The Measurement and Calibration of Sound Reproducing Systems

[gene]

This is the latest AES paper submission from Dr. Floyd Toole. It deals with the Measurement and Calibration of Sound Reproduction Systems.

The following discussions will embrace both large and small venue sound systems: cinemas for public exhibitions, home theaters and stereo systems for private entertainment, dubbing stages for movie sound track creation, and recording control rooms for music production. The physics of sound creation and propagation are the same in all of these, as are the perceptual processes of listeners, so substantial
commonality is anticipated.

Dr. Toole has made this paper available to the public for FREE.

Please download and read it and discuss here. If we generate a good discussion it may inspire some participation from the man himself. We can all use this as a great learning experience so I welcome lots of input.

 

[gene]

A few key points about Auto-EQ and Equalization as excepted below.

For Multiple Seats, Equalization Cannot:

• Add or remove reflections

• Change reverberation time

• Reduce seat-to-seat variations in bass

• Correct frequency dependent directivity in loudspeakers

• Compensate for frequency dependent absorption in acoustical materials and furnishings. The exception is in the highly reflective sound field at very low frequencies.

 

[gene]

About Early Reflections in Small Rooms:

Germane to this discussion are the findings of Bradley et al. [23] indicating that for speech intelligibility—a crucial consideration for movies—it is the early reflections that are the main contributors. They concluded that early reflection energy arriving within about the first 50 ms following the direct sound has the same effect on speech intelligibility scores as an equal increase in the direct sound energy.

Adding large amounts of absorption to achieve very short reverberation times may degrade intelligibility due to reduced early reflection levels.”


For stereo recording and listening:
Early reflections can reduce the timbral degradation and speech intelligibility loss in the phantom center image. It helps to fill the large spectral dip around 2 kHz, created by stereo/interaural crosstalk

 

[gene]

Live Rooms vs Dead Rooms: Which are better? It depends on what you're doing!

It turns out that in most small-to-medium sized

sound-reproduction spaces human listeners find these

multi-directional reflected sounds to be mostly benign, even

beneficial if the loudspeaker has relatively constant directivity.

A common perception is spaciousness—information

about the listening space, not timbre-damaging comb filtering.

This is certainly true for recreational listening, but professionals

may find that a less reflective space is preferred

for mixing but perhaps not for mastering recordings [12].


It is tempting to simply “eliminate the room” when mixing.

Some argue that it makes the job simpler. A recent

paper provided evidence that acoustically dead monitoring

environments may be preferred while mixing, but for mastering

a more reflective space is preferred [12].

 

[Speedskater]

The URL link is broken.

 

[jim1961]

How much and what kind of room response you want certainly depends on what the room is to be used for.

Mastering, mixing, AV and 2 CH listening rooms all need different things.

AS stated previously, the link doesn't work, so I dont know what specific Toole article is being cited.

 

[gene]

I fixed the link in the original post. Take a look.

 

[jim1961]

There is a lot there. What part did you want to focus on?

 

[TheWarrior]

A few key points about Auto-EQ and Equalization as excepted below.

For Multiple Seats, Equalization Cannot:

• Add or remove reflections

• Change reverberation time

• Reduce seat-to-seat variations in bass

• Correct frequency dependent directivity in loudspeakers

• Compensate for frequency dependent absorption in acoustical materials and furnishings. The exception is in the highly reflective sound field at very low frequencies.

Nor can it account for odd room dimensions, characteristic of many 'living room' home theaters. For example, a friends listening room has a two story, steep, slanted roof line on one side, with an overhanging walk way (balcony) on the other.

The speaker under the walkway (which was a normal 8' ceiling height) received a lot of gain from being corner loaded. Audyssey translated this as a phase issue. Upon my first visit I felt like I was being subjected to vestibular testing! "Yes, I have vertigo, now can we can turn this down, and identify the problem?!"

 

[gene]

There is a lot there. What part did you want to focus on?

• Benefits of Early Reflections
• Issues with Auto-EQ

 

[jim1961]

• Benefits of Early Reflections
• Issues with Auto-EQ

Could you quote the parts that submit or support this?

 

[gene]

Could you quote the parts that submit or support this?

You're gonna have to kind of skim through it and skip over the Xcurve stuff. The first few pages discusses many of these issues and you can search the quotes I put in prior posts to find those sections.

 

[TLS Guy]

I fixed the link in the original post. Take a look.

It still won't work for me.

