I didn't mean to side track this thread with all of this lurking.....
An externally hosted image should be here but it was not working when we last tested it.
No, I mean to win this contest why wouldn't I build a sub that just gives me a phallic peak at 45 Hz?
Not to argue over pebbles or anything, but 1 digit numbers at low freq is a big deal. I get 45/4=11,25 and 11,25*3=33,75Hz for doubling 1
33,75/4=8,4375 and 8,4375*3=25,3125Hz for doubling 2
And 1,15cuft in liters is 32,56437.
So that is (slightly rounded figures) 65,13L at 33,75hz and 130,26L at 25,31Hz.
1/2 octave down from 33,75Hz is 25! Not 22! It makes a difference!
Anyway, I really do not think those Bose numbers are realistic, I will agree on the freq/volume restrictions, but sensitivity of 85db seems unlikely at 8 ohm, maybe 4 ohm?
Originally Posted by turbodawg
- Sine wave output capablity of 106 db @ 1m 4pi @ 45hz
- Reference size of 14"H x 19"W x 7.5"D @ 18.8 lbs
- For each doubling of size, increase output 3db or improve low extension by 1/2 octave
Thus, if you were to double size twice to build a sub 75lb & 14"x19"x30", it should be capable of 109 db 1m 4pi @ 34 hz or 112 db 1m 4pi @ 45 hz or 106 db 1m 4pi @ 22 hz.
"the figures presented are a high side educated guess, purely a nominal figure for the sake of comparison. It would be interesting to see what one of these actually does with a 400w 45hz sine wave............LOL."
Obviously turbodawg realizes that 400 watts of sine wave driving a pair of 5.25" "woofers" would be a rather short event, and the sensitivity and power handling of the Bose are as he said, a guess. Without seeing any test results, we can only guess how educated his guess was.
As far as the 1/2 octave center frequency between 45 and 22.5 Hz, I'll leave that to the more math inclined.
However, two 1/2 octaves do make an octave, an octave down from the "purely nominal" non-ISO center 45 Hz frequency is obviously 1/2 that frequency, 22.5 Hz, not 22 or 25.
Art
- Sine wave output capablity of 106 db @ 1m 4pi @ 45hz
- Reference size of 14"H x 19"W x 7.5"D @ 18.8 lbs
- For each doubling of size, increase output 3db or improve low extension by 1/2 octave
Thus, if you were to double size twice to build a sub 75lb & 14"x19"x30", it should be capable of 109 db 1m 4pi @ 34 hz or 112 db 1m 4pi @ 45 hz or 106 db 1m 4pi @ 22 hz.
As turbodawg wrote in #39:
"the figures presented are a high side educated guess, purely a nominal figure for the sake of comparison. It would be interesting to see what one of these actually does with a 400w 45hz sine wave............LOL."
Obviously turbodawg realizes that 400 watts of sine wave driving a pair of 5.25" "woofers" would be a rather short event, and the sensitivity and power handling of the Bose are as he said, a guess. Without seeing any test results, we can only guess how educated his guess was.
As far as the 1/2 octave center frequency between 45 and 22.5 Hz, I'll leave that to the more math inclined.
However, two 1/2 octaves do make an octave, an octave down from the "purely nominal" non-ISO center 45 Hz frequency is obviously 1/2 that frequency, 22.5 Hz, not 22 or 25.
Art
I completely agree. But when you calculate 1/2 oct lower than 34hz, you will get a different answer than 1/1 oct down from 45hz, which is the reference? At 4pi the goal will be hard to overcome unless you calculate this as down 1/2 oct from each step. Whether or not material and bracing is included is not specified. Maybe there should be added 14-18% volume in material pending on desired limitations/spec.
45hz = 32,56437L needs 1/4 sheet of ply
33,75hz = 65,13L needs x1/2 sheet of ply
~25,31hz = 130,26L needs x1 sheet of ply
~19hz = 260,52L needs x2 sheets of ply
~14,25hz = 521,04L needs x4 sheets of ply
Seems reasonable/not completely impossible. The alternative list would be very hard to follow. Those low freq subwoofers crave space. Sheets of ply listed as reasonable amount of materials needed for box + bracing, no losses/leftovers, everything used. Quick ca reference only for efficient cutsheets.
Anyway, we can probably assume that 82db is the reference volume at 4pi 1W, so that is 2V at 4 ohm or 2,83V at 8 ohm.
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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.
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.
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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!
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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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.
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.
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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.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
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.
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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.
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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.
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