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Topic: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio? (Read 12114 times) previous topic - next topic
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Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #25 –
Quote from: pdq on
That's ridiculous. To have DC response it would have to be able to raise or lower the pressure in the room.

It can do that.
Regards,
   Don Hills
"People hear what they see." - Doris Day

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #27 –
Quote from: pdq on
Quote from: splice on
Quote from: pdq on
That's ridiculous. To have DC response it would have to be able to raise or lower the pressure in the room.

It can do that.
Point the fan at a barometer, then lower its speed to zero, and tell me what you see.

Obviously, no change because you aren't bringing any new air into the room or even sequestering air in a reservoir , just stirring up the air that is there.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #28 –
Quote from: pdq on
Point the fan at a barometer, then lower its speed to zero, and tell me what you see.

I think the way the fan works is that it modulates the blade angle, not the speed of the fan.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #29 –
Quote from: KozmoNaut on
Quote from: pdq on
Point the fan at a barometer, then lower its speed to zero, and tell me what you see.

I think the way the fan works is that it modulates the blade angle, not the speed of the fan.

That is my Impression as well.  The inherent problem is noise due to  turbulence of the air.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #30 –
Nonetheless, having zero amplitude at zero Hz does not constitute bandwidth to DC. Every speaker ever made has zero amplitude at zero Hz.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #31 –
Quote from: pdq on
Nonetheless, having zero amplitude at zero Hz does not constitute bandwidth to DC. Every speaker ever made has zero amplitude at zero Hz.

Right. At minimum the sound would have to be loud enough to be reliably perceived.

Most of us are familiar with how this works in practice. The most common ways that it is perceived involve displacing our bodies vertically fairly rapidly  by some means of transportation: car, elevator, plane.

I've heard subwoofers that made my ears feel like they wanted to pop, but I think that was actually more like incipient popping, not an actual pop like I have experienced by means of bodily transportation. But, I think it would be reliable, so it probably counts as reliable perception.

A fair number of the local group of ABX-ers also have very substantial subwoofers.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #32 –
It works by varying the pitch in both directions.

http://www.eminent-tech.com/howitworks.htm

So it can do DC, and that can be measured easily enough. Certain areas of the room would be pressurized and other areas not. If placed in a window, it would pressurize the entire room. Air moving in one direction only would seem to be about the only way to represent DC by motion of air. I think we all agree that motion of air is also how 20Hz is demonstrated.

At any rate, as I understand it this sub started out as a joke. I remember going to CES about 15-20 years ago and hearing weird rumors about a 'DC subwoofer' at the Eminent Technology room. Out of curiosity on my rounds I dropped in, and sure enough there was a one-page brochure that was mostly a photo of a hick sitting beside a large window fan. Bruce Thigpin had produced the brochure as a joke because so many people came in, took literature without reading it (or for that matter listening in the room) and left. He enjoyed the idea that later these people would find the document with no idea where it came from once they got home.

But apparently it got him thinking. If you read the text, the idea has a bit of merit- for example the sub is not limited by the excursion of a woofer, one of the more serious issues limiting all speakers. Of course, there's a limit to how fast he can modulate the vanes, but that's what crossovers are for. It really does work- I've heard them at shows.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #33 –
This could also be done in a sealed room with two valves. One connected to a source of compressed air, and the other venting to the outside.

Re: Do we "need" those <20Hz subsonic frequencies for high-fidelity audio?

Reply #34 –
While waiting for the cpu to render bass-eq on a movie I want to see, it is suitable to use the time to fill in with some comments on low bass.

The important aspects are already covered in the very first posts, so this will not add any new and revolutionary wisdom.

In music there is very little energy below 30hz, but it is there, if it was not filtered in the studio. Transients are short in time, and wide in frequency distribution. Low frequencies can be induced from large surfaces in the recording room, like when musicians move on a stage.

But the level of <20hz content is usually so low that you will only be able to notice it at very loud listening levels.

Some electronic-made music do contain lots of low freq energy.

Impulse response improves when frequency response is extended below "normal" hearing range. But before worrying about that, the range above 20hz is far more important to fix for resonances and timing problems.

On many recordings the full-range reproduction reveals sub-frequency noise - from the recording room, or due to close-mic placements, which can create a boost at very low frequencies. This was not intentional, and it is there because they did not hear it in the studio. Some will find this amusing, some will find it distracting.

But why I am doing the bass-eq on that movie. If the difference is so small, this movie is mostly dialog driven, is it worth the effort?

It is, because movie sound effects are different from music instruments. I could tell right away that this move is filtered - low frequencies are removed - because effects lack natural weight and size. A very steep 25Hz high-pass was applied, and bringing back what was lost will make a huge difference to the experience.