Decibel Equation

[trem]

Then you should be able to get extra credit by using loudthud's formula to get log base 2 of 0.25. Look up log10 of 0.25 then divide that by log10 of 2. What do you get?

I have no idea.....
I had never heard of a log table before this post...much less know how to use one.
I have a calculator that does Log10.
But the log tables I have seen do not (i do not think they do anyway) go below Zero.
Using my calculator:
Log10 (0.25) = -0.602
Log10 (2.00) = 0.301
If I divide those, my calculator says -2.00 +/- a bit
But how can I verify that from a Log table.?

If I use formula:
2). logb(m/n) = logb(m) – logb(n) ... (from that Internet link)
I get -1.75
Are either of those right.?

[Shadrock2]

I would not get to hung up on log tables. When I was a senior in high school I bought a "Slide Rule". Of all things. The very next year Texas Instruments came out with the TI-30 hand held scientific calculator. I bought one shortly there after and never looked back. The tables were found in the backs of math textbooks and designed so that you could estimate logarithm's as well as sine and cosines using a pencil and paper. Logarithm tables only went from 1 to 10 (producing values from 0 to 1). It was assumed you could figure out which decade (or the integer portion) of the log by inspection.

It should be noted that while logarithm results can extend from negative infinity to positive infinity the numbers (and expressions) that logarithms can be applied to can only be positive. for the same reason that you can not have a square root of a negative number.

#2 of your expression is correct.

[Steve A.]

I had also assumed the base 10 to be understood.
Having it typed out in line makes it confusing. Seeing it with the 10 lower than the word log takes away the confusion, but we can't type it out like that .
[ATTACH=CONFIG]33579[/ATTACH]

Yes! MS Word allows for subscript and superscript formatting- you could even assign hot keys to them. But HTML and Flash are more interested in bells and whistles than meat and potatoes.

[Dave H]

I have no idea.....
I had never heard of a log table before this post...much less know how to use one.
I have a calculator that does Log10.
But the log tables I have seen do not (i do not think they do anyway) go below Zero.
Using my calculator:
Log10 (0.25) = -0.602
Log10 (2.00) = 0.301
If I divide those, my calculator says -2.00 +/- a bit
But how can I verify that from a Log table.?

If I use formula:
2). logb(m/n) = logb(m) – logb(n) ... (from that Internet link)
I get -1.75
Are either of those right.?

-2 is correct

Sorry for suggesting log tables, my age is showing A calculator is better. The formula in 2). is not the one to use for this. You need to use loudthud's as you did to get -2 above. Formula 2). is for logs with the same base (b).

[Shadrock2]

Oops... My bad... Shot my mouth off again. Dave H is correct. (shows red face)http://music-electronics-forum.com/i...ies/tongue.png

Should be able to do Loud Thud's problem by inspection. 2^-2 = 1/(2^2) = 1/4 = 0.25

[trem]

-2 is correct

Sorry for suggesting log tables, my age is showing A calculator is better. The formula in 2). is not the one to use for this. You need to use loudthud's as you did to get -2 above. Formula 2). is for logs with the same base (b).

OK.....10-4.
So I kind of, sort of, know what I am doing. If a guy ever puts a gun to my head and says...
"Solve this Log5, or your life."
I will have you guys double check my answer first.
Thanks For All.......