John Sayers' Design Forum

John Sayers' Recording Studio Design Forum

A World of Experience
Click Here for Information on John's Services
It is currently Fri Sep 20, 2019 12:13 pm

All times are UTC + 10 hours




Post new topic Reply to topic  [ 36 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject:
PostPosted: Sat Aug 19, 2006 7:40 am 
Offline
Senior Member
User avatar

Joined: Wed Jun 18, 2003 6:09 pm
Posts: 760
Location: Antwerp/Belgium
:( Everytime I edit the above message the picture description in the titlebar of the uploads is lost (dissapears).


Anyhow, this comparison is rather unique on the net I think.
Hence the curious ones can study how those resonance frequencies behave by changing the use of those materials.

The Tables are build up in columns, with different buildups from the same material.

This are strict theoretical calculations based on the mass-spring system, ignoring other parameters as mounting method, flanking, or whatever other phenomenon.

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun Aug 20, 2006 3:00 am 
Offline

Joined: Tue Aug 08, 2006 12:59 am
Posts: 7
Wow, very interesting stuff - thanks! :)


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun Aug 20, 2006 4:44 pm 
Offline
Senior Member
User avatar

Joined: Wed Jun 18, 2003 6:09 pm
Posts: 760
Location: Antwerp/Belgium
Ozy,

Thanks.

A stupid question: If I make such model in US units how do USers express such thicknesses in fact (for plywood).
I can imagine that drywall goes in fractions to x/8", but plywood can go much thinner wher x/8 of an inch is too course.
When recalculating metric measures I come to 1/32 resolutions?

How do you guys express those thin thicknesses for plywood or hardboard? Searching the net gives me a lot of Metric stuff, but in Imperial it's not very clear to me.

Eric

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun Aug 20, 2006 9:05 pm 
Offline
Site Admin
User avatar

Joined: Mon Jan 27, 2003 12:46 pm
Posts: 5376
Location: Australia
Eric - I think the standard sizes and their equivalents rounded out are:

1/8" = 3mm
1/4" = 6mm
3/8" = 10mm
1/2" = 12mm
5/8" = 16mm
3/4" = 20mm
1" = 25mm

but they do use 3/16" 7/16" etc.

cheers
john


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 21, 2006 12:43 am 
Offline
Senior Member
User avatar

Joined: Wed Jun 18, 2003 6:09 pm
Posts: 760
Location: Antwerp/Belgium
John,

Thanks.

What surprices me if I go to a woodshop here I find much more thin panel thicknesses.

I searched further and found some links which look interesting (I still must look myself in detail):
http://www.ruraltech.org/projects/conve ... s_book.asp (look at links on page)
http://www.ruraltech.org/projects/conversions/

http://ts.nist.gov/ts/htdocs/210/sccg/ps1-95.pdf

http://hoganhardwoods.com/hogan/pages/t ... mation.htm

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 25, 2006 1:26 pm 
Offline

Joined: Fri Aug 25, 2006 7:33 am
Posts: 41
is this the thread that lead to the other thread where Ethan asked about adding a panel trap?



I would be honored to volunteer Audio Alloy - Green Glue Company - to test that... should be fairly fast / inexpensive to test. We'll just add a 4' x 4' panel trap to a 64 square foot test wall and report. That will take until the end of september.

That's always, always, always the best way - to test. I'd be grateful if somebody would email or post (and remind me!!) how to build the panel trap and attach it.

_________________
Technical director, Green Glue Company
(Audio Alloy)
All posted content copyright Brian Ravnaas or Green Glue Company except as noted and may not be reproduced without permission.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 25, 2006 1:58 pm 
Offline

Joined: Fri Jun 18, 2004 9:08 am
Posts: 251
Location: Ontario, Canada
Brian:

http://www.bobgolds.com/BassTrap_JeffCooper_pg127.jpg

I believe the membrane should be as large as possible, to make it more membrane-ish, and less structurally-damped-by-the-2x4s. So 4x8 sheets of plywood are good, and 2x8 sheets of plywood are less good.

The traditional formula is simple enough (ignores 2GOF):
d = 28900 / (f ^2 * m)
where
d = depth in inches
f = resonance frequency in hz
m = surface density in pounds per square foot


1) e.g. 50hz = 8.4" out, using 4x8 sheets of plywood and 2x10's on 4' centers (i.e. the edges of the plywood), with the 2x10's cut to 8.407".

8.407 inches = 28900 / ((50hz ^2) * 1.375 lb/ft^2)
where 1.375 is the surface density of typical 1/2" plywood.


2) e.g. 100hz = 2.1" out, again using 4x8 sheets of plywood and 2x3's on 4' centers, with the 2x3's cut to 2.1"

2.1 inches = 28900 / ((100hz ^2) * 1.375 lb/ft^2)


3) e.g. 50hz, but with Gypsum/Drywall instead of plywood:

5.25 inches = 28900 / ((50hz ^2) * 2.2 lb/ft^2)
where 2.2 is the surface density of typical 5/8" drywall/gyspum.


Last edited by z60611 on Fri Aug 25, 2006 2:07 pm, edited 1 time in total.

Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 25, 2006 2:03 pm 
Offline

Joined: Fri Jun 18, 2004 9:08 am
Posts: 251
Location: Ontario, Canada
Brian:

Ethan's Bass Trap link is
http://www.ethanwiner.com/basstrap.html
http://www.ethanwiner.com/BTPlans.gif
http://www.ethanwiner.com/BTParts.html & http://www.ethanwiner.com/BT2001.html


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat Aug 26, 2006 7:23 am 
Offline

Joined: Sat Aug 05, 2006 12:48 pm
Posts: 17
Location: San Diego, CA , USA
At this point, I surmise my 1st dumb question isn't all that dumb?

Anyway, Mr Desart I don't follow the graphs that you graciously posted.
:oops: could you - or anyone splain(explain) please?

Tony


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat Aug 26, 2006 8:40 am 
Offline

Joined: Fri Jun 18, 2004 9:08 am
Posts: 251
Location: Ontario, Canada
Tonio:

The day Eric posted it, at my home woman (no relation to Paul's woman) came in. Smiled at me curious about what I had found.
Woman said, "What's so interesting." She looked closer, frowned, "Oh, acoustics." and left.
She came back 15 minutes later and asked "How can you stare at that chart for half an hour?"
I replied, "Different chart" and scrolled up to the first one, and then back down to the second one.
She handed me a bowl of watermellon and strawberries, each cut up into 3 cubic centimeter pieces and said "Eat." and she sat down beside me and opened her book with her own bowl of the same on her lap.

Some people learn by formulas.
I learn by examples -- and then use the formulas grudgingly later to fine tune to specific situations I'm interested in.

The charts are a bunch of different examples of wall systems. Where it gets interesting is when you start comparing them, and discovering trends.

Image

This is relevant to Ethan's question because the traditional formula (1DOF - assumes infinite mass behind other leaf)
d = 28900 / (f ^2 * m)
where
d = depth in inches
f = resonance frequency in hz
m = surface density in pounds per square foot

75mm = 2.952 inches
surface density of 1/2" drywall is 1.8 pounds per square foot.

for the top left wall would be
f = sqrt( 28900 / (m * d) )
f = sqrt( 28900 / (1.8 * 2.952inches) )
f = 73hz.

same as Eric calculated for 'First Wall'.

If that second 'wall' is a membrane absorber you've just built, but you stick it on a similarly constructed current wall, then the resonances you end up with are not the target one you wanted. i.e. not 72hz, but rather something that's pretty good at 44hz and 117hz.

Within the limitations of Eric's disclaimers. namely
Quote:
This are strict theoretical calculations based on the mass-spring system, ignoring other parameters as mounting method, flanking, or whatever other phenomenon.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat Aug 26, 2006 9:31 am 
Offline

Joined: Sat Aug 05, 2006 12:48 pm
Posts: 17
Location: San Diego, CA , USA
Z,
Thank you, great splaining :D Now I feel dumber :evil: Just kidding
You know I get the same respond from the female gender about acoustical things :wink:

T


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat Aug 26, 2006 10:14 am 
Offline

Joined: Tue Dec 02, 2003 8:58 am
Posts: 21
Location: Brisbane Australia
very quick and simple output from WinFLAG, hope it helps

Andrew


You do not have the required permissions to view the files attached to this post.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 28, 2006 1:24 pm 
Offline
Senior Member
User avatar

Joined: Wed Jun 18, 2003 6:09 pm
Posts: 760
Location: Antwerp/Belgium
Andrew,

Do you have this graph also in numbers?
Exact mass, exact wool, exact whatever.

Can you also make the same without wool? (also with numbers if possible?)

Bob,

Nice conclusions you entered here. :) I expected those tables to trigger you.
But it were not just an arbitrary bunch, but I entered them as logical series.

If you want to check certain combinations just give them.

Warm regards
Eric

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 28, 2006 1:56 pm 
Offline

Joined: Fri Jun 18, 2004 9:08 am
Posts: 251
Location: Ontario, Canada
Eric_Desart:

Quote:
Do you have this graph also in numbers?

Have you ever heard of William Playfair (1759 - 1823). He invented charts and graphs. In 1786 he created the first published bar chart, which illustrated Scotland's 1781 trade surplus with America and its simultanious trace deficit with Russia. The reason I meantion it is you asked for numbers, and from American Scientist May-June 2006 pg 275:
Quote:
pictures created to represent observations were necessarily less accurate and more interpretive than were numbers themselves. A "general mistrust of pictorial representation" in British science continued into the early 19th century (and a cautious skepticism about graphic representation remains part of scientific culture today). Watt tactfully urged Playfair to provide tables to support his arguments, pointing out that "the charts now seem to rest on your own authority, and it will naturally be enquired from whence you have derived your intelligence."

Quote:
Graphical representation , he [Playfair] argues in the Breviary, can "facilitate the attainment of information, and aid the memory in retaining it." ... It conveys its message to the eye in an instant.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 28, 2006 1:58 pm 
Offline

Joined: Fri Jun 18, 2004 9:08 am
Posts: 251
Location: Ontario, Canada
Eric_Desart:

I have the formula for 1DOF with one wall infinite mass.

I've been meaning to see if one of my books answers these questions:
What's the formula for 1DOF with two normal masses?
What's the formula for 2DOF with two normal masses?


Report this post
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 36 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC + 10 hours


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group