Is infrasonic output with authority possible with dynamic drivers?

[Steve81]

Unfortunately for you, as the gentlemen noted above, very few movies, even so-called block busters, contain low frequency information below 30 Hz let alone 20 Hz.

So audio enthusiasts should only be concerned with the lowest common denominator, as opposed to reproducing the material on more demanding soundtracks?

you are seriously experiencing the point of diminishing returns.

Depends on your point of view I suppose. As I see it, a subwoofer system that can effectively deliver solid 10Hz performance isn't all that costly; a quad pack of Seaton F18's will set you back roughly $6k. That's chump change for people shopping in the KEF Reference / Revel Ultima range, and less than some high end power cords for those so inclined. Not only will the Seatons deliver the goods on soundtracks that do contain infrasonic content, they'll still sound great on soundtracks that are filtered at 20 or 30Hz, given that they'll be loafing along reproducing such material.

Also, sound isn't the only reason to enjoy a movie at the cinema.

I'm not sure how you feel this line of reasoning is relevant at a site called Audioholics. Perhaps you would feel more comfortable at Better Homes & Gardens?

 

[shadyJ]

Some movies do contain a lot of infrasonic energy. Tron Legacy, just to name one example. Here is an entire subforum that analysis bass content in movies, and you can find many examples of stuff digging down below 15 Hz and even into the single digits. How audible that stuff is and how much difference it makes is another discussion, but that content most certainly exists, and in today's big movies, it isn't uncommon.

 

[ATLAudio]

@Steve81
Yeah, but you’re missing the point about diminishing returns. First, how do you define “solid performance?” Let’s use THX Reference volume which is 95 dB with 20 dB of head room, or 115 dB with passable compression at the MLP.

To do this at 10hz is going to depend on your room. If the long dimension of your room (floor corner to opposite and opposing ceiling corner) is one found in a typical open floor plan with vaulted ceilings then you’ll not have appreciable cabin gain, even with your Seaton stack.

However, my room will give you 10hz with that Seaton Stack, compared to spending $1500 on two PSA XS15se if my goal is only <~20hz.

Someone in the market for Revel Ultimas isn’t typically chasing infrasonic frequencies, and no one here is buying exotic cables, so these comparisons aren't relevant.

 

[Steve81]

Yeah, but you’re missing the point about diminishing returns. First, how do you define “solid performance?”

Being able to faithfully reproduce what's encoded on the disk of your pleasure at the master volume level you care to set seems to be as good a definition as any.

Let’s use THX Reference volume which is 95 dB with 20 dB of head room, or 115 dB with passable compression at the MLP. To do this at 10hz is going to depend on your room.If the long dimension of your room (floor corner to opposite and opposing ceiling corner) is one found in a typical open floor plan with vaulted ceilings then you’ll not have appreciable cabin gain, even with your Seaton stack.

OK, so it's difficult to do in your hypothetical auditorium. That's why commercial theaters don't typically dig super-deep (though a pair of Cap 4000ULFs would probably fill as large a room as is likely to exist in most residences with 10Hz bass). What about a real room, like Josh Ricci's? Josh measured a single Funk 18.0 to deliver 105dB in his space at the listening position. A single Seaton F18 would likely do a little better than that on account of its larger enclosure. Add 12dB for a stack of four...there's your 115dB with some breathing room to spare, presuming a soundtrack that actually calls for 0dBFS at 10Hz. Josh didn't test the Cap 4000ULF in room, though given that it delivers >15dB more output at 10Hz than the Funk 18 outdoors, one expects even a single would deliver "adequate" output as well. Duals might just bring the house down.

Someone in the market for Revel Ultimas isn’t typically chasing infrasonic frequencies, and no one here is buying exotic cables, so these comparisons aren't relevant.

The comparisons are relevant for a couple very basic reasons.

1. Diminishing returns vs cost is a problem relative to one's budget. Does anyone think a pair of Salon 2's actually deliver more than four times the detail and performance than a pair of Revel F208's? Yet people still buy them. As a KEF man, I'm not under any delusions as to whether or not a pair of Blades is 10x more awesome than my pedestrian R500s. Of course if I hit the lotto, you better believe I'd own a pair. Never mind the diminishing returns of power cords...and people buy them too.

2. Relative to the costs of many of the extravagances of audio (high dollar amps, wire, etc.), a quad stack of Seatons, or the JTR Cap ULF 2400 or 4000 aren't really all that costly. There's also this puppy from PSA. Are they wasting their time too?

