Asking wave form measurament from Japan

[hirokazu negishi]

It is my great pleasure in participating this forum first time. Although my English is getting rusty and rattling, I hope we can share good understanding of how sound reproduced and get good satisifaction.

My first question to the subwoofer testing is that, why no wave form be there for reproduced sound in the archival test data?

It is often said that live acoustic sound, such as Wadaiko, Japanese traditional drum, could trigger hair standing excitement yet no reproduced sound could do the same. There could be many good reasons for creating discrepancies in between live and reproduced sound though, one of likely reason will be reproduced wave form deviates from live sound.

For acoustics and audio specialists, wave form image could be reconstracted through deciphering many data though, for me, it is almost impossible to do the same. Therefore, providing reproduced wave form in visual manner could help me a lot.

Thanks in advance for your effort to respond!

[Jon Liu]

I have no real knowledge in wave form, but I just wanted to comment on one thing you mentioned.

Live Acoustics certainly have an affect on people that as you mentioned can trigger hair-standing excitement but, I know in my system, I've experienced spine-tingling, hair-raising sensations on plenty of occasions.

[hirokazu negishi]

Hi Jon

Thanks for your effort in responding from Irvine, where I've been time to time in '80s. It is nice place not far away from the south of the border!

I agree that such an experience could be an exception as I too enjoyed such emotions often. One of possible reasons may be not all music include subwoofer range sound, hence it could be reproduced by inertia mass control region of dynamic loudspeaker. My understanding is that the mass control region could reproduce original sound wave easily therefore such an excitement could be triggered by listeners.

However, any music contains subwoofer range sound, which is border or south of the border region of the inertia mass control, wave form of reproduced sound may not reflect the original sound because of the principle of inertia mass control.

Though a lot of secondary characteristics such as frequency response, distortion, group delay and so on may imply such a deformation, comparison of wave forms for input and output could show directly the deviation.

[tonyvdb]

Hi and welcome to the Shack Hirokazu,

If you are referring to how a recording sounds on a decent system it is true that when initially doing the recording the studios do not consider what it will sound like in someones properly treated room. Even the best recordings usually do near field mic placement so they do not capture the dynamics that the live room may introduce even though they try to record in an acoustically flat and dead space.
Some jazz and classical/orchestra recordings take that into account and are recorded with the dynamics that lack in the pop and rock bands that record in a studio.

[hirokazu negishi]

Hi Tony

Thanks for your welcome from Canada, and pointing another aspect of difference in between live and reproduced sound.

Yes, you are right in inconsistency within recording/reproducing chain of sound. To me, it is like a telescope zooming surface of moon showing in detail, and as if implying this is what you could listen at the live space. Yet, such could be one of what is original sound question.

At live sound space, everyone wish to listen at a best place for him/her, but it could be according to their taste. Someone likes centre of hall or just in front of orchestra, or beside favourlite musician with wine. I have no doubt for every recording engineer, wishing to convey the best sound in his/her definition with best effort.

My definition for the original sound is recorded, captured, arranged or created, and supplied as the source for reproduction, no matter how it was organized.

[tonyvdb]

I do find that the newer movie soundtracks particularly on BluRay releases are much more true to the actual event is even sometimes over done.
Subsonic information that makes your entire body vibrate like in a good thunderstorm are usually reproduced quite well in movie soundtracks.
Musical instruments like the Kettle Drums used in a orchestra or the bass note on a dubble bass have lots of the "trigger hair-standing excitement" that you mention.

[hirokazu negishi]

It is good to know latest situation for BlueRay, as well as subsonic effect in movie and musical instrument reproduction in your system.

However, my main interest remains on wave form reproduction ability of subwoofer.

[lcaillo]

There are several ways to display a waveform on a PC. There are oscilloscope programs available or you can buy a USB interface to use your PC as a scope.

The reason you don't see anything discussed about waveform viewing is that a visual reproduction does not tell you much that you cannot learn with other measures.

[hirokazu negishi]

Hi Leonard

Thanks for your informative message from Miami where I've been 1973. They help me a lot. The former, PCbase viewers would help our activity very much whereas the latter triggered further questions.

1. Is that because the result of measured waveform just reflect the theory?
2. Or, not theory but design?
3. Although waveform tells you many discrepancy in visual manner, could it not match to what you listen?
4. Visual info is difficult to quantize but other measurements are not.
5. Something else dominates.

Any answer/comment welcome!

