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What makes speakers "disappear " and can it be measured?

Alexium

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Just came across this odd beast. Would be interesting to try this concept in a quick DIY prototype, seems easy enough:

1667510145875.png


Here's the review - seems favorable of the concept: https://hometheaterhifi.com/reviews...egend-l800-floor-standing-loudspeaker-review/
 

Tim Link

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Just came across this odd beast. Would be interesting to try this concept in a quick DIY prototype, seems easy enough:

View attachment 240981

Here's the review - seems favorable of the concept: https://hometheaterhifi.com/reviews...egend-l800-floor-standing-loudspeaker-review/
I've played with that method. It definitely works but not without the cost of some coloration, at least in my experience. I've owned earlier Polk SDA speakers back in the early 1990s. I never got it to work well back then for some reason. I didn't understand the concept. In later experiments just using four bookshelf speakers I got it to create a very wide sound field with the speakers right next to each other in front of me. The crosstalk cancellation is not too picky about how far from the speakers you are so as long as you are precisely between them the effect works.
 

Tim Link

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Hello @Tim Link,

I have been following/reading your recent posts with great interests since I have thought about, but not actually done, the similar multichannel experiments a few years ago with my rather flexible PC-DSP-based multichannel multi-amplifier multi-SP-driver setup.

One of the reasons for not going into "your approach/experiments" in my case is/was that I could well achieve the wonderful "disappearance" of SPs by perfect L&R SPL balance with 0.1 msec scale precision time alignment among all the SP drivers using the group delay functionalities of DSP EKIO, and I could develop my own primitive but reliable reproducible accurate objective time alignment measurement methods (microphone recording only by separate PC) on actual room air sound even at my listening position. You would please refer to my summary post here.

Let me simply ask you, therefore, whether have you achieved complete (0.1 msec precision) time alignment among all the SP drivers or not, and if your answer would be yes, then what would be the favorable results and subjective impression of "the precision time alignment" in comparison with your current multichannel reverse polarity experiments?
I think you are correct about the importance of high precision to create the "disappearing" effect. Slight differences in the response of each speaker can clue the ear in to there being two separate sound sources, causing the speakers to reveal themselves despite also creating a nice stereo sound field. Also I think that tonal response is important too. I have noticed my sense of the imaging changing from getting the bass level correct. I suspect differences in early reflections on the left and right side of the room might also contribute to clueing the brain in to the fact that the speakers are doing some sound making. If both channels are adequately identical sounding and realistic sounding in tone, it stands to reason that the system will do a better job at tricking our ears.
 
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Tim Link

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I got inspired to experiment with making speakers "disappear" by aiming them away from me and bouncing the sound off a wall. This is sort of a cheap trick, or stunt way of getting it to happen, but it does work! The sound stage is very wide and center image very solid. Unfortunately tonality is a problem. The wall sounds like what it does, and the lower frequency sound is going omni off the speaker and reaching the ears sooner and louder than the highs that are being bounced off the walls. The speakers weren't meant to be listened to this way. But, a speaker could be made with this in mind that might do a considerably better job and be useful with big flat panel displays that are mounted on the wall. I tried this at home as well and it seems the high frequencies do sound better when bounced off a shiny smooth surface, like a window.

Some potential here is that the apparent sound source is actually behind the wall, making it seem like you are further from the speakers and thus widening the sweet spot. The absorbers around the speakers don't seem to be super important. At home I didn't have any and the effect still worked. In a long skinny room played sideways the speakers could be on the same side as the listener, bouncing on to the screen or window and back to the listener, making the room sound wider, twice as wide. In any small space, getting the sound source to seem further away could be helpful. The bass reaching the ears too soon and too loud could be dealt with by designing a speaker with low frequency driver time delay and level adjustable according to use case. It actually makes sense to have the lower frequencies spaced further apart and closer to you than the higher frequencies, since that will reduce room mode problems and increase inter aural differences down lower where the waves pretty much have to travel across our head for us to notice the effect - per Greisinger.
PXL_20221104_181235085.PANO.jpg
 
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dualazmak

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Hello @Tim Link,

I essentially agree with you.

Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important; I well experienced and implemented these (I designed my house/rooms for these).

Please carefully look at photo of my SP physical arrangements;
WS00004914.JPG


The SP cabinets and drivers are not directed to my face sitting at listening position, but they are intentionally arranged in parallel with the side walls.

