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I got WinISD working on my computer and started modeling my driver in different cabinet size/port length combinations. At first I thought "lower is better." I put the info into WinISD to tune the port to the -6db point. Then I thought, what about the -3dB tune? NOTE: This is sensitivity, not pure SPL. The goal is to maximize the use of the subwoofer that I already have. Here's the relevant data that I pulled from WinISD:

6 ft^3, 16Hz tune --> -3dB=43Hz, -6dB=15Hz
5 ft^3, 19Hz tune --> -3dB=32Hz, -6dB=17Hz

Right off the bat you can see that the smaller box and higher tune basically loses 2 Hz of extension at the very low end of the sensitivity spectrum. But also notice that it has an 11 Hz extension advantage at -3dB over the lower tuned enclosure.

This still doesn't tell the whole story about which tune would be a better deal, however. What about the effect of the receiver's crossover would have on the subwoofer system. My receiver has a number of different low pass crossover points, including 90 Hz, 80 Hz, 60 Hz, and 40 Hz (there are more but I probably would never use them).

Without taking into consideration the slope of the crossover, I noticed a few interesting things. First, note that I can still turn the gain up on my amplifier; I've got plenty of power not being used. I also noted that sensitivity above the receiver's crossover point is pretty much useless; the mains take care of that portion of the audio spectrum, anyway. That means that my new "0dB" reference point is at whatever frequency my crossover is set to.

Here's the info that I noted about the sensitivity slopes of the driver in the two different enclosures utilizing different low pass filter points.

*Usable BW is the distance from the crossover point to -3 dB.

With 80Hz set as the 0dB reference
,

6 ft^3, 16 Hz tune --> -3 dB = 31.23 Hz, -6 dB = 14.4 hz; Usable BW = 48.77 hz
5 ft^3, 19 Hz tune --> -3 dB = 18.70 Hz, -6 dB = 17.0 Hz; Usable BW = 61.30 Hz

The higher tune has a 13.53 Hz advantage at -3 dB but loses 2.6 Hz of extension at -6 dB. Inversely, the lower tune has a 15.53 Hz disadvantage at -3 dB and gains 2.6 Hz of extension at -6 db. The higher tune has a 12.53 Hz bandwidth advantage at -3 dB.

With 60Hz set as the 0dB reference,

6 ft^3, 16 Hz tune --> -3 dB = 24.3 Hz, -6 dB = 14 Hz; Usable BW = 35.7 Hz
5 ft^3, 19 Hz tune --> -3 dB = 18.1 Hz, -6 dB = 16 Hz; Usable BW = 41.9 Hz

The higher tune has a 6.2 Hz advantage at -3 dB but loses 2 Hz of extension at -6dB. Inversely, the lower tune has a 6.2 Hz disadvantage at -3 dB and gains 2 Hz of extension at -6 dB. The higher tune has a 6.2 Hz bandwidth advantage at -3 dB.

With 50Hz set as the 0dB reference,

6 ft^3, 16 Hz tune --> -3 dB = 15.7 Hz, -6 dB = 13.8 Hz; Usable BW = 34.3 Hz
5 ft^3, 19 Hz tune --> -3 dB = 17.0 Hz, -6 dB = 16.0 Hz; Usable BW = 33.0 hz

The higher tune has a 1.3 Hz disadvantage at -3 dB and loses 2.2 Hz of extension at -6 dB. Inversely, the lower tune has a 1.3 Hz advantage at -3 dB and gains 2.2 Hz of extension at -6 dB. The higher tune has a 1.3 Hz bandwidth disadvantage at -3 dB.

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With all of this information at hand, which combination of tune and crossover would be the most effective use of my subwoofer?
 

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With all of this information at hand, which combination of tune and crossover would be the most effective use of my subwoofer?
Itwould help if you were to state what sub you are modeling, for anyone who would like to know. Secondly, post your WinISD file for the sub. That would make it easier for anyone wishing to verify your results.
 

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Switch to the cone excursion graph, increase the input power until excursion reaches Xmax or maximum power handling is reached, whichever comes first. Under the EQ/ Filter tab add a high pass filter and adjust the frequency until excursion is under Xmax. Now compare the results in the SPL graph.
 

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Discussion Starter #5
I think the Xmax that I'm using (5.7mm) has to be WAY off. According WinISD, Xmax is reached with just 45 watts between 25 and 30 Hz. I know I've fed the sub a LOT more power at those frequencies without any complaint from the sub and it's moving much further than 1/5-inch. I know what an over-driven sub sounds like and this ain't it.

If the advertised power handling is to be believed, than I believe Xmax (not xmech) is closer to 1/2 inch. I modeled the woofer in a sealed enclosure (in the volume that Sony recommends) and it reaches a 1/2-inch Xmax at 10 Hz right around 300w of power, which is what the RMS power hadnling is advertised to be. This power handling is also supported by my experience with this driver combined with my current enclosure and amplifier. Also, in watching the woofer's excursion at various power levels, I believe 1/2-inch is a low, safe estimate.

Having said that, I changed the Xmax from 0.22" to 0.5" and modeled the woofer in the specified enclosures. I'll have to interpret and post the results tomorrow after I get some sleep. ;)
 
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