I NEED infrasound... (seeking advice for sub20hz bass on a budget!) - diyAudio
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Old 28th March 2013, 05:44 PM   #1
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Default I NEED infrasound... (seeking advice for sub20hz bass on a budget!)

Hello, i joined years ago but haven't been very active for a long time.


I'm trying to understand the physics better of reproducing TRUE INFRASOUND to determine the best way to do it "on a budget". Mind you on a budget is relative, but as an example the "Thigpen Rotary Woofer" apparently does 115db reference levels all the way down to 3hz in room but apparently costs over $10,000 each. So i'd like to see either:
- How close I can get to that performance on moderately less of a budget like say 5k max
- How deep and loud (exclusively under 20hz, I dont care about 'loud' at 32hz)I can go on substantially less of a budget like say 2k
- Whether I can exceed that performance on the same budget even if not at all frequencies like blowing it away at 8hz but not 3hz

I don't know whether I absolutely need 3hz, but I do know there are hollywood movies being mastered down to at least 9hz (Black Hawk Down if I remember right) on systems apparently "capable of playing 8hz in the mastering room" though i'm not sure whats meant by that since i've heard 11hz in my car from a single low powered 12. I'm aware that sheer physics rapidly comes into play at lower levels... nonetheless i'm just curious of what ways are the best to push the limits as far as they can be taken. 3hz is apparently the limit of what is to some degree audible to a human even if it no longer 'sounds' like sound (i've 'heard' 5hz on a test CD on a quad 18 system in a small room as audible, I don't know what the SPL was though) and though the physics of the Thigpen allow lower they cant exceed 115db so allegedly it's not audible.

Part of my interest is actually MASTERING MOVIES just on the lower end of the budget scale, i'm a college student who will be taking film classes soon (part time, and over a long period of time/I wont be done in four years I mean) but I want to do absolutely no compromise audio. Hollywood actors and VFX is beyond me, but I at least want the sound to be able to blow people away and maybe be something that people buy to demo off, what I call "point 1 worship", or which might even get me recognized or hired to do something bigger, in a studio better equipped for such frequencies. But until that point it's out of pocket and at least half about the fun of it.


So i'm seeking help in brainstorming, suggestions from people about other successful projects and similar about the best way to achieve high SPL infrasound to experiment with. Acoustics and room discussion is WELCOME that's actually why i'm asking this now because building a special room is not beyond question and not even included in the budget - if special considerations need to be taken into account for even the room in which this is being done, then I want to know because i'm hoping to build my own house starting in about two years if all goes well. The eventual goal actually is to build a custom room for the home theater/mastering studio even if that ends up being something like a separate room inside the barn with strawbales stacked around it (dont laugh, even the narrower 20-24" two string bales have a sound transmission class of 55-60 for blocking noise, I figure two deep should do nicely) to make things quiet.


So what is the best way to actually get this to work with some degree of quality?

Is there anyone making a form of 'homebrew' rotary woofer to do the same?

Would an array of 21 inch Pyles in extended bass shelf enclosures be the way? Are any kind of 'homemade Parthenon' projects feasible? (heard something about a huge linear driver you practically attach large square panels to for a DIY woofer in the past, I thought it was called that anyways) I'm assuming sealed enclosures is a must, because despite the efficiency boost of vented and horn enclosures they either decouple or become counterproductive at some much lower frequency?

Should the acoustics be designed almost like a pressure chamber like they wall off car audio installs and the hardest stiffest walls possible? How will sound absorbing material in room affect infrasound/will it work against it?

Are horn woofers usable at lower frequencies without having a cabinet that costs so much more than the woofer that it makes more sense to just use 2 woofers in smaller cabinets with less efficiency? What about tapped horns? I've heard of the 'TH-SPUD' allegedly reaching 11hz or something and am interested, including if it could be gotten even deeper down using a larger driver or scaling up the design. I'm sure anything I make will require multiple cabinets and kilowatts but i'd rather do that with 4 cabinets than 24 obviously and 2kw rather than 16kw.

Would horn physics break down once the room gets down to a certain size or you have too many horns in an array in a small area? (like a stack of 8 tuba home theaters, by bill fitzmaurice in a 12x14 room)

How do cabinet physics work at all below the longest resonant frequency of the room?

