If you needed _4_Hz in room (but could pick the room) how would you? - AVS Forum
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Subwoofers, Bass, and Transducers > If you needed _4_Hz in room (but could pick the room) how would you?
homeomnimax's Avatar homeomnimax 08:45 PM 06-15-2013
This is an exploratory question concerning the frontiers of infrasound... if you had to create a mastering room capable of audibly reproducing very deep infrasound (current target 4hz - since apparently 7-8hz is routinely achieved by infinite baffle systems and seems fully feasible) how would you go about it?

This is a serious question, would ideally like to avoid the pages and pages of no i'm not seeking physical injury or getting my head examined or yadda yadda yadda which has occurred on other boards i've asked this question on. It wastes space, time and doesn't contribute to the topic. I'm told the ultimate bass fanatics are found on AVSforum and everyone keeps directing me here, so now i'm finally here with the same question. If anyone should know, i'm guessing it will be here.


One open variable is that you can specificy the room size - it can be the size of a minivan inside, I don't care, just enough room for at least a 32" HDTV and a mixing console, and a design which allows high fidelity on the higher frequencies. Ie - it cannot be a solid concrete chamber if that means having undamped walls that echo like hell at higher frequencies. However i'm assuming bass damping wont even affect things below about 1/4 wavelength so that shouldn't be a problem. However i'm told that infinite baffle systems have a lower limit on the size of either chamber, so it's possible that a larger room will actually work better than a smaller one or that there is a lower barrier on room size created by infinite baffle subs. (ie - I could double the subs, but would have to double the room size - same SPL and response, but cant play any deeper or louder)

This is a total package brainstorm though seeking a lowest total cost while meeting the goal. So if one person suggests just sitting inside the speaker enclosure (which is what the minivan-sized option really is probably, a car stereo 'wall' type enclosure just inside the home) and another suggests a giant quarter wave horn dug into your front lawn and piped in (though I think thats unfeasible sizewise below 10hz unless its a tapped horn) and another just says go with infinite baffle, everything is fine. However one big thing i'm concerned about is efficiency - by which I mean efficiency at 4hz trumps that at 20hz. I'm not seeking a 160db at 30hz car audio style system - i'm trying to get an honest audible (about 120db I think is the threshhold according to the guys that made the Thigpen rotary woofer) 4hz, in a room, with maybe around 2000 watts or so (or electrical demands out to the barn get more difficult - less be even better) which I think should be achievable, ideally in a larger room to double as a home theater room for a group (but if not then minivan sized still okay) of lets assume very solid construction and which is effectively isolated from the outside.

I'm told that you keep getting room gain as the frequency drops PROVIDED you have a completely closed off air environment. Even a slight leak of air pressure ruins this effect. This I think will be the critical factor making it feasible. If you can do it in a car I can replicate it in a home for instance. Let me worry about the HVAC system which will preserve life with enough oxygen inside a completely sealed room - i'm just seeking your suggestions of the best way of the physics to get 4hz within that environment IF that totally sealed room somehow completely changes the game.

Mik James's Avatar Mik James 09:09 PM 06-15-2013
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.
stereo2.0's Avatar stereo2.0 12:15 PM 06-16-2013
Quote:
Originally Posted by homeomnimax View Post

...if you had to create a mastering room capable of audibly reproducing very deep infrasound ... how would you go about it?...

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. tongue.gif
BeeMan458's Avatar BeeMan458 12:59 PM 06-16-2013
Quote:
Originally Posted by homeomnimax View Post

I'm told the ultimate bass fanatics are found on AVSforum and everyone keeps directing me here, so now i'm finally here with the same question. If anyone should know, i'm guessing it will be here.

I would check over at the DIY forum as that's where the ultimate kinda guys go.
datranz's Avatar datranz 01:07 PM 06-16-2013
^ +1. Diy section. Where all the bass but head are at. But wow! 4 hz. Going to be tough finding and amp powering it on a budget.
homeomnimax's Avatar homeomnimax 06:15 PM 06-22-2013
Quote:
Originally Posted by Mik James View Post

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. smile.gif

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. smile.gif

Quote:
Originally Posted by stereo2.0 View Post

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. tongue.gif

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. smile.gif 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?
Mik James's Avatar Mik James 08:03 PM 06-22-2013
Yeah I suppose i'm open to the idea of human hearing extending quite a bit below 20hz or 16hz (depending on who you ask).
Though I can only imagine the pressure involved in an audible 4hz...
This sounds like a neat idea but it also sounds particularly dangerous.
The Diy forum on avs is where most of the audio science and theory discussions happen, and there is also an audio theory and setup thread.
Bill Fitzmaurice's Avatar Bill Fitzmaurice 08:52 PM 06-22-2013
Quote:
Originally Posted by Mik James View Post

