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John Cafarella
June 30th 03, 11:44 PM
Over the last 6 - 10 months I've posted a few questions about improving the
acoustic performance of a church. It seems that funds are now available,
and that the work can proceed.

The room is approximately 40' x 55'. Currently there are brick walls on 3
sides, 20 -40 ft assymetrically sloping pine board ceiling, floor is covered
with thin carpet. The room is 95% used for band style worship, (drums elec
bass, amplified guitar, 4-8 vocal mics). The problem is excessive reverb
time reducing speech intelligibility and making the music muddy.

The plan is to construct 2" x 4' x 8' 703 panels covered with fabric. These
panels will be mounted to the walls, with a 2" spacing between panel and
wall.
The panels will cover approximately 40% of the brick wall area.

Is the material used to cover the panels important? It has been suggested
to me by the church people that they may want to cover them with the same
carpet as the walls. Will this be a problem?

Do you see any other problems with the overall plan?

Thanks for your time
--
John Cafarella
End Of the Road Studio
Melbourne, Australia

Ethan Winer
July 1st 03, 02:46 PM
John,

> The plan is to construct 2" x 4' x 8' 703 panels covered with fabric. <

That all sounds good. But you might consider making some of the panels twice
as thick, and putting those on the walls near the corners. That would help
reduce the low end mud a little more. In fact, even better is to built thick
panels just for the corners, and mount them straddling the corners at a 45
degree angle.

> they may want to cover them with the same carpet as the walls. <

That should be fine. The fiberglass will just extend the carpet's absorption
to a lower frequency.

--Ethan

William Balmer
July 1st 03, 04:02 PM
"John Cafarella" > wrote in message
...

> The problem is excessive reverb
> time reducing speech intelligibility and making the music muddy.
>
> The plan is to construct 2" x 4' x 8' 703 panels covered with fabric.

First, a caveat - I'm not an expert in this field, but I have done some of
this kind of work, and I have had some acoustical physics coursework in
college (100 years ago).

It seems to me that what you propose is designed for high-frequency
absorption, but I'm afraid that the lower frequencies may be causing the
bulk of your trouble, and I don't think your solution will address this.
I've seen similar attempts at solving intelligibility problems that only
made things worse by absorbing useful high frequencies while leaving the
lows bouncing around the room, still masking everything above them.

I would recommend adding some dispersion to your plan. You can make wall
units that look the same as the others, but have acoustically invisible (or
nearly so) fabric on the front, with a convex hard surface behind. The
curved surface will reflect the lower frequency waves back in a scattered
pattern which will allow them to decay more naturally in open space without
reflecting off of opposite walls creating standing waves. Or you could
simply make all of your panels curved, making them a high-frequency absorber
and low-frequency diffuser in one.

Of course, since you say you are building "703" panels, and I don't know
what those are, perhaps they are already curved and you already have this
covered.

Bill Balmer

John Cafarella
July 2nd 03, 12:07 AM
"Ethan Winer" <ethan at ethanwiner dot com> wrote in message
...
> John,
>
> > The plan is to construct 2" x 4' x 8' 703 panels covered with fabric. <
>
> That all sounds good. But you might consider making some of the panels
twice
> as thick, and putting those on the walls near the corners. That would help
> reduce the low end mud a little more. In fact, even better is to built
thick
> panels just for the corners, and mount them straddling the corners at a 45
> degree angle.
>
> > they may want to cover them with the same carpet as the walls. <
>
> That should be fine. The fiberglass will just extend the carpet's
absorption
> to a lower frequency.
>
> --Ethan

Ethan,

Good thought about the double thickness panels. I hadn't given this much
thought as my research seemed to indicate bass buildup in corners is not so
much of a concern in a large room as it is in a small room such as a control
room.

It's largely academic anyway as there are doors in EVERY corner of the
room, so that's not practical. The closest I can get is adjacent to doors
on only two walls. Would this still be worthwhile? If these panels are 4"
thick, they should be 4" off the wall, correct?

