# New Subwoofer Technology



## Guest (Sep 19, 2006)

Gentlemen, check out THIS http://blog.stereophile.com/cedia2006/091606thigpen/

and

THIS http://blog.stereophile.com/cedia2006/091906soundfield/

RG


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## Sonnie (Apr 11, 2006)

Yes... the sub fan has been the subject of discussion in couple of threads. The price was a little scary... :raped:

Good to see ya out and about Robert. :wave:


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## Jack Gilvey (May 8, 2006)

You're so vane...


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## Guest (Sep 21, 2006)

Any measurments on this thing...I heard it went down to 5 hz, How does it work???


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## Josuah (Apr 26, 2006)

I'm not 100% sure, but this is my understanding of it.

The fan blades spin (seem to be flat blades, so I'm not sure it pushes air one direction or the other, probably not or else it sitting between the two enclosed areas wouldn't work right???) and at the same time they vibrate at the frequency you are trying to reproduce. Therefore, the air being moved by the blades have the frequency.

I imagine it's a lot like when you talk into a standard fan.


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## azjimmy (Jun 5, 2006)

It works on the same theory as a helicopter rotor. It compresses air just like a speaker, only it uses variable pitch blades to push air instead of a moving cone. 
Pretty neat, really.
The video on the site is down right scary when they do the sweep. Looks like it's going to shuck a blade! You can even hear one of the guys saying not to get too close. Check it out http://www.youtube.com/watch?v=E7Bkrypxzs4
Jim


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## Guest (Sep 22, 2006)

Jack Gilvey said:


> You're so vane...


You probably think this song is about you, Dont you, Don't you


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## Chrisbee (Apr 20, 2006)

There are three videos on the TRW fan sub.

It would seem to offer not so much a signal to noise ratio as a noise to signal ratio! 

When I think of the lengths I went to to just to quieten the fan in my EP2500...!


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## Exocer (Apr 19, 2006)

Whenever people mention these fan subs I always wonder how musical content would sound. Something about musical bass notes comming from fan blades is incredibly interesting to me.


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## JimPeitersen (Jul 15, 2006)

Exocer said:


> Whenever people mention these fan subs I always wonder how musical content would sound. Something about musical bass notes comming from fan blades is incredibly interesting to me.


I see two issues:

Can the human ear distinguish between notes (fundamentals and harmonics) in the extreme infrasonics that this "driver" produces?

In the end, does it really matter what the transducer is since all speakers are simply mechanical interfaces between the electronic signal and our ears (they all excite the air, does it matter how?)

JP


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## Exocer (Apr 19, 2006)

JimPeitersen said:


> I see two issues:
> 
> Can the human ear distinguish between notes (fundamentals and harmonics) in the extreme infrasonics that this "driver" produces?
> 
> ...


1.Probably not.
2.Probably not.

However, with that said, i'd still love to hear a demo of one of these subs playing music. Music doesn't fall under the infrasonic range.With infrasonics it wouldn't matter at all what moves air because what we don't hear, we feel at those frequencies.


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## Josuah (Apr 26, 2006)

I guess your music would have to be classical with big drums, 1812 Overture type, or taiko drumming. Since this fan stops at 30Hz, I think.


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## Exocer (Apr 19, 2006)

Not my type of music...lol
You're right about the upper limit being 30hz though, i believe its -4db by 30hz. 

I do remember reading a post on another forum regarding low frequency information in modern day music getting as far as the mid to low 20hz range. Wish I had that link...


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## Josuah (Apr 26, 2006)

Not sure what "modern day" means.  But there have always been some "pop"ular songs that incorporated frequencies between 20-30Hz. I think Sarah McLachlan's Brown Man (something like that) has it. I think some of Leftfield's songs do.

But so what? A much cheaper subwoofer can deliver 20Hz and up reliably and definitely with enough SPL for music. My SVS subs for a 10th of the price of this sub can deliver 10Hz.

