hi ages ago someone gave me an equation for working out the 3db point of a woofer in a sealed enclosure . it was something like 0.707 ÷ qtc x fs
and then there was another one for working out the ideal size of the enclosure I can't remember either of them .
does anyone know these equations and could share them with me . I havnt used them for a while and I cant quite remember them now .
thanks in advance
and then there was another one for working out the ideal size of the enclosure I can't remember either of them .
does anyone know these equations and could share them with me . I havnt used them for a while and I cant quite remember them now .
thanks in advance
Correct Qtc of .707 for flat response Qtc .577 for flat delay response.
Vb=Vas×(Qtc2−Qts2)
Constants
Qtc = Total system Q (the damping of the system)
Qts = Driver's total Q (which includes the mechanical and electrical damping of the speaker)
Vb = Volume of the sealed enclosure (in liters or cubic feet)
Vas = Equivalent air compliance volume of the driver (in liters or cubic feet)
Using simple numbers for example
Constants
Qts = 0.5
Vas = 50 liters
Vb=Vas×(0.7072−0.52)
Vb=50×(0.499−0.25)
Vb=50×0.249
Vb=12.45liters
Vb=Vas×(Qtc2−Qts2)
Constants
Qtc = Total system Q (the damping of the system)
Qts = Driver's total Q (which includes the mechanical and electrical damping of the speaker)
Vb = Volume of the sealed enclosure (in liters or cubic feet)
Vas = Equivalent air compliance volume of the driver (in liters or cubic feet)
Using simple numbers for example
Constants
Qts = 0.5
Vas = 50 liters
Vb=Vas×(0.7072−0.52)
Vb=50×(0.499−0.25)
Vb=50×0.249
Vb=12.45liters
Or save time with a spread sheet with all formulas included.
Aka speaker emulators / software.
Couple hundred by now.
Still like WINISD because it has sum check for T/S parameters
So you wont calculate with wrong values or false parameters from manufactures.
Otherwise Virtuix Cad
Since you can change basic advanced parameters or error factor corrections
For no shared walls, 2 walls or 3 walls with ports.
AKA .635 to 2.227 for end correction on ports
Aka speaker emulators / software.
Couple hundred by now.
Still like WINISD because it has sum check for T/S parameters
So you wont calculate with wrong values or false parameters from manufactures.
Otherwise Virtuix Cad
Since you can change basic advanced parameters or error factor corrections
For no shared walls, 2 walls or 3 walls with ports.
AKA .635 to 2.227 for end correction on ports
thanks to everyone that's replied so far ! most of this I'd difficult for me to understand
Jean-Marc could I ask is there a different way to write those equations ie the way I would write them in the calculator ?
I'm struggling to understand them the way you've written them .
I feel like the equations went something like f3 = 0.707 ÷qtc x fs
and the box volume one went something like
fb = 0.707 ÷ qtc =(x)
(x)² -1 =👍
then vas ÷👍 = fb
I'm sorry if this is written completely incorrectly this type of maths isn't something that comes naturally to me
thanks again all
Jean-Marc could I ask is there a different way to write those equations ie the way I would write them in the calculator ?
I'm struggling to understand them the way you've written them .
I feel like the equations went something like f3 = 0.707 ÷qtc x fs
and the box volume one went something like
fb = 0.707 ÷ qtc =(x)
(x)² -1 =👍
then vas ÷👍 = fb
I'm sorry if this is written completely incorrectly this type of maths isn't something that comes naturally to me
thanks again all
thankyou . do you know if the other equation I quoted is correct ? to work out box volume ?
thanks in advance James
Try this. Should be easier to understand.
Using T/S parameters
Fs 28
Qts .36
Vas 58L
.707 ÷ .36 squared, minus 1
Vas divide by the above gives Box volume (vb)
So(rounded)
.707 ÷ .36 = 1.964
1.964 × 1.964 = 3.857
3.857 - 1 = 2.857
58 ÷ 2.857 = 20.3
Vb = 20.3L
Using T/S parameters
Fs 28
Qts .36
Vas 58L
.707 ÷ .36 squared, minus 1
Vas divide by the above gives Box volume (vb)
So(rounded)
.707 ÷ .36 = 1.964
1.964 × 1.964 = 3.857
3.857 - 1 = 2.857
58 ÷ 2.857 = 20.3
Vb = 20.3L
Why don't you use WinISD, enter your drivers parameter and have all data simulated at once? Just change the box volume until you get the desired Qtc
Try entering wildly inaccurate/unrealistic parameters and see what Winisd does. That's what he means
It will autocorrect your data input so it stays 'inline' with TS theory.
Just as it auto calculates most of the values in the program, there is a limited amount of datapoints needed to make a 'complete driver' from TS specs.
You will find that the mfg. specsheets are often off, and Winisd will not let you input the exact mfg. specs if it is not in line with T/S theory/physics.
Most other programs let you have more leeway with this, for better or worse.
sum check /checksum is pretty much the same meaning.
Last edited:
Hello James,
Here's how it's written in the source code (Javascript) of one of my web pages :
vb = vas/((qtc/qts)*(qtc/qts)-1)
fc = fs*qtc/qts
f3 = fc*Math.sqrt(((1/(qtc*qtc)-2)+Math.sqrt((1/(qtc*qtc)-2)*(1/(qtc*qtc)-2)+4))/2)
I'm not sure it's any easier to read than message #5.
Beyond that, if we stick to the usual Qtc=0.707 :
vb= vas/((0.5/qtc²)-1)
fc=f3= (fs*0.707)/qts
Best regards, Jean-Marc.