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Old 22nd January 2010, 10:45 AM   #21
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What about the low-frequency directivity? SL has theorised that maintaining uniform response is important across the spectrum?

The proposal seems to be direct only at upper frequencies, while being omni in the lower region, which is the traditional problem with typical box speakers.

SL seems to be gearing to proving or disproving his theory:
ORION/PLUTO Users Group • View topic - LinkwitzLab website up for 10 years!

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As you have seen from my very recent and last year's activities I am trying to establish with the AES community that stereo is more capable than commonly thought. I want to see tests with large groups of listeners and statistical data analysis, which confirm that loudspeakers and room disappear perceptually depending upon the radiation pattern of the speakers and their placement in the room. The Auditory Scene that is evoked has stereo system and recording dependent spatial distortion, which can be reduced to some degree by varying radiation pattern and room placement.

I am excited to know that such tests will take place next month, coordinated by David Clark of DLC in Detroit. The test results will hopefully confirm the existence of a solution to the loudspeaker/room problem even if my premise turns out to be flawed. More people will have learned something about hearing.
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Old 22nd January 2010, 11:08 AM   #22
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Quote:
Originally Posted by Key View Post
Hey Earl,
I like the paper. I think you have some good stuff in there. Some of it that you touched on I would be more tempted to make the whole paper about but that's just what I am fixated on I guess. This point kind of stuck out to me as something I don't think works.

"Recall now our discussion of image shift in a stereo situation where we
hypothesized that if the farther speaker could get louder as one moved
laterally while the closer speakers level decreased, that we might be able
to offset the time delay differences and maintain a fairly stable image
with listening position."

Thats a big "might". You can compensate with a delay for one side of the room but then you compromise the center and opposite side of the room. And I am pretty sure the delay (arrival time) is more important than the volume in terms of what will effect the stereo image. Also subjective reviews on other polar patterns than your own are very similar in this respect. Basically a report of a lack of shifting compared to the average loudspeaker. I am not sure it is exclusive to your design perceptually. I see why you could think that it is based on that physical alignment though. And yeah you could be right and that this sort of directivity is self compensating when moving around a room to a certain extent. I guess I just suspect there is something else going on.
Actually, this technique has been exploited for years in car stereo installations to provide a reasonable sound stage for driver/passenger positions. Imagine speakers installed in front doors/kick panels, pointed to ear height of the opposite seat.

The driver will hear on axis sound from the passenger side speaker, and off axis sound from the driver side speaker, and vice-versa, causing a more or less equal left/right levels at each position, due to the fact that the local speaker's off axis level will be less than the on axis level from the opposite speaker. If done right, the sound stage can be quite convincing.

Interestingly enough, under dash waveguides have even been available since the early/mid 90's, though maybe not as scientifically implemented as with Earls' techniques, I'm sure. Here's a link to a tutorial from the company that pioneered these waveguides for car stereo:
Tutorials at SpeakerWorks/USD Audio

Lukas
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Old 22nd January 2010, 01:11 PM   #23
durwood is offline durwood  United States
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Quote:
Originally Posted by Key View Post
Hey Earl,
I like the paper. I think you have some good stuff in there. Some of it that you touched on I would be more tempted to make the whole paper about but that's just what I am fixated on I guess. This point kind of stuck out to me as something I don't think works.

"Recall now our discussion of image shift in a stereo situation where we
hypothesized that if the farther speaker could get louder as one moved
laterally while the closer speakers level decreased, that we might be able
to offset the time delay differences and maintain a fairly stable image
with listening position."

Thats a big "might". You can compensate with a delay for one side of the room but then you compromise the center and opposite side of the room. And I am pretty sure the delay (arrival time) is more important than the volume in terms of what will effect the stereo image. Also subjective reviews on other polar patterns than your own are very similar in this respect. Basically a report of a lack of shifting compared to the average loudspeaker. I am not sure it is exclusive to your design perceptually. I see why you could think that it is based on that physical alignment though. And yeah you could be right and that this sort of directivity is self compensating when moving around a room to a certain extent. I guess I just suspect there is something else going on.
Correct you cannot compensate for the delay, azimuth is azimuth and is directly related to the ear spacing and source angle. Not to mention moving off-axis and moving closer to room boundaries also compounds this problem. Stereo attributes are strongest in the time sensitive region while the upper region dominated by levels is soley a monophonic area in our hearing. Therefore upper frequencies do not add to the stereo effect and can actually be more confusing and degrading to stereo. This artifact was well known even from the early days and by the inventor.

This "white paper" seems more like a marketing brochure. How many times is Summa mentioned? No official references either. I do applaud the work in supporting a position for good power response.

