Why aren't cinemas targeting sub 20hz response?

[CDMC]

As someone pointed out, the size of theaters makes loud ultra deep bass extremely hard. Two reasons, volume of the space requires more drivers to hit a given spl throughout the theater and they are large enough you are not getting any gains from reinforcement below the room’s lowest modal frequency.

I would be willing to bet you that with very few exceptions, most theaters bass rolls off starting about 40hz, as that is where most large sound reinforcement bass cabinets start to. Every time you cut the frequency in half, you have to quadruple excursion of the sub to get the same output. Also, having really deep bass at high output tends to mask the midbass, which makes it sound like less overall bass in the room.

I have never been in a theater that has any real output below 30hz. This includes the Chinese, Fox, and Egyption in Los Angeles and Dolby’s theater in San Francisco. In my own room I have a 7-8 db gain from 30 hz down to 15hz. Really deep bass isn’t heard, it is felt and feels like an earthquake as the room just shakes. I start to roll my subs off at 28hz, as it flattens my bass and actually makes it sound louder without the extra low frequency volume masking the 40-80hz range.

Finally, keep in mind that very few movies have significant sub 30hz output. There is a small group of them as well as a group of home theater buffs who pursue deep bass performance down to 10hz and below for those movies and some synthesized music. I think for the vast majority of people, aiming for high quality smooth bass down to 30hz is a better goal using multiple small subs rather than chasing that last little bit with a single large sub that may have ultra deep capability.

 

[JeffS7444]

This has been done before in the 1970s with "Sensurround", which I got to experience with the Charleton Heston movie "Earthquake", but as kids, the main attraction was getting to hear Heston swear! I recall the novelty of the low bass wearing off after about ten seconds.

https://en.wikipedia.org/wiki/Sensurround
https://en.wikipedia.org/wiki/Earthquake_(1974_film)

 

[Blumlein 88]

This has been done before in the 1970s with "Sensurround", which I got to experience with the Charleton Heston movie "Earthquake", but as kids, the main attraction was getting to hear Heston swear! I recall the novelty of the low bass wearing off after about ten seconds.

https://en.wikipedia.org/wiki/Sensurround
https://en.wikipedia.org/wiki/Earthquake_(1974_film)

Yes. I saw earthquake and Midway in theaters with Sensurround.

 

[richard12511]

So the reason we go deeper is essentially "because we can" ? - Or on the flip side, the cinemas would go deeper if it was feasible?

That may be a good way to put it. I've played around with cutting those sub 20Hz frequencies for certain music with deep bass (ex: Phoebe Bridgers Punisher), and the sub 20Hz content definitely does lead to a more enjoyable experience, in my experience. My guess is cinemas might try it more if it was more feasible.

 

[richard12511]

So would it for instance be better to work on achieving higher SPL between ~20-30hz and worry less below 20hz?

I would say no, as the sub 20Hz content is almost always the limiting factor for my system. With multiple 113kg subs that can play down that low, I've never been output limited by the 20-30Hz range, but that may also depend on room size.

 

[Duke]

I'm curious to hear opinions on how deep home theater / consumer subwoofers should dig?

My brother has a nice home theater system and he likes to use a spectrum analyzer to look at the low frequency content in movies. There is a movie called "Kon-Tiki" which has a strong 13 Hz signal during an encounter with a whale shark, and I think that's the lowest he's found.

His DIY subwoofer system is able to reproduce that 13 Hz signal at interesting levels, but I don't know what the in-room SPL was. The room shudders and your body shudders and you feel kinda swimmy, like your balance is uncertain even though you're sitting down.

He built a platform to raise the back row of seats for "stadium seating", and the subs are incorporated into the platform. They are big, stiff, low-tuned ported boxes. As I recall the math said something like 15 or 16 Hz tuning frequency, but then the actual port diameter turned out to be smaller than advertised, so the actual tuning frequency would have been a bit lower. Which in retrospect probably wasn't a bad thing.

 

[Neddy]

I'm curious to hear opinions on how deep home theater / consumer subwoofers should dig? I'm looking at equipment from JBL Pro for small cinemas, and their 2x18" subwoofer naturally goes to 22hz at -10dB, and can achieve down to 22hz -3dB with external EQ.
...

