Vented Enclosure Calculations?

[mramstedt]

Hi,

I want to desing a speaker enclosure around the SEAS P21RFX/P woofer and using the following formula, it gives me something around 10.6L which sounds strange to me.

What am I doing wrong here?

Vas = 48.3L
Qts = 0.23

Vb = 15 * Vas * Qts^2.87

Regards,

Marko Ramstedt
Nebraska

[mike.e]

This is Maximally flat alignment from memory.

For all sorts of ported box manipulations,use a modelling program

www.linearteam.dk 'winisd pro' is the easiest one.

Small driver and low Qts demands tiny box....

[Ron E]

That alignment is a curve fit by D.B. Keele of SC4 and QB3 alignments. While it works for low Q woofers such as the one you are using, it does not always give the best value. With the Keele Alignment, you get a bass cutoff in the mid 50's. With the Richard Small (of Thiele/Small fame) alignment (which WinISD uses) you get an even smaller box - ~7.6 liters

With your relatively high resonance woofer, you will want to oversize the box and tune lower. Try modeling a 28 liter box tuned to 38Hz with a 3" diameter x 11" port. This gives an Extended Bass Shelf (EBS) response that will squeeze more bass extension out of that woofer. You could also try a 20L box tuned to 44Hz wiht the same vent dimensions...

The above examples assume no series resistance. With low Q woofers, the effect of adding the series resistance in the crossover and the output impedance of the amp ( together these raise Qts) is important, so don't forget to allow for them.

Qes' = Qes*(1+Rs/Re), where Rs is the value of series resistance and Re is the DC resistance of the coil.

Qts effective = Qes'*Qms/(Qes+Qms)

[mramstedt]

Thanks guys, I'll try for a larger box. Do you know of any good measurement programs for download and how would I utilize my notebook to handle the work?

-Marko