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Discussion Starter #42 (Edited)
I must be doing something wrong ! four 5" by 40" ports seems wrong for a single 15?

What port requirement are you getting with the single GT5-15 in the 10 Cu-ft enclosure?

And this may be a bit of a newbie thing to ask, will two single 10 cu-ft enclosures achieve the same spl and LF results as the two 15" drivers in a 20cu-ft enclosure?

(And I thought it would be as simple as getting a nice 18" pro driver and building a copy of a JBL 4645C cinema subwoofer)

May I also ask, is using something like a Behringer DEQ 2496 worthwhile (or any of their active crossovers)?

What 18" pro drivers would be a close match to the JBL drivers used in their Cinema subs if I wanted to build a DIY copy?

JBL Cinema 18" subwoofer parameters,

Nominal Diameter: 460 mm (18”)
Rated Impedance: 8 ohms
Power Capacity1: 800 watts
Sensitivity 2 99 dB, lW, 1 m (3.3 ft)
Frequency Range3 25 Hz - 1.6 kHz
Power Compression4
d -10 dB power (80 W): 0.6 dB
@ -3 dB power (400W): 2 dB
@ rated power (800 W): 3.3 dB
Distortion5
2nd harmonic: <1.0%
3rd harmonic: <1.0%
Highest Recommended Crossover: 1 kHz
Recommended Enclosure volume: 140 - 340 1 (5 - 12 ft3)
Effective Piston diameter: 397 mm (15.6 in)
Maximum Excursion
Before Damage (peak to peak): 50 mm (2 in)
Minimum Impedance: 6.6 ohms
Voice Coil Diameter: 100 mm (4 in)
Voice Coil Material: Edgewound Aluminum Ribbon
Voice Coil Winding Depth: 25 mm (1 in)
Magnetic Gap Depth: 12.7 mm (0.5 in)
Magnetic Assembly Weight: 10.4 kg (23 lb)
Bl factor: 23.7 newton/ampere
Effective Moving Mass: 158 g
Polarity: EIA (Positive voltage to RED
terminal gives forward cone
motion)
THIELE-SMALL PARAMETERS6:
fs: 35 Hz
Re 4.7 ohms
Qts: 0.28
Qms: 5
Qes: 0.29
Vas: 283 1 (10 ft3)
SD: 0.124 m2 (192 in2)
Xmax: 9 mm (0.35 in)
VD: 1114 cm3 (GS in3)
Le: 1.25 mH
710 (half-space): 4%
Pe (Max)1: 800 W, continuous pink noise
MOUNTING INFORMATION:
Overall Diameter: 464 mm (18.27 in)
Bolt Circle Diameter: 441 mm (17.38)
Baffle Cutout Diameter
Front Mount: 427 mm (16.81 in)
Rear Mount: 428 mm (16.85 in)
Denth7: 203 mm (8 in)
Volume Displaced by Driver: 9 1 (0.32 ft3)
 

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Steve,

Can you afford 4 of the JBL GT5 15"s and the EP2500 or EP4000 amplifier? This would be a potent and fairly sensitive system.

If you are only going to get 2 15's just get the plate amp as you will not be close to needing the power of the EP amps. Actually 2 of the pro audio 18's would be better than 2 of the cheap car audio 15's. I would take 4 of the car 15's over 2 of the pro 18's though. After you decide what to purchase we can help you out with the details of the enclosure.
 

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Discussion Starter #45
Well I still have no idea what I really want to do.


The Car audio JBL's I keep having niggling doubts about, I think that's why I again looked at the JBL Cinema sub, though it looks like it may need EQ with the likes of some Behringer kit.

Of course this brings me back to Pro audio type 18"ers, which would probably need EQ. I have found a UK company which sells many drivers, the P Audio drivers look good value (one looks like it may be a suitable alternative to a JBL 2242 bass driver?) http://www.proaudioparts.co.uk/products.asp

The JBL cinema single 18" subwoofer box design looks like the sort of box I had in mind, maybe a single to start, and adding a second later?

I still like the plate amp, but I can get an EP4000 for £300 which makes a 500w 4ohm single channel of amplification for £230 seem a bit of a side step/waste?

Is there an active Behringer crossover or DEQ unit you guys recommend that would take care of low and high filters and maybe even some EQ?

