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Old 8th November 2012, 12:46 AM   #29071
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My mic arrays are much simpler, since I believe that our ears are aligned horizontally (generalization, of course) and cues of height are represented by reflections from the floor.
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Old 8th November 2012, 01:01 AM   #29072
gpapag is offline gpapag  Greece
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Jneutron
Air behaves quite close to an ideal gas for practical audio cases.Compressibility factor Z is a measure of how much a gas is close to an ideal gas (Z=1).
For compressibility of air, see bottom of this page:
Compressibility factor - Wikipedia, the free encyclopedia

Zair=0.9957 to 1.0020 over a range of 1-5 bar and 250-500d Kelvin


I did some calculations for to plug some numbers (in red boxes) on the waveform from the article of Dinsdale.
Looking at this waveform, how much do you think is the % 2nd harmonic distortion? Is it somewhere btn. 20% and 30% ?

This “air overload” mechanism of distortion will be stronger for higher frequencies. With lower frequencies, there is more time for heat diffusion, so the curve will be less steep, tending more toward an isotherm. The distortion will be considerably less.

The temperature difference due to adiabatic compression – expansion btn. top and bottom of the waveform changes the sound velocity locally. For the numbers there, the difference is 72m/s. This will skew the waveshape clockwise, adding higher orders of distortion.

How much is the sound pressure level of this waveform in db? 90 or 180?

George
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File Type: jpg adiabatic.jpg (55.2 KB, 146 views)
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Last edited by gpapag; 8th November 2012 at 01:04 AM.
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Old 8th November 2012, 01:42 AM   #29073
gpapag is offline gpapag  Greece
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Default Correction

Sorry
There was a mistake in the temperature of the center line of the waveform.
The corrected one is attached here.

George
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File Type: jpg adiabatic.jpg (55.1 KB, 145 views)
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Old 8th November 2012, 02:51 AM   #29074
RNMarsh is offline RNMarsh  United States
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R.I.Profile: Of course, other than the room itself, core issue is the 'polar' dispersion patterns of the speaker/drivers.
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Old 8th November 2012, 02:56 AM   #29075
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Originally Posted by fas42 View Post
Next problem, "Room Interface Profile", gives me 3 results in Google, all useless ...
Du...uh! After discovering it in 1981, I spent the next 2 decades trying to pin it down. I still dunno for sure though I'll pontificate if I have to. Floyd pretends to know but he dunno either.

That's the problem with discovering something from Listening Tests first. Then you gotta find a theory that fits the facts.

Far easier to dream up some high falutin' Golden Pinnae bull sh*t .. I mean carefully argued theory .. that explains life the universe & everything first. Then its easy to arrange all your tests (listening or otherwise) to show it exists and is of paramount importance.

Otala was world champion at that.

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R.I.Profile: Of course, other than the room itself, core issue is the 'polar' dispersion patterns of the speaker/drivers.
That's an important part but by no means the only or perhaps even the most important. See Floyd who takes this as paramount but with a very large pinch of salt.

I hope your speakers don't disperse too much. A fairly constant directivity pattern with frequency is good though it needs shaping.

Last edited by kgrlee; 8th November 2012 at 03:09 AM.
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Old 8th November 2012, 03:46 AM   #29076
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Originally Posted by kgrlee View Post
That's the problem with discovering something from Listening Tests first. Then you gotta find a theory that fits the facts.
Can be sometimes difficult ;-)
Between fact and us is our brain, quite clever to filter room modes or reverberations, while micro don't. Our brain can analyse the emitting surface. mikes don't. Our brain can isolate known sources from ambient noises, mikes don't..
Designing an enclosure is not fighting against electro acoustic but psycho acoustic.
Listening your video i was very surprised by the lack of bass presence, while i could feel that i would had them if i was in the room. Did it was the first passe, or several ?
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Old 8th November 2012, 03:54 AM   #29077
RNMarsh is offline RNMarsh  United States
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Originally Posted by kgrlee View Post
That's an important part but by no means the only or perhaps even the most important. See Floyd who takes this as paramount but with a very large pinch of salt.

I hope your speakers don't disperse too much. A fairly constant directivity pattern with frequency is good though it needs shaping.
If I connect the dots back to the Horn discussions, IMO it is the best reason for using a horn -- to control directivity... Other methods are useful also in this regard without increasing distortion. However, having said that, sound radiation patterns from musical instruments are vary different from one another and all being given a fixed pattern from a speaker is not conducive to realism in the room. Nothing short of a ridiculous system would over come that. Perhaps, soundfield recordings are the closest to reality we have at the present time.

