Help needed with new subsonic design, trial pics enclosed.... - diyAudio
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Old 3rd October 2009, 01:35 AM   #1
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Default Help needed with new subsonic design, trial pics enclosed....

Hello,
A few months ago I posted here looking for help designing a subsonic subwoofer for use in an art project. I wanted to create intense pressure that could be felt rather than heard. After getting great responses back (thanks to all, especially Mark Seaton, GM, and Just A Guy - so much great info), I made a simple ported 15" tempest subwoofer using formatube for the 340 litre enclosure and monstrous stormwater pipe for the port - just to get an idea of what I was up for....

Click the image to open in full size.

Those poor vienna acoustics speakers look so dwarfed....
The formatube is 500mm, 1900mm long, capped at either end with 32mm mdf routed to fit, all held together with sikaflex adhesive. The port is 225mm pvc pipe, about 1200mm from memory, with 50mm radiuses of mdf either end.

Click the image to open in full size.
Click the image to open in full size.

I am driving it with an old Perreaux 6200B (300W per channel) using both coils of the tempest separately (is this wrong?) When I dial the Perreaux all the way up the windows shake at 16Hz and the driver gives quite ridiculous excursions, with virtually no distortion. I realise that 16Hz is plenty low enough for me. Pure tactile sensation is what I am after, with overtones carrying up into the audio range (unavoidable and not bad).....

But, IT IS SIMPLY NOT ENOUGH PRESSURE. I need a driver and enclosure, or multiples of, that will provide a felt pressure wave in a room. I realise that this depends on the room size, material, what is in the room, etc - but the room will change (unavoidable), and I need some advice to start moving in the right general direction - extreme amounts of air moving, high spl, like what you get at a concert venue, but at 16-20Hz. I am reading up a little on acoustics, but it is hard to get the practical experience when equipment is so costly....
The audio I propose to put through it will consist of a series of 16-20Hz pulses, like heart beats, perhaps 1- 2 seconds long each, with a quick attack and a fast decay of around 2 seconds, the pulses spaced 8 seconds apart - so it is very intermittent. I do not need musical sound - I need it to push against your skin. The idea is that it will accompany projections of slow-motion colliding boxes (but that is another long post) that I want the audience to experience in a tactile way as well as visual.....
So, the output does not need to be particularly musical.

This is my trial run, and it has helped me work out what I need to do. I still have the tempest no matter what I do, and the enclosure building has given me an idea of what I am up against. I am probably needing a few more drivers and amps by the sound of it though. I just need a recap and any suggestions of where to go from here....

Questions -
How many drivers should I play with?
What would be the best sort of enclosure - sealed high transient punch, or ported/PR high spl?
Do I need a much higher spec amplifier?
Should I be looking at something like a Servodrive Contrabass like Dangus originally mentioned?
Mark Seaton had an interesting idea of a bass cardioid system - is there any more info on anything like this around? (Help needed for Sub-sonic subwoofer design....)
Am I a stupid crazy artist who has no idea what he is doing?

Thanks again for all the help that has been dished out - it was incredible to find such detailed help and support from people here - it is such an arcane area of knowledge and it was most appreciated!
I have had fun thus far, and I am just beginning.....
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Old 3rd October 2009, 02:53 AM   #2
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Default directivity

After scouring the net looking at cardioid subs (not setups) and servodrive, it seems that directionality would be a great thing.... I will try to research more, but it is difficult finding the needle in a haystack as I am no acoustician or audiophile.....
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Old 3rd October 2009, 03:18 AM   #3
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Interesting project.

The challenge of producing 16 Hz to 20 Hz signals at the levels you're suggesting is that you're going to need to move a lot of air to achieve that. That usually means big boxes, big drivers (and many of them too) and lots of power.

Or you can "cheat" a bit .

Where is this display going to be hosted? Do you know the dimensions of the room? Do you have access to it?

Here's what I'd be considering if I was in your position - I'd settle on driving the room at one of its lower resonant frequencies (these are dependent on its room dimensions), and designing a sub that has a massive peak at that resonant frequency. This suggests the use of an vented, bandpass or even tapped horn with a peak in its response that corresponds with the chosen resonant frequency. Furthermore, I'd place the sub in the room at the location that makes the most of that resonant frequency.

This is similar to what the car audio SPL guys do, 'cept of course the resonant frequency they settle on is a lot higher (smaller room = higher resonant frequencies).

You're likely going to need more than one 15" driver driven by 300W, but it's a start.
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Old 3rd October 2009, 03:34 AM   #4
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Brian, cheers for your response. The problem, and this is fundamental, is that the room will vary and I am never going to be able to get a perfect fit to what I want. I am looking at warehouse galleries - large solid places, low ceilings, concrete and brick. But I have not got a specific place yet, and cannot until I have finished the filming and made the speakers, etc....
Your idea of using the inherent room resonance is great - something that I will have to play around with....
And this, I guess, is the crux of the matter - I need to play around. I do not have experience in this field, so I need starting points. How does this sound - two tempest or maelstrom enclosures, a decent amp and a behringer DCX2496 (as suggested by Mark Seaton in a previous thread), and start playing around and trying to see what I can do in the room, as you both seem to suggest?
Does this sound like a good next step?
Cheers again!
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Old 3rd October 2009, 03:45 AM   #5
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Quote:
Originally Posted by orangealpaca View Post
Brian, cheers for your response. The problem, and this is fundamental, is that the room will vary and I am never going to be able to get a perfect fit to what I want. I am looking at warehouse galleries - large solid places, low ceilings, concrete and brick. But I have not got a specific place yet, and cannot until I have finished the filming and made the speakers, etc....
Your idea of using the inherent room resonance is great - something that I will have to play around with....
And this, I guess, is the crux of the matter - I need to play around. I do not have experience in this field, so I need starting points. How does this sound - two tempest or maelstrom enclosures, a decent amp and a behringer DCX2496 (as suggested by Mark Seaton in a previous thread), and start playing around and trying to see what I can do in the room, as you both seem to suggest?
Does this sound like a good next step?
Cheers again!

