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

[Parts]

Hi guys,

The room layout is a bit of an issue, its a solid concrete floor, but a suspended tile ceiling, walls are of the alloy stud partition with plasterboard and some of that is plywood skimmed. Within the center of that room on the left and right of the listening position, equaly distance at the points the room divides by three, are two large workstation/benches. Kit is brought in and not permanent in it's installation. Me and a collegue put the system together as a cinema away from home, we both have young children and had to make compromises at home. We were able to utilise a large workshop (within a large warehouse) at work under certain conditions.
We have an HD projector with a Sony Blueray player and the big Yamaha, I had picked the Cerwin Vega's due to their sensitivity and the room size, and they work quite well, apart from I feel they roll off around 50-40hz, plus the room is a little reflective and the amp is a little underpowerd.

The speaker placement is equidistant in a full circle around the listening area, with the 30deg and 110deg angles, seen in some diagrams. That seemed to offer the best set of performance and compromise in the room.

I would prefer the sub to be in line with the center/mains for now, the corners are quite a bit farther away than the mains, so it would probably have some sort of compromise.

My reasons for thinking of this 15" JBL is cost (around £70 per driver), I have plenty of 1" chipboard and 2"+2" batton, so now just need to work out an enclosure to stick two of these 15" JBL's in.

It will probably be rather ugly and rough, with plenty of screws and glue, I do not have a table saw so will make do with the basics. I can dress it up later (PA style to match the Cerwins and functionality), and will want to add some sort of metal grill to protect the drivers. If it works out cheap easy and functional, I may build an identical sub with another two 15" JBL's later, running of the left and right outputs of the EP4000. And probably have the pair flanking the centre.

I have also heard the 12" version of this, and it sounded far better than the Fusion 12" high excursion car sub I tried.

I am probably going to get a Behringer EP4000 for the subs, so how would I add a rumble filter to this amp? And would running the subs in series not affect the amplifier dampening capabilities? I am not sure if the JBL manual for the GT4-15 states parallel wireing and sealed cabs as better due to use in cars?

I will still contemplate a more elaborate design later, but think budget first, and build up from there, it should be a good learning experience

So does anyone have the TS parameters for the JBL GT4-15 sunwoofer? Or suitable cabinet drawings for a cab to house two of these?

And any graphs showing its sealed performance versus ported?

Thankyou,
Steve

[Mike P.]

The basic parameters are in your other thread, there are enough specs to model the sub.
Car audio recommendations have nothing to do with HT subs, they are different animals.
A rumble filter can be added by an outboard unit like the Reckhorn B1.
You can figure out cabinet dimensions from the calculator here:

http://www.hometheatershack.com/foru...me-calculator/

Green is ported, yellow is sealed. Ported is 7 cu.ft. for one sub, tuned to 25 hz. Double the volume for 2 subs.

[Parts]

Not quite sure if its me being a numpty, but I have no idea what I am doing with the Parameters and WinISD?

Where do I put sensitivity and power handling etc, I seem to have mine set up for litres not cubic ft too LOL...

Earlier I had played with the GTX 15 figures and noticed the graph looking good with a 600 litre cab with a 23.43 tuning? (the original cab was 491.53)

Need to work out this WinISD stuff, though I think its got an issue with Windows 7

[Mike P.]

Earlier I had played with the GTX 15 figures and noticed the graph looking good with a 600 litre cab with a 23.43 tuning?

The bigger the cabinet the less power it takes to reach Xmax. I'll post the file for the sub when I get off work. There is a WinISD tutorial here:

http://www.hometheatershack.com/foru...inisd-pro.html

If Windows 7 has a program compatitbility option, set it for Windows XP.

[Parts]

Ok,

I have decided to spend up to or around £400 for this first project, now just looking for a bit of opinion on what I am better buying?

Am I better getting a Behringer EP4000 amplifier, as it looks reasonable for the money and is used by some in here, which seems like good credentials, or the BK 500w into 4ohm subwoofer amp mentioned above?. I will have to leave the rumble filter until later/next month (no idea whats available in the UK).

