How much gain below 20hz

[TankTop5]

I have heard some people recommend up to 20db of gain below 20hz. I watch movies around 75db and I have dual HSU VTF-TN1’s. Thinking about giving it a shot with gain starting around 25hz and rising quickly to 20db gain at 20hz and below. Room is 800 ft.².

anyone have any thoughts on doing this?

 

[shadyJ]

That seems pretty nuts. If you want some more low-end oomph, I can see goosing up the range below 30Hz by a few dB. That should do the trick. 20dB of boost in infrasonic ranges is crazy. I guess you could try it. The problem is, you probably listen at a louder level than 75dB, and, while your subs do have a nice amount of headroom in deep bass, they don't have infinite headroom, and a 20dB boost below 20Hz is asking a lot of any sub system.

 

[m. zillch]

Content below 20Hz is called infrasonic for a reason.
- if reproduced at the accurate, true level experienced in even the most expensive/deluxe commercial theaters you won't hear/experience a thing
- no commercial subwoofers sold to theaters can reproduce it either
- the professional sound mixers who made the move did not hear/experience it nor intend you to.

What's next? Will people try to get ultraviolet light out of their video screens? It's like that.

 

[TLS Guy]

Content below 20Hz is called infrasonic for a reason.
- if reproduced at the accurate, true level experienced in even the most expensive/deluxe commercial theaters you won't hear/experience a thing
- no commercial subwoofers sold to theaters can reproduce it either
- the professional sound mixers who made the move did not hear/experience it nor intend you to.

What's next? Will people try to get ultraviolet light out of their video screens? It's like that.

I would be careful doing that. With room gain most subs with 15" or larger drivers will play to 16 Hz. Now the bigger issue is that most ported subs will be decoupling from the tuning by 16 Hz, so upping the power in that range is calculated to cause damage. For sealed subs the power has to increase enormously as there is a 12 db per octave boost below F3, which even for a large driver sealed sub will be north of 30 Hz. So I would say don't do it, or you may well be looking for a new sub.

 

[WaynePflughaupt]

In addition to what’s been said, in my experience artificially boosting the lows to a sub (i.e. via EQ) doesn’t sound nearly as good as having a sub that just gets that low naturally.

Regards,
Wayne A. Pflughaupt

 

[j_garcia]

Content below 20Hz is called infrasonic for a reason.
- if reproduced at the accurate, true level experienced in even the most expensive/deluxe commercial theaters you won't hear/experience a thing
- no commercial subwoofers sold to theaters can reproduce it either
- the professional sound mixers who made the move did not hear/experience it nor intend you to.

What's next? Will people try to get ultraviolet light out of their video screens? It's like that.

You don't seem to understand what infrasonic actually means. Yes, you cannot hear it, but the vibration is still present and is still detectable by humans as pressure. The article you linked mentioned earthquakes, which have vibrations that are felt but not necessarily heard. Even some music can contain information below 20hz, such as pipe organs.

As for films, it may not be intentionally put into the tracks, but it may be present within the a particular sound because, explosions as an example, are not a single wave pattern. While a sound has a fundamental, it also has other harmonics that could extend into infrasonic. Batman Begins is famous for having a scene that has a 2Hz drop, which can be measured, but obviously not heard (seems most home theater processors would filter it out anyway).

There are a lot of films that dip into infrasonic territory. There are also many home theater subs that extend below 20Hz, which you would need to get that infrasonic information; aka vibration. A sub that is -3dB @ 25Hz will more or less not reproduce it at all.

 

[m. zillch]

You don't seem to understand what infrasonic actually means. Yes, you cannot hear it, but the vibration is still present and is still detectable by humans as pressure.

When replayed at the level it actually occurs in the film without artificially boosting it, from the seated listening position? Nope.
[And noticing your remote control or empty wine glass is dancing around on top of your glass coffee table, or other similar sympathetic vibrations in the room (like the sub's power cord slapping against the cabinet) doesn't count as "detectable by humans": That annoying rattling noise is higher frequency and could even be recorded by a dirt cheap mic, say built into a cellphone].

