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Old 21st January 2013, 08:34 PM   #51
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Quote:
Originally Posted by KaffiMann View Post
~14,25hz = 521,04L needs x4 sheets of ply
With only three four by eight foot sheets of plywood one can make a four foot cube.
A four foot cube occupies 64 cubic feet, 1812.275 cubic liters.
That would be a large box, five times the volume of the Tub Sub.
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Old 21st January 2013, 09:29 PM   #52
badman is offline badman  United States
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Quote:
Originally Posted by weltersys View Post
With only three four by eight foot sheets of plywood one can make a four foot cube.
A four foot cube occupies 64 cubic feet, 1812.275 cubic liters.
That would be a large box, five times the volume of the Tub Sub.
And a couple more for bracing, no?
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Old 21st January 2013, 09:59 PM   #53
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Originally Posted by badman View Post
And a couple more for bracing, no?
Yes.

Sidenote:
Increase in internal volume greatly increases need of bracing. When I put together something, I plan the cutsheet, maybe decide on some points where there should be double layers in some cases, some that only need slight bracing, and some spots where the walls should connect to each other with brace. Normally for these designs it is more efficient to use the building material for horn segments/bass ports etc. If you not only calculate the volume of the box, but every single little brace or part of the horn/bass port/tl/whatever, I normally get fairly close to my rough estimates. The long thin leftover bits are perfect for horn segments, use them for "T" bracing, glue and screw them on horn segments to stiffen the structure, every little bit helps.

Last edited by KaffiMann; 21st January 2013 at 10:02 PM.
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Old 21st January 2013, 10:18 PM   #54
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2 pieces Beyma 12BR70, local pickup. 100$ each.
2 pieces ply sheets, ~100$ each.
1 pieces LM4780 kit including shipping from audiosector.com ~100$.

Cheating with abundance of spare transformers laying about (got 6 I am not currently using), already have glue, wool for dampening, connectors, screws, grit paper and varnish coat. PLLXO from my assortment of components.

Total 500$ for 2 subs.

Cheating was allowed, yeah?

Edit:
Phase is from 2pi, the rest from 4pi, the phase went weird in 4pi, but looks fine in other modes.

Edit2:
Thankew for inspiration Bjorno!
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File Type: png Beyma 12BR70.png (52.1 KB, 321 views)

Last edited by KaffiMann; 21st January 2013 at 10:36 PM.
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Old 21st January 2013, 10:37 PM   #55
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Originally Posted by KaffiMann View Post
Increase in internal volume greatly increases need of bracing. When I put together something, I plan the cutsheet, maybe decide on some points where there should be double layers in some cases, some that only need slight bracing, and some spots where the walls should connect to each other with brace.
Granted, a 64 cubic foot unbraced box (which takes 4 sheets of 4' x 8' ) would flop around a bit, but compared to the sound of the toy Bose sub, it may still sound tight .

You wrote in post #50 that:
~14,25hz = 521,04L needs x4 sheets of ply

Four sheets of 4' x 8' 3/4" plywood occupy 8 cubic feet, 226.5 liters.
Your 521 liter box using four sheets would only net 294.5 liters before the port and speakers are installed.
I like well braced cabinets, but that is over the top .

My 439.4 liter (gross volume) Keystone, which is braced well enough to be stiff with 4000 watt input uses a small fraction of a sheet of plywood for bracing. It's not how much wood you use, it's how you use it that makes the difference.
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Old 21st January 2013, 10:46 PM   #56
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Quote:
Originally Posted by weltersys View Post
Granted, a 64 cubic foot unbraced box (which takes 4 sheets of 4' x 8' ) would flop around a bit, but compared to the sound of the toy Bose sub, it may still sound tight .

You wrote in post #50 that:
~14,25hz = 521,04L needs x4 sheets of ply

Four sheets of 4' x 8' 3/4" plywood occupy 8 cubic feet, 226.5 liters.
Your 521 liter box using four sheets would only net 294.5 liters before the port and speakers are installed.
I like well braced cabinets, but that is over the top .