These are my current options of low cost subwoofer drivers, all car audio,

JBL GT5-15, 15" 1500w subwoofer driver £49.95
JBL GTO1502D 15" 1200W subwoofer driver £54.99
JBL GT4-15 15" 1000w Subwoofer driver £54.72

Well they are the cheapest prices for 15" drivers I could find.
The Eminence, PD and Fane models are all between £130 to £200, I can get two 18" Kilomaxes for £350, and a Vibe Black Death subwoofer (the off the shelf ported box item) for £400.

I am unsure if I am better off with two seperate 15" subs or a single sub with two 15" drivers?

Tonight the amp and drivers, tommorow working out the cabinet! (I guess )

[Mike P.]

Without knowing the parameters of the JBL GT5-15 and JBL GTO1502D, they would probably only be better if they had a lower Fs or higher Xmax.

I have always gone with separate subs, it allows more placement options.

[Ricci]

Is the 400 budget for just drivers or amp and drivers?

I think that 4 GT5-15's would be a good plan.

[Parts]

Well I cannot seem to get WinISD to save the parameters of the JBL GT5-15 driver, even though I have loaded the stated TS parameters I get a "Parameter Error list" for Qts, Qms, Qes and the help button does not work.

This is the GT5-15 Parameters,

DIAMETER: 15" (381MM)
SENSITIVITY (2.83V @ 1M): 92dB
POWER HANDLING: 300WRMS 1200WPEAK
FREQUENCY RESPONSE: 25Hz – 400Hz
NOMINAL IMPEDANCE: 4 OHMS
VOICE-COIL DIAMETER: 2" (51MM)
DIMENSIONS:
THIELE-SMALL PARAMETERS
VOICE-COIL DC RESISTANCE: REVC (OHMS) . . . . . . 3.63
VOICE-COIL INDUCTANCE @ 1KHZ: LEVC (MH) . . . . . . . 2.42
DRIVER RADIATING AREA: SD (IN2) . . . . . . . . 132.5
SD (M2) . . . . . . . 855.00
MOTOR FORCE FACTOR: BL (TM) . . . . . . . . 16.53
COMPLIANCE VOLUME: VAS (FT3). . . . . . . . . 3.76
VAS (LITERS) . . . . . 106.5
SUSPENSION COMPLIANCE: CMS (μM/N) . . . . 102.00
MOVING MASS, AIR LOAD: MMS (GRAMS). . . . 332.00
MOVING MASS, DIAPHRAGM: MMD (GRAMS) . . . 317.00
FREE-AIR RESONANCE: FS (HZ) . . . . . . . . 27.30
MECHANICAL Q: QMS . . . . . . . . . . . 5.70
ELECTRICAL Q: QES . . . . . . . . . . . 0.76
TOTAL Q: QTS . . . . . . . . . . . . 0.67
MAGNETIC-GAP HEIGHT: HAG (IN) . . . . . . . . . 0.31
HAG (MM) . . . . . . . . 8.00
VOICE-COIL HEIGHT: HVC (IN) . . . . . . . . . 1.45
HVC (MM). . . . . . . . . . 37
MAXIMUM EXCURSION: XMAX (IN) . . . . . . . . 0.57
XMAX (MM) . . . . . . 14.50

For £70 the JBL GT)1514 driver is available, and it seems to have a better spec, but I cannot load these either without the same error?

DIAMETER: 15" (381MM)
SENSITIVITY (2.83V @ 1M): 93dB
POWER HANDLING: 350WRMS (1400WPEAK)
FREQUENCY RESPONSE: 23HZ ~ 400HZ
NOMINAL IMPEDANCE: 4 OHMS
VOICE COIL DIAMETER: 2.0" (51.0MM)
DIMENSIONS: mounting depth 6-13/16" (172mm) cutout diameter 13-15/16" (354mm) outer diameter 15-5/16" (389mm)

