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early reflection of sidewalls: absorption or not?
early reflection of sidewalls: absorption or not?
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Old 18th January 2019, 07:58 AM   #11
AllenB is offline AllenB  Australia
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Originally Posted by DualTriode View Post
First reflections are important in crafting the sound stage.
There is already an image in the recording, does it need to be crafted?
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Old 18th January 2019, 02:18 PM   #12
RevMen is offline RevMen  United States
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Originally Posted by DualTriode View Post
You did not show up for the first lecture, you did not read the text and now you fail the final exam.
Hi.

I'm 17 years into my career as an acoustical engineer. I've designed auditoriums and other critical listening spaces.

Rather than being snarky and slapping up a link, show me where I'm wrong.

Last edited by RevMen; 18th January 2019 at 02:21 PM.
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Old 18th January 2019, 08:47 PM   #13
DualTriode is offline DualTriode  United States
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Originally Posted by AllenB View Post
There is already an image in the recording, does it need to be crafted?
AllenB,

You will likely tell me that the exception is the rule. I say not.

Is there not already an image in the recording? I say maybe to some extent, but not so much.

The recording is mixed. The illusion of the center channel is in the head of the person doing the mix. Localization and space are due to speaker placement and reflections; they are not in the recording, only in the head of the person doing the mix.

Now output this mix/recording and play it back over the best set of headphones that you can find. The center image, the localization and sense of space that the person doing the mix experienced are now gone, they are not in the recording.

Thanks DT
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Old 18th January 2019, 09:04 PM   #14
scottjoplin is offline scottjoplin  Wales
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Originally Posted by DualTriode View Post
Now output this mix/recording and play it back over the best set of headphones that you can find. The center image, the localization and sense of space that the person doing the mix experienced are now gone, they are not in the recording.
Binaural recording - Wikipedia
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Old 19th January 2019, 06:39 AM   #15
DualTriode is offline DualTriode  United States
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Quote:
Originally Posted by RevMen View Post
Hi.

I'm 17 years into my career as an acoustical engineer. I've designed auditoriums and other critical listening spaces.

Rather than being snarky and slapping up a link, show me where I'm wrong.
I will speak to two places that you do not have it correct. This is like a True/False question on the final exam.

True / False; First reflections are always bad? If there is one exception the answer is false.

First, you have forgotten who the client is. You seem intent to sell him a large live performance auditorium with adjustable sidewall diffusers. What your client has is a small 3000 cubic foot playback/listening room.

Secondly, early or first reflections are not necessarily bad or good, they are just the nature of the beast. You can manage and control them to your advantage. You do not need to put a stake in their heart to kill them.

One school of thought is to use Controlled Directivity speakers to aim or direct the speaker beamwidth where you want it to go. This approach limits unintended frequencies from just bouncing, without purpose, around the room. The right ear will receive direct sound from the right speaker. The left ear is in the sound shadow of the head and torso and will hear sound from the right speaker as a first reflection from the near wall. Vice versa for the left speaker, direct sound at the left ear, right ear is in the head torso shadow and the first reflections arrive at the right ear. Our brains are amazingly effective at extracting perceived soundstage information from this setup.

Thanks DT

I am a consultant of more than a few years. In this context my thing is more about noise and vibration. One School of Medicine research lab constructed of Ductile Moment Seismic Resistant construction shook so bad when a delivery truck drove down the street the field of view on the Scanning Electron Microscopes shook so bad that the building turned into facility offices and junk storage. A new replacement building of cast in place concrete (same thin brick veneer) was built next door in the parking lot.
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Old 19th January 2019, 07:27 AM   #16
mitchba is offline mitchba  Canada
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I wrote an article comparing two speakers with very different directviity indexes. You can really hear the difference the room sound adds from the wider directivity speaker, as I made binaural recordings of each speaker: KEF LS50 (David) Versus JBL 4722 Cinema (Goliath) Speaker Comparison with Binaural Recordings - Reviews - Audiophile Style

Since both sets of speakers in the room are setup along the long wall, and fire across the short dimension, the are no side wall reflections, as they are several feet away from the speakers. However, on the binaural recordings, one can clearly hear more room with the wider directvity speakers (i.e. KEF LS50) versus the much narrower directivity (JBL 4722) speakers.

While not directly related to sidewall reflections, it can determine ones preference for more direct versus more reflected sound. Which I believe is what is boils down to. A preference neither right or wrong...

In the case of measurements, and specifically an ETC measurement, the rule of thumb is that the first reflection and subsequent reflections should be -15 to -20 dB down from the main peak, within the first 20 to 40 ms of early reflection analysis.

May I humbly suggest in you specific case, the only way to find out is to listen to your setup with no treatments and then with enough acoustic treatment to make a difference, and listen again. Then you can determine your preference for more room sound or more direct sound, wrt sidewall reflections.

I spent +10,000 hours in control room chairs recording and mixing music. I prefer the in the corner or in the wall mounting of speakers over monitors sitting on the mixer bridge. Gives the cleanest sound minimising early reflections and to my ears produce a cleaner, more coherent sound field or auditory scene. The point I am trying to make is that it is you personal preference that matters most, as there is no right or wrong...
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Old 20th January 2019, 04:18 AM   #17
Monteverdi is offline Monteverdi  United States
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I am planning as mentioned initially to built speakers in a corner baffle. I can see that this would generate very little 1st refections from the front wall (where the speakers are located) and would also make a more space saving room setup as there this eliminates the space behind the speakers. But your -15-20 dB from the sidewalls would be not possible without absorptions. I guess some empirical experimentation will be required but some theoretical guidance would reduce the cost of this!
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Old 20th January 2019, 08:55 AM   #18
AllenB is offline AllenB  Australia
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Building speakers to properly fit the room corners without modifying the room gives a large delay for the early reflections, but building this way is challenging. Consider treating what you have if it falls into the early category.
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Old 20th January 2019, 08:59 AM   #19
AllenB is offline AllenB  Australia
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Originally Posted by DualTriode View Post
Now output this mix/recording and play it back over the best set of headphones that you can find. The center image, the localization and sense of space that the person doing the mix experienced are now gone, they are not in the recording.
Not even the reflections within the booths, or panning?

Irrespective, the room adds a constant but unrelated effect which is why this tends to be referred to as spaciousness rather than image.
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Old 20th January 2019, 09:59 AM   #20
scottjoplin is offline scottjoplin  Wales
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Originally Posted by Monteverdi View Post
That setup is used in many monitoring systems (e.g.:Moulton Laboratories :: The Real World of Project Control Room Monitoring) but almost never in domestic listening rooms and I wonder why.
I suspect it helps with the monitoring and mixing process, whether you want that kind of sound in your room is another issue
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