It's the rest of the music and movies that is why I need to build a sub that hits 5Hz....


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## Exocer (Apr 19, 2006)

Josuah said:


> Not sure what "modern day" means.  But there have always been some "pop"ular songs that incorporated frequencies between 20-30Hz. I think Sarah McLachlan's Brown Man (something like that) has it. I think some of Leftfield's songs do.
> 
> But so what? A much cheaper subwoofer can deliver 20Hz and up reliably and definitely with enough SPL for music. My SVS subs for a 10th of the price of this sub can deliver 10Hz.
> 
> It's the rest of the music and movies that is why I need to build a sub that hits 5Hz....


Indeed, a much cheaper sub can hit from 20hz and up..No disputing that. I don't see how that has anything to do with my comment, especially because I specifically stated how interested I was in hearing the rotary sub producing those bass notes, not a much cheaper sub.
Oh and by modern day music I meant todays pop music... guess my terminology wasn't clear. My apologies.




> It's the rest of the music and movies that is why I need to build a sub that hits 5Hz....


I too would love to build a sub that hits 5hz...with enough authority to feel it. Im pretty sure both of my sealed subs are hitting this low, but with nowhere near enough output to make it even worth mentioning.

I'd imagine most people using these rotary subs aren't using these alone? Maybe have the rotary sub take care of its sweet spot, and a sealed sub take from 30hz and up...


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## Josuah (Apr 26, 2006)

I just saw a post stating 20ms of group delay at 20Hz was desirable, by Mark Seaton. So I guess my knowledge of group delay needs to be improved.

Oh, and my so what wasn't so much with regards to your desire to figure out how the rotary sub would produce those frequencies, but a so what at the rotary subwoofer itself.  I think it might sound different, but I'm very skeptical it would sound better. That's all I meant.


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## Exocer (Apr 19, 2006)

It probably doesn't sound any better...I bet its a ton louder though :T


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## Guest (Oct 1, 2006)

hi folks, Ilkka sent me a PM over at avsforum regarding redirected bass, which I will test today with the rotary woofer (TRW). If you want to read more about the first home theatre install for the TRW, you can check out the blog at http://bassment.wordpress.com ... avsforum ultra hi end forum has a thread as well fwiw.
We first demo'd the TRW at my house about six months ago for a group of SF Bay area audio types, and since then I have been working with Bruce to install two TRW's in my media room. We've been hard at work for the last two weeks doing the install, and it's now about complete.

Ilkka, thanks for bringing the redirected bass issue to my attention.


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## Chrisbee (Apr 20, 2006)

How could one ever live with only a Wilson XS and two Watchdogs ever again after hearing a TRW? 

It's not just about reproducing very low frequencies either. It's all about level and it's all about very low distortion.

I had a couple of enjoyable years listening to my SVS 16-46 which I have measured to 15Hz at very silly output levels. It went loud at completely inaudible frequencies. So you ask yourself what more is there?

Then you hear an IB! Everything suddenly sounds as if it goes more than twice as deep. You have to ask yourself why. Exactly the same frequencies are being reproduced at very similar levels. The only obvious difference must be the lower distortion and greater extension affecting one's senses. 

The only way we mere mortals are going to get even more extension with lower distortion is by doubling the number of drivers in our IBs. Then doubling them again. 16 x 18" longthrow woofers in twin manifolds sounds like a lot of fun. I wonder how they would measure up to a TRW? The problem is you'd need a concrete cellar for a listening room to keep the house structure together. Plus an enormous volume for the rear wave to play with. 

Having seen the effects of four quite modest 15" drivers I'm not sure I'm ready for more. There have been times when the whole roof above my attic listening room has stretched and groaned. Spookey! On another occasion I was leaning with all my weight on a pair of locked doors which were literally bending 1/2" away from their frames. I couldn't do a thing about the enormous forces at work. The power that was moving the doors was completely indifferent to my efforts to hold them still.


