Single vs. Dual Manifolds

[severianb]

I'll be using 4 drivers. Read all the FAQs. I'll either put all 4 in one manifold between the speakers (or wherever testing dictates) or 2 manifolds, one under each wall-mounted speaker.

I don't have 2 subs, so I guess I can't test the latter option. I was worried about cancellation issues.

Any suggestions?

[ThomasW]

Since all our installations use multiple drivers, the option exists to build several smallish sealed test boxes to experiment with placement. Some are making their designs so that these test boxes are in actuality the manifolds they use for their permanent install.

[jman]

In theory, with dual manifolds can you run the IB in stereo?

[chrisbee]

jman said:

In theory, with dual manifolds can you run the IB in stereo?

Whether there is any directional information in the IB passband is the important question.

There may be cancellation issues between two widely separated bass sources.

It may be difficult to move a pair of IBs if serious cancellation is impossible to cure with a BFD.

Cancellation and reinforcement between the various units when using dual subwoofers can affect the voicing of the speaker system as a whole.

[fanbrain]

In my experience with normal floorstanding subwoofers, it's always better to use two (or more). Let's say you have a large dip at 44Hz. By placing the sub at the acoustical center of the 44Hz null, you raise that null, helping flatten your frequency response in the subwoofer region. Doing so however, takes energy out of that sub, reducing its capability. By implementing a second subwoofer, you can re-gain some of that energy back into the room and use the second sub to help with another problem frequency.

I'll be building a home in the next few months. It will have a room dedicated to music (our piano and wifes harp) and movies. I will be using a dual manifold design and I'll be testing them first on the ground before I start cutting holes in the ceiling. I'll be using a simple y-splitter for signal. I wouldn't mess with a stereo IB setup; you shouldn't be able to localize the subwoofers and having them not play together seems counterintuitive to me. I guess I just don't understand the concept of stereo subs.

[kadiddle]

I'm running my two manifolds in dual mono operation. This means each manifold is on a separate channel (output). This allows me to set the distance for each in the pre/pro and to equalize each manifold separately. In my case these were important issues as one manifold is in the front of the HT, the other in the rear at a different distance from the listening position.
When equalizing, it was highly advantageous to be able to EQ each one separately. Often when a null was found, I could reduce it by actually cutting output at the null frequency in just one of the manifolds. This takes some trial and error.
If you run yours in stereo off of one output then both manifolds need to be the exact same distance from the seating position in order to have them time aligned.
kadiddle

[fanbrain]

kadiddle said:

I'm running my two manifolds in dual mono operation. This means each manifold is on a separate channel (output). This allows me to set the distance for each in the pre/pro and to equalize each manifold separately. In my case these were important issues as one manifold is in the front of the HT, the other in the rear at a different distance from the listening position.
When equalizing, it was highly advantageous to be able to EQ each one separately. Often when a null was found, I could reduce it by actually cutting output at the null frequency in just one of the manifolds. This takes some trial and error.
If you run yours in stereo off of one output then both manifolds need to be the exact same distance from the seating position in order to have them time aligned.
kadiddle

Bingo. You can also use a dual-output PEQ like this: www.qscaudio.com/products/dsp/dsp4/dsp4.htm. This gives you the ability to set independant time delays, filters, and gain settings for each manifold. A win-win situation.

[ThomasW]

Any of the Behringer units offer 2 completely independent channels of EQ

[severianb]

Great ideas. I'll test the center location (under the center speaker, this is mostly for HT) and if it works, great. One manifold will be easy.

After reading about acoustic treatments and realizing how much ringing my small (13x15x8 sealed) room has, I've got to put in some corner bass traps and first reflection absorbers before I mess with IB. It never ends.