Thigpen Rotary Woofer - Page 3  

I had a (stereo) Krell KBX c/o fixed as lowpass c/o=35Hz @ 12db/octave for (two) W/A XS' to extend fullrange Grand Slamm's in their lowest Hz's for music playback. Such an external c/o works fine, however is not flexibel for testing.

Maybe a Casablanca could do the job better.

...I wish I could join you because I'm much interested in this idea... but I'm in Europe :(

Regards, Rene-L

In the specs I believe the MC-12B is good for about 5Hz, and even there that's a low frequency roll-off, hardly a brick wall. The other factor is if you will have the backside of the stairway open or closed? I recall it being a staircase with a pretty big door up top? I doubt anything annoying to neighboors would be heard outside if the door was open.

On the processing, I know of 2-3 possible DSP based options, but I have to do some checking. Main issue is that some of those units have rather noisy fans, but we could possibly just set them in the hall behind the door/manifold.

So far as measuring the response, the guys at PMI should be able to get accurate enough measurements of the VLF response by simply doing a difference measurement using the TEF. It's claimed accuracy is to ~6Hz, but gives you useful information down to almost 2Hz; especially when compared with loopback measurements for the same setting.

Rene

We would love to meet you. You have plenty of time to arrange air fare. I would be happy to put you up at my house. We would be honored to induct you as a member of BAAS

While I'm sure Bruce has his current design targeted for the use of an external chamber/baffle, I wonder if it wouldn't be possible to do a sort of push/pull design that uses the air from the room itself as both intake and exhaust. Perhaps by separating the two by a sufficient distance...?

Ahhh... but it's fun to start looking at what is "sufficient" at 10Hz! ~28' away would give you 1/4 wavelength where we might expect to see a nice cancellation in the right spot and you would need the back-wave to travel about 56' more than the front for it to be a constructive addition. Whatever chamber serves to pass through would also have a lenth and area that would have resonant acoustic properties; think t-line & horn behavior.

In the end, the case of loading this device into a listening room means that you are sitting IN the enclosure! If the adjoining space for the back-wave was the same volume as the room and similarly rigid, the effective box that the device has to work in is 1/2 that of the room. There are all kinds of interesting possibilities in what you could try to do with back wave, but they are all dependent on how the device handles back pressure.

What will be interesting in tzucc's room is that I suspect the maximum clean SPL will be limited by the pressure the device can linearly ramp up to. Of course that point may be past the maximum output capability of the device. Remember, a quantity of pressure modulation is SPL at any frequency. In room that could be 110dB or it may be 130dB, I don't know. I am curious as to what we end up seeing with the frequency response. The room will most certainly exhibit low frequency gain as down low (<20Hz) it's a sealed chamber.

If a crossover of 25-30Hz is desired, then the selection of electronics is much easier.

Mark and others, I have a question regarding the use of subs that go down this low. Even if it can go there, is the information encoded down there, in the sound tracks we get, intended to be heard ?

Art

I have felt for a while that most of the mixing engineers do not have equipment that can reproduce sub 20Hz material without substantial roll-off. As such, if it was meant to be heard it is likely much higher on the soundtrack than it should be in order to compensate for this.

Some diamonds are flourescent and will glow under a black light. That doesn't mean that is the way they are meant to be viewed.

Oneobgyn, this is a surprise... and very kind of you! I'm the one who is honored now. I guess the Bay Area has to be stretched a whole lot to fit Europe in. Therefor realistically spoken, I feel just fine as a none scientist to follow AVS and learn 1 or 2 things via www.
However, I will put my house on the market next month, maybe emigrate within EU (in progress), buy or build a new one after that, including my desperate wanted new audiophile entertainment room, than you and/or BAAS fellows are welcome to play a disk at my place... My promise, you get a wineglass which will never be empty as long as you stay... free of charge. :)

Regards, Rene-L

Personally I think there are multiple reasons and justifications to extend a system's response to these low frequencies. Gratifying Dyno-Stomps are but one benefit, not the soul purpose. Any more resolving system should be expected to show faults that might have been missed in the recording process. There in fact are some studios who have gone to great lengths to add low frequency capabilities. In their case it is often as important to KNOW what's going on down there as is the value of reproducing it. In other words, they want to know that they intended or made the decision to keep whatever is going on down there.

There are times when less careful editing can result in low frequency pops from what they might call "punch-ins". In quiet scenes and with a lot of subwoofage, you can sometimes catch these. More often though, the VLF energy we see is closely tied to big sonic and visual events. At minimum there was VLF energy present when the sound event was recorded. In the studio this may have been boosted in various ways. If they are employing low shelving filters, this will raise everything down low, and very possibly stuff below the effective extension of their system. At the same time, note that they aren't watching spectrograms to decide on the sound they are after, they are listening. Those VLF effects creep in, and with some of the products out there, I wouldn't be surprised if using a small pile of subs in a small studio might give some noticable effect at VLF. Most employ lots of limiting to still allow useful output at higher frequencies, there are more than a few that target extension down to 8-14Hz.