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## Guest (Oct 1, 2006)

the interesting issue to consider is that the 15's will drop after 20Hz in terms of reaching suitable SPLs. You have to have far too many 15's and amp power to get near the TRW's capability and then you are at massive replicated distortion. The TRW is not about 20Hz and above, in any case, but recreating the 0-20 spectrum, which does add significantly to the movie content. 
For years I have been after more 20-80, thinking that would increase the reality coefficient, but it turns out that 0-20 is where the really important psychoacoustics (for bass, not overall) may in fact exist. All I can say is that scary movies are much scarier, and action movies are far more violent with this infrasonics that one can HEAR and feel. Yes, you can hear 5-10Hz... it's not tonal, but you feel the waves in your ear and body, again, assuming enough SPL. My two 18" cone drivers at 2400Watts can create SPL at 10Hz, just like any subwoofer, but it just can't make any useful amounts, even if they are tearing apart. 

I suppose this all sounds a bit far fetched, and if I was reading someone else doing this a year ago, I would have been intrigued but very skeptical. The only way to understand what 0-20 does is to simply get the demo.


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## Chrisbee (Apr 20, 2006)

I certainly believe you. When I was struggling to describe the sound quality of my IB I noted that the IB gives one no warning of impending bass fireworks. It appears from nowhere with frightening dynamics then is gone just as quickly having conveyed tremendous weight in the briefest of moments.

I believe the fast rise time is important but also the lowest fundamental frequencies carry important information that one can sense. It may be by bone conduction or it may actually be audible once certain SPLs have been reached. But it is an essential part of our autonomic sensing of the audio power behind the briefest of sounds. Since man has been exposed naturally to infrasonics for millions of years he has not dismissed these inaudible sounds in his quest for survival. Rock and tree falls, vulcanism, the size of the animal rushing at him, the roar of the cataract and the crash of the wave have all been within his daily experience.

Now we simulate the dangers which were once man's daily struggle to live another day. We have not yet lost our audio skills at seperating the mundane from the terrifying. I believe that infrasonics have remained part of our survival kit. At least for impacts and other dynamic sounds like explosions, drums, heavy footfalls and gunfire.


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## Mark Seaton (Jun 22, 2006)

Josuah said:


> I just saw a post stating 20ms of group delay at 20Hz was desirable, by Mark Seaton. So I guess my knowledge of group delay needs to be improved.
> 
> Oh, and my so what wasn't so much with regards to your desire to figure out how the rotary sub would produce those frequencies, but a so what at the rotary subwoofer itself.  I think it might sound different, but I'm very skeptical it would sound better. That's all I meant.


I've heard the TRW, and have heard a variety of systems that have in-room response into the 10Hz range. This most certainly is a noticable addition and IMO it is quite beneficial subjectively with all playback.

As for the 20ms of group delay comment, I don't even know what that refers to or what the context was and I allegedly made the statement!?! :dontknow:


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## SteveCallas (Apr 29, 2006)

Chrisbee said:


> Having seen the effects of four quite modest 15" drivers I'm not sure I'm ready for more. There have been times when the whole roof above my attic listening room has stretched and groaned. Spookey! On another occasion I was leaning with all my weight on a pair of locked doors which were literally bending 1/2" away from their frames. I couldn't do a thing about the enormous forces at work. The power that was moving the doors was completely indifferent to my efforts to hold them still.


Have you found a way to resolve the dynamic range compression issue?

tzucc, the FR of your fans looks amazing, but I'm not quite understanding the desire to use three crossovers and three different subwoofer systems. I realize you are trying to force fit your current subs into the overall system, but I think you'd stand to gain quite a bit by simplifying the process. Do you have a FR from 0-100hz with all four units in play? Are the three subs collocated?


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## Guest (Oct 2, 2006)

Steve, we're far away from the dynamic range compression region of any of the subs. Not sure why actually, but we seem to be. The reason for the three bands to three different sub types is simple. It sounds much better that way, and it also looks alot flatter on the spectrum analysis. The current subs actually blend quite well together, once we got them connected to their sweet spot. I'll post the FR for the whole sub system some time by middle of the week.