THIELE-SMALL PARAMETERS
VOICE COIL DC RESISTANCE: REVC (OHMS) . . . . . . 3.80
VOICE COIL INDUCTANCE@ 1KHZ: LEVC (MH) . . . . . . . 3.05
DRIVER RADIATING AREA: SD (IN2) . . . . . . . . 128.7
SD (M2) . . . . . . . 830.00
MOTOR FORCE FACTOR: BL (TM) . . . . . . . . 17.13
COMPLIANCE VOLUME: VAS (FT3). . . . . . . . . 5.42
VAS (LITERS). . . . . 153.50
SUSPENSION COMPLIANCE: CMS (μM/N) . . . . 156.00
MOVING MASS, AIR LOAD: MMS
MD
(GRAMS) . . . 257.00
MOVING MASS, DIAPHRAGM: M (GRAMS) . . . 243.00
FREE-AIR RESONANCE: FS (HZ) . . . . . . . . 25.10
MECHANICAL Q: QMS . . . . . . . . . . . 7.08
ELECTRICAL Q: QES . . . . . . . . . . . 0.52
TOTAL Q: QTS . . . . . . . . . . . 0.49
MAGNETIC-GAP HEIGHT: HAG (IN) . . . . . . . . . 0.31
HAG (MM) . . . . . . . . 8.00
VOICE COIL HEIGHT: HVC (IN) . . . . . . . . . 1.45
HVC (MM). . . . . . . . . . 37
MAXIMUM EXCURSION: XMAX (IN). . . . . . . . .0.57
XMAX (MM) . . . . . . 14.50

I am still looking around to see what drivers are available, UK seems pretty poor for choice. Still can't decide on a couple of cheaper car 15" drivers such as the above, or a pro 18" driver?

[brandonnash]

Just enter QES, QMS, FS, RE, VAS, MMS, and XMAX and it should work fine. It likes to auto calculate specs and if it doesn't match with winisd's calculations it won't let it go through.

[Parts]

Got it working, had to let WinISD do automatic correction for Qts.

The JBL GTO1514 initially looks pretty even in a 300L box with a tuning freq of 20.3Hz, port length is 4.86" and 4.02 diameter with 1st resonance at 1392.06 Hz?

Having some trouble with the GT5-15 parameters still.... Edit, seems to be working, shows a slightly deviated response with more extension?

Most of the 18" pro audio drivers seem to have the max spl, but the JBL's seem to have more SPL at the lower octaves? This would seem to indicate EQ'ing a large 18" PA driver would be of not much benefit?

It looks like a single 15" JBL 320 litre cab will give me 113db at 20hz and 114db at 40hz, two 15" JBL 640 litre cab will give me 119db and 120db at the same frequencies? Does that sound right?

[Mike P.]

The JBL GTO1514 initially looks pretty even in a 300L box with a tuning freq of 20.3Hz, port length is 4.86" and 4.02 diameter with 1st resonance at 1392.06 Hz?

Model the input power to reach Xmax with the appropriate high pass filter. Then check the port air speed, increase the diameter of the port until the air speed is in the 26 -28 m/s range.

[Mike P.]

The GT5-15 in 10 cu.ft tuned to 18 hz is comparable to the GT1514 in 12 cu.ft. tuned to 18 hz. Both would need a high pass filter at 16 hz.

[Parts]

Quote; Model the input power to reach Xmax with the appropriate high pass filter. Then check the port air speed, increase the diameter of the port until the air speed is in the 26 -28 m/s range.


Any tips on what sort of filter settings I should be playing with?

What box alignment should I be looking at?

I guess I should input power at the signal box? If so doing so shows a massive increase in cone excursion at 28.41hz of 0.557 and then it drops off to 0.251 at around 20hz then shoots up way over the red line.

I guess it has to stay under that line, but so far when playing with port velocity and width to get the speed correct it seems I lose the LF?

Edit you put some details in as I posted, so I should model the high pass filter around the area where cone excursion reaches it's limits? When modeling with two drivers I am doubling cabinet volume and doubling power input?, but port velocity and lengths seem pretty big?

[Mike P.]

Apply a HPF so Xmax is not exceeded.

When modeling with two drivers I am doubling cabinet volume and doubling power input

Yes.

but port velocity and lengths seem pretty big?

Keep the air speed to 26 - 28 m/s.

[Parts]

Is the port length show supposed to be divided by the amounts of ports? As if I have two 5" odd ports, 40" length seems a lot?

[Mike P.]

Is the port length show supposed to be divided by the amounts of ports?

No, the length shown is for each port.

[Parts]

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)

[Mike P.]

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

With 350 watts input and a HPF at 16 hz, two 4 inch ports 18 inches long keep the air speed to a maximum of 25 m/s.

[Ricci]

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.

[Parts]

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

Steve

[Parts]

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

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............

[Mike P.]

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".

[Parts]

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

[Mike P.]

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.

[Parts]

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 )

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 )

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?