Personally, I have always found that with enough comparison, I can hear a character to the ultimate low end roll off of a system. In those cases where confined rooms have allowed me to couple into the room's transfer function and we achieve either very shallow or almost zero roll off to say 10Hz or lower (this is very easy to do in car audio), that "sound" largely goes away. The subjective sonic benefits of such a system are what interest me more. So far as the studios, I still say we have to provide them a means to monitor and reproduce it before we can expect them to figure out what to do with it.

As a point of reference from years back, note that in the first two reviews of the ContraBass (a 15+ yr old design), both reviewers described it to the effect of, "more bass than you could ever want or need in a home." By current standards, I consider a ContraBass just enough for optimal performance in a moderate size room, with multiples needed for larger rooms. I expect that as reproduction of sub 20Hz energy becomes more readily available, we will see people find more creative uses for it. Imagine if down the road they can create a "goosebump" pedal/key for use at just the right time in a movie. The best likeness to this that comes to mind is in the moments leading up to the train crash at the beginning of "Unbreakable."

Just my rambling on the matter...

My point is not is there information that low but is it intentionally part of the sound track and does getting it add to the enjoyment or not.... or worse dininish it.


Art

A last point I forgot to include (surprising how I could leave much out of that short novel :rolleyes: ). Given the "unknowns" of what is recorded at VLF (let's call that <20Hz), I would envision a desire to have either pre-sets or manual adjustment of the low frequency level. I could see the justification of an adjustable shelving filter and likely a selectable and adjustable 6 or 12 dB/octave (1st or 2nd order) high pass filter.

This is actually relatively easy to implement with current DSP audio processors currently on the market. You can actually remotely adjust defined parameters if so desired. You would of course want to measure and note the range of adjustment you have, but I think it could be a fun and useful feature.

So Mark are you saying one could, at a whim, say hey lets go down to 5Hz for this show and 15Hz for that one ?

Art

Mark and Art,

This sounds a bit like a "chicken and egg" question to me.

We may not have infra-sonic information on soundtracks because the recording engineers
don't put it there because nobody can reproduce it.

Simultaneously, we don't build sound systems that can reproduce infra-sonic information
because it's not on the soundtracks.

Somebody has to be first to break the impasse.

Sounds good to me ! :) I was just thinking about the subjective quality differences in the 16Hz tune of my subs compared to the 20Hz. The lower is probably flat down to around 12Hz. A couple of times I heard strange things that I wasn't sure what they were. Even things like the THX traliers had some strange sort of overtones. This is of course subjective, and I went back to the 20Hz tune just because it sounded cleaner to me.

Having the ability to go lower seems great to me, I was just wondering if it could end up exposing the equivalent of video noise that some DLPs show and CRTs don't.

Don't take this as a condemnation of this device , instead only just a question from a neophyte.

Art

As anyone who has talked with me well knows, I fully agree that there is no such thing as "more bass than you could ever want." My point was just that the general populus follows what marketing "teaches them." :rolleyes:

In other words, you need as much as we have to sell! :D

Years ago, head honcho's at pro audio companies used to say that there is no need for information below 70Hz. Of course that number later bumped down to 50Hz once they figured out how to do that, and later to the 30s when they kinda figured that one out. No, this doesn't relate directly to HT, but the point is that so long as you give me some processing and EQ, I'd bet I can find a useful way to put ever increasingly more bass energy to good use. :cool:

So far as tzucc's dual 'dogs and XS not cutting it, I'm confident that's first a function of setup and optimization. Of course I'm also quite certain there is more to be added to the experience that what his Wilson trio can provide.

Hi Morbius,

I fully agree, and that was really the summary point of my rambling above (thanks for the bit of clarity). First you have to make VLF reproduction available and get it in the hands of those creating and recording the sounds we play back. I can't believe the tremendous increase in low frequency content in movie soundtracks over the past 5-10 years is all faulty monitoring. If we look at the Bag End S21E review in the Way Down Deep report we find this comment from Keith Yates at the end:

"One last point: If you've got the dough and real estate to spare, don't shrug off the sub-20Hz content I've shown in the reference waterfall plots as unintended artifacts—say, scraps of subway rumble or HVAC noise—that somehow slipped through the filters during the mixing process. The content is program-related and meant to be there. So, okay, as a hardware matter, how did the engineers at Todd-AO who snagged an Academy Award for Best Sound for Black Hawk Down monitor all that gut-twisting infrasonic content—all those rumblings I've mentioned that lie just beyond the reach of even refrigerator-sized subs? They used big Bag End subwoofers—22 of 'em."

So, while the means were a bit extreme, some studios have cobbled together a chicken to allow them to create the egg. ;)

This was the exact same thing a subwoofer manufacturer in Canada kept hearing from some of their clients. The finally determined that what was needed was not more bass but more involvement in the film. Hence they created the Odyssee Motion Simulator.

With projectors, having more lumens or greater contrast or more bit depth doesn't make something that much more realistic if you are still in black and white. Adding color does. I think we are looking at kind of the same thing here - with responses down to 5Hz we are not talking about sound but something different that has to be felt. As such, we are getting into the realm of tactile and motion and not really sound.