[hirokazu negishi]

[QUOTE=hirokazu negishi;200860]Hi Leonard

Thanks for your informative message from Miami where I've been 1973.

Hi Leonard

Sorry about mistakes in my previous message quoted above. Your location is not Miami but northern part of Florida as well as grammatical mistake too.

[hirokazu negishi]

[QUOTE=hirokazu negishi;200860]


1. Is that because the result of measured waveform just reflect the theory?
2. Or, not theory but design?
3. Although waveform tells you many discrepancy in visual manner, could it not match to what you listen?
4. Visual info is difficult to quantize but other measurements are not.
5. Something else dominates.


I wonder whether my humble questions are meaningless or just frontiers for anyone therefore no response is coming back?

[lcaillo]

I suspect that we don't really understand what you expect to get from visual examination of a signal.

[hirokazu negishi]

Hi Leonard

Thanks again for your effort to answer my questions. My expectation reflects my previous experience, camera and photo copying. They are based on optics and one of its scientific standpoint is spatial frequency reproduction.

Suppose a fine line is a high frequency square waveform, whereas a very wide line is resembled to a low frequency square waveform. In mathematical theory, it is easy to achieve zero distortion reproduction and in case of electrical signal in audio range frequency, reproduction of these signals are also easy.

However, when a loudspeaker is coming to play, this is completely different arena. It converts electrical signal into audible wave signal, by moving air through driving cone. Dynamic loudspeaker is based on inertia control which has apparent limitation in low frequency reproduction. Metaphor to photocopy reproduction, fine line is fine but very wide line is difficult to reproduce like early days of Xerox. Needless to point though, subwoofer must straggle with this theoretical limitation.

It is my understanding that current subwoofer managed to reproduce very wide line by power game but quality of the square waveform be deformed because of the group delay. Thanks to the test archival, now I learnt that there are many different group delays which means different distortions in a very bold square waveform reproduction. I wonder how do they sound and is there any relation with group delay hence, different face of square waveform reproduction.

[hirokazu negishi]

Hi Leonard

In addition to my previous message, I wish to add further clarification for my understandings. That is human factor to those two completely different, yet still worth comparing world.

To look things by your eyes and to listen, that is depending on to our ears. As a sensor, eye has only one tenth of frequency range against what ear can hear. Sensitivity distribution is somewhat similar that both end of spectrum are loosing its gain. How we feel these frequencies are well-known. Our eye feel different color by different frequency in electromagnetic wave, whereas height of pitch in audio wave. Hence our sensitivity for low frequency sound is inevitably weaken by lowering frequency. It could be conventional theory's backbone as human could not distinguish difference of wave form in low frequency, hence group delay do not matter for majority of listeners.

By the way, apart from intrinsic electromagnetic wave frequency, I mean color, there is spatial frequency that I mentioned in last message. This spatial frequency should be compared to waveform of sound, rather than small color difference in red against change of color for low frequency sound. In case of your eye, the more the width is large, the more easy to recognize, whereas the more low frequency , the less we can distinguish the difference.

Yet, there is no adequate methodology to provide such a test audio waveform in the past as electrodynamic loudspeaker has its intrinsic limitation in reproducing real square soundwave of 20Hz. This comparison also incurs another aspect. Human listening by ear could be just part of our sensing. You will say low frequency vibrate our whole body whereas Dr. Tsutomu Ohashi insists that human brain could be excited by ultrasonic frequency.

Both story indicate that the 20Hz square wave should be judged not only your ear but also whole your body. Hair rising could be one of such sensing methodology.

[lcaillo]

As I understood your original request, you wanted to view the waveforms. Is that correct? If you want to see square waves it is rather easy to do so. There are a number of PC applications for viewing waveforms and many to generate the signal.

[Chester]

Considering that a square wave is an *instantaneous* change from one extreme to another... mechanically you would need the transducer to 'teleport' from one extreme to the other (instantaneous remember), while displacing the air in its path... if you are to use a voice coil to push/pull the transducer the closer to 'instantaneous' you approach, the more g-forces experienced by the cone... so there will be a limit eventually a true square wave would require there to be *instantaneous* displacement... such a speaker would (I think) have a 'perfect' impulse response though, so it would probably sound really good