Sorry about all this to'ing and fro'ing :daydream:

Steve
 

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Discussion Starter #46
My TS parameters for the GT5-15 must be wrong or I am doing something wrong with WinISD? , with a 10 cu-ft cab tuned to 18hz with a HP at 16hz, two 4" by 18" ports, I am getting rear port air velocity of 79.995 ft/s peak at 16.24hz :scratch:

JBL GTO 1502D's have appeared on ebay second hand, but these seem to produce poorer results (TS parameters seem to be within WinISD).

Those P Audio drivers look reasonable....

Decissions decissions............
 

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Decisions decisions...
That's easy, go with the GT5.

I am getting rear port air velocity of 79.995 ft/s peak at 16.24hz
That's about right. Right click on anywhere on the graph, select options. At the bottom is the "Air velocity". Click on "ft/s" until it changes to "m/s". Click on "OK".
 

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Discussion Starter #48
:T

OK what box alignment should I be choosing? What are these box alignments? And what is rear port gain?
 

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Basically, the alignments are different box sizes and tunings. How the sub will perform is different in each. The goal for a HT application is to find the best box size and tuning that will give you the best low end extension for a given sub. The bigger the box and lower the tuning gives more low end extension at the expense of overall SPL. The smaller the box and higher the tuning gives greater SPL at the expense of low end output. You want the best balance of low end output and SPL.

Rear port gain is how much output the port is contributing.
 

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Discussion Starter #50 (Edited)
OK update time,

I bought three JBL GTO 1502D 15" bass drivers, for a total of £70 . I am awaiting another one from an ebay seller (but this deal looks like it may be going sour, I was the only bidder, 99p with £10 delivery, but he is not responding :waiting:)

Anyway I guess this is it, do I build one per cab or a cab with two and build another later when I get another driver?

Will two single cabs side by side go as low and as loud as a dual 15?

I am still having PC problems, and WinISD seems to be showing a wild dip in SPL before 20hz or so? So what options are recommended?

Cheers,
Steve

The only TS Parameters I could find for this driver. (Can anyone confirm these or show their results with WinISD :sad:)

DIAMETER: 15" (381MM)
SENSITIVITY (2.83 V @ 1 M): 93 dB
POWER HANDLING: 300 WRMS 1200 W PEAK
FREQUENCY RESPONSE: 23 ~ 400 HZ
NOMINAL IMPEDANCE: 1 or 4 OHMS
VOICE-COIL DIAMETER: 2.0" (51.0 MM)

DIMENSIONS: mounting depth 5-5/8" (143 mm), cutout diameter 13-7/16" (341mm), outer diameter 15-1/16" (383mm)

VOICE COIL DC RESISTANCE: REVC (OHMS) . . . . . . 0.96
VOICE COIL INDUCTANCE @ 1 KHZ: LEVC (MH) . . . . . . . 0.50
DRIVER RADIATING AREA: SD (IN2) . . . . . . . 132.53
SD (M2) . . . . . . . 855.00
MOTOR FORCE FACTOR: BL (TM) . . . . . . . . 8.20
COMPLIANCE VOLUME: VAS (FT3) . . . . . . . . 6.04
VAS (LITERS) . . . . 171.00
SUSPENSION COMPLIANCE: CMS (μM/N) . . . . 164.70
MOVING MASS, AIR LOAD: MMS (GRAMS). . . . 246.90
MOVING MASS, DIAPHRAGM: MMD (GRAMS) . . . 232.50
FREE-AIR RESONANCE: FS (HZ) . . . . . . . . 25.00
MECHANICAL Q: QMS . . . . . . . . . . . 6.08
ELECTRICAL Q: QES . . . . . . . . . . . 0.55
TOTAL Q: QTS . . . . . . . . . . . . 0.51
MAGNETIC-GAP HEIGHT: HAG (IN) . . . . . . . . 3/8
HAG (MM) . . . . . . . . 9.00
VOICE-COIL HEIGHT: HVC (IN) . . . . . . . . . 1.00
HVC (MM) . . . . . . . . . . 26
MAXIMUM EXCURSION: XMAX (IN) . . . . . . . 5/16
XMAX (MM) . . . . . . . 8.50

Edit, I have to say I am getting rather poor results with the above parameters, even when following JBL's enclosure design for this driver in a twin ported 96litre box it's conflicting?
 

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Discussion Starter #52
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
 

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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.
 

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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. :T
 

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Discussion Starter #59
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
 

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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.
 
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