acoustic treatment

[archive]

From: "hoeks" <hooks@z...>
Date: Sun Oct 31, 1999 2:10 pm
Subject: acoustic treatment

Hi all,

I apreciate all posts on acoustic isolation etc.,
but my interest in the moment is treating the
acoustics of a room. I am heaving some bad
bumps in the characteristic of my studio (the
main one very sharp at 123hz). Can anyone point
towards info (preferably on the web and with metric
units since I am Dutch)) that gives a
clearcut manual for making a helmholtz resonator/
acoustic resonator to treat my studio?
I am aware of Alton Everest's -masterbook of acoustics
and it is informative, but it doesn't give a clearcut
recipe for building an absorber.

Any tips appreciated

Peter

[archive]

From: Dan Nelson <dprimary@e...>
Date: Sun Oct 31, 1999 5:10 pm
Subject: Re: acoustic treatment

I don't know of any web sites about helmholtz resonators, the lack acoustic
information (and the construction details) is one of the reasons I started
the site and mailing list. I can help you on the list and then I will turn
that information into a page for the site.

Are the bass problems modal ? Did you measure the bumps or calculate them?
What other frequencies are problems?
Most of the time I use a resonant panel to control bass problems since it
is rare to have a problem at one exact frequency, and they are easy to
build.

Can you list some common metric building material dimensions and what the
materials are called? What thickness of "plywood" can you get? 10mm-2 mm
This was going to be one the things I was going to bring up on the list
since materials are know by different names in different parts of the world
or even across the US. I know the site has viewed in 22 different
countries. About 20% of people on the list are outside of the US, I think
the US and maybe England are the only countries that aren't metric. If
everyone can post some materials and dimensions I will create a conversion
page for the site. I.E. - 1/8 masonite =3.2 mm hardboard

Dan Nelson
www.studiotips.com

[archive]

From: Brian Cassell <bcc2a@f...>
Date: Sun Oct 31, 1999 5:46 pm
Subject: Re: acoustic treatment

RE: Material Dimensions,
So can we agree to use US quantities, for the most part, since 80% are
in the US, and let those of us in the minority convert using the table?
There may be an existing conversion table at the Nat'l Institute of
Standards page, or at the BOCA page.

RE: Insulating your overhead door,
They make closed cell foam, usually in Blue or Pink, that is made for
insulating buildings. It is not the white "bead board" that leaves
little foam beads everywhere; it is a closed cell foam that has a much
higher R-value than the bead board. You can cut it into sections the
size of your garage door sections, and affix the sections to the
sections of the door. You can go as far as doing multiple layers of the
stuff. Just remember to ease the edges back on the foam where it lines
up with the hinged points of the door. This way, the foam doesn't bind
when raising the door. This is all assuming your overhead door hinges
in sections, and not every two inches. Hope it's helpful, Brian

[archive]

From: Mark Plancke <soundtch@M...>
Date: Sun Oct 31, 1999 6:01 pm
Subject: Re: acoustic treatment


I don't know about the UK, but I can still order 1/2" AC plywood from
the lumber store. They just deliver 12mm plywood.

It would be nice to offer the materials guide in metric as well since it is the
standard everywhere else except the US. Not to mention the fact that there
is no such thing as Owens Corning 703 in Canada, it's called AF530! It took
a ton of phone calls, including calls to Owens Corning reps (who didn't know
what 703 was). I eventually went to an acoustics specialty store and asked for
703 and they knew what I was looking for - AF530. Same stuff, different name.

Mark Plancke

SOUNDTECH RECORDING STUDIOS
http://SOUNDTECHRECORDING.COM
Windsor, Ontario Canada

[archive]

From: Dan Nelson <dprimary@e...>
Date: Sun Oct 31, 1999 6:41 pm
Subject: Re: acoustic treatment

That's exactly what I had in mind, the guide will be in both english and metric
and list the different names it is known by. Even the books call materials by
different names, then what the building supply store calls them.

Dan Nelson
www.studiotips.com

[Dan Nelson]

From: "hoeks" <hooks@z...>
Date: Sun Oct 31, 1999 7:57 pm
Subject: Re: acoustic treatment

Hi Dan,

Thanks for replying. You're absolutely right about
lack of information on acoustic treatment on the
net (and the world in general!)
I have to admit I don't know what modal means, but the
resonance I am experiencing is quite clear; I can 'ring it out
with a sine tone or even with eq on a more complex sound.
I have no other real serious problems, or rather don't want to
start looking at them, cause my studio is my living room as well!
It is a very narrow peak (+/- 20hz)and it doesn't really seem to reoccur at
multiples
of the 123 hz I measured. I tried moving speakers, furniture etc. but
that didn't help at all, so I guess it must have something to do with floor
/ceiling/ wall
to wall distance.
I would have to check for common measurements for stuff like plywood,
chipboard
perfboard etc.I will try to look into that and report back to you.
I will also do some more measurements (they'll be simplistic I haven't got
sophisticated measuring equipment) to give you more data to work with.
Would be nice to provide some data for the database you're trying to build,
so everyone can benefit from it!