 

[jinjuku]

Not sure why Gene's link isn't working but I tested this.

http://www.aes.org/tmpFiles/elib/20150820/17839.pdf

**here's the difference: 20150819 vs 20150820** They changed the URL.

 

[jim1961]

The new link worked yesterday, but doesnt today

Gene, I think it would be better just to quote the parts that make your case.

 

[jinjuku]

I posted a corrected link.

http://forums.audioholics.com/forums/threads/the-measurement-and-calibration-of-sound-reproducing-systems.95799/#post-1093667

 

[ski2xblack]

4 SMALL VENUE SOUND SYSTEMS
Rooms of a size appropriate for stereo or TV entertainment, home theaters, home studios, and recording control rooms do not require massive, highly directional loudspeakers.

Hmm. This seems more of a reflection of modern sensibilities when it comes to speaker size than anything having to do with actual performance benefits. Speakers that are highly directional can be used in lively, untreated rooms to great effect. Here is a piece put together by Bill Waslo over at AVS describing just such an approach. On top of the things he mentions, larger speakers tend to be more sensitive, which pays dividends as well: no need for herculean amplification; such speakers in a domestic environment operate low in their SOA, so cone motion and related speaker induced distortion is greatly reduced as compared to more WAF-friendly small speakers, not to mention more available headroom/dynamic range. In my own experience, big, highly directional speakers, implemented properly, result in some of the most effortless, clear, and natural/lifelike playback of any approach.

Toole is the man, though. Everyone who cares about getting the most out of their rigs should read his book, or at least read this paper very closely. Thanks for posting it, Gene. (Link still broken btw, Jinjuku's works.)

 

[jim1961]

4 SMALL VENUE SOUND SYSTEMS
Rooms of a size appropriate for stereo or TV entertainment, home theaters, home studios, and recording control rooms do not require massive, highly directional loudspeakers.

Hmm. This seems more of a reflection of modern sensibilities when it comes to speaker size than anything having to do with actual performance benefits. Speakers that are highly directional can be used in lively, untreated rooms to great effect. Here is a piece put together by Bill Waslo over at AVS describing just such an approach. On top of the things he mentions, larger speakers tend to be more sensitive, which pays dividends as well: no need for herculean amplification; such speakers in a domestic environment operate low in their SOA, so cone motion and related speaker induced distortion is greatly reduced as compared to more WAF-friendly small speakers, not to mention more available headroom/dynamic range. In my own experience, big, highly directional speakers, implemented properly, result in some of the most effortless, clear, and natural/lifelike playback of any approach.

Toole is the man, though. Everyone who cares about getting the most out of their rigs should read his book, or at least read this paper very closely. Thanks for posting it, Gene. (Link still broken btw, Jinjuku's works.)

There may be some similarity between a directional speaker, and a typical one in a well treated room (one that becomes directional in that its wide response is absorbed or redirected).

Ive been hesitant to say much up to this point because I am am one who favors getting rid of early reflections, but preserving later (>20ms) arriving ones.

I think there is some confusion in interpreting Toole. In particular his thoughts regarding speech intelligibility. Some people apply those principles to how a music listening room should be setup. Apples and oranges.

 

[gene]

It still won't work for me.

Damn editor! I think I finally got it to work. try again.
http://www.aes.org/e-lib/browse.cfm?elib=17839

 

[TheWarrior]

There may be some similarity between a directional speaker, and a typical one in a well treated room (one that becomes directional in that its wide response is absorbed or redirected).

Ive been hesitant to say much up to this point because I am am one who favors getting rid of early reflections, but preserving later (>20ms) arriving ones.

I think there is some confusion in interpreting Toole. In particular his thoughts regarding speech intelligibility. Some people apply those principles to how a music listening room should be setup. Apples and oranges.

First, 'directional sound' travels along a specific path with minimal dispersion. This is characteristic of a speaker with poor off axis dispersion. LEV - listener envelopment, will suffer as a result. And I think thats what you are missing. This article flies in the face of convention by stating that conventional steady-state amplitude response measurements deny any directional information, which Toole has effectively defined, as essential for Home Theater sized applications.

Figure 2a on pg 514 shows exactly why speech intelligibility stems from his beliefs in the absolute need for controlling low frequencies. Part of that is the handshake between the room and the summed radiating surface of all the drivers.

ASW - Apparent Source Width, is another key element Toole has defined as essential for describing room acoustics, which defies your perception of what early/ late reflections are. Both ASW and LEV are necessary to paint an accurate image, and it is the room dimensions that determine what, if anything, needs 'treatment'.