Oblong Woofers

[Oklahoma Wolf]

Well, since I had all my remaining review samples fail on me, and have nothing to review this week, I figured I would let you guys in on what my speaker building hobby is leading me to do in the coming few months.

I'm going to build a tapped horn. Or two. Or three. I have two good designs in hand, one for a computer sub and one for a home theater sub. This thread will be the story of the home theater sub.

Before I get into the details, here are the woofers:

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF2130.jpg

These are Tang Band W8Q-1071F's. They are 8x12" drivers with 12mm of Xmax. Believe it or don't, this design will get them louder in room than my Mach 5 IXL 18" build is, and the sub will play almost as low. I say almost because it has become quite apparent that the room makes the pursuit of subsonic content quite pointless. If I tried to get these to 11Hz, even with a tapped horn, they couldn't do it as well as the IXL can currently.

So, you may be asking yourself what a tapped horn is. Basically, it's a horn in which both sides of the driver get used to contribute to the sound. It's a bandpass horn, in other words. Advantages to the design include more output for size than a standard horn design would be, but only for the right drivers... you cannot use just anything in a tapped horn. A few work ok, very few work really well. These Tang Band 8x12's are in the former category... they're good but they could be better. I have a really good driver picked for the computer sub project, but that's a story for another day.

Now, some more pics of the woofers. One arrived with a metal shaving in the gap, making it necessary to fix it before I broke them both in.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF2129.jpg

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF2131.jpg

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF2135.jpg

These were purchased from Solen in Canada for about $110 each. Both woofers survived the lenghty burn in process, which consisted of running a 10Hz test tone for 24 hours at 10-12 volts.

A video of the test before burn in when I discovered the one driver's issues:

http://www.youtube.com/watch?v=1nbGp_EXbmg

And the burn-in itself, done in the load testing lab after I fixed the one woofer using the QSC pro amp:

http://www.youtube.com/watch?v=GbUaAuQxrbk

[Oklahoma Wolf]

Ok, on to the design itself. This is going to be a whopping huge subwoofer, because it's a horn with a 16Hz knee. Due to simple physics, I need this thing to be a quarter wavelength long at the lowest frequency I want to get from it. That amounts to a lot of horn. For modeling, I used the wonderful program Hornresp. This proggy has a steep learning curve, but I'm just about at the top of the hill now. This will model just about any design you can think of, including transmission lines.

Now, my requirements for this project:

-must be much thinner than the big IXL build, because it's going behind a projector screen. As designed, this one is going to be about 17" deep vs. the 25.5" depth of the IXL box.
-must play to 16Hz
-must be capable of over 120dB in corner loading to give me headroom, and it is... barely
-needs to be affordable... barely came in under that one too

And now for some screenshots from Hornresp. These are modeled in half space, so you can compare these results with the likes of Bassbox Pro and WinISD.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wlfhrn2r5spl.jpg

The SPL graph. This is how the box would perform in a perfect world just sitting out in the middle of a field somewhere. This is just before the woofers bottom out. If I model this in eighth space, or corner loading, I get around 125dB from it. That's an unrealistic expectation because Hornresp assumes you're using unobtainium for box materials, so I deduct 5dB for somewhat realistic numbers. Some of those response peaks won't be there in the final product, or will be reduced dramatically.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wlfhrn2r5param.jpg

This is what you put into Hornresp to get the previous graph. As mentioned, it's a steep learning curve. I had fun learning it though.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wlfhrn2r5impulse.jpg

Impulse response. This is a graph of time vs. pressure, and shows how much "ringing" there is in the horn. You want this to look as clean as possible so the horn will sound as clean as possible.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wlfhrn2r5phase.jpg

Phase response. What you want to look for here is for the lines to stay within 90 degrees inside the horn's intended passband. In this case, that's between 16 and 80 Hz. If it's not in 90 degrees, that can really mess up the sound.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wlfhrn2r5schem.jpg

Hornresp has a schematic window of the horn where you can see how big it will be before materials, as well as where the driver goes. The red circle is where one side of the woofer is placed in the horn, and the green circle is where the "tap," or the other side of the woofer is. Confusing? Well, here's my folding diagram to help with that:

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/Wolfhorn2Fold.jpg

The green line is right between where the two woofers mount. They will be placed magnets up on either side of that line, firing downward.

