Open Baffle Experience

@johnnycamp5 wrote: "We read in this thread a redundant dimension of about 3’ off front wall as a minimum with OB.

"I wonder if less distance (approx. 2’) with heavy drapes behind might work…"

Not really. Imo the issue is time delay, and you can’t get 3 feet worth of time delay with 2 feet plus heavy drapes.

Also a benefit of many open-baffle speakers is that the backwave has essentially the same spectral balance as the frontwave, and heavy drapes would selectively attenuate the short wavelengths (high frequencies), degrading the spectral balance of the backwave.

@johnnycamp5 wrote:  "I should be more specific - Are all OB open back tweeter? I thought some had forward only directivity . So the heavy drapes question was more for the mid range and bass frequencies."

Yes, some open baffle speakers have rear-firing high frequency energy and some do not.

@johnnycamp5 again: "7’ off front wall is always why these types of loudspeakers (dipole) are “non starters” for me... I’ve always been attracted to horns for their controlled directivity.

"But man that open spacious sound of OB is hard to beat if set up right…just a whole different flavor of goodness."

Very interesting.  Ime that goodness depends on having an adequate reflection path length for the backwave energy.  Linkwitz recommends a minimum of 6 milliseconds (approximately 6 feet total, corresponding to about 3 feet distance from the wall.  I shoot for 10 milliseconds delay (corresponding to about 5 feet from the wall), based on the writings of Earl Geddes and David Griesinger.

I'm into both dipole speakers (as a dealer) and horns (as a manufacturer), and agree with your observations about "the open spacious sound of OB".  So my horn speakers usually have user-adjustable rear-firing horns which are angled up-and-back, such that their reflections bounce off the wall and off the ceiling before reaching the listening area.  This way they can be placed within a foot or so of the front wall and the reflection path delay will be in the 10 milliseconds ballpark. 

My approach would not work well with heavy drapes behind the speakers, as they would absorb the high frequency energy.  Imo it is desirable for the reflection field to have approximately the same spectral balance as the direct sound for a variety of reasons, which I can describe if you wish.

Duke

@johnnycamp5, here are four reasons why I think the spectral balance of the reflections should be similar to the spectral balance of the direct sound:

1. Timbre is more natural when the reflections fully support the first-arrival sound. Where the reflections are spectrally different from the first-arrival sound, they can skew the perceived timbre towards that difference. Also a rich and spectrally-correct reflection field inherently supports good timbre (as long as it decays neither too quickly nor too slowly), as is demonstrated by the acoustics of a good recital hall or concert hall.

2. If there is a significant spectral discrepancy between the first-arrival sound and the reflections, the ear/brain system has to work harder to correct identify the reflections. This is because the ear/brain system looks at the harmonic structure of all incoming sounds to determine whether they are reflections or new sounds. The more the overtones in a reflection differ from those in the direct sound, the harder the ear/brain system has to work to correctly classify them as reflections, and over time the additional "CPU usage" can result in listening fatigue.

3. The effective in-room signal-to-noise ratio can be degraded if the overtones in the reflections become inaudible before the rest of the spectrum does. (This can also be caused by excessive in-room absorption attenuating the short wavelengths moreso than the longer ones.) Once the overtones in the decaying reflections have become too weak for the ear/brain system to recognize them as reflections, they cease to be "signal" and become "noise". The net result is a raising of the effective in-room noise floor and a corresponding reduction in dynamic contrast and liveliness.

4. Reflections are the carriers for the reverberation tails on the recording, which in turn convey the venue ambience. If the overtones in the reflections are too weak, the venue acoustics are no longer effectively presented and the "small room signature" of the playback room is more likely to be perceptually dominant.

@soix, I don’t think kenjit has raised a legitimate issue so I won’t waste everyone’s time by replying.

In response to Kenjit's post about me above:  For the record there are two apparently very different sides to the story, but imo this thread is not the place for either side.