Infinite Baffle Subwoofer Speaker Stand

[hulkss]

I built this IB subwoofer to act a a speaker stand for a Klipsch LaScala II center speaker in my home theater. Wow! This thing has some serious output and easily keeps up with the Khorn mid bass. It scares people.

It uses four custom IB subwoofer drivers from Acoustic Elegance.

IB15 Driver

You can see the performance analysis for 4 IB15's here:

IB15 Performance

You can get 4 of these for $500:

IB15 Store

The drivers are wired series/parallel for an 8 ohm load and I drive the sub with a Behringer EP2500 which puts out 1200 watts into 8 ohms when bridged to mono. With the 8 ohm load the amp runs cool and I could put in a very quiet fan. I used an EBM Pabst 8414 NGL fan. It bolts in as a direct replacement - just splice the wires.

600 watts gets you full linear excursion (12 liter displacement) at 20 Hz so there is 3dB of headroom in the amp. At that point the output is 120 dB.

Here are some photos:

The complete front speaker system with IB sub.


The sub ready to drop into the floor cutout


Looking down at the drivers.


The sub installed and reflector on bottom of LaScala

[longdrive55]

Very nice. I guess the woofers fire into your basement? Is that correct? Also, why did you opt to direct the output of the backwave into the listening area instead of the front as in many of the IB/Manifold-based installations I've seen?

Also, what is your crossover point and do you have any measurements on the frequency response?

Thanks for posting!

[hulkss]

Originally Posted by longdrive55

Very nice. I guess the woofers fire into your basement? Is that correct? Also, why did you opt to direct the output of the backwave into the listening area instead of the front as in many of the IB/Manifold-based installations I've seen?

Also, what is your crossover point and do you have any measurements on the frequency response?

Thanks for posting!

The IB chamber is the crawl space under the house. I built the system so it would drop easily into the floor from inside the house.

The sound is identical on both sides of the woofer cone. This way the important part of the speaker (motor and suspension) is in the house. Only the cones are exposed to the crawl space and they are treated with a sealant from the factory to resist humidity. The crawl space is about 60 degrees and 60% humidity year round. I did not want a mouse or bugs to make a home in a speaker motor.

The sub is controlled by the bass management in an Integra DHC9.9 preamp processor. It gets bass frequencies up to 100 Hz sent to it from the LaScala that is stacked on it. The corner horns cross over at 40 Hz.

I bought some pipe organ recordings so I would know what frequencies were being played. 16 Hz organ notes are scary. I have 1/4 inch laminated glass in the windows near the subwoofer. The other windows were plugged with two layers of 1/2 MDF with damping compound between layers.

I just got a calibrated mic which is essential to measure low frequencies. I'll measure it and post the results soon.

Here's a photo in the crawl space.

[badman]

Nice sub! You should flip 2 of the drivers to cone-in on the manifold and invert their phase, to get some additional distortion cancellation.

[hulkss]

Originally Posted by badman

Nice sub! You should flip 2 of the drivers to cone-in on the manifold and invert their phase, to get some additional distortion cancellation.

Push pull is nice, however, I prefer it the way it is for the reasons listed above. I'll measure the harmonic distortion and post it.

The Lambda speaker motor has very low distortion as compared to other subwoofer motor designs. Read this short 5 screen article:

Lambda Motor Design

[Brett]

Good job. I'd been meaning to ask about the IB after it being mentioned in the WG thread. I'd love to do this myself, but the apartment I'm living in won't allow it. I think the integration into a stand for the centre is a very neat touch.

[hulkss]

Originally Posted by longdrive55

Do you have any measurements on the frequency response?

Here's a plot of the frequency response and the 2nd and 3rd order harmonic distortion measured with a calibrated microphone. There is a peak at 90 Hz that is easy to EQ out and as you can see there is good output down to 12 Hz. This is the "straight wire" response with no EQ or filters of any kind.

[longdrive55]

Thanks for posting. Nice FR. I know I'm gonna have to go IB for my subwoofs at some point. Just can't quite bring myself to cut the hole in the ceiling yet. Very nice work. Enjoy!

[lennon_68]

Looks great! I just finished a 4 x AE IB15 build of my own (complete with EP2500 for power). It's also doubling as a stand for my center channel but it's an "outie" manifold. I still can't get over the quality of bass coming out of that thing, and at a reasonable price to boot

[badman]

Oh, ho, you want me to READ your whole thread before posting??!?!?

Just kidding, I missed the mouse and bug part. Fair enough!