 

[j_garcia]

I ran test tones on my former Aidre Tempest that was tuned to 14.5Hz (15", vented cylinder, custom built). Yes, below 22Hz, you could definitely not hear it. 22 and up you could feel it activate the air in my very large room, 32x15x20. Below that, it was just various things in the room having sympathetic resonance, like my closet door right at 16Hz.

Are you suggesting that content at and below 20Hz has no benefit to the listener? I agree that much of what people perceive as "rumble" is higher than that.

 

[m. zillch]

Movie sound reproduced accurately (so jacking up the sound they sell to us below 20Hz artificially via EQ, just so humans will detect it, is cheating), through state of art sound systems capable of even single digit bass reproduction, played at reference level ["0dB" on a calibrated THX certified AVR/prepro] never (to the best of my knowledge) contain content under ~20Hz, or so, at a level that either meets or exceeds our threshold for hearing/feeling down there. We are extremely insensitive down at those frequencies, in fact they usually stop graphing it around 20Hz but you can sort of extrapolate where threshold would be for, say, 10Hz:

[By my eye I'd say around ~95 dBSPL, which, keep in mind, is the minimum level we can only just barely start to detect under ideal conditions—isolated tone, in a sound-proof isolation booth so there is no background noise to mask it, nor simultaneous music/movie content going on, etc..]

[There's a third category beyond hearing and feeling by the way: nausea. Loud infrasound that the subject can't detect by feeling/hearing can sometimes induce nausea, according to some. I've never seen data on what levels are necessary though. Sustained infrasound is exceedingly rare in the real natural world—earthquakes, getting stuck in the middle of a herd of stampeding elephants, etc.—however it can easily occur with, for example, some large industrial machinery nearby and is monitored by health organizations such as OSHA.]

So unless one's goal is to rattle their dishware (my term for such noise is "unintentional arbitrary distortion") it makes no sense to me (at least for movies), in fact attempting to reproduce this frequency range increases woofer cone distortion in the audible band and is also very taxing on the amp, reducing "headroom" for the frequencies which do matter at 20Hz and above. This is why sensible movie sound tracks usually filter this infrasonic junk away in advance (unintentional mic/mic stand bumping, wind noise, mic pops, plosives, machine noise, etc.).

 

[William Lemmerhirt]

I have heard some people recommend up to 20db of gain below 20hz. I watch movies around 75db and I have dual HSU VTF-TN1’s. Thinking about giving it a shot with gain starting around 25hz and rising quickly to 20db gain at 20hz and below. Room is 800 ft.².

anyone have any thoughts on doing this?

IMO, 20db boost at 20hz is too random and broad a recommendation. It also is mental lol.
However. If the media has content that low, and your subs can take some boost, I don’t see a problem with a house curve.
There’s nothing quite like feeling your couch wobble with low teen hz.

 

[everettT]

Like @shadyJ mentioned, that's way too much and if your wanting more output below 20hz you need to boost above 20hz to effectively achieve that goal. I personally think you're chasing a paper tiger unless you're listening to pipe organs. You have a good sub, enjoy it

 

[m. zillch]

I personally think you're chasing a paper tiger unless you're listening to pipe organs.

The pipe organ (I just researched) was invented in the "3rd century BC". I'm pretty sure they hadn't conducted human hearing threshold tests back then to determine what lower frequency limits made sense, in fact I think their test generators for determining this sort of thing at the time was rather primitive by today's standard.

Seriously though, the first good hearing frequency range audibility tests were determined by large collections of differently sized tuning forks, such as this one at the Smithsonian:

The tuning fork was invented in 1711 by John Shore.

My point being proving infrasonic sound exists (say in a few pipe organ recordings) does not prove humans can necessarily detect it at the levels it is presented.