Bracing101 2021

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camp10
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Re: Bracing101 2021

#16 Post by camp10 » Tue Apr 13, 2021 3:52 pm

Ty Bill!....Seth, I am really into the science...and I try to question all things but I also like to get my technique straight from the horse's mouth...in this case...Bills mouth lol!!! That is an interesting link...People nowadays run simulations to show cause...matrix bracing is very sound theory and the man, who as far as I can tell, put it on the map for DIY, is Bill.

Grant Bunter
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Re: Bracing101 2021

#17 Post by Grant Bunter » Tue Apr 13, 2021 3:54 pm

camp10 wrote:
Tue Apr 13, 2021 7:25 am
Thanks to the bracing provided by the threaded and my new info regarding brace spacing (8"-12" separation) The side panels are near finished...The top/bottom baffles are 12" wide so, bracing is not needed there. I think a few cross members and some ribs jutting out several inches from the back wall running top to bottom will take care of the back baffle which is 32Wx29H...the front baffls are 12" wide and so no bracing needed there either.
Seth said no more than 8 inches. Where did you get 12" from?
Seth also generalised. Most plans suggest spacing somewhere between 6 and 9 inches apart depending upon cab width.

A 12" wide complete panel needs bracing. Ideally, at 6 inches...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

camp10
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Re: Bracing101 2021

#18 Post by camp10 » Tue Apr 13, 2021 4:03 pm

A guy on the AVS forum said 8-12".....Bill just stated 6" as being optimal. And now with your input we have 6-9" spacing....its all pretty close....

12" wide panel with 3/4" adjoining panels on each side leaves 10.5 of space in between...

6" is optimal

bare minimum ~9-12"? Maybe 9" is bare minimum...

What I am wondering now is whether one always has to create a full cross member...it would seem that adding a perpendicular board top to bottom jutting out maybe 4inches would create a good amount of rigidity also... sorta like in this pic

This is the type of bracing one might find inside a plastic...something...I forget...but I do recognize this type of structural building from plastic products.

IIRC rib style bracing is used on the fuselage where crossmembers cannot be placed....so it is likely 2nd to matrix bracing, but non the less useful in situation where one cannot or does not, want to run a full cross member.
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Strange Kevin
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Re: Bracing101 2021

#19 Post by Strange Kevin » Tue Apr 13, 2021 4:28 pm

Wait, your building our of 3/4" ply?

Most of Bills plans call for 1/2" or less.

With the thicker wood, you can get away with less bracing, but your end up carrying around a lot more unnecessary weight.

There is merit to your last statement, bill uses a similar method on the back pieces of the jack/Omnitop plans and on larger driver access panels that still need to be removable.
Authorized Builder - Phoenix AZ.
Main Rig - 6 DR200s - 6 T48s (30")
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camp10
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Re: Bracing101 2021

#20 Post by camp10 » Tue Apr 13, 2021 4:39 pm

Good point...Not everyone in DIY is on the level Bill is, regarding bracing, so the standard out and about is 3/4"....out of fear I just ran with 3/4"....figuring it couldn't hurt anything other than my back lol...If they get rebuilt, I am sure 1/2" ply, with 6" spaced, 1" beams, is my new status quo.

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Seth
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Re: Bracing101 2021

#21 Post by Seth » Tue Apr 13, 2021 5:08 pm

camp10 wrote:
Tue Apr 13, 2021 3:52 pm
Ty Bill!....Seth, I am really into the science...and I try to question all things but I also like to get my technique straight from the horse's mouth...in this case...Bills mouth lol!!! That is an interesting link...People nowadays run simulations to show cause...matrix bracing is very sound theory and the man, who as far as I can tell, put it on the map for DIY, is Bill.
Well then, I guess his response was sufficient for your inquiry. Straight from the horses mouth, "Experience"... not a bad technique. One of the best around really.

Glad to hear your desires are fulfilled :thumbsup:
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Bill Fitzmaurice
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Re: Bracing101 2021

#22 Post by Bill Fitzmaurice » Tue Apr 13, 2021 5:11 pm

Image

Very pretty...but can they fight?
In this case, not really. Far easier to build panel to panel braces will work considerably better. The purpose of bracing isn't to stiffen panels a bit, it's to make them inert. Braces that connect opposing panels do that better, using less material, than any other method. Spline bracing is OK if it's the only alternative, but that's the only time I use it. Bracing that comes within a few inches of the box corners is wasted material and unnecessary weight, as that's the strongest part of the box.