Peter

[archive]

From: SRF7@a...
Date: Sun Oct 31, 1999 11:33 pm
Subject: Re: acoustic treatment

In a message dated 10/31/99 1:06:15 PM Eastern Standard Time,
soundtch@M... writes:

<< I eventually went to an acoustics specialty store and asked for
703 and they knew what I was looking for - AF530. Same stuff, different name.

Mark Plancke
>>

You can also look for Johns Mansville's "Spinglass", and similar fiberglass
board products by Certainteed which are equivalent to Corning's 703 board.

Scott R. Foster

[Dan Nelson]

From: SRF7@a...
Date: Sun Oct 31, 1999 11:57 pm
Subject: Re: acoustic treatment

In a message dated 10/31/99 9:12:47 AM Eastern Standard Time,
hooks@z... writes:

<< I am aware of Alton Everest's -masterbook of acoustics
and it is informative, but it doesn't give a clearcut
recipe for building an absorber. >>

Ok... but don't you mention in a follow up post that you don't know what room
modes are. You need to go a step past being aware of this text and read the
chapters on room modes and the control of same.

I'd bet a doughnut and a cup of coffee that you have two axial modes piled up
at your 120 Hz bump. A brief overview of the topic of room modes is in
order... Everest's handbook would suffice.... then try some ceiling / wall
treatment to control those modes.

You might not need a tuned absorption structure.

I can send you a spreadsheet which you can turn room dimensions into a mode
table and then tweak the design for a slat absorber tuned to your needs. Do
you use Excel?

Scott R. Foster

[archive]

From: Dan Nelson <dprimary@e...>
Date: Mon Nov 1, 1999 12:58 am
Subject: Re: acoustic treatment

There is also a filemaker file that will calculate room modes in the file area
of the web site.
Stand alone run time versions will be there if a few weeks

Dan Nelson
www.studiotips.com

[archive]

From: "hoeks" <hooks@x??x.xxxxx.xxx
Date: Mon Nov 1, 1999 9:31 am
Subject: Re: acoustic treatment

Scott,

I will admit readily that my knowledge of acoustics
isn't very deep. I do know what room modes are, but
just didn't get it the way Dan phrased it.
Anyhow my room is very irregularly shaped and I haven't
been able to tie the resonance I am experiencing to the
dimensions of the room. It would be nice if you could mail
me the excel sheet (would be nice for Dan's site as well)
In the mean time excuse me while I mingle with you oh high
priests of sound propagation :-)

p.s. If you're right about the piled up axial modes I'll add a full
pack of napkins to the coffe and doughnut!

[archive]

From: Dan Nelson <dprimary@x??????xxxxx.xxxx
Date: Mon Nov 1, 1999 5:18 pm
Subject: Re: acoustic treatment

The excel speadsheet is up on the site Scott emailed it to me last night. You
can find it in the "file area" link remember it is in US measurements so you
will have to do some conversions. Or if someone wants to change the formula's
to metric I'll post a metric version too.

Dan Nelson
www.studiotips.com

[archive]

From: "Rose, Max" <mrose@x?????xxxx.xxxx
Date: Mon Nov 1, 1999 5:37 pm
Subject: RE: acoustic treatment

Most of the time I use a resonant panel to control bass problems
since it
is rare to have a problem at one exact frequency, and they are easy
to
build.

Can you elaborate on the construction of resonant panels please? Thanks in
advance

Max Rose
Mastering Engineer
Disc Makers/Seattle
mrose@d...
1(800)553-8906 (206)285-2642

[archive]

From: Dan Nelson <dprimary@x??????xxxxx.xxxx
Date: Mon Nov 1, 1999 5:47 pm
Subject: Re: Digest Number 10

There is a book review page on the site w /links to them amazon "Master
Handbook of
Acoustics" is a great place to start.
It has alot of information but it is fairly easy to read. I reread it every
time I start a
new studio construction project and I find, I still gain a little more insight
into the
subject. And I have all three editions, Everest keeps updating it every few
years.
The fabric can make a difference a tight weave may reflect more high
frequencies You can
calculate the amount you need with the help of programs in the file area rt60
is what you
will want calculate. You may want to get the book above first to help you
understand the
results. Suspended horizontal panels would work better in your case.

Dan Nelson
www.studiotips.com

[archive]

From: Mark Plancke <soundtch@x??x.xxxx
Date: Mon Nov 1, 1999 5:58 pm
Subject: Re: acoustic treatment

At 10:18 AM 11/1/99 -0700, you wrote:
>From: Dan Nelson <dprimary@e...>
>
>The excel speadsheet is up on the site Scott emailed it to me last night. You
>can find it in the "file area" link remember it is in US measurements so you
>will have to do some conversions. Or if someone wants to change the formula's
>to metric I'll post a metric version too.
>

Dan

I tried d/l'ing the PC Zip version and got an error that it was
an unregonized format when I tried to unzip.