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## Ayreonaut (Apr 26, 2006)

The fan design is novel, but ...

for $2500 you could build an IB with sixteen 18" woofers. What couldn't that do? :surrender:


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## SteveCallas (Apr 29, 2006)

tzucc, the dynamic range compression comment was to Chrisbee, sorry for any confusion.

Just seems like there is a lot of room for error in combining three subwoofers and a fan IB into one bass system - potential for lots of phase issues, especially if they aren't all collocated. If your FR at the seat is flat without much EQ though, more power to you.


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## Josuah (Apr 26, 2006)

Mark Seaton said:


> I've heard the TRW, and have heard a variety of systems that have in-room response into the 10Hz range. This most certainly is a noticable addition and IMO it is quite beneficial subjectively with all playback.


So, in the shared range of 20-30Hz (or even 10-30Hz), you felt that the TRW was better able to reproduce those frequencies than a traditional subwoofer? I'm not sure if you mean adding the TRW to a traditional sub was a noticeable improvement (because you now have two subs and all the benefits that go along with it, or if you mean the TRW is a better alternative? I'd imagine 10-20Hz the TRW would perform better. Little skeptical about 20Hz and above.



Mark Seaton said:


> As for the 20ms of group delay comment, I don't even know what that refers to or what the context was and I allegedly made the statement!?! :dontknow:


I think you were replying to someone asking about a subwoofer company stating 20ms or less at 20Hz to be a desireable group delay goal.


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## Guest (Oct 2, 2006)

SteveCallas said:


> tzucc, the dynamic range compression comment was to Chrisbee, sorry for any confusion.
> 
> Just seems like there is a lot of room for error in combining three subwoofers and a fan IB into one bass system - potential for lots of phase issues, especially if they aren't all collocated. If your FR at the seat is flat without much EQ though, more power to you.


agreed, but we got sort of lucky, except for one very high Q notch we suspected was caused by phase mismatch between the WD and the X1's, but we ameliorated that by adjusting the WD phase and then applying positive EQ with the Lake.


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## Chrisbee (Apr 20, 2006)

I'm still trying to get my head round the problem of bass sounding deeper when potentially the frequencies involved are completely inaudible. Same SPLs but sounding competely different. Perhaps its a masking poblem? Do higher frequency distortion components mask the lower frequencies? Even that doesn't make a lot of sense when different sounds have different audio spectra. Many sounds have weak fundamantals with strong higher frequency harmonic components. Yet they still sound much deeper on an IB. So much so that sometimes it drags one's attention away from the music. 

The important question is whether the (ULF) TRW actually makes things sound deeper than your subs on their own?


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## Guest (Oct 3, 2006)

Chrisbee, you can absolutely hear and feel below 10Hz, but understand you need sufficient SPL to get there. Look at the equal volume curve studies done for low frequencies...at enough SPL, your ear will hear even 1Hz, but it must be at SPLs of like 120-125dB. WHich is practically impossible for cone driver solutions.
Sub 20Hz is only thought of as completely inaudible, because they have not been presented with enough SPL in that freq range. 

On your question, my perception is not necessarily that things sound deeper than my other cone subs on their own. It's more that there is a whole new sound effect below 20Hz, feelings of pressure and concussion... the difference between watching fireworks DVD in a nice system and watching them up close in person, perhaps is one way to express what I observe.


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## Mark Seaton (Jun 22, 2006)

Josuah said:


> So, in the shared range of 20-30Hz (or even 10-30Hz), you felt that the TRW was better able to reproduce those frequencies than a traditional subwoofer? I'm not sure if you mean adding the TRW to a traditional sub was a noticeable improvement (because you now have two subs and all the benefits that go along with it, or if you mean the TRW is a better alternative? I'd imagine 10-20Hz the TRW would perform better. Little skeptical about 20Hz and above.


