Hello,
Quite an interesting approach you've got there, and nothing I've seen before. I shall follow this thread to see how it turns out.
I'm not entirely sure about the physical properties of hardboard, as I don't think I've ever worked with it before, but with something only 7mm thick I'd be worried about it losing it's rigidity if it's bent constantly for a long period of time, and become "soggy". Just a guess though, not sure how the tensile strength is.
Quite an interesting approach you've got there, and nothing I've seen before. I shall follow this thread to see how it turns out.
I'm not entirely sure about the physical properties of hardboard, as I don't think I've ever worked with it before, but with something only 7mm thick I'd be worried about it losing it's rigidity if it's bent constantly for a long period of time, and become "soggy". Just a guess though, not sure how the tensile strength is.
Thanks,
I don't think that it will become "soggy". Most people have had an old radio or record player with a hardboard back or bottom. I have a piece from an old organ that must be 40 years old and it still looks and feels fine.
Another thing: Maybe you fellows are discounting the effect of the foam that will fill the void. This foam will go a long way to reinforcing the structure by tying the skins together and locking the shape in place. It greatly increases the load distribution and provides some damping.
I'm blushing Cal...
OR was that an mild taunt? Whatever, I can handle either.
Gee, no one has commented on my driver selection or box design...everyone is hung up on the construction.
One concern I have is the sensitivity of the drivers, in particular the mid. At 87db it is quite a bit lower than the woofers and tweeter.
I may do some more digging to find a driver that is a bit more efficient.
Suggestions are welcome but I do want a 6-7 inch driver for this.
OR was that an mild taunt? Whatever, I can handle either.
Gee, no one has commented on my driver selection or box design...everyone is hung up on the construction.
One concern I have is the sensitivity of the drivers, in particular the mid. At 87db it is quite a bit lower than the woofers and tweeter.
I may do some more digging to find a driver that is a bit more efficient.
Suggestions are welcome but I do want a 6-7 inch driver for this.
I would be interested in trying 2 different materials for your sandwich; hardwood on the outside, something else on the inside.
These are very similar to the 3 ways I'm still working on. I ran into an issue with the mid, not the woofer. I used 2" MDF. The back panel is screwed on, not glued. It resonated like crazy right at 400 Hz. Added 15 more screws and the bump was gone. Blew my mind, the panel weighs 50 lbs.
Go for it.
These are very similar to the 3 ways I'm still working on. I ran into an issue with the mid, not the woofer. I used 2" MDF. The back panel is screwed on, not glued. It resonated like crazy right at 400 Hz. Added 15 more screws and the bump was gone. Blew my mind, the panel weighs 50 lbs.
Go for it.
I like the approach
John,
I like the approach with panels. I'd say try foam one and letting it cure a fair time and then check the stfiffness. If more is required space the panels further apart. That chart for aluminium shows a good increase until you get over an inch apart. I'd be a bit concerned with the thin corners and the connections where 3 panels meet.
Looking forward to following your work.
John,
I like the approach with panels. I'd say try foam one and letting it cure a fair time and then check the stfiffness. If more is required space the panels further apart. That chart for aluminium shows a good increase until you get over an inch apart. I'd be a bit concerned with the thin corners and the connections where 3 panels meet.
Looking forward to following your work.
How big was that panel? I did a quick calc considering thickness and MDF density and came up with 833 square inches which could be something like 20 x 40 inches. That sounds pretty darn big if it is only supported at the edges. At that size the resonant frequency would be around 200 Hz.
I'm sure you've seen pieces that have been under stress and are permanently warped as well.
You could always laminate the piece (ie make plywood), with something like plastic laminate.
dave
It was an taunt. It would be nice to see something like this with a couple 15's, a strong mid and nice horn tweeter in your plans. This business of a 1" dome tweeter just doesn't cut it when you use the word large John.
