AE IB15 Open baffle sub experiment

jk@home · « **on:** 20 Oct 2010, 02:29 pm »

Hey Folks.

I have a 2-channel music system in a 11/6' x 15' "home office" (aka man-cave

). Played at lowish to moderate volume levels.

For the mains, I'm using highly modified Magnepan MMGs. This is close to a dedicated room, so the Maggies are 5' from the front wall, and real room treatments will be added soon.

Once all the mods I have planned for the MMGs are finished, then will set up a couple of 2 cu.ft. 12" sealed subs I have to supplement, placed to the outboard sides. Have a Yamaha P3500S for sub power, along with a Behringer DI4000 and DCX2496 to convert, EQ and x-over.

I also have, still sitting in the four shipping boxes they came in, are a quad of AE IB15 drivers, that I bought for IB sub use in the HT system elsewhere in the house.

For kicks and giggles, before I do the IB project, I would like to temporarily set up the AE drivers in a pair of dual driver baffle configurations, to compare with the sealed subs. Who knows, maybe the sealed subs will end up in the HT.

Not interested in building a "W" or whatever enclosure just yet, just a couple of vertical plywood baffles.

So I'm looking for baffle size dimensions. I'll be running the MMGs full range, so the subs don't need to go too high (80-100 Hz.) or low (30-40 Hz.) for that matter.

John_E_Janowitz · « **Reply #1 on:** 21 Oct 2010, 02:18 am »

The larger you can go on the baffle the better off you will be on the low end. Ideally use The EDGE to simulate the baffle. If you're only looking at that range up to 80-100hz then centering the drivers on the baffle is your best option. You get more output if centered, but you also get the most bumped response. Offsetting the drivers about 1/3 to the side tends to give the smoothest response but you lose some output efficiency as well. In this case though the irregularity of the response doesn't matter as you will see it is much higher than the range you are using it. Wings on the sides that go back will add to the apparent width of the baffle.

This post I did was modeling a 450mm wide baffle and simulation of the IB15 in this use.
http://www.audiocircle.com/index.php?topic=62242.msg564684#msg564684

Keep in mind you'll want EQ to flatten the response. You can design the circuit with the Edge to correct for the response or something like the minidsp units would work well too. Good luck.

John

jk@home · « **Reply #2 on:** 21 Oct 2010, 11:13 am »

Thanks for the help John (and for my drivers too

). I'll be using the Behringer DCX2496 for EQ and crossover, so I should be able to make something happen. Worst case scenario I can piggyback one of my Behr DEQ units to it (digitally) for extra eq.

I'll try to dive into the Edge simulator, and report back here what I come up with. If all I need is a 18" baffle width, plus back wings, I can handle that (the sealed subs I now have are 18" cubes).

How about the height of the top of baffle and placement of the drivers in relationship to the floor and my ear level, is this critical? Will the Edge determine this also?

Two more questions. I have the 8 ohm version of your driver. If I go two drivers per side, should I wire them in series or parallel? The amp I will use is a Yamaha P3500S, which is rated in stereo 350 wpc @ 8 ohms, and 450 wpc @ 4 ohms.

Also, if I really like what I hear, but still want to proceed with the IB in the HT, will your OB15 drivers physically mount up identically to the same baffle openings?

Thanks
John K.

JohnR · « **Reply #3 on:** 21 Oct 2010, 02:12 pm »

Hi, you'd wire them in parallel.

It looks like you'll get about 2dB more output with a 600x1200mm baffle than you will with a 450x900mm baffle. Probably doesn't matter for an experiment.

jk@home · « **Reply #4 on:** 21 Oct 2010, 02:34 pm »

Hey JR

So I can use a 24" x 48" total baffle area for each side / pair of drivers? Would this be the same as an 18" x 48", with 3" wing widths on each of the sides?

And if I go with a finished product later, and say I laminate 4 -3/4" layers of material on top of each other, to equal a baffle depth of 3", does this equal to the same as the above?

Sorry for the OB class 101 questions, but we all have to start somewhere.

I'll have to buy 4'x8' sheet material anyway, so it would be just as easy to go to the larger size.

Thanks
John K.

scorpion · « **Reply #5 on:** 21 Oct 2010, 02:40 pm »

This is a simulation with MJK's Math-Cad models for a baffle 34" (H) x 20" (W). I have assumed two 8 ohm IB15s in parallel. Response is at 1 m and 2.83 volts input and with an 80 Hz 24 dB/octave Linkwitz-Riley Low Pass filter :

It seems you won't need much EQ.

/Erling

jk@home · « **Reply #6 on:** 21 Oct 2010, 02:44 pm »

Thanks Erling

Is that baffle size for one driver or two?

JohnR · « **Reply #7 on:** 21 Oct 2010, 02:45 pm »

Erling, does that model include the floor? I'm wondering how I can do that, I thought I had a program or spreadsheet that did it (and walls and ceiling), but can't find it now. I don't have MathCad unfortunately.

