Ported 12.5ft^3 AV15-X project (pics)

[VERTIGGO]

I have been on another forum for a while but I'm not getting much input, so I thought I'd hang out here, and if it warrants it, offer my project to be added to the database for anyone else looking at this driver and design.

I chose an AV15-X from Acoustic Elegance and I already have an EP2500 and a BFD1124 ready. This is for a home theater so I went big and plan to tune at 19-22hz. The ports will be two 6"id PVC pipes and I'll add a wood face to the box to flush mount the driver and flare the ports a bit. Here's my work so far:

I ordered a router jig but actually found my saber sawing to be plenty good enough for the internals (impatience is a killer).


I read that a rule of thumb for bracing is to eliminate any area of more than 144"^2, so I added some small pieces to split the large sections of MDF.

I have internal dimensions of 19.5"W, 28.5"H, and 38.25"L which is the "golden" rule. I calculated my effective volume (considering a driver and ports) at 22041"^3 and my two ports are currently at 20.5" each which should give me a 21.67Hz tune. My plan is to tack it together and run a rough test before sealing everything with silicone since I have room to swap out for ~28" ports (~19Hz). I also need to decide on dampening material if it's necessary...

I also got some 6lb. carpet padding for the inside since I'm at a loss as to what else to use... will that be plenty absorbant for any errant high freqs I have to deal with?

[Mike P.]

Welcome! Thanks for posting your build. There won't be any high frequencies to deal with in a sub. Lining the sub does help to damp the back wave. Carpet padding will work if it's open cell, I'm not sure what it is considered though.

[VERTIGGO]

Well its the multi-colored, multi-density stuff which is definitely permeable if that's the issue (as in you could feel the wind through it). My plan was to cover all of the inside walls with at least one layer, though maybe I need more? I can always add poly-fill later.

From what I've read the most important is thickness on the back wall (for me) since that's the lowest resonant dimension... please correct me if you can.

Also, should I tune below 21.67Hz even if it means a curve below the -7db line? I can tune it to 16-19Hz and achieve more sub-sonic response, but the curve will have to be heavily eq'd. Is this fine?

[Mike P.]

I haven't modeled the AV15-X yet. I will when I get a free moment.

[VERTIGGO]

Oh I'm sorry, simon5 at Acoustic Elegance forums modeled this for me:

It looks different in WinISD Beta for me though; it shows me a line at -3 (not -7) and below 45Hz the FR of this design drops below it. I don't know if this is as important as reaching 15Hz or not, but I sure would like to throw in some longer ports (47.5" each) and hit the sub-sonics if the EQ is enough to fix this drop...

[Sonnie]

15Hz looks better to me... I might even tune it a little bit lower.

Sounds like an interesting build.

Can you post the driver file for WinISD?

[Mike P.]

Here is the WinISD file for the AV15-X sub. AE Speakers AV15-X.wdr


22041"^3 is 12.75 cu.ft. Tuning to 17 hz would give you the best combination of low end out put and overall SPL.


The sub will handle 700 watts and you'll need a high pass filter at 15 hz to keep the sub within its Xmax.


Two 6 inch ports need to be 36.78 inches long to tune the box to 17 hz. Port air speed is maximum 18 m/s.

[VERTIGGO]

33" ports is my maximum with 17.85Hz (since my box is only 38.25" inches long), but that looks decent enough, and allows 750W without excursion. Port velocity is a bit higher but not too scary...

The issue I see with going extra long (48") is not necessarily the Vb which has plenty of leeway in this case, but how much it would cut into my maximum power without boosting enough LF to justify it.

[Mike P.]

What are you using for a high pass filter for over excursion protection?

[VERTIGGO]

I don't know how to do that yet actually. I have the EP2500 amp and a BFD1124. Can the BFD do that?

[Mike P.]

I'm not sure. But you're definitely going to need a HPF.

[al bundy]

1124 has no HPF

[VERTIGGO]

Well my remodeled design (33" ports) runs up to 750W without excursion so as long as I keep it down I won't need one.

[Mike P.]

You need to use WinISD Pro. Whether you use 750 watts or 250 watts the sub will bottom out without a HPF if this is a HT sub.

[VERTIGGO]

Oh! I get it. I'm just new to this. It makes sense considering the way movies always bring out the worst in my current subs! I'll have to look into that.

[looneybomber]

Vertiggo. You mentioned tuning lower to pick up the "sub sonic frequencies", which is true, it does that. But most importantly, it adds a bit of safety because it will take a lower frequency to unload the driver. Depending on how loud you listen to movies and how low you tune the box, you may be able to get by without a subsonic filter.

[VERTIGGO]

Well I can't seem to model a design that eliminates that need unless I'm listening at 50% (which I may well do once I hear how powerful the thing is!). But in any case, is the easiest way to be safe to run something like this?

Reckhorn S-1
http://leclubhifi.com/?q=node/516

I think I could look into a DIY subsonic filter, but the big question is, how low do movie LFE's go, and just as importantly, are they loud enough to be a huge problem?

[Mike P.]

how low do movie LFE's go

Low enough to cause your sub to bottom out which can be a huge problem. The Reckhorn B1 would offer you the protection you need.

http://www.creativesound.ca/details.php?model=B-1

[VERTIGGO]

I think I have it narrowed down to a tune of 15.7Hz (48.5" elbowed ports) or 17.5Hz (34" straight ports). That's all I can fit in the box. Either option has +/- results.

15.7Hz can handle 665W and needs HPF at 15Hz
17.5Hz can handle 725W and needs HPF at 17Hz

[Mike P.]

I don't see any advantage to a 15.7 hz tune. You're giving up 3 db at 20 hz for a 1 db gain at 15 hz and below.

[VERTIGGO]

sexy. I think I'll stick with the 17.5 then, since it's also much easier on my construction.

[VERTIGGO]

Here's some progress with 33.75" ports (including the .75" ply face I'm adding). I still need to pick up a router bit for the flaring...

I basically made the ports as long as possible while leaving 6" at the opening. Again I'm not sure if the padding is worth even the little time it takes, but it makes me sleep a little better.

[VERTIGGO]

Well my driver came Friday, and I have my enclosure "done". I threw it together with clamps to test it before gluing the sides on:


Detail of T-nuts. I put some small wood-screws next to them so they won't back out when its closed:


Gluing the sides:


Just because I had some Rockwool...


Looks kind of like the Vulnerability Access tunnels in the 2nd Death Star:


Just a shot of the top:

[VERTIGGO]

well I got it up and running, and besides an annoying hum when the BFD pro is in the loop it seems fine. My biggest problem is that I can't seem to get any BFD filters to work. Here's just the sub on the left and a slight continuation on the right (with NS-777):


Now REQW seems very helpful, and I got filters plotted:


...but no matter how many times I tell it to "send filters to eq..." it shows an empty progress bar, then disappears and the BFD sits there with a stupid grin. I've gone over the "setting up midi comms" etc. so many times I'm lost, and I successfully stored a few manual filters into the BFD but the sweeps before and after were identical. I can't get the BFD to change the response from what you see in the top left picture.

BTW the EP2500 is set to 30Hz cutoff (until my reckhorn b-1 comes) with clip limiter, stereo non bridged mode.

[chrisg411]

Looks like it's coming together quite nicely. Keep the info coming, for the time being I have to listen vicariously through your posting untill my AV15 arrives. Have you got to watch anything on it yet? Subjectively how does it sound?