New Subwoofer Technology

[bossobass]

Ilkka wrote:

I know that M&C has bass down to 1 Hz, I meant that it might not have very high amplitude material in some small frequency range (for example the wide notch in 3-6 Hz range). But I looked your graphs more closely and you are being correct. There is around 10 dB notch at 20 Hz with the TRWs on. That is very likely a phase issue. What kind of filters (HP or LP) you have there? What are their slopes?

I don't think there is material at 1Hz. There certainly isn't at the level shown in the graph.

I think the spikes at 1Hz, and actually from DC to around 4Hz, are noise from the structure of the house and baffles, or some such resonance phenomenon.

I wonder if there are graphs of scenes where it's known that there is material in single digits that is encoded at high levels, like F'in' Irene, Batman Begins scarecrow scene and WOTW lightning strikes, for comparison?

Bosso

[tzucc]

bossobass wrote:

I don't think there is material at 1Hz. There certainly isn't at the level shown in the graph.

I think the spikes at 1Hz, and actually from DC to around 4Hz, are noise from the structure of the house and baffles, or some such resonance phenomenon.

I wonder if there are graphs of scenes where it's known that there is material in single digits that is encoded at high levels, like F'in' Irene, Batman Begins scarecrow scene and WOTW lightning strikes, for comparison?

Bosso

Good question, however, you can still see the 1-10Hz stuff at lower SPLs that don't yet cause any shaking of room objects. The energy appears to be there. But I did have the same concern as you for when the walls were shaking ... some of that room interaction must show up in the spectral plots.

[MACCA350]

bossobass wrote:

I don't think there is material at 1Hz. There certainly isn't at the level shown in the graph.

I think the spikes at 1Hz, and actually from DC to around 4Hz, are noise from the structure of the house and baffles, or some such resonance phenomenon.

I wonder if there are graphs of scenes where it's known that there is material in single digits that is encoded at high levels, like F'in' Irene, Batman Begins scarecrow scene and WOTW lightning strikes, for comparison?

Bosso

This should clear up any doubt about sub sub 10Hz within source material.
Below is a graph produce by Sound Forge showing what is actually recorded in the DD5.1 track (for simplicity I combined all 6 channel to one) of the scene in The Hitch Hikers Guide To The Galaxy where the Earth gets Blown up at the end of chapter 4.


For comparison, below that is the Spectrum Analysis Graph on tzucc's site(I hope you don't mind) showing what the TRW is producing for that scene


Seems to be doing it's job

cheers

[bossobass]

Macca,

Thanks for the info. It looks to support my thoughts. There is a disparity as noted on the graph comparo below 5-6Hz of approximately 10dB from your graph to the in-room graph.

As I said before, I don't think it's room or boundary gain, but rather sympathetic subsonic resonances.

Of course, I could be reading the graphs wrong, and/or guessing wrongly at the cause of the differences I see.

Bosso

[MACCA350]

bossobass wrote:

Macca,

Thanks for the info. It looks to support my thoughts. There is a disparity as noted on the graph comparo below 5-6Hz of approximately 10dB from your graph to the in-room graph.

As I said before, I don't think it's room or boundary gain, but rather sympathetic subsonic resonances.

Of course, I could be reading the graphs wrong, and/or guessing wrongly at the cause of the differences I see.

Bosso

There can be a number of reasons for the differences, the simplest being that my graph is taken at a particular time stamp whearas tzucc's graph is "of a peak hold FFT during the scene"

But the graphs are very similar and shows that there is information that low in the source material and that the TRW is reproducing what is down there. How accurate it is and how well the TRW accomplishes this is something I can't answer.

cheers

[Chrisbee]

This is a fascinating subject. We really need to be reading the response of more subs below the 10Hz mark. There are some tantalising response graphs that seem to continue past 10Hz at much the same level as they do above that point. How useful that output would be is still a matter of conjecture.

