Dipole sub design questions...

[CJ Paul]

OK, like most here, I cant let drivers sit around when there is only a few bucks worth of wood between the drivers being used and sitting around for six months. So, the Stryke IB15s that I ordered cannot pull IB duty until I move into my new house in July. I'm considering making two dual-driver dipole subs in the meantime.

A) are these drivers suited for that use or am I wasting my time

B) what kind of output and frequency response should I expect? I know many people use dipole subs because they dont have the "boomy" problems that other subs can but I question how low they will extend. I have a BFD but I know EQing the bottom end up could run me into excursion problems pretty quickly.

C) what kind of design should I use? I've done a little research and I want to keep it really simple as it will be temporary. Would a simple U frame for each woofer work where I could maybe stack two for each unit?

Any ideas?

[Rob Gold]

Bog Simple! Assuming you got four for the $99 each "deal." Flat vertical baffle, forward-firing drivers, one over the other (if you do a stereo pair). Try a double layer of 3/4" MDF. Even if you do a single dipole with all four drivers, two stock sheets of MDF will do you just fine. A good layer of brown or white carpenter's glue between the MDF layers are sufficient. Two simple angled legs in back to stand the baffle up straight (you don't even need a base, really). You don't even need to bother countersinking these -- at these frequencies the little ripple hardly figures, so just bolt 'em on the front of the baffle.

For a four driver unit in a 36" wide baffle, you should see an Fequal around 65hz. A little basic EQ will give you an easy 35hz at around 112db @ 1m, and 103dB @ 25hz @ 1m -- all at Xmax. Here's the kicker -- spl above Fequal will be ENORMOUS. These won't be true subwoofers, but in the 80hz-100hz range where most rock kick drums live, you'll weld the air molecules together. And these will be awful damned sensitive, too, ca. mid-90s.

You will avoid any form of box resonances, and not excite lateral room modes. Get the panel about 1-1.5m out in front of the rear wall for best effect., but don;t worry about being close to a side wall.

[CJ Paul]

Hmmm, I dont know if I have enough room for a flat baffle containing all the woofers. I know that contradicts my "simple" request. Maybe I should take some measurements and tell you all how much room I have to work with.

[Jack Gilvey]

Absolutely try it, Paul. You may well forego any other plans you had for the drivers once you do. As Rob suggests, the output really deep will likely be too low for HT use (maybe equal to what one of your drivers would provide in IB/sealed), but the clarity on "music" bass (40Hz and up, where room problems typically manifest themselves) is unlike anything I've heard, including IB.
I've long thought that an IB rolled in under a dipole ~30Hz would be outstanding...such execution is beyond my simple grasp, alas...

[CJ Paul]

OK, I had an idea. What if I go out and buy 3/4" plywood in sheets of 2x4 and 2x2. I then make an H-frame for two 15" subs using 3 2x4 sheets and 2 2x2s (are we on the same page?). How would this work? I am running this through the dipole sheet on diysubwoofers.org and getting an Fequal of about 79Hz. What kind of in room response should I expect? If it worked, I could build another one for the other two woofers. This would be a very quick project as it would be temporary and its cold as crap outside right now. I would basically ONLY have to cut the holes for the drivers and screw it all together.

Any thoughts?

PS, why do I see people reverse one driver (physically) in the few H-frames I've seen? Is it for a reason? Dont you then wire it reverse phase so that the drivers are hitting in phase? Why not mount them both facing the same direction and in-phase?

[ThomasW]

Drivers generate even and odd order harmonic distortion. Mounting them one facing out and the other reversed, cancels these distortions. How audible this is, is up for debate.

Trying to determine the in-room performance of what you propose is impossible, unless you want to spend days trying to modeling room gain. You'll get better data measuring what you build.

Audio just like life, is one big experiment. Break some eggs, make some mayonnaise..... :wink:

[CJ Paul]

OK, Thomas. What do you think of my idea for baffle size, shape, driver configuration that I described? I'll build it, but I want to make sure I'm remotely on the right track.

[ThomasW]

I've never built one that way so don't know. I've put them on just a flat baffle with all the drivers facing out, and even that sound pretty good. Needed a bit of EQ in the lower frequencies.

The 'box' only needs to be big enough to hold a pair of drivers. The stiffening brace shown between the drivers in the pic below is a good idea. After you cut 2-15" holes there's not going to be much 'meat' left in the baffle.

The depth of the box determines at what frequency the front and rear waves meet (cancel).

This is an experiment so experiment!.

Make it so you can play with various lengths of side panels. Listen to what happens when you change the lengths of the panels.

Personally I wouldn't center the drivers front to back in the "H". I'd go for a "U", with the drivers slightly recessed back from the front to protect them.

[CJ Paul]

Personally I wouldn't center the drivers front to back in the "H". I'd go for a "U", with the drivers slightly recessed back from the front to protect them.

Gotcha. So you'd have the front almost flush with the sides and top/bottom, but not quite?

[ThomasW]

So you'd have the front almost flush with the sides and top/bottom, but not quite?

It would be a real bummer if someone accidentally kicked those really cool chrome phase plugs on the front of your drivers .... 8O

[CJ Paul]

It would be a real bummer if someone accidentally kicked those really cool chrome phase plugs on the front of your drivers ....

Yeah, a bummer for them

[Dennis H]

CJ, your proposed box dimensions sound fine for a sub if you can fit them in your room. Wider and deeper H-frames mean more SPL at low frequencies but they have problems at high frequencies because of two factors - Fpeak in the theoretical dipole model (3x Fequal) and the resonance of the deep frame. SL builds his H-frames smaller than you propose but he wants to cross at 120Hz, i.e. above normal sub frequencies, and he's going for a "compact" package. Some guys over on the diyaudio forum built subs with cheap pro drivers, about 3' wide and 2' deep, and raved about the sound so the big H-frame didn't bother them any. Your Stryke drivers probably have 4x the Xmax of those guys so a big H-frame should be killer. Another data point, Steve Dodds experimented with H-frame and U-frame. He ended up with the H-frame with the baffle in the center of the wings, just like SL.

PS, for all things dipole, SL's site is the bible. It's a bit hard to navigate but there's a wealth of info there if you dig around. Go to the Phoenix section where he discusses a lot of theory and has handy spreadsheet calculators, etc.

http://www.linkwitzlab.com

[Paul H]

I've got four of those speakers on orders with plans to use them as bass bins for dipole speakers. When they're done I'm going to cross them over to a vented 210l tempest I have, probably around 40 hz. As Thomas suggested, I'll be doing a bunch of experimenting with them. When I get the speakers and my new lspcad running and making sense I'll share any results here.

From everything I've read (i.e. I haven't seen them yet myself) they'll be very good dipole woofers/subwoofers, as long as they're not crossed too high (probably 200 at most, preferrably lower).

Paul