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giturar Unregistered guest | im building my first box for 2 adire shivas, and becuase its my first box, i was just going to do a simple square, so i wouldnt be messing with angle cuts or anything i keep hearing that if i do use a square box (or rectangle, whatever), itll sound like crap, is this true? thanks |
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New member Username: MrdarkPost Number: 6 Registered: Dec-04 | well mine are in a rectangular ported box that i made and sounds really good imo... are you comparing to a wedge? |
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Bronze Member Username: Help_2Post Number: 48 Registered: Dec-04 | perfect cube boxes can cause standing waves inside the box. They can effect sound quality by causing audible harmonics. You can remedy this by putting poly-fill or egg-crate shaped foam padding on the walls of the box. or either making pyramid shaped or small cube shaped chunks for the corners, and gluing them in. Its normally not an issue, but its an easy fix if it happens. |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 6702 Registered: Dec-03 | yup when the side of the box (back) opposing the subs is parallel to the (front) side with the subs, the sound waves can reflect off of the back of the box, and cancel themselves out. this cancellation will greatly reduce the enclosure's output. the fix to this is to angle the back of the box by about 15 degrees. very simple to do. when you draw it out, draw the box square, then take the back side, and subtract about 2" at the top and add 2" at the bottom. that'll give you enough angle to avoid any cancellation. problem solved and the box volume stays the same as it was square. |
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Bronze Member Username: CheapskatePost Number: 57 Registered: Mar-04 | as stated, square boxes (as well as rooms) cause standing waves. the "ideal" shape for any room or box is the famous greek "golden ratio" 0.6 X 1 X 1.6 which is probably why older speakers all used to have similar "slab shapes". if you can manage more complex shapes, then you can seriously reduce standing waves by making as few cabinet sides parallel as possible. that's why some speakers have angled sides and/or backs and the theory behind the snail shell shaped B&W nautilus speaker. egg crate foam is nice and cheap, but if you don't mind either building a larger box or compromising your internal volume (and spending extra $$$) acousical foam is even better. i bought a "nearly square" 12" cabinet for my sub as the 2 X 8" cabinet i wanted wasn't available anymore. i prefer tight punchy bass over gut massages. as all of the sides of the cabinet had only 1/2" mdf, i glued 3/4" mdf to the entire inside except the bottom which i double re-enforced in the base pedistal. then i stuffed the box with 4" acousical foam wedges in the back, and 2" or 3" wedges for the remaining sides, and turned the foam 90 degrees on the 4 sides that faced each other eg. up and down on the left and front to back on the right) to minimize standing waves. even with a tiny internal volume, i get more bass than i want out of my sub and none of it's sides are close to parallel. if you want to reduce standing waves, either minimize symmetry with cabinet dimensions or shape and/or with stuffing that breaks the symmetry. if you're looking for "ultimate sound" add a second layer of mdf to minimize cabinet resonances too. if you're going with a ported cabinet *gag hack cough*, buy an adjustable port so that you can more easily tune your "distortion frequency" i mean resonant frequency as adding any kind of stuffing will change your internal volume. square boxes can be used if you attend to standing waves. for what it's worth, if you go with a double layer sandwich cabinet and decent depth foam wedges, you will have a box superior to even a $1000 sub. hope something here is helpful. |
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Bronze Member Username: KarthalinTacoma, WA USA Post Number: 78 Registered: Dec-04 | I just read that square boxes are bad for higher frequencies, so the smaller interior speakers need to worry about that. The lower frequency bass lines have such a long sound wave that there isnt enough room inside our 1-3 ft^3 boxes to actually make a difference unless we are hardcore to the core 1rst place ISCA competitors. http://forums.bimmerforums.com/forum/showthread.php?t=293224 Read Jesters post at bottom. Now I know Glasswolf is a walking car audio encylopedia, so I was hoping Glass might be able to shed some light on this subject a little more? This guy says that destructive waves are only a problem if the box is over 30Ft large. Tis true? |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 6747 Registered: Dec-03 | first, you're taking audio advice from someone on a BMW owners' forum. keep that in mind. now let me clarify his mistake without even reading the article: while the box may be too small to mature a full wave, a full wave isn't needed for cancellation to occur. Much of what we do in car audio and even home audio is based on fractions of a full wave, such as a half or quarter wave as in the case of transmission line enclosures. All you need is a harmonic or exact fraction of a full wave to cancel itself reflecting off of a parallel surface. So in short, his logic is flawed. a smaller box can and will indeed cause standing wave cancellation, and when it happens, trust me, I've heard it, the box sounds absolutely awful and output can be drastically reduced. now budget minded there had some very good information on ratios and room dimensions. you can use egg crate in a square box to reduce standing waves, but the problem there is much like adding polyufill, it increases the apparent volume of the enclosure by about 10% which can give a boomy sound to the box at times. |
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Bronze Member Username: CheapskatePost Number: 72 Registered: Mar-04 | huh? increases apparent volume? that is the exact opposite of what i thought fill does. i've always gone by the theory that the more fill you add to a box, the less internal volume you have thus lowering your Q and rolling your bass off and increasing speed. that adding fill makes a woofer boomier is the total opposite of what i've always thought i knew. lower volume = LESS boom. one of the reasons that i "overstuffed" my sub was to lower my Q and get more bass rolloff and a tighter air spring. why don't you add your wavelenth knowledge to the debate i'm having in "ported enclosures pros and cons" glasswolf? i'm sure that you could elaborate on wavelengths better than i can. regardless, i'd like to know more about this theory that totally flies in the face of everything i thought i learned about box stuffing. |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 7015 Registered: Dec-03 | polyfill should be added at the amount of one pound per cubic fot of enclosure volume. that 'makes the sub think' the box is 10% larger than it really is. "Using Poly-fill: Enclosure sizes: Poly-fill can be used to make an enclosure seem slightly larger. It does this by slowing the movement of the air in the enclosure. This, in effect, smoothes the frequency response of the subwoofer's output and slightly improves its low frequency extension. This image shows, to what degree, it does both. The red line (no fill) has a slightly higher peak than the yellow line before it starts to roll off. The yellow line has a slightly improved low frequency extension when compared to the red line. The effect is not very dramatic but using poly-fill in this manner can sometimes make a subwoofer sound better. The red curve is has no poly-fill. The yellow line is 100% filled with poly-fill. 100% fill is equal to 1 pound of poly-fill per cubic foot of air space." http://www.bcae1.com/spboxad1.htm |