I wonder if John M could be persuaded to give us a few more Hz on the REW sweep? (perhaps as a guarded selectable option to protect subs that can't handle it) But then we'd need better microphones than the common RS meter. What's the lower useable limit on the Behringer ECM8000 calibration microphone? It only claims a linear response to 15Hz on the sales blurb.

[bossobass]

I have no doubts as to the claims of output capability of the rotary sub. I do however, question the system capability. I can't find info as to what player/preamp/amplifier is driving the rotary sub, but it looks to be rolling off well above 1Hz, IMO...probably at 5Hz the system is down 3dB by my guess.

In fact, I don't know of any system that's flat to 1Hz.

Tzucc, can you mention the upstream hardware in your TRW system?

Chris, you are absolutely correct and I think it's only a matter of time before we have another 1/2 octave or so of graphing capability from the various measurement software people.

I think that most of the 'flat-to-10Hz-in-room' graphs we've seen to date are the results of sympathetic subsonic structure noise, and those graphs will show output to below 10Hz that isn't coming from the subwoofer.

Still, it's the final frontier and very exciting info, IMHO.

[bobgpsr]

The individual calibration graph on the "Certificate of Traceable Calibration" for my LinearX M31 cal mic shows a smooth rise from +2 dB @50 Hz to +5.5 dB @ 10 Hz. No drop off shown. I wonder how low cal mics really go?

MDF (Microphone Data Format) File
Author=LinearX Systems Inc
Date=Nov 17, 2005  Thr  4:49 pm
Model=M31
Serial=158848
dBspl=   94.000
dBm=  -23.414
Points=   300
Index   Freq(Hz)       dB      Deg
   1      10.000      5.45      0.00
   2      10.281      5.29      0.00
   3      10.570      5.24      0.00
   4      10.868      5.00      0.00
   5      11.173      4.91      0.00
   6      11.488      4.81      0.00
   7      11.811      4.76      0.00
   8      12.143      4.68      0.00
   9      12.485      4.58      0.00
  10      12.836      4.52      0.00
  11      13.197      4.49      0.00
  12      13.568      4.47      0.00
  13      13.950      4.41      0.00
  14      14.342      4.33      0.00
  15      14.745      4.23      0.00
  16      15.160      4.11      0.00
  17      15.587      4.00      0.00
  18      16.025      3.89      0.00
  19      16.476      3.78      0.00
  20      16.939      3.69      0.00
  21      17.416      3.59      0.00
  22      17.906      3.52      0.00
  23      18.409      3.44      0.00
  24      18.927      3.39      0.00
  25      19.459      3.32      0.00
  26      20.007      3.27      0.00
  27      20.569      3.20      0.00
  28      21.148      3.15      0.00
  29      21.743      3.09      0.00
  30      22.354      3.02      0.00
  31      22.983      2.95      0.00
  32      23.630      2.89      0.00
  33      24.294      2.82      0.00
  34      24.978      2.76      0.00
  35      25.680      2.69      0.00
  36      26.403      2.63      0.00
  37      27.145      2.57      0.00
  38      27.909      2.52      0.00
  39      28.694      2.47      0.00
  40      29.501      2.42      0.00
  41      30.331      2.38      0.00
  42      31.184      2.33      0.00
  43      32.061      2.29      0.00
  44      32.963      2.25      0.00
  45      33.890      2.21      0.00
  46      34.843      2.17      0.00
  47      35.823      2.13      0.00
  48      36.831      2.09      0.00
  49      37.867      2.06      0.00
  50      38.932      2.02      0.00
  ...
 275   19993.297     -1.63      0.00
 276   20555.660     -1.80      0.00
 277   21133.842     -2.00      0.00
 278   21728.287     -2.12      0.00
 279   22339.451     -2.18      0.00
 280   22967.807     -2.28      0.00
 281   23613.836     -2.43      0.00
 282   24278.037     -2.68      0.00
 283   24960.920     -2.95      0.00
 284   25663.012     -3.16      0.00
 285   26384.852     -3.34      0.00
 286   27126.994     -3.58      0.00
 287   27890.012     -3.95      0.00
 288   28674.490     -4.36      0.00
 289   29481.035     -4.79      0.00
 290   30310.268     -5.30      0.00
 291   31162.822     -5.84      0.00
 292   32039.357     -6.43      0.00
 293   32940.547     -7.13      0.00
 294   33867.086     -7.95      0.00
 295   34819.688     -8.77      0.00
 296   35799.082     -9.56      0.00
 297   36806.023    -10.51      0.00
 298   37841.289    -11.41      0.00
 299   38905.676    -12.46      0.00
 300   40000.000    -13.51      0.00
End

