Purpose of flat response below 20Hz - Why does it matter? - Page 12

That seems as likely as any other explanation, yes.


120Hz crossover, drivers with inductance low enough and suspensions linear enough to play cleanly >1kHz, actually.


No. The thing is, small rooms simply work differently than big rooms, but too many people think that the lessons of the latter are directly applicable to the former. (Well, in fairness they work the same, but the frequency spectrum of the modal region is quite different, so as a practical matter they are simply different animals.)

A succinct summary, from Geddes (who, after all, did write a doctoral dissertation on bass in small rooms):

"In a small room in the modal region, the SPL rises rather slowly at the individual modes as the energy builds up. The point about this NOT being like a propagating sound wave is quite correct. The pressure throughout the room basically rise and falls virtually in unison at every point. Think about the rise time of a mode compared with the wave propagation time. If you plot out the pressure around the room you will see that the wave travels around faster than the pressure can respond and the entire room pressure rises and falls with no apparent wave propagtion. Once we reach the modaly dense region then this effect goes away because the wavelengths are shorter and the modes are denser."

Unfortunately, I don't have a cite for that quote. I apologize for that.

This quote has to sink in more! In free field, humans can localize sound till 40-80Hz, not as precisely as around 2k-6k Hz, but still can. Source localization falls apart in a room at the modal region. You can still perceive low frequencies (provided no excess distortion!) as coming from 'somewhere', but only because one ear receives weaker signal then the other, ie, sitting near a null and not related to source position.
If you have smooth sound field at modal region, you have also correct time behavior. Hard to believe with all those sources playing with different phases and levels, but it's true. This also prevents any localization ques in the modal region. (good topic is how to make modal behavior disappear, but so that localization could function at low freq)

To stay on topic, first get smooth 40-200Hz (important with naturally occuring sounds, music, some movie sounds) then worry about sub20.

Hi All,

Sorry to bring this thread back to life but I started reading some of the DIY collets by basso and team and wanted some more info. I think there is a case to be made for sub-15hz output... But here is my question. How big of an enclosure or how many drivers does one need to create a DIY sub that can extend down flat to below 10hz or 5hz? I just ordered a pb13ultra and it's absolutely the max size I can fit in my unsealed room... Do you low freq DIY experts have any suggestions? Can I get better (read: lower hz) performance in a smaller form factor?

Flat to 10 or 5 would be nice. I find that if it is not flat (+\\- 2 db ish) it gets drown out by the higher freq. My room has only vary little room gain as well. It is small room, but has two opening archways into a room with vaulted ceilings, so hard to pressurize.

Thoughts? Feel free to PM if this is too off topic.

I read about the first 4 pages...definitely good stuff to read. Right now I can only go down to 37hz and was wondering whether or not going down 20hz was worth it...anyone care to chime in?

Yes

yes, especially if you're into home theater and not just music.

You do realize you posted this on AVS??.......

Short answer: Yes.

My first sub (DefTech ProSub 200TL) went to 26Hz +/-3dB and thought it dug pretty deep.

My second one (SVS PB10-NSD) was rated at 20Hz +/-3dB and I noticed a significant improvement in bottom end (and overall performance). 20Hz was unmistakably better than 26Hz.

My third one (SVS PB12-NSD) was rated at 18Hz +/-3dB. The improvement in bottom end wasn't as significant, but there were times when I could tell that it dug a bit deeper. (With that sub, the more significant fact was that it could hit harder and play louder than the PB10.)

My current ChaseHT SS-18.T* subs play flat, loud and clean down to 17Hz. As with the move from the PB10 to the PB12, the improvement in bottom end was noticeable, but not significant. (Overall output, however, was much improved. And the sound quality - tighter / crisper / "bloat"-free - was also an improvement, to my ears, over the previous ported subs.)

(*The performance of my buddy's ChaseHT CS-18.T subs - which, in his ~30% smaller HT room, dig considerably deeper (down to ~10Hz, thanks to incredible room gain) and play considerably louder than my subs - crushes the performance of my subs and makes for a very different, and very impressive, auditory and tactile experience. )

All of this to say that, for HT, getting down to (at least) 20Hz is definitely worth it.

IMO, and YMMV.

From a practical standpoint, No. Since I'm told less than 1% source content (movies or music) have stuff below 20 hz.

Yes, if you have unlimted to resources and unwilling to live with any compromises.

If you were to hear a system that plays to 37hz vs. one that plays to 20hz, you would find the answer instantly. The difference is large. It can be heard and it can be especially felt. It's nearly an entire octave of both audible and palpable content. It's importance depends on you and what you listen to or watch. If you watch chick flicks and documentaries, it might not be that important. If you like action movies, sci-fi, horror, or some of the big budget animated films, the content in the deep bass range makes the movie a different and much more immersive experience.

I disagree. I'm not sure abort your <1% statement but it's probably accurate when you take into account the vast amount of movies is spent on normal dialogue. That said, those <1% are really really cool imo and worth it to a point. Everyone has to decide just how much it's worth to them. For me, it was $1500 and a little effort in my attic one Saturday afternoon. Hardly unlimited resources and well worth it imo. Are there still some compromises? Sure, but not near to the level you seem to be implying.