How would you do it if the main goal was a lesser overall cost, ie the money can go to amplifiers, drivers, or enclosures, nothing is fixed there, and acoustical design of the theater is "free" just say what it needs to work better. If everything is comparable i'd prefer less wattage (since more than two 20amp feeds just for the home theater starts to feel a little silly, along with the power bill)
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Old 28th March 2013, 07:14 PM   #2
18Hurts is offline 18Hurts  United States
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Ignoring what infrasonic frequencies do to buildings...

Black Hawk down was mastered using around 22 BagEnd Infra-18's or sealed boxes with huge EQ to get them flat to 8 Hz.

In reality--not theory, not marketing... and all that jazz. Infrasonic bass rules are increased VS above 15 Hz bass frequencies. Ask the French guy during the cold war what happens at 7 Hz

Since the room determines much more that the box at those low levels, the 8 Hz wavelength is 141 feet (43 meters) long, it will reflect in whatever building you use unless it is the Astrodome. You can throw such terms as "smooth" and "flat" straight out the window.

Since a sub in a box, be it horn loaded, ported, passive radiator, bandpass, tapped pipe etc demand a low Fs driver, to keep it simple and flattish--get rid of the box.

If you are in a barn say a loooong distance from normal folks--I'd run an infinite baffle sub system with as many Fi infinite baffle 18" woofers as required and a parametric EQ to adjust the response to
flat.

The cost is not insane, they run around $250 each so say around 12 of them and a 2 KW amp would need one 20 amp outlet. Throw in money for the EQ, the heavily braced and thick plywood manifold
and it would be less than $4,000.

You can model what 12 of them would do at 2,000 watts of total power to make sure they don't go past Xmax at 8 Hz (or whatever)
Since frequencies that low will jump way up there with room gain, you should be able to break the building, make yourself sick or kill small animals if they get too close.

Very simple build, parametric to flatten, the more the merrier and give them some power.

Now the $100,000 in damage you are going to do to the building? Well, you can build an underground bunker with rebar, cement and cinder blocks and then put the IB manifold on top....

A good way to test your sanity is get four of the FI IB 18's, build a
manifold, EQ them and bring it up to levels that start to stress the walls, ceiling etc... $1K for the woofers, $800 for the EQ and amplifier and $200 for the wood. It won't give you what you think you need, but it might give you what you can withstand in a traditional structure.

If all is well and you need more, purchase another 4 pack and amp and go to 8 of them...keep going until either you run out of money, destroy the building or get arrested for noise complaints.

8Hz stuff carries a loooooooong distance--ask the pipe organ folks about that stunt. One of the Swiss organs has an 8 Hz pipe, they can hear it from 2.7 miles away...just one of those infrasound things.

The much cheaper option is to get some rather large closed ear headphones. The sonic boom from the cannon shots on the 1812 Overture went down to 8 Hz....my headphones went flat to 10Hz.
I played the cannon shots through them, ripped the headphones off and threw them across the room. Found my limit you could say.

The headphone concept would be a good place to start, you'll have a good idea your limits first and build to them. (legal disclaimer applies)
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Old 28th March 2013, 08:05 PM   #3
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They do this stuff daily at avsforum, I think there's a guy there that hits 130 db at 10 hz with a bunch of sealed high xmax 12 inch woofers.

Using an underground concrete bunker as your listening room will help your cause and cut your costs exponentially.

If you only need to get down to 10 hz or so horns will work (as will ported) but below that sealed is probably best due to enclosure size. The DTS-10 is a commercial tapped horn that will go pretty low.

Click the image to open in full size.

The THT horn doesn't go low enough to claim "infrasonic".

I think these 18 inch drivers are the current value displacement leader if you want sealed or ported. The preorder price is $162.
Stereo Integrity | HT Subwoofers

I'll repeat the last guy's concerns - playing with this stuff at high levels can make you very sick and destroy your building.
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Old 28th March 2013, 08:40 PM   #4
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Wow, thank you for all the wonderful detail.


To comment by line:

I'm aware this may be "house damaging bass". (I say 'may' because 115db is loud but not the same as PA guys running 140db so i'm not as certain... now if I go nuts with 8 LABhorns in there then sure! :P) Thats why the room by definition would have to be specially built - it will be even if it's not in the barn to avoid annoying the house while mastering at 3am. What i'm trying to find out is how to design it... as small as possible (like a car enclosure) or can it be reasonable size like a small to mid home theater? Or could a person build what almost amounts to sticking your head inside a speakerbox with a single driver almost like a monster sub-headphone with some near field monitors inside, not with the purpose of exceeding 115db at ear, just to have a much smaller area to pressurize to low frequencies? (the latter isn't my long term solution, just a workaround to start on film projects before the real demo room is built, ie not final mastering) For that matter would the physics work that just sticking an 18 directly behind my head would give the db's desired (by halving and halving and halving the distance) or does that gain drop off below 1m distance? If it did work would it still work in an anechoic chamber?

