Acoustic foam?

[Irij]

well I have a simple question.

i own a place for my band's practice (rock) and for recording our
originals. (all in one room studio)

however i've covered all the corners with superchunk basstraps which i
was told to do to "treat" the room acousticly.

i am very unhappy with the flutter echo i get in this room, because
only corners ( + 1st reflection places) are covered with a material
that would kill the sound. I fell just fine when mixing.. but when
recording the flutter echo gets quite bad... same happens when
practicing.

would covering the paralell walls with acoustic foam (pyramids) make
my "room response" worse? (because they only absorb high and mid
frequencies) I'm not going to ask you if acoustic foam would take the
flutter echo away, because i already know it would :)

Thanks for your answers, Best regards, Jernej

[Ethan Winer]

Post by Irij
would covering the paralell walls with acoustic foam (pyramids) make
my "room response" worse? (because they only absorb high and mid
frequencies)

This is a good question. The treatment goal for all domestic size
rooms is for it to be broadband. As you understand, absorbing only mid
and high frequencies leaves the bass boomy and unbalanced. Acoustic
foam is okay, but it needs to be at least two inches thick. Four
inches thick is better, or use rigid fiberglass at least two inches
thick. While it's definitely possible to cover too much surface area,
it's not usually possible for absorbers to be too thick.

--Ethan

[Irij]

ok. first off let me start with saying that i am pleased to get
feedback from the legend named Ethan Winer... i respect you man,
really! I read most of the articles on your website:P and your opinion
means a lot to me!
ofc thanks to the others too :)

now back to the subject:

room dimensions are 6m x 3m (this one is causing me trouble) x 2,5m
(h)

i am about to use 2 inches tick foam with following characteristics:
125 250 500 1000 2000 4000 f (Hz)
0,22 0,34 0,83 1,10 1,07 1,03 a
where d= 70mm (2,7inch)

since it's enough to cover one wall but that kills your L/R imaging i
thought of making something like a "chessboard" with my 1x1m foam
pieces on both walls (the parallel ones)
this would eliminate the flutter echo caused by those two walls, and
the room still wouldn't be DEAD, if you know what i mean...

rear and front wall (when mixing) dont really cause flutter echo
trouble, but i'm not really sure about ceeling and floor reflections..
(those are kinda hard to notice since my ears are in horizontal
position :P.. if it turns out that i have a FE issue with ceeling/
floor, how would i figure that one out?

please give me some feedback on my "solution"

Best Regards, Jernej :)

[GregS]

Post by Irij
ok. first off let me start with saying that i am pleased to get
feedback from the legend named Ethan Winer... i respect you man,
really! I read most of the articles on your website:P and your opinion
means a lot to me!
ofc thanks to the others too :)
room dimensions are 6m x 3m (this one is causing me trouble) x 2,5m
(h)
125 250 500 1000 2000 4000 f (Hz)
0,22 0,34 0,83 1,10 1,07 1,03 a
where d= 70mm (2,7inch)
since it's enough to cover one wall but that kills your L/R imaging i
thought of making something like a "chessboard" with my 1x1m foam
pieces on both walls (the parallel ones)
this would eliminate the flutter echo caused by those two walls, and
the room still wouldn't be DEAD, if you know what i mean...
rear and front wall (when mixing) dont really cause flutter echo
trouble, but i'm not really sure about ceeling and floor reflections..
(those are kinda hard to notice since my ears are in horizontal
position :P.. if it turns out that i have a FE issue with ceeling/
floor, how would i figure that one out?
please give me some feedback on my "solution"
Best Regards, Jernej :)

Really the best way to test would be using an impulse sound from a computer
or some other impulse, and a FFT time analysis.

I also clap my hands and listen.

Rug on floor and acoustic tiles in ceiling is pretty much minimum standard.
I forgot what your doing exactly, but that should affect the layout.

You could also use a foot of gravel on the floor. Sorry !

greg

[GregS]

Post by Irij
ok. first off let me start with saying that i am pleased to get
feedback from the legend named Ethan Winer... i respect you man,
really! I read most of the articles on your website:P and your opinion
means a lot to me!
ofc thanks to the others too :)
room dimensions are 6m x 3m (this one is causing me trouble) x 2,5m
(h)
125 250 500 1000 2000 4000 f (Hz)
0,22 0,34 0,83 1,10 1,07 1,03 a
where d= 70mm (2,7inch)

What are the walls and floor, and ceiling, made out of ?


greg

[Ethan Winer]

i thought of making something like a "chessboard" with my 1x1m
foam pieces on both walls (the parallel ones)

This is a common solution that looks good and works well. As Angelo
said, if you attach the foam with the pyramid side toward the wall,
the foam will absorb even more and to a lower frequency.

--Ethan

[Irij]

Well, You've convinced me... i shall attach the foam with the pyramids
towards the wall... but i was thinking of adding another layer of foam
on top of that.. so the pyramids would be turned to both the wall and
the room... plus i gain on thickness which will result in better
absorbtion and to lower frequencies.

as i said i shall use the chessboard "technique" slowly adding pieces
and testing the reflections often (just like you said, it's very easy
to make a room too dead)

the only problem i have now is mounting... I consider myself inovative
because i've invented a brand new patent for mounting my superchunks
in ceeling corners :P..
but i can't seem to find a soluting here... if i just cover the wall
with glue and press the foam with pyramid side to the wall, i don't
think it will glue to the wall good enough...
Maybe hanging?

Does anyone have any expirience from this, because it wouuld be
helpful.

Angelo was talking about this Sonex... any idea how they did it?

Thanks in your advice!
Best Regards, Jernej

[Ethan Winer]

Post by Irij
the only problem i have now is mounting.