One other thought, will the performance of two 4' x 4' panels (not butted up
against each other) be less than the perfomance of a single 8' x 4' panel.
I ask because in some positions the spaced smaller panels may work better
aesthetically.
--
John Cafarella
End Of the Road Studio
Melbourne, Australia

Ethan Winer
July 2nd 03, 02:33 PM
John,

> my research seemed to indicate bass buildup in corners is not so much of a
concern in a large room as it is in a small room such as a control room. <

Large rooms are often very boomy, and have an excessive reverb time at low
frequencies. If all that matters is speech intelligibility, then you don't
have to worry about low frequencies. But if you EVER plan to play music in
there you should definitely aim to reduce the reverb time at low frequencies
too.

> It's largely academic anyway as there are doors in EVERY corner <

You can also use the corners formed at the top of the walls where they meet
the ceiling. If that's not practical, then do as you suggest and just put
the double-thick panels as close to the corners as you can. And again,
spacing the panels away from the wall extends their absorption to lower
frequencies. The ideal air gap is approximately equal to the thickness of
the panel.

> will the performance of two 4' x 4' panels (not butted up against each
other) be less than the perfomance of a single 8' x 4' panel. <

Cutting the panels in half will actually be a little better. If you have X
amount of material to cover the walls, then you're always better off
distributing it evenly. That is, alternating panels - for example, in a
checkerboard pattern - is always better than covering large areas.

--Ethan

William Balmer
July 2nd 03, 03:39 PM
"John Cafarella" > wrote in message
...
>
> Feel free to correct me if I'm wrong, but to be non-transparent
(therefore
> reflective) at low frequencies wouldn't a curved panel have to be quite
> massive and rigid? (and hence expensive)

Yes and no. I have seen good diffusers made from "sono-tubes" cut in half
lengthwise. These are generally used as forms for poured concrete pillars.
They are made from a thick, pressed paper product (think halfway between MDF
and heavy cardboard) and are fairly inexpensive. When painted to match the
room, they can be quite unobtrusive and effective.
>
> Anyhoo, I'm not convinced that this room needs any more diffusion.

Okay then. Of course I've never been in the room, and you're probably
right. Chalk it up to an exercise of useless theory! Good luck, and let us
know how it goes.

Bill Balmer

DavidMackBlauvelt
July 2nd 03, 06:02 PM
"John Cafarella" > wrote in
:

> Over the last 6 - 10 months I've posted a few questions about
> improving the acoustic performance of a church. It seems that funds
> are now available, and that the work can proceed.
>
> The room is approximately 40' x 55'. Currently there are brick walls
> on 3 sides, 20 -40 ft assymetrically sloping pine board ceiling, floor
> is covered with thin carpet. The room is 95% used for band style
> worship, (drums elec bass, amplified guitar, 4-8 vocal mics). The
> problem is excessive reverb time reducing speech intelligibility and
> making the music muddy.
>
> The plan is to construct 2" x 4' x 8' 703 panels covered with fabric.
> These panels will be mounted to the walls, with a 2" spacing between
> panel and wall.
> The panels will cover approximately 40% of the brick wall area.
>
> Is the material used to cover the panels important? It has been
> suggested to me by the church people that they may want to cover them
> with the same carpet as the walls. Will this be a problem?
>
> Do you see any other problems with the overall plan?
>
> Thanks for your time
> --
> John Cafarella
> End Of the Road Studio
> Melbourne, Australia


How about some poly's ala the late great Malcolm Chisholm? Build then in
boxes and hang on the wall. His son reposted his website, Link here: read
fuzpoly.txt:

http://pages.ripco.net/~chisholm/malcolm_chisholm/INDEX.HTM

They are basically bowed masonite; simple; dirt cheap, and as Malcolm
told me; nobody believes they work. I've built 4.

Also from Malcolm; he mentioned that a certain research lab told him that
6" of 703 theoretically absorbs lower torwards 60hz. "Theoretically"
because their anechoic chambers could not measure that low due to their
size -- room smaller than the wavelength sizes.

Best,

Mack