I'm not sure if my need is the same as guys saying "I need 150db in my Civic!" who have never even heard 130 and don't know what they are talking about - it's depth more than extreme volume i'm seeking, and the only reason i'm even considering louder than 115db would be if 3hz in room were attainable since lower frequencies apparently need a higher level to be perceived at all. :P I'd have to think it's possible though if i've heardfelt 5hz on the quad Eminence 18's in what must have been a 14x14 room. I can't rebuild the room once I have it, i'd rather design to take 16 drivers then find i'm happy with 4 than the other way around.

Dont worry about building integrity, it will probably be some combination mass of concrete, earthbags and strawbales that you won't even hear outside the double sequential entry doors even if things are completely jacked inside. I can build it strong, I just am not sure how to size and shape it for best infrasound. Even building it "anechoic chamber quiet" is an option (putting the strawbales inside the walls accomplishes this especially if two deep) - it's that that I wasn't sure what effect it has on the infrasound if a single wave cant even form in the space will you hear it the same, unlike a somewhat more resonant car interior.


Infrasonic bass rules are increased VS above 15 Hz bass frequencies. Ask the French guy during the cold war what happens at 7 Hz

I didn't understand what you meant by VS sorry, and what happens at 7hz? /o_o\ Would you recommend not designing for lower than 8hz or can I just notch out 7hz and still get 6, 5, 4 and 3!? >_> 7hz is supposed to be on the Black Hawk Down track anyway Way Down Deep II Bag End S21E | Home Theater

What are the advantages of infinite baffle over the enclosures, would that somehow be more efficient at low frequencies? Or is efficiency just impossible and all your seeking is large pistons to move anything at all? I guess i'm wondering why you recommend infinite baffle when the Bag End Infrasounds are acoustically sprung. (mind you the cost savings of redundant boxes could be why i'm just trying to understand physics and efficiency, if any - what gives the best db per watt at 8hz? Would IB beat the Bag End sealed boxes for instance since as I understand their enclosures are tuned high then they just overpower them below that point? Could 12 IB's give me the bass that '22' BagEnd's gave since they seem less efficient?)

Would there be any advantage of one speaker over another or just grab the cheapest Eminence 18's you can buy for sheer displacement per dollar? Or do IB's require special speakers due to the lack of almost any damping?

Who makes parametric EQ's that cover this low in the frequency spectrum and is it even possible to protect the drivers with some off the shelf solution? (i'm aware of the proprietary stuff Bag End uses for instance, along with other 'active servo' type feedback controls)

Since frequencies that low will jump way up there with room gain, you should be able to break the building, make yourself sick or kill small animals if they get too close.

I would have to assume thats hyperbole having seen all those 160hz burps with some moron inside the van on youtube, unless there's something fundamentally different about 115db at 8hz. Would near-anechoic chamber levels of quietness kill the "room gain" I assume/do frequencies below the lowest wave that can fit in the room require a 'live' room in order to play loudly? (this is an important point because having looked at high end home theaters, some design for total quiet/no acoustic reflections at all, some design for "good acoustics", some use nonparallel walls to eliminate all room modes, and i'm not sure whats "best") Does size or shape matter at all below the frequency that a single wave fits in the room anymore?


I think your suggested strategy of starting with 4 makes sense and i'd probably do that anyway, I just want to be sure I have the ability to upgrade later - I just need to know how to design the rest of the theater room around that so that I can.


As to headphones I already broke a $700 set of Sennheisers for wanting more bass than they wanted to give me. >_< Having stuck my head inside car stereo speaker enclosures and falling in love with pipe organ recordings with actual 64' stops like from Atlantic City (on that quad 18 system I mention above) my tolerance seems to be pretty high. If someone wants to recommend headphones they think will take the abuse i'm likely to dish out though i'm certainly willing to look for some to demo, I just dont want to throw another $700 down the drain.


PS - besides the mastering rig for Black Hawk Down, does anyone else have any references or knowledge of other infrasound-centric mastering rigs, or/and movies which are made with it in mind?
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Old 28th March 2013, 09:06 PM   #5
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by 18Hurts View Post
Black Hawk down was mastered using around 22 BagEnd Infra-18's or sealed boxes with huge EQ to get them flat to 8 Hz.
Hi 18hurts,

Could you share the source of that statement?
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Old 28th March 2013, 09:14 PM   #6
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115 db isn't very loud at 7 hz, you won't be able to hear it at all (provided low distortion) and it's just enough to start to be able to feel it. I go louder or forget out about it, personally.