Bob

[Chrisbee]

bossobass wrote:

I think that most of the 'flat-to-10Hz-in-room' graphs we've seen to date are the results of sympathetic subsonic structure noise, and those graphs will show output to below 10Hz that isn't coming from the subwoofer.

I don't think the effect of structural resonance would be so linear an extension of the frequency response. The curve would also depend a great deal on the structure itself. My listening room is very lightweight being an attic with all wood cladding internally with relatively large areas of thin glass. A concrete cellar should show a completely different infrasonic response to subwoofer excitation. This is something that could be easily investigated using the same model of subwoofer in two rooms of the same size but of totally different construction.

I know from experience that my windows and glazed doors are sympathetically resonant at sub-14Hz. It doesn't matter whether the excitation is coming from my IB or my big SVS cylinder. Neither sub is in the same position in the room. They are about 8 feet apart. I can easily get my roof to heave and creak at 10Hz.

Still, it's the final frontier and very exciting info, IMHO.

Agreed! All subwoofery is still in its infancy compared with the level of development reached by "normal" loudspeakers.

[SteveCallas]

There is a disparity as noted on the graph comparo below 5-6Hz of approximately 10dB from your graph to the in-room graph.

As I said before, I don't think it's room or boundary gain, but rather sympathetic subsonic resonances.

This low, does it really even matter? You'll be hard pressed to find any room that will allow for high accuracy into such low frequencies, and if you do, it will take a whole moo baby moo of a lot of fun out of the experience.

I can't find info as to what player/preamp/amplifier is driving the rotary sub, but it looks to be rolling off well above 1Hz, IMO...probably at 5Hz the system is down 3dB by my guess.

In fact, I don't know of any system that's flat to 1Hz.

Tzucc, can you mention the upstream hardware in your TRW system?

He mentions in his blog that he got lucky his Lexicon passed a pretty solid signal to 1hz using the XLR output. Using the RCA output, he observed a typical electronics rolloff.

[tzucc]

Hi gents. Bruce and I think the 3-5Hz dip is some sort of room mode. The 1-3Hz it NOT enhancement from room shaking or whatever... it's just output. I only say this because I see nothing happening or shaking in the room at that freq.

The room seems to resonate with 8-9Hz range... at that freq, the room seems to complain loudly and bitterly I simply will not demo 120dB (let alone 125dB which is easily possible) at 8Hz... if you were there, you'd be cringing too.

The mic that Bruce made for me cost $5 of radio shack parts, and he believes it is reasonably flat to 1Hz. I should have him post his design... it's pretty nifty. I'll put up a snap of it. Put it this way... it picked up a very low SPL 0-1Hz signal during a quiescent time in the room... we were going nuts trying to figure out what it was... then we figured it out. My AprilAire ERV was slowly pumping air through the room!!! Yeah, it's sensitive enough at low frequencies all right.

edit: you can barely feel this air flow by standing up to the ceiling registers, and only by wetting the back of your hand to the airflow. I am still amazed that cheap condenser mic could see that weak flow!

The signal path is:
- HTPC optical out
- Lexicon MC12B optical in
- Lexicon L and R stereo sub to XLR out
- Lake EQ XLR in, 2 channels summed to mono
- Lake EQ XLR out to TRW amp (converted to RCA for now), XLR out to Watchdogs and XS amps
- RCA into Bruce's custom made amp (nothing special, just designed for down to <1Hz, will have XLR and EQ in next revision) at about 200W into 4 ohms or something. The amp has phase, volume, boost and low pass filter controls. Simple and cheap.
- Bruce's amp out to the TRW via 50 ft of speaker cable

It appears that the Lexi is easily flat down to below 1Hz. Thank God, or we'd be nowhere in this project.