As it relates to the core question, the matter of diminishing returns is wholly irrelevant. If you've heard a system that can produce prodigious infrasonic bass, and you were shocked and awed, that's really all there is to it. The cost is what it is. Diminishing returns just don't enter into the equation.

 

[ATLAudio]

@Steve81

Steve,

My point being that we need something quantifiable, and at the very least above the noise floor of the room. That’s why I tossed out THX reference. "Solid performer," and "pleasurable," while fully descriptive to one, might be meaningless to another.

Steve, holding aside that my room is hypothetical, yet incredibly common, and Josh Ricci’s is real, and incredibly treated, arranged, and or constructed, I’m certainly not arguing that it can’t be done, but the cost returns are logarithmic, ie diminishing. For every lower cycle you want to achieve, it’s costing drastically more. While I don’t have charts and graphs to show it, I’m confident that the sweet spot is in the 16-20hz area. Also, while I haven’t done double blind experimentation to show it, I’m willing to hypothesize that this is a sweet spot for max performance as well. YMMV, and if you want to put two JTRs in a walk in closet and listen at 15 dB hot, then go on with your bad self. It’s all good!

I believe that there’s always a sweet spot, or equilibrium for max performance and dollar spent, but both need more information to prove definitively. I believe that all of the Seaton, Cap, Funk, high end KEFs, mentioned, and yes the new PSA, are on the side of the bell curve suggesting diminishing returns in all but the most extreme cases.

 

[Steve81]

I’m certainly not arguing that it can’t be done, but the cost returns are logarithmic, ie diminishing. For every lower cycle you want to achieve, it’s costing drastically more. While I don’t have charts and graphs to show it, I’m confident that the sweet spot is in the 16-20hz area.

Two problems with your thoughts,

1. What is "drastically more"?

2. In a system that exhibits a 12dB/octave rolloff outdoors, in room, every lower cycle may well cost you nothing at all. Going back to the example of the Funk in Josh's room, as mentioned, it delivers 105dB at 10Hz. Oddly enough, the output is practically identical at 20Hz, with a max of 106.3dB. As such, the question isn't a matter of how deep you want to dig, but how much output you desire.

Keeping those things in mind, lets take two real world examples that Josh measured,, the JTR Cap 1400 and the Cap S2.

http://www.data-bass.com/data?page=system&id=117&mset=129
vs
http://www.data-bass.com/data?page=system&id=133&mset=145

Using the comparison tool, you can see the Cap S2 largely equals or exceeds the Cap 1400's output from 16Hz on up, and it does so without unwanted issues like port compression and port noise. With cabin gain, extension is really only limited by where the amplifier itself rolls off. So for 50% more cost, you get more output from 32Hz on up, none of the aforementioned drawbacks of a vented system, and the cherry on top of extension down to 10Hz and below backed by two extremely capable 18" drivers. Personally, I don't see that as a drastic increase in cost, nor do I see the improvements as being trivial. YMMV.

 

[ATLAudio]

@Steve81

I mean, I understand how cabin gain works, but that's largely room dependent. Moreover, it's precisely a question of desired output at a given frequency, not just frequency. In room, I can dig 10 hz out of my 2 PSA XS15se at 85 dB, and maybe even more before noticeable compression occurs.

 

[Steve81]

I mean, I understand how cabin gain works, but that's largely room dependent. Moreover, it's precisely a question of desired output at a given frequency, not just frequency. In room, I can dig 10 hz out of my 2 PSA XS15se at 85 dB, and maybe even more before noticeable compression occurs.

It's room dependent, but as a wise man said earlier in this thread...

All but the most enormous rooms will give cabin gain or 6-12 dB at 15hz, which would be on top of their outdoor ground plane measurements. Corner loading will help even more.

But I think at this point, you're conflating what I'm trying to say. I'm not arguing that everyone should rush out and try to achieve extension down to 3Hz. What I am saying is that if you're curious what it's all about, it's not necessarily a terrifically difficult or expensive thing to accomplish extension beyond 15 or 20Hz. My advice would be to first check out the forums to see if you can get a demo. If it does something for you, great. If not, no harm, no foul. Second step would be to take measurements in your room to see how the room behaves (and it's a good idea in any case to extract the best performance from any subwoofer). If the room doesn't want to cooperate with your efforts to achieve ULF, again no harm, no foul. If you want to go further, time to break out the old wallet. Fortunately, even a pair of Cap S2s or a quad stack of Seatons is still cheaper than the aforementioned Revel sub.

