BR subwoofer design question?

[Helix]

I have bought a eminence kappa 15 LF speaker and i am now currently trying to figure out a alignment using winISD.

I think i have found out the Vb that i need, however i have a question which i am sure you lot will help me with :

Do i have to subtract the volume of the port from Vb?

I the best way of making a rough estimate of the volume taken by the driver is my measuring it as a cylinder and dividing by 2?

What is the average volume taken by a 15" driver?

do i have to adjust anything to take in account wadding?

 

[Ignite]

In my experience:
- yes, subtract the port volume.
- better estimation of speaker volume would be by measuring the speaker cone as a cone and the magnet/spider assembly as a cylender and adding the two plus a little bit extra for the frame.
- you probably don't need it measured to the millilitre as that's anal retentive and it's unlikely you'll make your box that accurately.
- 15" drivers are so different in size and shape that's not going to help you much.
- if you want to be really exact, yes, stuffing/wadding/whatever else should be taken into account.
- not to be sloppy but I find a box that's about what winISD says works pretty well usually. Extreme accuracy isn't all that neccesary. Hand-tune the port later and you'll find something you like.

 

[Eric]

*ADD* port volume, don't subtract!

The volume that WinISD calculates is exactly that: necessary volume for the driver to work as designed. Say, for example, that WinISD tells you that you need 150 liters. Take this volume, then ADD (don't subtract) the volume taken up by the port and the volume taken up by the driver. This new figure is the volume you should design your box for.

Here are a few numbers:
a) WinISD says volume needs to be 150liters
b) your port takes up another 15 liters
c) your driver displaces another 5 liters

Design your box such that its internal volume (before adding anything) is 150+15+5 = 170 (gross) liters. This way, by the time you add in your port and put your driver in the box, the net volume in the box that your driver interacts with is 150 (net) liters as originally called for.

Note that the numbers above are just for example. Calculate the volume of your driver as a cylindrical pyramid (rounding to the nearest liter will probably be fine). The driver manufacturer may be able to give you an exact figure for this.

Box stuffing is another matter. For most vented designs, the walls of the enclosure are usually lined, rather than "stuffing" the box. Lining the walls may give you a 5-10% increase in working volume. In most cases, leave the figures alone and line the box with stuffing. The result is rather subtle and usually gives you just a pinch lower response (for example, if you designed Fb =24 Hz, lining the box may give you Fb=22 or 23 Hz)

Hope this helps a little.


[Edited by Eric on 08-01-2001 at 09:36 AM]