The JBL Subwoofer for reference https://jblpro.com/en/products/4642a

I have the similar 4645C sub at home, same (or very similar specs).
Even though my mains (w/2216ND-1s) also go that low, I've found the sheer impact of the bigger sub can make a notable difference (cannon fire, earthquake effects). (They both do ~20hz w/eq pretty well.)

If you want to squeeze out just a few more hz, then this:
https://jblpro.com/en/products/sub18
Which uses the 2269H 18" woofer. I've often been tempted to drop one of those in my cabinet, but....$$$$.
I got the 4645C before the M2/4367 woofers; not sure I'd see the need if I'd had those all along - certainly the size of the cabinet might be a constraint. But since I have it, I see no need to remove or replace it.

 

[JeffS7444]

It appears that Eminent Technology's rotary woofer is still available:
http://www.rotarywoofer.com/

 

[trl]

Now this is something that I'd like to see tested here on ASR: http://www.rotarywoofer.com/index_files/RW_front.jpg, thanks for sharing @JeffS7444.

Achieving 20 Hz with a good linearity up to 100 Hz and a low THD means that the subs should get lower than 20 Hz, so probably around 15 Hz @-3dB should do. I guess it makes sense to design subs that can get below 20 Hz, because this is similar with a tweeter able to reproduce 30 KHz, although you will never need such bandwidth, not even to get mosquitoes crazy.

 

[Chromatischism]

Our hearing stops at 20 hz. Seems enough if subs do the same. I seem to remember one reason is with hearing below 20 hz we'd hear our joints creaking.

Plus there is the chance to make people sick, queasy or see illusions at high levels below 20 hz.

Much of the theater experience comes from tactile effects such as rumble, to further match our perceptions to what we are seeing and hearing. For that, you need strong output to around 15 Hz.

 

[North_Sky]

We can feel sub low frequencies ... 1Hz to 20Hz. Our rooms can shift, the floor can tremble, the ceiling can crack open, the walls fall down ... and we are inside the movie, not anymore just watching and listening.

That's what quality subs are for...to feel earthquakes and hurricanes gale forces.
...To shake the foundations and structures of our homes and skyscrapers tumbling down all around our living rooms.

 

[North_Sky]

Some movies (Live - Die - Repeat) @ the opening are a reminder.
Others now from Disney have pretty much abandoned the tactics, to not scare the children anymore. Bass addicts watch movies not for the film's value but for the bass content.

Some film directors put more creativity into sound effects and music than the film's cinematography, story and real value (brain). They go for the senses (aural) with a sharp scalpel right straight through the throat's main jugular vein...with bloody red dexterity.

 

[JeffS7444]

The quest for ultra low bass is at least as old as the high fidelity hobby itself, and enthusiast magazines of the 1950s would sometimes feature elaborate acoustic labyrinths built beneath the floor, or in an unused fireplace. But like the rotary woofer, such installations are large and can't be readily relocated. For situations where built-in woofers aren't practical, how's about using bass shakers instead?

 

[pwjazz]

120kg and intended for a car!
I wouldn't add anything weighing 120kg to a car, but then, I spent my whole carreer trying to make cars as light as possible.

What cars have you worked on?

 

[Frank Dernie]

What cars have you worked on?

Formula 1 cars mostly, I have done a CART car and a Le Mans car too though.

 

[Ron Party]

Now this is something that I'd like to see tested here on ASR: http://www.rotarywoofer.com/index_files/RW_front.jpg, thanks for sharing @JeffS7444.

Achieving 20 Hz with a good linearity up to 100 Hz and a low THD means that the subs should get lower than 20 Hz, so probably around 15 Hz @-3dB should do. I guess it makes sense to design subs that can get below 20 Hz, because this is similar with a tweeter able to reproduce 30 KHz, although you will never need such bandwidth, not even to get mosquitoes crazy.

I attended a home theater meet roughly 15 years ago at a colleague's purpose built 6000 cubic feet theater (read: below pull in garage) with the equivalent of a magnetic bank vault entry door, and with 2 of Bruce's rotary subs, along with 3 Wilson subs (one refrigerator sized XS and two WatchDogs). I experienced first hand the value of being able to reproduce VLF content. Some of that content is intentional and some unintentional (because the mixing and mastering tech did not have the proper equipment and simply did not know of the existence of that content).

