I've got a couple more minutes now so I'll try to make a couple points more clear.
The room's boundary rigidity (strength and stiffness of ceiling, floor, walls) and the leakage (airtight or not) will determine how much room gain you get (amplitude). The room size (longest dimension) will determine what frequency range you get that gain. You will get max gain (limited by boundary rigidity and leakage factors) from 0 hz up to the frequency determined by the longest dimension of the room (or car). This becomes very clear in about 5 minutes if you play with the simulation program.
That means that cars go boom because they are quite rigid and airtight (compared to a drywall room) and very small (compared to a living room). The rigidity and airtight quality give a lot of boost and the small size gives boost way up in the frequency range.
For our purposes here, we are primarily concerned with getting a LOT of gain, so we need to focus on boundary rigidity and as little leakage as possible. The room size is not so important because it's exponentially easier to make bass at higher frequencies than at lower frequencies. A coffin sized room would afford gain up to a very high frequency but gain up to a high frequency is not that important. You still won't get any more amplitude (at the frequencies where you do have gain) than you would in a similar stiff and equally airtight very large room. You are going to have a bunch of 18 inch drivers so it's relatively easy to do 120 db at 20 hz even in an open field. It is much much (exponentially) harder to make 120 db at 4 hz so that's why boundary rigidity and leakage control trump room size.
For some reason I have a feeling that still won't be clear enough but I don't know how to make it more clear, other than suggesting you play with the simulation program yourself.
Now on to horns. If your goal was 10 hz on the low end horns are a viable alternative. But a 4 hz bass horn is unheard of. The dimensions would be astronomical. It is possible to make a horn smaller than ideal but at some point it simply becomes a transmission line and not a horn at all. It's also basically impossible to transport it or get your money out of it if you sell the property so I would advise against a horn for this purpose. I can simulate a horn for you if you want but I don't see the point. It's not really possible to feed two separate rooms with a horn anyway, so an extra control room would not be possible. The price of drivers is so cheap these days it doesn't really make sense to go to the time and expense a horn design would require when you can achieve your goals with IB.
And I'm being called to work again, so that's it for now.
The room's boundary rigidity (strength and stiffness of ceiling, floor, walls) and the leakage (airtight or not) will determine how much room gain you get (amplitude). The room size (longest dimension) will determine what frequency range you get that gain. You will get max gain (limited by boundary rigidity and leakage factors) from 0 hz up to the frequency determined by the longest dimension of the room (or car). This becomes very clear in about 5 minutes if you play with the simulation program.
That means that cars go boom because they are quite rigid and airtight (compared to a drywall room) and very small (compared to a living room). The rigidity and airtight quality give a lot of boost and the small size gives boost way up in the frequency range.
For our purposes here, we are primarily concerned with getting a LOT of gain, so we need to focus on boundary rigidity and as little leakage as possible. The room size is not so important because it's exponentially easier to make bass at higher frequencies than at lower frequencies. A coffin sized room would afford gain up to a very high frequency but gain up to a high frequency is not that important. You still won't get any more amplitude (at the frequencies where you do have gain) than you would in a similar stiff and equally airtight very large room. You are going to have a bunch of 18 inch drivers so it's relatively easy to do 120 db at 20 hz even in an open field. It is much much (exponentially) harder to make 120 db at 4 hz so that's why boundary rigidity and leakage control trump room size.
For some reason I have a feeling that still won't be clear enough but I don't know how to make it more clear, other than suggesting you play with the simulation program yourself.
Now on to horns. If your goal was 10 hz on the low end horns are a viable alternative. But a 4 hz bass horn is unheard of. The dimensions would be astronomical. It is possible to make a horn smaller than ideal but at some point it simply becomes a transmission line and not a horn at all. It's also basically impossible to transport it or get your money out of it if you sell the property so I would advise against a horn for this purpose. I can simulate a horn for you if you want but I don't see the point. It's not really possible to feed two separate rooms with a horn anyway, so an extra control room would not be possible. The price of drivers is so cheap these days it doesn't really make sense to go to the time and expense a horn design would require when you can achieve your goals with IB.
And I'm being called to work again, so that's it for now.
Originally Posted by weltersys
You can't "scale down" a 113 foot long 10Hz wave, and how it sounds in a theater will be far different than the experience in a small concrete bunker, both in terms of achievable SPL and acoustical response.
