Interview w/famous speaker designer-covers common discussions

[dantheman]

We should all read this:

Searching for the Extreme: Andrew Jones of Technical Audio Devices

Dan

[Moondog55]

Thanx Dan, an interesting read, do you have part 2??

[AllenB]

Thanks for this Dan.

[graaf]

Originally Posted by dantheman

We should all read this: Searching for the Extreme: Andrew Jones of Technical Audio Devices Dan

the research Mr Jones refers to is the so-called "Archimedes" Eureka-funded research project: Project - EUREKA

it was joint project of Danmarks Tekniske Universitet, Bang & Olufsen and KEF

Bech is now Head of Research at Bang & Olufsen
on the part of Bang & Olufsen the follow-up to the project was the decision to licence the acoustic lens from Sausalito (of Moulton and LaCarruba) and to introduce their current line of horizontally omnidirectional Beolab speakers

what Jones says in this recent interview is the same what Moulton said in His 1999 interview for Recording Magazine: Moulton Laboratories :: Nick Batzdorf Interviews David Moulton
linked here many times, with no positive feedback (just no feedback or the Moulton's got His marketing agenda... blah blah stuff)

both gentlemen refer to the same "Archimedes" research project led by Bech, no wonder their conclusions are the same

yet when Jones says it then everyone should read it, but when Moulton says it it is just a childrens table

furthermore when Bech publishes His research papers He is great, but the fact that He is behind B&O-Moulton coooperation and Beolab line of omni speakers is conveniently overlooked:
http://www.bang-olufsen.com/graphics...essrelease.pdf

[LineArray]

From the interview with Andrew Jones:

"Which gets us back to what are, truly, the important speaker characteristics. It confirmed a lot of beliefs that ceiling reflections are one of the worst. Sidewall reflections can be good, adding to a sense of spaciousness, if the stereo speaker possesses well-controlled directivity. This same sidewall phenomenon happens in concert halls, on a different scale. The tall, narrow, long concert halls -- traditional ones -- were always the best halls. Sidewall reflections are lower-correlation than ceiling or floor, so they add spaciousness. Correlated signals, by contrast, add coloration."


To me the mention of correlation is a key part. There is a certain correlation
between the direct sound from the real sound sources and the reflections
(early to later ones).

And there is a certain interaural correlation in direct sound and reflected as well.


Correlation between direct and reflected sound will cause coloration, especially if
combing occurs somewhere say within the telephone bandwidth.

Too strong interaural correlation of the reflected sound will decrease spaciousness and
make the listening room more prominent to the perception.

My thinking is, that if you cannot manage to have the reflections (even the early
ones) diffuse enough, the only way is to avoid them by increasing the initial time
gap. The more diffuse reflections get, the more you can tolerate even the early ones without
combing artifacts causing to much coloration and having too much of image smear.

Because floor and ceiling reflections have higher interaural correlation than side reflections
and can follow the direct sound rather early, ceiling reflections should be diffused
(directed to the sides preferably) or (to some extent) absorbed in a broadband manner.
Carpets may adress floor reflections, some woofer arrangements in a speaker can reduce
LF combing due to floor reflections.

Whether to prefer absorbtion over diffusion to tame the perceptional role of early
reflections (or maybe make them "useful" in the thinking of some) is IMO answered
quite easily:

If you cannot make absorption near the speakers broadband and well balanced to leave
(get) the power response flat (or smoothly falling with frequency) you are better off
by using diffusivity. It is surely not forbidden to make use of both ...

If you have speakers with high DI you may want less absorption than when using
a speaker with lower directivity. A speaker having a directivity pattern
discontinuously variing with frequency causes the most trouble, because you cannot
find a consistent strategy in a real room to handle that, and the success
of any strategy will be highly dependent from listening position.

In the end the treatment of the room has to match the dispersion characteristics of the
speaker and its positioning. There is no room treatment without knowing what speakers
i have.

Having low DI speakers in a room with low absorbtion at least calls for high
diffusivity and listening distance quite close, if "critical listening" is the goal.

[Soundminded]

From the interview;

"You have a hierarchy: a mathematician, a physicist (which is a failed mathematician), and an engineer (which is a failed physicist)."