It's not for everyone. A couple of attendees, depending upon where they were seated or standing, particularly those standing near room corners, experienced temporary bouts of nausea. These were exceptions, though. Most did not report any such uneasiness.

If I had the right room and financial wherewithal, I wouldn't even blink an eye. I'd get one of the TRW's installed. VLF in spades with virtually no distortion.

Because of the back venting requirements for installation, it would seem that one's entire neighborhood will know when the rotary subs are in use. They can easily be experienced (read: felt, more so than heard) a few football field's away.

A few audio luminaries attended, including Mark Seaton and Keith Yates, the latter being the one who helped with the design of Amir's main showroom (if I'm not mistaken).

I don't remember Keith Yates participating here at ASR. Mark Seaton drops in from time to time. I'm sure he could add to this discussion.

 

[Zedly]

My brother has a nice home theater system and he likes to use a spectrum analyzer to look at the low frequency content in movies. There is a movie called "Kon-Tiki" which has a strong 13 Hz signal during an encounter with a whale shark, and I think that's the lowest he's found.

There's a project called Bass EQ that boosts ultra low frequency material on movies. They keep a database of EQ settings for specific movies that you can load into a miniDSP to bring out the low bass.

There's a thread at AVS (https://www.avsforum.com/threads/bass-eq-for-filtered-movies.2995212/) and a catalog of spectrogram data (https://beqcatalogue.readthedocs.io/en/latest/).

 

[Blumlein 88]

I attended a home theater meet roughly 15 years ago at a colleague's purpose built 6000 cubic feet theater (read: below pull in garage) with the equivalent of a magnetic bank vault entry door, and with 2 of Bruce's rotary subs, along with 3 Wilson subs (one refrigerator sized XS and two WatchDogs). I experienced first hand the value of being able to reproduce VLF content. Some of that content is intentional and some unintentional (because the mixing and mastering tech did not have the proper equipment and simply did not know of the existence of that content).

It's not for everyone. A couple of attendees, depending upon where they were seated or standing, particularly those standing near room corners, experienced temporary bouts of nausea. These were exceptions, though. Most did not report any such uneasiness.

If I had the right room and financial wherewithal, I wouldn't even blink an eye. I'd get one of the TRW's installed. VLF in spades with virtually no distortion.

Because of the back venting requirements for installation, it would seem that one's entire neighborhood will know when the rotary subs are in use. They can easily be experienced (read: felt, more so than heard) a few football field's away.

A few audio luminaries attended, including Mark Seaton and Keith Yates, the latter being the one who helped with the design of Amir's main showroom (if I'm not mistaken).

I don't remember Keith Yates participating here at ASR. Mark Seaton drops in from time to time. I'm sure he could add to this discussion.

Sounds good. It ain't a party Ron, until someone goes to the emergency room. So queasy feelings in the corner are getting close to being enough.

 

[Chromatischism]

We can feel sub low frequencies ... 1Hz to 20Hz. Our rooms can shift, the floor can tremble, the ceiling can crack open, the walls fall down ... and we are inside the movie, not anymore just watching and listening.

That's what quality subs are for...to feel earthquakes and hurricanes gale forces.
...To shake the foundations and structures of our homes and skyscrapers tumbling down all around our living rooms.

I have tried some scenes with different types of subs, including ones designed to eliminate vibrations.

For example, during Matt Damon's blast off at the end of The Martian, the room should be shaking as the rockets lift the ship through the atmosphere. You should feel like you're in the ship with him. If you can't feel anything, the experience just isn't the same. It's lifeless.

 

[North_Sky]

I have tried some scenes with different types of subs, including ones designed to eliminate vibrations.

For example, during Matt Damon's blast off at the end of The Martian, the room should be shaking as the rockets lift the ship through the atmosphere. You should feel like you're in the ship with him. If you can't feel anything, the experience just isn't the same. It's lifeless.

The Martian (Ridley Scott); excellent bass test. Cool flick too.

* Some movies, and music recordings too (digital), have bass content in the single digit Hertz (from 1 to 5Hz). Only addicts need to apply, everyone else please proceed ...