Tiny cabinet sealed box minimun size help

Hi. I'm building a small stereo tube amp PCL82 based (used on old TVs audio) Just 3W per channel and no deep bass nor very high frequencies. The idea is to build a nice retro-look wood cabinet with its own speakers, kind of a "retro futuristic boombox", old school shellac finish. :)

I get two (very) cheap 4'' speakers (one per channel) and I need to know the minimum sealed box volume of each cabinet.

Of course, no online data available for the speakers so I tested them with the LIMP software, added mass method (a coin of known weight). These are the output values:

Fs = 133 Hz
Qt = 0.01
Qes = 0.01
Vas = 4.82 liters

With such a small Qt and my not-so-high expectations, which should be the minimum size? Could be smaller than Vas?

Thanks in advance.


Joined 2003

No such thing as a driver with a 0.01 Qt, much less a cheap one as even a powerful $$$ field coil couldn't come close to doing it. A 1.0 Qt is reasonable though. Since you have well proven software, try again if not a typo since Qt is often higher with cheap, small drivers.

with unknown drivers or drivers without trustable t/s parameters, always measure them out, including frequency response and impendance. I use rew and dats V2 for that.

Just on a few parameters and looks, i can't tell. Vas is often the right place to start simulating, but often not where you end up.
Yes, the 0.01 value also looks weird for me, meaningless. But I repeated the test many times with the same absurd results. Sine test better than pink noise test, reasonable Fs but absurd Qts. I am almost giving up with calculations... Any "rule of thumb" for the old days? Remember...just 3W per channel and poor specs from the amplifier.


Joined 2003
Well, the pioneers had a Vas/1.44 vent tuned to Fs alignment for best trade-off between size, bass extension, so figure out its effective diameter/area and use a vent ~1/4 in area since it's low power.

The box will have a hollow sound, so put just enough damping on the top, back, one side to make it go away, then if it audibly 'rings' [under-damped], which it probably will, do the click test or use LIMP's impulse test to damp the vent if unacceptable and 'it is what it is':

Click test: Click Test | GM210 | Flickr

Are the proper units used for input?
I catch myself mixing metric and English units occasionally, or sometimes ounces instead of grams, inches or mm (or should it be meters?). :eek:

Nothing personal, but sometimes it's worth double checking units or settings in the software.

Otherwise, the previous suggestions will likely get you in the ballpark.
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These are two plots, the unloaded in grey and the added mass (coin) in black. Of couse, I agree is a nasty plot. Now I am travelling and away from home. Next week I will try again with another computer. I have also a little USB sound card. Is just a DAC and only has outputs and no inputs but maybe it could help.