18mm Baltic Birch vs 15mm Baltic Birch for speakers - stiffness - diyAudio
Go Back   Home > Forums > Design & Build > Construction Tips

Construction Tips Construction techniques and tips

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th June 2011, 05:52 AM   #1
diyAudio Member
 
Join Date: Jun 2011
Default 18mm Baltic Birch vs 15mm Baltic Birch for speakers - stiffness

My understanding is that a flat sheet of material gets stiffer by the cube, and that for a speaker, the stiffer the sides the better.

I have a 15mm BB kit coming.

However, doing a simply calculation, 18mm would be about a whopping 75% stiffer.

Questions: If I wanted a stiffer cabinet but the kit can come only in 15mm for a floor standing speaker, would it makes sense to purchase another sheet of 1/8 or 1/4" thick Baltic Birch and glue it on the outside to make the body thicker and stronger? 15mm sounds awfully thin to me but then I'm used to seeing mdf type cabinet.

What do you guys think?

This will be my first build and using a flat pack.

Thanks,
UL
  Reply With Quote
Old 20th June 2011, 05:59 AM   #2
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
15mm BB is on the same order of stiffness as 1" MDF, and much less massive. So to bring the resonant structure of the MDF in line with the BB you'd have to add on the order of 2x as much bracing to the MDF. The MDF would still have much greater energy storage & retransmission.

For the original frugel-horn 12mm was specifies. 15mm for FH3 is just fine. If you really want to take it up a level, i'd suggest adding a layer of plastic laminate. Very stiff for the mass, a dissimilar material, and with an addiitonal glue layer. it becomes the finish. Just doing the sides with natural everything else could have a very nice aesthetic.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 20th June 2011, 06:32 AM   #3
diyAudio Member
 
Join Date: Jun 2011
Dave, this post has NOTHING to do with baltic birch or FH3 or Alpair 7 or Helper Woofer or anyone of the many other subjects I've queried on different boards from here to AudioCircle.

Here's my question: HOW in the world do you keep up with so many board, forums and threads. It doesn't seem to matter whatever or wherever I post, you are on it in short order. Is there actually half a dozen people masquerading as 'Dave' or Planet 10? LOL - I'm not kidding but I'm literally shaking with laughter right now at how you seem to be everywhere all at once.

As far as I know, only one Being is omnipresent but you give me that feeling sometimes. Thanks for giving me good laugh in the best sense. It just strikes me as impossible.

Thanks again. I'll look into the plastic laminate. No idea what that is but it WOULD look very very sharp. i can see it in my mind's eye - black plastic on the side.... or perhaps dark grey with a grey Alpair driver would look sharp!

Regardless, thanks Dave.

UL
  Reply With Quote
Old 20th June 2011, 06:47 AM   #4
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Plastic laminate -- arborite, formica, more -- literally thousands of colours & patterns.

An example: Formica Corporation : Laminate

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 20th June 2011, 07:52 AM   #5
diyAudio Member
 
Saturnus's Avatar
 
Join Date: Jun 2005
Location: Copenhagen, Denmark
Quote:
Originally Posted by Ultralight View Post
My understanding is that a flat sheet of material gets stiffer by the cube, and that for a speaker, the stiffer the sides the better.
To my recollection that's only if the number of plys is the same in both which is usually not the case. Still if I recall correctly, each 3mm jump in plywood thickness with the assumption that 2 extra ply is used will double the stiffness. For example 18mm 13ply is twice as stiff as 15mm 11ply which again is twice as stiff as 12mm 9ply.
  Reply With Quote
Old 20th June 2011, 08:00 AM   #6
diyAudio Member
 
Join Date: Jun 2011
Other than cost and weight, is there any drawback with trying to go stiffer? I'll probably stay with the original 15mm. But would like to know.

Thanks,
UL
  Reply With Quote
Old 21st June 2011, 11:37 AM   #7
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Or you can do what I am doing and use two layers of 18 mm BB with Green Glue between them.
  Reply With Quote
Old 21st June 2011, 11:38 AM   #8
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Quote:
Originally Posted by Loren42 View Post
Or you can do what I am doing and use two layers of 18 mm BB with Green Glue between them.
Then you could change your name to UltraStiff...
  Reply With Quote
Old 21st June 2011, 04:01 PM   #9
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Quote:
Originally Posted by Saturnus View Post
To my recollection that's only if the number of plys is the same in both which is usually not the case. Still if I recall correctly, each 3mm jump in plywood thickness with the assumption that 2 extra ply is used will double the stiffness. For example 18mm 13ply is twice as stiff as 15mm 11ply which again is twice as stiff as 12mm 9ply.
For a given material, the stiffness increases with the cube (3rd power) of the thickness.........for an easy example, take a long 2x4 and place it between two saw horses laying flat, and compare it's stiffness when laying flat to when on edge.....then a 2x6, 2x8, etc.

Your "rules of thumb" are quite close; 18mm cubed is 5832, and 15mm cubed is 3375, and 12mm cubed is 1728. So 5832/3375=1.72 and 3375/1728=1.95 (not quite 2X for either of these, but 1.95 is close). Taking 5832/1728=3.37, so not quite 4X from thinnest to thickest.
  Reply With Quote
Old 22nd June 2011, 10:29 PM   #10
chrisb is offline chrisb  Canada
diyAudio Member
 
Join Date: Aug 2002
Location: victoria BC
UL - there are a number of reasons why we settled on the combination of 15 & 18mm BB for the FH flat-paks, including the quite signification factor of shipping cost. The approx 20% additional weight isn't the biggest issue, but the combined dimensions of securely wrapped parts would exceed Canada Post's length / girth limits per package.

For those folks building their own from FH plan-set, I can't think of any downside to using 18mm material for the entire enclosure, except for yield. Be aware that with the last couple of revisions to dimensions, there's lots to spare on a 4x8ft sheet, but I was not able to get all parts from a single 5x5 sheet, and the optimization works out quite differently on a batch run of 15 pairs compared to a single.
__________________
you don't really believe everything you think, do you?
community sites t-linespeakers.org, frugal-horn.com commercial site planet10-HiFi
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
source for baltic birch? qingcong Multi-Way 11 4th February 2011 05:52 PM
Super baltic birch Illusus Everything Else 59 17th January 2011 02:44 PM
Stain on Baltic birch flaevor Multi-Way 10 12th November 2006 12:15 AM
working with baltic birch plywood morbo Multi-Way 55 17th September 2005 05:09 PM
Baltic Birch and MDF? downward_dog Subwoofers 6 12th January 2005 11:09 PM


New To Site? Need Help?

All times are GMT. The time now is 08:59 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2