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infrasonic frequency

billybob

Member
I have a question, I read that the human ear can hear frequencies from around 20hz to 20,000hz. Is this just sine wave? Or would half wave square wave be different. Such as if I have a spark gap firing at 5 hz would I would assume I could hear that, but what is the definition of infrasonic? I always thought of hertz as beats per second or am I dead wrong? Also how could I play infrasonic on subs?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Yep, that is for sine wave; "pure" frequencies.

Anything other than a sine wave contains harmonics, so parts can be audible even if the repetition rate is subsonic.
The faster the rise and fall, the more harmonics it contains.

See the link here for some examples:

For a pure subsonic signal, you would need a sine wave generator that can go below 20Hz and a sub that can reproduce it.
 

billybob

Member
Yep, that is for sine wave; "pure" frequencies.

Anything other than a sine wave contains harmonics, so parts can be audible even if the repetition rate is subsonic.
The faster the rise and fall, the more harmonics it contains.

See the link here for some examples:

For a pure subsonic signal, you would need a sine wave generator that can go below 20Hz and a sub that can reproduce it.
Huh interesting, so a ramp wave will have more harmonics than a sine wave and a square wave even more. Would resonate frequencies such as the deadly 7hz still be obtained through different waves forms?
 

unclejed613

Well-Known Member
Most Helpful Member
actually you won't actually "play" infrasonics on most subs, but there are some home theater setups that have a small platform for your couch, chairs, etc and use "mass drivers" to move the platform so that you can feel the infrasonics. "mass drivers" are essentially a very large woofer magnet, but instead of the cone being connected to the voice coil, theres a large metal piston with a flange on it connected to the voice coil, and the flange is bolted to the platform. the magnet assembly mass works as a counterweight with enough inertia that the piston and flange can move the platform without the magnet assembly needing to be mounted to anything. instead of a paper or cloth surround to keep the voice coil centered, metal springs are used instead. it takes a pretty hefty amplifier to power one of these platforms...
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
My B&W PV1D sub is supposedly -6db at 6.5Hz, or something silly like that, but that's not exactly a common type and would have been over £1000 if I'd bought it new - I'm not that daft though.

My 300W RMS bass guitar combo (with 15" speaker) is rated to 17Hz so should still give a reasonable output somewhat lower than that.

It's not impossible, but you won't do it with a tiny "sub" as used in many cheap surround systems.
 

audioguru

Well-Known Member
Most Helpful Member
Putt, pause, Putt, pause is 2Hz but the "Putt" sounds have many much higher frequency harmonics that are heard. Your high voltage sparks are the same.2
A 2Hz sinewave cannot be heard since it is simply air smoothly flowing back and forth like the cone of a silent woofer would do.

You can feel the vibrations of high power infrasonic energy.
 

unclejed613

Well-Known Member
Most Helpful Member
you also want to be careful with infrasonics, especially if you aren't on a concrete basement floor, as housing structural members can carry the energy around the house and knock things off shelves.... even low bass in the range of 20-40hz can do this as some audio tech geeks found out while testing a huge transmission-line subwoofer a few years back https://www.passdiy.com/project/speakers/the-legend-of-el-pipe-o
 

billybob

Member
you also want to be careful with infrasonics, especially if you aren't on a concrete basement floor, as housing structural members can carry the energy around the house and knock things off shelves.... even low bass in the range of 20-40hz can do this as some audio tech geeks found out while testing a huge transmission-line subwoofer a few years back https://www.passdiy.com/project/speakers/the-legend-of-el-pipe-o
I just started researching experiments with infrasonic waves. There is some crazy stuff!
 

gophert

Well-Known Member
Most Helpful Member
I used the trick of playing a 40Hz sine wave though a bass speaker while i centered the foam when rebuilding the speaker. If the foam is out of center, you can hear the harmonics. If everything is centered, you just feel the rumble. Also, if you speak into the "silent" speaker playing the 40Hz sine wave, you get some great voice modulation effects.
 

billybob

Member
I used the trick of playing a 40Hz sine wave though a bass speaker while i centered the foam when rebuilding the speaker. If the foam is out of center, you can hear the harmonics. If everything is centered, you just feel the rumble. Also, if you speak into the "silent" speaker playing the 40Hz sine wave, you get some great voice modulation effects.
huh. interesting! yes I need to find a sub capable of such amazing stuff!
 

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