Axiom Home Page Forums General Discussion Technical Questions Amps and Power, for Micah

Michael, sounds like we went to the same school.... i was an Electrican on a sub out of pearl... If everyone here went to efunds no one would have questions....

finishing up my degree now, in Economics... a buddy from my division is getting his EE.....

As always, great info John. I never mean to doubt you, as you are a much more knowledgable man than I in this (and likely most other) area. It's just so hard to swallow some of this stuff when I've lived with what I thought was gospel for the last few decades. It's like walking into a church, burning the bible and exclaiming, "this is a lie".... WHAT, THERE'S NO SUCH THING AS RMS???

But after looking into it I see what you mean. RMS is based on an average of a power wave, not a constant figure. Still, it seems to be pretty widely used not only in car audio, but all audio as far as I could tell. I did stumble upon some rather humorous things while looking these things up. This one in particular was enlightning...

Clicky

Also, as long as it's all correct, Wikipedia had a lot of good info...

Wiki-clicky

I was expecially intrigued by this statement in the 'Power and Loudness in the Real World' section...

" The sensitivity of loudspeakers, rather than merely the often-quoted power-handling capacity, is important. Many high quality domestic speakers have a sensitivity of 84 dB for 1 W at 1 meter, but professional speakers can have a figure of 90 dB for 1 W or even 100 dB (especially for some large-coned woofers). I.E., An '84 dB' source "speaker" would require a 400-watt amplifier (assuming it didn't burn out) to produce the same audio energy as a '90 dB' source being driven by a 100-watt amplifier, or a '100 dB' source being driven by a 9.92 watt amplifier(though in practice modern sub-woofers are often driven by high power amps to overcome the restriction of a small enclosure through the use of equalization). This does not mean a bigger speaker can produce more sound with less overall power. Just that a larger speaker can typically handle more initial power and so requires less amplification to achieve the same high level of output. This means using a speaker with a higher dB rating can be more advantageous as many amplifiers inevitably produce a certain amount of distortion for a given level of amplification. So, (more speaker)+(less amp.)=(same "loudness")+(less distortion)".

It got me to wondering what the M80's sensitivity is. I had thought I'd seen it on here that they were around 87 db's. But looking them up in the products section under specs the only figure I could find was the 'SPL in Room1w/1m(db): 95 dB' and 'SPL Anechoic 1w/1m(db): 91 dB'... is one of these figures the sensitivity rating?

The other interesting thing I got out of it was this...

"The term "Music Power" has been used in relation to both amplifiers and loudspeakers with some validity. When live music is recorded without amplitude compression or limiting, the resulting signal contains brief peaks of very much higher amplitude (20 dB or more) than the mean, and since power is proportional to the square of signal voltage their reproduction would require an amplifier capable of providing brief peaks of power around a hundred times greater than the average level. Thus the ideal 100-watt audio system would need to be capable of handling brief peaks of 10,000 watts in order to avoid clipping (see Programme levels). Most loudspeakers are in fact capable of withstanding peaks of several times their continuous rating (though not a hundred times), since thermal inertia prevents the voice coils from burning out on short bursts. It is therefore acceptable, and desirable, to drive a loudspeaker from a power amplifier with a higher continuous rating several times the steady power that the speaker can withstand, but only if care is taken not to overheat it; this is difficult, especially on modern recordings which tend to be heavily compressed and so can be played at high levels without the obvious distortion that would result from an uncompressed recording when the amplifier started clipping".

It was this that got me thinking the guy who was trying to talk me into a 1000 watt amp to drive my M80's with was trying to account for these 'musical peaks'. If I'm listening to my speakers at a level that pulls around 10 watts of power from my amp normally, it would take 1000 watts of power to cover these peaks. I don't know this was the reasoning behind his advice for a fact, just speculation.

micah, a LOT of the guys that are selling audio or video equipment don't really know THAT much about what they are selling.... how many times have you gone into a store and known more about the product that they are selling than they did.... now i'm not saying every sales guy is incompetent and doesn't know his product... but i would feel safe in saying that most of those guys just don't care enough to learn their product to a level that you or I would hope. this is ESPECIALLY true if you go into best buy, or other similar chain stores.... if you go to the boutique stores those guys are more likely to actually know what they are talking about, but then you get to pay boutique store prices

Most definately. But then again you're not very likely to run into Chris or John working at BestBuy because... well because they're entirely too smart to work at BestBuy.

Micah. Here's another link for you. It deals with pro sound, but is also applicable to home audio. Most of the rock we listen to has on the order of 6db of dynamics. Its not until you get into classical that you see anything approaching 20db of dynamics.

