Originally Posted by Mik James
So you've posted this elsewhere and no one has mentioned yet that infrasonic bass isn't audible?
I imagine the Thigpen rotary woofer is to expensive.
You might look into some decent bass shakers.
There's multiple potential responses to that:
- The Thigpen guys say it is audible if the volume is loud enough. Even if not 100% essential I just picked around 125db as a seemingly good goal. I'd like some reserve past THX limits and by the sound of it more db is needed down low to really have an effect anyways.
- I've "heard" 5-16hz before. It doesn't quite sound like 'sound' at some point, but 'hear' it? Oh yes. For darn sure i've heard 16hz from pipe organ fundamentals, and 11hz in a car stereo system, and I think i've heard 5hz in one guy's home system (4 18"s, small very tight room, Crown amplifier, playing a sinewave that made the whole house flex and plaster come down) but I cannot rule out for 100% that I was actually some kind of noise or something instead. But the first two weren't just noise or chuffing or overtones.
- Sure people have mentioned 4hz not audible, yet it's recorded in AC3 anyways because of what you feel more than what you hear. People don't hear 7hz yet there are systems apparently on here built for reproducing it. I'm just trying to see if I can stretch it a bit lower. I'm told going to 2hz may not be possible due to things like the limits of electronic amplifiers not able to handle the signals, just figured i'd climb a smaller unclimbed mountain before going for Everest was all.
I thought it might be a rigamarole to go through the same discussion thread here for two pages before any real meat and potatoes discussion could be had, but maybe it will help clarify what i'm trying to do so it's worth writing afterall. But i'll still keep it short.
I'm hoping to be a sound engineer for film and for other motion picture bigger budget projects. (like Location Based Entertainment stuff - hence a reason for targets beyond THX standards, the argument "no real world theater plays that low" doesn't matter, because a custom one off installation can be made to) I need The Bass Room to experiment around with different types of infrasonic stimulation - not just the bass shakers but genuine pants flapping tones more suited to thunderstorms, volcanos, ocean waves, and space shuttles. As far as I know there are OSHA-type and safety limits for loudness at around 120db (seeking 125 is to have a reserve/not be at absolute limit), but going deeper is a different experience than just making it louder. Even though it can be harder to reproduce. So in part it will be for mastering up proposed boom tracks and answering questions like.... how does this work best, with a loud 20hz at 120db, or with 10hz plus the bass shakers on, or a 7hz tone plus a 14hz tone and a totally different waveform to the bass shakers or a 11hz tone and a 12hz tone to get the 'warbling'... etc.
Although the ultimate end-product, say some location based entertainment "experience" which potentially hundreds of people at once would have, would probably not use speakers due to efficiency reasons but something more like infrasonic flutes, pneumatic pistons or who knows what else for specialized infrasonic generators, since I don't want to go and build an endless series and combination of those generators it'd be easier for me to just play around with electronic sampling layering it up however I want until I answer questions about what gives the best experience on a budget that can be scaled up to a large room or even outdoor project. It's also meant for exploring what already exists (movies with true infrasonic signals), having some fun, some experimental electronic music and other stuff so I don't just want it to be generators that can't accept a recorded signal.
I'm currently a student so it's on a budget. (if I get big I can scale up the install, but to start.... it will be about half fun half serious) Not an impossibly low budget, but something where i'm hoping to not spend thousands where I don't have to. There are other things I need to spend thousands on. But i'd like to design for future expandability - possibly an infinite baffle system starting with 4 woofers and expanding up to 32 ultimately if it comes to that, if that's what it takes. However i'd have power limits to start of around 2kw so I was hoping to do it with that to start while still hitting my targets. I'm told there's already people here hitting 7hz in room response with rooms not totally sealed off, and movie tracks (War of The Worlds I think) hitting 4hz - I want to at least match that if not exceed it with greater efficiency due to a truly sealed room, for DEPTH of infrasound, not necessarily extreme SPL's. So the goal is 4hz just because I haven't heard of others doing 4hz yet. The difference is that I only need room to seat two people, a 32" HDTV and a mastering console. It CAN be bigger (and would be fun if it's also a general home theater room for everyone, one idea I considered, that since infinite baffle pushes and pulls between two rooms was to have a large home theater room and a small mastering room, and the sub is literally for both rooms - can only use for one room at a time obviously, and invert the phase when in the "other" room) but doesn't have to be.
