I would like to build a large AV subwoofer, but need some advice!

**Mike P.** · **07-07-09, 06:26 PM**

You're getting poor results because the recommended box size is for car audio, not HT. That sub models to 9 cu.ft tuned to 20 hz. With 300 watts it will start bottoming out at 16 hz with out a rumble filter.

**Parts** · **07-08-09, 03:11 AM**

Hi Mike,

I was trying various cabinet volumes and tuning with poor results, I mentioned the car audio cab design as even with that I get different results than JBL state in the diagram, which has me wondering if I am doing something wrong with the parameter input?

It's dual voice coil wired in series for 4ohm.

With a 9 Cuft ported to 20hz I seem to have too much cone excursion, 11.9mm at 31hz.

I get a dip in maximum spl starting at 46hz (114db) which dips down to 109db at 27.9hz and goes back up to 111.9db at 22.6hz before rolling off.

Rear port velocity is 16.4 ms at 19.1hz with two 4" ports 15.98" in length.

I am using a 4th order Linkwitz HP at 17hz

**Mike P.** · **07-08-09, 10:53 AM**

Quote:

It's dual voice coil wired in series for 4ohm.

With a 9 Cuft ported to 20hz I seem to have too much cone excursion, 11.9mm at 31hz.

Not possible with 300 watts input. The Re is 3.84 ohms for a 4 ohm load. It would take a little over 500 watts to reach Xmax at 30 hz.

Change the HPF to Butterworth second order.

**Ricci** · **07-08-09, 03:31 PM**

I'd put 2 15's in each enclosure.

Mike is right 9ft tuned to 20hz per driver looks good. However I'm seeing the same 12mm excursion at 30hz with 300w in that box. I wouldn't worry about exceeding xmax a little bit. I doubt that these drivers will get into trouble or bottom out until well over 30mm p2p. They just won't sound as clean. That's the point to having 4 of them.

**Mike P.** · **07-08-09, 03:40 PM**

Quote:

However I'm seeing the same 12mm excursion at 30hz with 300w in that box

What do you have the Re entered as?

**Ricci** · **07-08-09, 03:43 PM**

Re 3.84

**Mike P.** · **07-08-09, 03:52 PM**

Somethings not right. Can you upload the driver file for the sub?

**GPM** · **07-08-09, 06:03 PM**

Quote:

Ricci wrote:

Mike is right 9ft tuned to 20hz per driver looks good. However I'm seeing the same 12mm excursion at 30hz with 300w in that box.

FWIW, HornResp predicts 13.1279 mm.

GM

**Parts** · **07-09-09, 09:34 AM**

Hi all,

Ok I am not sure how to upload any driver file?

Regarding going with two drivers in a single enclosure, could I build a copy of the JBL 4642A Dual 460 mm (18 in) Subwoofer System cabinet and use these drivers?

This is 18 Cu. ft (506 liters) 30" high 48" wide 24" deep. I would probably have to use 1" chipboard throughout, though the above uses 19mm apart from the front and back panel. so I may have to remodel size in one dimesnsion, depth probably?

I would also like to keep the front panel removeable as I may put in two 18" drivers in future.

Should the drivers share the internal volume, it looks like the JBL design does.

I was thinking of slightly recessing the front panel an inch for future fitting of a metal grill, but unsure what bracing methods to use. Probably best using the 1" chipboard centre front to back vertical, and side to side vertical? Or a full side to side brace with a centre to middle and rear bracing at the two one third points.

This would make the front and rear and centre panels all east to remember at 28" + 46", I could use the 45mm +45mm batton as frame work for all the outer panels to screw and glue to. would probably not need clamps? Or a table saw?

I have 1" chipboard 5 x 60+75" sheets, and 5 X 60+52" sheets. I don't have enough 19MM MDF as this is all limited to a 15" width. I have 45mm + 45mm batton, 5x 95" and 130" of 95mm +43mm batton.

(I would like to build two of these cabs)

Steve

**Mike P.** · **07-09-09, 02:09 PM**

I think I figured out the excursion issue, I'm guessing you have it showing peak to peak which would show 13 mm Xmax with the limit being 17 mm for the sub. As long as you're under the red line you're fine. I have my excursion set at peak, which shows the one way excursion.

One big box sharing the volume for 2 subs is fine, just make sure it's well braced.

**Ricci** · **07-09-09, 03:09 PM**

Nope. I always use one way and get 12.5mm for 300w into the 9ft cab. Vc's in series for 3.84 re.

Parts,

That cab idea sounds fine. Make sure you get enough vent area. 6" port per driver should be ok.

**Parts** · **07-09-09, 03:32 PM**

Can someone else show their WinISD results with TS parameters showing?

Edit things are looking better, I have re-installed winISD and adjusted the TS parameters again, running a butterworh second order at 17hz with a 506 liter cab tuned to 20hz, looks reasonable?

Qts 0.504
Vas 6.039
Fs 25.00Hz
Re 3.840 ohm
Le 0.50mH
Xmax 8.5mm
Z 4.00 ohm
Qms 6.080
Qes 0.550
SPL 93.00 dB
Pe 300w
BL 8.20000 Tm
Dd 13.00 in
Sd 132.83

**Mike P.** · **07-09-09, 03:41 PM**

Ok, I got it figured out, I had the wrong BL enterd for a 4 ohm load. It is indeed 13mm excursion with 300 watts.

**Parts** · **07-10-09, 05:58 AM**

So are the RE and BL figures I entered above correct? Why does the JBL brochure state 0.96 for VC Dc Resistance? is this different when both are wired in series for a 4ohm load hence the figure 3.84 you guys mention?

With the above figures I have used, and a 600w input I am looking OK in WinISD, even with a 700 litre cabinet I look OK, it seems to have a more even maximum SPL line with less tail off than 506 litres? An extra 2 to 3db around 20hz? 114dB at 50hz down to 113db at 20hz with come excursion peaking at 7.9mm at 14.90hz and port velocity peaking at 13.572 m/s at 18.77 hz with four 4.02" + 10.85" ports

Cabinet size and design seems quite a lot of work, so I am still busy calculating what braces and battons and such equate to what volume........

**Mike P.** · **07-10-09, 10:33 AM**

JBL lists the specs for a 1 ohm load. Changing the Re to a 4 ohm load also changes the BL. Here's the file. Save it to the Drivers fold in WinISD.

JBL GTO 1502D.wdr

**Parts** · **07-10-09, 11:21 AM**

Thanks Mike,

Your file gives me that same dip between 45hz and 22hz in maximum SPL I was talking of earlier, is this a good or bad thing? Any way to smooth it out?

Cone excursion looks bad as well? I can keep it level with 300w signal, cabinet tuned to 19hz with a filter at 20hz? Any more and it gets out of hand.

**Mike P.** · **07-10-09, 11:59 AM**

You're using the wrong graph. Switch to the SPL graph, that shows you what you get with the input power and HPF that you use. In 9 cu.ft. tuned to 20 hz you should be able to get away with 200 watts input and a 2nd order HPF at 18 hz.

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