Critique this AV15-X build

**denkenz** · **07-07-09, 12:34 AM**

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

**Mike P.** · **07-07-09, 02:57 AM**

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.

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**driscoz71** · **07-07-09, 08:36 AM**

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.

**denkenz** · **07-07-09, 12:42 PM**

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?

**denkenz** · **07-07-09, 12:44 PM**

I actually already have the driver

**Mike P.** · **07-07-09, 01:06 PM**

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.

**denkenz** · **07-07-09, 01:32 PM**

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...

**Mike P.** · **07-07-09, 01:39 PM**

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.

**SteveCallas** · **07-07-09, 03:17 PM**

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.

**driscoz71** · **07-07-09, 03:29 PM**

Quote:

denkenz wrote:

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

**spanish68** · **07-07-09, 06:01 PM**

You can always use a PR design to save some space but will cost you more $. I'm still waiting for my AV15X driver to arrive (almost two months now) and the PR18-2100's which I ordered a couple of weeks ago. I will be building a PR set-up with 7cf (internal box) tuned to 16hz.

**driscoz71** · **07-07-09, 06:23 PM**

Quote:

spanish68 wrote:

You can always use a PR design to save some space but will cost you more $. I'm still waiting for my AV15X driver to arrive (almost two months now) and the PR18-2100's which I ordered a couple of weeks ago. I will be building a PR set-up with 7cf (internal box) tuned to 16hz.

I was told today that they hope to be completely caught up with the AV speakers on Friday.

**Mike P.** · **07-07-09, 08:12 PM**

Quote:

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

Air speed is not an issue if the port is built properly.

**denkenz** · **07-07-09, 08:18 PM**

I'm really interested in understanding whether slot ports that are bent multiple times really offer a way to cheat port resonance.

NEODan's designs are quite popular over on AVSforum and don't offer huge volume (typical design is roughly 8 ft3 after port / brace displacement), but are geared towards an 18" driver with 14Hz tune. The outer dimensions are 24x26.5x37.5 if I recall.

When I model such a design in WinISD I get port resonance of around 80, even worse than for my 5 ft3 box.

**Mike P.** · **07-07-09, 08:26 PM**

With a port resonance of around 80 hz you would have to use a lower 4th order crossover. With a 125 port resonance a 4th order crossover at 80 hz would do. Of course some people will argue the point as there hasn't been that much testing done on it. Just remember the fact that this is about HT subs and not critical music listening which is more demanding.

**looneybomber** · **07-14-09, 02:27 PM**

You can always modify Neo's easy button box. Shortening the port length increases the box volume. Or, design your own box with your own dimensions where it'll fit best in your room. That's the good thing about DIY, you get to custom build things to your specs with what fits best for you and your room.

**denkenz** · **11-02-09, 02:38 PM**

Sorry to resurrect an old thread, but I finally got done with all the woodworking for the box. I had to do quite a bit of traveling, so no time for my hobby

I managed to also get a first set of REW results. The level was calibrated using the Radio Shack 4050 to 75db. I'm using the ECM8000 to do the actual testing. The first sweep (in red) is at the listening position, using -12db. The second sweep (in blue) is with the microphone pointing directly at the sub about 1 meter away. I didn't calibrate with the SPL meter for the second sweep. This one is at -18db.

Since this is my first vented sub / REW experience, can anyone comment on if there's any problems/issues that might be visible from the REW graphs? Any other sweeps I should perform?

I'm using an older Pioneer VSX-D912 to drive the sub, no dedicated amp yet. The crossover is set at 100.

**sub_crazy** · **11-02-09, 10:19 PM**

Really nice looking sub. Got any more pics including the build process?

The REW graph is impressive down low, the only problem I can see is the dip in the 35 to 45 range but you may be able to move it around to alleviate that at your listening position.

**fredk** · **11-03-09, 02:57 PM**

It amazes me that you are getting some 30db of room gain at 10Hz! If you were using a radioshack meter I would question the measurement, but your ecm should be accurate that low.

Thats a very nice sub you have built. Had you done any veneer work before building it?

**denkenz** · **11-03-09, 05:03 PM**

I didn't take too many pics, but here's what I have:

Initial concept stage. Largely based on the End Table MAX design by NeoDan, but modified to be suitable for veneering and rounding outside corners later on.

Playing with bracing & vent ideas:

Mostly assembled, this is how the bracing turned out:

The vent was rounded over using a 1.5" roundover bit on the bottom and using a 3/4" roundover bit at the top.

Close up of the supporting brace. I made the cutout just large enough to slip in some closed cell foam tape. Once the driver passes through it sits in there very tightly.

Overall the vent length is roughly ~46-47 inches long by 2.5 inches high by 11 inches wide.

The vent trim piece is made from a whole piece of MDF. The outside was cut on a table saw to fit precisely into the opening of the vent. I then did a rough cut of the inside using a jig saw. Installed into the baffle and then used a 3/4" roundover bit with a bearing guide to roundover the trim and make it flush with the rest of the vent. The piece was then painted.

Testing that everything fits:

REW Testing. This picture shows off the rounded corners. I used a 1.5"

roundover bit for this. Was extremely painful process with a box that size, but I think the results are worth it.

Final dimensions are 21 wide, by 28 deep by 26 high. Still needs to have the final finish applied and attach the feet.

**denkenz** · **11-03-09, 05:06 PM**

More like 21db according to the refined model. This is my 3rd subwoofer project (the first two were both sealed) and the 4th project using veneer. So I'm still a bit of a newbie at this. The box was by no means perfect, there were plenty of little mistakes made. A good learning experience.

**sub_crazy** · **11-03-09, 05:27 PM**

That's an extremely impressive build

I really like the way the port looks and the veneer work is pro quality. One of the better looking DIY projects I have seen.

Thanks for sharing.

**spanish68** · **11-03-09, 05:59 PM**

Very nice work indeed! I like the finish too! I have the AV15X sub in a 7cf PR enclousure with ED LT1300 amp, tuned to 15.5hz. You will like it, specially its mid-bass. The SQ on this sub is excellent. Like you, I have the magnet of the sub resting in the brace. I finished mine a few weeks ago and I need to post it here.

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