Yeah I suppose i'm open to the idea of human hearing extending quite a bit below 20hz or 16hz (depending on who you ask).
Below 20Hz, yes, but not by much. The problem is that when you have wavelengths longer than 60 feet they pass through your body with the same impunity with which they pass through walls, and when that happens for all intents and purposes they appear on both sides of the tympanic membrane at the same time with equal pressure. If the eardrum doesn't move you don't hear anything. You can feel well below 20Hz, but you don't really hear it. What you will hear is the harmonics, not the fundamentals. Those who claim we can hear infrasound have never been able to prove it, as to do so would require speakers capable of producing single digit frequencies at levels loud enough to hear without producing harmonics that contaminate the result, and said speakers do not exist.
craig john's Avatar craig john 07:20 AM 06-23-2013
Quote:
Originally Posted by Bill Fitzmaurice View Post

Below 20Hz, yes, but not by much. The problem is that when you have wavelengths longer than 60 feet they pass through your body with the same impunity with which they pass through walls, and when that happens for all intents and purposes they appear on both sides of the tympanic membrane at the same time with equal pressure. If the eardrum doesn't move you don't hear anything. You can feel well below 20Hz, but you don't really hear it. What you will hear is the harmonics, not the fundamentals. Those who claim we can hear infrasound have never been able to prove it, as to do so would require speakers capable of producing single digit frequencies at levels loud enough to hear without producing harmonics that contaminate the result, and said speakers do not exist.

http://www.rotarywoofer.com/

Specifications

Specifications: Amplifier Requirement: 150 watts @ 8 ohms
Impedance: 8 ohms 0Hz - 40Hz
Frequency Response: 1Hz – 30Hz +/- 4dB
Suggested Crossover: 20Hz @ 18dB/octave
Sensitivity 94dB 1 watt 1 meter @10Hz
Maximum Acoustic Output: >115dB between 1 and 20Hz.
Distortion: Typically 3% or less between 1 and 20Hz @90dB




arnyk's Avatar arnyk 07:32 AM 06-23-2013
Quote:
Originally Posted by homeomnimax View Post

This is an exploratory question concerning the frontiers of infrasound... if you had to create a mastering room capable of audibly reproducing very deep infrasound (current target 4hz - since apparently 7-8hz is routinely achieved by infinite baffle systems and seems fully feasible) how would you go about it?

The relevant parameter with bass is displacement per dollar, installed. At 4 Hz, I believe that the winner still is: a well-designed and constructed cone-voice coil subwoofer.
arnyk's Avatar arnyk 07:42 AM 06-23-2013
Quote:
Originally Posted by craig john View Post

Quote:
Originally Posted by Bill Fitzmaurice View Post

Below 20Hz, yes, but not by much. The problem is that when you have wavelengths longer than 60 feet they pass through your body with the same impunity with which they pass through walls, and when that happens for all intents and purposes they appear on both sides of the tympanic membrane at the same time with equal pressure. If the eardrum doesn't move you don't hear anything. You can feel well below 20Hz, but you don't really hear it. What you will hear is the harmonics, not the fundamentals. Those who claim we can hear infrasound have never been able to prove it, as to do so would require speakers capable of producing single digit frequencies at levels loud enough to hear without producing harmonics that contaminate the result, and said speakers do not exist.

http://www.rotarywoofer.com/

Specifications

Specifications: Amplifier Requirement: 150 watts @ 8 ohms
Impedance: 8 ohms 0Hz - 40Hz
Frequency Response: 1Hz – 30Hz +/- 4dB
Suggested Crossover: 20Hz @ 18dB/octave
Sensitivity 94dB 1 watt 1 meter @10Hz
Maximum Acoustic Output: >115dB between 1 and 20Hz.
Distortion: Typically 3% or less between 1 and 20Hz @90dB

One missing relevant parameter is SNR over a range of SPLs. I understand that for this kind of subwoofer, it sucks at low SPLs.

