Is a flat extension to 20hz or less impossible to achieve in average sized rooms?

[yepimonfire]

I've been messing with REW a lot lately and I almost wish I'd remained ignorant to the train wreck room interaction causes in low frequencies. Measured outside, a sub that's supposed to extend to 20hz -3dB extends to 20hz -3dB. Indoors, this rarely happens if you relate the spl at 20 hz to the spl at whatever the first and loudest room mode is regardless of placement. Messing around with rew's room sinulator, it has become obvious that unless you're in a very large room with a length as long or longer than 1/4 wavelength of 20hz, you're never going to get equal spl at 20hz unless the room is decently sealed (such as the interior of a car). Forget infrasonic frequencies. Supposedly humans can't hear below 20hz, however, with sealed headphones, in ear monitors or with a subwoofer outdoors it became obvious to me that that's not entirely the case. 15hz and even 10 hz is definitely audible. In a medium sized room? Forget about it, it's just going to be felt rather than heard.

Even with heavy equalization getting a good response below 30hz seems impossible.

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[lovinthehd]

Details of your setup and dsp applied? I seriously doubt you're hearing 10hz or even 15, more likely harmonics but maybe you have superhuman hearing.

 

[yepimonfire]

Details of your setup and dsp applied? I seriously doubt you're hearing 10hz or even 15, more likely harmonics but maybe you have superhuman hearing.

I have a pair of iems that have a flat response down to 5hz as measured by headroom, 15hz is as audible as 20hz, 10 hz is pretty faint but I can still hear it. 15hz sounds like the low frequency sound of helicopter blades spinning. There's also been some studies showing humans actually can hear and respond to infrasound at higher spl (90-100dB). This particular study found that humans can hear down to about 8hz, a whole octave lower than previously thought. As the study states, the sound was picked up by the ear, not just felt, since the auditory cortex was active during the test.

https://www.sciencedaily.com/releases/2015/07/150710123506.htm

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[lovinthehd]

How can you accurately measure an iem? In any case, granted your abilities without your subs in play, if you have sufficient subwoofage you should have no problem getting to 20hz flat in your room, many have shown such measurements.

 

[shadyJ]

Good luck trying to get a flat response in a normal room from a single subwoofer to 20 Hz; it will never happen. What subwoofer are you using? You need multiple subs and a way to individually equalize them if you want a flat response down to 20 Hz.

I would guess that lovinthehd is correct that what you are hearing are harmonics of infrasound, not actual infrasound. While infrasound can actually be heard, the conditions where that happens have to be carefully controlled. Most speakers and earphones will generate a lot more harmonic distortion when trying to play back a 10 Hz tone than actual 10 Hz. You need an RTA to know what your equipment was playing back before you declare you were actually hearing stuff that deep. Chances are, it wasn't doing what you think.

 

[TLS Guy]

I have a pair of iems that have a flat response down to 5hz as measured by headroom, 15hz is as audible as 20hz, 10 hz is pretty faint but I can still hear it. 15hz sounds like the low frequency sound of helicopter blades spinning. There's also been some studies showing humans actually can hear and respond to infrasound at higher spl (90-100dB). This particular study found that humans can hear down to about 8hz, a whole octave lower than previously thought. As the study states, the sound was picked up by the ear, not just felt, since the auditory cortex was active during the test.

https://www.sciencedaily.com/releases/2015/07/150710123506.htm

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That sounds like woofer flutter. I bet that woofer is decoupled from the box. In any event I don't own a mic that will record as low as you are trying to do and I have some very pricey ones. It would be an exceptional mic that would have a response below 20 Hz that you could rely on.

 

[TLS Guy]

The whole issue of chasing infrasonic frequencies in home audio is a dead end. Practically you only need to go to 25 Hz, and 20 Hz at the very outside. Chasing lower stuff is a pointless endeavor and an unnecessary expense.

I think there is a lot of bunk about room responses and its consequences. As usual the problem is speakers and not most rooms.

When people speak in mot rooms their speech is not chesty and hard to understand. Play it though a speaker and it very well may be.

I have on occasions been lucky enough to have live musicians play in my home and it sounds fine. So a speaker should to, but they so often do not.

This is where I believe speakers that play fast and loose with time get into trouble. In addition there are still too many high Q designs out there, that really cause trouble.

Good speakers deliver good sound in almost any room unless it is a real dog. There are some. But the natural speech does not sound good in those rooms either.

I don't have any room treatments and have a room of very average dimensions. I'm never really aware of room problems.

So what does it look like.

Here is the response of my main speakers.

As you can see the -3db point is around 20 Hz. The HF roll off is an artifact of Omni mic.
Smoothing is 1/24 octave.

So here are the room responses with all 7 speakers playing including the LFE channel, 1/6 octave smoothing.

First a front row seating position

There is a peak maximal around 100 Hz of 10 db.

Now lets look at a rear row seating position. The blue curve is the rear, the red curve the average of front and rear seats.

So the end result is that the rear position does sound marginally better then the front row.

The front row still sounds very good with excellent speech discrimination and sounds in no way boomy. If the speakers were higher Q there probably would be a big difference between front and rear seats. As it is the difference is actually very subtle.

There is no equalization used such as Audyssey or REW.

As usual this problem is mainly speakers and NOT the majority of rooms.