Getting great output down to 20hz is not that tough. Many, many options exist that would likely fit the bill for you if you so desire. It's below 20hz that things begin to get difficult to attain. Again, many options exist that would allow you to get there but it becomes a game of compromises. Best of luck with whatever your choice is.

Aren't there some documentaries that have some passages with excellent low content? More to the topic of your post, I completely agree that 37hz to 20hz is a very noticeable change with many movies. It's below 20hz that people may not notice a change unless they have alot of displacement.

There are indeed a few documenatries that might come into play as well. The IMax Hubble movie comes to mind. The shuttle take-off scene is room-shaking.

That's the one I had in mind.

I am a 1%er! I love what the frequencies 20Hz and lower do for a movie. The cost certainly does start to go up a lot to get below 10Hz, but it is like anything else in life. If you have not heard the difference I don't know how you can make a comment like that or say that it is less than 1%. Most movies have this content and if your system can't play it than you are not experiencing the track as it was intended.

I want to demo a room that plays down into the single digits to experience that and see if it is worth chasing.

The way a movie was "intended" to sound is how the soundtrack plays in a MOVIE theater. Does any theater out there play below 20hz content?

Agreed, (though it still can be pretty cool)! But "intended" is not correct as you pointed out. I beleive a member here (FilmMixer?) actually deals with these soundtracks professionally, and he backs up the fact which you are pointing out....

As far as I know most commercial theaters roll of the low end to prevent bass from bleeding into the other auditoriums. I feel like I get a much lower response in my home setup.

If <10hz content is in the soundtrack then the sound engineers intended for it to be there. I don't buy into the idea that it's distortion in the microphones. If that was the case, the sound engineers could simply put a 20hz high pass on everything.

As to your theater question, almost all movie theaters(IMAX theaters maybe being the exception) can't any play below 20hz and many movie theaters(think your basic local theater) probably can't play below 30hz.

I disagree. Why would they ignore the growing number of home theaters, and the growing number of systems that can play well under 20hz?

If the only intent was reproduction of the movie in a movie theater there would be no need for anything less than 30hz, let alone the 2-3hz or 5-10hz content that's INTENTIONALLY put there.

Anyone who doesn't think sub 20hz content is captivating or adds to the experience hasn't experienced it. Is it necessary, of course not. Are you missing out, absolutely.

Nobody, regardless of how much they like/dislike movies or bass, leaves my theater room without a grin they can't wipe off their face.

Did he indeed say that? I remember one of his posts when he talked about working with Randy Thom, and Film Mixer said that Randy Thom believes that the two keys to great soundtracks were low end content and reverb. Randy Thom puts more sub 10hz content in his soundtracks than pretty much anyone, and it's never out of place.

I may be mis-remembering, but I thought he said something to this effect. I remember being pretty surprised when I read it. I'll see if I can find his posts.

Actually, now that I think about it, my wife just became friends with the wife of one of the editors from LucasFilm. I believe he has worked on the Transformers and Iron Man movies. I'll see if I can get it directly from the horses mouth. I understand he wants to come over and check out my Demo room anyway.

To make the assumption that bass content like this well below 20hz is unintentional is ridiculous:
http://www.avsforum.com/avs-vb/showt...8#post21244908

I stand corrected (sorry about that!), I did a quick search on FilmMixer, and it is pretty clear the ULF mixes are intentional. What the hell was I thinking or "remembering"? I guess I need a little more coffee!
Anyway, this has probably been answered before here and on other sites, but why would these ULF mixes be intentional if the theaters cannot produce them?? Obviously there is a good amount of money made by selling the DVD's/BR, but isn't most of the money made from the theaters? I'm guessing the percentage of home users that can actually reproduce this ULF must be fairly small. I am not complaining by any means, just a little curious....

Amen. It's so absurd a notion that, if I didn't know better, I'd be hopelessly at a loss to understand why anyone would believe it's unintentional content.

It keeps coming up because 99% of the people who frequent these forums who are just trying to sell subwoofers are selling subwoofers that offer weak-to-none <20 Hz playback.

If my system rolled off hard at 20 Hz, I guess I'd be telling everyone why content <20 Hz is unintentional, inaudible, too expensive, only 1% of content, not worth chasing, blah, blah... and, that graph you linked to would look one heckuva lot different.

Raise your hand if you give a flying flip what the local cinema thinks about audio.

Bosso

No problem. We all have those mornings. As to why are they in there, you should ask them to be certain but I'll hazard a guess and say that the sound engineers take pride in what they do and want their work to be as close to the real thing as possible even though the number of home theaters that can reproduce it accurately is exceedingly small as you point out. I'm also not sure how many mastering studios have rooms equipped to reproduce ULF well. I could very well be wrong about this but I think I remember one mastering studio having 12 18" sealed subs in one room.

What's a local cinema? Haven't been to one since I bought the ULS-15s.

Some folks would say it's just people getting "all hung up on performance".