What is the ideal directivity pattern for stereo speakers?

[keyser]

Originally Posted by speaker dave

Early lateral reflections lead to a different problem of a "twangy bounce" (listen to the game environmental simulation a few pages back), and are equally undesirable. David Moulton is at odds with all modern research in advocating wide dispersion studio monitors in conjunction with narrow rooms with hard sidewalls.

Actually, the direct sound + early reflections sounds best to my ears in this example!

Here's the link again:
Precomputed Wave Simulation for Real-time Sound Propagation of Dynamic Sources in Complex Scenes - YouTube

[keyser]

Tom, thanks for you contribution.

I have to say that the several times I set up my stereo outdoors I didn't notice the effect you describe. The first several times I did it, I was struck by the cleanness of the sound. The last time I noticed that the floorbounce had a great audible effect! This is probably because it is the only significant reflection.

BTW, your recording of the fireworks sounds amazing! The other ones are nice too, though.

[gedlee]

Originally Posted by Elias

Hi Oliver,

According my understanding up to date, group delay is purely an engineering term and means almost next to nothing in psychoacoustic perception in small room acoustic spaces.

- Elias

This is completely false as shown by both myself and Brian Moore.

[speaker dave]

Originally Posted by Elias

Second pic is with the sound absorbing pillow placed betwen the speaker and the listening position to attenuate the direct sound. The sound at 0.007s is almost eliminated.

What is group delay now? It can be seen that major energy arrives at 0.015s at all the frequencies, so one can say group delay has been improved by blocking the direct sound?

- Elias

Certainly the 7 mSec arrival is more even in level except for some interference at 500Hz. To claim that the speaker is improved by a pillow blocking the direct sound isn't something I would agree with. The pillow only partially blocks the highest frequencies, only about 10dB below 1000Hz. Plus the 15 mSec arrival is rougher than the direct arrival.

I'd guess the system sounds like a speaker with a pillow in front of it.

Otherwise, I'm not usually afraid of a little bit of group delay but you are forcing an 8mSec delay between direct arriving low frequencies and wall bounced high frequencies.

And why are your wall bounces stronger than the direct response, even without the pillow?

David S.

[ra7]

There is a school of thought (not mine) that believes floor bounce is not such a problem because your brain expects it. It is part of evolution that tells us we are near the ground versus being perched on a tree branch.

Comb-filtering because of the floor bounce may be a real problem, but is the reflected sound really a problem for localization?

[Elias]

Hi,

It may sound good sometimes even best, but it is against the modern research and thus you must be wrong with your opinion

I do research myself and I must say that many of modern researchers are totally lacking the big picture.

- Elias

Originally Posted by keyser

Actually, the direct sound + early reflections sounds best to my ears in this example!

[Bob Richards]

Originally Posted by 6.283

I agree with that but one minor correction in terminology: Controlled directivity is not the opposite of wide
dispersion. The opposite is narrow dispersion and both patterns can be controlled or "close to constant".


This is pretty much an audio myth. Even Toole says it somewhere (' don't have the book handy). This is only a good proof
that mics "listen" differently than ears/brain.
Reflections will always cause "combing" but certain types and amounts of reflections are desired. So the unwanted ones
should be given real names otherwise people will never stop believing that "combing" is bad in general.

By "controlled directivity" I meant more narrow. Less likely to involve room acoustics any more than is necessary. I don't know of a situation where comb filtering is desirable in hi-fi reproduction. It's a fact of life (law of physics) unless you're floating in space more than 75 feet from anything, or in an anechoic chamber, that you would be wise to fully understand and deal with somehow. Maybe you could explain yourself in much more detail. I'm confident that you misunderstood what Toole was saying, or I just don't get what you are saying.

[erjee]

And I like the sound and feel of the Harley being started in my room, I could almost smell the exchaust fumes

@Tom
Besides the 'broadband CD point source' characteristic there are two other aspects of the SH50 which are not found in normal indoor hifi speakers:
- very narrow directivity (50 deg beamwidth)
- the lack of any baffle which probably reduces the amount of diffraction

Do you consider the second aspect as an important property for a loudspeaker?

[Bob Richards]

Originally Posted by speaker dave

Acousticians do look at early to late ratios, for example speech inteligibility is related to energy level before vs. after 30 msec. I wasn't really going there, more thinking of the total reverberent level vs. the direct. As you sit off axis or use a wider dispersion speaker you will reduce the level of direct vs. all subsequent reflections. This was the macro view of acoustics.

The micro view is, what do the directional properties of the speaker infer about the first 5 or 10 room reflections? Taking out a few early reflections doesn't drastically alter the direct to reflected ratio but may make big improvements in sound.

David S.

David S.

Any reflections that are less than 1 mS can affect perceived image location on the horizontal axis dramatically. Proof of that pudding is demonstrated by the fact that the Carver Holographic generator uses 125 micro seconds of delay. Above about 1mS (milli second) the way room reflections affect image location is more about amplitude comparisons, part because your inter-aural crosstalk steps on imaging information in the lower midrange, and part because all the comb filter FR fluxuations will cause amplitude comparison analysis to be all over the place, depending on the exact location of your ears.

A good acoustician knows that you don't just separate the delay effects into 2 catagories. There are different psycho-acoustic effects for several different delay ranges (4 or 5 that I've read about and experimented with). According to David Griesinger, pioneer of digital reverb and long time senior consultant for Lexicon, voice intelligibility is most damaged by delays between about 50mS and 150mS. A 30mS delay might even make the voice easier to understand. Wider dispersion does the opposite of what you said; it increases room reflections, and the problems (or opportunities) that come with that. Delayed energies of less than about 6mS are never a good thing. Open baffle or dipole people would know this real well. That's why dipoles sound way better if they're at least 3 ft. out from any walls.

[Bob Richards]

Originally Posted by ra7

There is a school of thought (not mine) that believes floor bounce is not such a problem because your brain expects it. It is part of evolution that tells us we are near the ground versus being perched on a tree branch.

Comb-filtering because of the floor bounce may be a real problem, but is the reflected sound really a problem for localization?

The good news is that on anything but the left to right axis, the only way we can sense image location is by reverb analysis, or in the case of changing sounds, consistent changes in upper-midrange frequency response due to how the pinea works (I'm trying to say a lot in very few words here). So I agree that floor bounce could be an important part of our ability to sense depth and height. .

The bad news is that the floor bounce information that we use to perceive depth and height, might already be embedded in the recording, and so now you've got two floor bounce "echos" and the ear-brain mechanism may get confused by that, just as it does with two sets of interaural crosstalk information when you don't have some variation of the Carver interaural crosstalk cancelling mechanism. In the real world, it may be pretty rare that any floor bounce info is in a recording (it seems like most recordings are done with individual close mics, or mic trees hung from the ceiling for most classical music stuff), so I generally agree that floor bounce is not likely your biggest problem. It could even be a good thing if it makes a band sound like they are on solid ground rather than floating in the cosmos.