The picture describes the situation, but if you are faced with the practical application in a speaker box, a brace run the long direction, and set off centre is much more effective.
dave
Some people get the answer right and then some argue for pages for fun??
The answer to the OPs picture is that its overkill, its been proven 1000+ times but still some people argue its not overkill??
After Pallas post #8, I can not believe there is much more discussion at all but that is why the audio world is full of confused people
Expert designers from the likes of JBL, etc have been using dowels or T bracing with scrap 1" or 2" pieces for years with great success. Its a shame some people was so much time on pretty bracing and then think it actually matters, its up there with people who think there is something magical about wires, etc.
It find it even funnier they waste so much time on the box then use some cheaper driver, low performance driver....atleast stick a beautiful LMS-5400 in it to validate overkill!!!!
The answer to the OPs picture is that its overkill, its been proven 1000+ times but still some people argue its not overkill??
After Pallas post #8, I can not believe there is much more discussion at all but that is why the audio world is full of confused people
Expert designers from the likes of JBL, etc have been using dowels or T bracing with scrap 1" or 2" pieces for years with great success. Its a shame some people was so much time on pretty bracing and then think it actually matters, its up there with people who think there is something magical about wires, etc.
It find it even funnier they waste so much time on the box then use some cheaper driver, low performance driver....atleast stick a beautiful LMS-5400 in it to validate overkill!!!!
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A brace running along the centerline length of a rectangular panel creates a resonant mode (2,1). Each of the sub panels created has equal area and the panel is precisely divided into two, just as the previous example. I don't see where there should be a difference.
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The flat reinforcement is ties to 4 sides. 1 less degree of freedom of movement as a dowel. One can think of a dowel, or a row of dowels as a digitization of a full panel. Analogously this gives a HF limit to its effectiveness. In a subwoofer HF requirements are limited so a dowel may be sufficient to stop ballooning within the passband. In the case of a single centrally placed dowel, you may only push the resonance into a torus shape that is just high enuff in frequency to be more audible (ref Spendor).
The flat panel with perpendicular end pieces (ie i-beam) works pretty well.
In our builds we also use the full span brace to shunt mechanical energy from the driver to all the panels in the box, thus sharing it across 4 (or more) panels, thus sharing the energy across panels instead of concentrating it in the baffle. We found dowels far to fiddly to accomplish our needs.
dave
Dirk, don't beat your head over this. There are always going to be some people online that refuse to agree with anything they are not doing. You have to think about your audience, their history and their beliefs. Practical science and structural engineering isn't as important as what someone "feels" is right.
Some people get the answer right and then some argue for pages for fun??
The answer to the OPs picture is that its overkill, its been proven 1000+ times but still some people argue its not overkill??
After Pallas post #8, I can not believe there is much more discussion at all but that is why the audio world is full of confused people
Expert designers from the likes of JBL, etc have been using dowels or T bracing with scrap 1" or 2" pieces for years with great success. Its a shame some people was so much time on pretty bracing and then think it actually matters, its up there with people who think there is something magical about wires, etc.
It find it even funnier they waste so much time on the box then use some cheaper driver, low performance driver....atleast stick a beautiful LMS-5400 in it to validate overkill!!!!
"That's way overkill. It will only rob you of efficiency (due to lowered box volume) and make the sub heavier than necessary. No sonic or practical benefit.
For a sub that size in 1" MDF, you don't need anything more than maybe a dowel connecting the side walls. Depending on the size of your driver's motor, you may also want a shelf brace to support it."
Another dowel advocate!
That is simply a wasted manfacturing cost and wasted volume. I know why companies like JL does it, Pretty pictures always impress the uneducated masses
But there is not an audible measurement that you can provide that shows 100% effective '+' cross bracing vs overkill panels with silly routed holes (even with more silly round overs).
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Move the brace off centre see what happens. Also the frequency of the resonance is higher when the sunpanel is narrower, so you have less energy to excite the resonance (as long as it is pushed further from the bandwidth of the speaker)
dave
It's the same area no matter which way you divide it...
Moving the brace off center creates two resonant frequencies, rather than just one...
Thanks, I agree! I'm new around here. I don't know the "history"....
Honestly its not the site for high end subwoofer discussions. The majority here are not HT experts, they like music and like wimpy little 12" subwoofers to match their 2-channel setup.