After the number #1 priority of getting a flat response, secondary effects become important;

So, tell us about 'shaping' and what it means to you. Thx-Richard

Last edited by RNMarsh; 8th November 2012 at 04:06 AM.
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Old 8th November 2012, 04:33 AM   #29078
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It's not to simple!
What is "flat"? Flat curve, or flat waterfall?
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Old 8th November 2012, 04:51 AM   #29079
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Originally Posted by Esperado View Post
Between fact and us is our brain, quite clever to filter room modes or reverberations, while micro don't. Our brain can analyse the emitting surface. mikes don't. Our brain can isolate known sources from ambient noises, mikes don't..
Designing an enclosure is not fighting against electro acoustic but psycho acoustic.
As is pretty obvious, I'm in this camp: if the sound is not good enough then every problem, every deficiency of the loudspeaker, of the "interface" to the room glares at me; like having too strong a light, aiming in the wrong direction, on a fashion model's face. I can see every blemish, every pore, every discolouration - not a pretty sight. But, get the key elements of the sound right, and these theoretical problems are completely nulled, are now meaningless - like getting the lighting right for a fashion shoot ...

Frank
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Old 8th November 2012, 06:52 AM   #29080
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Between fact and us is our brain, .... but psycho acoustic.
Just a gentle reminder that in this case, the 'facts' are the results of Blind Listening Tests. eg

Why did this small speaker with a limited LF response elucidate good comments about bass lines bla bla while this monster with 2 x 15" drivers and measured flat low distortion response to 20Hz have negative comments about it's bass performance?

Quote:
IMO it is the best reason for using a horn -- to control directivity... However, having said that, sound radiation patterns from musical instruments are vary different from one another and all being given a fixed pattern from a speaker is not conducive to realism in the room. Nothing short of a ridiculous system would over come that. Perhaps, soundfield recordings are the closest to reality we have at the present time.
I said much earlier that I dunno what a perfect speaker needs to do. But I'm certain it will be some sort of surround system. To me, a surround sound system is a speaker; you put electrical signals in one end and it makes a noise at the other.

Quote:
After the number #1 priority of getting a flat response, secondary effects become important;

So, tell us about 'shaping' and what it means to you
It is possible to group factors into 1st order, 2nd order etc. You can compensate for deficiencies by juggling factors in the same order. eg Delayed Resonances are 1st order like response, directivity and the Room Interface Profile. Allowing small inaccuracies in one can be used to compensate for deficiencies in others giving more 'accurate' results to the listener.

If you'll allow me to throw one impossible requirement for a conventional speaker .. It will have a controlled response and excellent Delayed Resonance Response too in all directions Answers to how this 'controlled response' should vary with direction on a postcard please.

Some simple caveats.

If you make an omni speaker with flat response in all directions, ie a perfect omni, it will sound too bright. But in fact it is very difficult to make a 'good' speaker omni over a wide frequency range.

It's actually easier to make an accurate fig-8 over a large frequency range. But when you do this, the speaker sounds even brighter than the perfect omni. But the fig-8 has advantages that sometimes make up for their requirement for large size to give sensible levels .. though these are only badly understood by the unwashed masses.

A large part of this is cos we are accustomed to thinking of speakers as large ugly boxes that take up a lot of space (with apologies to Wavebourn & his line arrays)

Note that this has nothing to do with flat response @ 1m on treble axis bla bla (or your favourite prejudice) This measuring position is in fact a terrible place to listen to a speaker In particular, stereo will be poor and reliant on use of a Greene-Lee neckbrace.

It's just that at the present SOTA, the speakers which have good Room Interface Profile usually have flat 1m bla bla response too cos that's what designers have always done.

And all the above is about good 'conventional' speakers, NOT my perfect speaker. Pls excuse my diarrhoea

Ambisonic Info | Contributed Audio Here's a concise summary of some of my favourite recordings on Ambisonia. Some of these played on an 8 speaker Periphonic (with height) system, or even with a simple 4 speaker horizontal system give some idea of what I think a perfect speaker [1] should do.

The recordings were made with the closest approach to a perfect mike [2] in this and the previous millenium.

Sorry Frank, I think you definitely need the 1000W amp to do Concorde justice in stereo.

[1] still unknown
[2] known

Last edited by kgrlee; 8th November 2012 at 07:06 AM.
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