• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

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

thewas

Master Contributor
Forum Donor
Joined
Jan 15, 2020
Messages
6,755
Likes
16,200

His video description:

"This is an introduction to some basic concepts and vocabulary in the general area of room acoustics - with explanations and live demos. I make a couple of sweeping statements in here - but the idea is to help to provide an intuitive understanding of what's going on... Not to help you design a concert hall...

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.

I'm standing 1 m in front of the camera in all locations (except when I'm not...) and the zoom is set to the same focal length (28 mm) - so I'm not playing any tricks with the camera - at least not intentionally.

The microphone pair was kept in the same configuration for the whole video (coincident hypercardioids with an included angle of 110 degrees, placed just below the camera's lens - if you're interested). The gain of the microphone is the same in all locations for the entire video - except for the one short segment where I say that I've dropped the level...

There are a couple of segments where I talk about switching from stereo to monophonic playback. During the mono sections, the microphones are switched to a pair of coincident hypercardioids, both facing straight forwards. This is not really the same as simply summing the two channels in the stereo version - which is why you'll hear a slight gain change on the on-axis sound sources.

I hope that this is the first in a series of videos explaining and demonstrating acoustical concepts - but I won't make any promises at this point..."
 
Last edited:

Purité Audio

Master Contributor
Industry Insider
Barrowmaster
Forum Donor
Joined
Feb 29, 2016
Messages
9,051
Likes
12,150
Location
London
Absolutely super, thank you Geoff ( and for designing my favourite) loudspeaker.
Keith
 

napilopez

Major Contributor
Forum Donor
Joined
Oct 17, 2018
Messages
2,110
Likes
8,433
Location
NYC
This is one of the most succinct introductions to acoustics I've seen. As @Frank Dernie suggested, the demonstrations make some topics that can be rough to understand(or believe) on your first go much more palpable.
 

Frank Dernie

Master Contributor
Forum Donor
Joined
Mar 24, 2016
Messages
6,445
Likes
15,781
Location
Oxfordshire
This has been excellent food for thought.
Since timbral accuracy and enough dynamic range have been far more important to me in my enjoyment of my hifi than any spatial effects maybe I would always favour narrow dispersion speakers, since reflection from an adjacent wall had a much bigger timbral balance effect than I expected.
Maybe that is why I like my horns.
I have so far resisted buying Beolab 90s since I am 70 and have plenty of kit already. My biggest fear is dying before I get my money's worth!
I have looked for used ones quite often though.
 

Purité Audio

Master Contributor
Industry Insider
Barrowmaster
Forum Donor
Joined
Feb 29, 2016
Messages
9,051
Likes
12,150
Location
London
I have approached B&O on numerous occasions asking to represent the Beolab 90, so far without success, it is the only speaker I would like to add.
I fear that it’s like may not be made again.
Keith
 

tuga

Major Contributor
Joined
Feb 5, 2020
Messages
3,984
Likes
4,281
Location
Oxford, England
It's nice to see/hear how much close-mic'ing, particularly when using a single mic, affects timbre.

At 12:35 we can clearly hear the effects of early reflections from his hands. Amazing.
 
Last edited:

Frank Dernie

Master Contributor
Forum Donor
Joined
Mar 24, 2016
Messages
6,445
Likes
15,781
Location
Oxfordshire
If you have a decent headphone setup you can actually hear him from behind you at 2:15.
I started listened on my laptop but soon changed to headphones and noticed this. I even tried 2 different headphones and repeat to see if the important differences sounded the same magnitude on both.
 

geoffmartin

Member
Technical Expert
Joined
Apr 25, 2020
Messages
5
Likes
36
Hi,

Thanks for the kind words here... Just one comment...

The reason you hear my voice coming from the rear when listening over headphones has nothing to do with the actual audio signal, since there are no cues in the signals that have any relationship to Head Related Transfer Functions (HRTF's). That said, I hear it too... I would say that there are three reasons why the audio appears to come around the back in this case...

- You see me move off-camera, on my way to the back
- The panning trajectory points to a rear-ward end location for the stereo image
- I actually say something like "now I'm behind the camera"

In retrospect, I should have stayed there a little longer and said some stuff that had nothing to do with my actual location. That way, that portion of the recording could be looped in isolation so that the raw audio information could be taken as-is...

On the other hand, this gives me the inspiration to do a video about HRTF's and so-called "3D audio" (A term that I hate - but that's just me...)

FYI: I'm currently working on a follow-up video which will be almost exclusively about room modes... I should have it ready to put online in a week or so.

Cheers
- geoff
 

Frank Dernie

Master Contributor
Forum Donor
Joined
Mar 24, 2016
Messages
6,445
Likes
15,781
Location
Oxfordshire
Hi,

Thanks for the kind words here... Just one comment...

The reason you hear my voice coming from the rear when listening over headphones has nothing to do with the actual audio signal, since there are no cues in the signals that have any relationship to Head Related Transfer Functions (HRTF's). That said, I hear it too... I would say that there are three reasons why the audio appears to come around the back in this case...

- You see me move off-camera, on my way to the back
- The panning trajectory points to a rear-ward end location for the stereo image
- I actually say something like "now I'm behind the camera"

In retrospect, I should have stayed there a little longer and said some stuff that had nothing to do with my actual location. That way, that portion of the recording could be looped in isolation so that the raw audio information could be taken as-is...

On the other hand, this gives me the inspiration to do a video about HRTF's and so-called "3D audio" (A term that I hate - but that's just me...)

FYI: I'm currently working on a follow-up video which will be almost exclusively about room modes... I should have it ready to put online in a week or so.

Cheers
- geoff
Do you think the timbral shift from talking behind the microphones could be fooling us too? iirc they are cardioids.
 

geoffmartin

Member
Technical Expert
Joined
Apr 25, 2020
Messages
5
Likes
36
It's possible - but if it is, it's just an accident... They're actually coincident hypercardioids, so there are some polarity flips in the L/R as I walk around - and this might also be doing something weird.

However, if the impression is caused by magnitude / phase /polarity responses of the two mic's, then it would not have been the same with a different pair of mic - which is why I think that this is not really to blame.

Cheers
-g
 

maverickronin

Major Contributor
Forum Donor
Joined
Jul 19, 2018
Messages
2,527
Likes
3,308
Location
Midwest, USA
The reason you hear my voice coming from the rear when listening over headphones has nothing to do with the actual audio signal, since there are no cues in the signals that have any relationship to Head Related Transfer Functions (HRTF's). That said, I hear it too... I would say that there are three reasons why the audio appears to come around the back in this case...

It's possible - but if it is, it's just an accident... They're actually coincident hypercardioids, so there are some polarity flips in the L/R as I walk around - and this might also be doing something weird.

However, if the impression is caused by magnitude / phase /polarity responses of the two mic's, then it would not have been the same with a different pair of mic - which is why I think that this is not really to blame.

I'm primarily a headphone listener and I notice quite a few effect like this, even when they don't seem to intentional in the source.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,201
Likes
16,983
Location
Riverview FL
This little video is not particularly scientific but may be useful as a demonstration...

 
Top Bottom