JBL GTx 10 Question

**Alex2507** · **05-11-08, 09:35 AM**

A friend has a couple of these kicking around in his garage. My primary question is whether or not it would be worth while to build enclosures and buy amps to use these as a LF extention of my left and right speakers. I'm new to sub building but already understand that I don't know anything at all about it. Hearing that this would be a waste of time would free me up so that I could contemplate other options so there is no need to worry about insulting my "stuff". It's only stuff and it's not even mine.

This is the only info I could come up with on these subs:

Re: JBL GTx 10 parameters

Freq response: 30Hz-500Hz
Amp. Power Range: 20W-500W
Continious Power Handling: 250W
Peak Power Handling: 450W
Voice Coil dia: 2,0" (51mm)
Nominal Impedance: 4 Ohms
Sensitivity@2.83V RMS@1M: 87dB
Driver Displacement: 0,09 cu.ft. (2,55l)

Thiele-Small Parameters:
Fs = 31Hz
Vas = 1,85 ft² (52,4l)
Qts = 0,43
Qes = 0,45
Qms = 7,55
Re = 3,3Ohms
Le = 0,6mH
Xmax = 0,480 in. (12,2mm)
Xpk = 0,866 in. (22mm)
Sd = 0,3724 Sq. Ft. (0,0346 Sq.M.)
Vd-linear = 0,000422 Cu. M.
Vd-peak = 0,000761 Cu. M.

Thanks,
Alex

**Canadian_Dude** · **05-11-08, 11:34 AM**

I think this speaker has too little xmax to be very useful, but I am no expert. I modeled it in a 20" cube both sealed and ported and in a sealed box you get a -3db of about 60 Hz and in a vented box you get about 25 Hz at -3db. You would need a high pass filter for sure on the vented box at about 24 Hz and you hit xmax in the sealed box around 32 Hz.

This is the response curve:
(green is ported and blue is sealed)

And this is cone displacement:
(same colors)

**blaser** · **05-11-08, 01:47 PM**

This sub should be fine in 80 L, 25 Hz Tune, 4" (41 cm long) port and 300/350 W amp, a high pass is req. as tune is quite high

Here is WinISD modelling

**Alex2507** · **05-11-08, 08:05 PM**

Quote:

Canadian_Dude wrote:

I think this speaker has too little xmax to be very useful, but I am no expert. I modeled it in a 20" cube both sealed and ported and in a sealed box you get a -3db of about 60 Hz and in a vented box you get about 25 Hz at -3db. You would need a high pass filter for sure on the vented box at about 24 Hz and you hit xmax in the sealed box around 32 Hz.

Thank you Canadian_Dude,

It's usefulness has to be looked at in the function that it's intended for: the bottom end of a single channel main speaker that is X'ed-over at 80Hz and almost never gets played at reference levels because I live in a condo. I'm not looking for big bass, just nice well integrated bass. From you're post I understand that I need a ported enclosure with an internal volume of 8,000 cubic inches. I'm hoping that I'm allowed to reach that volume using dimensions other than a 20 inch cube.

I will have to do a little more learning to understand most of the other info info in your response. BTW, I went to high school in Calgary and visited Edmonton a time or two.

-Alex

Quote:

blaser wrote:

This sub should be fine in 80 L, 25 Hz Tune, 4" (41 cm long) port and 300/350 W amp, a high pass is req. as tune is quite high

Hi blaser,

I feel kind of like a kid in a candy store coming back to see two responses with graphs everywhere. Let me admit that I think 80 L is 80 liters and even though I'm not sure how big that really is, it sounds huge. Being a condo dweller, size really matters. Depth is my real enemy. Going with Canadian Dude's 8,000 cubic inch figure, I'm hoping to be able to use an internal set of dimensions of 12"x25"x27" DxHxW. That leaves 100 cubic inches for bracing. I know I want front firing and front or side porting is fine. It's starting to look like I am going to have to learn what all those little letters really mean. With any luck, by the time I figure this out, I will have had some fun and will walk away with a couple of subs to use as extensions of my left and right mains.

Best regards,
Alex

Note: I still have to decide to do this. I'm thinking of it as a good first step in sub building and a realatively inexpensive upgrade in SQ. I know there's lots to learn but I have time. Thoughts and suggestions are always welcome and I'm not thin skinned so you can say it like it is.

**blaser** · **05-11-08, 09:55 PM**

Alex,

How much space do you have? Give me dimensions and I'll suggest something.

**Alex2507** · **05-12-08, 04:16 AM**

Quote:

blaser wrote:

Alex,

How much space do you have? Give me dimensions and I'll suggest something.

The 12"x25"x27" DxHxW internal dimension mentioned above is about it. I want to say up front that I already know that these drivers might not be for me. There is nothing that says that says I can't buy a couple of Infinity Kappa Perfect VQ10's (?) down the road a ways. It's been a long time since I did metric conversions and only had time to get my hands on a chart last night.