Maybe you missed my post where I linked the current leading value/displacement drivers. There is no product that Eminence makes that it remotely suitable for trying to reproduce 7 hz at any reasonable level without the help of a horn. You want extremely high xmax if you go with sealed or ported.

IB is just a very large sealed box. Larger boxes provide more efficiency on the low end.

As you say, to get started it's reasonable to start with a single driver in very close proximity. Sit on the box if possible. And look into bass shakers for the same effect.
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Old 28th March 2013, 09:26 PM   #7
FE3T is offline FE3T  Norway
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I guess i would be what some will call a hifi and HT nut, but ill take clean 30hz over infrasonic mud any day.

Wasting loads of money on reproducing tunes i cant hear, at levels that easyli would compromise my living quarters, are in my opinion a waste of my time and my money.
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Old 28th March 2013, 10:59 PM   #8
Zero D is offline Zero D  United Kingdom
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@ Doggyboy

Hi, some very good info/advice already posted

I do understand your desire to achieve a "Name/Reputation"

What i wonder though is, just how many people actually experienced those 8Hz signals on BHD, either in a cinema and/or at home ? How many systems are even capable of reproducing Anywhere near 8Hz ? not many i would say !

Anyway i hear what you are trying to accomplish, so i wish you well with it. Here's several ideas/suggestions i'll offer.

DIY Bagend type low cost solution Sub-Woofer Controller + P48 Sub-Woofer Controller (Rev-A)

Linkwitz Transform low cost alternative Linkwitz Transform Subwoofer Equaliser

He also has several designs for various types of EQ, which can be customised. There are lots of companies who produce EQ's etc, from low $ to HIGH $

Designing an IB box/es to match the above, is not that hard, thanks to some nice Free software Paid is also available

Take a look at this - Graham Holliman - Velocity Coupled Infra Bass Speaker Graham Holliman Velocity Coupled Infra Bass Speaker?

Interestingly, achieving VLF's isn't difficult at lowish power, i've done it in the past. It's just that, attaining high SPL down there takes a Lot of power & excursion
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Old 29th March 2013, 12:41 AM   #9
18Hurts is offline 18Hurts  United States
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Ahhh the Cold War,

Back in the 50's, the French were screwing around and accidentally stumbled across the 7 Hz frequency. Built a 75 foot pipe and within 3 seconds almost killed everyone and shifted the foundation of the bunker the pipe was leaning against. 5 days later, after they got out of the hospital...they researched it. Built a 7 Hz whistle...created earth tremors, killed animals and blew apart rebar and concrete. Yep, they found the perfect death weapon but they could not control the sound from killing them. They stepped away from the monster...that was from 1957 to the early 70's.

Makes sense that BagEnd only goes down to 8 Hz. Even the military cuts their shipping container subwoofers at 10Hz... If you took a big enough hammer and smacked the planet--it would ring like a tuning fork at slightly over 7 Hz.

With that out of the way--how to do it on the cheap? Well, the reason I went for IB is cost and the way to fix all the huge problems you will have in a building is parametric EQ--IB needs that treatment anyway. At least with four of the FI 18 inch subs, the cost won't be insane and you can get the idea then calculate how big of a room you can afford, what level you need and get a working knowledge of what you are playing with.

My reasoning for IB is also the simple reason, it don't take up any additional space inside the room. If your room is smaller, the more people that walk in take up space and shifts your room gain even higher. Although I think subwoofers are cooling looking--the rest of the planet tends not to follow my tastes. Since a room that can handle insanely high infrasonic frequencies will also be very, very expensive--why waste all that money building the thing then filling it with a bunch of boxes?

You must remember total system including the room price. The money saved on 30 sheets of plywood by going IB can be used to make the room larger and more solid. It is also much easier to cut the vent larger and add more manifolds with IBs loaded into the the outside of the wall and not change the room acoustics much by taking up precious air space.

After you become successful enough, you can hire Thomas Danley to build you a Matterhorn....

The Matterhorn - Worlds Largest Subwoofer - YouTube
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Old 29th March 2013, 02:48 AM   #10
Djim is offline Djim  Netherlands
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Hi 18hurts,

No need to search, I already found a source/link
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