I NEED infrasound... (seeking advice for sub20hz bass on a budget!) - Page 3 - diyAudio
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Old 30th March 2013, 04:25 PM   #21
tb46 is offline tb46  United States
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Hi Doggyboy,

Ultimately this will all come down to building construction, as a simple option: sitting inside an externally well braced concrete structure just large enough to accomodate the 'engineer' and equipment/controls should make it possible to get to very high ultra low frequency SPL levels with IB speakers in the walls. Even the "door/hatch" will have to be considered carefully.

Here is another thread you might find interesting, e.g.: take a look at the system/link in Post #27.

Underground Sub

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Old 30th March 2013, 06:29 PM   #22
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Okay so here's my "approximate" design ideas then at the moment. Offer suggestions if you want.

I actually will go with a "dual room" configuration - this lets me both have the response for the mastering room (which only I have to be present for anyways, or another sound engineer) while using essentially the same system to entertain larger groups, even if I can't have quite the same level of bass it should still be pretty substantial.

I will plan for a quad 18 configuration to start with, which for the big room will be like in the lower corner, but for the small room will take up most of the back panel. The small room will be small to the level of about a minivan assuming that's plenty large for the subs to have on the backside (I basically want wall to wall woofer inside there - about a 42" wide and 42" tall box? of whatever depth it needs to be?), and the small size means it can be built extremely solid for the money - it will be sitting height only, near field 5 channel monitors, with a 32-42" HDTV (possibly behind a windshield like in a car, will the db potential blow out my screen? :P ) and my audio mastering MIDI fader console dupicated. I'll primarily use that room when 'fine tuning' the really deep bass, or when I want to experience someone else's work with boggling SPL. Think the equivalent of a bass van parked in the lower corner of the home theater basically. :P

I'm thinking the combination of "room gain" and how small of an area i'm pressurizing should let me take things as far as I reasonably can - I mean even if I built a 3x3 sub rig with 9 woofers, it takes up more space, so the room has to be larger - so even if I can hit louder and deeper in the larger home theater room, the small room is just the same SPL in a larger room - no real benefit. Dual 18's makes too small of a seating area, plus i'm thinking four should give enough db for the mid sized ~3000 cubic foot home theater to be happy for most situations anyways. Maybe i'll go with 9 woofers in the future or 16 to utterly blow people away, but none of those changes really improve my mastering room unless I go with something with even more xmax.

If I understand physics properly (why people 'wall off' bass vans) cutting the depth of that backroom would improve db within the 'mastering room' (since i'm pressuizing a smaller area) but might decrease efficiency of the subs in the main theater, since IB subs want a reasonably large volume backside? It would not even be inconceivable to have a variable displacement room in a case like that, ie almost like a solid box insert that would take up half the displacement in the mastering room if for some reason i'm not happy with the db as it is. :P

Does anyone care to speculate whether I could reach 4hz at 115db in such a construction? It should be pretty similar to boom cars filled with concrete by then. I would suspect nearing or exceeding 150db would be possible at more normal sub frequencies like 30-40hz afterall based on what others are doing with quad 18's in SUV's. If I eventually "upgrade" it will be more for the purposes of home theater - I might build a 2nd sub room on the other side of equal size to have stereo subwoofers and twice the bass for instance for guests - but the mastering room probably couldn't be improved much beyond that unless I made xmax of wall to wall woofers in the smallest room my sole criteria.

Jumping back to the Stereo Integrity woofers Stereo Integrity | HT Subwoofers it says recommended enclosure "Sealed = 4ft ^ 3", does that mean 4 feet on a side? (ie 64 cubic feet) For infinite baffle would I go with a sealed figure for choosing the room size? Would I go bigger for 'extended bass shelf' like designs or how much space should my quad pack of 18's actually take?


Mind you the conversation isn't over yet! This is just an exploration, and other ways to achieve this goal will still be fully considered since actually building this is awhile off yet. Ie - discussion of the Graham Holliman stuff and similar is still welcome since with the right room design it could provide high SPL's in the larger home theater room as well.

Quote:
Originally Posted by Inductor View Post
Doggyboy,
If you are still in business and you don't want to spend 10.000$ in a sub and want to get low 20's (Hz), and have a room to spare like it's needed for a fan (Rotary Subwoofer), why you don't use just one, two or more of the AE speakers for ~300.00 USD (sorry guys I didn't read all your posts, I don't know really what is going on).
Totally don't know what your talking about dude. Can you explain what AE speakers are? The posts are all about designing ideally a 3-20hz 115db capable system.