The TRW only reproduces below 20Hz in Tzucc's system. I stopped by breifly last night before I flew back to Chicago, and there is no question that you sense and experience things that aren't there with conventional systems. Multi-driver sealed or large IB systems that can couple into the room into the 10Hz range and below do give a related impression, but the exceedingly low distortion and effortless reproduction into the low single digits takes it to another level. While the effects still need the upper frequencies produced with authority to have the sharp attack and impact, the addition of the TRW adds a subjective scale, weight and realism by adding the all important underpinning foundation to sound effects. Watching Master & Commander even at healthy but in no way excessive levels (still below reference), so many of the sonic occurences are quite different and just draw you in with greater subjective intensity than without the TRW.


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## Guest (Oct 3, 2006)

well put Mark.


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## SteveCallas (Apr 29, 2006)

Mark, what was your impression of the implementation of the triple crossover?


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## Josuah (Apr 26, 2006)

Cool. Thanks for the info, Mark.


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## Chrisbee (Apr 20, 2006)

Thanks tzucc. I am very envious of this new level of ULF audio reproduction you are now enjoying. 

I wonder how soon such frequencies, distortion levels and SPLs becomes accessible to a wider audience? Clever as the TRW is, I feel another technology will surface which may take us half way there if not quite all the way. For rather lower cost and simplicity. 

There was a DIY subwoofer in the mags several decades ago which used full sized rectangular polystyrene sheet ABRs on all faces of the sub box. I even got as far as making one large ABR myself with a nice floppy rubber roll surround. Somebody should give this idea a modern workover in a wall-sized ABR driven by a number of large longthrow drivers via suitable ports. An IB manifold driving an 8'x4' ABR? Insane? Probably.


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## Guest (Oct 4, 2006)

I spoke with Bruce about cost in the future, and he is working on something much more cost effective and installable much as you would an IB DIY kit, in the attic for example. About one year out, so stay tuned to his website and we'll likely see something many more people can contemplate buying and installing.

We have to understand that right now volume is low, as the concept is new, and production costs are high, and installation/integration costs very high... professional installers and acousticians and home theater architects need to learn how to work with this new technology and it's particular constraints.


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## Chrisbee (Apr 20, 2006)

Excellent! Thanks. 

News of the release of such a product would go round the forums like wildfire. 
If he could manage a wider bandwidth that would be a real bonus.


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## Guest (Oct 11, 2006)

hi, posted some new output graphs captured during movie sequences. 
http://bassment.wordpress.com if you're interested.


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## SteveCallas (Apr 29, 2006)

tzucc, can you take a 1-100hz FR sweep? I still have a hard time imagining all 5 bass units getting along very well at the seat since they are located in various spots around the room, but I could just be pessimistic.


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## Josuah (Apr 26, 2006)

It couldn't use the same amount of installation space as a single fan.


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## Guest (Oct 11, 2006)

SteveCallas said:


> tzucc, can you take a 1-100hz FR sweep? I still have a hard time imagining all 5 bass units getting along very well at the seat since they are located in various spots around the room, but I could just be pessimistic.


I think we have one already... a FR of 0-100 based on a broadband pink noise. 
Let me find it and post it. 
There is, as you suspect, some phase adjustments to do to align everything time-domain wise. 
I'd say the 5 woofs are getting along quite well, from what I hear and feel, but from the numbers, there may be more work to do. Phase adjustments don't always seem to do the trick either... it's a complex problem.
You can see that without the TRW's, the output spans down to 18Hz or so in M & C.
With the TRW's the outspans down to 1Hz, BUT there seems to be a deep notch in the 20Hz area.
Phase? Time delay? Both? EQ too? Dunno... some combo of the above should ameliorate the notch.


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## SteveCallas (Apr 29, 2006)

> You can see that without the TRW's, the output spans down to 18Hz or so in M & C.
> With the TRW's the outspans down to 1Hz, BUT there seems to be a deep notch in the 20Hz area.
> Phase? Time delay? Both? EQ too?