Gotta go to work.

**blaser** · **05-12-08, 04:56 AM**

Why would they not work for you? Do you already have them? The boxes they need are not big FYI!

**blaser** · **05-12-08, 05:29 AM**

You need about 3 cu ft internal volume (including port volume excluding bracing). So Your dimensions could be 11.5*24*19" / box and that would be within the specified dimensions above.

**Alex2507** · **05-12-08, 04:25 PM**

Quote:

blaser wrote:

You need about 3 cu ft internal volume (including port volume excluding bracing). So Your dimensions could be 11.5*24*19" / box and that would be within the specified dimensions above.

Oh...okay. I misunderstood 80 L to mean 80 liters and did a quick mental conversion and thought of 20 US gallons and pictured four 5 gallon jugs of water that go on an office type water cooler. My mistake. I'm back on track now. What does "80 L" mean refer to?

Yes, the dimensions you came up with are well within my requirements and yes I have the drivers. Actually they belong to a friend but I could have them for the asking. Now that I understand that they can be used in this application, I will ask. This upcoming weekend I will test them. I'm sure that they are fine but I want to be positive.

I guess the next step for me is deciding what material to use for the enclosure. My first instinct is to go with 1" MDF. For the braces I thought to use 1"x1" oak. I'm not sure how this works but a set of plans/drawings would really do it for me. Do I need to come up with my own design or is there an easier way? I build things off of drawings regularly. I'm not at all afraid to build a slotted port.

**blaser** · **05-12-08, 04:44 PM**

Quote:

Alex2507 wrote:

What does "80 L" mean refer to?

80 L is 80 Liters.
1 cuft = 28.3 L

Quote:

I guess the next step for me is deciding what material to use for the enclosure. My first instinct is to go with 1" MDF.

OK, plywood is OK as well

Quote:

For the braces I thought to use 1"x1" oak. I'm not sure how this works but a set of plans/drawings would really do it for me. Do I need to come up with my own design or is there an easier way? I build things off of drawings regularly. I'm not at all afraid to build a slotted port.

Pls visit The members subwoofer database for ideas. You'll find my design to be the simplest (I think) and works very well.

**Alex2507** · **05-12-08, 06:49 PM**

25 years ago I went to high school in Canada and one of the things I remember about the metric system or SI is that 1 mm cubed is 1 mL. So I used that to confirm your conversion. It still doesn't seem reasonable but that is mind just not being able to get around it yet. Thank you for bearing with me.

I briefly checked out your sub build thread. Wow, all the way from Cairo! I am amazed by that. How do your neighbors like you now with those subs?

I have some reading to do and I have some time but one thing I do know to ask is about the port. What size and what length including the flares/flanges?

Thanks again,
Alex

**Canadian_Dude** · **05-12-08, 07:06 PM**

I think I agree with blaser... 80L is plenty big enough. I had no idea how much space you had so I just picked a number. With the 80L box and a 25Hz tune it looks nice. The extra 50L from the 20" cube makes very little difference. As for the box; the most common material is 3/4" MDF because it's super cheap and very dense. If you wanted you could get the diy plans from www.rythmikaudio.com and just cut the appropriate sized hole for your driver.

**blaser** · **05-13-08, 12:28 AM**

Quote:

Alex2507 wrote:

I briefly checked out your sub build thread. Wow, all the way from Cairo! I am amazed by that. How do your neighbors like you now with those subs?

Thank you. Just wanna hint out my brother's beadroom is below my HT

. During the day, I can listen loud nobody complains, nevertheless I can make them complain if I wanted to

, but one has to chose suitable moments not to disturb the others...

Quote:

I have some reading to do and I have some time but one thing I do know to ask is about the port. What size and what length including the flares/flanges?

4" diameter, 16.15" long including flare.

**Alex2507** · **05-13-08, 03:38 AM**

Thanks for your responses guys.

This meets my ten post objective. The design part of this is going to be time consuming for me. The drivers are still sitting safely on a shelf in my friends garage as they have been for years waiting to be put to use.

Back to the time thing, once again I'm out of it. Now it's time for me to be off to work. I guess my next step is to gather up some materials.

-Alex

**blaser** · **05-13-08, 04:20 AM**

It is not that difficult. I completed my subs in 4-5 full days. Yours are smaller and should take less time

**Alex2507** · **05-13-08, 07:22 PM**

Just an heads up that we have some forward progress. I realized that I have a book called The Car Stereo Cookbook which has a subwoofer section. Well I took it with me this morning to read on the train on the way to work. Of course My T/S parameters where at home but I'll have 'em with me tomorrow along with a calculator. If nothing else it'll reaquaint me with a calculator.

Every sub build has a beginning and this seems to be mine. Thanks for the encouragement and the help. I'm sure to be back with more questions.

-Alex

**blaser** · **05-13-08, 11:29 PM**

Anytime...

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