Help calculate enclosure volume

[Sillyboy]

I have another thread going where people are chiming in on what my first diy project should be... feel free to chime in there

However, I put too many questions in there and want to extract one out.

How in the heck do you calculate correct enclosure volume and what are the important speaker parameters that determine this?

I understand that WinISD is a favorite, but for the life of me I can't model these speakers. WinISD likes to complain about inconsistencies w/ the "Q" type params.
Qes(.63) Qms(3.91) Qts(0.52) Fs(56) Vas(.16 ft^3).

If I go w/ "sorta close enough" values by letting WinISD calculate Qms (which doesn't look that close to me), then I still can't get volumes that match this part's express list nor the volume used in this project

And the values on that list from part's express is freaking me out. There are some 6.5" speakers that should use a smaller enclosure than some 4" speakers!? crazy.

Also, not sure if other params are important (other than the Q* ones) when doing the modeling.

Lastly, do people usually talk liters or ft^3 for volumes?

So, help the noob get past this initial hurdle, please.
-Silly.

[nunayafb]

You have all of the data you need on parts express to enter into winisd. To confirm I entered this woofer into mine and no problems or errors. It suggested .36ft^3 and tuned to 43hz w/ and f3 of 38hz.

[Sillyboy]

And these are the values you used?! Did you enter them all, or let WinISD calc some?

Qes(.63) Qms(3.91) Qts(0.52) Fs(56) Vas(.16 ft^3).

And this is the version of WinISD? 0.50a7

Clearly this program hates me

[lndm]

I like a box calculating program to find the parameters for itself if I don't have them all, but only if it ask's my permission first, or I ask it to.

Anyway, I use litres but most programs will offer you whichever you feel more comfortable with.

There is a rule of thumb that suggests a driver will be happiest in a closed box that is about a third of the drivers Vas. I think AR was responsible for this finding a few decades back IIRC.

In such a box, the system's resonance will be at a frequency of twice that of the driver in free air. The system Q will be twice that of the Driver's Qts (in free air).

From this you can work backwards from what you want to achieve, to what you want to find in a prospective driver.

If all this doesn't work, just change the box size to suit. Closed boxes are not known for being too critical.

[AndrewT]

Hi,
Do you want a sealed box speaker or a vented box speaker?

When working with vented boxes this does not follow:

There is a rule of thumb that suggests a driver will be happiest in a ......... box that is about a third of the drivers Vas. I think AR was responsible for this finding a few decades back IIRC.

The optimum box volume depends on the driver's Qts. for Vas = 3times vented box volume, the required Qts is 0.29 I also suspect it is not true for sealed boxes either.

For a vented box this is wrong:

In such a box, the system's resonance will be at a frequency of twice that of the driver in free air. The system Q will be twice that of the Driver's Qts (in free air).

The Fb= 1.6times Fs when Vas=3times Vb and Q=0.29

[lndm]

I was talking only of closed boxes, not vented (sorry if I wasn't clear).

From an early version of the LDC, (IIRC) I found Vb =

Vas
-------------
./ /Qtc\2...\
| |----| - 1|
.\ \Qts/..../

and fc (IIRC) =

./Qtc\
|----| x fs
.\Qts/

(Ignore the dots).

It has been a while since I used these formulas and if I have made a mistake, I will stand corrected.

[AndrewT]

Hi Indm,
you made it completely clear you were discussing a closed box, that's why I removed the word in the quote.
But for comparison I gave the equivalent numbers for a vented box to show the option and to show that the volume and frequency rules vary with Qts. They are not fixed.

BTW your formulae match your description.

[richie00boy]

I agree on all counts with Andrew.

Sillyboy, you are only supposed to let WinISD calculate one of the parameters, given the other two. I would enter Qes and Qms and let it calculate Qts.

Be aware that at >0.5 Qts is really too high for a practical vented box.

[lndm]

Sillyboy,
I don't believe a closed box is necessary for good sound even though my post sounded like that, I just chose to talk about closed boxes.

I haven't used WinISD, if you like it will you let us know please?


AndrewT,
that's cool. I was just being careful, hate to think I was giving out bad formulas.

BTW I checked to be sure

http://www.arcavia.com/kyle/Equations/Closed.html

[AndrewT]

Hi Indm,
that Kyle site sure has a lot of formulae. Have you had a chance to check any (many) of them against another source/s?

Shame he has not solved the bracketing problem, ruins readability.