Hey everyone,

As some of you might have seen I've been doing my head in trying to design an enclosure for my sub. I've spent alot of time deciding whether or not to go with a ported or sealed enclosure. I've decided to go for a sealed enclosure instead.

I've been using Bass Box Pro to try and design an enclosure and I'm getting a bit frustrated

Here are the specs of the sub:

15"
Electrical Q Value -Qes: 0.58
Mechanical Q Value -Qms: 3.62
Total Speaker Q Value -Qts: 0.501
Free Air Resonance -Fs: 19.10 Hz
Equivalent Compliance -Vas: 207.0 liters
One-Way, Linear Excursion -Xmax: 54 mm
Efficiency -SPL 1W/1m: 85.81 dB SPL
Effective Piston Area -Sd: 810 cm^2
DC Resistance -Re: 4.2 ohm
Nominal Impedance -Znom: Dual 2 ohm
Thermal Power Handling -Pe: 2000 W
Force Factor -Bl: 18.16

Mounting Depth - 13.5"
Mounting Hole Diameter - 14.5"
Overall Diameter - 16"
Bolt Hole Circle - 15.25"
Motor Width - 10.5"
Motor Depth - 5"
Basket Depth - 8.5"
Displacement - 0.27 cu. ft.
Weight - 76 lbs

The minimum sealed enclosure size is 1.6ft^3, recommended is 2.1ft^3 and optimum is 2.4ft^3, according to RE. But heres where the problem lies. I will be running the sub in series.....After entering these specs into BBP and selecting 'series' for the 'VC Wiring,' halving the Qes to 0.29, doubling RE to 8.4 ohms, doubling Z to 4 (is that right?), increasing Power sensitivity (dB per watt@1m) by +3dB to 88.61dB, halving the Qts to 0.251 and doubling Bl to 36.32Tm, the program suggests a 0.6ft^3 enclosure. Rather small to say the least.....This achieves a Qtc of 0.707, which is great, but F3 of 71.44Hz, which seems quite high. Have I entered the specs correctly? I've tried changing the damping inside the enclosure without much success. I've entered the only specs given by RE into the program, leaving the other values blank without much of a change. I've entered these same specs and getting the program to calculate the other values also without much of a change.

When I entered the standard specs into the program (running seperate coils), I entered 2.4ft^3 as the enclosure size and achieved a Qtc of 0.78 and F3 of 34.06Hz, which seems great, except I won't be wiring the coils seperately

Obviously the specs of a driver change when wired in series or parallel, but why is the program suggesting such a small enclosure? And how can I achieve a resonable Qtc while keeping F3 low in series?

Any help with this would be great. I can email the bb6 files I've been playing with to anyone who wants them I'm sure it'd all make more sense if you had the files in front of you.

Cheers,
Luke.

I just loaded the previous model XXX 15 to compare. I hadn't entered the Bl correctly. It should be half, 9.08 for individual coils and 18.16 for wiring in series. Re should also be halved to 2.1 ohm for individual coils, and 4.2 for wiring in series. This made a huge difference to F3, decreasing it to 38.14Hz in a 2.4ft^3 enclosure, but Qtc is quite low at 0.438, which is less than the sub's Qts of 0.501. Shouldn't Qtc be more than the drivers Qts?

Yes. You cant lower Qtc below Qts. It only goes up.

Why did you change the sensitivity??

Doesnt sensitivity change depending on whether you have a DVC wired in series (sensitivity increases) or parallel (sensitivity decreases) I thought I read something about that somewhere, though I'm probably wrong!!

From what I've read, I thought you're supposed to increase the sensitivity by +3dB when wiring in parallel or series?

Nope you dont do that at all. It is increased by plus 3db over the individual coil when compared to wiring in series or parallel.
So it is the same sensitivity whether you wire it in series or parallel.

Oh ok. Thanks for the heads up

I've entered all the specs correctly now but I'm still getting Qtc lower than 0.501. Anyone got any ideas?

I just entered the specs into Bass box 6 and found the optimum enclosure for your XXX15 to be 134.9L excluding woofer, with a qtc of 0.707.
If you want a box that is smaller BB6 suggests a 37.49L enclosure excluding woofer, with a qtc of 1.08.

These are the options high fidelity and high output I didnt play around with it to get these numbers.

Pffft. 0.707 is overrated IMO.



Try aiming higher, say around 0.85 with polyfill.

LOL but then it wont play as low. I think it would depend on what music he would play with it. Some people swear by a qtc around the 0.5's.
Although with the increased qtc group delay is less, quite insignificant though from 0.707 to 0.85.

I was debating that myself. Whether or not to go with a higher or lower Qtc.

Although I mostly listen to House, Trance and Rap, I also listen to a bit of rock and classical. Strange mixture I know but I guess if I could find a compromise between tight with good low end I would be happy. If I had to though I would sacrifice a bit of tightness for some good low end.

Thanks for going to the effort 1point21gigawatts 134.9L seems huge though for a sealed enclosure, and 37L seems too small. This is sort of whats been confusing me.

I entered 2.4ft^3 (67.96L) as the enclosure size which achieved a Qtc of 0.78 and F3 of 38.64Hz. Would this be ok do you think? Will it play low enough?

Ok I've come up with four designs:

2.4ft^3 (67.96L) - With 'typical' damping

Qtc: 0.78

F3: 38.64Hz

2.4ft^3 (67.96L) - In 'classical' mode (no damping)

Qtc: 0.867

F3: 36.2Hz

2.1ft^3 (59L) - With 'typical' damping

Qtc: 0.814

F3: 38.96Hz

2.1ft^3 (59L) - In 'classical' mode (no damping)

Qtc: 0.908

F3: 36.74Hz

This is just a guess but would the last enclosure be a good option, since it would be quite tight with a Qtc of 0.908 but still get low with an F3 of 36.74Hz? Which do you think would be the best option based on the type of music I listen to (see above)?

Anyone got any recommendations?