Hmm, when the TRW's are not being used, isn't the 20hz highpass that's part of the crossover still in the signal chain feeding the XS? As for the notch at 20hz with the TRW on, my first assumption would be the crossover again. Do you happen to know what order it is?


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## Guest (Oct 11, 2006)

Hi Steve, yes the crossover for the XS highpass is of a low order, allowing plenty of 18-20Hz for a '20Hz' crossover point. I do think it's a notch resulting from phase.


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## Ilkka (Jun 8, 2006)

tzucc said:


> You can see that without the TRW's, the output spans down to 18Hz or so in M & C. With the TRW's the outspans down to 1Hz, BUT there seems to be a deep notch in the 20Hz area.
> Phase? Time delay? Both? EQ too? Dunno... some combo of the above should ameliorate the notch.


I think the reason is as simple as that M&C just doesn't have any material in that range. It's not wide band pink noise...


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## Guest (Oct 11, 2006)

huh? M&C audio track goes well down to 1Hz!!! What I am referring to in the thread above is that when using all five subs, there is a notch at 20Hz that is not there when I turn off the TRWs.

But M&C has excellent bass output well below 10Hz, at least in the cannon scenes. Check out the plots at my blog. Notice that those <10Hz energies also showed up with the TRW's off... but at low SPL levels. Which is unexpected... the crossover should have prevented anything at all in the freq range, at the XS.


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## Ilkka (Jun 8, 2006)

tzucc said:


> huh? M&C audio track goes well down to 1Hz!!! What I am referring to in the thread above is that when using all five subs, there is a notch at 20Hz that is not there when I turn off the TRWs.
> 
> But M&C has excellent bass output well below 10Hz, at least in the cannon scenes. Check out the plots at my blog. Notice that those <10Hz energies also showed up with the TRW's off... but at low SPL levels. Which is unexpected... the crossover should have prevented anything at all in the freq range, at the XS.


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?


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## Ilkka (Jun 8, 2006)

Here's a little comparison I made. Red line is without TRWs and yellow is with them. The notch is very narrow, so it can't be very audible.


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## Guest (Oct 12, 2006)

Ilkka said:


> 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 see. Actually the wide notch between 3 and 6Hz we believe is a room mode of sorts. We are working on figuring out the cause... the next amp Bruce will bring me has EQ capabilities... unfortunately the Lake doesn't let you set EQ parameters below 20Hz.

Regarding the filters, I'll shoot some snaps of the Lake Contour settings and upload later. That should answer some questions about what's going on.


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## Guest (Oct 12, 2006)

very short movie clip of the TRW being used at a haunted house in FLA... at the blog.


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## Guest (Oct 12, 2006)

added a sig for convenient linking to the blog.


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## bossobass (Jul 16, 2006)

Ilkka said:


> 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


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## Guest (Oct 14, 2006)

bossobass said:


> 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.
> 
> ...


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.


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## MACCA350 (Apr 25, 2006)

bossobass said:


> 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.
> 
> ...


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:T

cheers


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## bossobass (Jul 16, 2006)

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. :duh: 

Bosso


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## MACCA350 (Apr 25, 2006)

bossobass said:


> 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.
> 
> ...


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


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## Chrisbee (Apr 20, 2006)

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.


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## bossobass (Jul 16, 2006)

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.


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## bobgpsr (Apr 20, 2006)

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


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## Chrisbee (Apr 20, 2006)

bossobass said:


> 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.


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## SteveCallas (Apr 29, 2006)

> 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? :scratch: 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 hell 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.


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## Guest (Oct 17, 2006)

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?


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## Sonnie (Apr 11, 2006)

> 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.


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## Sonnie (Apr 11, 2006)

Chrisbee said:


> 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.


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## Chrisbee (Apr 20, 2006)

tzucc said:


> 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.
> 
> ...


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


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## SteveCallas (Apr 29, 2006)

> 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?


