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Old 2nd June 2013, 10:02 AM   #31
PRTG is offline PRTG  Latvia
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Correction for in post #6

Initial text:

"My conclusion from this picture is that for in-room listening for frontally lineary responding speaker the best dispersion pattern curve would follow this suggested equalization line, or directivity index curve following just inverted version of it."

Corrected version:

"One that designs correct loudspeaker system for in-room reproduction must aim for most linear frontal response measured in anechoic chamber combined with DI (directivity index) curve that follows attached psycho-acoustic correction EQ curve suggested by Zwicker/Fastl and that was suggested by Joachim Gerhard in his thread. In other words narrower dispersion at each given frequency would will excite less reflections which equals higher DI and makes direct signal less masked by reflections while wider dispersion (lower DI) will do the opposite therefore creating desired D/R EQ acoustically rather than electronically. Sum of direct/reflected signal will therefore be correct for in-room equall loudness perception. As this will most probably give correct finally perceived sound in particular room type achieving this DI for particular reference speaker will just set an average baseline for usage in different room sizes. Confirmed yet by few the curve shows with some probability how majority of people would like the sound to be reproduced in rooms to be perceived as linear in terms of equal loudness in particular room used in their experiments. Necessity of correction is highly disputable as it seems to be not widely adopted by industry yet.

For most precise reproduction experience in any particular room that has feature set (size, reflectivity, diffusivity) different from room used for EQ curve creation using appropriate Q (to be determined easily) for each parametric filter. This final EQ must be applied to direct signal to achieve resulting sound power curve that complements with the psychoacoustic EQ curve and satisfies desire for most linear perceived signal (yet to be determined). This may shift direct signal off linear on-axis response for very small levels, but it is the best compromise I can think of unless speakers are designed for the one particular room. Experiments with equalization of symmetrical omnidirectional speaker has shown that only correct sum is what matters, regardless of what we change, in this case EQ of both - direct and reflected signal. This part is the most controversial as it goes against to some historical canons I guess.

For loudspeakers having high average DI and/or used in larger rooms (latter to be yet determined) less of this type of correction will be needed. DI=0 at particular band sets sets maximum of the correction level needed in some 'standard' listening room used by Zwicker/Fastl to equal the correction level shown on the curve. Minimum correction level is yet to be determined or must be found emphirically. 'Critical midbass' or band of 400-500Hz may be a good starting point as speakers directivity at this band is usually is very low already (close to Shroedders frequency) but not yet influenced by room modes"
.

This essentially answers what in my opinion defines more rewarding loudspeaker directivity pattern for in-room stereo listening. May apply to mono loudspeakers as well. For multi-channel systems where frontal speakers are required to have much narrower dispersion compared to side speakers appropriately corrected DI curves must be achieved for each type.

If moderator could move this to the top before prologue it would be easier for more busy people to get to the point quickly without reading all through.

Any criticism is welcome -as always. Thanks!
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Old 2nd June 2013, 11:27 AM   #32
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by 6.283 View Post
This is not what I was referring to. Try pages 457 - 461.
I measured the direct/diffuse ratio at my listening point:
direct_diff left.gif direct_diff right.gif
Don't look for the response curve as is - the microphone was directed to the ceiling to get the full horizontal response.
Red is diffuse field without gate (total power response), green is direct response with 5 ms gate. It looks like I prefer only 2-3 dB difference compared to the 5 dB Klippel is talking about.
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Old 2nd June 2013, 11:47 AM   #33
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Quote:
Originally Posted by PRTG View Post
Any criticism is welcome -as always. Thanks!
The graph you've posted is only true for pure tones. We don't listen to pure tones.
Is that graph also true for phantom sources?
How much is perceived loudness determined by indirect sound and how much by direct sound?
The indirect sound field differs considerably between rooms - how is this incorporated in the proposed directivity-based equalization attempt?
Spectral balance is already corrected for in the production process, so why apply it a second time in reproduction?

Last edited by markus76; 2nd June 2013 at 11:50 AM.
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Old 2nd June 2013, 01:51 PM   #34
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PRTG,
Posted sensitivity plot and thesis is totally nonsensical approach for achieving desired perceptions.

Use a measurement microphone with flat response to record a sound and then play it back with speaker referenced to same level using same microphone placed at same distance used in recording. Speaker with flattest response sounds most natural.

Typical crap measurement microphone such as ECM8000 has rising response. Equalization of speaker with such requires calibration curve applied as correction, and likewise if microphone is used for above simple demonstration, correction equalization needs to be applied to recording as well.

