Designing sealed enclosure - problems

[Luke 0]

Hey everyone,

I posted a thread a while ago about trying to work out the ports for 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?

Any help with this would be great.

Cheers,

Luke.

Edited July 31, 2007 by Luke

[Luke 0]

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?

[///M5 2,833]

If 2.1cuft is actually optimal just ignore BBP as it isn't modelling that driver right for your application. Building a box to 2.1cuft is pretty easy.

2.1cuft (1728cuin/cuft) = 3628.8cuin is what the internal after bracing and subwoofer volume needs to be. Pick your two limiting sides and then bulid the third dimension of the box to take up that space.

[Luke 0]

I hadn't entered some of the specs correctly. After entering them correctly though, the program still suggests a 4.7ft^3 sealed enclosure to achieve the 'ideal' Qtc of 0.707. A little large I think I entered 2.4ft^3 as the enclosure size which achieved a Qtc of 0.78 and F3 of ~38Hz which seems alright. Will it still get low at that F3? Alternatively, I entered 2.1ft^3 as the enclosure size, which achieved a Qtc of 0.909 and Qtc of 38.95Hz. Both with 'typical' damping.

Edited August 1, 2007 by Luke