This is not really anything ground breaking either and if you must discuss stereo any further with directivity there are better concepts. If you want to discuss a system with level controlling directivity when moving about the room:

http://www.extra.research.philips.co...ers/aar01p.pdf

Last edited by durwood; 22nd January 2010 at 01:28 PM.
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Old 22nd January 2010, 01:37 PM   #24
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I can't speak for Earl, I'm sure he'll chime in, but I'm pretty sure that the off center sweet spot caused by on/off axis levels is purely a happy by-product of CD, not a design goal.

Lukas
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Old 22nd January 2010, 02:02 PM   #25
gedlee is online now gedlee  United States
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Originally Posted by LukasLouw View Post
I can't speak for Earl, I'm sure he'll chime in, but I'm pretty sure that the off center sweet spot caused by on/off axis levels is purely a happy by-product of CD, not a design goal.

Lukas
Hi Lukas

Yes, this is mostly correct. The amplitude versus time tradeoff is not perfect, but its a whole lot better than most common speaker setups for Hi-end speakers. Read the reviews on my web site, the technique does work and it is significant.

Durwood

Regarding Ron Aarts paper, its basically the same thing that my speakers do. The difference is that mine are practical cost effective products and the Aarts paper is just a theoretical discussion. Put into practice with real transducers, etc. and his technique won't work out all that well, or at least it must not have since we don't see any products of this type.

Yes, the paper is more of a marketing brochure than an engineering report. I wrote it because of the number of people who do not understand directivity and what it means. I also wanted to show some real responses since its extremely rare to see this type of data for commercial products. Given the results it is no wonder.

Someone mentioned SL and the Orions. I'd love to see data on those since I highly doubt that they are all that great as regards polar response. As far as LF directivity is concerned, the paper discusses why this is not important at LF. Since Dave Clark is an old friend and lives very close by, he told me of his study (I saw the Orions setup at his home on New Years Eve.) I don't think that it is going to come out quite like Mr Linkwitz is hoping. It won't be blind so it won't convince any sceptics no matter how it comes out.
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Old 22nd January 2010, 03:16 PM   #26
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Originally Posted by Key View Post
I am pretty sure the delay (arrival time) is more important than the volume in terms of what will effect the stereo image.
The effect is real and is called "trading" or "equivalence" in psychoacoustics. The displacement of a phantom source caused by an interchannel time difference can be fully compensated by an interchannel level difference and vice versa (see Blauert).

Problem is that this effect varies from person to person and is signal dependent. While the configuration suggested by Earl helps avoiding the complete breakdown of the stereophonic illusion when the listener leaves the sweet spot, it is not suitable to replace a center channel loudspeaker.

Best, Markus
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Old 22nd January 2010, 03:41 PM   #27
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Originally Posted by gainphile View Post
What about the low-frequency directivity? SL has theorised that maintaining uniform response is important across the spectrum?

The proposal seems to be direct only at upper frequencies, while being omni in the lower region, which is the traditional problem with typical box speakers.
Psychoacoustics knows a couple of parameters that describe spaciousness. The problem is that there are no studies that ever qualified those parameters for stereo reproduction in acoustically small rooms.

Within that context not only the loudspeaker is of interest but also the format (multichannel vs. stereo) and last but certainly not least the room. Linkwitz seems to forget about that just like Earl seems to forget that loudspeaker directivity down to 200 Hz may play a major role.

Best, Markus
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Old 22nd January 2010, 03:58 PM   #28
gedlee is online now gedlee  United States
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Originally Posted by markus76 View Post
Within that context not only the loudspeaker is of interest but also the format (multichannel vs. stereo) and last but certainly not least the room. Linkwitz seems to forget about that just like Earl seems to forget that loudspeaker directivity down to 200 Hz may play a major role.

Best, Markus
"Major role", I don't think so, "significant", maybe, "insignificant", maybe as well. I think for a "good design" one has to be careful of the trade-offs. This extension to lower frequencies is extremely expensive in terms of cost and size, so if its just a noticable improvement, but at an extreme cost, that is not going to be very appealling. Fine for a very rich man. in a very big room who wants to pay the excessive expense involved in making a "one-off" - when you find him let me know and send him my way! I need more clients like that.
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Old 22nd January 2010, 04:03 PM   #29
gedlee is online now gedlee  United States
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Markus

Or, did you mean a "paper" design? You know those Uber-designs that get written about around all the time, but somehow never seem to get made, so then no one can criticize them either way - its just "hypothetical" and "you never know". Yea let's ramble on for days about the kinds of things "that could be done"! One thing I learned being a productive engineer was that as soon as a project starts to look like that, its time to stop because your just wasting your time - "Blowing smoke", as they say.
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Old 22nd January 2010, 04:11 PM   #30
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Thanks for the link! Finally found the title of the Bauer paper I was searching for. Interesting to see that Bauer used dipoles and toe-in 50 years ago

Best, Markus
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