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I NEED infrasound... (seeking advice for sub20hz bass on a budget!)
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Old 29th March 2013, 03:03 AM   #11
CharlieLaub is offline CharlieLaub  United States
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I NEED infrasound... (seeking advice for sub20hz bass on a budget!)
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?

You can also just sit in the near field (outside) your subwoofer to experience higher SPL levels...
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Old 29th March 2013, 04:37 AM   #12
Doggyboy is offline Doggyboy  United States
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For some reason quoting wasnt working for me before but it is now, but now it's mangling my posts not allowing line breaks so sorry if the text is a bit mashed together.
Originally Posted by just a guy View Post
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.
I will take this seriously! That's actually what I meant by designing acoustics first. I don't know if a "concrete bunker" is what I want (extremely reflective surfaces may pressurize infrasound but i'd think would make normal audio sound like poop) but building a very small room suitable for only a "single seat sitting height only theater" is acceptable when fine tuning the deepest of the bass response. Literally building a room not much larger than a car or a van with a 42" HD and a mixboard in front of me, some nearfield monitors, and a pair of 18's behind my head. I just need to master it for now, not show it to twenty people at the same time, though if doing the last doesn't cost excessively more that could be fun too. (here's a wacky idea, since the infinite baffle both pushes and pulls between rooms, how bout having the small room behind it be my single person mastering room and the large room in front of it be the more public multiseat home theater?? Then I just invert phase and sit in the small room when I need accuracy to the lowest notes designed for.) That said I can still explore solutions for multiseat for fun cuz sure i'd like that, it's more about cost differential of need vs like... I am not averse to building a giant quarter wave tapped horn even if it means cross sections of multiple feet laid out in concrete forms in the floor. IL PIU' GRANDE SUBWOOFER DEL MONDO - by Roberto Delle Curti - Italy This is not out of the question if the total cost of bricks and the saved power lets me get low frequencies with more efficiency. :P Is AVSforum the place I should be asking these questions instead?
Originally Posted by just a guy View Post
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.
When I think of it more it's possible that what I was hearing was just distortion or port noise when I "heard" 5hz and 11hz before but i'm still not sure as when it sweeped up to 20hz it was absolutely pure in tone without overdriving amp or speaker, otherwise sure it becomes more audible once you start squaring off the waves... nonetheless 115db is all I need because that's the THX standard - this isn't a fun room, this is "match the real world mastering ability of the Thigpen or a room full of BagEnd Infra 21's on less budget". Or is what you meant that 8hz is a reasonable bottom floor to even attempt to master for? (I had heard that 3hz was the lowest perceptual threshhold for 115db and higher frequencies should be at least a bit audible above that) My interests below 8hz are substantially less anyways, it gives me the "fear of god" pedal for organ since no one has ever made a 128' organ stop. I saw the speaker link after I responded to the first guy. (which was delayed by moderation posting) At the low low low frequencies is that all that matters, diameter and Xmax? Or will one "18 inch woofer with 9mm xmax" play louder than another at 9mm due to efficiency issues? Any suggestions for "how many woofers/how much power" would be needed to get a given db level at a given frequency in a given size room, ie based on others? Despite my organ love I might decide afterall that 10hz is enough, it all depends upon relative cost, it just seems so close making me wonder if some minor design change can get down to 8hz with some improved efficiency like the Danley TH-SPUD's ive heard of playing 11hz, just a BIT more please... and maybe I could get the desired level on 1/4th the wattage. :P
Originally Posted by Zero D View Post
@ 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 ?
How many? Obviously the guys who mastered Black Hawk Down and those who appreciated their work enough. However acknowledging the above is part of why interest rapidly drops off below 8hz even if I decide that it's obtainable. It sounds like "multi 18's IB and 2kw" is a solid plan to fall back on to get... I dont know how many db, but a fair bit at 8-10hz, hopefully meeting my goal if not exceeding it. (if exceeding it and I can do it on less woofers/power into a smaller room i'm even happier) Yet the curious side of me is just curious how to either get it "even louder" (i'm not against listening to movies above reference levels :P), even deeper just to experiment with privately, "more efficient" at 8hz using very large tapped horns, "in the floor cement horns" like linked above, OR improved fidelity (able to use sound absorbing material on all walls, not needing a literal "solid concrete wall bunker") - for hopefully not too much more than I already expect to spend since I budgeted for more anyways. So forgive me for still asking questions.. now that 8hz seems attainable i'm wondering what 4hz requires. :P (i'm guessing 4x the power and 4x the displacement, or would it need longer xmax woofers all edge to edge to get the pressures needed? At what level do I have to change from the 'displacement-value leader' to the xmax leader with walls of edge to edge woofers?)
Originally Posted by FE3T View Post
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.
Not sure how that comment helps me. :( I can say that i'm a believer in infrasound, I know some people don't get it and think it's a waste but it's because most aren't conscious of it because it's a whole body perception more than 'hearing'. Just from my experience with pipe organs and seeing demonstrations of like virtual/electronic 64' stops or recordings of the real ones played on arrays of 18's they ADD something indefinable to the music, it has more power, even if it's not actually any louder. Or the difference of actually feeling a freight train pass in person vs on a home theater system that plays the same db level "at 20hz and up" it's NOT the same. Headphones aren't the same either even though you can 'hear' the frequencies sometimes. I want to truly truly explore this rarely experienced bottom end, if I could reach 2hz I would, i'd like a system where I give out before it does, and maybe i'd find I need to avoid certain frequencies yet those on either side are relatively safe but just like composer Wendy Carlos's personal and very expensive forays into surround sound way before it was used by others just because she wanted to know, i'd like to have a system that lets me explore it up down and sideways. Once upon a time before Jurassic Park we didn't even have consistent sound fidelity in theaters and they thought there was no market even if you did, now it's expected and normal. Maybe true infrasound is "that missing something" even if the nature of china-breaking physics prevents it from ever being widely employed in home theaters but will become the next must have in commercial theaters and high end home theaters, obviously a small minority of people already think so. Maybe tactile transducers can replace it satisfactorily or maybe not, without both to experiment with I wont really know.
Originally Posted by 18Hurts View Post
Back in the 50's, the French were screwing around and accidentally stumbled across the 7 Hz frequency.
Makes sense that BagEnd only goes down to 8 Hz. Even the military cuts their shipping container subwoofers at 10Hz...

