Amp wattage
KenH
Posts: 2
If an Amp is rated 100 watts (20Hz to 20,000Hz)
what would it's rating be if rated 40Hz to 20,000Hz? I'm trying to prove a point to my son. He thinks that more watts mean more power. I say that the "power" depends on how where the low end is.
Thanks!
Kenh
what would it's rating be if rated 40Hz to 20,000Hz? I'm trying to prove a point to my son. He thinks that more watts mean more power. I say that the "power" depends on how where the low end is.
Thanks!
Kenh
Post edited by KenH on
Comments
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Hi:
Sorry, but your son is more correct than you on this subject.
There are a lot of factors that determine the wattage output of an amp. The first and formost is the manufactures specs. Another one is the load the speaker puts on the amp rated in Ohms. You will notice that most amps have two wattage output ratings. A rating for 8 Ohms and a rating for 4 Ohms. My B&k is 200W @ 1KHz at 8 Ohm and 325W @1KHz at 4 Ohms per channel. Some amps are stable down to 2 Ohms.
More watts does mean more power. That is the whole reason to buy an amp with a higher wattage. The more power the better. More headroom, cleaner sound, clearer highs and deeper lows are the rewards of a good quality amp.
Hope this helps. That is the easiest way, that I know of, to explain it.
Gary -
All else being equal, the rating would be higher when you truncate the frequency range under question (especially for lower frequencies per your example).
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Thanks for the help! After re-reading my post, I realized that I needed to explain my situation. My son wants to buy an "all in one" system that has "200 total watts" There are no specs to be found anywhere on the box to tell me ohms of the speakes, total harmonic distortion, or HZ ratings. I was trying to explain that this manufacture was not giving us all the facts and was trying to sell us some "snake oil". This 200 watt system if rated the way my Onkyo is rated might only have 40 watts.
Thanks, Kenh -
""X" watts total power" is totally worthless as far as power ratings go. It's just marketing.
I hope you can convince your son to save his money and buy some decent components. In a few years, he'll be glad he did.
Power ratings, even when given into a specified impedence, at a stated bandwidth and distortion, vary greatly. I mean, my Denon (or your Onkyo) receiver rated 105 watts/channel, 20-20K, .05%THD, is pretty powerful for a Japanese receiver, but there are lots of seperate amps with lower WPC ratings that would eat its lunch. -
If you ask me, the original question as stated, gets an answer such as.... 100watts. If the amp in question, is rated at 100wpc, 20Hz-20kHz. It is stating minimum power (100watts) at any frequency between 20Hz-20kHz. The area of 40Hz-20kHz falls in there.
Had the original amp been rated at 100wpc, 40hz-20kHz, and the question been "power available at 20Hz, the answer would have been different. In my opinion. I also wouldn't let the kid buy a "total power" system either.
George Grand (of the Jersey Grand's) -
If the amp in question, is rated at 100wpc, 20Hz-20kHz. It is stating minimum power (100watts) at any frequency between 20Hz-20kHz.
The 100 WPC rating is a RMS rating (more akin to average or continuous power). -
Yes JohanK I agree. The MINIMUM, RMS, CONTINUOUS, power available, over a specified frequency range, at so many ohms resistance, with no more than so much THD, is what the amplifier manufacturers are required BY LAW to advertise. MINIMUM, RMS, CONTINUOUS power. Not "music", "dynamic", "IHF", or any other type power rating.
If they advertise the amp at 100wpc, 20-20,000 cycles @ 8 ohms, <.05%THD, and you get 105 wpc @ 8 ohms and everything else stays the same, the manufacturer is in the clear. Not so if the power numbers go down on the test bench and all other factors stay the same. That's my take on it.
George Grand (of the Jersey Grand's) -
George, I see what you're saying.
With respect to the original question, consider a 100 WPC (using continuous rating) amp @ 8 ohms b/t 20-20k w/ < .05% THD. What I'm saying is that, all else being equal, if you truncate the frequency range over which you gather the power rating, then the power rating will increase (i.e. amp is now, say, 102 WPC @ 8 ohms b/t 40 & 20k w/ < .05% THD). The actual increase will depend on what frequencies you discard and the actual amp.
Why? You are asking the amp to reproduce less (all else being equal) so it can produce more power over the range you ask of it. It is not much different than lopping off the upper frequencies for a THD rating of an amp so the THD numbers are lower.
Of course, the mfg. can play with the numbers a bit depending on how it wishes the specs to be. For instance, an amp with 102 WPC @ 8 ohms b/t 40 & 20k w/ < .05% THD can hypothetically also be represented by 100 WPC @ 8 ohms b/t 40 & 20k w/ <, say, .04% THD. Mfgs. can pick a point on the Power vs. THD graph to best fit what they think consumers want.
But, I think you know all this already...
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Yes I agree totally JohanK. There is an awful lot of these 40-20k amps out there right now. I used to think they were total junk. They probably still are. However, how robust do they have to be, if they are going to be used in conjunction with a powered sub, and will NEVER be asked to reproduce down to 20 cycles? I often wonder about this.
George Grand (of the Jersey Grand's)
