H frame bracing

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Lately I'm playing around with a few open baffle designs for the lower end. Currently I converted my 6cm thick flat baffles into H frames (40cm deep).

It's more of a sketch so it's a bit of a floppy build. The cross sectional area is also quite big but I don't mind it visually and it should add some dB's.

The question now, which I can't really find online, can I brace the top/bottom and sides like I did at the back to brace the woofer? Or will this cause any unwanted effects?

The frame is vibrating a lot right now so I think it's imperative to brace it, but how? 2 beams like at the back but in a cross?

See pics
 

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I'd brace and double wall it. In a space like that, you can roll the speaker around on a trolley or skateboard, so increased weight doesn't matter much.

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

Have you read this (emphasis is mine)?

"It is clear that a rising response starts to appear above 100 Hz in each case. The height of the peak determines the frequency of the applied 2nd order Linkwitz-Riley crossover filter. The small hump present in the OB SPL response allows a 200 Hz crossover frequency. For the U and H frames the quarter wavelength resonant peaks become more severe and require the crossover to be set lower in frequency at 150 Hz and 125 Hz respectively."

I realise that you can eq it flat, but it might also be a good idea to break up the parallel surfaces in the cavity, to spread those resonant peaks out.

EDIT - I'm assuming you are still crossing at 300Hz, and so these resonances will be in your passband.

chamfering driver holes

I'd do this too, even if there's not much effect <300Hz.
 
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Sure, no problem. Does it vibrate as a rigid body (front to back) or do the panels flex?

That's a big listening room by the way ;)

A bit of both actually. I braced the frames yesterday. The panels don't vibrate at all now but the whole frame does - a little - but I hope to get it perfecy rigid. Any tips?

The room is a bit too big haha. If I pause the music theres a 4 sec echo...
 
Does that vertical brace make much difference? My U-frames were vibrating, I sat them on cut up sorbothane insoles which cured it

It does make a difference for the top and bottom. As for placing the frame on go something, I tried some thick and sturdy rubber blocks but that just seemed to make it worse.

Right now there standing on 3 steel feet. Two in the back and one in the font. First I had two in the front one in the back but most of the weight is on the backside so two in the back is a bit more steady.
 
I'd brace and double wall it. In a space like that, you can roll the speaker around on a trolley or skateboard, so increased weight doesn't matter much.

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

Have you read this (emphasis is mine)?

"It is clear that a rising response starts to appear above 100 Hz in each case. The height of the peak determines the frequency of the applied 2nd order Linkwitz-Riley crossover filter. The small hump present in the OB SPL response allows a 200 Hz crossover frequency. For the U and H frames the quarter wavelength resonant peaks become more severe and require the crossover to be set lower in frequency at 150 Hz and 125 Hz respectively."

I realise that you can eq it flat, but it might also be a good idea to break up the parallel surfaces in the cavity, to spread those resonant peaks out.

EDIT - I'm assuming you are still crossing at 300Hz, and so these resonances will be in your passband.

chamfering driver holes

I'd do this too, even if there's not much effect <300Hz.

I'm crossing at 200 now with a 12db slope if I'm correct. Not sure because I've been testing a lot of things lately. Shifting the cabity depths is a good one, I haven't glued anything accept for the baffle itself. So I can shift it an do some measurements.

I did read the pdf several times actually and helped a lot!
 
So this is how I've done the bracing. A cross in front is something I'm not quiete sure about. This already makes it way more stuff. The brace on the back puts preasure on the casted frame of the driver to decrease micro vibrationz.
 

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Good to hear that the panels do not flex any more. Then you are finished ;)

Those braces appear to somewhat create a Helmholtz resonator because they decrease the open area, meaning that the unwanted quarter wavelength resonance shifts downwards in frequency which is not good. Whether it is significant can be examined by doing a frequency response measurement. Connecting opposite walls as you tried in the first place usually is more effective in avoiding panel flex and reduces the open area to a lesser extent.

Woofer magnet vent is also best left free to avoid chuffing noises. If you don't hear them, never mind.
 
Good to hear that the panels do not flex any more. Then you are finished ;)

Those braces appear to somewhat create a Helmholtz resonator because they decrease the open area, meaning that the unwanted quarter wavelength resonance shifts downwards in frequency which is not good. Whether it is significant can be examined by doing a frequency response measurement. Connecting opposite walls as you tried in the first place usually is more effective in avoiding panel flex and reduces the open area to a lesser extent.

Woofer magnet vent is also best left free to avoid chuffing noises. If you don't hear them, never mind.

I need to find some time to do some serious measurements soon, but I'm just too fond of them so they're just playing all the time now. Hope I get to it this weekend!

Thanks for the tips!
 
I did a quick one btw, they don't go very low on the measurements, 1 m in front (A bit in the middle of the horn and h frames height). They sound like they do go lower than what I see on the graph.

I got a bit of eq at the lower part and some minus eq on around 200 hz
 

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