 

[shadyJ]

Two problems with your thoughts,

1. What is "drastically more"?

2. In a system that exhibits a 12dB/octave rolloff outdoors, in room, every lower cycle may well cost you nothing at all. Going back to the example of the Funk in Josh's room, as mentioned, it delivers 105dB at 10Hz. Oddly enough, the output is practically identical at 20Hz, with a max of 106.3dB. As such, the question isn't a matter of how deep you want to dig, but how much output you desire.

Keeping those things in mind, lets take two real world examples that Josh measured,, the JTR Cap 1400 and the Cap S2.

http://www.data-bass.com/data?page=system&id=117&mset=129
vs
http://www.data-bass.com/data?page=system&id=133&mset=145

Using the comparison tool, you can see the Cap S2 largely equals or exceeds the Cap 1400's output from 16Hz on up, and it does so without unwanted issues like port compression and port noise. With cabin gain, extension is really only limited by where the amplifier itself rolls off. So for 50% more cost, you get more output from 32Hz on up, none of the aforementioned drawbacks of a vented system, and the cherry on top of extension down to 10Hz and below backed by two extremely capable 18" drivers. Personally, I don't see that as a drastic increase in cost, nor do I see the improvements as being trivial. YMMV.

One thing I would mention here is that sealed subs will run into a lot more distortion than ported subs where the port output supplements the response. You see a lot of people worrying about port chuffing and hailing sealed as the solution, but dB for dB, ported will be a lot cleaner at higher output levels. Chuffing can be an issue on poorly designed subwoofers, but any competent system, it will far outperform a sealed system, all other things being equal. When either design is pushed to their limits, they both run into audible problems, but the over-excursion of sealed designs usually occurs at a much lower drive level than audible port turbulence. I suppose if the sky is the limit on a prospective system, then get a whole pile of sealed subs and you never have to worry about them coming close to their mechanical limits. A nice system to be sure, but terribly inefficient.

 

[TheWarrior]

One thing I would mention here is that sealed subs will run into a lot more distortion than ported subs where the port output supplements the response.

That's two different things. If a single sealed subwoofer were asked to achieve the same max SPL groundplane, of course there would be distortion. The driver would be destroying itself. So yes ported subs offer +/-6dB, but anyone trying to give equal bass to all listeners in any room will need multiple subs, negating that difference. Without the additional resonance (the port tuning) sealed subs offer easier setup and smaller enclosures that make it a lot easier to live with a 4+ subwoofer layout.

 

[shadyJ]

That's two different things. If a single sealed subwoofer were asked to achieve the same max SPL groundplane, of course there would be distortion. The driver would be destroying itself. So yes ported subs offer +/-6dB, but anyone trying to give equal bass to all listeners in any room will need multiple subs, negating that difference. Without the additional resonance (the port tuning) sealed subs offer easier setup and smaller enclosures that make it a lot easier to live with a 4+ subwoofer layout.

Disagree. Ported subs do not have to eat up a lot of floorspace. Also, you post presumes that the user does not have floor space for multiple ported subs. If floor space was that precious, they may well not have room for multiple sealed subs either. Ported subs can have a small footprint, see for example the SVS PC-2000, a smaller footprint than most sealed subwoofers. I don't think ported are anymore difficult to setup than sealed either, unless you have a variable tuned sub, in which case it is only a little more involved than a normal subwoofer. Also, in a large room that doesn't see much low end gain, ported subs are a requirement if you want deep bass, unless you have so much displacement from a sealed system that it can handle that situation with a shelf filter to make the response flat down to x Hz.

 

[Steve81]

One thing I would mention here is that sealed subs will run into a lot more distortion than ported subs where the port output supplements the response. You see a lot of people worrying about port chuffing and hailing sealed as the solution, but dB for dB, ported will be a lot cleaner at higher output levels. Chuffing can be an issue on poorly designed subwoofers, but any competent system, it will far outperform a sealed system, all other things being equal.

