JBL GTO 1514, 15" sealed budget build - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 9 Old 01-04-14, 03:44 PM Thread Starter
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JBL GTO 1514, 15" sealed budget build

Hello, first time building anything, so I'll gladly take any suggestions you might come up with.

Due to space constraints, I couldn't have built the massive LLT subwoofer I wanted. My efficiency requirements are not massive so I figured I might as well build a sealed one, in hopes of also minimizing the amount of things that could potentially go wrong (port noise, resonances..). I also realized that since I won't be demanding more than moderate/low SPL from the subwoofer, I could also sacrifice some dynamic range to even out the frequency response! WinISD gave me a rather good looking simulation in a 165 liter cabinet excluding the volume of bracing and the sub element itself (so around 155L I presume).

Unfortunately the only type of plywood available was 15 millimeters thick, and I'm afraid it might be a bit thin and cause resonances easily, especially in combination with the large-ish dimensions. Hopefully the bracing is at least somewhat adequate.

External dimensions: 53cm x 53cm x 70cm

Pictures of the build:

We had very little wood to build with so we went with rather minimalistic bracing. Do you think it's enough for moderate volumes?

After the bracing and sides were glued and screwed into place (we used 3 screws for the 50cm sides and 4 screws for the 70cm sides), we put some 1.5" construction wool on the insides of the cabinet. It's fairly dense and heavy so I assume it goes some way to dampen the case, taking opinions!

Unfortunately I have to stop the building for today, having a massive migraine.

Coming up:
-attaching the final side to it's place
-sanding/rounding the edges and corners, painting, and of course measurements.
- ground plane THD and freq. response measurements with a t.bone MM-1 uncalibrated measurement mic, both running the subwoofer as it is, and with some EQ to even out the 20Hz response. I later on found out that equalizing to bring up the low-end on a sealed subwoofer is called a Linkwitz-transform. I'm not using a peaking shelf filter to accomplish this, as it seems that a regular parametric EQ works just as well while being slightly more efficient (besides I want to test that out since I came up with the idea myself)

Unfortunately I don't have a calibrated microphone, but I only need the relative measurements of half-space versus my own room to calculate the room gain below 50Hz. After I know the room gain, I can begin doing both room correction and adjustments to the low-end boosting EQ, to see do I prefer in-room flat, or half-space flat Science is fun!
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post #2 of 9 Old 01-04-14, 05:42 PM
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Re: JBL GTO 1514, 15" sealed budget build

What woofer are you using?

I would say YES, your cabinet walls will flex. If using small thickness ply I would either use double layer or brace at every 6" point. The baffle I always tend to do a double baffle. You can get away with a single one but the baffle may flex.

What length of screws are you using?

"Music is the space between the notes"
[T]o talk well and eloquently is a very great art, but that an equally great one is to know the right moment to stop.
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post #3 of 9 Old 01-04-14, 07:59 PM
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Re: JBL GTO 1514, 15" sealed budget build

Did you use wood glue when you put the panels together?
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post #4 of 9 Old 01-05-14, 04:14 AM Thread Starter
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The subwoofer is a JBL GTO 1514

Wood glue and about two inch screws were used. I'll see if I could get one or two more braces in from the leftover bits, a double baffle is possible from the last leftover bit.

I suppose the speaker should be remounted onto a double thickness baffle, rather than have the other baffle board mounted "around" the current mount, which might be aesthetically a bit more pleasing?
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post #5 of 9 Old 01-05-14, 04:44 AM
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Re: JBL GTO 1514, 15" sealed budget build

You can add a another panel around the currently mounted driver, that is how a flush mount is achieved.
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post #6 of 9 Old 01-05-14, 12:22 PM Thread Starter
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Re: JBL GTO 1514, 15" sealed budget build

My dad didn't have the patience to wait until we finished the second baffle, so we sealed it up and tested some tracks and movie scenes (this was something of a father-son project which was very nice tbh). I'm feeding it with a Yamaha R-V596 which gives aboutsies 190W to 4 ohms, and there are no significant/perceptible resonances so far, which leaves me very positively surprised!

Here's a preliminary in-room sine sweep, I had the 2nd order low-pass at 60Hz and a +9dB 20Hz Q 1.5 parametric EQ with -9.0dB of static gain to even out the response with a "ghetto Linkwitz-transform".

EDIT: just watched some Avatar scenes with big explosions after moving the sub to the movie room. My opinion of course is not educated as my previous subwoofer was a 3" bandpass with a passive radiator by Logitech, but wow. For small rooms (which this is built for mostly) I can't say I'd need more.

I'll be working on the front baffle and visual aspect of the wubwub later!

Last edited by seepra; 01-05-14 at 03:11 PM.
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post #7 of 9 Old 01-05-14, 03:29 PM
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Re: JBL GTO 1514, 15" sealed budget build

Nice build, Oh by the way we all said we didn't need more.

Onkyo TX-NR809 HT receiver
HPS-4000,SR-70, John Allen, Klipsch Heresy, Speakers for L.C.R.
QSC GX-5 power amp for L+R mains
Chase Home Theater PRO-10's for surrounds
Behringer EP 4000 pro amp for the Danley DTS-10 tapped horn sub
Oppo BDP-93 universal BD player
Toshiba HD XA2 HD dvd player
Sony VW-VPLPRO1 1080p PJ
Cinema White 1.0 gain 106" fixed frame screen
Dish network with 2 Hoppers and 1 Joey
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post #8 of 9 Old 01-10-14, 01:19 PM
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Re: JBL GTO 1514, 15" sealed budget build

tcarcio wrote: View Post
Nice build, Oh by the way we all said we didn't need more.
I wonder which one of us here at the Shack will be the first person to actually LIVE inside a giant subwoofer. Using something like Moore's Law for subwoofers, can we really be that far away from it? I'm no Nostradamus, but I predict that it will happen eventually.

- OJ -
DIY Ported Original Tempest Sub (offline)
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post #9 of 9 Old 02-10-14, 01:26 PM
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Re: JBL GTO 1514, 15" sealed budget build

Excellent subwoofer for the money
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budget , build , jbl gto 1514 15 , sealed

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