I have read of a 'transducer' made of buckypaper (carbon nanotubes that have been turned into a paper like substance) it is conductive and when an audio signal is applied it does function as a speaker however it works by heating the air (the very low mass of the buckypaper and its great thermal conductivity allow it to very quickly heat (and stop heating) surrounding air, perhaps a speaker 'transducer' based upon heating the air and not motion of a cone would be able to achieve a better square wave in the air... maybe a pulsed laser that would heat the air, or try taking a look at 'plasma tweeters' they use electrical heating of the air (through a modulating electric spark, sort of like lightning)... a big enough spark may be able to make a better 20 hz square wave; though since the air does not cool down instantaneously (or heat for that matter) I doubt you will be able to make a *perfect* square wave... (I think the electrical heating would be able to

besides the fact that your ear drums also take *time* to react to the pressure differential exerted by the square wave (assuming the spark gap makes one) so even if something can produce it, we cannot truly sense it because we hear with transducers (which are plagued by the inability to move through space instantaneously)... It could probably be measured by some sort of laser setup using a cloud of dust, tracking the displacement to show the instantaneous change in pressure over time

Please be aware, I am trying to take your scenario as seriously as possible; my post is not meant to be condescending (I said assuming a few times...); there are just some laws of physics that need to be broken to produce, let alone hear a square wave.

[hirokazu negishi]

Hi Matt

Thanks for your effort to let me have your view. As your comment contains several points, let's discuss one by one.

1. No one is perfect!

I agree that true square wave do need instantaneous change from A to B. Yet, we are talking about a subwoofer, not a full range loudspeaker. Suppose 20Hz square wave to be reproduced, any subwoofer should take responsibility for 20, 40, 60, 80, and may be 100Hz. Above 120Hz, it is for mid range driver. It is imaginable that any subwoofer reproducing 20-100Hz in single delay time should do the business perfectly as a subwoofer.

2. Buckypaper vs. Ultrasonic motor driven woofer

Thanks again for your informative explanation for the Buckypaper. It was quite new to me and reminded me to let you know what we are now challenging in Japan. Before going to detail, let's clarify one thing. Suppose a subwoofer taking part of creating 20Hz square wave form, ideally it may not need to provide instantaneous explosive air volume change. Rather, it should provide 20, 40, 60, 80, and provably 100Hz in single delay time reproduction and that's all.

With regard to our activity, the Ultrasonic motor driven woofer, is reported in AES few times already. Here is the list of them.

@ A Proposal for Low Frequency Loudspeaker Design Utilizing Ultrasonic Motor, 119th Convention, Oct 2005 NY

@ An Introductory Review for U-fa(USM Driven Woofer) Development, 120th Convention, May 2006 Paris

@ LOUDSPEAKER FOR LOW FREQUENCY BY TWO ULTRASONIC MOTORS, Japan section conference, August 2008 Osaka

Although these papers may not indicate directly, high mechanical impedance drive by ultrasonic motor, instead of low mechanical impedance voice coil, it could provide constant delay reproduction in any subwoofer region frequency, provided the drive torque could give commanding control of the cone motion.


3. Human Sensing is common to all sound listening

I agree that human sensing system has its own delay because of the mechanism. But it would work same for original sound as well as reproduced sound.


Thanks again for your effort to let me have your friendly persuasion! Your post is opposite to condescending one.

[Chester]

"Rather, it should provide 20, 40, 60, 80, and provably 100Hz in single delay time reproduction and that's all"
-So you basically want to create a transducer that has the same impulse 'response time' from 20-100 hz? Isn't that how 'conventional' transducers work?

[hirokazu negishi]

If the same impulse "response time" means single constant delay time, yes that is what I meant.

On the other hand, Isn't that how 'conventional' transducers work? may not be the case as presence of the group delay implies.

In my understanding, the inertia mass control theory, the backbone of conventional transducer works only well above the F0 region but unfortunately, subwoofer range is in the middle of F0 frequency region. Therefore as the group delay data indicates, delay time is frequency and design factors dependant, hence not a single constant delay.

[Chester]

ah; that does make sense now that I think about it a bit more your ultrasonic motor paper looked interesting btw (I am reading about ultrasonic motors now )

[hirokazu negishi]

Thanks for your interest on to our activity.

Just coincidence though, one of our paper will recieve an award from USE2009 tomorrow. You can check their following HP in young scientist award USE2008

http://www.use-jp.org/USE2009/en/award/index.html

2 Loudspeaker by Ultrasonic Motors and It's Control System Yusuke Masuda
(Chiba Institute of Technology)

[Chester]

congratulations!