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.
Okay no 7hz, important safety tip. >_> Not sure why the military would cut out their sub below 10hz though since it seems they would want that effect, hmm.. Do you have any reference for the French story? It's the first i've ever heard of it and i've studied every infrasound article I can get my hands on so far. I'm still just curious about 4hz and 2hz with the nuts digital simulations of 128' and 256' organ stops though that people have done before. Perhaps in the future i'll decide it lacks point to continue but until the itch is scratched it will be there threatening my wallet. :-P Do you think my "two room theater" with the same subs firing forward AND backward, a small mastering room and a larger multiseat home theater would actually work? Ie the back room would be probably the size of a van with the four woofers practically touching like how they do car audio walls, so it can play deeper and louder. Or does an IB require the subs to be equally spaced across the whole wall face and not a cluster of 4 in the middle to fire into the front room as well?

How much gain can one get by the equivalent of "subwoofers at the headrest" (like in some cars) vs the 1m db rating?
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Old 29th March 2013, 05:38 AM   #13
just a guy is offline just a guy  Canada
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Is AVSforum the place I should be asking these questions instead?
I don't want to drive traffic away from this forum but to be honest, THIS IS WHAT THEY DO at avsforum. That's not to say you won't find excellent help here, but you won't find threads like this here.

The New Master List of BASS in Movies with Frequency Charts
Have fun with that, it's a comprehensive list of bassy movies WITH response charts showing where the bass is, how low and how loud.

6 DIY eD A7S-650 kits with FP14K clone
I haven't read this one but it looks like this guy has a dozen very high xmax 12 inch woofers powered with a 14000 watt rms amp. In a concrete bunker.

Have fun.
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Old 29th March 2013, 06:03 AM   #14
just a guy is offline just a guy  Canada
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Some practical info -

Your IB idea is sound. You can definitely use an IB for two different systems in two different rooms, one side just needs reversed phase.

IB subs do not have to be equally spaced, in fact you can cluster them in manifolds if you like. Like all speakers, they will be more effective if placed near boundaries like other walls or corners.

All rooms are different. A concrete bunker is like a pressure cooker, vinyl siding is like a sieve. For that reason, simulations are still just a guess, moreso than at higher frequencies. I can't produce much bass at all in my house but in my brother's large, solid Victorian brick house a modest sub rattles your eyeballs. It's even more devastating in his basement.

If you want the lowest bass you need to select your electronics very carefully, most will start to roll off too high. For example, some plate amps start to roll off at 30 hz or so, and even electronics without a high pass filter rarely go flat down to 10 hz.

Amps are cheap these days, you can get 14000 watts rms for about $1000 delivered but you have to order direct from China. Driver prices are coming down fast too, as demonstrated in the link I posted previously.

What else do you want to know?
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Old 29th March 2013, 06:18 AM   #15
18Hurts is offline 18Hurts  United States
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I'm sure there is some form of standards for low frequency content in IMAX theaters--they are built stout but probably filter out those frequencies you are trying to achieve. I'm assuming you are attempting to duplicate the standards so it should be possible to do so...

Here is the link for Dr. Vladimir Gavreau's research on sound as a weapon.

Deadly Sounds - Dr. Vladimir Gavreau

At the end of the day, sound is just an air pump really--that energy has to go somewhere or be absorbed by something. You are going to need one heck of an air pump since 4Hz requires 4 times the air displacement than 8 Hz.

