please stop...

[Kenny]

Hello Again,

I have to say something.
The others commenting on scale is so far off the mark
The smaller the room the harder it is to analyze acoustically with mics.
There is no way to scale down a room and get accurate predictions about
acoustics.
Sorry,

The best thing to do is get a sine way generator that can sweep frequencies
for you.
Set it up in the room playing through a speaker.
place the speaker where your instruments or vocalist is going to be most of
the time.
Set the level for normal sound pressures.
and place a second mic in the room so you can watch increases in Level.
Place the two back to back. to start.
you can move them around the room but don't face them at each other.
Mark the frequencies that the room naturally amplifies.
my predictions are 94hz and 141 hz

Sweep the low end only from 20hz to 300 hz or maybe 350hz.
This is the range you want to work on.
The upper frequencies wont build like the lows will

after you identify the problem standing waves
you will need to build some traps.
there are some good books to instruct you on this
I think Mix Magazine could point you in the right direction
search for their website.

Good luck,

Kenny

[Rob Adelman]

Kenny wrote:
> Hello Again,
>
> I have to say something.
> The others commenting on scale is so far off the mark
> The smaller the room the harder it is to analyze acoustically with mics.
> There is no way to scale down a room and get accurate predictions about
> acoustics.

I was thinking this as well. Sound waves at audible frequencies are the
size that they are. You can't "scale them down" to go along with the
other scaled down parameters. This would seem to make such an experiment
meaningless.

-RA

[Scott Dorsey]

Rob Adelman <SPAMLESSradelman@mn.rr.com> wrote:
>Kenny wrote:
>> Hello Again,
>>
>> I have to say something.
>> The others commenting on scale is so far off the mark
>> The smaller the room the harder it is to analyze acoustically with mics.
>> There is no way to scale down a room and get accurate predictions about
>> acoustics.
>
>I was thinking this as well. Sound waves at audible frequencies are the
>size that they are. You can't "scale them down" to go along with the
>other scaled down parameters. This would seem to make such an experiment
>meaningless.

No, wavelength is inversely proportional to frequency. The way a 5 KHz
wave propagates around a room is exactly the same way a 50 KHz wave propagates
around a 1/10 scale model of the room. So you can use ultrasonic sources
for testing scale models out.

The Beranek book has a very nice discussion of this.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[mikethespark]

I think you will find that the BBC has done extensive work in scaling down
studio models for analysis and agree with Scott's answer.

Regards, Mike
"Scott Dorsey" <kludge@panix.com> wrote in message
news:bi5dth$ime$1@panix2.panix.com...
> Rob Adelman <SPAMLESSradelman@mn.rr.com> wrote:
> >Kenny wrote:
> >> Hello Again,
> >>
> >> I have to say something.
> >> The others commenting on scale is so far off the mark
> >> The smaller the room the harder it is to analyze acoustically with
mics.
> >> There is no way to scale down a room and get accurate predictions about
> >> acoustics.
> >
> >I was thinking this as well. Sound waves at audible frequencies are the
> >size that they are. You can't "scale them down" to go along with the
> >other scaled down parameters. This would seem to make such an experiment
> >meaningless.
>
> No, wavelength is inversely proportional to frequency. The way a 5 KHz
> wave propagates around a room is exactly the same way a 50 KHz wave
propagates
> around a 1/10 scale model of the room. So you can use ultrasonic sources
> for testing scale models out.
>
> The Beranek book has a very nice discussion of this.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

[Kenny]

IF you are going to multiply the frequencies by 10 and build a scale model
at 1/10 then okay.
But, I am talking reality here. The guy who needs help with his room is not
going to do this.

Let's try to stay on the planet earth... where real people live.


I know from experience that recording spaces are very hard to analyze
using time alignment and TEF equipment.

The reason is the relatively slow speed sound travels.
The human ear can't even tell there is a delay until sound travels over 40
feet.

Think about it...
If you are analyzing a large space, like and auditorium. 200 feet.
and a step in a wall is causing a frequency to bounce hard back at the mics.
You wont ever see it on a TEF screen unless it is 40 feet away. from the
mic.
Then is looks like a slap echo at it's favorite frequency.

A room that is 12 x 12 x 48 is going to be a bad room period.
it is a long echo chamber with sides that are equally divided into the
length.
the worst possible combination.

Kenny


"mikethespark" <micheal.hastings@btinternet.com> wrote in message
news:bi68rs$909$1@titan.btinternet.com...
> I think you will find that the BBC has done extensive work in scaling down
> studio models for analysis and agree with Scott's answer.
>
> Regards, Mike
> "Scott Dorsey" <kludge@panix.com> wrote in message
> news:bi5dth$ime$1@panix2.panix.com...
> > Rob Adelman <SPAMLESSradelman@mn.rr.com> wrote:
> > >Kenny wrote:
> > >> Hello Again,
> > >>
> > >> I have to say something.
> > >> The others commenting on scale is so far off the mark
> > >> The smaller the room the harder it is to analyze acoustically with
> mics.
> > >> There is no way to scale down a room and get accurate predictions
about
> > >> acoustics.
> > >
> > >I was thinking this as well. Sound waves at audible frequencies are the
> > >size that they are. You can't "scale them down" to go along with the
> > >other scaled down parameters. This would seem to make such an
experiment
> > >meaningless.
> >
> > No, wavelength is inversely proportional to frequency. The way a 5 KHz
> > wave propagates around a room is exactly the same way a 50 KHz wave
> propagates
> > around a 1/10 scale model of the room. So you can use ultrasonic
sources
> > for testing scale models out.
> >
> > The Beranek book has a very nice discussion of this.
> > --scott
> >
> > --
> > "C'est un Nagra. C'est suisse, et tres, tres precis."
>
>

[Scott Dorsey]

Kenny <watch777@adelphia.net> wrote:
>IF you are going to multiply the frequencies by 10 and build a scale model
>at 1/10 then okay.
>But, I am talking reality here. The guy who needs help with his room is not
>going to do this.

Lots of folks used to do this for room analysis, and nobody does it any
more. I was basically just point this out. This was one of the standard
architectural analysis techniques, starting around 1900 when Sabine started
doing it with spark gaps and schlieren photography, and was still used quite
a bit in the sixties when I started out.

Today, though, a lot of people use raytracing software, which effectively
does the sort of thing, in that it models the actual paths that waves take
throughout the room.

>I know from experience that recording spaces are very hard to analyze
>using time alignment and TEF equipment.
>
>The reason is the relatively slow speed sound travels.
>The human ear can't even tell there is a delay until sound travels over 40
>feet.
>
>Think about it...
>If you are analyzing a large space, like and auditorium. 200 feet.
>and a step in a wall is causing a frequency to bounce hard back at the mics.
>You wont ever see it on a TEF screen unless it is 40 feet away. from the
>mic.
>Then is looks like a slap echo at it's favorite frequency.

Right, which is why stuff like TEF analysis isn't the right tool for the
job. On the other hand, most of the serious problems in small rooms will
be on the low end, where an analyzer (or just a sweep generator and your
ears) really can help a lot at finding problems. And most of the higher
end problems in smaller rooms can just be treated as frequency domain issues
and fudged around with diffusion or absorption to get the frequency response
in the ballpark, again because the room is so small that the ear can't hear
the delays.

>A room that is 12 x 12 x 48 is going to be a bad room period.
>it is a long echo chamber with sides that are equally divided into the
>length.
>the worst possible combination.

Yup. But easy to fix by adding built-in bookcases that bring the walls in
a foot or so on one side, and a divider to block the long side up into two
unequal sections.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."