# Sealed cab resonance???

Discussion in 'Amps and Cabs [BG]' started by friedtransistor, Feb 6, 2014.

1. ### friedtransistor

Dec 9, 2013
I have no experience with thiele small, and I don't have any parameters for the speaker I have. I only know the xmax, which is about 1cm p-p. it's an 8" speaker, which gives me this: suface area= ~50.25 sq in., displacement= ~19.78 cu in., and the cab has a volume of about 1440 cu in.. Knowing this information, how do I calculate the resonant frequency at xmax? I haven't been able to find info on google because a) every equation uses data I don't have or can't get since I don't have the equipment to measure the speaker, and b) the ones that might work use constants that I can't calculate since I don't know the required parameters...

There has to be a way to calculate resonance with just volume and displacement, right? Or is there more black magic involved than I thought?

2. ### DukeLeJeunerational romantic mystic cynical idealistSupporting MemberCommercial User

Nov 24, 2008
Princeton, Texas
Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
You don't have enough information, as you found out.

I suggest you find two or three apparently similar 8" speakers and look at their parameters and from there make an educated ballpark guess about yours. Plug your estimates into the equations and see what you get. It won't be precise, but will be better than nothing.

3. ### Downunderwonder

Aug 26, 2009
New Zealand
Pretty high xmax, might be a car sub, notoriously lacking for bass guitar.

4. ### Vince Klortho

This value of surface area is a bit high because it does not account for the surround of the speaker which is subtracted from the radius. I am going to take a guess that a typical 8" speaker will have a surround of 0.75 inches so its effective radius is 3.25 inches. This works out to an area of 33.2 in[SUP]2[/SUP].

I had a look at the data for one of Eminence's speakers and its area is 0.021m[SUP]2[/SUP] which works out to 32.6in[SUP]2[/SUP] so it appears that 0.75 was pretty close - the actual value is 0.78.

FWIW, the recommended sealed cabinet volume for that speaker is 0.18 to 0.25ft[SUP]3[/SUP] which is 311 to 432in[SUP]3[/SUP]. This page has the specs for several 8" woofers so you can see the values for others.

5. ### friedtransistor

Dec 9, 2013
I'm sorry, the xmax is actually lower than I thought. It's more like 0.5cm, not 1cm. It's not a sub, just a cheap no-name speaker with a paper surround. Plus, my cab volume sizes are just an estimate, I'd have to measure that at some point. My cab is about (roughly) 12"x12"x10", that is, if you subtract the area taken up by the head.

Edit:
Ok, so the xmax is closer to 0.25cm, as I didn't realize xmax meant from center to fully extended, I thought it meant P-P.

Dec 9, 2013