Displacment per dollar seems to be wanting as well.
MKtheater's Avatar MKtheater 07:42 AM 06-23-2013
I believe it is not hard, it just takes some money. It takes a solid, well built room, power, and displacement. If the room is not solid then it takes even more displacement, power, and low end boost. I think many people with multiple sealed subs and lots of power are getting it but can't measure it like me. My measuring gear can't go that low, especially the sound card. Anyways, hit up Bossobass about his system and even more important his signal shaper, that is how you do it!
Bill Fitzmaurice's Avatar Bill Fitzmaurice 08:07 AM 06-23-2013
Quote:
Originally Posted by craig john View Post

http://www.rotarywoofer.com/
Now show us a measured response chart of below 10Hz content with inaudible THD. That's not going to happen. Yes, it can reproduce 5Hz. Yes, you can feel the air compression in the room resulting from that 5Hz. But what you'll hear is harmonics, not the fundamental.
One method to test what you can really hear is to use a very low THD very high sensitivity speaker outdoors, where there isn't enough air compression to feel. I've done so, and even at 110dB levels if it were not for the meter registering output below 20Hz you would not know the speaker was playing.
popalock's Avatar popalock 08:56 AM 06-23-2013
Reserved.

Hard to read a thesis on my cell...
MKtheater's Avatar MKtheater 09:19 AM 06-23-2013
When I was running 125 dB sine waves at 10hz I heard all the walls cracking and bookshelves rattling. This was in my rack room and not in the theater. Hard to hear inside.
Mark Seaton's Avatar Mark Seaton 03:02 PM 06-23-2013
Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by Mik James View Post

Yeah I suppose i'm open to the idea of human hearing extending quite a bit below 20hz or 16hz (depending on who you ask).
Below 20Hz, yes, but not by much. The problem is that when you have wavelengths longer than 60 feet they pass through your body with the same impunity with which they pass through walls, and when that happens for all intents and purposes they appear on both sides of the tympanic membrane at the same time with equal pressure. If the eardrum doesn't move you don't hear anything. You can feel well below 20Hz, but you don't really hear it. What you will hear is the harmonics, not the fundamentals. Those who claim we can hear infrasound have never been able to prove it, as to do so would require speakers capable of producing single digit frequencies at levels loud enough to hear without producing harmonics that contaminate the result, and said speakers do not exist.

I assume you're ignoring the info linked earlier and the experimentation Thigpen has done. Please don't brush off what Bruce Thigpen has done as a marketing effort, as he's much more an inventor/engineer than marketeer.

Your mention of bass passing through the body is the first I've seen of such a hypothesis. Of course if that was really the case I wonder how we could sense changes in barometric pressure and related phenomenon. All that is needed for perception is a difference in pressure across the ear membrane, not a perfect isolation of each side. I wouldn't be surprised if the issue you describe is partly related to reduced sensitivity, but I don't see anything that would eliminate such perception.
Mark Seaton's Avatar Mark Seaton 03:07 PM 06-23-2013
Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by craig john View Post

http://www.rotarywoofer.com/
Now show us a measured response chart of below 10Hz content with inaudible THD. That's not going to happen. Yes, it can reproduce 5Hz. Yes, you can feel the air compression in the room resulting from that 5Hz. But what you'll hear is harmonics, not the fundamental.
One method to test what you can really hear is to use a very low THD very high sensitivity speaker outdoors, where there isn't enough air compression to feel. I've done so, and even at 110dB levels if it were not for the meter registering output below 20Hz you would not know the speaker was playing.

The device has been installed and demonstrated many times where single digit THD has been observed and measured. I'm not sure if you consider that low enough.
Mark Seaton's Avatar Mark Seaton 03:30 PM 06-23-2013
Quote:
Originally Posted by arnyk View Post

Quote:
Originally Posted by homeomnimax View Post

This is an exploratory question concerning the frontiers of infrasound... if you had to create a mastering room capable of audibly reproducing very deep infrasound (current target 4hz - since apparently 7-8hz is routinely achieved by infinite baffle systems and seems fully feasible) how would you go about it?

The relevant parameter with bass is displacement per dollar, installed. At 4 Hz, I believe that the winner still is: a well-designed and constructed cone-voice coil subwoofer.

Agreed. This is even more true as the volume/size of the listening environment gets smaller.

Quote:
Originally Posted by arnyk View Post

http://www.rotarywoofer.com/

Specifications

Specifications: Amplifier Requirement: 150 watts @ 8 ohms
Impedance: 8 ohms 0Hz - 40Hz
Frequency Response: 1Hz – 30Hz +/- 4dB
Suggested Crossover: 20Hz @ 18dB/octave
Sensitivity 94dB 1 watt 1 meter @10Hz
Maximum Acoustic Output: >115dB between 1 and 20Hz.
Distortion: Typically 3% or less between 1 and 20Hz @90dB

One missing relevant parameter is SNR over a range of SPLs. I understand that for this kind of subwoofer, it sucks at low SPLs.

