Originally Posted by stockmonkey2000
To have headroom at 6hz I would probably need 32 18" drivers or a couple of rotary woofers. As a side note - I once had lightning strike about 20 feet away from me. My ears were ringing for days afterward. I could feel the hairs on my arms stand up right before it struck. I really do not want to try and recreate that in my theater
You may not be aware just how powerful your IB will be. A system such as yours will have so much native
extension, that the signal path electronics will likely be the ultimate limiting factor. The spec for LFE production is 3-120hz. If one's system is not covering that bandwidth, there will be material missing that the sound engineering team intended you to experience. There are those that believe that the infra sound octaves below 20hz have no importance, typically, they're not owners of high resolution LFE systems. The sounds we encounter in our lives contain frequencies down to 3hz, and lower. Percussive wavefronts that accompany a variety of sounds frequently have elements this low. A well recorded soundtrack can have elements easily down to 3hz. The sound designers carefully craft the infra sound octaves, just as they do the audible octaves; to achieve the desired effect of realism.
One of many examples of this is Open Range. The special effects recording and soundtrack are outstanding in the release. Here you can see the bulk of the spectral content lies in the octave between 30-60hz. However there is significant energy in the area below 5hz, placed there for systems that can reproduce it for added realism. That extra wallop down low creates a very realistic leading edge transient,....that accompanies the fundamental frequencies.
Another example is the famous lightning strikes in War of the Worlds. Spielberg, and his team, wanted to create a sense of impending doom....they succeeded. The resulting soundtrack is something of legend, a good test for a sub system;
At 1m, without factoring in the benefits of room gain, you'll easily have 130db@20hz and above,... and this is with a drive level of 225w/per driver, and a 50% lossy corner load. This is conservative and achievable. Your longest dimension is 26 feet, so room gain onset will occur at approximately 23hz. So you'll enjoy about 18db of gain at 6hz. So calculating this, and including a very reasonable room gain quantity, you could achieve 128 db@12hz@4 drivers@225w/per driver@1m.
Room gain, theoretically is identical to a sealed system roll off. Whatever your sub rolls off, the room gives back. In practice, the numbers vary somewhat, but you'll have significant capability
I wouldn't be suprised if you could achieve flat to 5hz.
So as you see, you'll not need (32)18's to achieve this, you already there. As long as your electronics possess good extension toward DC, you'll have strong performance in the lowest octaves. Also, the equal loudness curves dictate that in order to hear 10Hz you need sound pressure levels above 100dB. To hear 5Hz you need sound levels above 110dB. So 120db at 5hz is merely 10db above audibility.
As a side note - I once had lightning strike about 20 feet away from me. My ears were ringing for days afterward. I could feel the hairs on my arms stand up right before it struck.
I can't imagine what that was like for you, but I too have had two close calls,..not fun.
So in summary,...if you don't want that type of realism, you can always filter it out with a high pass at 20hz