Originally Posted by duc135
That is not at all what you said. This is what you said:
Your math is all over the place. 20x the power of 2W is 40W, not 200W (2 x 20 = 40). 100x the power of 2W is 200W not 400W (2 x 100 = 200). A 20dBS headroom as specified by THX reference standard requires approximately 128x the power not 20x nor 100x.
Ok let's do the math if your speaker require 2W to achieve 86dBs then to reach 105dBs you will need 256W not 400W since every 3dBs increase doubles the power requirement. Look at the below table I've created for you:
86dBS = 2W
89dBS = 4W
92dBs = 8W
95dBs = 16W
98dBS = 32W
101dBs = 64W
104dBs = 128W
107dBS = 256W
Now you know the actual numbers and you won't need to compute the power needed to avoid clipping.
So at -6 you are looking at 101dBs peak according to the table above. So you're saying that there is nothing wrong with a 600W amp that clips while pushing 64W? That's less than 11% of its rated power.
That being said, I'm guessing that your original number about what you are drawing is off. 86dBs @ 2W is at a 1m distance. I'm assuming your are sitting a little further away from you Salons than 3.3'. Power requirement doubles for every 1m increase beyond 1m. So here is the modified table based on a 3m distance from the speakers.
86dBS = 8W
89dBS = 16W
92dBs = 32W
95dBs = 64W
98dBS = 128W
101dBs = 256W
104dBs = 512W
107dBS = 1024W
Now it starts looking more reasonable that your amps are starting to clip at -6 on the MV. Like I said, either there is a problem with your setup or your numbers are off.
Actually, I was hastily replying as I was running out the door.
I meant 20 DB requires 100 times the power.
I do not disagree with any of these tables. I used the conservative 2 watts for 86 DB because there are room size and stereo speakers.
If I plug these values into the Crown Amplifier Power Request Calculator:
Distance: 3 meters
Desired listening levels: 86
Efficiency: 83 (I knocked it down 3Db since Salons since they are basically 4 ohm speakers)
Required Amplifier power = 18 watts
Which is even more than your last table.
I have never been sure why anyone would doubt that approaching 0 reference volume with a Speaker like the Salons would clip most amps, even one as powerful at the ATI3005.
My main point is that you can clip these amps before hitting the reference of 0 and the resulting compression is not easily detected.
I do not mind limiting my volume to -10 for music because that very loud.
This morning, I setup my OmniMic 2 to measure the volume while watching "Indiana Jones and the Last Crusade" with myRevel 5.1 system. Salons, Voice, Studios.
I turned off the Sub.
Normally, I would listen to a movie like this with the AV8801 at 54 (-34) but I decided to go a bit louder to 60 (-28).
During reasonably quiet scenes the reading at my seat (10 feet) was in the 60's.
Loud conversations would rise into to 70's.
Loud Action scenes rose into the 80's (barely)
The peak measured 104. In either table, that is loud.
To me this suggests that THX specs are reasonable for my use. 105 DB (excluding the .1 bass) is all I need for me to enjoy an action movie.
However, for most of the film the amps is cruising down in the 20 to 50 watt range.
At peak volume, pick your table, but It would be likely over 200 watts.
The 86 DB average seems high though because that is quite loud.