Need equations for designing ported subwoofers

venki

Member
2005-05-07 7:13 pm
india
Hi,

I am in a process of desiging a proted 3-way system. I would really appreciate if any of you can provide me with the equations/ links to sites to calculate the box size, port size (if i want to design it based on the QTC - similar to designing sealed systems). I got some equations from the diysubwoofers.org site. But the equation is suited for only one type of design.

Thanx,
Venki:D
 
Hi

Do you have the following ,

1 Multi meter capable of current measurements
2 Audio Signal generator

I have been over your problem with the Dainty driver ( the source is Chinese - though the source was limited by a strict price structure set up by the Indian Importer)

the qts is around 0.8

try this - press the cone inwards with a light force evenly spread over the body of the cone

next pull it outwards from behind - with roughly the same force applied before

you may find that the cone does not move upwards as freely as it doeas downwards

this is = that the suspension is non - linear - if this is so - or if you carefully study the spider if it appears pushed inwards - or the rollof the surround not symmetrical on both its edges - that is the outer edge and the one pasted to the cone

go in for a sealed cabinet as the above leads to distortion and poor phase responce etc.

you will find more information on non linearites - please search for my replies / threads here in Diy

as for the parameters - every one will advise to compare the results by :-

calculating manually & with your PC

If you have the above Multimeter etc. I can mail you the procedure pls mail me at [email protected] or ill post it here on the thread as you like it

Suranjan Das Gupta

Transducer Design Engineer
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
venki said:
I would really appreciate if any of you can provide me with the equations/ links to sites to calculate the box size, port size (if i want to design it based on the QTC - similar to designing sealed systems). I got some equations from the diysubwoofers.org site. But the equation is suited for only one type of design.

There is no way to design a ported box based on Qtc. Qtc is only defined for a closed box system. The equations at diysubwoofers.org are correct. They do represent only one way of doing things - you are free to design a box with whatever Vb, Fb you want as long as it meets your target response.

You need to know Fs, Qts, Vas at a minimum to figure out a Fb, Vb to start with.

Measuring parameters is easy, you just need a voltmeter, a ~10 ohm resistor and your computer soundcard (download a signal generator program). Do a search for a program called DPC (Driver Parameter Calculator) and it will guide you through the steps.