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stevem
10-07-2005, 02:19 PM
Is there any reason why I shouldn't use angle iron or metal (steel, aluminum, etc.) for cabinet bracing (besides weight issues)? I think I will get better rigidity without taking up as much internal volume. Anyone have any thoughts on this? Thanks!
Mr. Widget
10-07-2005, 02:22 PM
Tap your angle iron with a hammer and tap a KD 2 X 4... which sounds better?


Widget
edgewound
10-07-2005, 02:32 PM
Once your angle iron is bolted tightly to the cabinet wall, any ringing issues will be mitigated.
Mr. Widget
10-07-2005, 02:35 PM
It will be dampened by the wood... but why go there in the first place?


Widget
JuniorJBL
10-07-2005, 02:39 PM
You could also coat the bar with spray-on bed liner or cover it with the asphalt based window sealing tape (very sticky):)
edgewound
10-07-2005, 02:45 PM
It will be dampened by the wood... but why go there in the first place?


Widget

Because he wants to, it'll be stronger, if he needs to...he can use it as a fly point....and most of all....because he wants to.:)
Mr. Widget
10-07-2005, 02:48 PM
If the goal is to save on volume, use extra fiberglass or foam damping material and gain virtual volume. Don't use dacron as it is less effective.


Widget
JBLnsince1959
10-07-2005, 02:50 PM
Tap your angle iron with a hammer and tap a KD 2 X 4... which sounds better?


Widget

Just tried it..... the angle iron sounds much better. The 2 X 4 didn't give much of a sound at all. :D
Mr. Widget
10-07-2005, 02:51 PM
See! :D


Widget
JBLnsince1959
10-07-2005, 02:54 PM
See! :D


Widget

:rotfl:
edgewound
10-07-2005, 03:18 PM
Just tried it..... the angle iron sounds much better. The 2 X 4 didn't give much of a sound at all. :D

I think the 2x4 has a much warmer tone;)...of course it's hooked up to a tube amp.:)
Mr. Widget
10-07-2005, 03:22 PM
In all seriousness I am sure metal can be made to work... I prefer 2X4's made up from birch plywood. It is strong, stiff, and it doesn't ring.

Here are some subwoofer cabinets I'm working on. They are dual 18s.

Widget
JBLnsince1959
10-07-2005, 03:23 PM
I would tend to agree with Mr. Widget. It's not something I would do. Everything has it own resonant freq. that it will vibrate at ( or ring). why take the chance?
scott fitlin
10-07-2005, 04:34 PM
4 of those dual 18in cabs should do wonders for someone! Lots of air moving!

:D
stevem
10-07-2005, 05:35 PM
Your points are all well taken. What I had I mind was screwing down angle iron (the kind with holes drilled along the length), while also gluing it to the panels with Gorilla glue. I'm not sure that it would ring at all. My cabinets are long and narrow, and adding wood bracing will make them even narrower. I probably have issues with standing waves that I will have to address first anyway. It's probably easier to just use hardwood.
johnaec
10-07-2005, 05:39 PM
The thing I'd be concerned about with metal is resonance. In car driveshafts, they have what's called "driveline critical speed", and it's based on the stiffness of the driveshaft material vs. length. vs. speed. I can imagine something similar happening here...

John
edgewound
10-07-2005, 05:49 PM
The thing I'd be concerned about with metal is resonance. In car driveshafts, they have what's called "driveline critical speed", and it's based on the stiffness of the driveshaft material vs. length. vs. speed. I can imagine something similar happening here...

John

I can't imagine that being a problem at all. There would no rotational inertia whatsoever to be concerned about. Besides that, the resonant frequency of angle iron is much higher than the resonant frequency of the low frequency drivers exciting the enclosure walls....not to mention they'd be damped further by the wood enclosure.

The higher the pitch of the thud when knocking on the enclosure wall is a good thing. It means the box is tighter,stiffer, and more resonance free than a lower pitch. Knock on a concrete wall...that's the ideal.
Dougie
10-08-2005, 01:37 AM
I've been doing a search for a pair of pro nearfield monitors to use with my computer and was looking at Genelec's when I came across these enclosures made of cast aluminum....go figure. It goes against everything I've learned about damping and cabinet resonances :(

This is copied directly from the Genelec website:

Optimized die-cast aluminium structure
Genelec have developed a very stiff and sturdy, yet thin and light die-cast aluminium enclosure. The cabinet wall curvature has been designed for best rigidity-to-weight ratio and optimal damping to minimize wall resonances. This also maximizes the internal volume improving LF-efficiency. The extremely durable semi-matt finish and acoustically optimized metal grilles, allow for intensive handling without damaging the monitor. http://www.genelec.com/news/images/8000_al_structure.jpg
frank23
10-08-2005, 01:38 AM
Besides that, the resonant frequency of angle iron is much higher than the resonant frequency of the low frequency drivers exciting the enclosure walls

exactly, so the low freq subs will excite the iron braces and they will be resonating at their preferred frequency, which might be a few 100Hz and you will be wondering where this strange ringing comes from.

if you are using solid metal like in a wooden beam then it will be okay, but if you are using T or I or L profiles there will be thin parts that will resonate

have you tried tapping an L profile that was glued to a wood board, how does that sound?

or any other combination that you might want to test-hammer?

frank