JK, I think the answers to your questions are not really, and no. 3" wings won't have much effect on a baffle that wide. But if you're going to put wings on it, you could just make them bigger and stick a top on it and you have an H frame

Having said that, I think you might be surprised at what you get with just a flat baffle.

jk@home · « **Reply #8 on:** 21 Oct 2010, 02:50 pm »

Yes, I'm leaning towards a flat baffle, the subs will be sitting next to and outboard of the maggies. If I can stay in the dipole null area of the magnepans, hopefully the subs won't effect the mains too bad.

scorpion · « **Reply #9 on:** 21 Oct 2010, 03:02 pm »

Two IB15s ! It is not very effecient but will do 100 dB at 30 Hz with about 12 mm cone movement.

John, yes floor effect is accounted for in MJK's model.

/Erling

jk@home · « **Reply #10 on:** 21 Oct 2010, 03:13 pm »

Good deal Erling, now I'm gettin excited.

If/when I build the finished subs, does extra bracing struts help, like what I did to my maggies? (Tacky looking I know, but they sound great!) These will eventually be covered with a MG12 sock.

JohnR · « **Reply #11 on:** 21 Oct 2010, 11:37 pm »

You'll need something like those struts anyway, I think, as there's a lot of force on the baffle with subs going. The way those are mounted looks like there might be a little movement in the joint - that will probably rattle. (Not trying to be a wet blanket ...

)

JeffB · « **Reply #12 on:** 22 Oct 2010, 12:13 am »

Why does the modeled response drop from 60Hz to 80Hz?

JohnR · « **Reply #13 on:** 22 Oct 2010, 12:17 am »

Quote from: JeffB on 22 Oct 2010, 12:13 am

Why does the modeled response drop from 60Hz to 80Hz?

The -3dB of the lowpass filter is at 80 Hz, but it starts rolling off before that.

jk@home · « **Reply #14 on:** 22 Oct 2010, 12:29 am »

Quote from: JohnR on 21 Oct 2010, 11:37 pm

You'll need something like those struts anyway, I think, as there's a lot of force on the baffle with subs going. The way those are mounted looks like there might be a little movement in the joint - that will probably rattle. (Not trying to be a wet blanket ... )

No wet blankets here

I've been running these speakers for a good four months now, no rattles. The brackets are tight into the 1-1/4" oak wood dowel, secured by bolts and lock nuts, and t-nuts into the frames. The struts are so strong that I can pick up the speaker (which now weighs over 50#s, with just the struts. No moment or flex. Since these two updates on the MUG, I've flipped the panels back around to the factory position:

http://db.audioasylum.com/cgi/m.mpl?forum=mug&n=156044&highlight=hardwood+frames+deli+style

http://db.audioasylum.com/cgi/m.mpl?forum=mug&n=157804&highlight=deli+frames+in+the+oven&r=

Of course you are right though, the sub panel may need more.

JohnR · « **Reply #15 on:** 22 Oct 2010, 04:14 am »

Heh, the membrane won't exert any force, whereas several hundred grams of woofer cone moving back and forwards 20 or 30mm is a bit of a different story

Give it a try anyway, it's quite interesting and there's only one way to find out

jk@home · « **Reply #16 on:** 22 Oct 2010, 11:30 am »

Here's some pics I took off the DiyAudio's "ultimate" OB galley, for support ideas:
(minus the mid/high drivers of course)

This design looks fairly popular, but I really want to incorporate a tilt, to match the MMGs.

Maybe something like this, but with the center baffle flush with the front of the side supports. Although if I did it just like this, I could cover the front with speaker cloth, and get the same visual effect.

I'll be using butcher block bases, like the MMGs, so I could attach the bottom of the baffle sides to the sides of the bases.

Or something in-between.

Which would work the best as far as performance? And with the final finished baffle, will it be better to flush mount the drivers, or surface mount them?

I found a scrap 1/2 size piece of 3/4" plywood, so hopefully next week I can whip out the test baffles.

JohnR · « **Reply #17 on:** 22 Oct 2010, 12:16 pm »

Something like the second looks pretty good to me

Flush mounting won't make any difference for subs.

jk@home · « **Reply #18 on:** 22 Oct 2010, 12:20 pm »

I like that one too. Thanks

Russell Dawkins · « **Reply #19 on:** 22 Oct 2010, 04:52 pm »

The second configuration does seem to make great sense. I imagine a refinement could be to swing the baffle board slightly forward so that it is tilted, say, 5º back from vertical. This would allow a measure of time alignment and reduce the reflective surface area that sideways-going sound waves from the mid range driver will encounter, while still allowing clearance for a grill cloth.
I'd also use some absorptive foam or equivalent on the inner surfaces near the mid and HF drivers.