Since i've heard way low tones in a sealed up car before I assumed a small van sized mini-room might be the best way to do this on a budget. There's no resonance or anything happening anyways at those frequencies, it's all about pressurizing a space - and I assume a smaller space is easier to pressurize, plus I didn't fully understand what I was looking at but was told in truly sealed spaces "room gain" just goes UP AND UP as frequency drops making what is normally impossible suddenly feasible! So the goal turns into just truly seal the room.
I'm told infinite baffle wants 10x Vas, so it's possible that a lower room size limit is placed by this (ie you cant squish the room down into the size of a walled compact car for instance) so that probably sets an ultimate limit on infrasonic efficiency and volume at a given wattage. Doubling speakers would require doubling the room size - which I might do later if I wanted to bring monster bass to the home theater side. But is fine to start with alot less. (the whole construction would be a 'room within a room' inside a barn, rebuilding the small room in the future is not a big deal)
It doesn't HAVE to only be infinite baffle though - someone else suggested just make a sealed extended bass shelf box, then sit inside the box instead of on the outside to achieve the same effect. Which is most efficient - I don't know yet. I just had multiple people in mutlple places tell me "AVSforum does this all the time, you need to ask there" so I finally am.
Originally Posted by stereo2.0
Just build a room like these guys did. http://vbn.aau.dk/files/54564231/Watanabe_and_Moller_1990a.pdf
(Note that Section 2.3 states it has a low frequency limit of just 0.2Hz)
According to them, you don't need 120dB to hear 4 Hz. (Check out Table_1 on the second last page to see the list of hearing thresholds they derived empirically) Though having greater than 120dB capability down that low would be greatly appreciated.
That's actually pretty similar to how i'm hoping to do it. Being extremely solid and totally closed off is not the problem, it's gaining fidelity without losing efficiency - i'd like it as quiet as an anechoic chamber if possible, I figured a double layer of strawbales (though they take up alot of space - so just make the room bigger) would absorb so much higher frequency noise to get me darn close to that - a single one thick is something like Sound Transmission Class 55-60 which is alot cheaper than endless layers of Quietrock and green glue - but don't know how it would affect the bass or infrasound, possibly not at all because it's not even 1/4 of the wavelength. I'm hoping to do some fairly low buck construction techniques - earthbags for mass and to keep the sound inside, strawbales on the inside of an earthbag 'wall' for sound insulation, one inch thick or greater if needed wood subwoofer mountings, the ventilation system i'm still working out (and is less important, at this moment, than the ability to generate bass) but i'd considered things like Roots blowers (which are a positive displacement blower/totally sealed but can still force air through a room at life support levels) with sound deadening, at lower speeds they aren't too noisy. I could even turn them on and off - like run them on high, then have an "off for 3 minutes" button so I can watch some piece of video footage, in a quiet room, and just feel the bass. Oh and that's just the "infrasound" mode, there would be a normal quiet blower and air inlet/outlet for when the room didn't need 100% sealing. I'd close that door when testing the deepest tones (to get that efficiency) and only then.
Needed or not if i'm going to the trouble to build a room like this I wouldn't mind ramping it up a bit though. The next limiting factor after a solid room is probably wattage, so it's a question of how much bass can I get on say 1000w or 2000w max of bass. Which drivers would be the most efficient and budgetarily decent. I'd rather not have to use 48 drivers to obtain it.
But i'm willing to give up some infrasound efficiency for higher frequency quality. (anechoic chamber type quietness) Some means a few db or so unless it's more efficient than I thought, then i'd give up more.
Oh and if it matters i'm considering nonparallel walls on every surface so that even if there were any room modes possible with all that straw, there wont be afterwards. I'd like it to be an all purpose mastering room when it's not being used for the deepest bass.
(to Datranz - it's not letting me copy more than one quote for some reason)
DIY section... here at AVSforum you mean? Or some other site?