My garage subs will only go down to about 22 Hz with slightly more than half a horsepower pushing the motors. My house sub drops into the teens which is good enough and my picture window won't withstand too much more.

Enjoy the article!
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Old 29th March 2013, 07:10 AM   #16
Don Hills is offline Don Hills  New Zealand
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Originally Posted by 18Hurts View Post
... You are going to need one heck of an air pump since 4Hz requires 4 times the air displacement than 8 Hz. ... !
This is only true in free air or a lossy room. The OP's idea of a "small room / large room" configuration is good, provided that the small room is solidly constructed and more or less airtight down to near DC. (Make the ventilation ducts long enough that the Helmholtz resonance of the room and ducts is close to DC.) Once you achieve this, you're in the pressurisation region where the SPL is determined by excursion - the SPL is dependent only on the volume ratio difference between the volume displacement of the speakers and the volume of the room. So (say) 120dB SPL at 4 Hz requires the same displacement as 120dB SPL at 8 Hz. The attached spreadsheet will let you work out what SPL you can achieve, and any box modelling program will let you work out how much power will be required to achieve it.
Attached Files
File Type: zip Room_SPL.zip (1.8 KB, 16 views)
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Old 29th March 2013, 09:08 AM   #17
Zero D is offline Zero D  United Kingdom
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Default 7 - 8Hz

Tesla was experimenting with VLF's in 1895 !

Earths natural f = circa 7.83Hz. "Hey, let's be careful out there "

Tesla's electro-mechanical oscillator or earthquake machine

Schumann resonances

Tesla discovered that the resonant frequency of the Earth was approximately 8 hertz (Hz).[7] In the 1950s, researchers confirmed that the resonant frequency of the Earth's ionospheric cavity was in this range (later named the Schumann resonance).

I agree that "some" studios, & an extremely small amount of others have access to experience such VLF's, but regular cinema goers & HT's do not.

Don is right. Most Amps are AC coupled so filter out VLF's. You would have to find DC coupled ones, or in most cases change the HP input filter, oh & the feedback HPF capacitor too. Not only that, ALL your sound equipment from the source, be it soundcard or otherwise, right through to the Amps, would need to be capable of VLF's. If not they would need modifying as well. As everything in the chain with HPF's accumilate the rolloff.

Well it sounds as if you won't rest until you get down as low as you can. I'll be following your progress, so all the best with it


Almost forgot. Check out this guys system www.Basspig.com The Bass Pig's Lair

Last edited by Zero D; 29th March 2013 at 09:22 AM.
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Old 29th March 2013, 06:57 PM   #18
weltersys is offline weltersys  United States
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Originally Posted by Doggyboy View Post
Okay no 7hz, important safety tip.
How much gain can one get by the equivalent of "subwoofers at the headrest" (like in some cars) vs the 1m db rating?
The 7 Hz myth is just BS, astronauts are subjected to SPL levels of around 160 dB down to nearly 0 Hz on blast off with no dire consequence.

Sound falls off at 6 dB per doubling of distance, placing the subs close to your ears would lower the cost requirements, but pressurization of the room to get the "feel" is better done with speakers in wall.
Make sure the subs are mounted in opposition (pointed at each other in a plenum) or the walls will shake, wasting energy and making annoying rattles.

I have found the resonant frequency of my control room 2x4 stud sheet rock walls to be around 15 Hz, it takes surprisingly little SPL (less than 105) to make the walls "flop" at that frequency.

Thick concrete walls are a good idea for high SPL if you want to go loud and clean below 20 Hz, and the usual studio acoustical treatment of the walls won't absorb frequencies that low.
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Old 30th March 2013, 12:52 AM   #19
tb46 is offline tb46  United States
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Using the driver suggested by 'just a guy' in Post #3 you can build a nice T-TQWT that will get you to the sub 10Hz region (depending on your low cut filter), and will let you evaluate whether this is too much or if you need to add multiples. Because of their size these enclosures should be build into the room structure, which has to be treated anyway to handle the resulting acoustic stresses, as well as the unavoidable room modes.

Maybe, play around a little with the attached simulation, e.g.: export it to AkAbak.....

Attached Images
File Type: jpg SI_18D2_TTQWT_Dual_Input.jpg (32.5 KB, 277 views)
File Type: jpg SI_18D2_TTQWT_Dual_SPL.jpg (31.0 KB, 272 views)
File Type: jpg SI_18D2_TTQWT_Dual_Schematic.jpg (21.6 KB, 272 views)
File Type: jpg SI_18D2_TTQWT_Dual_Excursion.jpg (24.3 KB, 271 views)
File Type: jpg SI_18D2_TTQWT_Dual_GD.jpg (28.7 KB, 204 views)
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Old 30th March 2013, 02:50 AM   #20
Inductor is offline Inductor  Portugal
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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).
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