Also just wanted to insert this even though it's out of order:

Quote:
Originally Posted by CharlieLaub View Post
If you just build a subwoofer into a large sealed box and get inside, you will get insanely high SPL levels. This will probably also induce vomiting. Maybe this is the effect that you are seeking on your infrasound quest?
Why does everyone assume that the only people wanting to explore certain frontiers are either stupid or unworthy of consideration? My goal is not nausea, hearing damage, abdominal pain, loss of bowel control, organ rupture, or death. Obviously any combination of frequency and decibel level resulting in any of those ISN'T REALLY AN OPTION TO USE. Or why is the assumption that it would simply be blasting high db levels for hours and hours until it resulted in that? Every story i've heard of people reporting disorientation and stuff usually involved them doing that, exploring a new feeling sort of like children will eat a whole box of cookies until they are sick and then don't want any of it for weeks afterwards. What I want to find out is what frequencies CAN be used, and CAN be mastered into an audio mix, and HOW MUCH can be used without being too much, for playback on extremely high performance systems, to get effects which just plain are not available on systems which only play 20hz and above. Even if the result is most often fear (what seems to be commonly reported) that should be great for survival horror videogames or horror movies. Even if the goal is not fear but just realism, it will finally then simulate the real world effects of war, ocean waves, thunderclaps, whales, tiger roars, space shuttles, mining trucks, seismic events, enormous diesel locomotives and the 64 foot stops on a handful of pipe organs with far more accuracy.

Infrasound is probably like cayenne - a little goes a long way so use it sparingly. It's entirely likely that the total infrasound content of a 2 hour movie i'd make will be 20-30 seconds - and yet that little bit of spice doled out carefully at certain places and times will make all the difference in immersion and manipulating the persons emotions to feel what the director wants them to feel, typically what the on screen characters are feeling. It's similar to listening to an audio system with incredible dynamic range, lets say it hits 130db - you dont listen to it at 130 ALL DAY, it's the occasional spikes to that level off a constant level of say 105db that make everything feel more alive than a system clearly flatlined not able to push out one ounce more. If someone actually watched a movie I made and said "wow, what incredible infrasound content, those subwoofers are amazing" i've probably failed, just like a good subwoofer shouldn't draw attention to itself separate from the mains, the reaction shouldn't stand out to the point where people are commenting on it, they should just be saying how totally into the movie they were or how scared they were or how realistic the sound was or whatever.
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Old 30th March 2013, 07:09 PM   #23
Zero D is offline Zero D  United Kingdom
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@ Doggyboy

The reason i, & others, posted with Warnings/Links about the Very real dangers associated with VLF/ULF f's, was prudent i believe.

After your latest post, it's a lot clearer what your position is

Quote:
It's entirely likely that the total infrasound content of a 2 hour movie i'd make will be 20-30 seconds - and yet that little bit of spice doled out carefully at certain places and times will make all the difference in immersion and manipulating the persons emotions to feel what the director wants them to feel, typically what the on screen characters are feeling.
The question i posed earler still remains though, how many cinemas/HT systems would actually be capable of reproducing these f's, either at the levels you will mix at, or at all ?

I'm not saying don't try to achieve it, i'm sure you will
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Old 30th March 2013, 09:48 PM   #24
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For reasons mentioned by weltersys (and for other reasons that he didn't mention), your best bet for IB is a manifold. In that case you can fit five 18 inch drivers in an 18 inch cube. If you put them all flat on the wall as you seem to be planning you are going to lose a lot of spl to wall vibrations, and the wall will make it's own spurious noises. If you use manifolds you can fit twenty 18 inch subs in a 42 square inch section of your wall.

The Graham Holliman sub is not going to do what you want. I can promise you that. ALL the other ideas presented here are a much better idea than that thing.

The thing about infrasound is that some people are more susceptible to ill effects than others. Some people can take it at high db levels all day, some will feel ill almost immediately. It's common courtesy to let people know what you have in store for them, it's not cool to try to "scare" them without disclosing what you're packing under the hood. And at high levels it really can be dangerous, to yourself, your guests and to the structural integrity of your house. That's why people keep mentioning it.

Quote:
Does anyone care to speculate whether I could reach 4hz at 115db in such a construction?
What construction? The most important thing is pressurization and you haven't mentioned if the walls are concrete or drywall. You haven't mentioned if there are leaks like doorways to other rooms that can't be closed or HVAC system. Without mentioning little details like this it's completely impossible to even guess what you might get. Like I said, I can't do in my house with a dozen subs what I can do in my brother's house with one sub. The room is everything - the room IS the box.

Regardless, I don't think it's going to be possible to get flat down to 4hz, I don't think there's any electronics that will go that low. Even the guy in the link I posted is only flat down to around 6 hz. He knows what he's doing and he's pretty serious about all this so if he isn't doing it you probably won't be able to either.

No, you won't blow out your monitor. That's absurd. The reason car spl windshields break sometimes is because they are part of a box (the car body) that is holding in immense pressure. Your monitor is not part of the structure and it isn't responsible for containing the pressure in the room. If you try really hard you might be able to vibrate it to death but you won't hurt it with pressure.

Last edited by just a guy; 30th March 2013 at 10:07 PM.
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Old 30th March 2013, 10:05 PM   #25
18Hurts is offline 18Hurts  United States
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Sounds like a good plan

Don't forget IB subs demand at least 10 times their rated Vas to work properly. That is much larger than a mini-van but at least you won't
be in a tiny torture chamber!

The FI IB 18" sub has a Vas of 381 liters so four of them, then multiply by 10 is a 15,240 liters--don't forget you take up space! That would be 15.24 cubic meters or around 540 cubic feet.

