Converting ported box into sealed

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#22
bwank said:
All a question of how much effort and detail on sound engineering you would like to spend vs trial and error. For engineered results, I'd suggest to measure your TS parameters using a PC-based free frequency generator program to your liking, a (>1W) power resistor between 20-100 Ohms, your amp, and measure your impedance from 20-120Hz to calculate your fs, f(-3dB), from there your Q's after measuring coil DC resistance with a multi-meter. Possibly, and carefully, with a DC current source for better resolution. Make sure you operate with "small signals" under 1V for small signal parameters. Repeat in 0.1Hz steps around fs and f(-3dB) for accuracy. After measuring in sealed enclosure, repeat measurements in free air, carefully suspending chassis, ie suspended from ladder, calculating Qt. Then repeat measurement with a few pennies taped carefully on top of speaker dust cover, calculate compliance from Vas/Vb. Measure R(0) with Ohmmeter. Now it may not be worth spending a whole weekend on this, but you will know for sure what to expect instead of assuming a large variety of ported alignments that could get you Qb's from the 0.3 (flat) to 1 (boom). For simplicity you can also try stuffing the box with different density until you like it, changes your "effective" volume as seen from the speaker as much as 15%. Or add a Variovent (if they still make those), or consider even a passive radiator. Have a fun filled weekend!
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Can I make this measurements in the original enclosure and/or shall I seal the port or leave it open for the measurement?
cheers
 
#23
phivates said:
Your driver's xmax is probably minimal, so don't expect big output down low. That's what the vent is for.
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I am not looking for big output, because I have a smallish room (12m2) and live in a block of flats too, so the system will be used only at moderate volume level. Accuracy and sound reproduction is more important to me in this case. Can Xmax be measured at home without hassle?

cheers
 
#24
I find a 1.5 volt battery gives me a look at what a driver "wants" to do. Very crude. Decades ago very few woofers had xmax over 4mm, or 8mm peak to peak. For low levels you'll be fine. SL's transform is intended for modern drivers with 3X the excursion. Listen for popping noises if you EQ.
 
#25
I haven't been around for a while. It just looked like there is too much guessing around the optimal box size and didn't have time for experimenting much with it, so I decided to keep it ported since its sounds good that way too.
Thanks for your inputs and help anyway.
 
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