Axiom Home Page Forums General Discussion Technical Questions Understanding Power Requirements

Just found a web page that explains some of the stuff I have been wondering about with respect to power requirements for speakers. I was wondering what sort of head room requirements I might have depending on the dynamics of the music I am listeneing to, the volumes and listening distances.

The page even has a link to a calculator you can use to figure out what you need for your particular situation. Its meant for professional musicians, but it should work just fine for the rest of us as well.

I found their suggestions for headroom for different types of music (as much as +25db for some types of music) quite interesting.

Crown audio link

Enjoy.

P.S. I know, I know, M60s are easy to drive. Any decent receiver will do. I'm bored...

OOooooh, this is fun!

M60 at 2.5 meters, 95 db spl and 10db headroom = 99w
Bump that to 105 db spl and the max power required jumps up to 313w!

So, if you listen to music with a lot of dynamic range, your power requirements really jump.

Want to handle 25db peaks withoug clipping at 95db spl? You will need a cool 3,132 amps of power!

Fred

...and a hearing aid.

Meh... need a hearing aid already...

For me, playing with the calculator really drove home what folks here have been saying. I guess I am a visual guy, because I couldn't quite put it all together before playing with the calculator.

One thing I still wonder about is what the danamic range I can expect out of the music I listen to. The Crown website seems to suggest +15db peaks is reasonable

Something Alan Loft wrote in his article about power has stuck in my mind. Music played cleanly as high spls dosn't sound loud.

Put that together with a speaker like the M80 or less efficient speakers in a larger space with music that has high dynamic range, and I can see how you very quickly exceed the power requirements of your average receiver if you want clean playback at reasonable volumes.

As for hearing loss, I wonder if very short peaks 25db above and average listening volume of 85db will lead to hearing loss. Thats a lot different than running equipment for 8 hours a day that generates a continuous 110db of noise.

Fred

Good article. I like the quick way the calculator adjusts for sensitivity and dyanmic range.

Holsts' The Planets has about 50 db range so to listen at a mere 60db @ 2.5 meters, for the quiet parts the Amp requirements jump to 198W and that's if I use the in room sensitivity of the M80s. When using the anechoic I need - 496W

I think this speaks to have distributive power :)Not all your channels need to have this at the same time. I would use 25db as a realistic expectance..

When listening to the Planets, SPL meter in hand, the range peaks at 53 db. so 25 would not suffice, as we are talking total range.

So plan on 50+? Will do.

Gosh like I needed another reason to get a new amp.

John. I agree: pretty cool!! I think these two pages should be stickied on one of the forums here. Its a very concise explanation of power requirements and the things that AND it gives examples of spl's and headroom for various types of music.

Mark. It took a while to parse that first sentence, but I get you. I don't think a lot of people appreciate just what Axiom has done with their new amp.

If +25db is a reasonable requirement for peaks, at 85db spl, I would need 200 amps to drive the M60s clean... but I can get to about +23db on 120w On the Crown page they use +15db peaks as typical for home audio. For +25db I would need around 200w.

So, how much power I need really, really depends on how loud I like to listen to my music. This is something I want to establish when I go to give various speakers a listen at Axiom.


This is where I get confused when people talk about dynamic range. Are youl talking about total range as in from the quietest to the loudest? If I understand the way the calculator works, they are talking about peaks above average spl.

Another interesting thing on the link is that their chief engineer says that amplifyer continuous and peak power are virtually identical. Maybe he was refering only to Crown's amps, but I don't think so.

Fred

Curious, how do you measure this with a SPL meter? I ask as mine is analog and the most range I can see at any range band is 16db.

I've been told by a few audio manufaturers of amps that you can't totally trust the RS meter. You would need a more sophisticated meter like used in labs that cost lots more and respond much faster. Usually if a song has a 20dB spike, the RS meter will only respond as seeing 10dB.

So get my friend who has a sudio with multiple SAs to pay me a visit

Was curious how Jake measured this

I just listened with my meter(not RS and digital) out in front of me and the medial low range was 53 for the quieter moments and I went back to the peak points with my meter in max hold range and found the loudest point was 103db, a 50db range on that cd.

I watched it for max spl while noting the low average and the average high was about 95db. I would guess using 40db insted of 50 would be a closer reality as the sudden and brief 103 db would be in that clipped area that might not be noticed.

Using the 40 db range gave me an amp power rating of only 50W while 2.5m @60SPL for 91 sensitivity.

Thank you, I understand now you made a couple of measurement passes. Will offer my version a listen with the RS analog meter tomorrow as time allows.

Many thanks Again.

