THE TEXT BETWEEN THE LINES IS THE SAME IN BOTH HERE AND THE DEDICATED ROOM BOARD - this is to explain the project, even though I expect each thread of discussion to be completely different. Here it's primarily for a discussion on the subwoofers, amps, electronic problems, there it will be for the room design.
After several recommendations of others, i'm finally moving the discussion over to... what I hope is the right board.
Original threads were http://www.avsforum.com/t/1477487/if-you-needed-4-hz-in-room-but-could-pick-the-room-how-would-you
was the original topic, as well as posts on another board DIYaudio http://www.diyaudio.com/forums/subwoofers/232978-i-need-infrasound-seeking-advice-sub20hz-bass-budget.html
(PS I still haven't caught up with every post in both places, i'm just starting this thread, so I can post a thread closer in each place directing future followups to here on AVSforum)
Unless you want to read everything there i'll bring anyone here up on the brief factoids:
- I'm aware infrasound may not be "audible", but it is perceivable
- I do not only want tactile bass transducers/bass shakers though I also plan to have that, the perception is interesting but not the same as infrasound waves
- I am not crazy, seeking self injury, colon rupture, cerebral hemmorage, or death of guests. Designing a system for too much doesn't prevent me from turning it down, most of this is about reserve capacity, dynamics, and extremely low response. My interest is more for DEEP bass than the loudest bass. (far more interested in 4hz reproduction at 130db than I am 160db at 45hz, even if a system may technically be capable of either) By deep bass I mean AC3 LFE .1 worship stuff, i've seen the waterfalls go down to 4hz on some movies. Some of those maybe were blind mastered (I don't know if anyone actually listened to them on a 4hz capable system) but since I want to do that myself, I want to be sure I can hear what i'm putting in.
- Yes i'm serious and this isn't a trolling post. Although i'm aware people elsewhere just can't control themselves, filling the thread with dozens of 'humorous' commentary doesn't really help the project. :-/ By what I can tell AVSforum may be the only place I can have this discussion with actual enthusiasm and sincerity so maybe that comment isn't even necessary... i'm just frustrated at how off topic some past conversations got..
Aka in brief yes i'm planning on building this and am seeking advice from others on how to do so rather than suggestions on why I should not or why they don't think I need to, even though it's probably 1-2 years off and early in the design phase. Which is good because it means the plans can still be totally changed without loss.
WHAT IS THIS?
I'm trying to create an all purpose audio mastering room capable of incredibly low "infrasonic" bass response on what's actually a fairly low budget relative to the performance. I'm an ambitious film student that wants to master LFE worshipping audio tracks not only for film, but possibly/ideally for Location Based Entertainment projects where the budgets or specifications can be even higher than what THX can reproduce for db limits or low frequency response. My first goal was to at least equal the performance of a Thigpen Rotary Subwoofer on alot less budget which apparently puts out 110db at 3hz. (and lower but not 'audible' below that) Other infinite baffle subwoofer projects seem to be able to reach 7-8hz routinely enough, so I was curious what would be involved in extending that response down even further. I picked 4hz just because it's one octave lower and i'm not sure how obtainable 2hz is.
Because efficiency drops off so much at low frequency and because of budgetary limitations "billions of watts and square kilometers of cone area" is actually NOT the primary focus, but rather room design. From my understanding (which others have told me/I am totally new to this and don't even understand how this works yet) if you can create an effectively air-sealed, extremely solid room, the efficiency at low frequencies actually goes UP between the two closed off chambers. Scientific experiments seemed to show responses to sub 1hz levels anyways. However I probably don't want to sit in a solid concrete room just listening to infrasound all day, it has to reproduce all frequencies well, which is where the design challenges come in. I'm willing to compromise a few db here or there (on a system that by all accounts should already be able to play way too loud) for quality, but not give up the chart which shows room gain going up massively with each dropping octave into forever with a sealed room.
The biggest compromise i'm willing to make so far has been room size. One possibility was literally me sitting inside the speaker enclosure. Others had the suggestion that infinite baffle was the way to go. Because infinite baffle speakers are mounted between two rooms, I potentially can have it play bass into both rooms, so I proposed having a small (like minivan sized maybe?) back room as a single seat mastering room, with a 32" HDTV and some nearfield monitors, so that the bass level in that room would play as low and loud as possible. The same subwoofers would also be the home theater bass, just assumedly not as loud since it's a larger area, and inverted in phase for the signal obviously. It would be NICE if I could have the same monster bass to share with others, but it's most needed (at least at the beginning/I can always expand later) in just the mastering room, which can be the backroom of the IB subs for now.
The other design spec i'm willing to plan is having a room with effectively no air leakage to the outside world. Ignoring the needs of ventilation to like, not die from lack of oxygen (for which i've got several ideas to design around) it sounds like the tighter I can make the listening room, the more "room gain" I can rely upon keeping, similar to how car subwoofers seem to be capable of playing phenomenally low. (12hz with the sealed system in my car seemed audible anyways and that's merely a dual 12 inch) I don't know whether that has to be on both sides of the infinite baffle, or just the side you want the deepest bass in though.
I'm also aware that I will need a solidly engineered room because very low frequencies at 125db is normally house breaking bass, I don't need to be re-re-re-warned.
That's why the room will be a custom construction.
I'm hoping to use "poor boy bass traps" of lots of strawbale inside the constructed room (not a hard rule, just an expedient idea at hand/suggest alternatives) - I don't care if the room smells like straw, since the proposed home theater/mastering room will be built inside a barn anyways, they're pretty comparable to an STC of 55-60 by what i've heard.
However i'm wondering whether this will negatively impact infrasound efficiency all that much. The wavelength of infrasound is too long to be attenuated, but the room may not "appear" as solid to the speakers if there's lots of thick squishy acoustically absorbent material on every surface.
Room SHAPE can be anything - I was considering a room with nonparallel walls to eliminate most of the potential for room modes to begin with so I mostly have to dampen higher frequencies with room treatments. I'm not sure whether the infrasound cares what shape the room is though..?
I don't mind alot of speakers in the long run (8-20 subs in IB manifolds) but if possible i'd prefer to keep total sub wattage under 2kw because of wiring demands to the barn, but if I understand "room gain" properly this shouldn't even be a problem. I may wish to run stereo subs, or even three - stereo either IB or more conventional subs plus a separate IB LFE subwoofer channel with alot more cones. Lexicon's designer whose name I forget is a believer in stereo subs plus LFE for more immersion anyways and i'm hoping to eventually have an MC-12 in the signal chain.
I will add more information as I go (including some already in those threads i'm moving over from) but for now I just wanted to post this to see who else I can seriously discuss the project with.
That's the intro text (same as the room design board), but here i'm asking for insight and commentary into the speakers, amplifiers, electronics and similar side of the equation. Case in point - i'm told many normal electronics will not work well under 20hz, and perhaps not work at all at 5hz (or such was suggested as one of the hurdles the Thigpen sub had to overcome), and others had suggested using servo amplifiers for the LFE channel to get around it...
Also the decision for infinite baffle is still not set in stone, but i'm assuming that it will give me the best efficiency at 4-8hz or so. Horns I assume would be impossibly large, even tapped horns, and extended bass shelf sealed speakers are basically AFAIK
just like a poorer version of an infinite baffle.