps of current too...my Yamaha doesn't even have it rated on the spec sheet.

 

[whoaru99]

I wouldn't put too much stock into the current specs published with most amps. Sure, I agree there are more capable amps, particularly if comparing separates to receivers, however the current specs with most amps are not defined well enough to give true meaning.

Case in point, 60 amps. What impedance? For what time duration? If it's into essentially a short circuit (most likely) and for something like a fraction of a millisecond, it's little more than marketing fluff. This is not to disparage the amp itself, I'm sure it's a fine amp, however unqualified/incompletely qualified specs are BS, IMO.

Sorta like saying, "My car runs 9 seconds." Depends on whether that's 1/4 mile, 1/8 mile, 0-60, 0-100, or what ever, to better understand if it's something to be impressed about.

 

[operaman]

Alright, but let's say we are talking about real WPC in an older and more powerful amp. Theoretically, is it a good idea to run MORE than the speaker's wattage handling (mine say 20-150w) - or not? Theoretically, I mean, without disparaging the amp for having bogus specs, which is irrelevant to the question.

 

[cityslicker]

I think it's always better to have more power than you need. If 50wpc is enough power for you, then you should have 100wpc on hand. If you start clipping that 50 watt amp, you can do damage to 100 watt speakers. The more clean reserve power, the better.

 

[whoaru99]

Alright, but let's say we are talking about real WPC in an older and more powerful amp. Theoretically, is it a good idea to run MORE than the speaker's wattage handling (mine say 20-150w) - or not? Theoretically, I mean, without disparaging the amp for having bogus specs, which is irrelevant to the question.

That's a really loaded question.

It really just depends on what you're trying to get from the speaker. If you're trying to get the most out of it, then yeah, IMO, you should have an amp that is at the top or beyond the rating of the speaker.

If you're not trying to get the max from the speaker, then there is really good no reason to have power that meets or exceeds the power handling or the needs of the situation.

In any/all cases, the main thing is that the amp needs to have enough power to stay out of clipping for the intended use of the speaker. Also note it is quite possible to damage speakers with too much power too; either by over excursion of the drivers or by overheating the voice coils / thermal damage.

So, how's that for a non-specific answer to what is actually a fairly complex question.

 

[SaSi]

I tried listening to a pair of KEF 105s using two Technics SE-9060 power amps. There is a bridge/stereo switch in the back of the amp that makes switching between the two modes a snap.

In normal stereo mode, these delivere 2x70W RMS with a rated THD of 0.02%. Bridged, they deliver 180W with the same THD.

Now, even with 10W output, the speakers delivered more than adequate sound levels and the amps didn't appear to clip unless I turned the volume knob all the way. And even then, clipping was far and between.

But driving the speakers with 180W capacity, firstly I obviously didn't have to turn the volume up all the way for more than loud levels and the sound appeared cleaner. Not only clipping wasn't there, the sound is now much more relaxed and although louder, it doesn't "seem" that loud as lot's of distortion that subconciously one understands as "loud" is gone. I understand now what power compression is all about.

 

[operaman]

So first, thanks for your explanation.

I've read here on AK that to power speakers rated for 20-150watts, I should have an amp on hand with at least 150 or higher in order to get the full warmth, tightness, etc. from the speakers. NOT just for the loud stuff (I live in an apartment and am no way near clipping these) but also for the quieter listening where one wants warmth and clarity and detail.

Is this not your experience? The power rating is just a matter of handling the loud end?

 

[whoaru99]

Power is, IMO, more a matter of being able to reproduce dynamics properly than of purely loud. Sure, power does equal loud too, but that quickly reaches a point of diminishing returns because it takes 10 times more power, all other things equal, for the sound to get twice as loud.

So, it's easy to go from 10 watts to 100 watts and perceive fairly big difference with many speakers. However, it's much harder to go from 100 watts to 1000 watts and gain the same increase in continuous volume unless you're using some very capable speakers.