Fred, I quickly(too quickly)read the article and punched some of my typical numbers(3 meter listening distance, 89dB speaker sensitivity, 80dB average listening level, 20dB headroom above that to allow for an occasional peak on the most dynamic recordings)into the calculator. The result came up 113 watts, which was clearly far too high as I had in the past measured and calculated the power usage as about 32 watts in that 100dB peak situation. So, I read the article a little more closely to see what was wrong and saw that the factor they used in their distance formula was simply 20xlog(D2/Dref), and applying that indicated that what the calculator was doing with distance was reducing the sound level 6dB for every doubling of the distance. This is correct for an omnidirectional sound source operating either in an anechoic chamber or out of doors where room reflections don't reinforce the sound level, but a complete analysis in a typical listening room requires that this be taken into account, and makes a major difference.

Curiously, the article makes this rather basic point clear only near the end under "Other Considerations", where it's stated that the calculations apply only to anechoic or outdoor environments and suggests that a 6dB correction(i.e., reducing the power required to 1/4th of the previous result)be employed to account for the listening room. Following this suggestion, I used 14dB rather than 20dB of headroom in the calculator, and sure enough the result was 28 watts, much more closely in agreement with the 32 watt figure that I'd calculated.

So, without the room correction the calculator doesn't "work just fine for the rest of us", but gives power requirements about four times too high. Hopefully the fact that Crown deals in very high powered professional amplifiers wasn't a factor here.

I think your calculation is highly sensitive to your assumption that 40 db is sufficient. If you run the calculator at 40db you get 50W as sufficient.

However at just 43db you need 99W and if you tried to avoid clipping and used 50db, 496W. Once you hear it, clipping distortion is highly audible because its so annoying.

I actually like this AllegroSound calculator better because it factors in 5db room gain by adding it into the speaker sensitivity and uses peak SPL at the highest end of the range in the calculation.

http://allegro-sound.com/Power.html

Funny thing is with the pop industry recording the music with very little dynamic range, it makes it easier to run lower wattage amps, since you have very little need for large amounts of head room. You would think the amp manufacturers would jump all over(support) the more dynamics in recording movements that are out there, which would hopefully lead to better recording again.

Thanks for pointing that out Johnk. I noticed it too, but I am not use to thinking in logarithmic terms.

Edit: I need to learn to read more carefully. First tiem 'round I assumed they did the subtraction in the formula.

OK, I built the calculator in Excell (minus rounding 'cause I know how you audiophiles like accuracy ) and it works.

So, where do I plug in the room adjustment? Where the formula adjusts for headroom? Hmm... need a sound engineer's help here. Now where would we find one of those??

Edit: ok, I see how the formula works now. Add 5 to sensitivity or take 5 off of listener spl or headroom, its all the same.

Maybe I should stick to simpler things at this time of night like cleaning my tub.

Actually its better to add room gain correction to speaker sensitivity. Check out the calculator I posted above from Allegro Sound.

I checked out the Alegro calculator. You get the same result adding 5 to the sensitivity or subtracting it from listener spl or headroom. In the formula those three numbers are just added or subtracted to/from each other, so order (where you apply the 5db room correction dosn't matter).

Either way it dosn't matter, with the room correction and the M60s I'm back to... what was that thing you guys kept telling me?

Oh yea, "The M60s are easy to drive. Any decent receiver will work just fine"

Yes, but as the results are showing, it depends on how loud you like to listen and how much dynamic range is involved. For most of us the usual amps and receivers are what we can afford and they do the job admirably.

Both these calculators produced required watts beyond my equipment specs. The typical listening level for movies sits near a max level for required wattage and possibly beyond on more limited occasions so a separate amp for that system is still required.

Listening to music while cooking in our kitchen, 21 feet or 7m from the main system with 91dB sensitivity at 85dB preferred sound level (slightly louder than JohnK's preference) and 20dB of headroom provides for 309W (or 389W w Allegro).
The amp is only rated for 225W aside, best case scenario.
Obviously i have not attained such conditions successfully.

Buy as much power as you can comfortably afford if you are a person who likes to turn things up and/or step further away from one's system.

Very good advice, I tell people this same exact thing when asked how much power is needed.

Well, OK I was being a little glib. I think an 80w receiver might be marginal for the M60s. I am thinking that the soon to be released Yamaha RC-V663 will be a good match for me, particularly if it has the same power supply/amp section as the 659. That unit got very good reviews for its amp section at Audioholics.

I found it interesting that the folks at Crown were suggesting 1.5 to 2.5 times the speakers rated maximum power as a guideline for choosing an amp.

For the M60 that would be 300 - 500w!!

One of the things I plan to do when I visit Axiom is to see where my comfort level is with volume. OK, I'm pumped to go do some listening.

One spec I usually take note of in the product list as a guideline is maximum amp power. Its 240W for the M60s.

I wish I could afford a nice outboard amp, as I do usually have my system pretty loud as I'm frequently in the next room.

Two quick points, though: I think John's note of their inconsistencies aren't surprising in that they DO sell amps.

Secondly, on a less "suspicious" note, they are also in the market for the professional, live sound musician, where the dynamic range can be quite a bit wider than the recordings most would listen to at home. And, as they correctly point out, it's dynamic range that really "hogs the watts".