Displacment per dollar seems to be wanting as well.[/quote]

From what I recall in a couple demos and talking with Bruce, "sucks" might be a bit a bit strong... or a good pun. The manifold used in the installation can reduce noise significantly. It's noisy by very isolated room standards, quiet by comparison to many rooms. I'd agree it's certainly not economical until a room/space is really large and where the primary interest is the very lowest frequencies. What I did find the device very useful for was actual experimentation and listening tests at low levels of harmonic distortion and significant SPL. A few listening occasions left me thinking the VLF range was well worth pursuing; especially with lower distortion audibility.
FOH's Avatar FOH 04:36 PM 06-23-2013
+1

Thigpen is no PT Barnum ....


Also, anyone being doubtful;
Be mindful, in addition to the wonderful and oft discussed benefits of PVG, there's also the reciprocal support of the ULF, at a more significant level as the associated harmonics.

Win-win
Bill Fitzmaurice's Avatar Bill Fitzmaurice 08:28 PM 06-23-2013
Quote:
Originally Posted by Mark Seaton View Post

Your mention of bass passing through the body is the first I've seen of such a hypothesis.
I was introduced to that concept by Tom Danley.
There's also been a lot of research done with respect to animals who use ULF for communication, especially elephants. We know that they make ULF vocalizations, as it's been measured, although we can't hear them. It also seems that they might not hear them either, apparently their feet are used as receptors for ULF vibrations via ground conduction.
homeomnimax's Avatar homeomnimax 02:04 AM 07-30-2013
Mostly finishing up the topic (as i'll move most of it to DIY) but just showing that I did read and consider everything said here.

Quote:
Originally Posted by MKtheater View Post

I believe it is not hard, it just takes some money. It takes a solid, well built room, power, and displacement. If the room is not solid then it takes even more displacement, power, and low end boost.

Well that's kind of my plan, start with an extremely solid and for acoustical purposes effectively airproofed room.

The variables that I don't understand the physics of so far are:
- What is the effective minimum size possible? (caused by the 10x Vas infinite baffle sub designs creating a lower limit) Aka, the level at which I can't increase output or extension by shrinking the room down further, because efficiency at lowest frequency is lost. Assume a single driver, even if the resulting room is too small for habitation - then i'll simply add drivers (ie 2x, 4x) and make the space larger accordingly. I don't have specific drivers in mind, just looking for a rule of thumb ballpark. Are we talking something smaller than a minivan?
- Does room shape matter much when frequency wavelength exceeds the longest room dimension? My guess is i'm basically just pressurizing a space, whether it's a dodecahedron, pyramid, L shaped whatever, etc. (i'm aware those would ruin upper frequencies, its just to understand the point)
- Would thick sound absorbing material, such as a strawbale from 18-36 inches thick on every surface, reduce infrasound output? I'm not sure at which point it starts absorbing infrasound energy... maybe none at all when thickness is less than 1/4 of the wavelength? (some have suggested) I need the efficiency for infrasound, but for definately audible frequencies i'm willing to give up efficiency for quality. Even anechoic chamber quiet would be fine at audible frequencies. Being in a concrete room is fine, if the walls are deadened with strawbale or another thick sound absorbing material preferably more affordable than the "cost 5 digits to dampen your room" pro bass trap stuff, but if infrasound demands hard reflective surfaces that's probably more compromise than i'm willing to do, because then it's ONLY useful for infrasound, not general audio mastering.

Quote:
Originally Posted by Bill Fitzmaurice View Post

Now show us a measured response chart of below 10Hz content with inaudible THD. That's not going to happen. Yes, it can reproduce 5Hz. Yes, you can feel the air compression in the room resulting
Quote:
Originally Posted by Bill Fitzmaurice View Post

Below 20Hz, yes, but not by much. The problem is that when you have wavelengths longer than 60 feet they pass through your body with the same impunity with which they pass through walls, and

For purposes of easing the discussion i'll simply withdraw the term 'audible' and replace it with perceivable. I still want a room capable of generating fairly precise (aka - produced by speaker cones, not just an infrawhistle putting out one note sine waves) infrasonic pressure waves, and not just using 'bass shakers' or similar. The effect is not the same. I plan to/hope to experiment/master up normal music and environmental audio soundtracks with and without bass shakers, with and without reproduced infrasound, but I need the ability to do both and experience both if i'm going to decide which is the most appropriate to actually use, or to experiment and see where 'bass shakers' are an appropriate substitute for massive cone movements, and where they are not. Although aware of the discussion that "you cant hear infrasound, you can only feel it" nonetheless reproducing it furthers the realism of what is generally an audio-centric reproduction medium. If i'm playing the 1812 Overture Super audio CD edition, the cannon thumps are going to move infrasonic air if the system can keep up. So will space shuttle recordings, ocean waves, tiger growls and a number of other natural phenomena.