Attachments
The only other material I thought about using for this was 1/4" Baltic birch plywood. I think it would be a better choice but it is quite a bit more expensive and this design is a bit of a risk. Next time maybe.
Beyong that, I wouldn't consider anything less than 16 gauge steel or 12 gauge aluminum sheet. This would be the next level.
I will pay special attention to the corners. The 10 degree fillets as seen in the posted pics of the mock-up will be made wide to allow an even broader gluing surface and provide more support. The vertical cleats for the back corners will be solid hardwood rigidly glued in.
I did a little test this evening:
That is the longer piece loaded with 30lbs of brick. This is just a 3" wide section and with that much weight there wasn't any measurable deflection.
Tomorrow I'll find some more weight to put on it to see how much it takes to have it deflect. It's quite strong.
Yes but those have been subject to a lot of moisture. AND once again we are not recognizing the BIG role the urethane foam will play.
To seal the hardboard on the inside of the box I'll give these a coat of polyurethane. It will stop moisture absorption.
P-laming these panels is not what I want to do - I'd rather go for a superior material in the first place.
Realistically I don't think there's cause for concern.
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The panel is 48" x 14." The rest of the box is super rigid. The vibrations traveled around the box, through the screws holding the back panel, which were only screwed on the sides. Sounds goofy (pun intended) I know. I could put my ear to the sides and front of the box and they're dead. Put my ear to the back of the box and it rang like crazy. I didn't run calc's, too lazy. I use an old graphic EQ in the system to find issues, Came out around 400Hz per the EQ. Probably other freqs in there too.
The overall size is 50" x 16" x 18"
Similar layout as the ones discussed in this thread; tri-amp'd, analog xo's.
I too was going to use 2 large woofers but the amount of $$ needed got in the way. All Eton drivers.
Pictures are in the systems picture thread.
The outcome of this is going to be interesting, functional or not.
The overall size is 50" x 16" x 18"
Similar layout as the ones discussed in this thread; tri-amp'd, analog xo's.
I too was going to use 2 large woofers but the amount of $$ needed got in the way. All Eton drivers.
Pictures are in the systems picture thread.
The outcome of this is going to be interesting, functional or not.
My resonant frequency spreadsheet comes up with a resonant freq of somewhere between 330 Hz and 415 Hz for that panel depending on the quality of the MDF. Nice to know that the clacs and the real world experience line up sometimes.
I'm not. You biggest potential problem is the foam blowing out the sides as it cures.
dave
I've wondered about that. I once used a high expansion foam (I didn't realize there was a difference) to seal around the window frames while our hose was being built and then spent many hours cutting out foam to straigthen out the sills. I suspect using a pegboard for one side would alleviate the problem by allowing the ecxess foam to leave the panel. The downside is the amount of time required to cleanup the excess and then you'd probably want to laminate another layer of hardborad to the peg board.
It would be poured in "lifts" - 3 or 4 inches at a time. Filling the whole this at once would be a recipe for disaster. Using the 2 part pourable type (as opposed to spray foam in a can) should make the process fairly quick as it sets up in a short amount of time.
Please John, don't think I regard your project as a bad one; the idea of a sandwich structure using bended sheets isn't bad and is even nicely innovative! Only the materials you choose aren't enough performing for such a large enclosure; please consider at least to place some braces...<<<You have no faith my friend.
**** Oh YES! in myself, but only sometimes
<<<Curving the panel massively increases strength -
**** indeed..."massively"...but not enough!
<<<the way these panels are designed and joined together leaves only one "weak" point: the vertical centre axis of the tallest panels may flex slightly.
**** Unfortunately the actual weak point will be the entire panel
<<<To help combat this I will use steel flat bar for the divider
**** good material and shape for the divider; problem isn't the divider, problem is the entire structure; think about: what are the stiffness properties of thin hardwood vs really stiff materials such as concrete or steels and on...? How much do you gain by bending such panels? Between the two sheets you have only two choices: dampen or stiffen...foam will not make the job.
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