freq

Depends on the frequency and VOLTAGE of the line you are holding!!

And maybe SpellCheck could lead you somewhere.

Just remember: Seven HURTS!

(7 Hertz is the approximate resonant frequency of the gut. At high levels, it is reported to cause extreme discomfort and nausea.)

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

There was a MythBusters episode that dealt with this subject. I'm not sure if they went down to 7Hz, but I think they did, and they did refer to the so-called "brown noise". At the frequencies they did use, at (at least)120dBspl (iirc), there were no ill effects.

On the other hand, SouthPark did a related episode, too. The results were much different.

Bob

Achieving 120 dB at 7 Hz is a tall order.

Consider what dort of loudspeakers are needed to achieve 120 dB at 30 or

50 Hz. Go ahead with an SPL meter, loudspeakers, sinewave oscillator, and amplifier. Outdoors that gets to be a tall order much past point blank range.

Ever see a local band or a DJ with really good really loud deep bass? My experience is that the most impressive deep bass was from bass bins whose frequency response was full blast only down to about 50 Hz. Maintaining high loudspeaker efficiency to lower frequencies requires the loudspeakers to be proportionately larger.

For example, one in "ideal half space" needs to have a volume around .01% of a cubic wavelength of the lowest frequency at which it works well to have efficiency only about 1-2% from that frequency on up. (Narrowband designs can be smaller.) Efficiency increases roughly with volume, though significantly begins to level off around 20% (at which point you can maintain increase in "sensitivity" by having the loudspeaker large enough to be directional).

.01% of a cubic wavelength is roughly a 6 foot cube at 7 Hz.

- Don Klipstein ( snipped-for-privacy@misty.com)

Here are some of the details:

The test sessions were conducted in a large parking lot at Golden Gate Fields racetrack, on the shores of San Francisco Bay. Savage stood in the middle of the subwoofer ring, where he experienced the effect of very low frequency sounds (down to 5 Hz) at extremely high levels (120 dB SPL with a

9 Hz sine wave, up to 153 dB peak with narrow-band noise), though the higher levels were possible only above 20Hz. Safety was a prime consideration: tests were limited to about five minutes in each frequency range, and industrial-grade hearing protection was used above 120 dB. Savage was wired to medical monitoring machinery and watched closely by paramedics during the tests, while additional protection for those working in close proximity to the subwoofer stack was provided by a box of extra-large Depends.

Bob

I seem to recall an early study on the 7 Hz phenomenon that involved factory workers. When the sound was on (which of course they couldn't "hear" directly at that low frequency), some workers became ill. I got the impression that this was an ongoing exposure, much longer than 5 minutes. Dont' recall anything about the sound levels, or even if they tried to measure them throughout the factory.

I don't think they used speakers for this. It was pre-1960s so there wouldn't have been much available anyway. I believe it was some sort of steam whistle. (I have also seen mention of someone, early 1900s I believe, who made a giant low-frequency steam whistle that allegedly was so powerful it killed him "instantly" when he started it up. YMMV )

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

I gotta build me one of them steam whistles!

Bob