If speaker is equalized flat from off axis, i.e. 30 degrees, and listened to at same angle for above demonstration, result is natural. If speaker has typical characteristic of direct radiator, and is listened to on axis using such EQ, it will sound too bright.

With flat on axis response, the further back the listening position is in a live room, the more apparent the perception becomes that the sound is being beamed.

With flat off axis EQ, listening further back, the bright on axis energy is illuminating the room, accentuating its liveliness. This leads to all manner of perceptions that are all highly dependent of the room and listener position.

Walking the polar pattern of speaker set up outside makes this very clear. EQ on axis may lead to region 010 with very natural sound. EQ at 30 off axis leads to two zones in horizontal plane for possible coverage of 40 with natural sound.

With off axis EQ of conical radiator, much greater volume is controlled. For Pluto type speaker with 2" full range as tweeter, I tilt tweeter up about 5, and EQ at about 10 off axis. At listening position tweeter shoots over head, and sound changes very little with toe-in changes of 20. Swapping to 1" dome tweeter extends this to usable toe-in range of about 30.

Better overall balance is achieved with speaker with wide uniform pattern, or treatment of the room, or combination of the two. Treatment also includes particular placement of listener and speakers, including orientation of speaker axis (unless it is truly omnidirectional), and choice of equalization axis.
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Old 2nd June 2013, 02:09 PM   #35
PRTG is offline PRTG  Latvia
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Quote:
Originally Posted by markus76 View Post
The graph you've posted is only true for pure tones. We don't listen to pure tones.
Is that graph also true for phantom sources?
How much is perceived loudness determined by indirect sound and how much by direct sound?
The indirect sound field differs considerably between rooms - how is this incorporated in the proposed directivity-based equalization attempt?
Spectral balance is already corrected for in the production process, so why apply it a second time in reproduction?
Markus, thanks for the questions!

It could be the same regarding complex signals due highly resolutive nature of human perception of the sound. At least that's what I'm hearing which isn't satisfactory proof alone, of course. I'll try to find the ground for this in the Toole's book once I get to it.

I also can't answer about phanthom sources, but if I remember correctly their perception are mostly delivered through specific frequency band. I must check this, too.

Spectral balance of recordings can vary depending on recording techniques, skill, hearing condition and personal taste of recording, mixing, mastering and finalizing engineers. If engineers have used controlled directivity monitors in moderately diffusive studio control room, or mastering grade headphones or both, result will have good chances to be close to pleasant. I personally always have used Sennheisser HD25-C II for ocassional finalizing tasks of already recorded and mixed material and usually was happy with the result. If D/R EQing gives better percieved balance of the loudness of particular audio bands it should just more precisely reveal the result of studio work as it is.

Perhaps you are asking what will happen to reverberant cues that are put into the final mix in some proportion with direct recording - will they be multiplied or perceived 'as is'?
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Old 2nd June 2013, 02:44 PM   #36
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Quote:
- By the way, what's the baffle width of upper midrange speaker of Linkwitz's LX521 and NaO Note RSII?

Jānis Irbe,
Riga, Latvia
The LX521 upper mid baffle width is 4.5 inches, 114mm. Can't speak for the Nao note as I don't own them.

Keith
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Old 2nd June 2013, 02:50 PM   #37
6.283 is offline 6.283  Germany
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Quote:
Originally Posted by Rudolf View Post
It looks like I prefer only 2-3 dB difference compared to the 5 dB Klippel is talking about.
And you are certainly not alone with this. This probably goes into the same direction like musicians and mixing people like less reflected sound.
Meanwhile I see the 5dB as an upper limit and I would probably find myself in the 3...4dB range.
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Old 3rd June 2013, 06:40 AM   #38
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Quote:
Originally Posted by Rudolf View Post
I measured the direct/diffuse ratio at my listening point:
Attachment 352215 Attachment 352216
Don't look for the response curve as is - the microphone was directed to the ceiling to get the full horizontal response.
Red is diffuse field without gate (total power response), green is direct response with 5 ms gate. It looks like I prefer only 2-3 dB difference compared to the 5 dB Klippel is talking about.
Red is not diffuse response. It is direct + diffuse. So plots compare windowing of complete response of perhaps 100ms v direct response with windowing of 5ms. Without appropriate normalization and referencing methods for different window lengths, the results do not show a D/R relationship as the area between two plots.
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Old 3rd June 2013, 08:27 AM   #39
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by Barleywater View Post
Red is not diffuse response. It is direct + diffuse.
That's right. And I'm not happy about that labeling either.
But I was referring to the Klippel experiment explained on pages 457 - 461 in Toole's book. I don't have the original Klippel source, and Toole isn't very precise about how he defines "Ldiffuse". He calls it the "total sound power". Since in the experiment (Ldiffuse - Ldirect) is always >0, Ldiffuse must be the total response including the direct response.