You need to be able to move a lot of air to achieve what you want to achieve. I think two Maelstrom vented subs driven by as much power as you can afford would be a good start. Make the enclosures big enough, and vary the response peak by varying the port length (or, if you go with PRs, the weight attached to the PRs) to match the room resonance mode you're trying to excite.
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Old 3rd October 2009, 03:53 AM   #6
wg_ski is online now wg_ski  United States
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I think you're going to need a corner-loaded horn to get the required SPL unless you want to buy and power 50 of those 15's. If the venue is big and open enough that you don't have a corner handy, you can make a "corner" fire it into out of 2x4's and OSB and make it part of the display.
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Old 3rd October 2009, 04:42 AM   #7
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Hi, I remember you and your project quite well, although I don't remember anything that was said except for a few details. Thanks for the update.

Anyway, if I remember correctly, at that time you did not have a rock solid frequency response or spl goal, but from the sounds of it now you do - 16 to 20 hz bursts at concert levels. A very clear goal will help a great deal, so that's a step in the right direction, even if the goal is going to be very very hard - or impossible - to achieve. 16 hz at concert levels isn't going to be easy.

I'd prefer not to add any additional ideas before at least going back and reading what I said in the first place (which I can't do right now), but I do clearly remember telling you to look into the safety issues involved, especially for staff that will have to experience this over and over all day long. I'd like to remind you of this above all else, just in case you forgot. A LF effects machine like this has the potential to make a lot of people very very sick, damage the building (and contents) and it will be almost impossible to contain the "sound" in the presentation room. That is where Mark's cardiod solution could help, but then you trade specific localization with sub optimal sub placement locations.

I'll go back and reread that old thread when I have time to see if there's anything else I can contribute, but I think we covered all the bases fairly well the first time around.

Just as a refresher, repost the estimated average room size these will be used in (huge IIRC), max size per enclosure, max total size, budget, any equipment you already have that could be used, etc.

You are going to want to stay away from sealed, unless you have a massive budget for subs and amps and all your presentation locations have a LOT of power on tap.
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Old 3rd October 2009, 05:28 AM   #8
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just a guy, thanks for the reminders!
i have looked back at the previous thread and need to soak it all in - excuse me if i miss points - this is a stretch for me - i am learning (and this seems a steep curve to do it on, but hey - no pain no gain....)

i hear what you say about the safety issues. this is becoming a priority now that i reliase what I am doing. this is another reason Mark's idea of the cardioid setup appealed to me - controlling the flood of bass at least a little would be great....

several things you asked -
the installation will be in an average room 8 x 16m. hypothetically.
the maximum enclosure size is governed by what i can fit onto my trailer, and get into a normal door (just in case there are no doubles or roller access)
budget is rolling and escalating - I do not have much funds, but I just received a $20,000 grant from the government - not that all of this would be spent on speakers by any means. I would put the budget at around $5000 for the audio. I have one 15" tempest and a few old perreaux amps.

other things -
the audio pulses, 1-2 secs every 8 secs or so, will last for 3 minutes, after which they will be silent for 3 minutes. this is part of the audio-visuals fading to reveal the actual crashed boxes (read "art" with a lowercase a) in the gallery. so it is intermittent in that respect. ALSO, the whole thing is triggered in the gallery by a motion sensor, so it will be off when there is no audience (expected 70% of the time - hypothetically)
and i realise that i am asking for alot in this exercise, so i want to get as much as i can and learn as much along the way also. the idea o setting up something flexible for trialing and trimming within the space sounds good to me - two enclosures, as Brian said with PR's with weights to play with the resonance, perhaps a behringer DCX2496 to play with cardioid placement of the two enclosures....
you are all right - i need to play, but that is expensive, and i need to find a flexible system that i can learn with and use to give me some hopeful possibilities TOWARDS what i want.
so i guess that is what i am asking.

why has it taken me so long to work that out? no wonder i was so confused and no-body could help me!!!

apologies and thanks again.
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Old 3rd October 2009, 05:31 AM   #9
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oh, and another thing - the audio is sourced from recordings of colliding hollow copper boxes, which i then manipulate in soundtrack pro and other programs - so i have maximum flexibility in what the audio actually is - i can trim and notch to make it whatever it needs to be for this (subtle?) effect of pressure on the body.....
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Old 3rd October 2009, 06:54 AM   #10
FlipC is offline FlipC  United States
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Build a clone of the Danley 221 ...
Or just lease a real one ... or the mattter horn!

Air cannons ?
Or just build a false floor on top of some servo's.

Side note.
Built some BIG McCualey 6174 (is that correct? ben awhile)
that did 20-31 Hz at 95 db. Had 6 of those on a 5 way system as center fill.
In a 15K square foot room you couldnt be at the back (facing subs) as your eye balls wouldn't focus and your testicles would bounce around.

SO if you did get this done
remember you will make people sick. ALSO that **** travels a LONG way.
You wont be playing it very long. And hell at what point do you start to cause structural damage? If not ton the building your in, then the other art work?
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