IMO he got it backwards (knowing enough physicists myself which is how he describes himself that comes as no surprise to me.) A mathematician lives in a world of pure abstraction apart from the real world. He lives in a system of closed logic all its own. Physicists use mathematics to explain the real world. Their mathematical models can never be exactly right of course, they are inherently approximations but they are often useful. Their theories stand until they are disproven by examples that cannot be reconciled with their current theory and so it is dismissed even if a better one hasn't come along. Naturally they don't have the time to devote to develop their knowledge to as much mathematical skill as mathematicians do. Engineers must take the knowledge gained by physicists and other disciplines such as chemists, biologists etc. and create circumstances in part of the real world that operate predictably, reliably to control that world to the degree and in a way that those they design for expect and require. Their mistakes can have catastrophic consequences such as a defective vehicle or nuclear power plant design. They must learn and use physics and mathematics to understand the problem they are trying to solve and how to apply it. Those who pay them don't accept excuses for failure and don't give them forever to come up with answers. Naturally engineers don't have the time to devote to learn as much physics as physicists know or as much mathematics as mathematicians know. I'm an engineer, my mother was a mathematician. In college my roommate was a physics major. I respect these people for what they know but I recognize that their knowledge while useful is invariably an abstraction while mine must be applied in ways that prove their worth in the world of reality, not just of the mind.

[DDF]

Originally Posted by graaf

furthermore when Bech publishes His research papers He is great, but the fact that He is behind B&O-Moulton coooperation and Beolab line of omni speakers is conveniently overlooked:
http://www.bang-olufsen.com/graphics...essrelease.pdf

OT but Bech's AES papers are generally phenomenal. He's one of the most under-appreciated lights in audio IMO.

Dave

[planet10]

Originally Posted by LineArray

Because floor and ceiling reflections have higher interaural correlation than side reflections and can follow the direct sound rather early, ceiling reflections should be diffused (directed to the sides preferably) or (to some extent) absorbed in a broadband manner.

The latter eaily done by havinf a sloped ceiling. My room has virtually no ceiling reflections, but (probably) strong floor reflections. Room sounds very good.

http://www.diyaudio.com/forums/blogs...ing-space.html

dave

[phivates]

"Easily done" say you? Some of us live in ordinary houses. Are we unworthy of good sound? OK it can be done but I agree, the ceiling is a major issue. I've addressed it with a kind of line source approach but it requires multiple midbass drivers and enclosures with more than 6 pieces. Oh well. Most of the extra bits aren't real big.

[speaker dave]

Originally Posted by LineArray

Whether to prefer absorbtion over diffusion to tame the perceptional role of early reflections (or maybe make them "useful" in the thinking of some) is IMO answered quite easily:

If you cannot make absorption near the speakers broadband and well balanced to leave (get) the power response flat (or smoothly falling with frequency) you are better off by using diffusivity. It is surely not forbidden to make use of both ...

If you have speakers with high DI you may want less absorption than when using a speaker with lower directivity. A speaker having a directivity pattern discontinuously variing with frequency causes the most trouble, because you cannot find a consistent strategy in a real room to handle that, and the success of any strategy will be highly dependent from listening position.

In the end the treatment of the room has to match the dispersion characteristics of the speaker and its positioning. There is no room treatment without knowing what speakers i have.

I don't think there is any research to support that reflection absorption has to somehow correct off axis frequency response. Certainly the case for some required power response is not supported by any of Toole's research (or Bech's) and if a particular power response is not required then it is hard to argue that a particular response of each room reflection is required.

The 2nd Bech paper actually went into varied frequency response of different reflections. Both the first and second studies simulated a speaker in a typical room by simulating the strength, delay and arrival angle of the first 17 reflections. In the first study he used a generic polar curve for the speaker that changed level vs. angle. In the second study he used the exact frequency response the simulated speaker would have at each radiation angle. The general effect was to give some reflections considerably less level in the 500 to 2000Hz range. Rather than noticing some particular timbral change from this it mearly shifted the threshold of detection by an amount similar to the reduced midrange level.

This also follows the work of Lipshitz and Vanderkooy that found that the ear was fairly insensitive to holes in the power response.

It is an appealing audiophile notion that wall reflections must have a spectral balance compatible with the axial response but there isn't any proof of it that I have found.

David S.