There's also an online mode/rtc60 calculator on the
SDG Acoustics site.

http://www.sysdevgrp.com/cgi-bin/calculator.pl5

Mark Plancke
SOUNDTECH RECORDING STUDIOS
http://SOUNDTECHRECORDING.COM
Windsor, Ontario Canada

[archive]

From: Mark Plancke <soundtch@x??x.xxxx
Date: Mon Nov 1, 1999 6:11 pm
Subject: Re: acoustic treatment

At 12:58 PM 11/1/99 -0500, you wrote:
>
>There's also an online mode/rtc60 calculator on the
>SDG Acoustics site.
>
>http://www.sysdevgrp.com/cgi-bin/calculator.pl5

This is the correct URL for the SDG acoustics
site.

http://www.sysdevgrp.com/acoustics.html

SOUNDTECH RECORDING STUDIOS
http://SOUNDTECHRECORDING.COM
Windsor, Ontario Canada

[archive]

From: Dan Nelson <dan@x???xx.xxxx
Date: Mon Nov 1, 1999 8:32 pm
Subject: Re: acoustic treatment

I just tried it on a PC and WinZip opened it fine, did you right click it to
download or grab the mac - sea compressed one by mistake. Or maybe it is a new
version of Zip. I posted the zipped filed file that Scott emailed me but every
thing I have opens it. I don't have FTP setup yet so these are http downloads. I
haven't figured out how to setup virtual FTP yet. WSDG also has some
calculators
you can download if you problem with this one but, their site may be down,
yesterday it looked like they transfering their site to an in house server.

Do you know the name of the company the makes AF530 you used?

Dan Nelson
www.studiotips.com

[archive]

From: SRF7@x??x.xxx
Date: Mon Nov 1, 1999 8:38 pm
Subject: Re: acoustic treatment

In a message dated 11/1/99 4:33:13 AM Eastern Standard Time,
hooks@z... writes:

> I mingle with you oh high
> priests of sound propagation :-)

Hold on there little buddy.... I'm a lapsed agnostic and no expert on
acoustics.... just an interested observer (and listener).

> p.s. If you're right about the piled up axial modes I'll add a full
> pack of napkins to the coffe and doughnut!

Its a bet!

For sake of argument, if it aint room modes, then what causes it?

I' have sent the spreadsheets to Dan to post at his site if he wishes. I've
been using them (and reusing them), but they need tweaking to match any real
room (I just banged some numbers in... if you need help on your room let me
know). First I guess we'd have to figure out what your modes are. Do you
have a sketch of the room with dimensions?

Scott R. Foster

[archive]

From: Dan Nelson <dprimary@x??????xxxxx.xxxx
Date: Tue Nov 2, 1999 6:21 am
Subject: Re: acoustic treatment

A resonant panel or diaphragmatic absorber is used to absorb low frequencies.
They work by vibrating at these low frequencies and turning the sound energy
into heat. The drywall in wall construction acts as a resonant panel and
absorbs a considerable amount of bass. If you a ever been in a empty masonry
or concrete room you might have noticed the amount of bass build up when you
try to talk in the room. Compare that to an empty room in the average house
with sheetrock walls there will be some reverb but the bass build up like in
the concrete room. When you calculate the acoustic absorption of the room
remember to account for the bass absorption of the drywall.

The simple way to build a resonant absorber is to mount panel on a 2 by 4
frame with fiberglass batt (R11) or 703 inside of it. If you use 703 leave at
least a1/4" space between the panel and the fiberglass or else the panel won't
be able to resonant properly.

Approximate Plywood Panel absorption peaks on a 2 by 4 frame 3.5 " deep
1/8" = 150 Hz
1/4" = 110 Hz
3/8" = 87 HZ

You can also build them into the corners of the room which will give a
variable depth increasing the bandwidth of the absorption.

I had a recording room with plaster over brick walls that had a nasty problem
at 250 Hz well it just happens that R19 insulation with the paper facing the
room has a peak absorption @ 250 Hz. I built two 8' high by 4' frame in two
corners put in R19 with the paper facing the room. They fixed the bass problem
right up. I finish them by adding some 1/4" wood molding on top of the frame
and stretched some fabric across the frames to finish them. The molding is to
keep the fabric from touching the paper.

If Everest hadn't of pointed out the absorption of R19 in his handbook I would
never thought of it.
I made this a little long winded so I could have a good start on the subject
for the site.

Dan Nelson
www.studiotips.com

[archive]

From: "Alvise Migotto" <amigotto@x??x.xxxx
Date: Tue Nov 2, 1999 2:48 pm
Subject: Re: acoustic treatment

I would find this table very useful. Could you please send me one or post to
the list (or the web site?).

Thanks,
Alvise Migotto


>

[archive]

From: Dan Nelson <dprimary@x??????xxxxx.xxxx
Date: Tue Nov 2, 1999 4:16 pm
Subject: Re: acoustic treatment

The spreadsheet is in the file area of the www.studiotips.com web site.