As noted above, it really takes the S2 with dual 18" drivers and a 4kW SpeakerPower torpedo amp to have a sealed sub that can throw down with the 1x18", 1.4kW Cap 1400. That goes to show the efficiency / advantage of a vented system at tune. However, once the sealed sub starts to reach parity with the vented sub's abilities at tune, the picture changes a bit. Here's a snapshot of the Cap 1400 vs the S2 at a 110dB drive sweep:




Given the signal shaping employed by JTR, the S2 digs much deeper than its ported counterpart, which isn't really a surprise. The THD charts show one of the corresponding drawbacks to the additional efficiency of the port: massive distortion below port tune. Last but not least is the compression chart, which paints a less than stellar picture for the Cap 1400. It's not at its limits, but the system is compressing by nearly 5dB around port tune, while the S2 is still practically compression free even though it's also closing in on its limits. Even in the 105dB sweep, the Cap 1400 exhibits 3dB of compression at tune.

Think about that for a minute. At the 110dB sweep, the S2 produces 106.4dB at 16.113Hz in the 110dB sweep, which is nearly a perfect result relative to the 90dB base sweep. Going by the Cap 1400's base sweep, it should also be producing a bit more than 106dB at 16.113Hz in the 105dB sweep, but instead it delivers 103.2dB. IOW, if you calibrate both subs for an identical FR, the S2 may be producing more output at port tune relative to the vented Cap 1400 when both systems are within their limits. It's only after you drag the vent kicking and screaming that it produces the additional output you expect, and surpasses the S2.

 

[ATLAudio]

I love the sealed ported discussion. I really do. It's important to note that neither is universally beneficial. Before you even consider sealed subs you need to evaluate your room. Is it an open floor plan with a vaulted ceiling, or is it a sealed off bonus room? I’m fortunate enough to have the latter. To each his own, but I’d lean ported if you have the former. Why? Room-gain. Ideally you’d want your room-gain to start supplementing your sealed subwoofer (which it does at 6dB an octave IIRC) within an octave of the sealed sub’s roll off (that’s my personal goal at least). As @Steve81 mentioned, in the right room even a modest sealed system will not only slam at 20hz (universally accepted as beneficial) but reach 10hz with “decent authority,” and limited distortion, whether you like it or not.

To find out where your room gain begins run this formula 565/sq.rt(H^2+W^2+L^2).

 

[Steve81]

To find out where your room gain begins run this formula 565/sq.rt(H^2+W^2+L^2).

FWIW, room gain is a very tricky affair. It's not just a matter of room dimensions, but room construction as well. Even then, calculations are only an approximation of what is really happening, not to mention the issues that occur in the modal region.

My personal case is somewhat interesting.
FR:

EQ (white line is the cumulative effect of the various filters employed):

Actual Native Response:


First thing to note is that most of what I'm doing is cutting out peaks in the response. The second is that with those peaks removed, it takes very little boost to get a reasonably flat response down to 20Hz. Given that the native response is more than 15dB down at 20Hz relative to the 50+Hz range, I consider myself fortunate in that regard. I also doubt that's an effect of room gain, but instead part of the room's modal response. You can also see the effects of room gain on the far left side of the FR graph where there is minimal boost occurring: the room is perfectly supplementing the 12dB/octave rolloff of the system. At that point, I only really need a shelf filter to raise the low end response further (and sufficient output to back it up, which is coming).

As for the room itself, it's one half of a basement, separated only by a bit of drywall. The exterior walls are all cinder block, with a concrete slab floor, and a sturdier than average ceiling. The way I figure it, the layer of drywall splitting the basement doesn't do much to stop a 50+ foot long sound wave, so the effective space for a room gain calc is much more than you might expect. OTOH, the sturdy construction means that the gain I do get is quite good. Not a bad trade-off in my view.

 

[ATLAudio]

@Steve81

I'll post some measurements when I get home, but I'm in a similar boat. I have to make a few cuts (one large one at 60hz), some notch boosts, and a modest low shelf I have flat response down to 10 HZ. It's not hard, and sounds fantastic at reference volume.

Bottomline, like yourself, I have no business with ported subs in my situation, but that's not the case for everyone.

 

[Steve81]

Bottomline, like yourself, I have no business with ported subs in my situation, but that's not the case for everyone.

Poor bastards they are Seriously though, it goes to show the importance of picking the right room to set up a theater in the first place, particularly if you're serious about your bass.

