Basic Introduction to Room Acoustics video by Geoff Martin from B&O

[PaulD]

They are excellent intro videos! Many thanks!

Here are a couple that I have used when teaching some basic acoustics, a little more on the "entertainment" side, they are still very useful for making the timbrel effects of reverberation are very clearly audible:

And with voice

 

[thewas]

Part 4 is now online

Video description:

This is an explanation and demonstration of phantom imaging in a 2-channel stereo playback system. The voice was recorded using a single cardioid microphone, 1 m from the source, in an anechoic chamber at Bang & Olufsen in Struer, Denmark. All stereo effects presented in this video were done using custom-made digital signal processing. Note that the values I use for the IAT and ITD examples were found by Gert Simonsen (Simonsen, G. (1984). Master’s thesis, Technical University of Denmark, Lyngby) Different Values have been found in other studies, as listed here:
http://www.sengpielaudio.com/InterchannelLevelDifferencesAndInterchannelTimeDifferences1.pdf

 

[tuga]

It's interesting to note how distinct inter-channel amplitude difference sounds from inter-channel time difference.

 

[thewas]

Video description:

This is an intuitive explanation of the effects of a perfect acoustic reflection at a single listening position when the source is within 1 wavelength of the reflecting surface. Note that all of the acoustical effects that you hear in this video are actually happening because of the surroundings. No extra artificial effects were added. For the video portion, the microphone and Sound Pressure Level (SPL) meter are 10 m from the reflecting wall. The microphone is a DPA 4011 condenser cardioid. The two frequencies used in the demonstration were 43 Hz and 55 Hz - but this really doesn't matter... The signal was generated using Cycling74's Max/MSP running on an Apple Macintosh, connected via HDMI to an standard AVR. (The reason I do this is that the AVR can act as the sound card and power amplifier all in one.) The loudspeaker driver is a 13" Scan-Speak woofer in a sealed cabinet made of 25 mm MDF (one of the old prototype woofers left over from the original BeoLab 90 development process...)

 

[tuga]

Thanks @geoffmartin for your teachings. But shouldn't this be Part 5?

 

[Alexanderc]

I have a couple of questions about the loudspeaker configuration video (part 4). I don't know if this is the best place for my questions, but as they relate to one of the videos here, I'll start here and move if I need to.

1). In Part 4 "Loudspeaker configuration," a series of adjustments are made to the amplitude difference and time difference in a few brief spoken passages including descriptions of where one should hear the "phantom image." On my system the time differences appeared as described, but the amplitude differences did not. The sounds that were supposed to be 10 degrees, 20 degrees, and 30 degrees from center were more like 7, 16, and 25 (with the 30 degree image coming from the inside edge of each speaker--about 6-7 inches from the tweeter axis). This was true on both the left and right side. The centers of my speakers are 100 inches apart (254 cm) and 104 inches from my ears (264 cm), so not a perfect equilateral triangle, but reasonably close. They are large, 3-way towers, toed in but not firing directly at the listening position. Is it immediately obvious to anyone here why this might be occurring? Sidewall reflections?

2). At 9:25 in the same video, Dr. Martin demonstrates what can happen when the amplitude and time differences are opposite. In his demonstration he explains that one should either hear the phantom image from the right speaker or with some frequency bands appearing in each speaker. What does it mean that the phantom image appeared entirely in the left speaker in my system? I am concerned about some deficiency in my equipment or setup, but I have no idea where to start.

Thanks!

 

[PaulD]

The 4 inches of difference combined with lateral reflections could be enough to show the discrepancy you mention in point 1.

For your point 2, IID and IRD trading is a somewhat complex psychoacoustic phenomenon, I will add a diagram from Self that illustrates it. I doubt that there is anything seriously wrong with your equipment, particularly if in point 1 you get a stable centre image. Although I might be tempted to check the polarity between the channels just to make sure. It could easily be frequency dependent reflections causing the issue.

 

[kach22i]

Great videos guys about natural fundamentals of sound and mono/stereo microphone recording.

If you are ready to jump into the deep end off the high diving board, check out this video on studio mixing.

I love the simplified graphics, and explains why some instruments seem to shift position within the same song.

It was mixed that way!

 

[Alexanderc]

I am really enjoying these videos from Geoff Martin. They are so well done. Really are fabulous demonstrations!

 

[prasanth.nath]

Where is "buy me a beer" button, when you desperately want to buy somebody a beer!
Splendid, splendid series of videos. Many thanks @geoffmartin.

 

[Cote Dazur]

At 9:25 in the same video, Dr. Martin demonstrates what can happen when the amplitude and time differences are opposite. In his demonstration he explains that one should either hear the phantom image from the right speaker or with some frequency bands appearing in each speaker. What does it mean that the phantom image appeared entirely in the left speaker in my system?

Just discovered those video, amazingly interesting. Thank you @geoffmartin for doing those.
Like you @Alexanderc i have the same phenomenon on my system #2, not tested #1 yet. The sound stays on the left speaker. Wondering how common that is. My system #2 is near field equilateral with 38% position 2 calculator set up.
I can “clearly” hear Geoff behind me in the other video when he goes behind the camera on that set up.
Alexander, did you get an answer to your question and been able to correct the situation?

 

[Alexanderc]

Just discovered those video, amazingly interesting. Thank you @geoffmartin for doing those.
Like you @Alexanderc i have the same phenomenon on my system #2, not tested #1 yet. The sound stays on the left speaker. Wondering how common that is. My system #2 is near field equilateral with 38% position 2 calculator set up.
I can “clearly” hear Geoff behind me in the other video when he goes behind the camera on that set up.
Alexander, did you get an answer to your question and been able to correct the situation?

I was never able to discover what was happening. I don’t have that system (or the room it was in) anymore so I can’t revisit the issue either. I would love to know if you find out anything.

 

[Cote Dazur]

I would love to know if you find out anything.

I will report, thank you for the reply.
So, on your new set up, all works as intended? the sound is no longer in the left speaker in those conditions?

 

[Alexanderc]

I will report, thank you for the reply.
So, on your new set up, all works as intended? the sound is no longer in the left speaker in those conditions?

I no longer have a dedicated listening room, just a family media room now with a 5.1 setup. I had forgotten about this video, but now that you've reminded me I'll have to try it in my current setup. Thanks!

EDIT: I forgot to mention that I do have a low budget office system, but I have not spent any time setting it up properly. I played the video on this system and did NOT have the problems I described in point #1 above--the amplitude difference moved the phantom image as described. However, I had exactly the same experience as I did in my original post, point #2--the phantom image appeared in the left channel, not the right.

I feel like I can easily attribute this to speaker placement in my current setup, whereas in my original test 3 years ago I had spent hours perfecting the speaker positioning and listening position.