If you are sitting 8-12 feet from your gear listening at reasonable levels, say 80db (pretty loud) you will be using a whole 1 watt for the 80 db content. Add 20db dynamic peaks and you are using a whopping 57 Watts at peak. This is using the M80s at 95db sensitivity.

Note also that when they talk about 20db dynamics I believe that is from the quietest to the loudest passages, so on average, you would need to have power available for maybe half that to avoid clipping. As your listening level goes up, you will need correspondingly more power for dynamic peaks.

Follow the calculator link on the page linked above and play with it for a bit. It will give you a much better idea of how much power you really need.

Micah, the Elliot article is excellent and the Wiki article is generally fine(few quibbles we don't need to get in to). They among other things make the point that there aren't any "RMS" watts, and that RMS is properly applied to voltage and current.

As was said, a watt is a fixed quantity, the standard technical definition being that it's the power resulting from 1 joule of energy being applied for 1 second(that answers everything, doesn't it?). A couple hundred years ago James Watt was comparing the power of his steam engines with rival horses(never had anything to do with electricity), but now his name lives forever in electronics. One fact is that about 746 watts equal 1 horsepower. Now this might not seem to be the most useful piece of information, but if you run into an obnoxious audiophile who's bragging about his new 500 watt amp, after telling him what he can do with his 500 watts(he'll only need 1 most of the time)you can point out that it's only about 2/3rds of a horsepower(weak!).

By the way, did you happen to satisfy yourself about the relatively small effect of a 3dB sound level increase, as was suggested here a couple weeks ago when you questioned it?

And “horse power” is a term that’s nothing more than a descriptor for a mathematical summery of torque over time, much like the term “watt”.

Fred, just to clarify, my M80's sit 16 feet from my seating position. On an average day I would say 80 db's would be about an average of what I play them. When my lady is in the room working with me I turn them down lower. But then there are also times when one of my favorite songs are on, and I really crank them over to 'feel' the bass notes coarse through my bones. This is an addiction I picked up during my car audio years. Having a pair of 12 inch drivers a mere 3 feet from your back being fed by a high watt amplifier that needs only fill a small space produces quite a bit more bass than can be achieved in a 5000 square foot room.

Also, let me make it perfectly clear that I in no way took the gentlemans recommendations for buying 1000 watt mono blocks for each channel serioiusly. I merely wondered why he would have had such an opinion concerning my M80's. I have made speculatory statements in an effort to provide theories as to his reasoning. But those shouldn't be taken as my opinion in the matter. The XPA-3 drives them to levels I already can not tollerate. It was just an interesting comment is all.

John, I satisfy myself on a regular basis... er, oh wait that isn't what you meant is it?

Seriously though, I wish I could find the thread that gave me the opinion that I shared in your link. I'm guessing I understood what was discussed incorrect. It wasn't too long ago, and we were discussing the effects of having to double the wattage to achieve even just a few extra db's of output. After that fact was established I made the comment that if the 300 watts my XPA-3 was providing only produced 3 or 4 more db's of output than the 125 watts my Denon provided, then there was a BIG difference in those 3 or 4 db's. And as I remembered it, I thought you agreed that while 3 db's looks like not much on paper, in the real world a 3 db increase was in fact a substantial amount of volume.

As is seems, I guess I remembered that conversation incorrectly. I apologize for providing misleading information, but it wasn't intentional, I thought that was the verdict we'd come to. So anyway, that takes me back to square one in that area then. As I've discribed before, with the Denon I could only get the volume knob to around 90% max volume before the speakers sounded overloaded. There was obviously a lot of clipping occuring at this level. Once I hooked the M80's up to the Emotiva, taking the volume knob to the same position produced an extrodinary greater amount of volume (levels that I could not tollerate), but at the same time the speakers seemed to handle those levels with ease instead of sonding like they were about to break.

So now I'm left wondering, how could an amp that only produces a little over twice the power make that big of a difference in percieved volume? I know that the Denon had to have been making somewhere between 100 - 120 db's of output because at SRoodes house he was using a Denon similar in power rating as mine, and he showed me on his SPL meeter that we were listening at 100 db's. And we have the same equipment. And I have fully grasped notion that the volume position has nothing to do with how much power is being used between the two amps because of the power curve at play. But the way I understanding it, if my new amp can only add an extra 3 or 4 db's increase in volume, then why is the percieved output so much greater?

Miach...


i just to have 3 JL 10 W6's powered by a 1000w phoenix gold amp.....

i don't think i will EVER own anything that loud again... i think it would take 4 ep600's to get close to how loud that damn car was.....

after that car i went the 2 12's route, and the 12's were much more subdued if you will....


i have been thinking about getting a second EP-600 though.....