 

[its phillip]

Calibrated umiks will measure down to 5hz:
http://cross-spectrum.com/measurement/calibrated_umik.html

There are plenty of people with systems flat to well below 20hz (can see a bunch on avs) but most have multiple sealed 18s or something similar. Definitely above average in the subwoofer department

 

[TLS Guy]

Calibrated umiks will measure down to 5hz:
http://cross-spectrum.com/measurement/calibrated_umik.html

There are plenty of people with systems flat to well below 20hz (can see a bunch on avs) but most have multiple sealed 18s or something similar. Definitely above average in the subwoofer department

Then my nest question is: - What's the point of it all?

 

[William Lemmerhirt]

Then my nest question is: - What's the point of it all?

I think for some it's about proving a point. "Because I can".

And also shaking your guts with infrasonic waves is pretty amazing. The thing about going below 20hz is power and excursion, and those things cost money. How low do you want to spend? Lol
To the question, I think flat to 20 isn't unreasonable, but not without first having equipment that will do it, then finding the best placement and then a little eq/room treatments.


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[its phillip]

Then my nest question is: - What's the point of it all?

I would imagine the point is to fully reproduce whatever content is on disc (or whatever you are viewing/listening to).

Regardless of how many (or few) movies/albums have sub-20hz content people will want to experience it.

http://data-bass.ipbhost.com/index.php?/topic/134-the-longest-most-intense-bass-scenes-from-movies/

http://data-bass.ipbhost.com/index.php?/topic/525-the-martian-discussion-and-poll/
http://data-bass.ipbhost.com/index.php?/topic/506-missionimpossible-rogue-nation-discussion-and-poll/
http://data-bass.ipbhost.com/index.php?/topic/534-star-wars-the-force-awakens-discussion-and-poll/

 

[lovinthehd]

Then my nest question is: - What's the point of it all?

Does it need a point? Why have massive home audio systems at all, most wives seem to believe there's no point to that either

 

[shadyJ]

The thing about infrasound hearing is that while human hearing does indeed sense it, we can not discriminate different frequencies in that region. So most of it is just 'sound'. That being the case, there isn't any practical to attempt ultra-low frequencies, unless you just want to know if they exist in whatever content you are currently listening to; it's not like 8 Hz is going to sound different from 11 Hz. You would also need a hell of a system to play extremely low frequencies that are not swamped with harmonic distortion.

 

[yepimonfire]

The whole issue of chasing infrasonic frequencies in home audio is a dead end. Practically you only need to go to 25 Hz, and 20 Hz at the very outside. Chasing lower stuff is a pointless endeavor and an unnecessary expense.

I think there is a lot of bunk about room responses and its consequences. As usual the problem is speakers and not most rooms.

When people speak in mot rooms their speech is not chesty and hard to understand. Play it though a speaker and it very well may be.

I have on occasions been lucky enough to have live musicians play in my home and it sounds fine. So a speaker should to, but they so often do not.

This is where I believe speakers that play fast and loose with time get into trouble. In addition there are still too many high Q designs out there, that really cause trouble.

Good speakers deliver good sound in almost any room unless it is a real dog. There are some. But the natural speech does not sound good in those rooms either.

I don't have any room treatments and have a room of very average dimensions. I'm never really aware of room problems.

So what does it look like.

Here is the response of my main speakers.

As you can see the -3db point is around 20 Hz. The HF roll off is an artifact of Omni mic.
Smoothing is 1/24 octave.

So here are the room responses with all 7 speakers playing including the LFE channel, 1/6 octave smoothing.

First a front row seating position

There is a peak maximal around 100 Hz of 10 db.

Now lets look at a rear row seating position. The blue curve is the rear, the red curve the average of front and rear seats.

So the end result is that the rear position does sound marginally better then the front row.

The front row still sounds very good with excellent speech discrimination and sounds in no way boomy. If the speakers were higher Q there probably would be a big difference between front and rear seats. As it is the difference is actually very subtle.

There is no equalization used such as Audyssey or REW.

As usual this problem is mainly speakers and NOT the majority of rooms.

Unfortunately I am stuck in an almost square room. There is a massive difference in the response across the room. I've used 3 different subs and it's the same problem.

The two problem frequencies are 40hz and 58 hz. The 58hz peak runs across the width of the room and the 40hz peak runs across the length of the room. If I position the mic at exactly 38% from the back wall and side wall I get a mostly flat response. Move outside that area length wise and I either get a cancellation or a peak at 40hz and below, move width wise and I get the same problem at 58hz. Except for a dip centered at 70hz, everything above 60hz is flat enough to not matter.

I'm positive it's the room. Placing the sub in a larger room that's more rectangular gives a much more even response.

I agree with the low frequency comment. For the majority of music a response below 40hz isn't even necessary, even for movies with a lot of lfe a good portion of it is 30hz and above.

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[lovinthehd]

What happens when you use multiple subs?

 

[yepimonfire]

I get a different response, I was toying with independently crossing them over, one bandpassed at 40-80hz and one low passed at 40hz and was getting some interesting results, what I'm probably going to have to do is just manually eq it to sound as decent as I can and just deal with it unless I moved it to another room.

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[William Lemmerhirt]

Can you move the LP?


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[yepimonfire]

Can you move the LP?


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I can, but it doesn't help enough.

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[yepimonfire]

Then my nest question is: - What's the point of it all?

Because there's content in movies well below 20hz.

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[William Lemmerhirt]

What are the subs in use?


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