Axiom Home Page Forums General Discussion Technical Questions 4 ohm towers Hooked to 6 ohm amp

Jason, the dynamic range on a recording is usually considered to be the range from the lowest level to the highest peak, not from the average level to the highest(which is often said to be about 20dB on some highly dynamic compositions). There are quite a few classical compositions which require a dynamic range of about 50dB or even slightly more when properly performed and recorded(e.g., about 50dB when the volume is set so that the lowest level is audible, which then might hit 100dB on brief peaks). Even these peaks, however, don't require anything which isn't easily within the capability of typical receivers with a rating anywhere around the 100 watt area.

Some of the online power calculators are grossly inaccurate(on the high side)when they take into account a factor such as distance, but fail to fully account for the contribution of room reflections. Notable is the one of a maker of high power amplifiers whose initials are Crown, which drew some praise here last year, but I pointed out that the calculator came up with a number about four times higher(about 140 watts compared to 35 watts)than I'd measured and calculated for a certain high level. A statement that it was only accurate for anechoic conditions, and giving an arbitrary correction number was somewhat buried at the end, and reduced the prior result to less than a third of the previous value.

John. From the Crown page that links to the calculator:

"The calculations discussed here apply to anechoic or outdoor conditions. If the sound system is inside a venue, the room reverberation will increase the SPL typically by 6 dB. You can use this room gain as extra headroom."

While they don't explicitly include the adjustment in their calculator, they are certainly very clear that room gain needs to be taken into account.

I still think the page linking to the calculator is excellent. It was the first place I found that all the elements relating to power requirements were gathered together in one tidy package.

As to the numbers I originally posted using the calculator, that was operator error (me), not an inacurate calculator. A separate box for room gain would simplify the calculator though.

I can't imagine hitting 105db in my room. I suspect that has as much to do with the fact that the room is highly reflective as it does with me not listening to music at reference levels.

I do wonder how that would change if I had a more well behaved room though.

JohnK, I see what I did wrong in my examples, for the calculators to work correctly you would be using the average finding as the listening SPL value, I should be using 92-93db from my previous example, for the main listening SPL level; as the Dynamic Range is made up of the low and high on either side which then drops the required power output from the amp considerably.

I just had it in my head that while listening to Holsts': The Planets, the tracks are very quiet for a large portion of them but have large peaks, I found myself turning the volume up considerably to hear the quiet passages. This had me thinking of the lowest points of the range as the average(desired SPL on most calculators) listening level, which it really isn't.

It's late or early depending on your time frame, does this make sense?

Fred, it apparently isn't all that clear since both here and elsewhere I've seen the calculator used without adding the 6dB correction for room reflections(which is adequate for the typical listener distance of about 3 meters, but would still result in an inaccurate power number at significantly longer distances) which is found only in "other considerations". There's been a lot of "operator error" beside yours.

Jason, sure the composer sometimes intends part of his composition to be heard at a very low barely audible level. Turning the low level parts up louder defeats that intent and is a form of self-imposed volume compression as to those segments(and if not corrected before a sudden loud segment comes, you might get blasted out of your listening chair). On The Planets the volume setting for Neptune should be the same as for Mars and Jupiter.

OK, I guess I'll just like the site all by myself then.


I'm envisioning Jason flying out of his chair and smacking into the wall Ironman like.

Damnit! I haven't seen the movie yet and now you spoiled it for me.

I was thinking more like stuck to the chair as in those old Maxell(?) ads. ala jakeman's avatar.

I'm usually the last person on the face of the planet to watch a movie!

So we won't tell you what "Rosebud" mean!