So this is just a catchup post, does anyone else have comments on infrasonic reproduction and room physics thereof? I wasn't sure if DIY mostly covers the physical building of speaker cabinets, or if the most knowledgeable people for acoustics in general frequent there just as much as here. smile.gif
BeeMan458's Avatar BeeMan458 05:58 AM 07-30-2013
Quote:
Originally Posted by homeomnimax View Post

So this is just a catchup post, does anyone else have comments on infrasonic reproduction and room physics thereof? I wasn't sure if DIY mostly covers the physical building of speaker cabinets, or if the most knowledgeable people for acoustics in general frequent there just as much as here. smile.gif

From cabinet start to plugged in finish and everything to one's heart's content in the middle., stop by the DIY forum and ask some questions as opposed to asking questions here.

This forum is more a showroom floor forum where folks talk about how to deal with, like a car, setting up the subwoofers they bought from their local subwoofer showroom floor and how to get the best out of their subwoofer system in the room they're going use for subwoofer playback. This includes tweaks and room acoustic measurements so one can know and understand how to properly integrate their subwoofer into their room's acoustics but has nothing to do with how to build a 4Hz subwoofer system and accompanying room.

The DIY forum is the subwoofer garage where everybody digs around under the hood and builds their own engines and transmissions There's also a build your own Home Theater forum where folks deal with room acoustics and how to get the best out of your dedicated Home Theater room acoustics as opposed to the majority of us who use a living room for our Home Theater sound playback.

(and please everybody, don't bust my chops over what constitutes a Home Theater vs what is a dedicated Home Theater as the answer is a subjective response)
nube's Avatar nube 10:07 AM 07-30-2013
Some really smart people on this thread, so I'll try not to embarrass myself with too much speculation or verbosity.

First, as many have mentioned, this thread really needs to be in the DIY and/or the Dedicated Theater Design & Construction forums. You have a lot of complex questions to consider, and those forums are visited by experts who have years and years of experience answering many of the questions you're going to need to ask, as well as firsthand expertise in building the solutions to fit the answers to those questions.

Second, to Mik & Bill, "infrasound" is a misnomer, and the "audible" range of 20-20KHz is limited conventional wisdom, mostly due to Fletcher & Munson's limited testing. Auditory sensitivity decreases with frequency, but there is no brick wall that limits hearing. Auditor55 and I had this discussion a couple of years ago in this very forum, and the scientific research on humans pretty conclusively points to average people being able to hear (not merely perceive) fundamentals down to 2hz and likely lower. However, we also perceive those frequencies with the additional sensory corpuscles (forget the scientific name) in the ear, e.g. pressure, etc. If you're curious to read the peer-reviewed literature, look in my sig for a couple, and I could link to the discussion from the past. Long story short: we do hear well below 20hz, and we also sense those ULF frequencies - so who knows what's more important in the production, mixing and sound design of a particular type of content - but I'd rather not blow this thread too far off course.

Third, I am not a mixer or sound designer, but I've been around a few who mix for movies & TV, and I think they most frequenctly work in big mixing studios. But, recall that there's a difference between the sound designers and the mixers. If what you're wanting to do is mix for large exhibitions (movie theaters), I think you need a big room. I've also been in a lot of different movie theaters (when I worked for a movie theater equipment manufacturer), and there's just something significantly different about how the sound "develops" in a large room that you can't easily replicate in a small booth. For that reason, and because your budget is tiny, I think the only way you're going to get close to the numbers you want is to go with an IB setup, and I think it's worthwhile to put it in a room built to seat in 3-4 tiers at least 9-12 people comfortably, for that "big sound."

Fourth, there are two big problems I see with an IB setup, right off the bat. As with any sub system, your placement is critical. But, when building a room with an IB, you kinda have a chicken & the egg scenario. How do you know what placement is going to sound best before you build the room and fill it; how can you design the room without knowing where the best placement will be? More experienced guys in the Dedicated Theater Design & Construction forum, as well as over at the Cult of the Infinitely Baffled, can help you approximate this stuff based on room dimensions and construction materials, but with an IB in new theater construction you're really limited - you have one shot to get it right. For that reason, you should probably increase your budget to at least $3K and plan to build two or more sealed subs that can be moved around the room to help get a flat response. A really flat response is what you want, by the way. No house curves in your proposed area of mixing. wink.gif

