Is Linkwitz Wrong? Phychoacoustics in Stereo Triangle.

[Pano]

OK, sorry. Looks like I killed the thread with my last two posts
What happened? It was such a good discussion. I'll go into read only mode in this thread if that helps.

 

[wesayso]

I don't think you killed it, but the momentum sure seems gone.

Anyway my 2 cents worth would be: make speaker + room work together, whatever that takes. This could mean an OB solution, horns or direct radiators. My personal opinion is comb patterns do matter, ironically I have build full range line arrays that are infamous of having combing problems . I have no regrets though...

 

[graaf]

Doing some research into alternate approaches, I came across a website with completely different conclusions. These conclusions are marketed primarily for the creation of music, not reproduction, but can still be applied. A summary of conclusions as follows:

• Not all early reflections are bad -most are beneficial- but first reflections are bad, as they perceptually mask first reflections present in the recording.

• Treatment of first reflections makes it possible so you can accurately produce imaging that is the same as recorded. Treatment of the first reflection points of a room allows you to hear the first reflections in a recording.

• Untreated first reflection points cause comb filtering/ time smearing.

• To maximize precedence effect, first reflection points less than 15ms must be treated to attenuate 1khz-8khz by at least 10dB (This is incredibly easy).

• Hearing of the originally recorded acoustic space is maximized by ITDG/ISD maximization.

• This is done by having your rooms ISD gap larger than the recorded ITDG gap. World class concert halls have an ITDG gap of 12-25ms. Obviously recordings made with smaller rooms will have smaller values. To aching a ISD gap of 20ms, the direct sound must travel 22.5 feet before hitting your ears again. This means you must sit 11.25 feet from the back wall, or use absorption/diffusion.

How to Build a "Reflection-Free Zone" to Treat Early Reflections

those alternate approaches go against scientific research done in the subject matter

those people didn't do their homework

 

[upsha]

Linkwitz's conclusion is that stereo speakers can not accurately reproduce the soundstage of recorded material; it can only produce an "illusion" as long as reflections are copies of the direct sound (constant directivity designs).

Mathematically, we can record and recreate the original session by doing the following.

1. Find a close surface enclosing the volume we like to record.
2. Record the field (pressure/velocity) everywhere on the close surface.

To recreate the field “in the volume”, we just need to create the same close surface and play the field on that surface. Wave theory guarantees that everywhere in the volume will be exactly the same as the recording. This is very useful, since the recording/playback problem is reduced from 3D to 2D.

In reality, we have to take finite samples on the close surface. To satisfy Nyquist criteria at 20kHz, we need to place microphone/speaker with half-wavelength spacing on this close surface, which is only 8.5mm. This is certainly not feasible. On the other extreme, using two or even 20 microphones/speakers, are still very poor approximations to the wave theory requirement.

Until someone built "the future speaker" as Lynn Olson puts it, any stereo audio is an illusion.

A very good summary on spatial audio by Francis Rumsey, Chair of the AES Technical Council, can be found at: https://www.youtube.com/watch?v=y82nth2Pnwk