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Old 3rd June 2013, 09:29 AM   #40
PRTG is offline PRTG  Latvia
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Hello Barleywater,

Quote:
Originally Posted by Barleywater View Post
PRTG,
Posted sensitivity plot and thesis is totally nonsensical approach for achieving desired perceptions.
Thanks for following. My apologies for bad English, I'm really struggling as it's not my native language, and this sure makes understanding of idea less clear. What do you mean by 'sensitivity' plot? If you meant an equal loudness curve it actually deals with perception.

I'd like to continue using term 'correct perception' by meaning 'accurate' instead of 'desired' unless we agree that what we desire is accuracy

Quote:
Originally Posted by Barleywater View Post
Use a measurement microphone with flat response to record a sound and then play it back with speaker referenced to same level using same microphone placed at same distance used in recording. Speaker with flattest response sounds most natural.
This is true only for anechoic chamber, don't you agree? If done in the room results will be vary depending of variations of off-axis response of speakers even if the all have flat on-axis response.

Quote:
Originally Posted by Barleywater View Post
Typical crap measurement microphone such as ECM8000 has rising response. Equalization of speaker with such requires calibration curve applied as correction, and likewise if microphone is used for above simple demonstration, correction equalization needs to be applied to recording as well.
Attached is statistically average typical Behringer 8000 curve. In my opinion it's good enough for the midrange region as it fits within Class 1 tolerance up to 5K. By using correction file I believe to have reduced the non-linearity to production variations limit. Mic has the same capsule as used by Linkwitz but having more limited dynamic range (noise floor, THD) as it is connected the standard way unlike Linkwitz's which uses non-standard connection.

What is the mic you are using?

Quote:
Originally Posted by Barleywater View Post
If speaker is equalized flat from off axis, i.e. 30 degrees, and listened to at same angle for above demonstration, result is natural. If speaker has typical characteristic of direct radiator, and is listened to on axis using such EQ, it will sound too bright.

With flat on axis response, the further back the listening position is in a live room, the more apparent the perception becomes that the sound is being beamed.

With flat off axis EQ, listening further back, the bright on axis energy is illuminating the room, accentuating its liveliness. This leads to all manner of perceptions that are all highly dependent of the room and listener position.
I'm not in doubt about side-flat hard-toed-in loudspeaker setup sound being natural. But in my opinion their direct response must following specific curve to define right spectrum for reflections, and not be totally flat.

Side-flat hard-toed-in loudspeaker setup surely is another method how to create correct spectral balance between direct and reflected signal and create stronger engagement of late reflections as 'on-axis' signal hits the opposite wall first. Plus it allows for wider coverage in bigger rooms. While travelling to opposite wall its on-axis (now rather assymetric of-axis) spectrum changes as decay rate is higher for higher frequencies and walls and audience absorb some part of it. It may quite well complement with last part of Zvicker/Fastl curve which could be even measureable by placing mic near the wall and taking measurements against the wall with poper gating applied. By the way don't you ever do additional EQing to better fit such loudspeakers to particular room size?

Quote:
Originally Posted by Barleywater View Post
Walking the polar pattern of speaker set up outside makes this very clear. EQ on axis may lead to region 010 with very natural sound. EQ at 30 off axis leads to two zones in horizontal plane for possible coverage of 40 with natural sound.
So on-axis becomes non-flat actually. Doesn't it really matter what spectrum you're sending to opposite walls to illuminate the room? If it matters, what is the correlation of optimal direct response curve with different room sizes? I bet you don't know the answer but you're working on it.

Quote:
Originally Posted by Barleywater View Post
With off axis EQ of conical radiator, much greater volume is controlled. For Pluto type speaker with 2" full range as tweeter, I tilt tweeter up about 5, and EQ at about 10 off axis. At listening position tweeter shoots over head, and sound changes very little with toe-in changes of 20. Swapping to 1" dome tweeter extends this to usable toe-in range of about 30.
Sounds reasonable.

Quote:
Originally Posted by Barleywater View Post
Better overall balance is achieved with speaker with wide uniform pattern, or treatment of the room, or combination of the two. Treatment also includes particular placement of listener and speakers, including orientation of speaker axis (unless it is truly omnidirectional), and choice of equalization axis.
I agree. But that means very wide variations of actions without good starting point as a baseline. Also big problem being our adaptation rate being too fast. We just start liking every the new setup too quickly.

Your post gave more food for thought, thanks!
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