help with the basics

Archived from groups: rec.audio.tech (More info?)

Could some expert out there please verify whether my basic assumptions are
correct or not?

1) 3db increase in volume is a preceivable increase (i.e. slightly louder)

2) 10db increase in volume is preceived as twice as loud

3) each 3db increase in volume requires double the amplifier power

4) If a speaker was producing 100db at1 meter with 1 watt of input then
adding a second identical speaker, also with 1 watt of input, would only
raise the volume to 103db at 1 meter. 4 identical speakers would yeild 106
db, and 8 identical speakers would yeild 109 db

5) phasing issues between 2 speakers can produce "dead spots" and "super
spots" throughout a room. In theory the dead spots could go to zero and the
super spots could be twice as loud (+10db?)

I'm sure theres a mistake here somewhere, as #4 says a second speaker can
only add 3db and #5 says a second speaker can add 10db (in certain spots).
Could someone help?

Thanks

Archived from groups: rec.audio.tech (More info?)

"Dan K" <danielgkNOSPAM@voomtech.com> wrote in message
news:41af4a08$0$85071$a1866201@visi.com

> Could some expert out there please verify whether my basic
> assumptions are correct or not?

Listen for yourself by downloading musical samples recorded at different
levels from

http://www.pcabx.com/technical/levels/index.htm


> 1) 3db increase in volume is a preceivable increase (i.e. slightly
> louder)

Yes.

1 dB is pretty readily audible if you can do close comparisons.

0.4 dB differences might be audible as some kind of an indistinct but
noticable change under ideal conditions.

> 2) 10db increase in volume is preceived as twice as loud

Usual rule of thumb, YMMV

> 3) each 3db increase in volume requires double the amplifier power

Yes, presuming the loudspeaker is linear which isn't always true.

> 4) If a speaker was producing 100db at1 meter with 1 watt of input
> then adding a second identical speaker, also with 1 watt of input,
> would only raise the volume to 103db at 1 meter. 4 identical
> speakers would yeild 106 db, and 8 identical speakers would yeild 109
> db

Depends on how the sound from the speakers combines which relates to the
directional patterns of the speakers and the room this all happens in.

> 5) phasing issues between 2 speakers can produce "dead spots" and
> "super spots" throughout a room.

You don't need two speakers for this to happen, a speaker and a flat surface
that reflects its sound can suffice.

> In theory the dead spots could go to zero

Yes, and can come startlingly close to zero (-40 dB) in the real world.

>and the super spots could be twice as loud (+10db?)

Make that +3 dB and add caveats from the question about speaker output
summing (4).

> I'm sure theres a mistake here somewhere, as #4 says a second speaker
> can only add 3db and #5 says a second speaker can add 10db (in
> certain spots). Could someone help?

I tried! ;-)

Archived from groups: rec.audio.tech (More info?)

"Dan K" <danielgkNOSPAM@voomtech.com> wrote in message
news:41af4a08$0$85071$a1866201@visi.com...
> Could some expert out there please verify whether my basic assumptions are
> correct or not?
>
> 1) 3db increase in volume is a preceivable increase (i.e. slightly
louder)
>
> 2) 10db increase in volume is preceived as twice as loud
>
> 3) each 3db increase in volume requires double the amplifier power
>
> 4) If a speaker was producing 100db at1 meter with 1 watt of input then
> adding a second identical speaker, also with 1 watt of input, would only
> raise the volume to 103db at 1 meter. 4 identical speakers would yeild
106
> db, and 8 identical speakers would yeild 109 db
>
> 5) phasing issues between 2 speakers can produce "dead spots" and "super
> spots" throughout a room. In theory the dead spots could go to zero and
the
> super spots could be twice as loud (+10db?)
>
With respect to point "5", this is called comb filtering.
It induces horrible, violent frequency response variations that vary from
centimeter to centimeter (distance depending upon the frequency) as you move
your head.
However, psychoacoustic research has revealed that the ear-brain system, for
some reason, filters out the effect of comb filtering when a stereo signal
is played. When two speakers are used for monophonic playback, it is quite
audible and irritating.

Archived from groups: rec.audio.tech (More info?)

Randy Yates <yates@ieee.org> writes:
> [...]
> E[V^2] = E[(X+Y)^2]
> = E[X^2 + 2XY + Y^2]
> = E[X^2] + 2E[XY] + E[Y^2].
>
> If X and Y are uncorrelated, then E[XY] = 0. Then
>
> E[V^2] = E[X^2] + E[Y^2],
>
> which means that if the two sources are the same power levels, the result
> is twice the power, or 3 dB higher.

I should have stated the following:

1. "E[Z]" denotes the expected value of the random variable
underlying the random process Z, where Z is ergodic.

2. We assume X and Y are zero-mean processes.

3. Given assumption 2, E[Z^2] is the variance of Z, which is the
same as the power in the signal.

--RY


--
% Randy Yates % "My Shangri-la has gone away, fading like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% <yates@ieee.org> % 'Shangri-La', *A New World Record*, ELO
http://home.earthlink.net/~yatescr