That is not a small room--think a prison cell size so if you want the option to add another 4 of them, shoot for around 1,200 cubic feet to make up for you, some equipment etc and it will allow you to run 8 if/when needed. If you don't need them--at least the room will be useful for a few people to get in there.
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Old 30th March 2013, 10:12 PM   #26
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Quote:
Originally Posted by 18Hurts View Post

Don't forget IB subs demand at least 10 times their rated Vas to work properly.
Not really. Ideally your back chamber would be infinite (hence the title "infinite baffle") but a reasonable approximation is 10x VAS. That does not mean you can't use less. In fact much less. The rule of thumb is to use at least 4x VAS if you want to call it infinite baffle but even if you use less, it's still a large sealed box and it will still work. You just end up with a different system q and not as much efficiency in the low end. Which matters not even a little bit if you have enough displacement, power and dsp.
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Old 30th March 2013, 10:50 PM   #27
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At their tuning frequency, ported boxes apply a lot more pressure to the cone of the driver, virtually stopping cone excursion.

Would it make sense to go for a ported (the ports can exit in the big room) enclosure?

I'm assuming this set-up will be eq'd to death anyway, so if there's some free SPL to be had...
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Old 30th March 2013, 10:56 PM   #28
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Quote:
Originally Posted by Doggyboy View Post

I'm thinking the combination of "room gain" and how small of an area i'm pressurizing should let me take things as far as I reasonably can ...

Dual 18's makes too small of a seating area, plus i'm thinking four should give enough db for the mid sized ~3000 cubic foot home theater to be happy for most situations anyways. Maybe i'll go with 9 woofers in the future or 16 to utterly blow people away, but none of those changes really improve my mastering room unless I go with something with even more xmax.

Does anyone care to speculate whether I could reach 4hz at 115db in such a construction? It should be pretty similar to boom cars filled with concrete by then. I would suspect nearing or exceeding 150db would be possible at more normal sub frequencies like 30-40hz afterall based on what others are doing with quad 18's in SUV's.

Totally don't know what your talking about dude. Can you explain what AE speakers are?

The posts are all about designing ideally a 3-20hz 115db capable system.
Probably you don't have any idea of the room gain you have in a car vs. in a home theater (your mid sized ~3000 cubic foot home theater).
Where did you get those numbers (3Hz/dB)... dude?!
As you see and will learn is not difficult to add >20dB to the low extension ~10/20Hz from room gain. Calculations most of the time are made for free field, you never mentioned that fact, not only car vs. home.
Loudspeaker Design Software
Room Mode Simulator

AE speakers is a brand of drivers.
I have some difficulty reading trough so much garbage that I don't know what you will set for in the end if a Bertha with Levan extensions from Paradise G. or a dual 10" type of loudspeaker. Sorry, maybe I can clear my mind later. If you say you "suspect" "150db would be possible at sub frequencies like 30-40hz" you must be referring to car audio and you want to "upgrade" to "3-20hz 115db capable system" ?!

Just for my reference do you mean something like this
DYNACORD´s COBRA-PWH 28
maxSPL/1m 140dB - ( -10dB )33 Hz - 2 kHz
DYNACORD – Cobra-4 Systems – Cobra-PWH

Last edited by Inductor; 30th March 2013 at 11:06 PM. Reason: DYNACORD´s COBRA Basshorn
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Old 30th March 2013, 11:22 PM   #29
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Drivers that will reach 115dB at 4 Hz in a sealed small space are readily available. As you point out, electronics are the problem. Bruce Thigpen had problems finding amplifiers that would work with his rotary sub. They would either roll off early or trip their protection circuitry when fed signals below 5 Hz. Industrial servo amplifiers designed for DC output may be better than audio market amps in this case.

I have a pile of bricks looking for a home, and a corner of a concrete-walled garage. I've been toying with the idea of a tiny room, just big enough for a couple of chairs, some near-fields and a small widescreen TV. The "Room-SPL.xls" spreadsheet I included previously is pre-set for the setup I was considering. (7.7 cubic metres, 126 dB SPL from 4 cheap car 12" subs requiring about 120 watts.) 115dB in a somewhat larger enclosure using quad 18s should be quite easy.

You are going to have significant room mode (resonance) problems in a small room. Fortunately, because the room is small, the resonances will start at a relatively high frequency which makes them easier to trap / damp. Allow extra height and length to fill with damping material.

If you want to actually hear/feel 4 Hz, you will need significantly more than 115 dB. The lower the frequency, the higher the SPL has to be for it to be audible. The standard equal-loudness curves (ISO 226:2003) only go down to 20 Hz, and at that frequency 115dB would sound about as loud as a 75 dB midrange signal. You'd need about 130dB at 4 Hz.

Assuming you're planning on midrange peaks of 105 dB, you'd need over 130dB at 20 Hz, and almost 150 dB at 4 Hz.
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Old 30th March 2013, 11:36 PM   #30
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Assuming 4x FI IB3-18 in a 15 cubic metre enclosure, 135 dB should be achievable. What we need now is a firming-up of the likely room size and the intended drivers.

Last edited by Don Hills; 30th March 2013 at 11:39 PM.
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