Infrasonic Speaker - Need advice for undergrad thesis project

[weltersys]

Originally Posted by weltersys

Blizzardbuffalo,

The references you posted do have footnotes tying them to NIOSH and OSHA, both use dBA, not dB SPL.

The "quickly closing a door reached 49.07db(A) at 28Hz " would read about 40 dB higher (89.07) read without weighting.

Those readings were from outside the car, inside the VLF could be another 40 dB higher.
Funny study, thanks for the link.
Art

[MiiB]

I think at those frequencies we hear with the full body, so while the ears may be less sensitive, we feel the pressure and sound anyway. I am confident that there's actually a lot on info IRL that we miss on recorded material compared to live events.

[Don Hills]

Originally Posted by blizzardbuffalo

... If they are using a weighting scale, they do not mention it.

(Almost) every country uses IEC 61672-1:2003. It mandates A weighting.

For the US, NIOSH 98-126 specifies A weighting.

[Rive]

Originally Posted by lightlinked

what is your budget? I built one of these Lab12 - Tapped Horn - for an interactive new media bull poop installation when I was in college. It will reasonably hit 16 hz and lower if you are careful. however its quite impractical afterwards, too low for a pa sub, great for a theater. its BIG. Building it wasn't too bad but if you've never used a table saw before it might be a tad ambitious. you might be better off with a dual 18 and careful management with a max msp patch since most speaker management dsp wont go below 20hz.

You, sir, are speaking my language. I built a pair of PA's for myself using a tapered horn very similar to the technique pictured in your build (which was very well done, I might add).

My current most likely option, depending on wood costs, is to do something like this. I've been a bit intimidated though, because of the gigantic proportions needed to reach 10 Hz. If you say your build got down to 16 Hz reasonably well, I'm sure a little adjustment could get me down a bit farther and I am willing to compromise.

I was actually planning to compose mostly with Max/MSP, actually. However, I don't quite understand what you mean when you mention using a patch to manage dsp? Could you explain a bit further?

[Rive]

Originally Posted by jwmbro

Hi,
if you want to go low, you need to go big. I have an idea for a dual LAB-12 big box horn that might suffice, and depending on your wood costs could be <800$. But it's a 3000l monster - floor to ceiling height, over 1m^2 cross section, and probably about 10 (!) sheets of plywood to build. But it would do 120db from 10Hz and up if properly corner loaded.

I doubt you can get much more than that at your budget using traditional drivers - low frequencies eat cone excursion for breakfast, and unless you can control it with proper horn loading, you'll run out soon. And horn loading at this frequency requires vast truck-length horns - think 20 thousand liters or more. Probably not in the money/time budget to build

Wow, that is a behemoth of a build. This was what I was worried about, though you're right, there's really not much of a way around it using traditional drivers. I've looked at other methods including that rotary woofer, but mostly everything is either conceptually outside of my ability or fiscally outside my ability.

I am pretty sure that I will have to compromise and make my targe frequency above 10hz. I was thinking perhaps somewhere between 12 and 16. Things are a bit more manageable in that area. Do you have plans for that build, btw?

[Rive]

Originally Posted by DUG

Think outside of the box:

ACP&D Limited - How servo hydraulic amplifiers work
Woodward | Hydraulic Amplifier

I don't know about cost, but it is another way.

This is a really really cool idea. I suppose I would have to attach it to some extremely large diaphragm, though?

[weltersys]

Originally Posted by Rive

My current most likely option, depending on wood costs, is to do something like this. I've been a bit intimidated though, because of the gigantic proportions needed to reach 10 Hz. If you say your build got down to 16 Hz reasonably well, I'm sure a little adjustment could get me down a bit farther and I am willing to compromise.

The LabSub design rolls off at below Fc, about 32 Hz.
In room, cabin gain can make up for some of the roll off.
Tom Danley gave away the Labsub (Live Audio Board) sub design when he came up with tapped horns. The Emminence Lab 12, designed for the Labsub, also works very well in low tuned tapped horns.
A tapped horn can go far lower per size than a front loaded horn, it does not depend on a huge mouth to go low and loud.
This is evident in that the Gjallerhorn is not much larger than the LabSub, but goes considerably lower and louder.

Art

[jwmbro]

Originally Posted by Rive

Wow, that is a behemoth of a build. This was what I was worried about, though you're right, there's really not much of a way around it using traditional drivers. I've looked at other methods including that rotary woofer, but mostly everything is either conceptually outside of my ability or fiscally outside my ability.

I am pretty sure that I will have to compromise and make my targe frequency above 10hz. I was thinking perhaps somewhere between 12 and 16. Things are a bit more manageable in that area. Do you have plans for that build, btw?

Nothing I have physical buildable plans for yet, just an idea in my head with some corresponding hornresp simulations. But basically picture something like the Lab12 Tapped Horn linked previously, just double the height, width and depth, and add in a second driver to fill up the double width. it definitely needs to be at least a 4-path fold horn, or else you won't get the ~10m path length you will need for infrasonic output.

[jwmbro]

I should be working on a presentation right now, which is why I'd much rather doodle subwoofers on my notepad - here's a quick sketch of something I have in mind:



This one is sketched with efficient usage of 4x8 foot sheets of plywood in mind - I'm assuming you are based in USA like your flag suggests, and this is the size of wood available to you. The two biggest sides are 4x8 foot sheets, and the internal width of the horn is 2 feet. My markings on the doodle are metric though - all in cm. Should be buildable using 5 sheets for the box, plus maybe 1 whole extra sheet (or any scrap wood you have) for bracing - a big box like this is going to need to be very well braced.
Here's how hornresp simulates the output, at maximum (100Watts / 3Ohm) with the box placed in a rigid room corner:

[weltersys]

Originally Posted by jwmbro

Here's how hornresp simulates the output, at maximum (100Watts / 3Ohm) with the box placed in a rigid room corner:

Good work James!

Does only 100 watts make the drivers hit Xmax (13mm)?

One note, though a 2 food depth is great for wood use, the Lab 12s are 12.25" and would either need to be put at a bit of an angle, or a divot chiseled (or routed) out at the top and bottom of the speaker mounting location.

For a cabinet that big, I'd want to put at least four or even eight 12", 129, 136 dB at 15 Hz in room...
Don't try it full tilt boogie in a plaster and lath constructed house unless you plan to rebuild .

Art