My 439.4 liter (gross volume) Keystone, which is braced well enough to be stiff with 4000 watt input uses a small fraction of a sheet of plywood for bracing. It's not how much wood you use, it's how you use it that makes the difference.

You are correct I made a mistake, but that list was assuming internal volume only, should have been specified. But anyway, it is 521L + materials. Please beat my suggestion for sub above :-) Let's compete! That is what the thread is about anyway.

Last edited by KaffiMann; 21st January 2013 at 10:56 PM.
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Old 21st January 2013, 11:19 PM   #57
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Originally Posted by KaffiMann View Post
You are correct I made a mistake, but that list was assuming internal volume only, should have been specified. But anyway, it is 521L + materials. Please beat my suggestion for sub above :-) Let's compete! That is what the thread is about anyway.
The challenge specifications are for net volume, not internal. If you choose to fill your entry with plywood rather than air and drivers, that is OK.

The challenge rules have us competing against a tiny Johnny-one- note cabinet only required to make a certain amount of noise at 45 Hz.

Jbel's sim beats yours by the challenge rules, why bother posting losers?

I prefer results over simulation, and already submitted my entry, which after 57 posts still seems to be the only actual built and measured unit.

Last edited by weltersys; 21st January 2013 at 11:22 PM.
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Old 22nd January 2013, 03:16 AM   #58
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Quote:
Originally Posted by KaffiMann View Post
2 pieces Beyma 12BR70, local pickup. 100$ each.
2 pieces ply sheets, ~100$ each.
1 pieces LM4780 kit including shipping from audiosector.com ~100$.

Cheating with abundance of spare transformers laying about
http://www.ti.com/lit/ds/symlink/lm4780.pdf

LM4780 is a 60 watt per channel single chip amp.... Even with 'transformer' cheating... I'm not sure how that helps ...
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Old 22nd January 2013, 08:56 AM   #59
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Quote:
Originally Posted by jbell View Post
http://www.ti.com/lit/ds/symlink/lm4780.pdf

LM4780 is a 60 watt per channel single chip amp.... Even with 'transformer' cheating... I'm not sure how that helps ...
Yes, but the kit is 2 x LM4780, so that is 2x120W. At any rate, I do not see the need for more power than 120W, 3db increase from 120W is 240W, ~10db increase would be around 1000W total, why on earth would you ever want to use a design that requires more than 120W is beyond me, thermal losses and issues start building up and distortion figures when the voice coil heats up will probably be something to think about. If you make a design that requires 300-1000W to perform that is just wasteful. All the good magic happens at lower wattage.

I just tried to interpret the base rules of the design in such a way that you could actually achieve realistic results. By all means, can you actually make a viable design that delivers 82db/1W in 4pi space using net/total volume everything included following my list at 25hz or lower, I will have to come up with something to reward you with. But this is not my thread though. Maybe turbodawg would be so kind as to lay down the rules one final time, I hope they will be more realistic than the previous listings.

Don't argue, compete! Do better!

Edit:
I have built something similar to my posted design, directly comparable in terms of volume, materials used, drivers, spl/w, power amplifier, and filter.

Last edited by KaffiMann; 22nd January 2013 at 09:11 AM.
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Old 22nd January 2013, 02:22 PM   #60
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Quote:
Originally Posted by weltersys View Post
With only three four by eight foot sheets of plywood one can make a four foot cube.
A four foot cube occupies 64 cubic feet, 1812.275 cubic liters.
That would be a large box, five times the volume of the Tub Sub.
I did some very quick calculations, if using 18mm ply, each sheet (Assuming 244cm*120cm*1,8cm if you can use absolutely everything) is around 52L. If making a 521L internal volume box + bracing and horn expansion i get 668L, increase of volume by 147L or nearly 3 sheets. I stand corrected.

So I guess you *could* make the biggest bits out of 18mm ply and the braces++ out of 12mm ply you have the potential to shave off some $ and an amount of volume.

Last edited by KaffiMann; 22nd January 2013 at 02:27 PM.
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