The second big problem I see with the IB setup is that your budget is just too small to build a real theater + mixing studio, or one room that doubles as both. "There's no replacement for displacement" and "displacement is key," as the smart guys like to say, and it doesn't come cheap. I don't really know a whole lot about infinite baffle systems, but I'm pretty sure you'll need large subs with a lot of stroke and relatively "good" sensitivity in the lower end of the range to get to your particular dB target. Your best bet is probably to go with something that's reasonably priced but still a world-beater, such as the FTW-21 from iST (Mach 5). These are "pretty reasonably priced," afaik, but I'd check with them via email to see about REAL availability, as delivery & QA has been somewhat of a problem for them on occasion. If that won't work, maybe you can get a good deal on 6-8 of the SI 18" drivers - I dunno if they're still at introductory pricing or not.

Fifth, and maybe most importantly, you're REALLY going to have to pay attention to your signal chain rolloff if you want to get this kind of impressive output at 4hz, because 120dB is insane. This means you're going to have to go with fairly high end equipment that has been independently tested to have minimal rolloff until 3hz. This means your processor, your EQ/LT circuit, and your amps all have to have excellent capabilities. This doesn't come cheap, but it's doable. IMO, this will likely be the biggest limiting factor in whether or not you can reach your target AT ALL.

Lastly, I think that the idea that rooms must be hermetically sealed to get PVG (what we like to call "room gain") is overblown. IIRC, you'll see gain in nearly every room up to the point of 1/4 wavelength, no matter if it's sealed or not. Sealing will likely increase the gain, but I wouldn't worry too much about making it absolutely perfectly sealed, especially since it will have an HVAC, and it'll be detached from the main house by being out in the barn. I'm guessing that addressing room modes and rattles is going to be a much higher priority once you get in and construct this place.

I'd hope I'm not leading you too far astray, but I'd like to get this discussion back on track in terms of recommendations. I'm really interested to see where you take this project! I'm guessing much more experienced people will have additional and better input for you, if the discussion can get on track. wink.gif
bossobass 12:10 PM 07-30-2013
I have no earthly idea how you get flat to 4 Hz @ reference level in 3500 cubes. I just got lucky...


bossobass 12:14 PM 07-30-2013
It's probably gonna be difficult to hear <2% THD, but what would I know about that vs the experts?


bossobass 12:22 PM 07-30-2013
I'm not real sure, but it probably makes sense that if the signal you feed your subs has no 4 Hz content, you probably won't get 4 Hz playback in any room:


nube's Avatar nube 06:17 AM 07-31-2013
All good stuff for the OP to know, Dave. You're one of those experts I was thinking about when posting.

I'm very interested to hear what sort of recommendations you have to help him reach that level of performance in a large-ish room, and reasonably near his posted $2k budget.
bossobass 01:45 PM 08-01-2013
Thanks Abraham for the kind words and consistently good posting. It would be nice if you could also post some details of your system, on which you did a superb job. I'm sure your playback results are just as good. cool.gif

Here are the brass tacks:

1) Signal chain: Flat to 3 Hz. Without this, there will be no success <10 Hz.

Here are some versions of signal chain using the required L/T configuration accomplished through various hardware options from the player to the AVR/Preamp to the signal shaper to the amplifier. All have a 2nd order LPF @ 250 Hz in line. NOTE The light blue trace is through a DCX using only a shelf filter, as some suggest using. Obviously, there can be variations of that single curve based on what AVR/Amplifier is used:



It should require no comment as the graph tells the story of how the final response will be influenced by what signal chain is employed.

2) Driver displacement: .01 liters per cubic foot of listening room. Example: 2000 cubes = 20 liters of displacement minimum. That requirement's met by employing 3 UXL-18s, 4 SI-18s, 6 SI 15s, 7 Dayton HO-18s, 6 Dayton 15 Ultimax, 7 SA-15s, etc.

Alignment: Sealed. Ultimate "efficiency" <20 Hz is determined by box size, but must be balanced with excursion protection, which is an investigation, like the signal chain investigation, requires careful thought and final testing and will be dependent on the parameters of the driver chosen vs the Vb chosen with caution being exercised against the need to alter the signal chain in a way that eliminates the bandwidth of interest.

Amplification: Approximately 5W peak per cubic foot of listening space. This is based on a system designed with proper signal shaping to mate the system with the room. This requires a fairly accurate measurement of the naked system response compared to the system response in-room, from which comparison the Room Gain profile may be determined. The input signal may be altered to affect a new system FR that's designed to mate the system so that the result is a flat response to the desired frequency. . It's assumed that the amplifier(s) will be supplied by the proper AC and that the system will be operated only by responsible persons after proper setup, calibration and limits testing in-room using the actual program source of interest.