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## Sonnie (Apr 11, 2006)

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. :scratch:


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## Mark Seaton (Jun 22, 2006)

tzucc said:


> 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.


This really isn't "modal" behavior, but probably a combination of structural absorption (mass loaded walls on RC channel) in combination with various attached or coupled air pathways such as the HVAC ducting and the multiple chambers created with the rear "room" for the sub and the pathway to the garage. We don't think of these things as resonances for most woofers since they are out of the operating range, but such VLF resonances are not uncommon in HVAC systems that have not given consideration to it. Many workspaces deemed "uncomfortable" are so due to high-Q resonances that tend to be just below the threshold of audibility (as a tone/sound). There are also plenty of documented cases of alleged "hauntings" which were traced back to structural and/or acoustic VLF occilations.



> 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.


Years back in the DIY speaker building communities (anyone else from the old BASS-List still around?) there were a few published projects using the Panasonic mic capsules. You used to be able to purchase assembled kits with cal-files that were referenced to a calibrated B&K. I believe they used to sell for about $40. I have one of the old assembled kits in my basement somewhere that I should dig out some time. Note that this same capsule is what is commonly used in many of the cheaper mics like the Behringer ECM and the SuperLux measurement mic. I think people are mistaken to expect that a generic correction curve can be used for some of the cheaper mics, especially something like an RS-meter. They meet their spec of consistency in measuring pink noise, but frequency response is not a target tolerance. Fortunately the bigger variations I've seen are at higher frequencies, not low. Bruce should be able to give some better insight as to what the typical variation is capsule to capsule and the tolerance inherent to the pre-amp circuitry.

In doing some prodding at the VLF extension issue on my own, what jumps out as the path of least resistance is in using a digital input signal all the way to the amplifier. The pro market has already made this step, so we'll see how much of that ever makes it to the HT world. All that's needed is a digital audio signal output that can be connected to common pro-audio DSPs that almost all handle digital I/O these days. One can only hope that with Dolby now owning Lake Technologies someone from opposite sides of the house might realise that they should be talking!


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## Mark Seaton (Jun 22, 2006)

Sonnie said:


> 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. :scratch:


There are a few major cost contributors here, but the Behringer and SuperLux mics are good examples, and in large quantity, you'd see that the pricing suggests this level of internal parts quality. I would wager a guess that a huge % of the cost is the metal housing of the microhpone. There is also other circuitry inside, and remember, they're going to charge whatever people are willing to pay. Why sell a mic for $35 when you are killing the competition at $49?  

The other factor is calibration and consistency of the microphone. I don't claim to be an expert on microphones, but basically you have two subsets of microphones. Those with polymer based diaphrams and those with various metal diaphrams. The much more expensive microphones from B&K, Earthworks, etc., all use metal based diaphrams. The most significant difference is the environmental stability of the microphone. Metal diaphram microphones shift by only hundreths of a dB per deg C of change. Polymer/plastic based diaphrams can shift both temporarily and permanently with significant environmental changes. Both have their place, and there is an order of magnitude in cost between them, but do realize the <$100 mics are not the same as the top quality microphones, even if they may have no added benefit for your particular application.

I do feel we are sorely lacking a reasonble cost, well documented measurement microhpone, and I have personally been harrassing Mark Schifter and those working on their RDES unit to integrate a mic preamp into the unit as you already have to connect via USB to program the unit. Tough to say if or when that might come to be yet, but it is being looked at.


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## bossobass (Jul 16, 2006)

Here is a comparo between higher priced mics and the panny electret cap:

http://www.purebits.com/miccomp.html

This is the kit I have from ACOPacific. The 1/2" cap is only a relatively small portion of the cost. The stainless case contains the preamp, there is a power supply, choice of mic caps, etc. IIRC, the total kit $ was around 1500.00:

http://www.acopacific.com/micsystems.html

Point is you need a fairly precision supply and preamp with the Panny cap, which SC provides from the higher priced mics, but doesn't mention in the comparo.