Glue the foam to large sheets of cardboard. Then you can tack the
cardboard to the wall with just a few small push pins (or small dots
of glue) to minimize wall damage.

--Ethan

[Angelo Campanella]

Post by Ethan Winer

Post by Irij
the only problem i have now is mounting.

Glue the foam to large sheets of cardboard. Then you can tack the
cardboard to the wall with just a few small push pins (or small dots
of glue) to minimize wall damage.

That is a very good plan:

1- It assures placement and flexibility as needed.

2- The cardboard, laying normally a fraction of an inch away from the wall,
provides anoter panel absorption element resonating at a few hundred Hz,
helps at mid-frequencies.

3- The "Checkerboard" pattern is very good and flexible. Space between
panels is useful since diffraction increases sound absorption area around
the panel perimeters. I suggest a nomoinal reveal of about one foot width,
varying that to find the maximum reveal where slap- or flutter-echo is still
suppressed.

Ange

[GregS]

Post by Irij
well I have a simple question.
i own a place for my band's practice (rock) and for recording our
originals. (all in one room studio)
however i've covered all the corners with superchunk basstraps which i
was told to do to "treat" the room acousticly.
i am very unhappy with the flutter echo i get in this room, because
only corners ( + 1st reflection places) are covered with a material
that would kill the sound. I fell just fine when mixing.. but when
recording the flutter echo gets quite bad... same happens when
practicing.
would covering the paralell walls with acoustic foam (pyramids) make
my "room response" worse? (because they only absorb high and mid
frequencies) I'm not going to ask you if acoustic foam would take the
flutter echo away, because i already know it would :)
Thanks for your answers, Best regards, Jernej

Covering only ONE wall should eliminate that flutter.
Acoustic foam need not be pyrimid shaped. Thats good
for frequencies way up there. Regular open cell foam, or rigid
fiberglass panels are similar. You can also use drapes in conjunction
with other methods. You should get some good answers
here and in rec.audio.pro

Might explain the room in more detail and layout

greg

[Angelo Campanella]

Post by Irij
i own a place for my band's practice (rock) and for recording our
originals. (all in one room studio)

It will be nice to know the room dimensons, W, L, H.

Post by Irij
however i've covered all the corners with superchunk basstraps which i
was told to do to "treat" the room acousticly.

I'm sure they will "treat".... the question is "how much".

Post by Irij
i am very unhappy with the flutter echo i get in this room, because
only corners ( + 1st reflection places) are covered with a material
that would kill the sound. I fell just fine when mixing.. but when
recording the flutter echo gets quite bad... same happens when
practicing.

Flutter echoes are cause by two parallel facing surfces that are much
larger that a wavelength (100Hz=11', 1kHz=1.1'), It's most usually caused by
facing parallel wall segments, which can much more symmetrical (resulting in
sharper echoes), than the floor ceiling facing pair.

Post by Irij
would covering the paralell walls with acoustic foam (pyramids) make
my "room response" worse?

Pyramids are urban legends (or eye candy). They really don't compute as
a cost-efficient cure-all. Sonex mounted with the lumps turned toward the
wall (out-of-sight - tsk, tsk) provides more sound absorption.

My best recommendation for low budget sound absorbers is suspended
carpets or plush old curtains. They have to have an area mass of 12 to 40
ox/square yard. They should be suspended up to 6"and not less than 2", from
the walls. They need not be contiguous. A patchwork of whatever you can
rescue from the scrap pile or storerooms will do just fine. Starrt near wall
centers and spread out, wil revela in between until satisfied. As far as
distribution, consider that a room has six surfaces (4 walls +
floor+ceiling. coveriing any three adjacent walls will make the room about
as dear as you'll ever get it (sound can bounce there only once). And one
end is "dead" and the other end is "live"

Post by Irij
(because they only absorb high and mid
frequencies)

Right. to get low end absorption, you need area mass and distance. the
resonance (best absorption) frequency is calsulated from
Fr = 170/SQRT(W*D), where W is the area mass in pounds persquare foot and D
is the spacing from the wall in inches. Thus, a 40 oz/ square yard (about
0.37 PSF) carpet spaced six inches from the wall will have good asorption
at 130 Hz.

Post by Irij
I'm not going to ask you if acoustic foam would take the
flutter echo away, because i already know it would :)

Foam woks OK, It may workenough for your purpose. The finer the pore
size (it needs to be open-cell foam, since closed cell foam does not absorbu
high frequency sound), the beter the bsorption at all frequencies. Raised
away from the surface, it will have improved low frequency absorption while
maintaining its high freqiuency absorption.

Post by Irij
Thanks for your answers, Best regards, Jernej

[Tony]

Post by Angelo Campanella
Flutter echoes are cause by two parallel facing surfces that are much
larger that a wavelength (100Hz=11', 1kHz=1.1'), It's most usually
caused by facing parallel wall segments, which can much more
symmetrical (resulting in sharper echoes), than the floor ceiling
facing pair.

To add to Angelo's answer, the reflections will occur whenever there are
parallel and opposite surfaces. But they are audible as a "flutter echo"
only when most other reflections are suppressed. You don't get flutter
echoes in a rectangular room with hard walls, floor and ceiling. But, cover
the surfaces with absorbent material, except for one pair of opposite
parallel walls, and the flutter echo will be very obvious. The reflections
were there all along but they are exposed by suppressing other
reflections. (Personally I haven't found that there is any significant
difference between the flutter between walls, and that between floor and
ceiling.) And remember that you can suppress flutter echoes using diffusion
as well as absorption.

I "echo" Greg's remarks about bass absorption. Foam is not the answer for
bass absorption, in most rooms you can't fit enough thickness to be useful.
Professionally designed studios use membrane absorbers, apart from a few
that use Helmholtz resonators.