Furthermore, behind the wide plane between L&R SP drivers, we have open air space of our dining room; I believe this is critically important. Although you can see the sliding glass doors behind the main SP cabinet, the Yamaha NS-1000 cabinets are fully sealed ones with no rear bass-reflex ports. The large heavy sub-woofers, Yamaha YST-SW1000, have open ports in front not in rear.

Edit:
As for the unique position (under the main SP cabinet) of L&R super-tweeters Fostex T925A, please refer to my post here.

I also have fairly large open space (actually another room) behind my ears as you can see in this photo;
WS00004913.JPG


As wrote in my post here, the rear room is a Japanese style tatami-mattress-floor room which is acoustically well "dead" and effectively minimizes the sound reflections and resonances. Of course, the sliding doors between the rooms are kept open during the listening sessions as shown in the above photo.

I often place sound absorption sponge mattress in front of the white wall and the opened glass door leading to the corridor;
WS00004911.JPG


As shared in my post here, I identified "that wall" causes very slight sound reflection and standing waves. Consequently, at the occasions of my really precise "measurements", including the SP transient characteristics/behavior measurements, I put further intensive insulation/deadening treatments to the wall as shown in this photo;
WS00004912.JPG


As also shared here, the ceiling of the listening room is covered by microporous diatom panels carefully selected with proper sound absorption performance. On the wooden floor, we have the large carpet also selected with suitable sound absorption properties.

Edit:
For the subjective (and possibly objective?) assessments of "disappearance of speakers", it would be also important utilizing and listening to common/consistent "audio sampler music playlist" consists of excellent recording quality music tracks of our preference selected from various genres/categories. You may find an example of such "music sampler playlist" here and thereafter on my project thread which has been summarized here and here.
 
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Doodski

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Hello @Tim Link,

I essentially agree with you.

Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important; I well experienced and implemented these (I designed my house/rooms for these).

Please carefully look at photo of my SP physical arrangements;
View attachment 241242

The SP cabinets and drivers are not directed to my face sitting at listening position, but they are intentionally arranged in parallel with the side walls.

Furthermore, behind the surface plane of SP drivers, we have open air space of our dining room; I believe this is critically important. Although you can see the sliding glass doors behind the main SP cabinet, the Yamaha NS-1000 cabinets are fully sealed ones with no rear bass-reflex ports. The large heavy sub-woofers, Yamaha YST-SW1000, have open ports in front not in rear.

I also have fairly large open space (actually another room) behind my ears as you can see in this photo;
View attachment 241243

As wrote in my post here, the rear room is a Japanese style tatami-mattress-floor room which is acoustically well "dead" and effectively minimizes the sound reflections and resonances. Of course, the sliding doors between the rooms are kept open during the listening sessions as shown in the avobe photo.

I often place sound absorption sponge mattress in front of the white wall and the opend glass door leading to the corridor;
View attachment 241245

As shared in my post here, I identified "that wall" causes very slight sound reflection and standing waves. Consequenly, in the occasions of my really precise "measurements", including the SP transient characteristics/behavior measurements, I put further intensive insulation/deadening treatments to the wall as shown in this photo;
View attachment 241246

As also shared here, the ceiling of the listening room is covered by microporous diatom panels carefully selected with proper sound absorption performance. On the wooden floor, we have the large carpet also selected with suitable sound absorption properties.
I used sound deadening panels behind my head. The result was very good. I used two of the 1m x 2m x 10cm office divider panels. Can you hear the difference?
 

dualazmak

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I used sound deadening panels behind my head. The result was very good. I used two of the 1m x 2m x 10cm office divider panels. Can you hear the difference?

There are Japanese-style sliding doors (should I say sliding panels?) between my listening position and the rear Japanese-style room. I can easily compare, therefore, the sounds with the sliding panels and without (fully opened) them (as shown in above photos).

Since the closed panels are rather near to my back-of-head, I can easily hear the difference. As you my guess, of course I like and prefer having large open space behind me during daily listening sessions as shown in above photos.
 
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Doodski

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As you my guess, of course I like having large open space behind me during daily listening sessions as shown in above photos.
Yes, I guessed you would enjoy and prefer the open door. Eliminating the rear reflections is better.
 
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