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Infrasonic Bass Generator

Discussion in 'Subwoofers' started by G.C.H., Jul 1, 2004.

  1. G.C.H.

    G.C.H.
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    Hi All

    Does anyone know where I can get detailed plans for constructing the above. There was an article detailing plans in Hi-Fi answers back in the late 70's by Graham Holliman. I actually built one of these and would like to do so again. The basic construction was a cabinet approx. 5ft long by 3ft high by 2ft 6" wide.

    It used an 18" specially designed Richard Allen drive unit mounted on top of the cabinet firing through a port into an internal chamber, the basic principal as I recall was to excite the air inside that chamber, the sound then exited through two sided horn loaded ports.

    This is a very basic description of the design but this little beauty was designed to operate where most subwoofers roll off i.e., 20hz down. I'm not sure of the actual roll off frequency but I do know the further down it went the greater the output and was capable outputting frequencies well below 7hz. These were I believe originally designed for augmenting the lower fundamentals of church and cathedral organs which may give you a clue to the power of these little beasts.

    I do remember the one that I constructed was absolutely awesome in its output, couldnt hear a thing, just objects shaking and moving about. I do recall that certain measurements for the construction are critical i.e., port dimensions, internal cabinet size, horn flarerings etc., therefore to build one again I would need detailed plans.

    If anyone knows of such could they please let me know as these things are capable of making any subwoofer sound like a tweeter, these things really do move air.

    Any help would be appreciated :lease:
     
  2. ShinObiWAN

    ShinObiWAN
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  3. ShinObiWAN

    ShinObiWAN
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    Just a note to anyone who decides to build one of these.

    They are dangerous. Even with a naff 10" speaker they are impressive but use something like a 15" tempest or tumult and you could suffer serious damage.

    This isn't BS, infrasonic waves effect every organ in the human body but particularly and worryingly, the heart rhythm and brain.

    If you want the full low down do a search on infrasonic weapons on google.
     
  4. G.C.H.

    G.C.H.
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    Hi,

    Many thanks for the link.....

    In the correct context yes, infrasonics can be dangerous and can even kill. There are certain human organs that have a resonant frequency of 7hz and if amplified to the correct level yes, they can kill. If memory serves me correctly a certain German phycisist back in the 1940's was experimenting with infrasonics, I believe for use as a weapon, stood in front of his invention and promptly dropped dead, even the Brits experimented with this idea during the war for use as a weapon, but because of the state of technology at the time was impractical.

    The one I built back in the 70's was very powerful but at that time there was little recorded media capable of reproducing frequencies anywhere near this level, now-a-days with the advent of digital i.e., CD/DVD etc., this idea is a more viable proposition. The only way I could produce those kinds of frequencies at that time was by using a frequency generator. Also amplification and crossover needs to operate down to DC and a suitable drive unit with a low resonance Q is preferable.

    I do plan to build one again in the very near future, if I survive, I will let you know how I get on :)
     
  5. Nimby

    Nimby
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    Fascinating stuff. I was browsing on infrasonics only recently.

    My 6th order, coupled cavity, series bandpass, DIY subwoofers could make me nauseous at will driven by an audio frequency signal generator. The didn't roll off as quickly as the design intended and still had output at 10Hz on the SPL meter. I believe 11Hz was the "get off the bus NOW!" frequency that made me ill. A slight turn on the frequency control kob and the feeling was gone again.

    The "Plans" text came out fine but the graphics were invisible thanks to a "unable to load graphics filter Windows '97" error message. Is there any other way I can see the graphics of the Holliman design? All I have to go on are the drawings from the patent. I'd really like to see the design even if it means asking someone to kindly e-mail them to me. (I have broadband so no problem with file size my end)

    Nimby
     
  6. G.C.H.

    G.C.H.
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    Hi

    Just to let you know I will be posting Graham Hollimans design very shortly. Its horn loaded and rather complex in its construction. This will be from memory so it may only be about 80-90% accurate as its at least 25 years since I built this beast.

    So when I do post it I will be looking for replies as to its working feasability before construction, but it will give you a very good idea as to its working principles and construction and also just what it is capable of. If memory serves me correct I do believe back in the late 70's these designs were used in the Royal Albert Hall for augmenting the lower fundamentals of there organ.

    If I were to describe the effect of the one I built back then it goes something like, and a colleague of mine at the time agreed with me on this, there was a sense of real menacing in the air like a pressure on the ears as if you could also feel the whole air in the room moving backwards and forwards. Perhaps similar to being deep under water, feeling the pressure of water on your body. One curious observation at the time was objects in the kitchen shaking. I'm not very good at describing the effects but if that makes any sense to anybody hopefully it will give you an idea. Also I agree with a previous comment, the room it is used in should be almost hermetically sealed to work correctly and there are certain aspects of the design and construction which are very critical and must be correct for it to work at all. Get these right, and it took me quite a bit of hassle and the effects are absolutley awesome.

    Mine was constructed from kitchen worktops believe it or not, this time I'm hoping to use two layers of MDF bonded together to give added rigidity :smashin:
     
  7. Daneel

    Daneel
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    Quoted for emphasis. From speaking to people far more knowledgable than I in this area, the effects of sound at these frequencies can be anything from nauseating to serious physical harm. Be very careful.
     
  8. Nimby

    Nimby
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    After further thought I would agree entirely with Daneel. I ask the purpose of reproducing such low frequencies? Surely they have no place in either music or film sound reproduction? What is the point?

    While this project is technically very interesting (even fascinating from an audio reproduction point of view) the effects of infrasonics should not be underestimated. The fact that a closed room is required. Suggests that the room actually becomes the second chamber in a coupled cavity system. When the listening room is pressurised there is no way of knowing the true effects (long or short term) on the human body.

    If the system was being fed by a signal generator under carefully controlled and externally supervised conditions. Then one might have more confidence in the safety of the system in use.

    Fed with a modern dynamic sources such as DVD or CD. Using modern near-DC response powerful amplifiers and modern loudspeaker drive unit technology. Then there is no way of knowing beforehand what reproduced levels of ULF sound pressure might be reached in the listening room. There would be no external control or safety device to stop reproduction if the listener got into serious trouble. The listener might be in no state to turn it off himself!

    Have a read of this link. I have no idea if it represents the whole truth. But it certainly gives a taste of the power and potential dangers of infrasonics.

    http://www.borderlands.com/archives/arch/gavreaus.htm

    I remember the ease with which I could produce nausea in myself with a wimpish little 30 Watt amp, an audio frequency signal generator and only one of my (10" drive unit) coupled cavity subs being fed at low volume. I once considered this an exciting result for my hard work in building these subs. Perhaps I now have a more mature attitude to this foolish event? By all means have fun. But who really needs a martyr to bass?

    What's next? Dangerous Sports Club status and postumous mention in the Guiness Book Of Records? Followed by legislation against subwoofers to save us from ourselves? Where is this race for 1Hz reproduction and aircraft engine sound pressure levels really taking us?

    Nimby
     
  9. IronGiant

    IronGiant
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    More likely a mention in the Darwin awards :laugh:

    Dave
     
  10. jeff-o

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    Well, it would give new meaning to saying you have a "killer setup!"
     

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