Transmission loss calculation: A debatable subject when speaking about <100 Hz, but the losses will obviously vary by construction method. This is the part of the equation that most folks confuse with "a sealed room".

All of my own imperial evidence from 10 years of measuring suggests that how sealed a room is, regarding air tightness, is largely irrelevant. Contrary to conventional wisdom, a drivers motion does not affect a change in the ambient pressure of a room. Rather, the drivers motion creates a sound pressure wave that travels through the air in the room. The air in any particular room may vary in temperature and/or humidity which both effect the behavior of the pressure wave, but the differences in that variable are unmeasurable unless one lives in a tent in the woods in the mountains or some similar unrealistic and irrelevant extreme.

The gain from the rooms boundaries increases as frequency decreases because the longer the sound wave vs the distance to boundaries, the more interference becomes constructive and conversely, the less the chance reflections can be destructive. Using this premise to explain 'room gain', a completely enclosed room may actually have less room gain than one which is partially open. The pertinent factors are; Item 1) above, item 2) above, transmission losses in the bandwidth of interest, the coincidence of resonant frequencies of the structure with the BW of interest and the placement of the system within the listening space.

Transmission losses through the boundaries will determine how much gain you realize at any given frequency, assuming all of the above have been considered and executed optimally. Obviously, if half the pressure wave is lost through the boundary to outside the room, then only 1/2 can be reflected back into the room to continue reflecting as it decays.

In any case and regardless of one's personal opinions regarding the mechanics of the phenomenon known as "Room Gain", measured responses of systems taken outdoors at GP vs in-room from Ilkka, Ed Mullen, Josh Ricci, MKT, notnyt and myself in rooms ranging from <2000 cubes to >4000 cubes show that "Room Gain" begins around 30 Hz and continues to increase in a similar pattern as frequency decreases down to the signal chain rolloff, which then dominates in-room response at the lowest octaves.

Using 2000 cubes listening room and DIY boxes loaded with 4 SI-18s (21.2 Liters), MiniDSP, a "clone" amplifier, the system will cost < $2500. It will meet the 4 Hz in-room response requirement at a properly calibrated reference level in any room that size.

In my case:



ROOM: 3500 cubes
DRIVER DISPLACEMENT: 36 Liters (Formula suggests: 3500 X .01 = 35 Liters)
SIGNAL CHAIN: (FR shown in graph) Oppo BDP-105 as pre/pro/player ==> SEQSS analog signal shaper =>> clone amplifier version (2)
AMPLIFICATION: 2 amplifiers, each @ 9KW peak (18KW total). Formula suggests: 3500 cubes X 5W = 16,500W peak.
IN-ROOM results: (shown in graph).
Playback Accuracy at Reference Level graphed from the LP:

http://picasion.com/i/1VXeB/

This is the basic formula. It will work for any room. If more output is desired, more displacement/amplification is required, which is scaled at +6dB per 2X. The formula can be deviated from only if the desired bandwidth is truncated on the low end by design or by deviating from any single point of the formula.
MemX's Avatar MemX 11:22 AM 08-02-2013
Hey Bosso, thank for your really helpful post for us noobs smile.gif


Your example is remarkably close to what I'm considering!
Quote:
Originally Posted by bossobass View Post

Using 2000 cubes listening room and DIY boxes loaded with 4 SI-18s (21.2 Liters), MiniDSP, a "clone" amplifier, the system will cost < $2500. It will meet the 4 Hz in-room response requirement at a properly calibrated reference level in any room that size.

c.2188cu ft room, 4xSI18s in a sealed configuration... My only concern is that the Clone amp won't be reliable and there will be no real aftersales support frown.gif the iNukes roll off too high (10Hz), and the CV5000 that could be another option might draw too much power on my already heavily used ring main in the lounge/kitchen/diner!

Decisions...
dominguez1's Avatar dominguez1 11:28 AM 08-02-2013
Quote:
Originally Posted by bossobass View Post

Thanks Abraham for the kind words and consistently good posting. It would be nice if you could also post some details of your system, on which you did a superb job. I'm sure your playback results are just as good. cool.gif

Here are the brass tacks:

1) Signal chain: Flat to 3 Hz. Without this, there will be no success <10 Hz.

Here are some versions of signal chain using the required L/T configuration accomplished through various hardware options from the player to the AVR/Preamp to the signal shaper to the amplifier. All have a 2nd order LPF @ 250 Hz in line. NOTE The light blue trace is through a DCX using only a shelf filter, as some suggest using. Obviously, there can be variations of that single curve based on what AVR/Amplifier is used:



It should require no comment as the graph tells the story of how the final response will be influenced by what signal chain is employed.