However, you are mixing for facilities that have little or no cabin gain.
The "biggest difference is that a normal theater will have less low end response and less dB" is not just a big difference, it is a HUGE difference.
Four times the excursion is required for the same SPL for each octave lower extension.
That means response to 20 Hz takes four times the power and loudspeakers as 40 Hz.
Response to 10 Hz takes four times the power and loudspeakers as 20 Hz.
Response to 5 Hz takes four times the power and loudspeakers as 10 Hz.
You can use a simple calculator to figure those differences, but soundproofing and making a building structurally hold up to loud VLF increases also hugely increases building costs, as more people turn to home theater from public theaters, the increased costs of VLF as you can achieve are not viable commercially.
Although you can create a mixing environment that can go extremely loud and low, theater (and home theater) economics dictate that your mix environment will not relate to the actual use, unless the actual playback is also in a small concrete box.
Mixing at vastly different levels with a system with vastly different LF extension in a room with vastly different acoustics than the intended playback environment is simply not a good idea.
For anecdotal evidence that the above statement is true, one simply can look at equal loudness hearing contours.
Your mix may sound impressive in your bunker, but pathetic by comparison when played back on a typical theater system.
Art
You can't "scale down" a 113 foot long 10Hz wave, and how it sounds in a theater will be far different than the experience in a small concrete bunker, both in terms of achievable SPL and acoustical response.
A sealed concrete small room will have enough cabin gain which makes loud VLF possible without spending more than a small fortune.
However, you are mixing for facilities that have little or no cabin gain.
The "biggest difference is that a normal theater will have less low end response and less dB" is not just a big difference, it is a HUGE difference.
Four times the excursion is required for the same SPL for each octave lower extension.
That means response to 20 Hz takes four times the power and loudspeakers as 40 Hz.
Response to 10 Hz takes four times the power and loudspeakers as 20 Hz.
Response to 5 Hz takes four times the power and loudspeakers as 10 Hz.
You can use a simple calculator to figure those differences, but soundproofing and making a building structurally hold up to loud VLF increases also hugely increases building costs, as more people turn to home theater from public theaters, the increased costs of VLF as you can achieve are not viable commercially.
Although you can create a mixing environment that can go extremely loud and low, theater (and home theater) economics dictate that your mix environment will not relate to the actual use, unless the actual playback is also in a small concrete box.
Mixing at vastly different levels with a system with vastly different LF extension in a room with vastly different acoustics than the intended playback environment is simply not a good idea.
For anecdotal evidence that the above statement is true, one simply can look at equal loudness hearing contours.
Your mix may sound impressive in your bunker, but pathetic by comparison when played back on a typical theater system.
Art
You make a good point here, most of the next gen kids are more than happy watching movies on their Iphones with the built in speaker.
But as I pointed out earlier, there are a lot of people that do have small concrete home theaters these days. 6 DIY eD A7S-650 kits with FP14K clone
I don't know how much of the market share has this type of HT but as prices drop it's becoming much more common. And people that have the capability will actively seek out media that will show off this capability even if the movie itself is terrible.
There's even music that goes below 10 hz these days. Here's a screenshot of Bass I Love You. (Full song analysis) This track has been around for years, I can see it was uploaded to youtube in 2008 but it might be substantially older than that.
An externally hosted image should be here but it was not working when we last tested it.
Here's a thread featuring music by Dub King, all tracks available for free download.
"The Truth Hz - Your DIY Setup Can't Handle This" - a compilation of infrasonic music by Dub King
He doesn't usually say how low each track goes but here's a post that goes into some detail. (Bold provided by me to point out the 4 hz note.)
There's also links to at least a couple of other artists that do the same type of thing. There's also a bunch of videos of people with crazy HT systems playing back these tracks. I don't know if any of it is any good but I'm going to download a few tracks and try them out in my car.
So there is a market for this type of stuff. There are people that have systems that can handle it. It's not a big market but it's growing as prices on electronics and subwoofers drop to levels we used to not even dare to dream about.
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Some great info here have been investigating a true subwoofer protect for some time i.e. <10Hz bass 🙂
I see you also posted in the Graham Holiman thread. You're looking in the wrong places if you are interested in that thing.
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