In Sound Reproduction, Floyd Toole says:
"The optimum difference between the direct and reflected sound fields is about 3 dB for speech, 4 dB for a mixed program and 5 dB for music.
A good loudspeaker for this purpose would therefore be one that has two qualities: wide dispersion, thereby promoting some amount of reflected sound, and a relatively constant directivity index, so that the direct sound and reflected sounds have similar spectra... An associated requirement of considerable importance is that at least some of the off-axis sounds be allowed to reflect" (p. 186).
It seems tough to come up with an ideal design in the face of this for an outdoor system. I'm working on a unity horn design for my backyard, for movie viewing with 8-10 people. In the likely orientation, the sides of my deck will be to the left and right of the horn mouths. In other words: not much for sound to reflect off of. How should an ideal design deal with this kind of environment?
"The optimum difference between the direct and reflected sound fields is about 3 dB for speech, 4 dB for a mixed program and 5 dB for music.
A good loudspeaker for this purpose would therefore be one that has two qualities: wide dispersion, thereby promoting some amount of reflected sound, and a relatively constant directivity index, so that the direct sound and reflected sounds have similar spectra... An associated requirement of considerable importance is that at least some of the off-axis sounds be allowed to reflect" (p. 186).
It seems tough to come up with an ideal design in the face of this for an outdoor system. I'm working on a unity horn design for my backyard, for movie viewing with 8-10 people. In the likely orientation, the sides of my deck will be to the left and right of the horn mouths. In other words: not much for sound to reflect off of. How should an ideal design deal with this kind of environment?
You could move them further away. Or not use horns. That's all I can think of right now, I'm tired lol
Being outside is a lot different than inside for reflected sound. Another thing could be more speakers of same timbre to emulate reflected sound
It's outside, you are over thinking it. 😉
Toole struggles with INSIDE reproduction (where it's a LOT more difficult to come up with a median response/power-response).
Basically look for enough coverage (flat response at least +/- 20 degrees) for whatever listening positions you have for each channel.
Reflection isn't mandatory. Besides, there are some that feel there should be no early reflections if possible, and this doesn't cause a problem. Intelligibility has come to be a term that can create confusion.
Not having reflected sound means you won't require the expense of installing acoustical absorption that proper cinemas always include in their designs to minimize broadband reverberation.
Ideally, in addition to left/right speakers, your design should also include a center speaker, subwoofer(s) and surround speakers as any good modern cinema also does.
The reverberation you hear in the soundtrack ideally comes from the mix through the speakers, not walls, ceilings and floors of a room that have no acoustical relation to what you see on screen.
ScottG, weltersys, AllenB and mike7877 are all right, outside is a completely different thing.
Firstly, the short reflections are the main problem - which you (most likely) don't have. The 'long' reflections got a lot different, way lower importance and don't interfere with the intelligibility as much, they are on a lower level (literally) and the brain can 'filter them out'.
Secondly, Toole is only talking about Stereo sound reproduction. In movie sound the phantom sound sources are most of the time replaced by real sound sources, the movie sound mix and surround speakers mostly replace them with active room reproduction (surround speakers). And what's much more important: The directional effects are much more exaggerated than conventional stereo mastered sources (music). Usually that's quite emphased compared to stereo recordings. That means, even if you just use down-mixed sound to 2 front speakers, you'll still get a much wider room impression than you'll get on usual stereo sources.
To get the best reproduction you need to cover all seats, your speaker placement should grant a good midrange coverage on all seats since there's the voice range, the dialogue is usually the most important part to be covered. If you can't follow the plot, the movie is reduced to looking at (more or less) visual effects. If you can't cover every seat, you might need a front/center fill speaker.
If there are people sitting behind others, the speakers should be rised over the heads so you've got a line of sight onto the speakers from every seat, heads and bodies, chairs etc absorb sound and that makes it more difficult to understand the actors and it swallows details more or less. Higher placed speakers, tilted a bit down towards the audience improves the intelligibility and reduces the dispersion to non-wanted areas a LOT (neighbours ie). A unity horn is very good for that placement because the beamwidth is constant over a very large frequency range.
Free air eats bass like hell, you need approximately double the number of subs (or more) to get to the same spl in the bass/sub range because you don't have any room gain, you'll lose approximately ~6dB. For the bass it might be beneficial to create a cardioid subwoofer array to minimize noise levels for the neighbours but I don't know which spl is needed or even if there are neighbours at all or if they are covered by buildings etc. but there aren't any informations on the location yet so it's very hard to tell what's really needed.
Firstly, the short reflections are the main problem - which you (most likely) don't have. The 'long' reflections got a lot different, way lower importance and don't interfere with the intelligibility as much, they are on a lower level (literally) and the brain can 'filter them out'.
Secondly, Toole is only talking about Stereo sound reproduction. In movie sound the phantom sound sources are most of the time replaced by real sound sources, the movie sound mix and surround speakers mostly replace them with active room reproduction (surround speakers). And what's much more important: The directional effects are much more exaggerated than conventional stereo mastered sources (music). Usually that's quite emphased compared to stereo recordings. That means, even if you just use down-mixed sound to 2 front speakers, you'll still get a much wider room impression than you'll get on usual stereo sources.
To get the best reproduction you need to cover all seats, your speaker placement should grant a good midrange coverage on all seats since there's the voice range, the dialogue is usually the most important part to be covered. If you can't follow the plot, the movie is reduced to looking at (more or less) visual effects. If you can't cover every seat, you might need a front/center fill speaker.
If there are people sitting behind others, the speakers should be rised over the heads so you've got a line of sight onto the speakers from every seat, heads and bodies, chairs etc absorb sound and that makes it more difficult to understand the actors and it swallows details more or less. Higher placed speakers, tilted a bit down towards the audience improves the intelligibility and reduces the dispersion to non-wanted areas a LOT (neighbours ie). A unity horn is very good for that placement because the beamwidth is constant over a very large frequency range.
Free air eats bass like hell, you need approximately double the number of subs (or more) to get to the same spl in the bass/sub range because you don't have any room gain, you'll lose approximately ~6dB. For the bass it might be beneficial to create a cardioid subwoofer array to minimize noise levels for the neighbours but I don't know which spl is needed or even if there are neighbours at all or if they are covered by buildings etc. but there aren't any informations on the location yet so it's very hard to tell what's really needed.
You could add large baffles or a huge single baffle if you're front projecting. This would push the baffle step to lower frequencies, well into the territory of the subwoofers. The baffles also improve the LCR imaging needed for music, dialogue and panning effects to be enjoyable. The surrounds would need more power as well, due to the absence of walls. Nevertheless, you won't be needing the infamous 'X-curve', as some straightforward EQ should suffice.
The overall setting is more like a stadium, although some movie theatre tricks could still be used. I think horn speakers would be more suitable for this application, as they reduce the loss of energy into directions other than that of the audience. But I'm sure someone would like to disagree.
The overall setting is more like a stadium, although some movie theatre tricks could still be used. I think horn speakers would be more suitable for this application, as they reduce the loss of energy into directions other than that of the audience. But I'm sure someone would like to disagree.