I use a 700wpc amp (yes, 700 real, FTC-rated watts) with speakers rated 15W-350W, and don't have any problems because I can tell when the speakers are nearing their limits. I used to use 250wpc amp (again, 250 real, FTC-rated watts) with these speakers and the maximum playback volume is essentially the same. But, when pressing the system, it's clear the 700wpc amp allows it to remain more dynamic and "lively" where the 250wpc amp was running out of steam and taking on a flat, non-dynamic sound.

 

[operaman]

Thanks, SaSi and WhoarU!....

So, it's easy to go from 10 watts to 100 watts and perceive fairly big difference with many speakers.

Exactly! So if I'm using an amp that maybe puts out only 30 real watts per channel, it sounds like I can do better with a more powerful amp. I indeed experience that sense of "diminishing returns" when, on a clear saturday afternoon, I indulge myself in some loud stereophonics and find that the sound, while powerful, is not exactly true or clear or warm. I'm going to beat bushes for an amp that has 100 good watts per channel, I suppose.

 

[Renzor213]

Another thing to consider is how you run your system. If you frequently run your small SS amp flat out into clipping, then your tweeter's are in danger. Clipping SS amp's tend to generate a lot of high level, high frequency harmonic's, that tweeter's don't like. That's where the more powerful amp is safer for speaker's thing comes into play.

 

[operaman]

I am having trouble getting info about the real wattage output of the Kenwood KR-V6010. I know it's rated at 100w in 8ohms but how does one determine what it truly does? Do I need a gauge of some kind?

 

[whoaru99]

There are a number of ways. Sort of depends on the level of accuracy you desire. At 100 watts level, the difference between 100 and 75, or 100 and 125, doesn't have too much forbearance on things....a difference of about 1dB.

If, for instance, you were trying to validate factory specs, you'd need a load bank, likely an oscilloscope, a distortion analyzer, and a signal generator.

Some of the rub in measuring power is knowing the distortion. The more distortion you allow in the measurement, the higher the power rating generally will be.

At a minimum, an oscilloscope and load bank would be necessary. The signal generator could come in the form of test tones burned onto a CD and played back. Connect the load bank, start the test tone, and slowly crank up the volume control until you see the top of the waveform on the 'scope just begins to flatten, then back off until the flat disappears. That's your peak voltage, multiply by 0.707 to get RMS volts, then it's volts squared / resistance to get the watts. It'll probably be a bit optimistic since you're not controlling for distortion very accurately.

 

[operaman]

Ok, Probably not worth my energy. I assume the real WPC for this model is the same for all of them? Or do they vary from unit to unit?

 

[whoaru99]

There may be some small variance between them just due to component tolerances, but not enough, IMO, to be worth trying to hand select them for a few watts one way other the other. Assuming, of course, nothing is broken on any of the units.

 

[talzer]

How would you go about determining the "real" wpc of an amp?

Mine's rated at 60 wpc, 95 max. x5 because its 5.1.

 

[whoaru99]

Measure, as previously described.

 

[Jon_Logan]

.......you know, I've been working on amps, etc for a long time. I don't ever remember a product not meeting it's power output spec. ....not one. Somethings were hard to verify. Things such as FM sensitivity, when you don't have access to a shielded room.

I think a lot of this lying or stretching the truth from manufacturers was largely car stereo, or instrument amp makers.

 

[whoaru99]

...I don't ever remember a product not meeting it's power output spec. ....not one. ...

That's a good point. It's more a factor of understanding what the specs say, than the product not meeting them. If it's printed, the product likely will meet or exceed the spec, PROVIDED, it's tested under the exact same condtions as the mfg rates it.

 

[Renzor213]

If your Kewood's rated 100 watt RMS both channels' driven into 8 ohm's, 20 to 20khz below 1 percent THD, then that's what I'd go with. Years ago lot's of wierd stuff wattage rating stuff was going on until the FTC stepped in. As a kid I had a Lafayette integrated amp rated 50 watts/channel IHF +/- 1db into 8 ohm's. McIntosh used to hold free clinic's at better Hi Fi store's providing the exact testing "whoaru99" descibed, to show how bogus some of these rating's were, and their's all rock solid RMS. My Little amp barely made it to 15w rms in one channel, before bass distortion fell off the chart. Still have the test print out. Would loved to own a McIntosh at age 13, but could barely afford the Lafayette.