I think you're conflating amplifier dynamic headroom with spl formulae?No, actually not 10 kW. According to your example, you need 20 kW. The problem comes down to what we mean by "Watts".
The first mistake in all the calculators is that there is no such thing as "Watts RMS" in these calculations.
Unfortunately, for music, one must guess, average, or survey for different types of music and their crest factors (average to peak ratio). Highly compressed pop music can be 3dB. Very dynamic music like certain classical will be over 20dB.Now, in your example, you were quoting a 20 dB crest factor. I only subscribe to 10 dB, which I have justified above. However, the broadcast industry's program material model may be too compressed for the movie industry, and 20 dB may be closer to the truth. If that were true, then add another 10X to amplifier, and get 20 kW required power.
While you're right about reference level referring more accurately to 0dBFS, you're mixing up average dialogue level with peak level. Peak is 105dB. Average is 85dB.Since nobody has really address this question, I will. Reference level is not 75db or 85db. It is actually 0 digital reference, or the loudest digital signal before system overload. So reference levels for the cinema would be 105db for each main channel, and 115db for the LFE based on 0 reference. This would be continuous output, and nobody can really stand this kind of output continuously.
While I agree that a common design to achieve these higher levels is using a horn, or a horn/compression drivers, I don't think thermal power handling comes into play for the peak levels being discussed. From what I read, and what speaker designers say, thermal compression is for longer signals. The brief transient peaks are limited more by other mechanical compression and magnetic compression effects.However that doesn't factor in thermal compression. Even if your amp can drive your speakers to 105db, your speakers may lose their compusre at those peaks.
Most people's systems can't do reference levels properly. Regular tweeters just don't have the thermal power handling to do so.
How long is brief? How short is brief?While I agree that a common design to achieve these higher levels is using a horn, or a horn/compression drivers, I don't think thermal power handling comes into play for the peak levels being discussed. From what I read, and what speaker designers say, thermal compression is for longer signals. The brief transient peaks are limited more by other mechanical compression and magnetic compression effects.
Paul Appollonio said:Music definitely has peaks, and averages, but they move about so quickly without a quantifiable definition we are waving at flies with our hands. Let us assume a peak with a duration of 0.1 second. That is a reasonable amount of time to call a peak a peak. We could integrate it longer or less, but I would argue integrating less than 33 milliseconds is likely useless, as that seems to be the approximate integration time of our ear brain mechanism. So, regardless of the duration of the peak, the VC will eventually get hot. What you find in a speaker is two time constants, one for the VC, and another for the motor surrounding it. You could count the box as a third, but this is a tertiary effect. The VC time constant of a small woofer like this is probably on the order of 3 seconds. Now, if you look at music which is typically played or recorded today, you will find the actual dynamic range QUITE limited. This means the difference between peaks and Rms is now very small. That makes a difference. Todays recordings have a dynamic range which is very limited relative to for example, a recording of a symphony orchestra.
As for heating and compression, this is not difficult to measure. ANYONE who can come up with $15 and find their way to Radio shack can buy a meter that will measure DCR. Measure the speaker at the terminal with the amp disconnected, and the woofers cold. Play your speakers for an hour, as loud as you want to, then quickly disconnect the amp, and measure the speaker again. As long as there is no loud noise after you turn off the speaker, or as long as you don't have a fan or wind blowing at the cone, you should be able to get a somewhat stable DCR reading. That will tell you just how far off center the heat has pushed the device. I can measure it other ways, but I've thousands of dollars worth of gear to do that. You can calculate the heat in the VC based on the difference between the starting and stopping DCR (assuming any series choke presents a negligible amount of DCR in addition to your VC). All speakers heat up. My point was if I want 105 db EITHER peak or Rms in the room (RMS would be loud too) then having 8-10 db more sensitivity to begin with is a big advantage.
Hmm I see well after the fact I meant, "They can withstand 105dB for a fraction of a second quite readily."While you're right about reference level referring more accurately to 0dBFS, you're mixing up average dialogue level with peak level. Peak is 105dB. Average is 85dB.
You're right that people can't stand 105dB, and fortunately, they never need to. They can withstand 105dB quite readily.
Just a question, when you say set the volume at 0dB, do you mean the AVR volume ? My Yamaha AVR's volume display reads in negative values at low volume( it starts at -80, then goes up to +15 ) so the closer you get to 0, the louder it gets, and if you go louder, the numbers become positive values up to +15. At 0 volume, it is excessively loud, and past half volume, -10 is very loud. I find this negative volume display very confusing on Yamaha AVRs..can anybody shed some light on why it's a negative value on the loud end ? How do you read it ? ( I also find the dBFS negative reading confusing on dB meters, but I'll start a thread somewhere else for that ) Thank-you in advance.Reference level is the volume at 75db (decibels) in your room using full band pink noise. When you set up your system and you run pink noise through your speakers one at a time setting each level using an SPL meter to 75db you will (after all channels are done) and your volume control is set to 0db you will achieve "reference" when playing back movies or music. Movies will tend to reach peaks of 115db with your system set up properly.
This is not always easy to do as most home theatre systems can not reproduce this without distortion and is usually louder than most people go. Unless you have fairly expensive gear and larger speakers you likely wont achieve this without distortion.
That is the best explaniation I have heard. It makes total sence to me when you put it that way. :TMy reference level is far from 90% of the people on here. it is the actual level of being on the stage with the musicians, or in video, the level it would take to convince a blind man the sound was not coming from speakers but was really happening near him. 99% of all systems fail to deliver this. It is called a "reproduction system" for a reason.