Certainly such a infra-woofer would not have any use for a music system unless you are looking only for synth bass enhancement - no instruments get even close to that depth. So we are looking at such a thing just for movies and in that regards I think that while this is a great concept and if it works as well as I hope it would be a wonderful addition to home theater, it is probably not going to add what Tony and many others are looking for - more involvement in the film.

Lower frequency response is great. More bass output is great. However, those are not really going to give the level of enhancement that adding motion to the system could do. Just my $0.02, $0.03CDN.

Once you have a system that can deliver that elusive "enough" down to say 5Hz, yes, this would not be hard to do at all. If we wanted to, it could be put on a couple of knobs or buttons (or via touchpanel/remote) to allow you to select the Fc of the cut-off (-3 or -6dB point) as well as the roll off slope as 1st to even near brickwall cut-off (which might be quite useful for vinyl lovers). No, the required components to execute this aren't cheap, but they aren't outrageous either. I've found some creative ways to create effective filters below the lowest number you can punch into most of these DSP's, but from what I can tell this is mostly just getting the programmers to allow it. The lowest frequency settings I've seen in production devices is 10 and 12 Hz with the majority of devices stopping at 20Hz, with some OEM DSP devices allowing 5-8Hz settings. Most devices have good throughput into the 10Hz range with maybe 0.5 to 3dB of roll off by this point, so the devices are certainly capable, and we can make many of them work down into the 5-8Hz range.

The final complication is that at this point, none of the required components do anything for you. They do what you tell them to. Deciding what you want them to do is the tricky part that requires careful measurements and understanding of how the various devices work.

With my obvious bias I'm of course going to dissagree. :cool:

I do agree though that motion and coupled mechanical energy (shakers) are very much worth the investigation and experimentation. Even from the acoustic perspective, I suspect that careful integration of mechanical shakers have their place in the range below 15-25Hz.

I do dissagree with the statement that: "...no instruments get even close to that depth."

There is a very wide spectrum of energy found in the precussive pluck or strike of many instruments. This transient tends to be a spectrum of shaped noise, not just fundamentals and harmonics. Of course we're back to a chicken and egg thing about it actually making it into the recording.

I would also refer back to my earlier point that a system that exhibits linear response to very low frequencies offers the potential to have much better accuracy to the input waveform. At what point this becomes audible is open for lots of debate as it's quite difficult to achieve in the first place, let alone without incurring other problems.

Mark,

"...so long as you give me some processing and EQ, I'd bet I can find a useful way to put ever increasingly more bass energy to good use."

Maybe I'm missing your point; why would

Thanks

You know Mark, great minds think alike. I was about to mention Mr. Wishmeyers BASSAULT beastie.

I was talking to Jim one day and stated that while the sub was great, i could go to Hawaii for the cost... His response; "Hawaii is fleeting, Bass is forever"

Using all Bag end gear was the only time i have heard people at an event say there was too much Bass.

For those of you wondering what we are talking about...

http://www.bagend.com/bagend/bassault-r.htm

THe first time i "heard" it i was about 200 metres from the room it was in when i sensed its presence. It needs about 2K watts to really get humming

That MIGHT make Tzucc happy. :D

So if I cut a hole in my ceiling and put one in my attic would it improve my LFE ?

Art

THE IMPASSE CAN BE BROKEN WITH A SUBHARMONICS SYNTHESIZER
http://media.zzounds.com/media/brand...e11f11ee39.jpg

Plenty of movies exist with sound below 20Hz. The most outrageuos is Hitchhikers guide which has reference level content (the earth explosion) around 1-3Hz. Some room doors have a difficult time with this. Based on the construction I believe tzuccs room can handle it and it will be an excellent place to make a determination about what we can and cannot hear/feel/sense.
Some amplifiers and processors will not pass content this low and the hitchikers guide passage simply goes silent if the electronics exhibit a steep rolloff below 5hz. For this demo to be meaningful it is important that the electronics have good response to at least a few hertz.
The SPL goal for the demo is 110dB 0Hz to 20Hz in tzuccs room. This is a self imposed limit and is defined by the torque of the motor. The pressure limit for the woofer is somewhere above 130dB in a room, which depends on a number of factors which I will be glad to explain.
I believe that subwoofers and shakers are mutually beneficial, that content for either will benefit both.
The woofers we designed for this event are good from 0Hz to about 15-20Hz. The intent was to use the watchdogs to their low frequency limit and then be able to switch the rotary woofer on and off and demonstrate if there is any value in having content reproduced well below 20Hz.
If someone knows of a good crossover solution please let us know.
I will try and provide more information about the woofer and answer questions in the next couple weeks. Mark, thanks very much for commenting on this thread. It will be a pleasure to meet everyone.


Bruce T

Too bad that unit has a high pass filter above 20Hz! With today's soundtracks and what we know about perception below 16-20Hz, I don't see any good justification for such a device. We are having a hard enough time reproducing current soundtracks at reference level down to 16Hz or lower, no need to add more when we could certainly benefit from shelving up this range during playback.