Critique this AV15-X build - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 23 Old 07-06-09, 11:34 PM Thread Starter
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Critique this AV15-X build

Hi everyone,

I'm gearing up to build a ported AV15-X design. I'm constrained by WAF and also don't want a box that is too big that it takes over the room. I'm mostly interested in Home Theater application, but it should also do music. So probably 80 HT, 20 Music. I understand the sub will be a bit of a compromise, but that is ok. I've built two DIY subs before, but both have been sealed. This is my first venture into the ported world.

So here's what I've come up with so far: 26" x 21" x 28" hwd design, similar to Neo Dan's Easy Button End Table design. The internal volume before bracing or ports is roughly 7.7 cubic feet. This will have 3 ports, 2" x 66" in length. With 3 vertical internal braces and 2 horizontal which form the ports, exactly like the easy button end table design. After port & brace displacement, the volume will be 5.045 cubic feet. I'm still undecided on the amp / eq combination, but I'm thinking of ep2500 & bfd 1124. Anything else I need?

Attached are bass box pro simulations. Should I do anything differently? The box outer dimensions are about as far as I want to go.

Thanks
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Last edited by denkenz; 07-06-09 at 11:40 PM.
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post #2 of 23 Old 07-07-09, 01:57 AM
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Re: Critique this AV15-X build

Quote:
Should I do anything differently?
Yes, you need to start over. 26" x 21" x 28" would have an internal volume of 7.3 cu.ft. Ports, sub and bracing would be about 1 cu.ft. Net volume would be 6.3 cu.ft. With 1000 watts input you would need a rumble filter at 18 hz. Porting would be two 4 inch flared ports 24.75" long to tune the box to 20 hz. Air speed would be maximum 30 m/s at 18 hz. It would not be possible to use three 2 inch ports as the airspeed would be 80 m/s.

Here's a box volume calculator that will take everything into account.

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

FYI - 5 cu.ft with three 2 inch ports 66 inches long would result in a tuning frequency of 8.6 hz.

Critique this AV15-X build-15x.jpg




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post #3 of 23 Old 07-07-09, 07:36 AM
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Re: Critique this AV15-X build

If you are planning on building one you should probably order the sub now, I have been waiting 4 weeks for mine and was told it might ship this friday.
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post #4 of 23 Old 07-07-09, 11:42 AM Thread Starter
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Re: Critique this AV15-X build

Hi Mike,

Oops, you're right about the box volume, I mis-remembered that. Here are the calculations: Internal box dimensions are 24.5 h x 19.5 w x 26.5 depth which gives an internal volume of 7.327 ft3.

I will be using a 2" wide slot port, with two 2x0.75 braces running the length of the port. This results in a 2" x 6" x 66" port length, which gives me a tuning of right around 17.

The port volume + port bracing displacement is 19.5 x 2 x 66 = 1.49 ft3. There will be roughly 5 braces displacing about 0.82 ft3 of space. This gives a net volume of roughly 5 ft3 and F3 of ~39 Hz. Do you guys think I should tune higher for better F3 but sacrifice low end?
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post #5 of 23 Old 07-07-09, 11:44 AM Thread Starter
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Re: Critique this AV15-X build

I actually already have the driver
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post #6 of 23 Old 07-07-09, 12:06 PM
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Re: Critique this AV15-X build

Slot port, understood. Your first port resonance is 109 hz, it should be 125 hz minimum if using a 4 th order crossover at 80 hz. A slot port that is 2" high by 16.75" wide would do it with one .75 wide brace down the middle.




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post #7 of 23 Old 07-07-09, 12:32 PM Thread Starter
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Re: Critique this AV15-X build

Hi Mike,

Yes I'm aware of the 1st port resonance being too low. However, I'm going by what NEO Dan has said in the Easy Button End Table MAX thread over on AVSForum. Since the box design is extremely similar, I'm hoping the resonance won't be a significant issue (WinISD shows ~80 hz 1st port resonance on the easy button end table max design)

17Hz seems to be the lowest practical tuning I can get in this box. I'm still wondering whether I should tune higher for lower F3...
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post #8 of 23 Old 07-07-09, 12:39 PM
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Re: Critique this AV15-X build

Tuning to 20 hz would only give a 1 db increase in SPL in the 20 to 30 hz range. The disadvantage would be reaching Xmax at 17 hz compared to 14 hz with a 17 hz tune, assuming you aren't using a rumble filter.




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post #9 of 23 Old 07-07-09, 02:17 PM
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Re: Critique this AV15-X build

2" x 6" seems like far too little cross sectional port area for a 15" driver.

Don't underestimate the significance of a low first port resonance unless you want to hear the same tone rearing it's head on a fair amount of material. 109hz is way, way, way too low. I would strongly recommend keeping it above 190hz.

You acknowledge this subwoofer is going to be a compromise, yet you're still trying to get your cake and eat it to. Something has to give. Raise the tuning into the low 20s and use a highpass filter - that's the best fit for this size subwoofer.


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post #10 of 23 Old 07-07-09, 02:29 PM
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Re: Critique this AV15-X build

Quote:
denkenz wrote: View Post
I actually already have the driver
well, I already have a 7ft3 box tuned to 19hz ready, so you could ship it to me and i will let you know how it sounds
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