Still, I'm sure one could use the cap and add a decent Mic pre/PS and fashion a case and purchase accessories (cables, clamps, windscreen, etc., for a good bit less.

Also note, that even though I know SC graphs to 1Hz, their test is only to 10Hz.

Bosso


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## bossobass (Jul 16, 2006)

I'm still sticking with my original thoughts regarding the graph of M&C. Here is the spectrograph of the entire scene. I just think there are better scenes to make the point clearer as far as in-room response to 1Hz that could also be compared to this one.

Much appreciated if there are such comparo measurements...

Bosso


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## Sonnie (Apr 11, 2006)

Hey Bosso... is this merely heatshrink around the cap and wires? Amazing results!


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## Guest (Oct 19, 2006)

Bosso, good sleuthing. But I am not sure how accurate I would take that software reading... I'd have to think carefully about the FFT windowing algorithm and how it affects and is able to capture short peaks. Not saying you are wrong, just not convinced yet either way. Of course the FFT windowing on my end, the HTPC doing the measurements off the mic has the same question. 

I think we'd need a signal processing expert to weigh in here... I am real rusty on that stuff nowadays, though I used to do it for a living.

On the mic, I have asked Bruce to post a schematic of his mic, along with a parts list. I should step back from saying the mic is flat to 0Hz... I really have NO idea that this is true. What I should have said, is that the mic has surprising sensitivity down to 0Hz. I think to properly and accurately calibrate the mic would have required equipment well beyond what I have or am willing to pay for.

I will ask Bruce about this... he has spent alot more time at his shop with this cheapie mic configuration and can speak more to it's correction curve.

About the RS digital meter, I found it's useless under 18Hz... when I did the measurements you'll find on my blog posting of last nite, I didn't include the RS meter readings cause no matter what f and SPL that the SpectralLabs showed, the RS meter seemed to vary randomly between 75-79Hz. 
This contradicts Bruce's findings which he does us an old RS analog meter and he has come up with his own callibration 'file' for it down to 5Hz. I think he said at 5Hz the RS meter reading was -19dB too low.

p.s. on my mic... you gotta believe that it's sensitivity goes down as frequency goes down... so if the SpectraLabs shows a big rise in SPL levels during M&C cannon shots, one has to believe the air pressure change is more than there at the mic.
Also interesting is that the cheapie built in sound chip/circuit doesn't AC couple the mic input... they just let it all in!


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## Mark Seaton (Jun 22, 2006)

tzucc said:


> On the mic, I have asked Bruce to post a schematic of his mic, along with a parts list. I should step back from saying the mic is flat to 0Hz... I really have NO idea that this is true. What I should have said, is that the mic has surprising sensitivity down to 0Hz. I think to properly and accurately calibrate the mic would have required equipment well beyond what I have or am willing to pay for.
> 
> I will ask Bruce about this... he has spent alot more time at his shop with this cheapie mic configuration and can speak more to it's correction curve.


I recall Bruce mentioning that the mic was corrected via a calibration file that gave him flat response to about 1Hz. I'm sure it is useful below there, but may not be calibrated. In your own system the mic is unlikely to live outside the basement room, and is likely to stay quite consistent over time.


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## bossobass (Jul 16, 2006)

Sonnie said:


> 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.


Hi Sonnie,

I missed this post the first go around.

You're Beta testing the new TrueRTA version that graphs to 0Hz? I sure hope you'll update us here, if you don't mind. Is there a link to a thread where this is being discussed?

Appreciate the heads up:bigsmile: 

Bosso


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## Sonnie (Apr 11, 2006)

Actually we are beta testing the new Room EQ Wizard which does indeed graph to 0Hz. The next release will be nothing short of awesome.

Unfortunately there's not a public thread for discussion right now, but hopefully the full release will be available soon... I just don't know an exact date. John is working on it as best he can and doesn't have a date yet. We'll most likely have another beta version or two before full release.


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