And yes, the final box really will be 42" x 74" x 17." Bigger than the IXL box. But it'll be able to hide behind this, so I won't mind:

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF2002.jpg

No, I don't have a projector for it yet. That comes later this year :(

First, I have no less than three sheets of plywood to buy so I can build this project. And I'll still need to use leftover wood from the IXL build. Sadly, the rest of the project will now have to wait for old man winter to leave so I can go outside and play with the saw.

[madmat]

Any news? I'm watching... can't wait to see more.

I've got some stuff I'm working on too.

[Oklahoma Wolf]

Not much - will be in the city next week buying some power tools and a few of the more hard to find needs of the project, but there's still snow on the ground outside. Once that's gone, I'll be buying some wood. I am chomping at the bit to get this built.

Fun fact - cone area (Sd) of the IXL is given as 1029 square centimeters. The two Tang Bands combined add up to 920... that's more than most 15's I've tried to model in tapped horn alignment. For oval shaped woofers, they're beefy suckers. This subwoofer might actually do all right :D

Incidentally, I've found that the IXL also models well in tapped horns. Only problem is, it needs some kind of massive horn on the order of 800-1000 liters. Still on the fence about doing that... I can get better results from a couple Hifonics Atlas 12's.

[madmat]

I know where you can get 18" passive radiators :) Tunable ones at that. Toss a pair of 18" PR's in a box with the IXL.

By the by, you've now got a piece of history with the IXL... Mach 5 isn't making it any longer. :(

[Oklahoma Wolf]

Hadn't heard that. There are half baked rumors running wild about the next big thing from him though, so I'll wait and see what he cooks up.

Personally, I'm having too much fun with the tapped horns right now to worry much about it. Cooking up some designs for the Hifonics Atlas and Olympus 12's... strangely enough, the very parameters that make them less than ideal for the usual home theater designs makes them just about perfect for tapped horns. My rule of thumb - look for low Vas and high-ish Fs. Car SPL woofers usually seem to model well for me, though it's not guaranteed.

[madmat]

This was up in another forum:

Mail sent to Mach5:

"I notice there are no MJ18's listed on your site, is this due to the site
going down and all your products not getting relisted or are they done?

Also since leaving SSA I heard some rumors about Mach 5 ownership change, is this just rumor?"

From Mark/Mach5:

"the MJ's are no more. Something else will replace them but not for
awhile. Mach 5 is expanding, but there isn't much more I can expand on
right now.

Thanks,
Mark"

My bad, it's not the IXL.

[Oklahoma Wolf]

Ah, yeah - that one I had heard.

[Oklahoma Wolf]

Gasp - something's actually happening!

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCF4197.jpg

This is the week, folks - I have wood, I have spare time, I have PL Premium, and I have no semblance of sanity. This thing's getting built. That's a new 98" saw guide next to the wood - cheap, but should work I hope.

Wood shopping went ok. Home Depot was a disappointment as usual - Arauco only up to 5/8" and not very cheap at $45 a sheet. So, I ended up at Windsor Plywood where the best and cheapest they had was, once again, import 11 ply C2 shop birch. $40 a sheet.

After getting these sheets down to the basement, I'm wondering again why I thought I needed to use 3/4" stock. This project is going to be heavy as all get-out.

[Oklahoma Wolf]

Progress has been made, but since I'm tired of updating multiple threads, I'll just point those interested in this project to this here thread:

http://www.avsforum.com/avs-vb/showthread.php?t=1212571

[Oklahoma Wolf]

Ok, one last update.

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCN4996.jpg

Yep, I done went and built a subwoofer that stands six feet two inches tall (actually, it's a little bit over that).

I've already measured 120dB at the mouth from this thing during War of the Worlds - the IXL has nothing on it :D

More info can be found in the link I posted last time.

Looking down the mouth of the beast:

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/DSCN4999.jpg

And last, my in room response, no EQ, 10Hz subsonic filter:

http://img.photobucket.com/albums/v297/Oklawolf/Speakers/The%20Wolfhorn%20Project/wolfhornii-noboost.jpg

[Oklahoma Wolf]

Anybody want to see an SPL meter hitting 119-120dB at listening position?

http://www.youtube.com/watch?v=ofTvTk-sFos

I'm in the process of designing a revised horn with different woofers that will come out a little smaller. Sometime next year, I'll have two of these tapped horn things in the basement :D