2) Driver displacement: .01 liters per cubic foot of listening room. Example: 2000 cubes = 20 liters of displacement minimum. That requirement's met by employing 3 UXL-18s, 4 SI-18s, 6 SI 15s, 7 Dayton HO-18s, 6 Dayton 15 Ultimax, 7 SA-15s, etc.

Alignment: Sealed. Ultimate "efficiency" <20 Hz is determined by box size, but must be balanced with excursion protection, which is an investigation, like the signal chain investigation, requires careful thought and final testing and will be dependent on the parameters of the driver chosen vs the Vb chosen with caution being exercised against the need to alter the signal chain in a way that eliminates the bandwidth of interest.

Amplification: Approximately 5W peak per cubic foot of listening space. This is based on a system designed with proper signal shaping to mate the system with the room. This requires a fairly accurate measurement of the naked system response compared to the system response in-room, from which comparison the Room Gain profile may be determined. The input signal may be altered to affect a new system FR that's designed to mate the system so that the result is a flat response to the desired frequency. . It's assumed that the amplifier(s) will be supplied by the proper AC and that the system will be operated only by responsible persons after proper setup, calibration and limits testing in-room using the actual program source of interest.

Transmission loss calculation: A debatable subject when speaking about <100 Hz, but the losses will obviously vary by construction method. This is the part of the equation that most folks confuse with "a sealed room".

All of my own imperial evidence from 10 years of measuring suggests that how sealed a room is, regarding air tightness, is largely irrelevant. Contrary to conventional wisdom, a drivers motion does not affect a change in the ambient pressure of a room. Rather, the drivers motion creates a sound pressure wave that travels through the air in the room. The air in any particular room may vary in temperature and/or humidity which both effect the behavior of the pressure wave, but the differences in that variable are unmeasurable unless one lives in a tent in the woods in the mountains or some similar unrealistic and irrelevant extreme.

The gain from the rooms boundaries increases as frequency decreases because the longer the sound wave vs the distance to boundaries, the more interference becomes constructive and conversely, the less the chance reflections can be destructive. Using this premise to explain 'room gain', a completely enclosed room may actually have less room gain than one which is partially open. The pertinent factors are; Item 1) above, item 2) above, transmission losses in the bandwidth of interest, the coincidence of resonant frequencies of the structure with the BW of interest and the placement of the system within the listening space.

Transmission losses through the boundaries will determine how much gain you realize at any given frequency, assuming all of the above have been considered and executed optimally. Obviously, if half the pressure wave is lost through the boundary to outside the room, then only 1/2 can be reflected back into the room to continue reflecting as it decays.

In any case and regardless of one's personal opinions regarding the mechanics of the phenomenon known as "Room Gain", measured responses of systems taken outdoors at GP vs in-room from Ilkka, Ed Mullen, Josh Ricci, MKT, notnyt and myself in rooms ranging from <2000 cubes to >4000 cubes show that "Room Gain" begins around 30 Hz and continues to increase in a similar pattern as frequency decreases down to the signal chain rolloff, which then dominates in-room response at the lowest octaves.

Using 2000 cubes listening room and DIY boxes loaded with 4 SI-18s (21.2 Liters), MiniDSP, a "clone" amplifier, the system will cost < $2500. It will meet the 4 Hz in-room response requirement at a properly calibrated reference level in any room that size.

In my case:



ROOM: 3500 cubes
DRIVER DISPLACEMENT: 36 Liters (Formula suggests: 3500 X .01 = 35 Liters)
SIGNAL CHAIN: (FR shown in graph) Oppo BDP-105 as pre/pro/player ==> SEQSS analog signal shaper =>> clone amplifier version (2)
AMPLIFICATION: 2 amplifiers, each @ 9KW peak (18KW total). Formula suggests: 3500 cubes X 5W = 16,500W peak.
IN-ROOM results: (shown in graph).
Playback Accuracy at Reference Level graphed from the LP:

http://picasion.com/i/1VXeB/

This is the basic formula. It will work for any room. If more output is desired, more displacement/amplification is required, which is scaled at +6dB per 2X. The formula can be deviated from only if the desired bandwidth is truncated on the low end by design or by deviating from any single point of the formula.
Great summary bosso. One of the best posts I've seen on avs. Bookmark this one folks. It's an excellent guideline. Chef bosso reveals a great recipe. Salt to taste as needed...
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