Beyond the Ariel

[kevinh]

Hi John the 60 ms is from a series of articles in Audio magazine from the late 70's. Not sure how you are measuring the decay of your room. There are some good papers at the RPG acoustics site about optimizing rooms for critical listening.

Here are some links to their library.

http://www.rpginc.com/news/library/T...ffCritList.pdf

This on diffusion in critical listening rooms.

Here is a link with other articles on room acoustics.

http://www.rpginc.com/news/library.htm

They explain it a lot beter than I could. I have heard a very good system in a room treated with their stuff and it was terrific. I have no affilation with RPG or their dealers.

[Lynn Olson]

Good discussion of room acoustics, guys, much appreciated. I've been dealing with a minor medical trouble (some weird allergy), but I think I've got a handle on it now. At least my mobility is much better, I'm walking around unassisted for short distances, and using a cane for longer trips. So far so good.

I was thinking about the B*** 901 setup business - the 3~3.5 mSec reflection is exactly the same as the floor reflection. Hmm, no accident there, methinks.

Moving from meta-theory to how we hear sounds in the physical world, the floor reflection is always present unless you're sitting in a tree, hardly a typical way to listen to music. Looking at how recordings are made, it's either close-miked (an inch or so away from the instrument or singer) or a distant stereo mike, which is typically hung well above normal listening level (an overhead position), or a combination of both.

In close-miked recordings, there's a floor bounce, but this is well down in magnitude compared to the much stronger direct sound from the singer or instrument. Anyone that's measured a speaker in the nearfield knows how little room sound remains in the measurement - same for close-miked recordings. A "truthful" playback of the original close-miked acoustic would have the singer or instrumentalist right next to your ear - a very unnatural and unpleasant result. The whole point of digital or EMT-plate reverb is to remove the "up-close" quality, mask the acoustic signature of the isolation booth, and create the impression of a larger space.

For distant microphones, there can be a spread of left, right, and center omni-pattern microphones, and sometimes these are at normal listening height, but more commonly suspended from booms, well above the orchestra (for more "brilliance" from the violins). Stereo microphones (Blumlein X/Y, crossed-cardioids, or ORTF near-spaced) are more commonly hung from booms or cables, well above the orchestra.

As a result, the majority of tracks on commercial recordings do not in fact have a significant floor bounce in the 3~3.5 mSec interval of a normal listening room. Boom-mounted microphones have a much longer floor-reflection interval, and close-miked microphones have a strongly attenuated floor reflection in the 7~8 mSec range (straight down, straight up). Only stand-mounted microphones that are distant from the musicians have a floor reflection in the 3~3.5 mSec range.

The primary intention of the engineers (aside from soloist-highlighting special effects on certain tracks) is to create a sound similar to real musicians in the room, with its inevitable 3~3.5 mSec reflection that all real acoustic sources would have.

The recording is mixed down using large monitors that are above and beyond the console, so there are reflections off the console as well as off the floor of the recording booth. Near-field monitors mounted right on the console are used as well, but these are more of a "consumer-grade" cross-check, since near-field monitors are lower-quality than the main monitors, and not considered a reliable guide for overall tonal balance, dynamics, or stereo/surround-sound perspective.

What I'm suggesting is the absence of a reflection in the 3~3.5 mSec range will in fact sound unnaturally close to the listener, since all real, physical, actually-existing sounds have a reflection in this range (unless we're in a tree or at the edge of cliff). Stand-mounted microphones that are distant from the performing ensemble are only occasionally used; more common microphone techniques have encoded floor reflections that are at longer intervals and have (substantially) lower magnitudes.

[Pano]

Interesting thinking, Lynn. So you think that the typical loudspeaker floor bounce helps the image? I don't know enough about studio recording technical to know what goes on, I was always a live engineer. But there should be some people on this thread how can chime in.

Recording, mic and mastering technical certainly make a difference to the ambient sound of a recording. The hard part is to build a room and speakers that do justice to all, or most recordings. I can be done, but it isn't cheap or easy.

Many years ago Dennon produced a wonderful gold CD recording of the Osaka Philharmonic Orchestra playing in an anechoic space. A great tool for hearing your room. Several microphone techniques were demonstrated, too.

Anechoic Orchestral Recording

The CD is long out of print and hard to find. I've been searching. If anyone has it, please let me know!
But it was a great tool for listening with real music to what your own room acoustics are doing. There may be others like it.

