sealed boxes

[95Prober 10+ year member]

hi guys. now i know that it takes a bit of calculation for a ported design, with port, tuning etc. but now say if you want a sealed box. would you only get ONLY the ONE result even if you had many different people trying to do it?? i mean, its basically easier i assume, and since there is no tuning and port, wouldnt the inside dimensions be ALWAYS the same if say 5 guys tried to design a SEALED box with the same subs??

also, is there any particular equation to find out your TOTAL inside dimensions for a sealed? of course i have my T/S numbers. thx!!

Click to read more...

 

[djjdnap 10+ year member]

??

I'm a lil confused, but depending on how much area you use the boxes will sound diff.

Also the material you make the box out of.

And also how well you seal it.

Also things inside the box will make diffrences as well, by displacing more area, such as braces and what not.

You can also use polyfill and other things to make your sealed box sound diff.

 

[95Prober 10+ year member]

well, im going with mdf 3/4". also, this is this first box, so i wont put poly-fill untill i try without it.

i guess basically, if you went with a rectangular shape and not hard to build (the cuts), how do determine the inside volume?? from T/S numbers ??

 

[squeak9798 5,000+ posts]

but now say if you want a sealed box. would you only get ONLY the ONE result even if you had many different people trying to do it?? i mean, its basically easier i assume, and since there is no tuning and port, wouldnt the inside dimensions be ALWAYS the same if say 5 guys tried to design a SEALED box with the same subs??

No no no no no.

Different sized sealed boxes will give you different alignments, which is called the Qtc. Along with the differing Qtc's, you'll get different F3's (point at which the low end response rolls off to -3db down), different Fc (resonant frequency of the "system" [sub in the box]), different frequency responses, different transient responses, different group delay.....anything that can be different will be different.

The bigger the box, the lower the Qtc. The smaller the box, the higher the Qtc. Qtc of .5 is considered to result in perfect transient response. Qtc of .577 will have maximally flat group delay. Qtc of .707 (what most people consider to be the "ideal" Qtc - it has the best set of trade-offs) will have the flattest frequency response and lowest F3, with a transient response and group delay that "isn't too bad". And as you go higher in the Qtc range (.8, .9, 1.0, etc) you start getting a larger and larger peak in the frequency response in the upper bass/lower midbass region (which most people will claim makes the sub sound "tight" or "punchy"), worse and worse transient response/group delay, and worse and worse low frequency extension.

So, what you want to do is figure out what Qtc value you want to go for. If you want to go for a Qtc of .707, then you will need to find the appropriate box size. If you want a Qtc of 1.0, you again need to determine the appropriate box size.

Now, keep in mind that as box size increases, mechanical power handling decreases (efficiency increases), and as box size decreases, mechanical power handling increases (less efficiency). Also, the smaller box sizes will have more output than the larger box sizes.

Now that I'm sure I have you sufficiently confused (I **** at explaining things), here are some good links on the subject:

http://www.diysubwoofers.org/sld/ (be sure to click the corresponding links to the left)

http://www.carstereo.com/help/Articles.cfm?id=29 (nice graph and good general info)

also, is there any particular equation to find out your TOTAL inside dimensions for a sealed? of course i have my T/S numbers. thx!!

And you would use the T/S parameters to determine what box size is needed for which Qtc value, aswell as what the actual F3 points and such would be.

 

[djjdnap 10+ year member]

isn't .707 what you multiply Voltage by to get rms?

weird its the ideal qtc also

 

[flakko 5,000+ posts]

wow... thats a mouthful squeak...

 

[95Prober 10+ year member]

Vb = Vas/((Qtc/Qts)^2-1)

well this is what i got assuming with Jmac's formula, and as squeak said, if i want what the typical ideal route is and go with .707 Qtc......

Vb = 1.94cu.ft / ((.707/ .31)^2-1 = 3.801

is this right ?? i think its wrong!

also, what does Vb stand for? box volume?

my total would be...?? PLUS 0.089 for sub displacement correct?? so....my grand

total would be ??

*NOTE- my Fs = 25 on my subwoofer spec sheet

 

[squeak9798 5,000+ posts]

//content.invisioncic.com/y282845/emoticons/word.gif.64b12e39f936af3b4fff38a1c0bd0244.gif

One thing Jmac forgot to mention was the Vas needs to be in liters for the formula, not cubic feet. So;

Vb = 54.934L/((.707/.31)^2-1) = 13.075L

Then you convert that to cubic feet; which is 0.462cuft (as Jmac said)

And yes, Vb is box volume.

 

[95Prober 10+ year member]

//content.invisioncic.com/y282845/emoticons/word.gif.64b12e39f936af3b4fff38a1c0bd0244.gif
One thing Jmac forgot to mention was the Vas needs to be in liters for the formula, not cubic feet. So;

Vb = 54.934L/((.707/.31)^2-1) = 13.075L

Then you convert that to cubic feet; which is 0.462cuft (as Jmac said)

And yes, Vb is box volume.

PLUS .0089 for sub displacement ?? if so = 0.551 cu.ft PER SUB.

also, if i use MORE than one sub, then just multiply by the amount of subs ???

 

[squeak9798 5,000+ posts]

PLUS .0089 for sub displacement ?? if so = 0.551 cu.ft PER SUB.
also, if i use MORE than one sub, then just multiply by the amount of subs ???

Yes and yes

 

[squeak9798 5,000+ posts]

It works with either one ... If you use Vas in liters, you'll get Vb in liters ...

If you use Vas in cubic feet, you'll get Vb in cubic feet ...

Vb = 1.94/((Sqrt(0.5)/0.31)^2-1)

Vb = 0.4615845506 ft^3

Vb = 54.93468239/((Sqrt(0.5)/0.31)^2-1)

Vb = 13.07061891 liters

0.4615845506*1728*2.54^3/1000 = 13.07061891

What can I say, I'm a 'tard. Brain farts ****.

 

[95Prober 10+ year member]

seems so small of a box for a single sub. even considering they are the pioneer premier line. so , a small box like this compared to a lager box would give me what type of sound? i mean a small sealed or a med./large sealed. is there a HUGE difference in sound?? i know ported makes i big difference.

 

[squeak9798 5,000+ posts]

is there a HUGE difference in sound??

Can be, yes. If you start going larger, you'll start lowering the Qtc of the enclosure. This will give you less overall output, and a sound that some people would probably consider "dry" or "lifeless". Plus the enclosure would start it's low frequency roll-off higher in the frequency band. Transient response and group delay would technically increase though.

 

[95Prober 10+ year member]

Can be, yes. If you start going larger, you'll start lowering the Qtc of the enclosure. This will give you less overall output, and a sound that some people would probably consider "dry" or "lifeless". Plus the enclosure would start it's low frequency roll-off higher in the frequency band. Transient response and group delay would technically increase though.

haha! so im simple newb terms and in ur opinion, i should stick with the Qtc. or .707 ??

 

[95Prober 10+ year member]

i mean, is the overall consensus, usually stiick with the .707??