Macca, thanks for posting that chart. I assume it's an FFT done right off the DVD bits, which is quite useful to see what the true output frequency spectrum is. Confirms we have a room mode ... which is strange... at these wavelengths, I just don't get how.

Anyway, I am going to look for SoundForge and run some of that analysis... anyone know which software it is that also gives you those cool color waterfall charts showing freq vs output vs time?

[Sonnie]

The mic that Bruce made for me cost $5 of radio shack parts, and he believes it is reasonably flat to 1Hz. I should have him post his design... it's pretty nifty.

Off topic... uh...errr... well, maybe not. It might be considered new subwoofer "measurement" technology for that price. I've read somewhere that someone could build a very flat mic from inexpensive parts, but lost where I read it.


Seriously though, if you can share this with us, please start us up a new thread in whichever forum would be appropriate (I may copy and sticky it in a couple of forums). One thing I'm curious of though... how can we be sure of how flat it is down to 1Hz? Has there been any calibration against a worthy mic. We can certainly compare it down to 10Hz. I'll build one and compare it myself, but I don't know how accurate I'd be below that.

[Sonnie]

Chrisbee wrote:

I wonder if John M could be persuaded to give us a few more Hz on the REW sweep? (perhaps as a guarded selectable option to protect subs that can't handle it) But then we'd need better microphones than the common RS meter. What's the lower useable limit on the Behringer ECM8000 calibration microphone? It only claims a linear response to 15Hz on the sales blurb.

This is a done deal, the next release sweeps from 0Hz. We are beta testing it now and hopefully John will have it ready soon... lots of new and useful features.

My ECM is calibrated to 10Hz, but most of them are out of the box -2.5db+ from 15Hz on down.

[Chrisbee]

tzucc wrote:

Hi gents. Bruce and I think the 3-5Hz dip is some sort of room mode. The 1-3Hz it NOT enhancement from room shaking or whatever... it's just output. I only say this because I see nothing happening or shaking in the room at that freq.

The room seems to resonate with 8-9Hz range... at that freq, the room seems to complain loudly and bitterly I simply will not demo 120dB (let alone 125dB which is easily possible) at 8Hz... if you were there, you'd be cringing too.

edit: you can barely feel this air flow by standing up to the ceiling registers, and only by wetting the back of your hand to the airflow. I am still amazed that cheap condenser mic could see that weak flow!

Macca, thanks for posting that chart. I assume it's an FFT done right off the DVD bits, which is quite useful to see what the true output frequency spectrum is. Confirms we have a room mode ... which is strange... at these wavelengths, I just don't get how.

Why couldn't your room volume resonate as whole just like any other Helmholtz resonater?

[SteveCallas]

This is a done deal, the next release sweeps from 0Hz. We are beta testing it now and hopefully John will have it ready soon... lots of new and useful features.

My ECM is calibrated to 10Hz, but most of them are out of the box -2.5db+ from 15Hz on down.

Sonnie, will you be extending the RS meter calibration files down to single digits as well then?

[Sonnie]

If I can find someone to calibrate my ECM down to 0Hz for a reasonable price I will attempt to calibrate the RS meter, although I'm not sure if the RS meter mic can handle it, being it is so far off at 10Hz now.

I'm really interested in what Bruce and tzucc have going on with their home made mic with $5 worth of parts that is supposedly flat to 0Hz. I have read previously how the capsules in the very expensive mics are very inexpensive themselves. What I don't know is what makes them expensive. I'm having a hard time believing we can make a mic with $5 worth of parts that is flat down to 0Hz or even 10Hz for that matter, and Behringer, B&K, and all those expensive mic manufacturers can't do the same for hundreds and thousands more money.