[kevinh]

Depending on how the miking is done would the 'floor bounce' reflection be captured as part of the recording process? I am thinking of a symphony recording for example (not close miked)? Acoustic treatment should strive to make the room 'invisiable' to the ear brain system.

Just as some electronic distortions are more objectionable than others some types of 'room distortions' are more audible and some are not. The Haas effect indicates that if the initial ROOM reflections are >8ms after the direct sound, and dispersed, the ear can ignore the room and 'hear' the recording.

I would certainly agree that a 3+ms delay is far better than 1-2 ms 'specular reflection.

Glad to hear you are getting more mobile Lynn, between the leg, the computer and the allergy you've been getting really whacked around, hopefully things will calm down for you.

[mige0]

Hi

The corners of the front wall (behind the drapes) are cut at 45 degrees, and there is a stuffed, ....

JohnK, whereas I am with you in preferable RT60 I can't see benefits of the 45 deg room corners in your listening room..






As can be seen in the sketch above they add another mirror source with relative low delay and almost in the direction of the original source. In addition due to the low angle there is almost full SPL from the rear wave as is for the front wall phantom source.

Is there a special concept behind that ? Bass traps for example would find an excellent position there, reducing RT60 in the lower octaves.


Greetings
Michael

[Bill F.]

This mixed discussion of recording techniques, room signature, and imaging amounts to a good reality check about our playback goals.

It all starts with the recording, and no two recordings are created equal. Close miked or far-field? Mono, stereo, or multi-miked? Mike make, model, and transfer function? Large or small venue? Direct-to-disk or juiced up? There are so many radically different ways of creating the raw material of a piece of audio software--some aimed at resolution, some at ambiance bloom, some at imaging, etc.

If not direct-to-disk, then comes the mixing and mastering wizardry. What ideals did the guy behind the console shoot for? What types of monitoring did he use? Nearfield or farfield? What was their transfer function? How was the studio set up? What was the room transfer function? At what SPL? What effects did he apply? Etc, etc. The original performance is completely at his mercy.

When it's all said and done, you end up with a recording that may excel or fail at delivering actual resolution, imaging, ambiance, etc.

Then comes the next layer of coloration--your playback setup/venue.

So any consumer who has one primary goal--imaging, for example--is bound to be perplexed by many recordings.

Maybe your nice hardwood floor and live acoustic is adding a second helping of floor bounce to a distant-miked recording that already had enough, or maybe your anechoic chamber is sucking the last drop of live acoustic from a close-miked recording that had none to spare.

Even when it sounds right, there's a good chance it's a serendipitous room/speaker artifact coloring in a recording that had a corresponding lack. So you're music isn't in color, it's colorized.

Until recording and mastering are standardized, there can be no absolute home-playback standard, only a rough median that does more of your chosen recordings well than not.

[Salas]

Its like chaos. Only with time some pattern emerges. A median that sonic culture of each era roughly calls 'good sound'.

[john k...]

Thanks for the links Kevin. I'll take a look. Diffusers are a good thing as the scatter the reflected sound over a wided time period compared to a flat surgace. But that's different than decay. Still 60 msec decay is pretty meaningless unless there is a reference. You know, starting at t= 0, the level of the reverberant field decays by how many dB in 60 msec, 10, 20, 40, 60? It's kind of a meaningless number without a reference to level.

You may want to do a search on the BBC articles on controled image design. The work is directed at control rooms for optimizing the enviromnet for best image. It translated directly to listening rooms in general, IMO.

By the way, are you referring to the 1978 article in Audio on the Sabinne reverberation equation? To quote from that article, "....typical meeting rooms in hotels have been found in some cases (RT60 < 0.5 sec) to develope no reverberant sound field, where as in others RT60 > 0.7 sec a [reverberant] field appears. "

[kevinh]

I'll check out the BBC stuff this is an area that I don't know enough about and need to learn more about.

The articles I am referring to are a series of IIRC 3 on LEDE rooms. They did address the RT for the listening room. I have seen the articles for 27 years (lost them in a move). So your memory may be far better than my porous memory .

Depending on the room some may have better results with the CD/wave guide and some may fare better with the ribbons.

This is a pretty subjective that depends on the types of recordings one likes to listen to, the size of the room and what your significant other will allow in the way of acoustic treatments.

[Zene Gillette]

RFZ replaced LEDE and DELE rooms by most noted engineers in the field years ago.
So, is the current thinking here just LEDE related?
Not even sure if RFZ hasn't been overshadowed by something better.
Zene