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Seth
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Re: Bracing101 2021

#23 Post by Seth » Tue Apr 13, 2021 5:13 pm

camp10 wrote:
Tue Apr 13, 2021 4:39 pm
Good point...Not everyone in DIY is on the level Bill is, regarding bracing, so the standard out and about is 3/4"....out of fear I just ran with 3/4"....figuring it couldn't hurt anything other than my back lol...If they get rebuilt, I am sure 1/2" ply, with 6" spaced, 1" beams, is my new status quo.
You'd do well to purchase a set of Simplex 18 Subwoofer plans (matter of fact, just buy the whole set of plans on CD/thumb-drive) there's a lot of good info in them and you can see firsthand what he does for bracing.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

camp10
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Re: Bracing101 2021

#24 Post by camp10 » Tue Apr 13, 2021 7:08 pm

I took the idea of 1/2" plywood complimented by 6" spaced 1" thick beams....0.5/.75=1.5(6)=9" so with 3/4" ply, 9" spaced crossbeams might do the trick....Very crude conversion but...its all I got lol.

Seth - I like Bills designs but non of them are tuned as low as I'd desire...I know that he does not design for 18" woofers as well for reasons of diaphragm rigidity....I think that issue is actually a problem of the past considering the quality of todays hi end pa 18"s...depending on which model I'm sure...I have acoustic elegance 18H+'s but still it would seem a smaller woofer diameter is desirable. The idea that a driver buried inside the horn hides THD is something I did not consider 2 years ago when I started this design....so the direct radiator way is to use are large a woofer as possible in order to reduce excursion and thus THD....we never heard my friends bandpass sub being mutilated inside either lol!

the thing about horns of 4th order is that it is the best of both worlds....low group delay of sealed and output of vent....decay seems to behave like a sealed most of the time also....I've modelled my current design as a truncated horn and liked what I saw but the phase flip scared me off...I'd have to use a linear crossover to make it work and I've been building around minimum phase expectations.

I'd want a horn tuned to 30hz or lower...and to remain within xmax at 30hz @ 1 meter @ 115db or better....that has been my criteria. I could maybe do this with smaller woofers...I'd have to start modelling in Hornresp...My current design PPSL, is "technically" a 4th order, extremely truncated horn...actually if the vent section were any smaller the drivers would not fit lol....

I just noticed that the simplex is a cab built for 18" woofers...lol....I'm sure Bills designs are definitely worthy, especially to those who do not know how to build cabs from scratch...I've been learning to do that for the last 2 years.

Bracing was the last frontier for me and Bill has blessed me with his wisdom. (ty seriously)

Regarding my current design.. center to center spacing is a big deal and I have combined 2 18" drivers into an output roughly 920cm2 CSA....thats a big a deal...considering a 15" will sit on top of that and be able to couple with the 18's for a considerable increase in efficiency. On top of that is a horn for the tweeter, crossed at 300hz or possibly lower... center to center spacing is really good compared to any other design you may find, in particular using a horn on top.

This design is meant to be a Strauss mf 2.1 killer.....as anyone DIY hates manufactured speakers....there's plenty to hate about this 64000 dollar set of speakers lol!!!

If I could combine the bottom output with the midbass output within the same horn (like they do with mids and tweeters in synergy horns) that would be pretty amazing....I think smaller drivers would have to be used in order to keep size reasonable and qts down in the rear sealed chamber...Im not sure if that idea would fly anyway given the discussion we just had about the high pressure environment inside a horn that increases as tuning is lowered....for the synergy/MEH designs dealing with midrange, pressure has not shown itself as an issue.

CarterKraft
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Re: Bracing101 2021

#25 Post by CarterKraft » Fri Sep 17, 2021 4:13 pm

Bill Fitzmaurice wrote:
Tue Apr 13, 2021 7:14 am
camp10 wrote:
Mon Apr 12, 2021 8:53 pm
I was almost certain that the pressure swing in vented design was less than a sealed considered the pressure is relieved by the vent..
That's a common misconception. The vent doesn't relieve pressure. It increases it, because it's not a simple hole in the box, it's a Helmholtz resonator. Many is the bass player that uses a sealed cab because they think it controls excursion better than vented. The opposite is true. This is related to how a vent works. The usual assumption is that the rear wave from the driver escapes the enclosure via the vent. It doesn't. The air mass within the vent vibrates back and forth, just like a driver cone, creating its own wavefront that emanates from where that air mass meets the outside air.
Don't try this at home....

When we built the truck tuba and had not installed the driver yet I blew air into the cutout hole where the cut had just been made into the finished cab,
I was attempting to blow out the remaining sawdust I wasn't able to vacuum up.

The driver chamber of the TT visually swelled in both axis from puffs of compressed air into the 8" woofer hole.
This perplexed me a lot because as I told my son "it is open on the end of this, why does it hold pressure?".

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Bill Fitzmaurice
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Re: Bracing101 2021

#26 Post by Bill Fitzmaurice » Fri Sep 17, 2021 4:48 pm

I can see that happening with sufficient velocity and volume.

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