gedlee said:
I would have to disagree with you. A brace works best if it divides a panel into sub-panels that have a higher aspect ratio than the panel it is bracing. As configured it does just that, and braces the 4 panels that do not have bracing. The side panels are inherently self-braced. This is structurally a multiple H beam kinda structure.In practise the sides do not move.
dave
gedlee said:
Depending on how you count it, the worlds largest business might be JP Morgan, with assets of 1.6 trillion or so. Certainly the largest salaries for its managers. As said by an economics professor "finance is the art of moving money around until there is nothing left". The artists are working overtime these days.
Sheldon
planet10 said:
The vertical bisecting the side panels would provide the most strength, but you mention reflection and that's what I thought of also. The horizontal will be nearly as effective, as it will also bisect the side panel.
Another possibility would be a "strongback"(construction term), a solid hardwood cleat or rib that runs from top to bottom, middle of the panel. Not as good as the full brace, but better than leaving it alone.
So, when should I start building?
Hi Earl,
Yes, we had a discussion last fall about how difficult it would be to make the baffle of wood if I were to build a Summa-like speaker.
I have figured out how to do it but not just using wood and I'm quite sure it's unsuitable for commercial venture. I would build it using stitch and glue wood/epoxy technique as is done for small boats. It took me quite a while to draw plans that make practical sense.
Material costs are reasonable but the investment in time both for learning curve and construction very considerable indeed! Having never used this technique, I'd have to make models and a test piece first. If there was a well designed kit available it certainly would be an attractive alternative.
So come up with the kit. MDF's not a problem:
I've got speakers made of both plywood and MDF. I've had them for years and they're quite satisfactory for what they are.
I think the argument about the acoustic difference between the two materials is quite funny. They're both made of cellulose and glue, aren't they? ''
Yes, we had a discussion last fall about how difficult it would be to make the baffle of wood if I were to build a Summa-like speaker.
I have figured out how to do it but not just using wood and I'm quite sure it's unsuitable for commercial venture. I would build it using stitch and glue wood/epoxy technique as is done for small boats. It took me quite a while to draw plans that make practical sense.
Material costs are reasonable but the investment in time both for learning curve and construction very considerable indeed! Having never used this technique, I'd have to make models and a test piece first. If there was a well designed kit available it certainly would be an attractive alternative.
So come up with the kit. MDF's not a problem:
I've got speakers made of both plywood and MDF. I've had them for years and they're quite satisfactory for what they are.
I think the argument about the acoustic difference between the two materials is quite funny. They're both made of cellulose and glue, aren't they? '
'
FrankWW said:Hi Earl,
I think the argument about the acoustic difference between the two materials is quite funny. They're both made of cellulose and glue, aren't they? '
EXACTLY! Now if we were comparing plastic composite to wood products that might be something. But even there I have not found the cabinet material to be significant (been there, done that). Internal bracing is, but Dave and I don't see eye to eye on how to do that.
I skimmed a lot of this thread but I just keep coming back to this relatively simple engineering thought:
the resonant frequency of a given panel in a speaker is determined by the panel's stiffness. the stiffness is a function of the moment of inertia of the panel's section.
Assuming a "good panel" is one that resonantes outside the limits of human hearing (and that it'd be very hard to make them resonante in the single digit hertz range. oh my.), then you want to increase resonant frequency by increasing stiffness, by increasing panel area moment of inertia. Like an I-beam.
who cares what material you use as long as it blocks the passage of air, is easy to work with, and looks sexy when finished?
the resonant frequency of a given panel in a speaker is determined by the panel's stiffness. the stiffness is a function of the moment of inertia of the panel's section.
Assuming a "good panel" is one that resonantes outside the limits of human hearing (and that it'd be very hard to make them resonante in the single digit hertz range. oh my.), then you want to increase resonant frequency by increasing stiffness, by increasing panel area moment of inertia. Like an I-beam.
who cares what material you use as long as it blocks the passage of air, is easy to work with, and looks sexy when finished?
"Structural engineering is somewhat of a specialty of mine, but if your convinced of your position there is no more to be said."
Hello Earl
What do you recommend?? How would you brace a standard enclosure?? I use 3/4 MDF and 2X3 bracing through out. All glue and screws. Try to space things so the braces are at odd intervals like 3rds or 5ths of the panel lengths. Use front to back baffle braces as well. Is there any benefit from trying to use the braces to break up the panels into odd sizes??
Have tried some roll on panel dampening compounds I figure it can't hurt but don't think I can get enough thickness to matter. Looks good Makes one heavy box though.
Rob
Hello Earl
What do you recommend?? How would you brace a standard enclosure?? I use 3/4 MDF and 2X3 bracing through out. All glue and screws. Try to space things so the braces are at odd intervals like 3rds or 5ths of the panel lengths. Use front to back baffle braces as well. Is there any benefit from trying to use the braces to break up the panels into odd sizes??
Have tried some roll on panel dampening compounds I figure it can't hurt but don't think I can get enough thickness to matter. Looks good
Makes one heavy box though.Rob
Robh3606 said:
The principles to keep in mind are these. Bracing placed on the panel made of MDF or plywood will not be very effective because these materials are not strong in bending. Putting a fairly rigid bar between two panels - through the middle - will be extremely effective because woods like Oak are extremely rigid in compression. So a single Oak rod (maybe 1") across the enclosure will do more than many time that amount placed on the walls, and there is NO interior acoustic effect. If I connect the side walls, for example, with an oak rod at the centers, then for all practical purposes the centers of those walls can't move. Since this WAS the point of maximum deflection this yields a maximum change in the walls displacement and a large net reduction of vibration. But it also prevents a breathing mode, while not as readily surpressing a dipole mode. But the breathing mode is the one that radiates the best, the dipole is very inefficient. Three rods joined in the center of the enclosure makes it incredibly stiffer with virtually no interior volume loss and no acoustic effects at all. Its also very cheap if you use scrap oak, like flooring.
Damping placed on a wall does virtually nothing. Only if it is constrained between two sheets will it do anything. I use CLD on my baffles (and back plate) as this technique is very effective. The other walls don't really need it as they are well braced.
gedlee said:
I have to respectfully disagree. The rod approach just joins the two surfaces together so they resonate together. It does nothing to minimize the resonance. To do this you need to triangle brace with a rod from the cetre of one panel to the centre of the adjacent.
Easier way is to us a full panel bisecting the space down the middle, from side to side which will brace all sides.
A brace like this would go a long way:
Attachments
MJL21193 said:
You've overlooked one important aspect. Opposing panels are in generally vibrating such that the panels are moving in the opposite direction at any given point in time when unbraced. It's like a balloon that is expanding and contracting with the driver supplying the air pressure variations. Tie the centers of the opposing panels together with a stiff rod and they will no longer move due to a driver signal at what was the peak movement point, the center.
There's not going to be much in the way of random or uncorrelated vibrations of opposing panels. Even those would be reduced because any one panel that would move has to move both simultaneously since they are coupled with the rod.
Dave
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