No one here has remotely high end subwoofers to start with that I have seen. Other sites have better knowledge, better setups to reference and better history in terms of building the best subwoofers. I doubt anyone here even owns two LMS5400s. I have many subwoofer designs that would make most people wet their pants (from IB to twin LMS5400s + 8000Watts) and I do not have the best system vs others on a site like AVS.
Pretty bracing is just a waste of volume. It shows a lack of structural engineering knowledge. Great for pictures but that is about it.
The most important fact that matters is that you can build based on your knowledge. I say let people waste $$$ and time doing what they "believe". Who cares what they choose for themselves, we do not buy or follow their builds at all. When they are ready to maximize their $$ and time then they will figure out who to ask if they follow the history of different sites.
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It is actually quite an elegant way of dealing with a problem. Often allows the use of 15mm BB instead of 30mm MDF. Particularily when you add active vibration cancellation via application of push-push drivers.
dave
An impressive driver. But currently unobtainium, and at $1000 each not in most people's budget. And with the box volume required not in people's space allowance. We'll accept that yours is bigger than most people's. Hope you have a big room to support it (and a big room next door to accomodate the "box"). In most rooms likely an "over-engineered" solution.
dave
Everyone has a different application, if you are going to sacrifice wall thickness then obviously there are more requirements. Bill F. had this discussion in a thread recently where he has went down to 1/4".
The discussion has to have some reference point though and I read 1" and assumed minimum of 3/4.
Dual sealed designs with vibration cancellation aligment is also a great addition too!!
heck, most drivers have disappeared from the DIY market
so its hard to find any value choice. Mach5 (a Canadian company out west) is coming out with a new 18" and 21" and AESpeakers is finally getting the AV series back to the market. I found 2 AV15X on PE recently, I couldn't buy them fast enough...Best 15" subwoofer out there for 20Hz to 200Hz. I have 4 sealed boxes for the AV15X (multiple sub placement ala Toole or Geddes). 3 boxes have 1"x1" strips used as bracing. One had overkill bracing....absolutely zero audiable differences in my room, incl. measurements. 3/4" BB was used.
The volume requirements for the LMS5400 actually is very impressive!! 3.5cuft + 4000Watts gets a design that plays down to 10hz.
Im pretty sure our reference points and requirements are different. My focus is 100% HT in a custom room, I want the best 10hz performance out there (still working on it) and my box size reference point has come from 11cuft ported boxes and IB arrays where the attic is the box. A 4 cuft sealed design with amazing output is something hard to find.
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Whoa, I had never heard of the LMS 5400 until now! Yeah, that's more than I can afford right now. I did order a B&C 18PS100 yesterday though.
What other sites have really good subwoofer information? Can you share please? I have become convinced that low distortion is critical in the subwoofer range because of the Fletcher-Munson curve. We are far more sensitive to the harmonics produced by a subwoofer vs. the fundamental frequency.
I used to design percussion equipment, your diagrams struck a cord.
Your illustrations show freefield struck membrane resonance, like a drum head. Wood, sheet metal, etc. while still a membrane under constant tension is not struck in the case of a speaker. The pressures +/- inside a speaker work differently, think of it as pressing on the entire surface in and out. The circles that I used in my diagram are only representative of the short distance of each subpanel which indicates the dominate subpanel resonance.
I use three steps to keep my cabinets quiet.
1. divide the large area into subpanels to rase the resonant frequency of each open area
2. connect the opposing sides to damp the primary resonance of the panel + damping braces, which is lower than the original primary resonance because of added mass. (a dowel would work for this)
3. add an impedance mismatch layer to the open panel areas, thick pond liner glued down with silicone to damp/block the HF resonances of the subpanels.
ahem... not quite. my reference theater system 14Hz-20kHz +/-2db
if you want 10Hz performance i'm sure Tom Danley could help you out. He's around here somewhere. I recommend the DTS-10
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Most often, the best tool for a job is not the biggest one.
I'd take 4 12" sealed subs spread around the room over that rubenesque coffin any day of the week.Anyone tried threaded rod and turn buckles to pull the panels taught inward? Simple engineering principle which will allow you to progressively tune the enclosure to whatever frequency you like. Use basic $0.49 plumbers rod hangers, 5/16" rod and turnbuckles. As you twist the buckle, the rods are drawn in effectively pulling in at the sides far more effectively than any hardwood, screws and glue. Slightly more pricey than hardwood bracing but certainly a time saver.
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Hmmmm.... pre-stressed panels! interesting idea. Maybe another use for warped plywood...
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