Placement Question

[pgoko]

Hi,
I installed my IB (line array) at the middle, right-hand side of my HT, and there was a null at the center. Now I moved it and have it installed at the far upper left hand side using an "outie" manifold. The sound improved (no null) but at very low bass notes, there is this horrible vibration. My crawl space is only 17.5" deep.
I did not experience this with the line array installation. I went up to my crawl space (just around the opening) and buffered all I could, there is no improvement. I am afraid to turn up the bass for fear of hearing the vibrating noise. Any suggestions? I like the bass, I am not giving up just yet. By the way, I am using two
MJ-18s, wonderful subs. Thanks.
NB: How do I get rid of a null?

[ThomasW]

One gets rid of a null by moving the sub.

The 'vibration' is obviously something resonating. With someone to assist you, play some low frequencies and wander around listening and feeling for what is being excited by the sound. Usually these aren't all that difficult to locate. Think heating ducts, pictures on walls, stuff like that.

I have no idea what you're talking about when you say 'buffering'.

[pgoko]

Does anybody have a line array installation midway between the sitting position and the front speakers on the side, how does it sound? Mine sounds very thin at the sitting position. Has anybody had a similar experience and how was it corrected? Thanks.

[ThomasW]

Let's see a frequency response plot.

[chrisbee]

I'm not being facetious but changing from a vertical array to a manifold increased my bass so much it feels like I have three times as much power. The manifold is in exactly the same place as the old array in the wall beside the left speaker.

Thomas will tell you that my flexible wall was the reason for this remarkable and totally unexpected increase in performance.

How flexible is your wall?

[canaris]

Chris..so you're telling us that because of a lossy wall you increased your bass going from a array to a manifold...?

I thought because of the lossy wall ..you're bass was down.

Like I said before I have my array installed in a structural 2x6" supporting wall..I wonder if I go the manifold route if it will help the vibration problem in the adjacent back wave room and increase bass too?

[chrisbee]

The bass in my IB enclosure has gone down as much as the bass in the AV room has increased. Can't explain it but it has happened.
It used to be very uncomfortable out in the enclosure with music playing. Now it's not.

The bass used to be very loud in the bathroom below the IB enclosure. Now it's hardly audible. I had occasions with the array when I felt almost nauseous from the loud bass in the bathroom. Now I struggle to hear anything with music playing upstairs.

The only change was installing an opposed driver manifold in the same place as the array. I gained at least 12dB because that was how much I turned down the gain overall to match the array.

Your baffle wall must be very much stiffer than mine. So it sounds as if poor placement was the main problem with your array.

[pgoko]

Yes Chrisbee, I think poor placement is the problem. Thing is I moved the installation (now manifold) to the far left upper corner firing into the crawl space between the theater (basement) and the living room above. The sound is good, but I hear vibrations when I try to turn it up. Just for the heck of it, I will try moving it back using a manifold this time and observe the difference. Just maybe I will get rid of the null...very annoying. Thanks for your input Chrisbee, much appreciated.

[canaris]

I have it installed near a corner...




I don't have the option of putting it anywhere else... I am satisfied with it... just wondering if a manifold could do even better?


I guess there's only one way to find out.

[pgoko]

Nice looking install. Mine was on the side at middle of room, firing from the side into the room.

[chrisbee]

The corner should be the stiffest place on a stud wall thanks to the adjacent wall at right angles to driver thrust forces. Though it pays to test this position with a conventional sub for a reasonable response to be absolutely sure before attacking the scenery.

The advantage of trying a manifold in place of an array is the ease of blocking off the upper open area where the baffle reached higher on the wall. The manifold can then be sized to replace the lower section of the array. Remember to allow for the skirting board height when you calculate your manifold opening to be 4 x Sd for best performance. I had to place my new manifold on blocks because I have a 10" stage in the AV room but not out in the IB enclosure.

Since the manifold replaces the array it will be ample proof of the advantage of either without introducing new variables into the equation.

If you save the array baffle you can quickly replace it if the array proves to be better than the manifold. It certainly looks much more impressive than an invisible manifold if you can get away with it.

You can also get away with a much larger manifold opening because your partner will be used to seeing something much larger there. You could even double the number of drivers compared with the array and use the whole height!

(Just thinking aloud) ;D