Going away from IB.

[chambers1517]

Thought I have a serious issue. I have 4 18"fi drivers in an ib configuration in the front wall. It absolutely destroys the upstairs by shaking it. I have 2 rows of seating. The front row is dead center and has less bass than anywhere in the house. I have been considering putting the drivers in closed boxes, 2 at the front and 2 in the rear. Would this help the center row and help contain the bass in my movie room?

[dan77]

You might consider borrowing a traditional subwoofer that is in an existing enclosure that you can place in different places in your home theater. Then perform the ‘subwoofer crawl’. There are a few approaches to this activity. I prefer to place the subwoofer on the very seat that I want the bass to be the strongest. Then I move around the room listening for where the bass is the strongest. Once that location is found, that would be the final resting place for the sub itself. This would require you to have the ability to generate a constant 30HZ tone (or 20 or 40, whatever works best for you).

This process can be repeated for multiple sub locations if you have more than one sub.

You can perform this the opposite way. Meaning place the sub somewhere in your room and then sit on the chair of concern and listen to see how strong the bass is. Then get up, move the sub, jump back into the seat and compare. I find that approach exhausting as the enclosed subs I own are very heavy and comparing the strength of the bass becomes very subjective.

It sounds like your subs are creating standing waves that are cancelling each other out. The only way to correct that is to move the subs. It makes no difference if they are IB or traditional. It has only to do with sub location.

There is also software that can help you with subwoofer location. I think REW is one of those. I have only used the sub crawl method.

I have 4 15 inch FI IB’s in the floor of my HT. They are about 2 feet away from the wall. But before I punched the holes in the floor, I placed a traditional subwoofer all over my HT and listened to various movies for about 2 full months. I would move the sub constantly throughout the movie to see where I liked it best. Moving the sub REALLY made a difference. When I felt I finally found a location that worked well aesthetically as well as acoustically (I am married so I do have limitations) - I cut out the carpet and punched out the holes. I find that I simply cannot turn them up all the way as they can easily overpower all my other speakers. They are powered by a 3000 watt Bherenger.

I am running martin Logan line array speakers along with 6 mid level bass modules that is fully atmos compliant in a 17 x 13 x 10 dedicated room. My home theater is a 7.10.4. All in it is about 11000 watts RMS (That is not peak. Peak is a whole different critter). I run with a dedicated sub panel.

Note that even with 6 SVS SB 3000 MLB units, my 4 15 inch FI IB’s can still overpower all of them on a whim.

It sounds like (pun intended) you have standing waves to contend with, so location is most likely your challenge, not sub type.

[ThomasW]

So 2 problems in total.

Yea what he said regarding test placement of a sealed box in the HT

IB or not, nothing is going to contain the bass in the HT unless the walls are solid concrete.

[dan77]

Agreed. The OP did mention that the bass was actually stronger outside of the room. This sounds very much like a standing wave issue. Box type, IB, open back, etc. No sub design will offset that issue. Need to work on location challenges before committing to the final location of any sub install. Hope is not a strategy and you do need to research where each sub should be placed since each install is unique. I spent months moving subs around my current HT before I committed to the installation of my IB’s.

Back when I had a crap HT with two used 15 inch ported subs (from a garage sale) I could position them in my living room where I could shake the bathroom mirror on the second floor as well as the dishes in the kitchen. However, when I was in the HT room itself, there was about three places in the HT itself where I could stand and hear about 20% or less of the bass being played. If I moved my head 10-12 inches in any direction suddenly I would get the full force of the bass. From that I learned that sub specs are absolutely useless until you get placement right. The best sub in the world will in no way eliminate standing waves. Room treatments and location are paramount for solving these concerns.

That testing I did with those two subs was done back when DVD’s ruled and I had one that played a constant HZ like 40. That was back before I even knew what an IB was.

So don’t worry about specs or cost until you figure out how to avoid the standing wave issue that seems to exist in your room. And like the ThomasW said, even after you address that issue you will still, of course, light up the rest of the house.

[chambers1517]

Thanks for the responses. I need to clarify. The bass in the front row sounds great and is plenty loud but the rear row and everywhere else is tearing stuff up. The front wall was the only place for an ob which I wanted.

[dan77]

“The bass in the front row sounds great and is plenty loud but the rear row and everywhere else is tearing stuff up (very loud)”
You are describing a standing wave issue. Your description is textbook. Your HT is the poster child of standing wave issues.

“The front wall was the only place for an ob which I wanted”
Freestanding subs, whether open back, ported or sealed will have very unique performance characteristics based on location. You can move a sub about 12 inches and get a whole different set of standing waves.
You have not posted a picture, but don’t you have the entire front wall to play with? Did you experiment with other locations on the front wall?

My IB’s are about 2 feet from the wall on the floor, just moving them another 18 inches towards the middle of the room created an entirely different sound signature.

Regardless, with subs that you can move around, you will be able to solve your challenge. Don’t be surprised when the location best suited for bass might be right in front of your seats or semi blocking the entrance to your HT. Meaning that in the end, if you insist on the best bass possible, you may take a digger with where they end up sitting.

I personally do not like being able to echo locate the location of any subwoofer. I also do not like passing through any standing waves created by bass notes. That is why I have so many SB 3000’s and a stereo IB setup (10 subs - 8 locations). In my opinion, a single sub (of any type), cannot create as immersive as an experience as multiple subs can. Timing becomes your next challenge when going for a multi sub setup. But I choose that problem over the one you are having. In my book, it is the lesser of the two evils - by far.

[chambers1517]

Not exactly sure how to post a pic. I have 3 lascalas with 2 of the woofers on each side of the center.

[chambers1517]

The front wall is built like a tank so I'm stuck with it. I may actually have to build a new rear wall and shorten the room to change the center point. I just hate the fact is built how I wanted it and other than the null is great.

[frantzm]

Hi

One of the nest solution could be to add one sealed subwoofer, say an SVS SB-2000.

Several studies from luminaries have shown that the best bass in in most any room, especially if you have several rows and want uniformity in the bass, i-e having similar response in all (most? seats, can only be obtained with multiple subwoofers. However good a lone subwoofer is , multiple subs, even lesser subwoofers have the potential to provide better response in most rooms. Harman published papers studies on that. Earl Geddes of Gedlee published on he subject and seem to have arrived at the same results as the peple in Harman, simultaneously
It will take some times to integrate multiple subwoofer in such a way that work well together.

This will requires some , relatively modest cash outlay :
miniDSP 2x4 HD ........ $300. perhaps less. A DSP/Crossover, that allow you immense control on the subwoofers.
miniDSP Umik-1 a measuring microphone about $125.00
REW a free , incredibly and useful software $0.oo. I suggest a donation... can be whatever you want.
MSO another software made to integrate multiple subwoofers. $.00 I suggest a donation... can be whatever you want.

It will take time to master and understand al this. I believe the results are worth the (considerable) effort.

Peace.