 

[yepimonfire]

I love the sealed ported discussion. I really do. It's important to note that neither is universally beneficial. Before you even consider sealed subs you need to evaluate your room. Is it an open floor plan with a vaulted ceiling, or is it a sealed off bonus room? I’m fortunate enough to have the latter. To each his own, but I’d lean ported if you have the former. Why? Room-gain. Ideally you’d want your room-gain to start supplementing your sealed subwoofer (which it does at 6dB an octave IIRC) within an octave of the sealed sub’s roll off (that’s my personal goal at least). As @Steve81 mentioned, in the right room even a modest sealed system will not only slam at 20hz (universally accepted as beneficial) but reach 10hz with “decent authority,” and limited distortion, whether you like it or not.

To find out where your room gain begins run this formula 565/sq.rt(H^2+W^2+L^2).

You'd need a large room for room gain to actually be beneficial, small rooms can actually push the -3dB point up, for example, my 12x11 bedroom has modes at ~50 and 45hz, since it's nearly square, I get a nice 10dB bump centered on 50hz, pushing my small subs 30hz f3 down 6dB.

Let's say a sealed sub starts next rolling off anechoically at 35hz, and it's down 12dB at 20hz. We would need a room that was at least 25' long

Sent from my 5065N using Tapatalk

 

[panteragstk]

Unfortunately for you, as the gentlemen noted above, very few movies, even so-called block busters, contain low frequency information below 30 Hz let alone 20 Hz. If you're spending money of equipment with intent on reproducing below 20 Hz (infrasounds) content, you are seriously experiencing the point of diminishing returns.

Also, sound isn't the only reason to enjoy a movie at the cinema. I went to see the Dunkirk in 70 mm and it was beautiful, movie was mediocre, but it looked and sound great. Btw, it won't coming to a home theater any time soon.

I saw Dunkirk in 70mm as well. Agree about the movie.

However, there are plenty of movies with infrasonic soundtracks. That list is a bit out of date, but it shows some good data.

That and just because a movie doesn't get below 20hz doesn't mean having a system capable of sub 20hz is a waste. Most subs that are capable of producing infrasonic frequencies can produce the normal range very well. For the movies that do have such content, it's nice to be able to replicate it.

Having said that I'm in my subs for around $600 including all 4 drivers and the amp. Just because they go low, doesn't mean they are expensive.

 

[ATLAudio]

@yepimonfire

"You'd need a large room for room gain to actually be beneficial"

This is completely false.

"small rooms can actually push the -3dB point up, for example, my 12x11 bedroom has modes at ~50 and 45hz, since it's nearly square, I get a nice 10dB bump centered on 50hz, pushing my small subs 30hz f3 down 6dB."

Half of this is nearly nonsensical. The other half seems to be your anecdotal experience with your *very* small room.

"Let's say a sealed sub starts next rolling off anechoically at 35hz, and it's down 12dB at 20hz. We would need a room that was at least 25' long"

Now you're making stuff up...

It's really simple. If you do that formula you'll have a good idea where your room gain will begin to build, generally at 6dB per octave. YMMV, but generally the larger the room, the less impact room gain will have, not the other way around. Yes, you'll get room modes which can occur with infinite randomness based on your room, but the room gain will still occur.

 

[TheWarrior]

@yepimonfire

"You'd need a large room for room gain to actually be beneficial"

This is completely false.

"small rooms can actually push the -3dB point up, for example, my 12x11 bedroom has modes at ~50 and 45hz, since it's nearly square, I get a nice 10dB bump centered on 50hz, pushing my small subs 30hz f3 down 6dB."

Half of this is nearly nonsensical. The other half seems to be your anecdotal experience with your *very* small room.

"Let's say a sealed sub starts next rolling off anechoically at 35hz, and it's down 12dB at 20hz. We would need a room that was at least 25' long"

Now you're making stuff up...

It's really simple. If you do that formula you'll have a good idea where your room gain will begin to build, generally at 6dB per octave. YMMV, but generally the larger the room, the less impact room gain will have, not the other way around. Yes, you'll get room modes which can occur with infinite randomness based on your room, but the room gain will still occur.

Thinking that 'room gain' is going to solve any problem is also wasted time. The flexibility of DSP allows most of that to be nonsense, accepting that adequate power and diaphragm (total) radiating area vs. cubic volume of listening space is a usable ratio. (size of one driver is meaningless; Assuming multiple subs are used, you need to be able to vibrate enough particles in your listening space to NOT make an audible difference seat to seat. Calculating room modes vs. L,W,H, dimensions gives you a 'map' pf sorts to work with)

I think both of you guys need to buy Floyd Toole's 'Sound Reproduction' 3rd edition.... I know I still need more studying!